Showing papers by "Dalhousie University published in 1990"
TL;DR: Exposure of hamsters and rats to light pulses at those phases of the circadian rhythm during which light can shift the rhythm caused increased immunoreactivity for the product of the immediate-early gene c-fos in cells in the region of the SCN that receives retinal fibers.
Abstract: Lighting cycles synchronize (entrain) mammalian circadian rhythms by altering activity of cells in the suprachiasmatic nucleus (SCN) of the hypothalamus, a circadian pacemaker. Exposure of hamsters and rats to light pulses at those phases of the circadian rhythm during which light can shift the rhythm caused increased immunoreactivity for the product of the immediate-early gene c-fos in cells in the region of the SCN that receives retinal fibers. Light pulses also increased messenger RNA for the Fos protein and for the immediate-early protein NGFI-A in the rat SCN. Similar increases in mRNA for NGFI-A were seen in the SCN of hamsters. Thus cells in this portion of the SCN undergo alterations in gene expression in response to retinal illumination, but only at times in the circadian cycle when light is capable of influencing entrainment.
547 citations
TL;DR: The results of time-course immunocytochemical and antiserum studies suggest that some striatal neurons express c-fos protein-related antigens but not c- fos protein after haloperidol injection, and theories concerning the biochemical mechanism of action of haloperIDol are discussed.
342 citations
TL;DR: 4-year-olds were presented with the certainty task, involving both modal and mental terms, and with tasks assessing their understanding of false beliefs, representational change, and the appearance-reality distinction, showing that all of these tasks were intercorrelated.
Abstract: 2 experiments examined children's understanding of the expression of speaker certainty and uncertainty and its relation to their developing theory of mind. In the first experiment, 80 children between 3 and 6 years of age were presented with a task in which they had to guess the location of an object hidden in 1 of 2 boxes. As clues to location, the children were presented with contrasting pairs of statements by 2 puppets. Different trials contained all of the possible pairwise combinations of either the modal verbs must, might, and could or the modal adjuncts probably, possibly, and maybe. Results showed that while 3-year-olds did not differentiate between any of the modal contrasts presented, 4-year-olds and older children were able to find the hidden object on the basis of what they heard. Performance was best for contrasts involving a highly certain term (either must or probably) paired with a less certain term (might, could, possibly, and maybe). Experiment 2 was designed to determine whether competence with modal terms was related to competence with mental terms in the same task, and whether performance on the certainty task was related to other aspects of the child's understanding of the nature of beliefs. 26 4-year-olds were presented with the certainty task, involving both modal and mental terms, and with tasks assessing their understanding of false beliefs, representational change, and the appearance-reality distinction. Results showed that all of these tasks were intercorrelated, implying that what may develop at 4 years of age may be a general understanding of the representational nature of belief.
315 citations
294 citations
TL;DR: This review examines current information regarding the effects of diet-induced changes in plasma membrane fatty acid composition on several specific enzymes (adenylate cyclase, 5'-nucleotidase, Na(+)/K(+)-ATPase) and cell-surface receptors (opiate, adrenergic, insulin).
Abstract: In recent years, there has been growing public awareness of the potential health benefits of dietary fatty acids, and of the distinction between the effects of the omega6 and omega3 polyunsaturated fatty acids that are concentrated in vegetable and fish oils, respectively. A part of the biologic effectiveness of the two families of polyunsaturated fatty acids resides in their relative roles as precursors of the eicosanoids. However, we are also beginning to appreciate that as the major components of the hydrophobic core of the membrane bilayer, they can interact with and directly influence the functioning of select integral membrane proteins. Among the most important of these are the enzymes, receptors, and ion channels that are situated in the plasma membrane of the cell, since they carry out the communication and homeostatic processes that are necessary for normal cell function. This review examines current information regarding the effects of diet-induced changes in plasma membrane fatty acid composition on several specific enzymes (adenylate cyclase, 5'-nucleotidase, Na(+)/K(+)-ATPase) and cell-surface receptors (opiate, adrenergic, insulin). Dietary manipulation studies have demonstrated a sensitivity of each to a fatty acid environment that is variably dependent on the nature of the fatty acid(s) and/or source of the membrane. The molecular mechanisms appear to involve fatty acid-dependent effects on protein conformation, on the "fluidity" and/or thickness of the membrane, or on protein synthesis. Together, the results of these studies reinforce the concept that dietary fats have the potential to regulate physiologic function and to further our understanding of how this occurs at a membrane level.
259 citations
TL;DR: Many children who reported severe pain manifested few of the behavioral indicators of distress used in the CHEOPS and may limit the applicability of current behavioral scales as sole measures of pain intensity in younger children.
256 citations
TL;DR: In this article, satellite observations of ocean transparency, coupled with climatological surface heat fluxes and ocean density profiles, are used to show that solar radiation in visible frequencies, usually assumed to be absorbed at the sea surface, in fact penetrates to a significant degree to below the upper mixed layer of the ocean which interacts actively with the atmosphere.
Abstract: Recent satellite observations of ocean transparency, coupled with climatological surface heat fluxes and ocean density profiles, are used here to show that solar radiation in visible frequencies, usually assumed to be absorbed at the sea surface, in fact penetrates to a significant degree to below the upper mixed layer of the ocean which interacts actively with the atmosphere. The net effect is a reduction of the heat input into the upper layer; for a 20 m-thick mixed layer this is equivalent to an annual reduction in temperature of about 5-10 K. The results provide a natural explanation for the discrepancy between the SSTs predicted by models and those observed.
233 citations
TL;DR: This paper describes an efficient implementation of a nested decomposition algorithm for the multistage stochastic linear programming problem and results compare the performance of the algorithm to MINOS 5.0.
Abstract: This paper describes an efficient implementation of a nested decomposition algorithm for the multistage stochastic linear programming problem. Many of the computational tricks developed for deterministic staircase problems are adapted to the stochastic setting and their effect on computation times is investigated. The computer code supports an arbitrary number of time periods and various types of random structures for the input data. Numerical results compare the performance of the algorithm to MINOS 5.0.
232 citations
TL;DR: The purpose of this epidemiological study was to estimate the degree of change in periodontal attachment level in a sample of adults examined in 1959 and 1987 in Tecumseh, Michigan, and the individuals with high LPA increase had the following characteristics significantly different from those with low LPA rise: age, smoking, and presence of tooth mobility.
Abstract: The purpose of this epidemiological study was to estimate the degree of change in periodontal attachment level in a sample of adults examined in 1959 and 1987 in Tecumseh, Michigan. Out of 526 individuals between the ages of five and 60 years in 1959, a sample of 325 resided within an 80-km-radius area in 1987. Of those, 167 were re-examined. Loss of periodontal attachment (LPA) was determined with a Michigan #0 probe on four tooth sites (disto-buccal, mid-buccal, mesio-buccal, mid-lingual) for all teeth present. Of the individuals contacted, 28 had lost all their teeth during the 28 years. Of the 167 adults examined, two refused periodontal probing. Out of the 165 adults with LPA measurements in 1987, only 22 (13.3%) had an average increased loss of 2 mm or more per person between 1959 and 1987; five adults (3.0%) had an average LPA increase of 3 mm or more, and only two adults (1.2%) had an average LPA increase of 4 mm or more. The attachment level in 59.3% of all the tooth sites examined in 1959 in the...
223 citations
TL;DR: Analysis of muscle weight, fiber length and physiological cross‐sectional area indicate that there was greater reduction of the musclesacting on the limbs than of those acting on the mandible, i.e., diminished growth of the skeleton is correlated with reduced muscular activity.
Abstract: Avian embryos can be completely paralyzed by injection of neuromuscular-blocking agents. We used a single injection of decamethonium iodide to paralyze embryos at 7, 8, or 10 days of incubation and analyzed the growth of individual bones (clavicle, mandible, ulna, femur, tibia, humerus) and of individual muscles that act upon some of those bones (clavicular and sternal heads of m. pectoralis, and mm. biceps brachii, depressor mandibulae, pseudotemporalis, and adductor externus). Growth of the bones is not equally affected by paralysis. Only 27% of clavicular growth (by mass) but 77% of mandibular growth occurred in paralyzed embryos, whereas the four long bones exhibited 52-63% of their normal growth. Analysis of muscle weight, fiber length and physiological cross-sectional area (weight/fiber length) indicate that there was greater reduction of the muscles acting on the limbs than of those acting on the mandible, i.e., diminished growth of the skeleton is correlated with reduced muscular activity. Specific retardation of clavicular growth is due to fusion of sternal rudiments and collapse of the thorax, as well as virtual absence of the musculature that normally attaches to the clavicle. We discuss these results in the light of intrinsic and extrinsic factors governing growth of the embryonic skeleton. Paralysis reduces skeletal growth by reducing both the movements taking place in ovo, and the loads imposed on the bones by muscle contraction, changes that represent alterations in the mechanical environment of the skeleton.
218 citations
TL;DR: Using artificial tanning devices appears to be a risk factor for melanoma, and the risk was greater and significant for both sexes for domestic use of sunbeds/sunlamps, and increased with duration and amount of use.
Abstract: Data are presented from a large case-control study (583 cases, 608 controls) to estimate the association of melanoma with the use of sunbeds and sunlamps. Odds ratios of 1.88 and 1.45 were found for ever having used a sunbed or sunlamp in males and females, respectively, which was statistically significant in males and of borderline significance in females. These effects persisted when adjustments were made for age and a variety of potential confounders. The effect was slightly stronger for lentigo maligna and for lesions of the face, head, neck, and arms. The risk was greater and significant for both sexes for domestic use of sunbeds/sunlamps, and increased with duration and amount of use. A comparison of 43 cases interviewed before a diagnosis of melanoma had been made with the other 540 cases suggests that recall bias was not responsible for the association. The authors conclude that use of artificial tanning devices appears to be a risk factor for melanoma.
01 Dec 1990
TL;DR: Subsidence analysis of wells in the central North Sea and Labrador-Grand Banks and the West Greenland, Scotian shelf and United States Atlantic margin shows distinct quantitative stratigraphic correlation patterns of circum North Atlantic sites as discussed by the authors.
Abstract: Subsidence analysis of wells in the central North Sea and Labrador-Grand Banks and oft the West Greenland, Scotian shelf and United States Atlantic margin shows distinct quantitative stratigraphic correlation patterns of circum North Atlantic sites. A significant departure from the overall decrease in subsidence for the Pliocene occurs in many wells, when the rate is found to have increased one or more orders of magnitude from Oligocence/Miocene rates. Wells were selected along transects from shore to basin to find if relative basin position is influenced by differential basin subsidence. Although stratigraphic resolution is not detailed, more basinward sites experienced up to four times larger subsidence rates in the late Neogene than in the Oligocene/Miocene, with a peak in the Pliocene. Wells at the basin edge experienced much less subsidence or showed uplift. The observations are consistent with a rapid change of intraplate stress at the cause for this observed transition in Neogene subsidence. Major reorganizations of spreading direction and rate occurred during the Pliocene along the entire Atlantic spreading system, possibly in conjunction with more global changes in plate motions. We propose that the associated changes in intraplate stress caused the excess margin subsidence. Relative uplift along basin edges is consistent with this mechanism of relative movement and may explain apparent eustatic changes in sea level.
TL;DR: Homogenate derived pHi values are concluded to represent the effective mean pHi by taking into account pH gradients, and the volumes and buffering of cellular compartments, and are especially useful to assess rapid changes in pHi, e.g. in exercising animals.
TL;DR: It is clear that parasitic amoebas can decimate sea urchin populations so that kelp forest dominance is assured, and the importance of carnivory in limiting urchins in the subtidal community is unclear in the absence of appropriate manipulation experiments.
Abstract: Large seaweeds are often structurally dominant in subtidal and intertidal rocky shore benthic communities of the N.W. Atlantic. The mechanisms by which these algal assemblages are maintained are surprisingly different in the two habitats. In the subtidal community, kelps are dominant space competitors in the absence of strong grazing interactions. In contrast, the large perennial seaweeds of intertidal zones (fucoids and Chondrus crispus) are competitively inferior to both sessile filter feeders and ephemeral, pioneer algal species. Intertidal seaweed beds are maintained by carnivory of whelks, which reduces filter feeder populations, and by herbivorous periwinkles which reduce ephemeral algal populations. Through most of the intertidal zone, disturbance, both biological and physical, dictates which species shall compete and equilibrium conditions obtain subsequently. The roles of subtidal consumers are quite different. Sea urchins are the major algal herbivores and these voracious animals maintain an equilibrium state in which large tracts of subtidal coralline pavement are kept free of kelp forests. Urchins do not seem to play a successional facilitative role for kelps in the way that periwinkles do for fucoids in the intertidal. Control of herbivore populations is thus a key to the maintenance of subtidal foliose algal beds. It is clear that parasitic amoebas can decimate sea urchin populations so that kelp forest dominance is assured. However, the importance of carnivory in limiting urchins in the subtidal community is unclear in the absence of appropriate manipulation experiments. It is possible that carnivorous decapods and fin fish control sea urchin populations and hence foliose algal abundance, but this must remain speculative. The seaweed-dominated state of the subtidal system is an alternative equilibrium condition to the urchin/coralline alga configuration. The structure of the kelp beds is relatively uniform in responding to frequent small-scale, infrequent large-scale, or no, disturbance.
TL;DR: Nutrient limitation of production at scales ranging from the organism to the ecosystem is one of the most important topics of research at present, the relevance of which extends well beyond the tropics.
Abstract: The abundance of interdisciplinary studies of coral reef metabolism means that coral reefs are amongst the best understood of marine benthic communities in terms of the determinants of primary production and nutrient fluxes, and their variation, at different levels of integration. Recent work has extended our understanding of the variation in coral reef productivity at different spatial and temporal scales. Nutrient limitation of production at scales ranging from the organism to the ecosystem is one of the most important topics of research at present, the relevance of which extends well beyond the tropics.
TL;DR: Electron microscopic observations indicated that intact liposomes penetrated into the skin and deposited in the dermis where they acted as a slow release depot system and a hypothetical model for liposome-skin interaction is proposed.
Abstract: The fate of liposomes and the encapsulated drug was studied after topical application on the skin. Lidocaine applied on the forearm of human volunteers produced greater local anaesthetic effect in the liposomal form than in the cream form (p≤ 0.001 after 1h application). Autoradiography demonstrated higher concentration (p≤001) of 14C-lidocaine in the epidermis and dermis of guinea pigs treated with liposome-encapsulated lidocaine as opposed to lidocaine in Dermabase® cream. Electron microscopic observations, using colloidal iron as an electrondense marker, indicated that intact liposomes penetrated into the skin and deposited in the dermis where they acted as a slow release depot system. On the basis of results in the human volunteers and animals, a hypothetical model for liposome-skin interaction is proposed.
TL;DR: While the analysis had to be carried out without caries data, it was concluded that total tooth loss is a social-behavioral issue as much as it is disease-related.
Abstract: Over 500 residents of Tecumseh, Michigan, were dentially examined in 1959 as part of a community-wide health study. In 1987, the dental examinations were repeated, with use of the same criteria as in 1959, for 167 dentate persons from the original group. Another 28 reported by telephone that they had become edentulous since 1959. This report uses a historical cohort analysis for exploration of the risk factors for tooth loss, both total and partial, over the 28-year period. Over that time, the edentulous lost an average of 18.0 teeth (95% confidence interval 15.5, 20.7), whereas the age-matched 90 dentate persons lost only 3.2 (2.2, 4.2) teeth each. Descriptive data showed the edentulous to have higher baseline scores for plaque, calculus, and gingivitis, and a higher proportion of them smoked, though only loss of periodontal attachment (LPA) of 4 mm or more, early loss of first molars, and educational attainment were significant risk factors in regression analysis. Odds ratios for these three variables were 4.0 (1.2, 12.8), 2.0 (1.3, 3.1), and 0.6 (0.4, 0.9), respectively. The strongest risk factors for partial tooth loss among 116 dentate persons were baseline gingivitis (which was correlated with LPA of 4 mm or more) and the baseline number of teeth present, with odds ratios of 2.4 (1.2, 5.2) and 0.8 (0.7, 1.0), respectively. While the analysis had to be carried out without caries data, it was concluded that total tooth loss is a social-behavioral issue as much as it is disease-related. Social-behavioral factors were less clearly related to partial tooth loss in dentate persons; oral disease characteristics were the most prominent risk factors for partial tooth loss.
TL;DR: The NOVACODE module of the Dalhousie ECG Program classifies ECGs according to the Minnesota Code, supplemented with new sets of logic criteria for conduction defects, acute myocardial infarction, and serial ECG changes.
Abstract: The Dalhousie ECG Program was designed specifically for the needs of epidemiologic studies, health surveys, and clinical trials. The program logic is dynamic in that it can accommodate any combination of ECG leads, record length and sampling rate. The NOVACODE module of the program classifies ECGs according to the Minnesota Code, supplemented with new sets of logic criteria for conduction defects, acute myocardial infarction, and serial ECG changes. Improved statistical models are incorporated for enhanced detection of myocardial infarction using the Cardiac Infarction Injury Score, and for quantification of left ventricular mass estimation. It is anticipated that these program improvements will enhance its utility particularly in monitoring progression and regression of cardiac involvement in hypertensive and ischemic heart disease, and in the assessment of the effectiveness of intervention on cardiovascular disease risk factors.
TL;DR: It is suggested that malformations of the central nervous system may be responsible for most cases, and a significant number of patients with the Apert syndrome are mentally retarded.
Abstract: In this paper, we present available central nervous system data from our series of patients with the Apert syndrome. Combining our own data with that available in the literature, 30 patients had malformations of the corpus callosum, the limbic structures, or both. Other frequent findings included megalencephaly (7 cases), gyral abnormalities (8 cases), encephalocele (4 cases), pyramidal tract abnormalities (2 cases), hypoplasia of cerebral white matter (4 cases), and heterotopic gray matter (2 cases). Progressive hydrocephalus seems to be uncommon and has frequently been confused with nonprogressive ventriculomegaly in the past. Psychometric evaluations, neurological findings, and neuropathologic reports from the literature are critically reviewed. It is clear that a significant number of patients with the Apert syndrome are mentally retarded. It is suggested that malformations of the central nervous system may be responsible for most cases.
TL;DR: A strong relationship is shown between the acquisition and decay of the enhanced postischemic ventricular recovery and the hyperthermic induction of the heat-shock response indicated by the accumulation of heat- shock protein HSP71 (mol mass 71 kDa) and the increase in catalase activity.
Abstract: Hyperthermia induces the synthesis of the 71-kDa heat-shock protein (heat-shock response) in all rat tissues, including heart. We examined whether induction of the heat-shock response alters the re...
TL;DR: The differential roles of infection as a microbial phenomenon and sepsis as a host response were studied in 210 critically ill surgical patients, finding the magnitude of the host septic response is an important determinant of outcome in critical surgical illness.
Abstract: • The differential roles of infection as a microbial phenomenon and sepsis as a host response were studied in 210 critically ill surgical patients. Infections occurred In 41.4% of all cases and In 82% of nonsurviving patients. Both infection and the expression of a septic response, measured as a sepsis score, were associated with significantly increased Intensive care unit morbidity and mortality. Nonsurviving patients with infection had significantly higher sepsis scores than did survivors. Nonsurvivors with sepsis, on the other hand, did not differ from survivors with respect to any variable reflecting infection but did have higher mean sepsis scores. Maximum sepsis scores and sepsis scores on the day of death were similar in patients dying without infection and those dying with uncontrolled infection. The magnitude of the host septic response, independent of the presence, bacteriologic characteristics, or control of infection, is an important determinant of outcome in critical surgical illness. ( Arch Surg. 1990;125:17-23)
TL;DR: In this article, an exact solution for the daily integral of photosynthesis by phytoplankton in a vertically homogeneous water column is presented, and the impact of photoinhibition on daily primary production is quantified and discussed.
Abstract: An exact (analytic) solution is presented for the daily integral of photosynthesis by phytoplankton in a vertically homogeneous water column. The photosynthesis-light curve on which the results are based is sufficiently flexible to accommodate the effects of photoinhibition. A comparison of the available methods for the description of diurnal variation in surface irradiance reveals that for long days at high latitudes a second-order sinusoid is preferable to the conventional first-order sine function. Previously published geometrical approximations to the instantaneous and daily integrals of water-column photosynthesis are examined and explained. The impact of photoinhibition on daily primary production is quantified and discussed. A polynomial approximation is given to the exact solution for the daily integral of photosynthesis. This function is, for all practical purposes, free from error in estimation, and will decrease computation time by a factor of about 3 $\times $ 10$^{5}$ compared with a numerical integration. For maximum generality, the solutions and discussion are framed in terms of dimensionless quantities: the results are also tabulated in this form so that they can be applied where computation facilities are lacking. The solutions can be used at all hierarchical levels in the analysis of aquatic systems, including the interpretation of results from discrete stations (local scale), the use of remotely sensed data on ocean colour (regional scale) and modelling biogeochemical fluxes for climatic research (basin and global scales).
TL;DR: Paleoecological analysis of the sediment record of 12 Adirondack lakes reveals that the 8 clearwater lakes with current pH < 5.5 and alkalinity < 10 μ eq l-1 have acidified recently as mentioned in this paper.
Abstract: Paleoecological analysis of the sediment record of 12 Adirondack lakes reveals that the 8 clearwater lakes with current pH < 5.5 and alkalinity < 10 μeq l-1 have acidified recently. The onset of this acidification occurred between 1920 and 1970. Loss of alkalinity, based on quanitative analysis of diatom assemblages, ranged from 2 to 35 μeq l-1. The acidification trends are substantiated by several lines of evidence including stratigraphies of diatom, chrysophyte, chironomid, and cladoceran remains, Ca:Ti and Mn:Ti ratios, sequentially extracted forms of Al, and historical fish data. Acidification trends appear to be continuing in some lakes, despite reductions in atmospheric sulfur loading that began in the early 1970s. The primary cause of the acidification trend is clearly increased atmospheric deposition of strong acids derived from the combustion of fossil fuels. Natural processes and watershed disturbances cannot account for the changes in water chemistry that have occurred, but they may play a role. Sediment core profiles of Pb, Cu, V, Zn, S, polycyclic aromatic hydrocarbons, magnetic particles, and coal and oil soot provide a clear record of increased atmospheric input of materials associated with the combustion of fossil fuels beginning in the late 1800s and early 1900s. The primary evidence for acidification occurs after that period, and the pattern of water chemistry response to increased acid inputs is consistent with current understanding of lake-watershed acidification processes.
TL;DR: The cooccurrence and topographical dissimilarity of the "N200" and N400 suggest that the N400 may not be a delayed or a generic N200.
TL;DR: The results suggest that actinorhodin production inS.
Abstract: Actinorhodin production inStreptomyces coelicolor A3(2) was relatively insensitive to the carbon source concentration but was elicited by nitrogen or phosphate depletion, or by a decline in the growth rate. In starch-glutamate media with nitrogen limitation, increasing the nitrogen supply delayed the onset of antibiotic synthesis and, at concentrations above 30 mM, decreased its rate. In a similar medium with phosphate limitation, increasing the initial phosphate concentration delayed actinorhodin formation and, above 2.5 mM, reduced the rate of synthesis. Experiments in which actinorhodin synthesis was elicited by phosphate depletion at various nitrogen concentrations demonstrated strong suppression by residual glutamate. Cultures in which actinorhodin biosynthesis was initiated by nitrogen depletion were not similarly suppressed by increasing amounts of residual phosphate. The results suggest that actinorhodin production inS. coelicolor A3(2) responds to interacting physiological controls, notable among which is nitrogen catabolite regulation.
TL;DR: Wheelchair- related accidental death is uncommon (about 0.2% of serious accidents per year), but some types of accidents appear to be preventable.
Abstract: Of the 3.3 of every 1000 persons in the United States who use a wheelchair, an estimated 3.3% per year have a serious wheelchair-related accident. Yet, only isolated case reports of fatal accidents have appeared. To obtain a better estimate of the incidence and nature of fatal accidents, a search was carried out of the death certificate database (1973-1987) of the National Information Clearinghouse of the Consumer Product Safety Commission; 770 wheelchair-related deaths were identified. The majority, 596 persons (77.4%), experienced a fall from their chairs or tipped over. Of 85 deaths (11%) caused by environmental factors, stairs were implicated in 51 (60.0%). Of 48 fatal burns (6.2%), 27 (57.3%) were related to smoking. Asphyxia owing to restraints occurred in 44 persons (5.7%) of all ages and caused 10 of the 17 deaths (58.8%) among persons 1-20 yr old. Wheelchair-related accidental death is uncommon (about 0.2% of serious accidents per year), but some types of accidents appear to be preventable.
TL;DR: The results demonstrate the importance of phytoplankton as a diet for the sea scallop, but indicate that detrital particles can contribute to energy gain during periods when phy Topolankton are less available to meet energy demands.
TL;DR: Herkenham et al. as mentioned in this paper showed that classical synaptic neurotransmission is important for entrainment, but not for rhythm generation, and that the SCN contains a cholinergic marker like ChAT and is responsive to cholineergic agents but does not bind nicotine or ACh.
Abstract: This discussion of the roles of transmitters in the circadian system has focused mostly on the entrainment mechanism because it is not clear to what extent neurotransmission is important to the other major function of circadian systems, rhythm generation. Schwartz et al (1987) have presented evidence that the circadian pacemaker in the SCN continues to run, but cannot be entrained by light, when tetrodotoxin is used to block sodium-dependent action potentials. Although other forms of intercellular communication are not ruled out, these results suggest that classical synaptic neurotransmission is important for entrainment but not for rhythm generation. That the SCN contains a cholinergic marker like ChAT and is responsive to cholinergic agents but does not bind nicotine or ACh reflects a general problem in reconciling functional, physiological, and anatomical markers of neurotransmission. A mismatch between the anatomical distributions of transmitters and their receptor-binding sites is a common observation, the meaning of which remains enigmatic (Herkenham 1987). Also, the neurophysiological consequences of injections of drugs into parts of the brain involved in rhythm regulation remain largely unknown. Interpretations of the effects of these treatments on rhythms are predicated on assumptions that may not be valid; e.g. that a bolus injection of an excitatory substance has its primary effect by activating neurons. Still to be established is whether the effects of drugs when they are administered in behavioral pharmacology studies reflect their effects on cellular functions and on neuronal responses to photic cues when they are delivered at near-physiological levels to single neurons.