Showing papers in "Proceedings of The Royal Society B: Biological Sciences in 1977"

Ferrier Lecture: Functional Architecture of Macaque Monkey Visual Cortex

Abstract: Of the many possible functions of the macaque monkey primary visual cortex (striate cortex, area 17) two are now fairly well understood. First, the incoming information from the lateral geniculate bodies is rearranged so that most cells in the striate cortex respond to specifically oriented line segments, and, second, information originating from the two eyes converges upon single cells. The rearrangement and convergence do not take place immediately, however: in layer IVc, where the bulk of the afferents terminate, virtually all cells have fields with circular symmetry and are strictly monocular, driven from the left eye or from the right, but not both; at subsequent stages, in layers above and below IVc, most cells show orientation specificity, and about half are binocular. In a binocular cell the receptive fields in the two eyes are on corresponding regions in the two retinas and are identical in structure, but one eye is usually more effective than the other in influencing the cell; all shades of ocular dominance are seen. These two functions are strongly reflected in the architecture of the cortex, in that cells with common physiological properties are grouped together in vertically organized systems of columns. In an ocular dominance column all cells respond preferentially to the same eye. By four independent anatomical methods it has been shown that these columns have the from of vertically disposed alternating left-eye and right-eye slabs, which in horizontal section form alternating stripes about 400 $\mu $m thick, with occasional bifurcations and blind endings. Cells of like orientation specificity are known from physiological recordings to be similarly grouped in much narrower vertical sheeet-like aggregations, stacked in orderly sequences so that on traversing the cortex tangentially one normally encounters a succession of small shifts in orientation, clockwise or counterclockwise; a 1 mm traverse is usually accompanied by one or several full rotations through 180 degrees, broken at times by reversals in direction of rotation and occasionally by large abrupt shifts. A full complement of columns, of either type, left-plus-right eye or a complete 180 degrees sequence, is termed a hypercolumn. Columns (and hence hypercolumns) have roughly the same width throughout the binocular part of the cortex. The two independent systems of hypercolumns are engrafted upon the well known topographic representation of the visual field. The receptive fields mapped in a vertical penetration through cortex show a scatter in position roughly equal to the average size of the fields themselves, and the area thus covered, the aggregate receptive field, increases with distance from the fovea. A parallel increase is seen in reciprocal magnification (the number of degrees of visual field corresponding to 1 mm of cortex). Over most or all of the striate cortex a movement of 1-2 mm, traversing several hypercolumns, is accompanied by a movement through the visual field about equal in size to the local aggregate receptive field. Thus any 1-2 mm block of cortex contains roughly the machinery needed to subserve an aggregate receptive field. In the cortex the fall-off in detail with which the visual field is analysed, as one moves out from the foveal area, is accompanied not by a reduction in thickness of layers, as is found in the retina, but by a reduction in the area of cortex (and hence the number of columnar units) devoted to a given amount of visual field: unlike the retina, the striate cortex is virtually uniform morphologically but varies in magnification. In most respects the above description fits the newborn monkey just as well as the adult, suggesting that area 17 is largely genetically programmed. The ocular dominance columns, however, are not fully developed at birth, since the geniculate terminals belonging to one eye occupy layer IVc throughout its length, segregating out into separate columns only after about the first 6 weeks, whether or not the animal has visual experience. If one eye is sutured closed during this early period the columns belonging to that eye become shrunken and their companions correspondingly expanded. This would seem to be at least in part the result of interference with normal maturation, though sprouting and retraction of axon terminals are not excluded.

Mechanical Properties of Mother of Pearl in Tension

Abstract: Mother of pearl, or nacre, is one of a number of characteristic skeletal structures of molluscs, occurring in cephalopods, gastropods and bivalves. It consists of plates of aragonite, about 0.3 $\mu $m thick, arranged in sheets, with a tenuous protein matrix. Mechanical tests of nacre from all three classes show that it has a tensile strength of between 35 and 110 MN m$^{-2}$. It is slightly viscoelastic, and shows marked, though not extensive, plastic deformation. The maximum measured strain was 0.018. While undergoing plastic deformation the material shows considerable optical changes. The regions where plastic flow is occurring show 'tension lines', probably equivalent to similar lines in bone. These are probably caused by voids forming in the protein matrix. The work of fracture is very different in different loading directions, being about 1.65 $\times $ 10$^{3}$ J m$^{-2}$ when fractured across the grain, and 1.5 $\times $ 10$^{2}$ J m$^{-2}$ when fractured along it. Nacre shows considerable ability to stop cracks. An attempt is made to explain qualitatively the mechanical behaviour of nacre in terms of its submicroscopic structure. It is concluded that the precise geometric arrangement of the plates is most important, and that this constraint may make nacre less suitable for shells that must be built quickly.

Relaxation and Fluctuations of Membrane Currents that Flow through Drug-Operated Channels

Abstract: The theoretical background is presented for (a) the relaxation towards equilibrium of drug-induced membrane currents, and (b) the fluctuations of membrane current about its equilibrium value that originate in the opening and closing of membrane ion channels. General expressions are given that relate the relaxation current, autocovariance function, spectral density function, fluctuation variance and mean open channel lifetime to the rate constants and single channel conductances for any theory of drug action based on the law of mass action. The question of how much can be validly inferred from experimental spectra that appear to have only one component is discussed. The equations are illustrated by their application to some simple theories of drug action that are currently under consideration.

Transmitter leakage from motor nerve endings

Abstract: When endplates of anti-esterase treated frog muscle are subjected to a massive ionophoretic dose of curare, a small local hyperpolarization is recorded in many fibres, amounting on the average to about 40 $\mu $V. The origin of this effect may be attributed to leakage of cytoplasmic acetylcholine (ACh) from nerve terminals, building up an ACh concentration of the order of 10$^{-8}$ M in the synaptic cleft and causing a minute steady depolarization of the endplate. It is calculated that such a steady leakage of ACh, although producing a barely detectable electrical effect, could exceed the efflux due to spontaneous quantal discharges by two orders of magnitude, and account for the assayed amounts of ACh release from resting muscle.

Two Mutations of Synaptic Transmission in Drosophila

Abstract: Evoked transmitter release is abnormal at the larval neuromuscular junctions of two Drosophila mutants. Following a single nerve impulse, the increased calcium conductance at the nerve terminal, which lasts for 1 ms in normal larvae, lasts for at least 60 ms in one mutant and several seconds in the other. Both mutations appear to affect the same gene on the X-chromosome. Normal larvae treated with 4-aminopyridine, a potassium channel blocking agent, mimic the abnormal synaptic transmission of one mutant. Normal larvae treated with tetraethylammonium, another potassium channel blocking agent, mimic the abnormal synaptic transmission of the other mutant. From these and other experiments, we suggest that the abnormal neuromuscular transmission in these mutants may be caused by defective potassium channels in the nerve terminal membrane.

Electrophysiological differentiation of oxytocin-and vasopressin-secreting neurones

Abstract: Antidromically identified neurosecretory cells of the paraventricular (p.v.) and supraoptic (s.o.) nuclei of the hypothalamus were recorded in lactating rats under urethane anaesthesia during reflex milk ejection (m.e.) and haemorrhage. Eighty one p.v. and s.o. neurones were studied. Their background firing rates ranged from < 0.1 to 6.3 spikes/s and three distinct patterns of activity were encountered: slow irregular (73%), fast continuous (10%) and phasic (17%). Forty units (49%) displayed a brief (2-4 s) high-frequency discharge (30-60 spikes/s) correlated with suckling-induced m.e., and these were classified as m.e. (oxytocin-secreting) neurones. The remainder of the cells showed no activation at this time and were classified as non-m.e. neurones. Ten m.e. neurones tested through haemorrhage (5 ml of blood) showed a gradual acceleration of firing rates, reaching a maximum of 3.7 $\pm $ 0.7 spikes/s (mean $\pm $ s.e.) about 20 min after blood withdrawal. The firing pattern of the m.e. neurones therefore changed from a slow irregular to a fast continuous type. By contrast, 11 non-m.e. neurones tested with the same procedure showed a rapid activation reaching a maximum of 6.4 $\pm $ 0.6 spikes/s by the fourth minute. Non-m.e. neurones which were initially of the slow irregular type, first became fast continuous and later evolved into a highly characteristic phasic pattern of activity which was never induced in the m.e. neurones. After the blood was replaced, all the cells returned to their original firing pattern. In a parallel series of experiments, plasma samples taken 5 and 25 min after haemorrhage showed a ten-fold elevation in antidiuretic activity. A slight but non-significant increase in m.e. activity was also observed. Thus p.v. and s.o. neurosecretory cells may be electrophysically differentiated into two functionally distinct populations: (1) oxytocin releasing neurones which show a high-frequency discharge before m.e. induced by suckling, and (2) vasopressin-releasing neurones which adopt a phasic pattern of firing during vasopressin release induced by haemorrhage. We suggest that the rate of vasopressin secretion into the circulation largely depends on the proportion of vasopressin neurones firing phasically, their firing rates within the phases and the duration and degree of synchronization of the phases.

Coral Skeletal Chemistry: Physiological and Environmental Regulation of Stable Isotopes and Trace Metals in Montastrea annularis

Abstract: A detailed study has been made of the $^{13}$C, $^{18}$O, calcium, magnesium, strontium, and iron contents of a coral skeleton deposited during a two-year period for which environmental data are available. Strong seasonal variations in $^{13}$C and magnesium contents have been found. These appear to be linked to changes in growth rate, and should be considered in future work. $^{18}$O content does not show equilibrium physicochemical temperature effects, and its lack of correlation with $^{13}$C indicates complex metabolic isotope fractionation. Strontium content shows little variation. This difference from magnesium is predicted on grounds of biochemical ion transport. Iron is detrital in origin. Seasonal records of trace constituents in coral skeleton are shown to differ from those predicted by previous investigators, indicating that metabolic effects cannot be ignored in paleoenvironmental interpretation of carbonate skeletal chemistry. Stable isotopes are demonstrated to be useful tools in understanding overall carbon metabolism of photosynthetic calcifying organisms. A model of carbon isotope fractionation is developed, and used to place bounds on the sources of carbon used in photosynthesis and calcification. It is estimated that approximately 40% of the carbon supply is from seawater bicarbonate and 60% from recycled respiratory CO$_{2}$.

Analysis of Occluding Contour.

Abstract: Almost nothing can be deduced about a general three-dimensional surface given only its occluding contours in an image, yet contour information is easily and effectively used by us to infer the shape of a surface. Therefore, implicit in the perceptual analysis of occluding contour must lie various assumptions about the viewed surfaces. The assumptions that seem most natural are (a) that the distinction between convex and concave segments reflects real properties of the viewed surface; and (b) that contiguous portions of contour arise from contiguous parts of the viewed surface - i.e. there are no invisible obscuring edges. It is proved that, for smooth surfaces, these assumptions are essentially equivalent to assuming that the viewed surface is a generalized cone. Methods are defined for finding the axis of such a cone, and for segmenting a surface constructed of several cones into its components, whose axes can then be found separately. These methods provide one link between an uninterpreted figure extracted from an image, and the 3-D representation theory of Marr & Nishihara (1977).

Colour Coding in the Superior Temporal Sulcus of Rhesus Monkey Visual Cortex

Abstract: In the rhesus monkey, the posterior bank of the superior temporal sulcus forms part of the prestriate visual cortex and has two regions, a medial one and a lateral one, which have their own separate callosal connections. The afferent input to these two regions was studied in experiments where the corpus callosum was sectioned, and labelled amino acids were injected into other visual areas. By this method, it was found that area 17 projects to that part of the superior temporal sulcus occupied by the more medial of the two callosal inputs. By contrast, the part of the sulcus occupied by the more lateral callosal input was found to receive a strong projection from the fourth visual complex, an area rich in colour-coded cells. Recordings were made from single cells in the superior temporal sulcus in animals in which the corpus callosum had been sectioned previously. The degeneration produced by this procedure was used to provide anatomical landmarks enabling us to assign cells to the lateral or the medial regions of the sulcus. Such recordings revealed that receptive fields were topographically organized in the lateral part of the sulcus and that most cells were colour specific. By contrast, cells recorded from in the region of the more medial callosal patch within this sulcus were directionally selective, without any obvious colour coding. It was concluded from these combined anatomico-physiological experiments that there are at least two distinct regions in the superior temporal sulcus which have different afferent connections and functional properties.

Abnormalities in reproductive function associated with the destruction of the suprachiasmatic nuclei in female rats.

Abstract: Extensive lesions of the suprachiasmatic nuclei result in failure of ovulation in the female rat. Damage to adjacent structures (optic chiasma, anterior pole of the arcuate nuclei, anterior hypothalamus, preoptic area) is neither necessary nor, in itself, sufficient to cause failure of ovulation. All anovulatory animals showed a high level of sexual receptivity and some ovulated after mating but few became pregnant. There was no consistent relation between the incidence of ovulation after mating or after progesterone administration and the occurrence of a facilitation of gonadotrophin secretion by progesterone administration to oestrogen-primed animals after ovariectomy. Nor could these responses be correlated with the extent or anatomical location of the lesions. It is suggested that the failure of ovulation may be related to the abolition or disruption of the normal diurnal variation in sensitivity to the facilitatory effects of ovarian steroid hormones.

Measurement of calcium transients in frog muscle by the use of arsenazo III.

Abstract: Intracellular injection of the calcium indicator dye arsenazo III was used to measure the calcium transients occurring during depolarization of frog skeletal muscle fibres. A quantitative estimate of the rise in intracellular free calcium during a twitch was made, and the relation between membrane potential and calcium release was examined. The results also indicate that calcium in the bathing solution plays no important part in the generation of calcium transients during single twitches.

The ‘suprachiasmatic syndrome’: endocrine and behavioural abnormalities following lesions of the suprachiasmatic nuclei in the female rat

Abstract: Lesions of the suprachiasmatic nuclei that caused failure of spontaneous ovulation in female rats consistently produced abnormalities in other functions that are normally influenced by the light-dark cycle. In such animals morning plasma corticosterone concentrations were abnormally high and evening values abnormally low though the response to stress was unaffected. Pineal serotonin N -acetyl transferase activity was abnormally high in animals killed during the day and abnormally low in those killed at night. Although the animals were in persistent be­havioural oestrus, total voluntary wheel-running activity was not con­sistently altered but was distributed evenly between the light and dark periods rather than being confined principally to the dark periods as in normal animals. Similarly the proportion of the daily water and food intake that occurred during the dark period was reduced. The incidence of these associated abnormalities was low in lesioned rats that continued to ovulate spontaneously.

The anionic permeability of the inhibitory postsynaptic membrane of hippocampal pyramidal cells

Abstract: The anion permeability and current sensitivity of inhibitory postsynaptic potentials (i.p.s.ps) of CA1 hippocampal pyramidal cells have been studied with intracellular recording techniques. Passage of depolarizing current through the microelectrode increased the size of i.p.s.ps while hyperpolarizing current decreased and eventually reversed the i.p.s.ps. The early portion of the i.p.s.p. was most sensitive to current. The results obtained from the injection of anions into the pyramidal cells indicated that a sharp dichotomy existed: either the anion was permeable as shown by a depolarizing shift in the i.p.s.p., or the anion was impermeable, there being as a consequence a hyperpolarizing shift in the i.p.s.p. The permeable anions include Br$^{-}$, NO$_{2}^{-}$, NO$_{3}^{-}$, SCN$^{-}$, OCN$^{-}$, ClO$_{3}^{-}$ and HCO$_{2}^{-}$, while the impermeable anions included citrate, glutamate, sulphate, methylsulphate, bromate, chromate, acetate and fluoride. These results are identical to those obtained by ion injection into motoneurons. Diffusion of anions into pyramidal cells supported the results from ion injection; namely, that there was a sharp dichotomy between permeant and impermeant anions. However, acetate, and to a lesser extent bromate and glutamate, were exceptions, since these anions led to an abolition or reduction of the hyperpolarizing i.p.s.p. and yet from ion injection studies these anions were clearly impermeant. Possible explanations for this paradox are given in the following paper. The present findings suggest that the anion permeability of the inhibitory postsynaptic membrane in hippocampal pyramidal cells is similar to that reported for spinal motoneurons.

Structural requirements for opioid activity of analogues of the enkephalins.

Abstract: Structure-activity relations of a series of analogues of the two endogenous morphine-like peptides, leucine-enkephalin and methionine-enkephalin are examined on the basis of (a) effects on the mouse vas deferens and the guinea pig ileum and (b) affinities for the rat brain opiate receptor. In the mouse vas deferens, metabolism of the peptides by proteolysis is not a major influence on activity. In contrast, however, brain opiate receptor preparations contain an abundance of proteolytic enzymes, the effects of which can be minimized by conducting opiate receptor binding assays at 0 degrees C and in the presence of bacitracin. The potentiation of biological activity and opiate receptor binding affinity by replacing the Gly$^{2}$ residue in the natural enkephalins by D-Ala, is discussed both in terms of increased stability of the Tyr-D-Ala bond to aminopeptidases and of the stabilization of the peptide conformation as present in the receptor-peptide complex. The substitution of the Leu$^{5}$- or Met$^{5}$-residue by the corresponding D-amino acid contributes little to proteolytic stability, which emphasizes that the predominating site at which metabolism occurs is the Tyr$^{1}$-Gly$^{2}$ bond. Of the analogues described, [D-Ala$^{2}$, D-Leu$^{5}$]-enkephalin is the most active peptide in the three assay systems, the mouse vas deferens, the guinea pig ileum and the rat brain opiate receptor preparations. Substitutions by the respective D-amino acids D-Tyr and D-Phe at positions 1 and 4 reduce both the potency and binding affinity and emphasize the importance of stereochemical acceptability at these positions. The promotion of receptor binding by D-amino acids is examined, particularly with respect to implied peptide conformations. The experimental data have been analysed for the relative influence of metabolic and conformational factors.

The physiological optics of Dinopis subrufus L. Koch: a fish-lens in a spider.

Abstract: The posterior median eyes of Dinopis subrufus are probably the largest simple eyes found in arthropods, and may reach 1.40 mm in diameter. For a lens 1.325 mm in diameter the focal length is 0.771 mm, giving an F-number of 0.58. This, coupled with the large diameter of the receptors (20 $\mu $m), means that the light absorbed per receptor will be about 2000 times as great as in a diurnal spider such as a salticid, or in the human eye looking at the same extended field. For a lens of this size to produce a resolution of 1.5 degrees - the visual subtense of each receptor - it is shown that spherical aberration has been overcome. This is achieved partly by the lens having a double structure, with an outer region of low refractive index, and a harder core whose apparent refractive index is 1.67. It is argued from the observed resolution of the lens that the core is probably inhomogeneous, like a fish lens, with a central refractive index that could be as low as 1.52. The hemispherical eye-capsule is modified to bring the retina close to the rear surface of the lens, a feature necessitated by the relatively short focal length. The large, hexagonal receptive segments are tightly packed, but there is no tapetum. Some retinal anomalies, the structure of the other eyes of Dinopis, and the relation of its visual optics to its nocturnal habit are also discussed.

Neuronal and behavioural responses in rats during noxious stimulation of the tail.

Abstract: In rats anaesthetized with urethane, extracellular unit activity has been recorded from neurones in the central nervous system during noxious stimulation of the tail Accurately graded and sustained stimulation was achieved by immersing the whole tail in water at controlled temperatures Neurones were found chiefly in the marginal layers of the dorsal horn near the entry of the dorsal roots supplying the tail and in the ventrobasal nucleus of the thalamus; a few neurones were also found in the somatosensory cortex Both dorsal horn units and thalamic units showed very similar responses as the tail temperature was gradually raised At 42°C there was an increase in firing rate which rose sharply with increasing temperatures to reach a maximum at 46°C At higher temperatures activ­ity declined and at temperatures above 50°C was largely extinguished The temperature-response curves were bell-shaped The decline in activity depended on temperature and not on time: sustained firing for many minutes was seen when temperature was at or just below the peak of the bell-shaped curve The dorsal horn and thalamic cells also responded to noxious mechanical stimulation of the tail The receptive fields at both levels were similar, being variable in size, often bilateral and sometimes covering the whole tail None of the central neurones showed any response to noxious stimulation other than on the tail; neither did they respond to movement of the tail nor to light mechanical stimuli applied to the tail or elsewhere In behavioural experiments conscious rats had their tails exposed to water at various temperatures The rats lifted their tails from the water at a threshold temperature of 437 ± 06°C, i e just above the threshold for the central nociceptive neurones The findings are compatible with a specific nociceptive pathway ascending to the ventrobasal thalamus

Photosynthetic Components and Activities of Nitrogen-Fixing Isolated Heterocysts of Anabaena cylindrica

Abstract: Isolated heterocysts of the N 2 -fixing Anabaena cylindrica , prepared by a combination of lysozyme and Yeda press treatments, are metabolically active with over 90% of the measurable nitrogenase activity being located in the heterocyst preparations after disruption of the intact filaments. The photosynthetic activities of such isolated heterocysts are characterized by an inability to carry out the photolysis of water or to fix CO 2 . The lack of O 2 evolution appears to be due in part to the deple­tion during heterocyst differentiation of Mn, a central component of the photosystem II reaction centre in O 2 -evolving algae. There is evidence that components of the photosynthetic electron transport chain on the reducing side of the photosystem II reaction centre are present and functional in heterocysts. These include cytochrome c 554 , plastocyanin, plastoquinone, cytochrome b 559 , P700, cytochrome b 563 , and iron-sulphur proteins which appear to correspond to centre A and centre B of higher plant chloroplasts. Soluble, or loosely bound ferredoxin is also present and involved in electron transport from ferredoxin to NADP. Isolated heterocysts photoreduce methylviologen when reduced 2,6-dichlorophenolindophenol and diphenylcarbazide serve as electron donors. They show P700 photo-oxidation and photoreduction, photosyn­thetic electron transport which is inhibited by 2,5-dibromo-3-methyl-6-isopropyl- p -benzoquinone an antagonist of plastoquinone, photophos­phorylation, oxidative phosphorylation and ferredoxin-NADP oxido-reductase mediated reactions. The photosynthetic modifications of the heterocyst are such that electron transport and the generation of ATP for nitrogenase can occur without concomitant O 2 evolution and with­out nitrogenase having to compete with CO 2 fixation for ATP and reductant.

The Anatomy and Function of 'Free' Nerve Endings in an Amphibian Skin Sensory System

Abstract: The skin of the body and tail in embryonic and young larval Xenopus is innervated by sensory neurones with cell bodies lying along the dorsal midline of the spinal cord. These Rohon-Beard cells have naked peripheral neurites, usually under 1 $\mu $m in diameter, which form a loose network under the skin. In the electron microscope narrower neurites from this network are found running into the skin between the cells. The neurites are periodically varicose and, between the superficial skin cells, these bulges are invaginated into the skin cell membranes where some terminate. Responses of Rohon-Beard cells to skin stimulation can be recorded extracellularly using a suction electrode. Impulses were evoked by light touch or stroking of the skin with fine hairs. These discharges adapted rapidly and quickly fatigued when stimulated repeatedly. Receptive fields (mean area 0.16 mm$^{2}$) were mapped and related to the total number of Rohon-Beard cells and the area of skin to be innervated. This showed that there were enough Rohon-Beard cells to innervate the skin from 1.5 to 2.5 times. The anatomy of the fine, varicose 'free' nerve endings of the Rohon-Beard cell neurites is discussed in relation to their function in detecting transient, touch stimuli to the skin and their role in evoking swimming of the embryo.

Heterogeneous heterozygosities in Mus musculus populations.

Abstract: Both chance and adaptation have effects in determining the genetical constitution of local populations of any organism, but opinions differ widely over their relative importance. This study describes the frequencies of electrophoretically detected alleles at 22 loci in 1538 house mice (Mus musculus L.) from 27 population samples collected from the Faroe, Shetland and Orkney archipelagoes; the mainland of Great Britain plus three small off-shore islands; and a sub-Antarctic island (Macquarie) lying between Australia and the Antarctic Continent. Neither the average heterozygosities nor the distribution of allele frequencies in the different populations showed any discernible pattern, but at least three loci (Hbb, Es-2, Dip-1) underwent seasonal changes in frequency which could only be due to selection. Moreover the overall variances of allele frequencies were significantly heterogeneous (P $\approx $ 0.001), suggesting that different factors affect different loci. The key to understanding this apparent randomness of frequencies is recognizing that selection pressures are non-constant, and particular traits may affect fitness only spasmodically. The occurrence and frequency of an allele in any population may reflect only chance historical factors, but the trait(s) affected by it is potentially subject to selection at any time. For example, the proportion of heterozygotes at the Hbb locus in one population (Skokholm) living entirely independent of man, increased in five summers out of six. Winter death in mice is cold-dependent, and the exceptional summer followed a particularly mild winter when the usual decrease in heterozygotes did not take place. An r-selected species like the house mouse is more likely to reveal the interplay of genetical chance and purpose than a numerically less volatile one in which short-term genetical adjustment will be relatively uncommon.

Hormones and behaviour.

Abstract: Interest in the roles of hormones rests on the fact that specific behavioural patterns of great biological importance can be regulated by chemical substances produced outside the brain; this discovery, the most important, underlies all subsequent work. Though most studies have been made on sexual behaviour, hormones are also known to be concerned with other categories including aggression, ingestion and, perhaps, adaptive behaviour. Hormones may only be a special case of this phenomenon, since other substances (including those in the diet) may alter intracranial function in a way which is behaviourally significant. Furthermore, it is becoming apparent that events in the environment, including the behaviour of other animals or chemical substances produced by them, may modify the interaction between a hormone and its effects on behaviour. The results of such studies have been applied to humans, though current information on primates suggests important differences between them and the more commonly investigated rodents. A most intriguing discovery has pointed to a role for hormones in a differentiation of sexually dimorphic behaviour, in addition to their activating effect in the adult. This suggests that brief exposure of some hormonally-sensitive part of the brain to a given hormone during a ‘ critical ’ period results in permanent alteration in its function. The nature of this change remains obscure though neuroanatomical findings which may be relevant have been described. Understanding of the way hormones alter neural functions is still primitive. Binding of steroid hormones to neural receptors is well known but the functional significance of this remains enigmatic. Interaction of hormones with endogenous cerebral compounds such as monoamines and peptides is only now being studied, though this may prove a turning point for the future.

Mother-Infant Separation and the Nature of Inter-Individual Relationships: Experiments with Rhesus Monkeys

Abstract: During the late fifties the extent to which a period of separation from the mother figure could have adverse effects on the development of a human child was a matter of some dispute. While some psychiatrists and paediatricians held that the consequences could be severe (see for example, Bowlby 1951, 1958; Ainsworth 1962), their views were based largely on clinical and retrospective evidence, and conflicted with established medical and social practice. Since controlled experiments with human subjects were out of the question on ethical grounds, we decided to see what progress could be made with rhesus monkeys. It was apparent from the start that the consequences of a separation experience could not be studied in isolation - it was, for instance, necessary for us to do some initial work on processes of intraspecific communication in rhesus monkeys, and on how the mother-infant relationship develops. Some of this work was reviewed previously (Hinde & Spencer-Booth 1968). As the work progressed it became apparent that ( a ) the consequences of a separation experience vary with the nature of the mother-infant relationship, and ( b ) that the nature of the mother-infant relationship varies with the social situation. Furthermore, a number of conceptual issues arose in the course of the work, such as precisely what one means by a ‘relationship’, and how the important but somewhat intangible ‘natures’ or ‘qualities’ of relationships could be assessed and compared in a hard-headed manner. The aim of this paper is not to review the current state of the evidence bearing on any one of these problems, but rather to demonstrate, from the work of one laboratory, how the various problems are inter-related.

Leishmania in phlebotomid sandflies. IV. The transmission of Leishmania mexicana amazonensis to hamsters by the bite of experimentally infected Lutzomyia longipalpis.

Abstract: Leishmania mexicana amazonensis was cyclically transmitted in the laboratory from hamster to hamster by single bites of experimentally infected Lutzomyia longipalpis. The sandflies were denied suitable conditions for oviposition and were induced to take a second, infecting, meal while still gravid. In three transmissions, cutaneous lesions developed rapidly on two hamsters, whereas that on the third remained small for 8 months, almost disappeared, and then grew to the usual large size. In some infected flies, parasites migrated to the pharynx and buccal cavity but then died and disintegrated; in others, healthy parasites were attached to the cuticular intima of the oesophagus and pharynx by hemidesmosomes. The common failure of leishmaniae to become established in the foregut of many experimentally infected sandflies may be because parasites die after migration and not because they fail to migrate. One cause of the death may be a lack of plant juices, a food of sandflies in nature. At the second potentially infecting feed, sandflies usually probed many times and took either no blood or only a small meal. It is suggested that parasites in the foregut block the pores of cibarial sensilla which probably control engorgement; such an interference would be an advantage in the evolution of Leishmania.

A possible transepithelial pathway via endoplasmic reticulum in foetal sheep choroid plexus

Abstract: Choroid plexuses from early (30-60 days gestation) and late (125 days) sheep foetuses were examined by various ultrastructural techniques in order to investigate possible explanations for the greater penetration of protein and non-electrolytes from blood into cerebrospinal fluid (c.s.f.), which occurs in the early foetus in contrast to later stages. The greater penetration occurs despite the presence of well-formed tight junctions between the epithelial cells and the development of some of the characteristic ion gradients between c.s.f. and plasma. A tubulocisternal system of endoplasmic reticulum appears to connect the basolateral and the apical cell surfaces in the early but not in the late foetuses. Several types of connection between the endoplasmic reticulum and the cell membrane were present in the early foetuses; these may account for some of the different permeability properties of the immature choroid plexus.

Neural events underlying learning in insects: changes in pacemaker.

Abstract: Computer-controlled operant-conditioning training procedures were used to raise (up-learning) or lower (down-learning) the mean frequency of discharge of the anterior adductor coxa motoneurone of the locust Schistocerca gregaria. Intracellular recordings were made from the soma of the motoneurone during training. The neurone appeared capable of spontaneous discharge in the absence of synaptic input since its mean pacemaker rate was measured after blocking synaptic inputs by infusing high Mg$^{2+}$/zero Ca$^{2+}$ saline into the neuropile associated with the neurone. Rates were determined before and after the training procedure was applied. It was found that a stable increase in the mean frequency of the pacemaker occurred during up-learning and a decrease during down-learning. The pacemaker shift accounted for a little over half the overall learning change. The remainder was attributed to changes in the activities of interneurones that directly, or indirectly, affect the motoneurone pacemaker. Conventional synaptic potentials that could have accounted for the remainder were not conspicuous in the soma recordings.

Analysis of catecholamine effects in single atrial trabeculae of the frog heart.

Abstract: A study was made of the time course of the effects of adrenaline and isoprenaline on both twitch tension and the intracellular action potential of single atrial trabeculae from frog heart, under a variety of experimental conditions. Twitch tension and overshoot of action potentials rose and subsided in a parallel fashion during build-up and decline of catecholamine action. Cessation of stimulation during drug application had little effect on the tension responses to the drugs. These, and also results obtained with step changes of external calcium concentration during drug exposure, suggest that tension enhancement is a direct consequence of the increased calcium inward current produced by the catecholamines. Exceptional results from trabeculae of ‘hypodynamic’ hearts are described and interpreted on the basis of previous findings obtained in the ‘hypo-dynamic’ condition. Under suitable conditions, including the use of brief periods of drug exposure (≤20 s), three phases of ( β -catecholamine action were discernible: (1) a latency period, of up to 15 s, which preceded tension and potential rise after drug application. Results are presented suggesting that this latency mainly reflects the time which it takes for drug-combined receptors to activate adenylate cyclase in the cell membrane. (2) A sub­sequent phase was critically dependent, in both its magnitude and time course, on phosphodiesterase activity, as was shown by the application of the specific inhibitors papaverine, ICI 63 197, and Ro 20-1724. This phase is probably controlled by the build-up and decline of cAMP within the cells and the subsequent activation and deactivation of a protein kinase. (3) A third phase, associated with the final portion of the decline of catecholamine action, was relatively insensitive to moderate inhi­bition of phosphodiesterase activity. It is attributed to a change of phosphorylation of sites at the internal surface of the cell membrane, the process which, it is assumed, determines the size of calcium inward current during an action potential. Tension decline after a short staircase occurred with a time course closely similar to that of the final phase of the declining catecholamine response. A common final step in the sequential cellular processes under­ lying the two responses is proposed. In some 40% of the trabeculae examined, adrenaline responses were of ‘mixed’ origin: in addition to the relatively slow β -adrenergic action, an initial rapid tension change was present, and experimental tests suggest that this is mediated by α -type receptors.

Simultaneous anatomical demonstration of the representation of the vertical and horizontal meridians in areas V2 and V3 of rhesus monkey visual cortex.

Abstract: This paper describes an experiment undertaken to demonstrate anatomically the representation of the horizontal and the vertical meridian of the visual fields in areas V2 and V3 of the same hemisphere. [ 3 H]Proline was injected into V1 in the region of horizontal meridian representation at 30° from the centre of gaze in an animal in which the corpus callosum had been sectioned. The histology of the prestriate cortex revealed two small patches of label, separated by a 500 μm gap, between two regions of callosal fibre degeneration. The centre of the 500 μm gap was taken to be the boundary between V2 and V3. This demonstration leaves no doubt that not only are the two areas topographically organized but they both receive a direct input from area 17 (V1).

1H nuclear magnetic resonance studies of the tyrosine residues of selectively deuterated Lactobacillus casei dihydrofolate reductase.

Abstract: A selectively deuterated dihydrofolate reductase, in which all the aromatic protons except the 2,6-protons of the tyrosine residues have been replaced by deuterium, has been prepared from Lactobacillus casei grown on a mixture of normal and deuterated amino acids. The aromatic region of the $^{1}$H n.m.r. spectrum of this enzyme contains only resonances from the five tyrosine residues. For each tyrosine, the 2- and 6-protons have the same chemical shift, indicating rapid interconversion of the two conformers related by 180 degrees rotation about the C$\_{\beta}$-C$\_{\gamma}$ bond. The effects of substrate, inhibitor and coenzyme binding on the tyrosine residues have been investigated; four of the five residues are affected by ligand binding. Using the weakly binding ligands 2,4-diaminopyrimidine and p-nitrobenzoyl-L-glutamate to connect the spectra of the free enzyme with those of the complexes, it is possible to give a detailed description of the effects of ligand binding on individual residues. In the binary complexes, methotrexate affects three tyrosine residues, only one of which is affected by folate, indicating a significant difference in the mode of binding of substrates and inhibitors. The co-enzymes NADP$^{+}$ and NADPH lead to broadly similar changes in the spectrum, except for one resonance which is shifted in opposite directions by the two co-enzymes. The oxidized and reduced coenzymes also differ in their effects on the changes produced by inhibitor binding; the spectrum of the enzyme-NADPH-methotrexate complex is similar to that of the enzyme-methotrexate complex, while that of the enzyme-NADP$^{+}$-methotrexate complex is not. In contrast to the behaviour seen in the binary complexes, the spectrum of the enzyme-NADP$^{+}$-folate complex is very similar to that of enzyme-NADP$^{+}$-methotrexate. Evidence is presented that some, at least, of the changes in chemical shift of the tyrosine residues are due to ligand-induced conformational changes. The binding of p-nitrobenzoyl-L-glutamate to the enzyme-2,4-diaminopyrimidine complex is found to be tighter than that to the enzyme alone.

The resolution of neuronal assemblies after cobalt injection into neuropil.

Abstract: Cobalt ions are incorporated by many interneurons of the insect central nervous system after injection of cobalt chloride or cobalt acetate into the neuropil. Entire nerve cells are subsequently revealed by sulphide precipitation which is followed by silver intensification of whole brains and ganglia. The number of neurons resolved depends upon the optimal timing of an injection phase, followed by a period of diffusion. These, and the site of injection, can be adjusted so as to demonstrate arrangements within and between complete populations of morphological classes of interneurons. This novel use of cobalt reveals cytoarchitectural features of neuropil that are refractory to other histological procedures and shows that in columnar visual neuropil the nerve cell arrangements are limited to a few basic modes of assembly.

An analysis of acetylcholine in frog muscle by mass fragmentography

Abstract: Extracts of frog sartorius muscles were assayed for their acetylcholine (ACh) content by means of pyrolysis-gas chromatography/mass spectrometry. Freshly dissected whole muscles contained 43 $\pm $ 3.1 (22) pmol ACh, and apart from ACh, no other related ester was detected. The ACh content varied among different animals, but was relatively independent of muscle mass. In denervated muscles the ACh content began to decrease after a delay of two days and, by the eighth day of denervation, reached a steady value of about 26% of the control. Muscles were divided into endplate free segments and segments containing endplates. ACh was localized predominantly in the endplate segment, but a small amount was found in the endplate free region. The endplate segments of denervated muscles contained ACh at the same low concentration as ACh in non-endplate segments. The ACh concentration in non-endplate segments was not affected by denervation. During incubation in the presence of diisopropylfluorophosphate muscles released 2.1 pmol/h into the medium. During the incubation the ACh content of the muscles remained constant. It is concluded that there is about 12 pmol extraneural ACh in sartorius muscle, and that about 30 pmol is in the nerve terminals. If it is assumed that one half of the neural ACh is contained in the synaptic vesicles of motor nerve terminals, then each vesicle would contain, on the average, some 8 $\times $ 10$^{3}$ molecules of ACh.

Sporulation and the Development of Planktonic Blue-Green Algae in Two Salopian Meres

Abstract: Factors affecting akinete formation and the survival of planktonic blue-green algal populations after the formation of 9water blooms9 were investigated in two eutrophic kataglacial lakes. It is considered that the induction of sporulation may be due to extreme conditions at the water surface during the summer to which the algal bloom is exposed, rather than to nutrient, especially orthophosphate, deficiency. It has not been shown conclusively that akinetes constitute an overwintering stage of the planktonic algal life cycle, or that akinetes germinate in the spring to produce the inoculum for subsequent vegetative growth. Comparisons of planktonic, sedimenting and benthic algal material indicate that germination shortly after maturation may provide the greater part of the over-wintering planktonic vegetative populations. Population sizes and life cycles appear to be influenced by the physical factors which control the stability of the water column.