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J K Chapin

Publications and source records attributed to J K Chapin.

At least 37 records · Page 2Linked to original sources
PubMed1995

Sensorimotor encoding by synchronous neural ensemble activity at multiple levels of the somatosensory system.

Neural ensemble processing of sensorimotor information during behavior was investigated by simultaneously recording up to 48 single neurons at multiple relays of the rat trigeminal somatosensory system. Cortical, thalamic, and brainstem neurons exhibited widespread 7- to 12-hertz synchronous oscillations, which began during attentive immobility and reliably predicted the imminent onset of rhythmic whisker twitching. Each oscillatory cycle began as a traveling wave of neural activity in the cortex that then spread to the thalamus. Just before the onset of rhythmic whisker twitching, the oscillations spread to the spinal trigeminal brainstem complex. Thereafter, the oscillations at all levels were synchronous with whisker protraction. Neural structures manifesting these rhythms also exhibited distributed spatiotemporal patterns of neuronal ensemble activity in response to tactile stimulation. Thus, multilevel synchronous activity in this system may encode not only sensory information but also the onset and temporal domain of tactile exploratory movements.

Animals↗
PubMed1995

Development of direct GABAergic projections from the zona incerta to the somatosensory cortex of the rat.

The postnatal development of direct thalamocortical projections from the zona incerta of the ventral thalamus to the whisker representation area of the rat primary somatosensory cortex was investigated. Cytoarchitectonic analysis based on Nissl staining, cytochrome oxidase histochemistry and immunohistochemistry for glutamic acid decarboxylase, GABA, parvalbumin and calbindin D28K revealed that the zona incerta can be clearly distinguished from surrounding diencephalic structures from the day of birth. Moreover, four distinct anatomical subdivisions of this nucleus were identified: the rostral, dorsal, ventral and caudal. Of these, the ventral subdivision is by far the most conspicuous, containing the highest density of neurons, and the highest levels of cytochrome oxidase, glutamate decarboxylase, GABA, parvalbumin and calbindin D28K. In contrast, the dorsal, rostral and caudal subdivisions contain fewer cells, lower levels of glutamic acid decarboxylase and GABA and very few parvalbumin-positive and calbindin-positive neurons. Small injections of rhodamine coated microspheres or Fluoro-gold in the primary somatosensory cortex of animals at different stages of development revealed the existence of retrogradely labeled neurons in the rostral and dorsal subdivisions of the zona incerta from postnatal day 1. At this age, retrogradely labeled cells were also found in the ventral lateral, ventral posterior medial, posterior medial, centrolateral, ventral medial and magnocellular subdivision of the medial geniculate nuclei of the dorsal thalamus. The density of the incertocortical projection reaches its maximum between the first and second postnatal weeks, decreasing subsequently, until an adult pattern of labeling is achieved. Tracer injections combined with immunohistochemistry revealed that the majority of the incertocortical projection derives from GABAergic neurons, implying a potentially inhibitory role for the incertocortical projection. These results demonstrate that the rat trigeminal system contains parallel thalamocortical pathways of opposite polarity, emerging from both the dorsal (glutamatergic, excitatory) and ventral (GABAergic, inhibitory) thalamus since the day of birth. As such, these findings suggest that, contrary to the classical notion, not only the dorsal but also the ventral thalamus may play a special role in both cortical maturation and function.

Animals↗
PubMed1994

Differential phasic modulation of short and long latency afferent sensory transmission to single neurons in the primary somatosensory cortex in behaving rats.

Single neurons were recorded in the forepaw area of the primary somatosensory (SI) cortex of awake rats during rest and running behavior. Locomotor step cycle dependent changes of the transmission of the short (4.5 +/- 0.1-10.5 +/- 0.1 ms, SEURs) and the long (10.6 +/- 0.6-28.5 +/- 2.3 ms, LEURs) latency evoked unit responses were tested by generating post-stimulus time histograms of these neurons' responses to stimulation through electrodes chronically implanted under the skin of the forepaw. Times of footfall were determined by way of frame-by-frame analyses of video recordings, and peri-footfall histograms were generated to differentiate a total of 55 SI cortical neurons into two types: footfall responsive (n = 37) and footfall unresponsive (n = 18) neurons. Peri-footfall gating patterns were determined for both types of cells. The SEURs and the LEURs showed significantly different phasic sensory modulation patterns. A major difference in sensory modulations between footfall responsive and footfall unresponsive cells was noted during the swing phase of the locomotor step cycle. In footfall responsive cells, the SEURs were suppressed most strongly just after footfall, while the LEURs were phasically suppressed following both footfall and footoff. The SEURs were disinhibited during the swing phase. In footfall unresponsive cells, the SEURs were tonically suppressed during the whole locomotor step cycle phases. However, the LEURs were phasically facilitated during the early swing phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1994

Behavioral associations of neuronal activity in the ventral tegmental area of the rat.

The ventral tegmental area (VTA) is a central element in a system that mediates the reinforcing properties of natural stimuli (such as food), brain stimulation, and drugs of abuse. Although considerable effort has been applied to understanding how drugs of abuse influence this system, relatively little work has examined its function during conditioned reinforcement tasks in awake, behaving animals. In the present studies, bundles of four to eight microwire electrodes were chronically implanted in the VTA or prefrontal cortex (PFC) of male Wistar rats. Following recovery from surgery, simultaneous recordings from multiple single neurons and unit clusters were obtained in rats pressing a lever for a sucrose solution on a fixed-ratio schedule of reinforcement. Consistent with the hypothesis that these neurons encode information related to motivation, most of the neurons in both VTA and PFC showed significant modulation of firing rate associated with one or more events occurring within the response/reinforcement cycle. These events included lever presses, onset and end of a tone signaling sucrose delivery, and onset and end of sucrose consumption. Significant decreases in firing rate were observed, coincident with onset of the tone and sucrose delivery, or with consumption. These decreases were sustained through the end of sucrose consumption. A number of neurons also discharged bursts of activity associated with individual lever presses. These findings provide a clear demonstration that VTA neuronal activity is modulated during motivated behavior. Similar information about events within the ongoing response/reinforcement cycle appears to be distributed through many neurons within the VTA, and may be mirrored in target structures such as PFC.

Action Potentials↗
PubMed1994

Spatiotemporal structure of somatosensory responses of many-neuron ensembles in the rat ventral posterior medial nucleus of the thalamus.

Classically, the rat ventral posterior medial (VPM) nucleus of the thalamus has been considered as a simple passive relay for single-whisker information to the primary somatosensory cortex (SI). However, recent reports have suggested that the VPM could contain a much more coarsely coded and spatiotemporally complex representation of the rat whisker pad. To address this possibility properly, we have carried out chronic simultaneous recordings of large numbers (up to 23) of single neurons, distributed across the entire VPM, in both awake and lightly anesthetized adult rats. Quantitative, computer-based reconstruction of receptive fields (RFs) revealed that single VPM neurons exhibit significant responses to discrete stimulation of as many as 20 single whiskers (mean +/- SD RF size, 13.7 +/- 4.8 whiskers). By defining multiple response magnitude (RM) thresholds it was possible to subdivide these large VPM RFs quantitatively into a prominent center (mean +/- SD, 1.41 +/- 0.70 whiskers, RM > 95%) and an excitatory surround (up to 18 whiskers, RM < 95%). VPM neurons exhibited both short-latency responses (SLRs, from 4 to 10 msec poststimulus) and/or long-latency responses (LLRs, 15-25 msec), each followed by inhibitory responses. Though LLRs were weaker (mean +/- SD, 47.19 +/- 33.34 Hz) than SLRs (119.63 +/- 50.12 Hz), they often defined RFs that differed considerably from those defined by the SLRs of the same cell. In particular, VPM cells with short-latency RFs centered in caudal whiskers (e.g., C1, D1, E1) showed a poststimulus time-dependent shift of these RF centers toward the rostral whiskers (e.g., C4, D4, E4). These caudal-to-rostral (C-->RF shifts occurred in neurons with the largest RFs of our sample (17.2 +/- 2.4 whiskers). On the other hand, VPM cells with short-latency RFs centered in rostral whiskers had the smallest RFs (13.1 +/- 4.1 whiskers) and usually did not exhibit time-dependent RF center shifts. Multivariate analysis revealed that these two groups of VPM neurons, C-->R shifting and rostral position (RP) cells, could be statistically distinguished according to a combination of three RF attributes (short-latency RF center location, RF size, and magnitude of RF center shift). Quantitative, computer-based reconstruction of "population response maps" demonstrated that the "place" coding for each single whisker in the VPM involved a distinct weighted contribution from a large proportion of the simultaneously recorded neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Anesthesia↗
PubMed1993

Dynamic and distributed properties of many-neuron ensembles in the ventral posterior medial thalamus of awake rats.

The traditional view that the map of the face in the ventral posterior medial thalamus (VPM) is static and highly discrete was derived largely from qualitative studies that reported only small, robust, and nonoverlapping receptive fields (RFs). Here, by using more quantitative techniques, we have provided evidence for an alternative hypothesis: the RFs in the VPM are large and overlapping and tend to shift as a function of post-stimulus time. These results were obtained through simultaneous recordings of up to 23 single neurons across the whisker representation in the VPM of rats. Under both awake and anesthetized conditions, these neurons responded robustly at short (4-6 ms) and/or long (15-25 ms) latencies to discrete vibromechanical stimulation of single facial whiskers. Computer graphics were used to construct three-dimensional plots depicting the magnitudes of neuronal responses to stimulation of each of several whiskers as a function of post-stimulus time. These "spatiotemporal RFs" demonstrated that (i) the RFs of VPM neurons are quite large, covering up to 20 whiskers and (ii) the spatial locations of these RFs may shift dramatically over the first 35 ms of post-stimulus time, especially from the caudal-most to the rostral-most whiskers on the face. These results suggest that the VPM contains a dynamic and distributed representation of the face, in which stimulus information is coded in both spatial and temporal domains.

Animals↗
PubMed1993

Induction of immediate spatiotemporal changes in thalamic networks by peripheral block of ascending cutaneous information.

Peripheral sensory deprivation induces reorganization within the somatosensory cortex of adult animals. Although most studies have focused on the somatosensory cortex, changes at subcortical levels (for example the thalamus) could also play a fundamental role in sensory plasticity. To investigate this, we made chronic simultaneous recordings of large numbers of single neurons across the ventral posterior medial thalamus (VPM) in adult rats. This allowed a continuous and quantitative evaluation of the receptive fields of the same sample of single VPM neurons per animal, before and after sensory deprivation. Local anaesthesia in the face induced an immediate and reversible reorganization of a large portion of the VPM map. This differentially affected the short latency (4-6 ms) responses (SLRs) and long latency (15-25 ms) responses (LLRs) of single VPM neurons. The SLRs and LLRs normally define spatiotemporally complex receptive fields in the VPM. Here we report that 73% of single neurons whose original receptive fields included the anaesthetized zone showed immediate unmasking of SLRs in response to stimulation of adjacent cutaneous regions, and/or loss of SLRs with preservation or enhancement of LLRs in response to stimulation of regions just surrounding the anaesthetized zone. This thalamic reorganization demonstrates that peripheral sensory deprivation may induce immediate plastic changes at multiple levels of the somatosensory system. Further, its spatiotemporally complex character suggests a disruption of the normal dynamic equilibrium between multiple ascending and descending influences on the VPM.

Animals↗
PubMed1993

Differential phasic modulation of short and long latency afferent sensory transmission to single neurons in the ventroposterolateral thalamus in behaving rats.

Single neurons were recorded in the forepaw area of the ventroposterolateral (VPL) thalamus of awake rats during rest and running behaviors. Locomotor step cycle dependent changes of the transmission of the short (4.0 +/- 0.1-10.1 +/- 0.3 ms, SEURs) and the long (10.2 +/- 0.2-26.0 +/- 2.1 ms, LEURs) latency somatic sensory responses were tested by generating post-stimulus time histograms of these neurons' responses to stimulation through electrodes chronically implanted under the skin of the forepaw. The magnitudes of firing during these responses were measured and normalized as percent increases over background firing. Times of footfall were determined through frame-by-frame analyses of video recordings and peri-footfall histograms were generated to differentiate a total of 40 VPL thalamic neurons into two types, footfall responsive (n = 21) and unresponsive (n = 19) neurons. Perifootfall gating patterns were determined for both types of cells. The SEURs and the LEURs showed significantly different phasic sensory modulation patterns across the locomotor step cycle. Major difference of the sensory modulations between footfall responsive and footfall unresponsive cells was noted during swing phase of the locomotor step cycle. In footfall responsive cells, the SEURs were suppressed most strongly just after footfall, while the LEURs were tonically suppressed during late stance and swing phases. The SEURs were disinhibited during the swing phase, while the LEURs were disinhibited during the middle stance phase. In footfall unresponsive cells, the LEURs were suppressed more strongly around footfall event than the SEURs were.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Somatotopic maps within the zona incerta relay parallel GABAergic somatosensory pathways to the neocortex, superior colliculus, and brainstem.

Neurons located in the zona incerta (ZI) of the ventral thalamus project to several regions of the central nervous system, including the neocortex, superior colliculus, and brainstem. However, whether these projections are functionally segregated remains unknown. This issue was addressed here by combining neuroanatomical tracers with immunohistochemical staining for gamma-aminobutyric acid (GABA) and/or parvalbumin, coupled with neurophysiological mapping. GABAergic projection neurons were found in four distinct subregions of the ZI including: (1) the rostral pole of the ZI, from which neurons project to the supragranular layers of the neocortex (especially layer I); (2) the dorsal subregion of the ZI, where both ascending projections to the neocortex and descending projections to the pretectal area were observed; (3) the ventral subregion of the ZI, whose neurons project to the superior colliculus; and 3) the caudal pole of the ZI, from which descending projections to the lower brainstem and spinal cord were observed. Somatotopic representations of the contralateral cutaneous periphery were also identified in the dorsal and ventral subregions of ZI, both of which were found to receive dense direct afferent projections from the trigeminal complex, and dorsal column nuclei. These results suggest that the rat ZI is a major somatosensory relay in the ventral thalamus, carrying feed-forward inhibitory signals to neocortical and subcortical targets, in parallel with the excitatory somatosensory pathways.

Afferent Pathways↗
PubMed1991

Neonatal whisker removal in rats stabilizes a transient projection from the auditory thalamus to the primary somatosensory cortex.

A normally transient cross-modal thalamocortical projection from the magnocellular subdivision of the medial geniculate nucleus (MGm) to the primary somatosensory (SI) cortex of rats was found to remain unchanged throughout adulthood following unilateral removal of whiskers in newborn animals. The normal MGm projection to the auditory cortex is not lost in these neonatally whisker-deprived adults rats but some of the MGm neurons send collaterals to both primary auditory and SI cortices. Parallel electrophysiological experiments demonstrated the multimodal character of some MGm neurons, since they responded to both auditory and cutaneous stimulation. These results suggest that the areal distribution in the cortex of thalamocortical projections arising from a multimodal thalamic nucleus, such as the MGm, may be determined during early postnatal development by the normal flow of sensory information from the periphery to the thalamus and that an early postnatal somatosensory deprivation may prevent the normal withdrawal of a cross-modal projection from the MGm to the SI.

Aging↗
PubMed1991

Thalamic plasticity induced by early whisker removal in rats.

Neurophysiological mapping was used to study the effects of early postnatal removal of mystacial whiskers on the organization of cutaneous receptive fields (RFs) within the ventral posterior thalamus (VP) of rats. This sensory deprivation induced an extensive reorganization of the thalamus, as reflected in larger facial or continuous overlapping face-body RFs and a higher proportion of slowly-adapting responses. Mapping of the VP of young rats (2-3 weeks old) demonstrated that the functional organization of the immature VP thalamus resembles that of the sensory-deprived VP, suggesting that an early postnatal sensory deprivation may interfere with the normal process of thalamic development.

Aging↗
PubMed1991

Ontogeny of corticocortical projections of the rat somatosensory cortex.

Rhodamine-coated microspheres (RCMs) were injected into the primary somatosensory cortex (SI) of rats ranging in age from postnatal (PN) day 1 to adulthood. Ipsilateral corticocortical and callosal projections within the SI were identified as early as PN day 1. At the end of the first PN week, ipsilaterally projecting neurons located in sublayer VIb were the first to assume an adult-like pattern of connectivity. Injections at subsequent postnatal ages revealed that an adult pattern of lamination of ipsilateral corticocortical projections within the SI is established between PN weeks 2 and 3, comprising projection neurons from layers II/III, layer V, and sublayer VIb. Therefore, local interactions in the rat SI are mediated not only by pyramidal neurons of layers III and V, derived from the cortical plate, but also by a subpopulation of ontogenetically older neurons located in the sublayer VIb, which may correspond to the subplate neurons of other species. Overall, these results suggest the existence of three independent short-range corticocortical systems of projections within the rat SI, which differ in terms of the laminar distribution and ontogenetic origin of their cells.

Aging↗
PubMed1990

A major direct GABAergic pathway from zona incerta to neocortex.

Retrograde fluorescent tracers were used to demonstrate a previously unknown but sizable direct gamma-aminobutyric acid (GABA)-containing neuronal pathway from the zona incerta to the neocortex in rats. This incertocortical pathway was found to project bilaterally to the entire neocortex and exhibited a rough corticotopic organization. Many of the zona incerta neurons projecting to the parietal and occipital cortices could also be immunohistochemically stained with antibodies to glutamic acid decarboxylase and GABA. Few of these neurons were immunoreactive to tyrosine hydroxylase antibodies, which identify dopamine-containing neurons. Injections in the frontal and entorhinal cortices labeled many neurons near or within the dopaminergic A13 subdivision of the zona incerta. In addition, the incertocortical system was found to be significantly larger during early postnatal (2 to 3 weeks) development. The projection pattern of this newly discovered pathway resembles that of the monoaminergic and cholinergic systems, arising from the brainstem and forebrain, suggesting possible similarities of function.

Animals↗
PubMed1990

Modulation of afferent transmission to single neurons in the ventroposterior thalamus during movement in rats.

Single units (n = 135) were recorded in the ventroposterolateral nucleus of the thalamus in awake rats. The responsiveness of neurons to sensory activation during rest and treadmill locomotion was tested by stimulation through electrodes implanted under the skin of the forepaw. The averaged evoked unit response was suppressed by a mean 31% during movement as compared with rest. This is to be compared with the mean 71% sensory suppression observed previously in the somatosensory cortex. These findings are consistent with the hypothesis that sensory information ascending to, and within the SI cortex is successively modulated at several levels during movement.

Action Potentials↗
PubMed1990

Movement induced modulation of afferent transmission to single neurons in the ventroposterior thalamus and somatosensory cortex in rat.

Single neurons were simultaneously recorded in the forepaw areas of the primary somatosensory (SI) cortex and ventroposterolateral (VPL) thalamus of awake rats during rest and running behaviors. Movement dependent changes in somatic sensory transmission were tested by generating post-stimulus histograms of these neurons' responses to stimulation through electrodes chronically implanted under the skin of the forepaw, while the animal ran on a timed treadmill. As viewed in post-paw-stimulus histograms, the evoked unit responses (EURs) could be differentiated into short (4.5 +/- 0.1-10.9 +/- 0.2 ms) and longer (12.9 +/- 0.4-31.3 +/- 0.9 ms) latency components ("SEURs" and "LEURs", respectively). The magnitudes of firing during these responses were measured and normalized as percent increases over background firing. By comparison with resting behavior, treadmill movement suppressed both SEURs and LEURs in the thalamus, as well as the cortex. The SEURs, however, were much more strongly suppressed in the SI cortex (-48.3 +/- 2.7%) than in the VPL thalamus (-28.1 +/- 6.7%). By contrast, similar magnitudes of suppression of LEURs were found in the SI (-25.8 +/- 8.6%) and VPL (-26.5 +/- 11.1%). These results suggest that the suppression of LEURs observed in the SI cortex may result from modulatory actions on subcortical circuits. Major suppression of SEURs, on the other hand, may occur intracortically, with a minor component occurring subcortically. Thus, VPL thalamus and SI cortex in the rat appear to be differentially subject to movement related modulation of sensory transmission.

Animals↗
PubMed1990

Mapping the effects of motor cortex stimulation on somatosensory relay neurons in the rat thalamus: direct responses and afferent modulation.

Single unit recordings were used to map the spatial distribution of motor (MI) cortical influences on thalamic somatosensory relay nuclei in the rat. A total of 215 microelectrode penetrations were made to record single neurons in tracks through the medial and lateral ventroposterior (VPM and VPL), ventrolateral (VL), reticular (nRt), and posterior (Po) thalamic nuclei. Single units were classified according to their: 1) location within the nuclei, 2) receptive fields, and 3) response to standardized microstimulation in deep layers of the forepaw-forelimb areas of MI cortex. For mapping purposes, only short latency (1-7 msec) excitatory neuronal responses to the MI cortex stimulation were considered. Percentages of recorded thalamic neurons responsive to the MI stimulation varied considerably across nuclei: VL: 42.6%, nRt: 23.0%, VPL: 15.7%, VPM: 9.3%, and Po: 3.9%. Within the VPL, most responsive neurons were found in "border" regions, i.e., areas adjacent to the VL, and (to a lesser extent) the nRt and Po thalamic nuclei. The same parameters of MI cortical stimulation were used in studies of corticofugal modulation of afferent transmission through the VPL thalamus. A condition-test (C-T) paradigm was implemented in which the cortical stimulation (C) was delivered at a range of time intervals before test (T) mechanical vibratory stimulation was applied to digit No. 4 of the contralateral forepaw. The time course of MI cortical effects was analyzed by measuring the averaged evoked unit responses of the thalamic neurons to the T stimuli, and plotting them as a function of C-T intervals from 5-50 msec. Of the 30 VPL neurons tested during MI stimulation, the average response to T stimulation was decreased a mean 43%, with the suppression peaking at about 30 msec after the C stimulus. This suppression was more pronounced in the VPL border areas (-52% in areas adjacent to VL and nRt) than in the VPL center (-25%).

Animals↗