Showing papers in "The Journal of Physiology in 1962"

Receptive fields, binocular interaction and functional architecture in the cat's visual cortex

Abstract: What chiefly distinguishes cerebral cortex from other parts of the central nervous system is the great diversity of its cell types and interconnexions. It would be astonishing if such a structure did not profoundly modify the response patterns of fibres coming into it. In the cat's visual cortex, the receptive field arrangements of single cells suggest that there is indeed a degree of complexity far exceeding anything yet seen at lower levels in the visual system. In a previous paper we described receptive fields of single cortical cells, observing responses to spots of light shone on one or both retinas (Hubel & Wiesel, 1959). In the present work this method is used to examine receptive fields of a more complex type (Part I) and to make additional observations on binocular interaction (Part II). This approach is necessary in order to understand the behaviour of individual cells, but it fails to deal with the problem of the relationship of one cell to its neighbours. In the past, the technique of recording evoked slow waves has been used with great success in studies of functional anatomy. It was employed by Talbot & Marshall (1941) and by Thompson, Woolsey & Talbot (1950) for mapping out the visual cortex in the rabbit, cat, and monkey. Daniel & Whitteiidge (1959) have recently extended this work in the primate. Most of our present knowledge of retinotopic projections, binocular overlap, and the second visual area is based on these investigations. Yet the method of evoked potentials is valuable mainly for detecting behaviour common to large populations of neighbouring cells; it cannot differentiate functionally between areas of cortex smaller than about 1 mm2. To overcome this difficulty a method has in recent years been developed for studying cells separately or in small groups during long micro-electrode penetrations through nervous tissue. Responses are correlated with cell location by reconstructing the electrode tracks from histological material. These techniques have been applied to

Some quantitative aspects of the cat's eye: axis and plane of reference, visual field co-ordinates and optics

Abstract: The present study grew out of an investigation into the projection of the visual fields on the lateral geniculate nucleus (LGN) in the cat. The new methods we have developed for studying this projection using single-unit recording and the precision we have found in the projection itself directed our attention to many of the basic problems inherent in the idea of topographical localization in the visual system. The present paper is concerned with an examination of these problems particularly as they pertain to the eye. The nature of the projection of the visual fields on the LGN will be described in the following paper (Bishop, Kozak, Levick & Vakkur, 1962). In order to describe a direction in the visual field a suitable system of co-ordinates is required, the direction being defined in terms of angles from a reference axis and plane. Under experimental conditions the visual field will consist of a tangent screen or perimeter. In addition, the reference axis and plane of the visual field co-ordinate system must be defined in relation to the projection of retinal landmarks into the visual field. Unless this is the case the nature of the projection of the visual fields on to the brain centres will vary with the position of the eyes. Thus the orientation of the eyeballs should be known and for this purpose an axis and plane of reference for the eye must be defined in relation to appropriate retinal landmarks. Even before the development of vision the direction of gravity provided the vertical co-ordinate as the basic reference for the orientation of the organism in its environment. The development of vision, particularly binocular vision, has added a second fundamental reference, namely the horizontal co-ordinate determined visually from the horizon. The direction of gravity and the plane of the horizon are the axis and plane of reference used by the animal in its interpretation of the visual world. If our system

The identification of single units in central visual pathways.

Abstract: There have been many single-unit studies on central visual pathways in recent years and several of these studies have been concerned with unit activity in or near the lateral geniculate nucleus (Tasaki, Polley & Orrego, 1954; Freygang, 1958; Lennox, 1958a, b; De Valois, Smith & Kitai, 1959; Erulkar & Fillenz, 1960; Griisser-Cornehls & Griisser, 1960; Hubel, 1960; Widen & Marsan, 1960; Hubel & Wiesel, 1961). In some cases the identification of the nature of the unit (i.e. presynaptic axon, cell-body, postsynaptic axon, etc.) has been made on a single criterion, e.g. latency. While this may suffice for many units, it is obviously desirable to improve the accuracy of identification by using as many criteria as possible. In connexion with our studies on the visual system we have found it essential to be able to distinguish between optic-tract axons, geniculate cells and radiation axons. The present paper is concerned with the criteria which we have found useful in this respect when recording extracellularly from central visual pathways. The criteria have been established for tract and radiation axons by recording directly from these pathways after having inserted the electrode under stereotaxic control. The information obtained in this way could then be applied to recordings obtained from the lateral geniculate nucleus (LGN) or its vicinity, situations in which a knowledge of the position of the electrode did not necessarily assist in the identification. In this way the three groups mentioned could be distinguished from one another. The possibility of other groups occurring will be discussed later. The wave form of the extracellularly recorded response, its attenuation with distance from the unit and other features are critically dependent on the type of electrode used; hence our findings in this respect cannot be applied indiscriminately to situations where the electrodes are of different shape, material or resistance. These points are discussed below. Probably for this reason, our results are not in entire agreement with those of previous investigators in this field. Some of the material presented here has appeared in earlier shorter communications (Bishop, Burke & Davis, 1958, 1959; Bishop, Burke, Davis & Hayhow, 1958). The antidromic

Presynaptic inhibition of the spinal monosynaptic reflex pathway.

Abstract: At present two distinct types of inhibition in the lumbosacral spinal cord of the cat are known. One type is effected by changes in the membrane potential (the inhibitory post-synaptic potential, IPSP) and in the excitability of the post-synaptic cell, and may, therefore, be referred to as postsynaptic inhibition. The characteristics of the IPSP have recently been reviewed (Eccles, 1957, 1961a, b; Kuffler, 1959; Frank & Fuortes, 1961). The second type of inhibition is characterized by a depression in the size of the excitatory post-synaptic potential (EPSP) without any detectable change in the resting membrane potential or in the excitability of the postsynaptic cell (Frank & Fuortes, 1957; Frank, 1959; Eccles, Eccles & Magni, 1960, 1961). Since there is evidence that the EPSP depression is a consequence of a depolarization of primary afferent fibres (Eccles, Eccles & Magni, 1961; Eccles, Magni & Willis, 1962; see also Eccles, 1961 a, b), this type of inhibition may be termed presynaptic inhibition. A convenient method of testing for inhibition in the spinal cord is to study the effect of conditioning volleys in various afferent nerve fibres upon the height of the monosynaptic reflex spike produced by a particular motor nucleus (Renshaw, 1942; Lloyd, 1946a, b; Laporte & Lloyd, 1952). The results of the present study show, by using this technique under conditions suitable for the production of presynaptic inhibition, that there is a powerful and prolonged depression of the monosynaptic reflex discharge; and arguments are presented that the reflex depression observed is due to presynaptic inhibition.

Effect of changes in blood gas tensions and carotid sinus pressure on tracheal volume and total lung resistance to airflow.

Abstract: Asphyxia, hypercapnia and hypoxaemia constrict the trachea (Loofbourrow, Wood & Baird, 1957) and bronchi (Roy & Brown, 1885), and also change the mechanical properties of the lungs in a manner attributed to bronchoconstriction (Einthoven, 1892; Dixon & Brodie, 1903). These effects are largely dependent on the integrity of vagal conduction. In analysing the responsible mechanisms Daly & Schweitzer (1951) concluded that stimulation of carotid body chemoreceptors in dogs causes reflex bronchodilatation, and Daly, Lambertsen & Schweitzer (1953) decided that hypoxaemia and hypercapnia of the central nervous system produce nervously mediated bronchoconstriction. The experiments cited above usually involved assessment ofthe relationship between inflation pressure and tidal volume during cyclical changes in volume. This relationship is, by analogy to electrical theory, closely related to the 'impedance' of the respiratory system. The term impedance will be used to describe these measurements in this paper. At the usual frequencies of ventilation, impedance measurements are very insensitive to changes in airway resistance and greatly influenced by alterations in compliance. Therefore, results based on impedance measurements cannot be unequivocally attributed to changes in airway resistance, and give no quantitative information about airway diameter. This paper describes the actions of hypoxaemia, hypercapnia, and changes in carotid sinus pressure on the volume of a tracheal segment and on the total lung resistance to airflow in dogs. We have also studied the nervous mechanisms mediating these changes and have controlled the rate and depth of ventilation and attempted to eliminate the effects of changes in lung compliance and transpulmonary pressure. An abstract of some of the results has been published (Nadel & Widdicombe, 1961).

Central pathways responsible for depolarization of primary afferent fibres.

Abstract: In the first electrophysiological observations on the central nervous system Gotch & Horsley (1891) recorded from the surface of the spinal cord electrical potential changes which were associated with reflex activity. The subsequent investigation of this phenomenon began with a systematic examination of the various components of the cord potential produced by an afferent volley in a dorsal root, and the attempt to correlate these components with the reflex contractions of muscles (Gasser & Graham, 1933; Hughes & Gasser, 1934 a, b). In the initial investigation (Gasser & Graham, 1933) evidence was presented that the prolonged (about 200 msec) positive wave of the dorsum of the cord (the P wave) was associated with a depression of the initial negative potential wave (the N wave) evoked by a second dorsal root volley, whether in the same or in a different ipsilateral root. It was suggested that the P wave was due to the flow of current in structures which were oriented dorso-ventrally and depolarized at their ventral ends, and that these structures were interneurones. The recording of potentials electrotonically propagated along the primary afferent fibres and so into the dorsal root was introduced by Barron & Matthews (1935, 1938) and has the great advantage over the cord dorsum leads in that it appears to give a selective lead from the mechanism generating current flow within the spinal cord. It was remarkable that in response to all varieties of afferent input the dorsal root potentials (DRPs) were uniformly in the depolarizing direction. It was concluded that the DRP and the P wave of the cord dorsum are produced by the same potential generator in the spinal cord, and this identification has been accepted by all subsequent investigators (see Bremer & Bonnet, 1942; Bernhard, 1952, 1953a; Koketsu, 1956a, b; Eccles, Magni & Willis, 1962). Subsequently there have been many experimental investigations both of the cord dorsum potentials (Bernhard, 1952, 1953a, b; Bernhard &

Replacement of the axoplasm of giant nerve fibres with artificial solutions.

Abstract: In 1937 Bear, Schmitt & Young showed that substantial quantities of axoplasm could be squeezed out of the cut end of a giant nerve fibre of Loligo. This technique has been widely used for obtaining samples of axoplasm, but little attention has been paid to the electrical properties of the thin sheath which remains after the contents of the nerve fibre have been extruded. Since extrusion involves flattening the axon with a glass rod or roller it is natural to suppose that the membrane would be badly damaged by such a drastic method of removing axoplasm. However, in the autumn of 1960 impulses were recorded from extruded sheaths which had been refilled with isotonic solutions of potassium salts (Baker & Shaw, 1961) and on further investigation it turned out that such preparations gave action potentials of the usual magnitude for several hours (Baker, Hodgkin & Shaw, 1961). Tasaki and his colleagues at Woods Hole have also been successful in perfusing the giant axons of Loligo pealii and several methods, some evidently developed before ours, were described by Oikawa, Spyropoulos, Tasaki & Teorell (1961). We have made no serious attempt to compare different methods and all the experiments described here were carried out by perfusing sheaths from which the bulk of the axoplasm had been removed by extrusion. The first paper deals with technique and with some general properties of perfused fibres, including histology and electron microscopy. The second is concerned with the electrical effects of changing the internal solution and ends with a discussion of both sets of results.

The mechanism of solute transport by the gall-bladder.

Abstract: In the preceding paper (Diamond, 1962a) it was shown that an absorption of isotonic NaCl, similar to that observed in many other epithelia, is the biological driving force by which the gall-bladder concentrates bile. The present paper will be concerned with the active and passivemechanisms by which solutes cross the gall-bladder in vitro; the mechanism of water transport will be deferred to the following paper. When an epithelial membrane which transports salt and water separates two identical solutions, it has invariably been found that an electrical potential difference (p.d.) is set up across the membrane under at least some experimental conditions. For example, the inside of frog skin becomes positive by up to 130 mV, and this p.d. is due exclusively to active transport of Na+ inwards. The p.d. carries Clinwards passively, hence active transport of Na is sufficient to account for the transport of NaCl effected by frog skin (Ussing & Zerahn, 1951). In numerous other tissues the side of the preparation towards which NaCl is transported becomes positive by 20-130 mV, owing to active Na transport (e.g. large intestine, foetal stomach, urinary bladder, placenta, rumen, and kidney proximal tubule). In a few cases where the p.d. has the opposite sign, active transport of Cl has been demonstrated (e.g. stomach, bethanecholstimulated intestine, and adrenaline-stimulated frog skin). Thus, the sign of the p.d. between identical solutions provides a simple test as to the mechanism of salt transport. In the gall-bladder it has turned out unexpectedly that active salt transport is not associated with any measureable electrical p.d. and that this organ provides the first instance of an apparently neutral NaCl pump. In addition, symmetrical permeability characteristics make the gallbladder a favourable system for testing the ability of the constant-field equation to predict tracer fluxes.

The effects of changes in internal ionic concentrations on the electrical properties of perfused giant axons

Abstract: This paper is concerned with the effects of altering the composition of the internal fluid on the electrical properties of giant axons from which the bulk of the axoplasm had been removed by extrusion (Baker, Hodgkin & Shaw, 1962). To begin with, we shall consider a series of experiments which show that the difference in potassium concentration between the internal and external fluid provides the main electromotive force for generating the resting potential. In order to reduce the error introduced by junction potentials and to avoid making uncertain estimates of the activity coefficient ofK+ in K2S04 it was simplest to work with an internal solution consisting of mixtures ofKCI and NaCl. The high concentration of chloride did not have any markedly deleterious effect, for fibres filled with isotonic KCI were usually excitable and had a resting potential only about 5 mV less than in those filled with isotonic potassium sulphate.

The determination of the projection of the visual field on to the lateral geniculate nucleus in the cat.

Abstract: Henschen (1897, 1898) was the first to provide direct evidence in favour of a retinotopic projection in the lateral geniculate nucleus (LGN). He described a woman suffering from blindness of the lower left quadrants of both visual fields who was subsequently found to have a lesion limited to the dorsal half of the right LGN. Actually these early observations are not in accord with the later experimental studies on primates by Brouwer and subsequent workers (see below). Further early human clinico-pathological observations were made by Wilbrand & Saenger (1904), Ronne (1913, 1914) and Winkler (1912), but the extreme rarity of sufficiently restricted lesions, particularly in the nucleus itself, made it unlikely that the details of the retinotopic projection in the LGN would be unravelled in this way. By enucleating the eye of a cat and studying the distribution of the secondary degeneration in each LGN, Minkowski (1913) provided the first direct experimental evidence that the crossed and uncrossed optic fibres were distributed differently in the nucleus (cf. Minkowski, 1920) and that the binocular part of a visual field projected only to the medial part. The first detailed study of the retinotopic projection in the LGN was, however, carried out by Brouwer and his colleagues (Brouwer, Zeeman & Houwer, 1923). By making small retinal lesions and subsequently studying the degenerating fibres in Marchi preparations they established the quadrantic projections ofthe retina in the rabbit and cat and the quadrantic and intraquandrantic projections of the central and peripheral retinal segments in the monkey (Brouwer & Zeeman, 1925, 1926; Overbosch, 1927). Further details in respect to the monkey were added by Brody (1934), Penman

The central control of the dynamic response of muscle spindle receptors.

Abstract: The present experiments were performed to search for differences between the effects of intrafusal muscle fibre contraction on the primary and on the secondary endings of muscle spindles. These two kinds of afferent endings are differently arranged with regard to the intrafusal muscle fibres (Ruffini, 1898; Barker, 1948; Boyd, 1961), but in the situations so far examined the effects of intrafusal fibre contraction upon them have appeared to be similar (Hunt, 1954; Harvey & Matthews, 1961 a, b). The behaviour of single endings was studied in decerebrate cats in the hope that the intrafusal fibre contraction maintained physiologically in this preparation as a result of 'spontaneous' fusimotor activity would reveal differences not hitherto demonstrated by electrical stimulation of efferent fibres. The effects of this physiologically maintained activity can be assessed by comparing the responses of individual endings to a standard extension applied before and after de-efferenting the spindles by cutting the appropriate ventral roots (Eldred, Granit & Merton, 1953). The present paper is concerned solely with the effects of intrafusal fibre contraction on the sensitivity of the endings to the dynamic component of a slowly applied stretch (3 mm/sec). The dynamic sensitivity of an ending may be measured by determining the slowing ofits discharge which occurs when the dynamic phase of stretching is completed and the final extension is maintained. In the absence of intrafusal fibre contraction the dynamic sensitivity of secondary endings is appreciably less than that of primary endings (Harvey & Matthews, 1961 b; P. Bessou & Y. Laporte, personal communication); and this has also been shown for innervated spindles in the decerebrate cat (Cooper, 1959, 1961). The present experiments show that intrafusal fibre contraction has little effect on the small dynamic response of secondary endings. The larger dynamic response of primary endings was usually increased by fusimotor activity, as has also been found for the sensitivity of these endings to vibration (Granit & Henatsch, 1956). But the most important observation was that there was no simple

Selective excitation of corticofugal neurones by surface‐anodal stimulation of the baboon's motor cortex

Abstract: Understanding of the precise mode of action of a focal electrical stimulus on the complex systems of neurones embedded in the conducting medium of the cerebral cortexis still far from complete (Liddell, 1953). The first demonstration that the resulting corticofugal discharges contained a direct component, due to electrical stimulation of corticofugal cells, and an indirect component due to stimulation of corticofugal cells by way of other intracortical neuronal systems, was given by Patton & Amassian (1954). Evidence of direct electrical and of indirect synaptic excitation of cortical pyramidal neurones was found in intracellular records by Phillips (1956). Also, in stimulating the cerebellar cortex, Granit & Phillips (1957) found that the Purkinje cells could be excited both directly and indirectly. In both types of cortex those corticofugal neurones which were situated on the convexity of a gyrus or of a folium were stimulated by smaller currents if the focal cortical stimulus was made anodal. The threshold for focal cathodal stimulation was higher, and the stimulus stirred up more complex effects. This paper extends these investigations to the motor cortex of a primate, the common African baboon (Papio sp.). The method of intracellular recording from pyramidal neurones was not used because the time, labour and material needed to collect enough observations would have been prohibitive, and because it seemed unlikely that the modes of direct and synaptic excitation of these neurones would differ materially from those already seen in the cat. Critical distinction between direct and indirect stimulation of cells demands minimal stimulus, with minimal spread in the cortex, to elicit the minimal, most circumscribed response. Since the electrical threshold for movement is higher than the threshold

Single-unit recording from antidromically activated optic radiation neurones.

Abstract: Antidromic activation of cells in the central nervous system has proved to be a most useful method of studying the properties of neurones and the part these play in synaptic transmission (see e.g. Renshaw, 1941, 1946; Araki, Otani & Furukawa, 1953; Brock, Coombs & Eccles, 1953; Frank & Fuortes, 1955; Granit & Phillips, 1956; Phillips, 1956, 1959; Coombs, Curtis & Eccles, 1957a, b; Fatt, 1957; Fuortes, Frank & Becker, 1957; Martin & Branch, 1958; Bennett, Crain & Grundfest, 1959; Freygang & Frank, 1959; Machne, Fadiga & Brookhart, 1959). The method is also valuable in establishing the identity of various cells and in determining the extent of a tract, on the principle that an antidromic impulse will not cross a synapse (e.g. Woolsey & Chang, 1947). However, the existence of recurrent collaterals is a complicating factor here. We have stimulated the visual cortex in cats whilst recording extracellularly from units in the lateral geniculate nucleus (LGN) and optic radiation with both these objects in mind. The LGN projects to a large area of cortex and in these experiments no attempt was made to stimulate this entire area but only the most anterior part. Evidence will be produced to show that the majority of our records result from a true antidromic activation of the unit. This is a necessary step, because it has been suggested that the visual cortex sends an efferent supply to the LGN (e.g. Vastola, 1957; Wid6n & Marsan, 1960 a, who also give a list of references to earlier work). Our results do, however, lend some support to this idea, because a few units could be activated only after rather long latencies. However, the results are most useful for the study of the process of impulse initiation in the cell body and in this respect support the theories advanced by Araki & Otani (1955), Coombs et al. (1957a, b) and Fuortes et al. (1957).

An analysis of the primary cardiovascular reflex effects of stimulation of the carotid body chemoreceptors in the dog.

Abstract: It has been shown previously that stimulation of the carotid body chemoreceptors in dogs breathing spontaneously causes variable changes in heart rate (Bernthal, Greene & Revzin, 1951; Daly & Scott, 1958, 1959, 1962). A detailed study revealed that the change in heart rate was dependent upon at least two mechanisms. The first of these is a primary cardiac reflex arising from the chemoreceptors themselves, which causes slowing of the heart. The other mechanism was identified as occurring secondarily to the concomitant reflex increase in respiratory minute volume and causes an increase in heart rate. This secondary effect is due, at least in part, to a stretch reflex from the lungs and to a lowering of the arterial blood PCO2, and may be excluded by maintaining pulmonary ventilation constant by means of a pump (Daly & Scott, 1958, 1959). When pulmonary ventilation is maintained constant in this way during chemoreceptor stimulation, the primary cardiac reflex response becomes apparent (Daly & Scott, 1958). The purpose ofthe present investigation was to discover the mechanisms by which the primary cardiac response was brought about and to make observations on the changes in vascular resistance resulting from stimulation of the carotid bodies. Our results have been reported briefly elsewhere (Daly & Scott, 1961, 1962).

Changes produced by light in the standing potential of the human eye.

Abstract: A potential difference occurs between the cornea and the fundus of the living eye. In vertebrates the cornea is positive to the fundus (Du Bois Reymond, 1849) while in invertebrates, where the sensory cells lie anterior to the neurones, the potential gradient is reversed (Dewar & M'Kendrick, 1876). These facts suggested to early workers that the potential difference (called the standing potential, to distinguish it from the evidences of light-evoked retinal nervous activity) was also developed in the retina, a view confirmed by experiments which showed a sharp change of potential at the ora serrata (de Haas, 1903). Moreover, there are potential differences across the isolated retina (Kuhne & Steiner, 1881) and also the pigment epithelium (Dewar & M'Kendrick, 1876), which are almost as great as the standing potential measured in the opened eye (Kuhne & Steiner, 1881). The site of origin of the potential has recently been still further localized. Drugs which selectively alter the standing potential can be shown to damage the pigment epithelium (Noell, 1953), while the passage of a microelectrode through the retina reveals the presence of several charged membranes, and the one across which most potential is generated is situated in the pigment epithelium (Brindley, 1956; Brown & Wiesel, 1958; Tomita, Murakami & Hashimoto, 1959-60). If in man electrodes are placed on the skin, one on either side of the eye, the potential difference between them changes as the eye rotates. This potential is called the eye movement potential, and it is considered that the intra-ocular retinal potential generators are responsible for its production. Similar potentials can be recorded in animals if the eyes are rotated passively, but disappear when chromate is injected into the posterior segment (Mowrer, Ruch & Miller, 1936). In addition, the amplitude of the eye movement potential is related in a simple manner to the degree of rotation of the eyes (Fenn & Hursh, 1937; Leksell, 1939; Miles, 1939c). This finding can be explained by supposing that the eye is an electrical dipole, orientated in the optic axis, which is indeed what had been shown by the early animal experiments on the standing potential.

Influence of nerve-ending activity and of drugs on the rate of paralysis of rat diaphragm preparation by Cl. botulinum type A toxin

Abstract: Since the studies of Guyton & MacDonald (1947), Ambache (1948, 1949, 1951) and Burgen, Dickens & Zatman (1949) on the action of botulinum toxin it is generally agreed that the paralysis is caused by failure of release of the neurohumoral transmitter at the effector site (see also Brooks, 1954, 1956; Ambache & Lessin, 1955). So far, however, it has proved difficult to modify the course of the neuromuscular paralysis caused by the toxin. Guyton & MacDonald (1947), using intact animals, and Burgen et al. (1949), using the isolated rat diaphragm preparation, were unable to modify by drugs either the rate at which paralysis took place or the rate of recovery of the paralysed muscles. The only observations showing some modification of the rate of intoxication are those of Bronfenbrenner & Weiss (1924), who showed that the survival times of guineapigs given lethal doses of toxin could be considerably prolonged by anaesthesia. This suggested that inactivity delayed the onset of paralysis, as was borne out also by the following observations made by May & Whaler (1958) during experiments on the intestinal absorption of toxin. It was noticed that in intoxicated rabbits respiratory distress and inability to hold up the head often preceded paralysis of the limb muscles. Since the groups of muscles thus involved are in a state of continuous activity it seemed likely that the degree of activity might be important in determining the rate of onset of paralysis. This has now been confirmed on rat phrenic nerve-diaphragm preparations. Moreover, it has also been possible to alter appreciably the rate of onset of neuromuscular paralysis by means of drugs known to modify acetylcholine metabolism and function.

On the mode of action of acetylcholine in evoking adrenal medullary secretion: increased uptake of calcium during the secretory response.

Abstract: Acetylcholine is generally believed to be the physiological transmitter of sympathetic nerve activity at the adrenal medulla. Recently Douglas & Rubin (1961a, b) described experiments indicating that the stimulant effect of acetylcholine involves some calcium-dependent process. They found that removal of calcium from the extracellular environment greatly depressed or even abolished the secretory response to acetylcholine; that the secretory response varied directly with the calcium concentration not only when this was low but also when it was high; and, finally, that calcium itself in certain conditions was a powerful stimulus to secretion. These findings, considered along with the known effects of acetylcholine at other sites in the body where it seems to act by causing some change in the permeability of the 'receptor membrane' to common species of ions, led them to suggest that acetylcholine evokes catecholamine secretion by causing calcium ions to penetrate the adrenal medullary cells. The present experiments were designed to test the possibility that acetylcholine increases calcium uptake by the adrenal medulla. A preliminary account of our findings has appeared elsewhere (Douglas & Poisner, 1961).