Biomedical subjects

R W Dykes

Publications and source records attributed to R W Dykes.

At least 19 recordsLinked to original sources

PubMed1999

Evidence for homeostatic adjustments of rat somatosensory cortical neurons to changes in extracellular acetylcholine concentrations produced by iontophoretic administration of acetylcholine and by systemic diisopropylfluorophosphate treatment.

We describe the responses of single units in the awake (24 cells) or urethane-anesthetized (37 cells) rat somatosensory cortex during repeated iontophoretic pulses (1.0 s, 85 nA) of acetylcholine, both before and after systemic treatment with the irreversible acetylcholinesterase inhibitor diisopropylfluorophosphate (i.p., 0.3-0.5 LD50). The time-course of the response to acetylcholine pulses differed among cortical neurons but was characteristic for a given cell. Different time-courses included monophasic excitatory or inhibitory responses, biphasic (excitatory-inhibitory, inhibitory-excitatory, excitatory-excitatory, and inhibitory-inhibitory), and triphasic (excitatory-excitatory-inhibitory, inhibitory-inhibitory-excitatory, and inhibitory-excitatory-inhibitory) responses. Although the sign and time-course of the individual responses remained consistent, their magnitude fluctuated across time; most cells exhibited either an initial increase or decrease in response magnitude followed by oscillations in magnitude that diminished with time, gradually approaching the original size. The time-course of the characteristic response to an acetylcholine pulse appeared to determine direction and rate of change in response magnitude with successive pulses of acetylcholine. Diisopropylfluorophosphate treatment, given 1 h after beginning repeated acetylcholine pulses, often resulted in a gradual increase in spontaneous activity to a slightly higher but stable level. Superimposed on this change in background activity, the oscillations in the response amplitude reappeared and then subsided in a pattern similar to the decay seen prior to diisopropylfluorophosphate treatment. Our results suggest that dynamic, homeostatic mechanisms control neuronal excitability by adjusting the balance between excitatory and inhibitory influences within the cortical circuitry and that these mechanisms are engaged by prolonged increases in extracellular acetylcholine levels caused by repeated pulses of acetylcholine and by acetylcholinesterase inhibition. However, this ability of neurons in the cortical neuronal network to rapidly adjust to changes in extracellular levels of acetylcholine questions the potential efficacy of therapeutic treatments designed to increase ambient levels of acetylcholine as a treatment for Alzheimer's disease or to enhance mechanisms of learning and memory.

Acetylcholine↗

PubMed1999

Temporally structured impulse activity in spontaneously discharging somatosensory cortical neurons in the awake cat: recognition and quantitative description of four different patterns of bursts, post-recording GFAP immunohistology and computer reconstruction of the studied cortical surface.

We elaborated two methods used in two previous publications [J. Martinson, H.H. Webster, A.A. Myasnikov, R.W. Dykes, Recognition of temporally structured activity in spontaneously discharging neurons in the somatosensory cortex in waking cats, Brain Res. 750 (1997) 129-140 [16]; H.H. Webster, I. Salimi, A.A. Myasnikov, R.W. Dykes. The effects of peripheral deafferentation on spontaneously bursting neurons in the somatosensory cortex of waking cats, Brain Res. 750 (1997) 109-121 [21]]: (A) a procedure for detecting and classifying brief epochs of high-frequency extracellular impulse activity (bursts) recorded chronically in the somatosensory cortex of the awake cat, and (B) a modification of an immunohistochemical technique [L.A. Bevento, L.B. McCleary. An immunochemical method for marking microelectrode tracks following single-unit recordings in long surviving, awake monkeys, J. Neurosci. Meth. 41 (1992) 199-204 [5]] for visualization of electrode tracks and electrolytic lesions around the tip of tungsten-in-glass microelectrodes [D.M.D. Landis, The early reactions of non-neuronal cells to brain injury, Annu. Rev. Neurosci. 17 (1994) 133-151 [15]] weeks after lesions were made in cortex. The burst recognition and classification method uses an interval threshold to determine the beginning and end of one epoch [M. Armstrong-James, K. Fox, Effects of ionophoresed noradrenaline on spontaneous activity of neurons in rat primary somatosensory cortex, J. Physiol. (London), 335 (1983) 427-447 [3]] in the original sequence of interspike intervals (ISIs) to segregate and analyze separately a burst. The threshold is based on the duration of the shortest modal ISI found in the autocorrelogram [J. Martinson, H.H. Webster, A.A. Myasnikov, R.W. Dykes, Recognition of temporally structured activity in spontaneously discharging neurons in the somatosensory cortex in waking cats, Brain Res. 750 (1997) 129-140 [16]]. The technique allowed recognition of bursts with several distinctive patterns: (i) an initial, longer ISI followed by progressively shorter ones; (ii) an initially shorter ISI followed by progressively longer ones; (iii) patterns where the intermediate ISI could be either longer or shorter than surrounding ones; and (iv) consecutive ISIs of relatively equal duration. Among the cells discharging in bursts with equal ISIs, the technique allows recognition of cells generating only short (up to three to five intervals) bursts, and others generating mixtures of a short and long (up to six or more intervals) bursts. Finally, frequency distributions of the probability of encountering bursts having intervals of a stated length is described. The visualization of tracks from chronic recording experiments is important for relating neuronal function to a specific cytoarchitectural region and a specific cortical layer. Several modifications of the procedure of immunostaining for GFAP allows identification of recording sites in clearer relationship to the cytoarchitectonic details of cat somatosensory cortex.

Animals↗

PubMed1999

Differences between the tactile sensitivity on the anterior torso of normal individuals and those having suffered complete transection of the spinal cord.

Using the method of limits and a magnitude estimation procedure, the sense of touch was examined at multiple sites on the anterior torso of normal subjects. Their performance was compared with the performance of individuals having experienced a functionally complete spinal cord transection more than 6 months prior to the tests. Near the insentient regions of the spinal cord-injured patients there was a zone wherein the threshold for light touch was elevated and variable. Within this same transition zone, estimates of the magnitude of a brushing stimulus increased as a linear function of distance from the border for approximately 12 cm away from insentient skin. Throughout the rest of the thorax, spinal cord-injured patients displayed touch thresholds 67% higher than normals and, at the same test sites, spinal cord-injured patients offered estimates of the intensity of the brushing stimulus that averaged 62% higher than normal subjects. The greater intensity of the sensations experienced by spinal cord-injured patients with even very weak stimuli and the smaller range within which they were able to scale stimulus intensity, produced a situation wherein the patients made frequent errors of judgement even on skin regions far from the body parts affected by the lesion. These observations support the hypothesis that spinal cord lesions interrupt tonic modulatory mechanisms having global influences on the sense of touch. This loss produces an elevation of the touch threshold and a reduction of the normal dynamic range of tactile sensory perception for all skin surfaces on the anterior torso.

Abdomen↗

PubMed1998

Effects of D-AP5 and NMDA microiontophoresis on associative learning in the barrel cortex of awake rats.

Experiments involving single-unit recordings and microiontophoresis were carried out in the barrel cortex of awake, adult rats subjected to whisker pairing, an associative learning paradigm where deflections of the recorded neuron's principle vibrissa (S2) are repeatedly paired with those of a non-adjacent one (S1). Whisker pairing with a 300 ms interstimulus interval was applied to 61 cells. In 23 cases, there was no other manipulation whereas in the remaining 38, pairing occurred in the presence of one of three pharmacological agents previously shown to modulate learning, receptive field plasticity and long-term potentiation: N-methyl-D-aspartic acid (NMDA) (n=8), the NMDA receptor antagonist AP5 (n=17) or the nitric oxide synthase inhibitor L-nitro-arginine-N-methyl-ester (L-NAME) (n=13). Non-associative (unpaired) experiments (n=14) and delivery of pharmacological agents without pairing (n=14) served as controls. Changes in neuronal responsiveness to S1 following one of these procedures were calculated and adjusted relative to changes in the responses to S2. On average, whisker pairing alone yielded a 7% increase in the responses to S1. This enhancement differed significantly from the 17% decrease obtained in the non-associative control condition and could not be attributed to variations in the state of the animals because analysis of the cervical and facial muscle electromyograms revealed that periods of increased muscular activity, reflecting heightened arousal, were infrequent (less than 4% of a complete experiment on average) and occurred randomly. The enhancement of the responses to S1 was further increased when whisker pairing was performed in the presence of L-NAME (27%) or NMDA (35%) whereas AP5 reduced it to 1%. During the delivery period, NMDA enhanced both neuronal excitability and responsiveness to S1 whereas AP5 depressed them. However, the effects of both substances disappeared immediately after administration had ended. L-NAME did not affect the level of ongoing activity and responses to S1 significantly. From these data, we concluded that, since the changes in the responses to S1 lasted longer than the periods of both whisker pairing and drug delivery, they were not residual excitatory or inhibitory drug effects on neuronal excitability. Thus, our results indicate that, relative to the unpaired controls, whisker pairing led to a 24% increase in the responsiveness of barrel cortex neurons to peripheral stimulation and that these changes were modulated by the local application of pharmacological agents that act upon NMDA receptors and pathways involving nitric oxide. We can infer that somatosensory cerebral cortex is one site where plasticity emerges following whisker pairing.

2-Amino-5-phosphonovalerate↗

PubMed1998

Control of size and excitability of mechanosensory receptive fields in dorsal column nuclei by homolateral dorsal horn neurons.

Both accidental and experimental lesions of the spinal cord suggest that neuronal processes occurring in the spinal cord modify the relay of information through the dorsal column-lemniscal pathway. How such interactions might occur has not been adequately explained. To address this issue, the receptive fields of mechanosensory neurons of the dorsal column nuclei were studied before and after manipulation of the spinal dorsal horn. After either a cervical or lumbar laminectomy and exposure of the dorsal column nuclei in anesthetized cats, the representation of the hindlimb or of the forelimb was defined by multiunit recordings in both the dorsal column nuclei and in the ipsilateral spinal cord. Next, a single cell was isolated in the dorsal column nuclei, and its receptive field carefully defined. Each cell could be activated by light mechanical stimuli from a well-defined cutaneous receptive field. Generally the adequate stimulus was movement of a few hairs or rapid skin indentation. Subsequently a pipette containing either lidocaine or cobalt chloride was lowered into the ipsilateral dorsal horn at the site in the somatosensory representation in the spinal cord corresponding to the receptive field of the neuron isolated in the dorsal column nuclei. Injection of several hundred nanoliters of either lidocaine or cobalt chloride into the dorsal horn produced an enlargement of the receptive field of the neuron being studied in the dorsal column nuclei. The experiment was repeated 16 times, and receptive field enlargements of 147-563% were observed in 15 cases. These data suggest that the dorsal horn exerts a tonic inhibitory control on the mechanosensory signals relayed through the dorsal column-lemniscal pathway. Because published data from other laboratories have shown that receptive field size is controlled by signals arising from the skin, we infer that the control of neuronal excitability, receptive field size and location for lemniscal neurons is determined by tonic afferent activity that is relayed through a synapse in the dorsal horn. This influence of dorsal horn neurons on the relay of mechanosensory information through the lemniscal pathways must modify our traditional views concerning the relative independence of these two systems.

Animals↗

PubMed1998

Blockade of cholinergic receptors in rat barrel cortex prevents long-term changes in the evoked potential during sensory preconditioning.

We offer evidence that acetylcholine (ACh) is involved in the emergence of functional neuronal plasticity induced by whisker pairing. Evoked potentials were recorded within the barrel cortex of awake, adult rats before, during, and after one of five paradigms. In the pairing procedure, each of 50 deflections of a whisker (S1) was followed 150 ms later by the deflection of a second whisker (S2). The explicitly unpaired control procedure differed by the lack of contiguity and contingency between the stimulation of S1 and S2. In the three remaining groups, pairing was performed 30 min after an intraperitoneal injection of either 0.5 ml of saline (150 mM NaCl), 100 mg/kg of atropine methyl nitrate (0.5 ml of AMN in saline), or 100 mg/kg of atropine sulfate (0.5 ml of ATS in saline). Changes in responsiveness to S1 were compared with, and adjusted by, changes in responsiveness to stimulation of S2. Changes in potentials evoked by S1 were interpreted as a change in neuronal excitability occurring when the first innocuous stimulus systematically predicted the appearance of the second innocuous stimulus. When whisker pairing was performed alone or in the presence of either saline or AMN (a blocker of muscarinic cholinoreceptors that does not cross the blood-brain barrier, BBB), responses to S1 increased, whereas, in the presence of ATS (blocker of muscarinic cholinoreceptors that does cross the BBB) or following the explicitly unpaired control, they decreased. The effects of saline, AMN, and ATS on the evoked potential without vibrissae pairing were opposite to those observed when these substances were injected and pairing occurred. Analysis of the behavioral state of the animal showed that the changes observed in the evoked potential could not be attributed to changes in behavioral state. The changes in responsiveness to S1 induced by whisker pairing were independent of neuronal excitability, did not occur in the absence of contingency and contiguity between S1 and S2, were blocked by the muscarinic receptor antagonist ATS, but not by blockade of muscarinic modulation of normal synaptic transmission. Thus activation of muscarinic cholinoreceptors within the CNS were a necessary condition for this form of neuronal plasticity.

Animals↗

PubMed1997

Differential control of cortical activity by the basal forebrain in rats: a role for both cholinergic and inhibitory influences.

Using microdialysis and high-performance liquid chromatography, we measured acetylcholine (ACh) release simultaneously from two cortical sites in anesthetized rats. One site was always in the somatosensory cortex, and the other was in either the visual or the motor cortex. After baseline measurements were obtained, selected sites in the basal forebrain (BF) were stimulated to increase ACh release. Some BF sites provoked more release in one microdialysis probe than in the other, suggesting some degree of corticotropic organization of the cholinergic projections from the BF. BF sites optimal for release from the visual cortex were separated from optimal sites for release from the somatosensory cortex by greater distances than were the best sites for release from the somatosensory and the motor cortex. Stimulation of a single BF site often provoked similar release from the latter two cortical areas. Electrical stimulation of the BF also modified cortical neuronal activity. Activation of some BF sites provoked an intense discharge of many neurons in the vicinity of the cortical recording electrode, and the same stimulus site in the BF provoked release of large amounts of ACh in the cortex. Stimulation of other BF sites produced strong inhibition of ongoing cortical activity and no increase in cortical ACh release. When other sites were stimulated, they had no effect or they generated stereotyped bursting patterns in the cortex without any observable effect on ACh release. BF sites that generated inhibition of cortical neural activity were generally located near the sites that activated the cortex and provoked release of ACh. These data suggest an elaborate control of the sensory cortex by a mechanism involving both gamma-aminobutyric acid-containing and cholinergic neurons of the BF.

Acetylcholine↗

PubMed1997

Correlating cytoarchitecture and function in cat primary somatosensory cortex: the challenge of individual differences.

Principles of organization for the primary somatosensory cortex are generalizations derived by examining data obtained in different individuals. The manner in which these data are combined influences the conclusions derived. We found the line representing the widest anteroposterior distance across the sigmoid gyrus to be a useful reference in the cat somatosensory cortex for combining and comparing electrophysiological and cytoarchitectonic data from different individuals when we constructed cytoarchitectonic and functional maps of the bank of the medial ansate sulcus; maps prepared from combined data sets had boundaries similar to those found among individuals. Nevertheless, we argue that, for reasons inherent to the nature of the cerebral hemispheres and cortical maps, such references will never allow combinations of data capable of defining a unique high resolution prototypical map of individual body parts; the somatotopic order of body representations is, as are certain other attributes of somatosensory cortex, idiosyncratic. The genetic, developmental and use-dependent reasons for this situation are discussed.

Acetylcholinesterase↗

PubMed1997

The effects of peripheral deafferentation on spontaneously bursting neurons in the somatosensory cortex of waking cats.

Single neurons (n = 356) were studied in the forelimb representation of awake, quietly resting cats. Thirty-five spontaneously bursting neurons in a sample of 206 cells recorded before forelimb deafferentation were compared to 39 spontaneously bursting neurons in a sample of 127 neurons studied 1-3 weeks after deafferentation. The probability of encountering bursting neurons increased significantly following deafferentation from 17% to 31% of the sample (P < 0.005). The same 5 classes of bursting cells were observed after deafferentation but there were significant changes in the duration of interspike intervals in some classes, in the probability of observing certain classes, and in the proportion of spikes found in bursts. The probability of encountering class III cells, a class thought to consist primarily of non-inactivating pyramidal burst neurons, nearly doubled and the average interspike interval length within the burst increased from 1.9 to 3.0 ms. The burst structure in the other classes did not change but they were found less frequently. These other classes may include inhibitory interneurons which receive less excitatory drive after deafferentation and therefore provide less inhibition to class III cells. The differential behavior of the different classes of bursting cells may be one reason why the overall level of spontaneous activity does not change after deafferentation and it suggests that there are homeostatic mechanisms in primary somatosensory cortex that maintain a certain level of neural activity.

Afferent Pathways↗

PubMed1997

Recognition of temporally structured activity in spontaneously discharging neurons in the somatosensory cortex in waking cats.

We describe a method to automate the detection and analysis of structured neuronal activity obtained in relatively non-restrictive experiments in awake animals. Several different, regularly occurring, discharge patterns consisting of groups of spikes were identified in extracellular recordings from the somatosensory cortex of awake cats. The introduction of an interspike interval threshold made it possible to segregate these bursts from single spikes. The threshold interval was obtained from the modal interval in high-resolution autocorrelograms (up to 0.1 ms/bin) of the spontaneous neural activity. Single spikes were those separated by intervals greater than the threshold, while those within the group were of less than threshold value. When intervals were arranged and averaged according to their order of occurrence within the burst, four distinctive burst patterns were observed. These four patterns occurred in both normal and deafferented cortex and we believe them to be characteristic of particular cell types, a feature that will be useful for studying such cells in intact cellular networks.

Action Potentials↗

PubMed1997

Mechanisms controlling neuronal plasticity in somatosensory cortex.

gamma-Aminobutyric acid containing neurons in the somatosensory cortex are the major controlling element determining receptive field size and location. This control of the excitability of cortical neurons can be modulated by activity arising in the basal forebrain. A hypothesis is developed stating that both cholinergic and gamma-aminobutyric acid containing projections from the basal forebrain play important roles in the production of a state in cortex permitting neuronal plasticity to occur. This proposed mechanism involving a simultaneous reduction of inhibition and increased release of acetylcholine allows sensory signals to induce long-term changes in the location and responsiveness of cutaneous receptive fields, thereby changing the somatotopic organization of primary somatosensory cortex.

Acetylcholine↗

PubMed1996

Acetylcholine release from frontal cortex in the waking rat measured by microdialysis without acetylcholinesterase inhibitors: effects of diisopropylfluorophosphate.

Acetylcholine (ACh) release was measured in frontal cortex of awake quietly resting rats by microdialysis without using cholinesterase blockers in the perfusate. Resting release was 16.61 +/- 2.05 fmol/h (+/- S.E.M., n = 18). Injection of sublethal doses of the acetylcholinesterase blocker, diisopropylfluorophosphate produced dose-dependent increases in ACh release, reaching 79.9 fmol/h with a dose of 0.7-times the LD50. Although this irreversible inactivation of acetylcholinesterase increased ACh recovery to more than 700% of control values, levels of ACh in the perfusate never reached those seen in physostigmine-treated animals. The relationship between the amount of acetylcholinesterase inactivation and the quantity of ACh in the perfusate suggests that the extracellular ACh concentrations are controlled by simple enzyme kinetics. Within 2 h after enzyme inactivation, extracellular choline levels fell significantly, suggesting that ACh degradation by acetylcholinesterase plays an important role in regulating the amount of choline in the extracellular space.

Acetylcholine↗

PubMed1996

Bilateral contributions to motor recovery in the monkey following lesions of the deep cerebellar nuclei.

A unilateral lesion of the deep cerebellar nuclei in monkeys produced a transient inability to perform a reaching task with the limb ipsilateral to the lesion. The deficit recovered within 2 weeks following a time course having a initial rapid and a subsequent slower phase. After a second lesion of the cerebellar nuclei on the opposite side, the animals developed a bilateral deficit. Recovery occurred bilaterally after this second stage but following the slower rate observed after the first lesion. From these experiments we conclude that the initial, more rapid phase of the recovery after a unilateral cerebellar lesion depends upon intact contralateral cerebellar circuitry and that the slower rate of recovery was mediated by other parts of the motor system.

Animals↗

PubMed1996

Evolution of morphological and histochemical changes in the adult cat cuneate nucleus following forelimb denervation.

Morphological and histochemical changes were studied in the ipsilateral cuneate nucleus between one and 52 weeks after forelimb denervation in adult cats. The deafferented nucleus and neighboring fasciculus were noticeably reduced in size within four weeks and decreased further by 13 weeks. The intensity of acetylcholinesterase staining decreased within one week and was further reduced one month after nerve transections. This reduction in acetylcholinesterase staining was transient, approaching control levels within one year. Parvalbumin immunostaining was also altered by the nerve transections; on the deafferented side, the neuropil staining in the cuneate nucleus and fasciculus decreased, but the number of parvalbumin-positive cells was consistently greater than in the contralateral side. These cell counts returned to normal levels within one year. One month after the injury, cytochrome oxidase activity was reduced. This reduction persisted and was even more apparent after one year. In parallel, the cell clusters of the nucleus became progressively less distinct. These observations in an adult mammal indicate that peripheral nerve injury imposes molecular and morphological changes on second-order sensory neurons which evolve differentially with time. Although some changes developed rapidly after deafferentation, the onset of others was slower; and whereas some seemed irreversible, others eventually regressed. Taken together with the functional studies of others, these findings suggest that early molecular changes observed in cuneate neurons reflect adaptive reactions to lesion-induced alterations in afferent activity. Permanent deprivation of the normal input, however, would eventually lead to chronic, and perhaps irreversible, degenerative changes.

Acetylcholinesterase↗

PubMed1996

Quantitative analysis of anatomical changes in the cuneate nucleus following forelimb denervation: a stereological morphometric study in adult cats.

The consequences on the cuneate nucleus of the transection of the major nerves of the forelimb in adult cats were studied quantitatively with stereological procedures on celloidin-embedded material. The cell cluster region of the normal cuneate was 2.93 +/- 0.41 (mean +/- SD) mm3. This volume decreased significantly 4.5 weeks after the injury. The decrease amounted to 11-23%, and persisted until the longest survival studied (36 weeks). Despite this reduction in nuclear volume, there was no significant loss of neurons. The normal cell cluster region contained 48.8 +/- 7.3 (mean +/- SD) x 1000 neurons. Neuronal density showed a significant 16.8% mean increase between 4 weeks and 36 weeks of deafferentation. Perikaryal volume decreased by an average of 15.2%, between 1 and 36 weeks, but since cell bodies make only a small fraction of the total volume, much of the overall volume reduction observed must be attributed to a concomitant reduction of the neuropil. The distribution of cell size suggested that there are two populations of neurons, presumably corresponding to interneurons and projection neurons. This bimodal distribution was maintained after deafferentation, but after 4 weeks it shifted to the left, showing an increase in small cells and a decrease of large cells. These findings demonstrate that peripheral deafferentation causes a substantial and persistent decrease of cytoplasmic mass in the cuneate nucleus, involving both neuropil and neuronal cell bodies, but does not lead to neuron loss, at least up to 36 weeks after injury. These effects suggest that the altered synaptic input and trophic support subsequent to deafferentation leave the cuneate nucleus in a permanently compromised, albeit seemingly stable, state.

Animals↗

PubMed1996

Changes in extracellular levels of dopamine metabolites in somatosensory cortex after peripheral denervation.

This study examined the effects of a nerve transection on monoamine release from primary somatosensory cortex. The technique of microdialysis was employed to sample extracellular levels of norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) in the barrel field of freely moving rats following the surgical transection of the contralateral infraorbital nerve. Microdialysates obtained 3, 4, and 5 days after deafferentation were analyzed using high-performance liquid chromatography with electrochemical detection. We found a significant increase in the release of the dopamine metabolites, DOPAC and HVA from the deafferented cortex. Three days after deafferentation the release of DOPAC was three-fold higher in the deafferented than in the control animals, and remained about 100% higher in the next two days in this group of animals. The release of HVA showed a gradual increase following the deafferentation procedure, since a 92% larger value on day 3 increased to a 338% difference on day 5. On the other hand, the release rate of NE and the levels of the serotonin metabolite 5-HIAA were not significantly affected by the deafferentation procedure. These results are discussed in the context of the possible participation of dopamine in the reorganization of the deafferented somatosensory cortex.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1996

Changes in cortical acetylcholine release in the rat during day and night: differences between motor and sensory areas.

By sampling simultaneously from two microdialysis probes placed in the left and right hindlimb somatosensory cortex, or in the somatosensory and visual or in the somatosensory and motor cortices, we compared the release of acetylcholine in functionally different regions. Samples were taken hourly from freely moving, adult male Sprague-Dawley rats for periods of 10-24h. A generalized increase in acetylcholine release occurred in all cortical regions with the transition to the night-time period of wakefulness and activity; however, the change was significantly greater in the two sensory regions (56%) than in the motor cortex (20%). Decrements in release during the active period seldom decreased the amount released below the values observed during sleep. During the active period, the amount of acetylcholine released in the somatosensory cortex was strongly correlated with the amount released in the contralateral somatosensory region and was only slightly less well correlated with the amount released in either the visual or motor cortex. The correlation between release in the somatosensory and motor cortex was not present during the day, when rats habitually sleep. These data confirm that a global change in the level of acetylcholine release occurs with a transition in behavioural state; however, because the change is not equal in all areas and, because the correlation between motor and sensory cortex can be uncoupled, it seems likely that there are additional mechanisms available for independent control of acetylcholine release within specific cortical regions.

Acetylcholine↗

PubMed1996

Acetylcholine innervation of sensory and motor neocortical areas in adult cat: a choline acetyltransferase immunohistochemical study.

Light microscopic choline acetyltransferase (ChAT) immunocytochemistry was used to examine the distribution of the acetylcholine innervation in primary motor (4 gamma) and sensory (3a, 3b, 41 and 17) cortical areas of adult cat. In every area, scattered immuno-reactive cell bodies were present and a relatively dense meshwork of ChAT immunoreactive axons pervaded the whole cortical thickness. These axons were generally thin and bore innumerable varicosities of different sizes. A few thicker and smoother fibers and occasional clusters of unusually large varicosities were also visible. Overall, area 17 was less densely innervated than the other areas. In each area, layer I showed the densest innervation. Innervation of underlying layers was rather uniform in area 17, but patterned in other areas. In areas 4 gamma and 3a, layers II, upper III and V showed preferential innervation. Innervation of layer IV was the strongest in areas 3b and 41. Area 3a was transitional between 4 gamma and 3b. Except in area 17, the laminar pattern of acetylcholinesterase staining was consistent with that of ChAT. In the light of current data on the distribution of this cortical innervation in different species, and of its presumed ultrastructural features, it appears likely that such regional and laminar features subtend widespread, modulatory roles of ACh.

Acetylcholine↗