Search PubMed⌕ Search

Biomedical subjects

B H Pubols

Publications and source records attributed to B H Pubols.

At least 19 recordsLinked to original sources
PubMed1996

The raccoon lateral cervical nucleus: mediolateral organization of GABA-positive and GABA-negative neurons and fibers.

In the lateral cervical nucleus (LCN) of the cat, GABA-immunoreactive neurons and substance P-immunoreactive fibers are concentrated in the medial part of the nucleus, whereas in the monkey LCN no preferential locations have been identified. In raccoons, substance P-immunoreactive fibers display a distribution pattern similar to that in cats. However, the presence and distribution of GABA-immunoreactive neurons in the raccoon LCN has not been examined, and it is therefore not known whether raccoons are similar to cats or primates in this respect. Thus, in the present study, the raccoon LCN was examined for the presence and distribution of GABA-immunoreactive cells with respect to their numbers, locations, and sizes. The distribution of GABA-positive fibers and varicosities within the LCN was also investigated. The results of measurements of cross-sectional areas of LCN neurons indicate a trend toward decreasing cell size along the dorsolateral to medial axis of the raccoon LCN. Compared to neurons of the centrally located ventromedial division, neurons are statistically significantly larger in the dorsolateral division and smaller in the medial division of the nucleus. Cell counts in post-embedding-stained semithin sections through the nucleus revealed an average of 8,700 neurons per LCN. Approximately 4% of LCN neurons are GABA-immunoreactive. These neurons are small and most (80%) of them are located in the medial third of the LCN. In contrast, GABA-immunoreactive fibers and varicosities are present in about equal density throughout the raccoon LCN. Thus, the distributions of GABA-immunoreactive neurons and neuron sizes in the raccoon LCN conform closely to those in cats. Together with previous observations in cats and raccoons, the present findings support the notion that these small GABA-immunoreactive neurons may be local circuit inhibitory neurons and indicate the presence of a mediolateral segregation that may be of fundamental importance for the functional organization of the carnivore LCN.

Animals↗
PubMed1995

The raccoon spinocervical and spinothalamic tracts: a horseradish peroxidase study.

The locations of the cells of origin of the spinocervical tract (SCT) and spinothalamic tract (STT) were examined in relation to the somatotopic and laminar organization of the cervical enlargement of the raccoon dorsal horn (DH). In different animals, either the lateral cervical nucleus or the lateral thalamus was injected with a 2% solution of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). Following 24 h or 4 days, respectively, the animals were sacrificed and both injection and target sites (spinal cord segments C6-T2) were processed using the TMB method. All labelled cells were counted in every fifth 50 microns section. Following injection of WGA-HRP into the lateral cervical nucleus, all labelled SCT cells were located ipsilateral to the injection sites. Most (84%) were in laminae III and IV, laminae known from other studies to contain cells preferentially responsive to light tactile stimulation, with very few (3%) in lamina I. Nearly 50% of labelled cells were located in the medial 1/3 of the DH, the region of representation of the glabrous surfaces of the raccoon forepaw. The mean number of labelled SCT cells per section was 4.19. After tracer injections of the lateral thalamus, more than 75% of STT cells were located contralateral to the injection sites. Forty-three percent were located in lamina I and 24% were in lamina V, laminae whose cells have been shown to be responsive to more intense forms of stimulation, as well as to light touch. Only 22% were located in the medial 1/3 of the DH. The mean number of labelled STT cells per section was 0.83. The results suggest that the SCT may play a more critical role in relaying discriminative light tactile and nociceptive information from the glabrous surfaces of the forepaw, but that there may be a greater role for the STT in relaying nociceptive information from the forelimb as a whole.

Animals↗
PubMed1993

Substance P-like and serotonin-like immunoreactivity in the lateral cervical nucleus of the raccoon.

The distribution of substance P and serotonin in the lateral cervical nucleus (LCN) of the raccoon was examined by light microscopic immunohistochemistry. Substance P-immunoreactive fibers were found to be clustered in the ventromedial part of the LCN, whereas only few such fibers appeared in the dorsolateral part of the nucleus. This organization is closely similar to that previously observed in the cat, and provides further evidence for an anatomic and functional segregation along the transverse axis of the LCN in carnivores. In some sections, substance P-positive fibers were found primarily in areas of the ventromedial LCN containing small neurons, indicating that such fibers may be involved in functions of the LCN associated with nociceptive projection neurons and/or local circuit neurons. The raccoon LCN also received a relatively sparse innervation of serotonin-positive fibers that were distributed throughout the nucleus, an organization similar to that previously observed in the cat. The functional role of the serotonergic fibers is unclear. However, their presence suggests that descending influences on transmission in the spinocervicothalamic pathway, in addition to the well-documented descending control of spinocervical tract neurons, may be present also at the level of the LCN.

Animals↗
PubMed1993

Nociceptive neurons of the raccoon lateral thalamus.

1. Responses to noxious mechanical and thermal stimuli were examined in 48 thalamic neurons in barbiturate or chloralose-anesthetized raccoons, with special attention to neurons whose peripheral receptive fields (RFs) included glabrous skin of the forepaw. Recording loci were in the core of the ventrobasal complex (VB; n = 32), its ventral or dorsal border (n = 5), or the medial division of the posterior nuclear group (POm; n = 11). 2. Twenty-one VB neurons and 7 POm neurons were classed as wide dynamic range (WDR), whereas 2 VB neurons and 4 POm neurons were classed as nociceptive specific (NS). Response properties of 14 light touch (LT) neurons located in VB were also examined. 3. WDR and NS neurons were not segregated, but rather were intermixed along the ventral and dorsal borders of VB, as well as in POm, and WDR and LT neurons were intermixed in the core of VB. Within the VB core, both LT and WDR neurons were somatotopically organized. 4. All WDR neurons had larger high-threshold than low-threshold RFs, and this difference was greater for POm neurons than for VB neurons. RF areas of LT neurons and low-threshold RF areas of WDR neurons were comparable to those previously reported for raccoon VB units. 5. Out of 25 WDR cells tested, 20 had heat thresholds > 53 degrees C; the range of thresholds in the remaining 5 was 49-53 degrees C. Four out of five NS neurons tested had heat thresholds > 53 degrees C; the threshold of the fifth was 51 degrees C. Of the six neurons with heat thresholds < or = 53 degrees C, two each were in the core of VB, along the border of VB, and in POm. 6. Sensitization to heat after a mild heat injury to the glabrous RF (53 degrees C for 90 s, or 55 degrees C for 30 s) occurred in 8 out of 16 neurons tested, and persisted for up to 2 h. Median thresholds decreased from > 53 degrees C before injury to 47 degrees C after injury, and responses to suprathreshold stimuli were enhanced. There was a significantly greater likelihood (P = 0.02) for sensitization to occur in POm neurons (6/7) than in VB neurons (2/9). 7. It is suggested that a small proportion of neurons located in VB and POm contribute to the sensation of heat pain. Furthermore, sensitization of these neurons may contribute to heat hyperalgesia after an injury to glabrous skin.

Adaptation, Physiological↗
PubMed1991

The raccoon lateral cervical nucleus: a single-unit analysis.

1. Properties of 90 lateral cervical nucleus (LCN) neurons responsive to light tactile stimulation of ipsilateral body surfaces were examined in pentobarbital sodium-anesthetized raccoons. Peripheral receptive fields (RFs) of 60 of these lay totally or partially on glabrous skin of the forepaw. There were 71 neurons antidromically activated from the contralateral thalamic ventro-basal complex (VB) or medial lemniscus. Results were compared with previous findings in the raccoon spinocervical tract (SCT) and the dorsal column-medial lemniscal system (DC-MLS). 2. RFs located on glabrous skin of the digits were significantly smaller than those located on glabrous skin of the palm. All RFs, whether on glabrous skin of the forepaw or elsewhere, tended to be larger than those of either SCT or DC-MLS neurons. LCN units with glabrous forepaw RFs tended to be located ventrally within the nucleus. 3. Of those LCN neurons for which the RFs lay totally or partially on glabrous skin of the forepaw, relative numbers that were rapidly adapting (RA; 77%) versus slowly adapting (SA; 23%) were comparable with those found in the SCT and in VB. Relative numbers of LCN neurons that were classed as light touch (87%) versus multireceptive (13%) were comparable with those found in the SCT. 4. In contrast to both the SCT and VB, but in common with the prethalamic DC-MLS, indentation velocity coding functions of both RA and SA units fell within homogeneous groupings, power function exponents for RA units tending to be steeper than those for SA units (range of b = 0.710 - 0.919 vs. 0.448 - 0.883). 5. It is concluded that the raccoon spinocervicothalamic system (SCTS) as a whole lacks the "modality and place specificity" associated with the DC-MLS. Although the SCTS probably makes significant contributions to properties of VB neurons, these properties primarily reflect those of neurons of the DC-MLS.

Adaptation, Physiological↗
PubMed1990

Slowly adapting type I mechanoreceptor discharge as a function of dynamic force versus dynamic displacement of glabrous skin of raccoon and squirrel monkey hand.

The effects of dynamic force and dynamic displacement on single unit discharge rate during ramp stimulation were examined in 10 raccoon and 8 squirrel monkey slowly adapting Type I (SAI) mechanoreceptive afferent fibers, all having receptive fields on glabrous skin of the hand. In all 18 cases, power function exponents were higher for effects of dynamic displacement than for effects of dynamic force on discharge frequency. Thus, these SAI mechanoreceptors are more sensitive to variations in dynamic displacement than to variations in dynamic force. This differential sensitivity may be explained by the fact that the relationship between dynamic force and dynamic displacement is, itself, nonlinear, dynamic displacement being a power function of dynamic force, with exponents less than 1.0.

Action Potentials↗
PubMed1989

Somatotopic organization of forelimb representation in cervical enlargement of raccoon dorsal horn.

1. Somatosensory representation of the forelimb in the dorsal horn of spinal segments C5-T2 was examined in 13 North American raccoons anesthetized with pentobarbital sodium. Single- or multiple-unit responses to light mechanical stimulation were recorded at a total of 504 loci, which were subsequently reconstructed from stained, transverse sections. From these, dorsal view maps of forelimb representation in Rexed's laminae III and IV were synthesized. 2. There was a shifting, serial overlap of representations of different forelimb regions in both the rostrocaudal and mediolateral axes of the dorsal horn. The rostrocaudal progression of receptive fields was from preaxial forelimb to forepaw to postaxial forelimb, whereas the mediolateral progression was from the volar glabrous forepaw toward the trunk. 3. Representations of the glabrous surfaces of the digits and palm pads showed considerable overlap, with the digital representations extending more laterally, but the palmar representations extending more rostrally and caudally. One-third of all recording loci were devoted exclusively to glabrous skin representation. 4. Comparison with results of earlier studies in raccoons indicates that representation of a given digit or palm pad is more restricted in rostrocaudal extent in the dorsal horn than in the dorsal roots, and that, compared with various nuclear regions of the dorsal column-medial lemniscal system, the glabrous surfaces of the forepaw are underrepresented in the dorsal horn. 5. The results suggest that there is a dorsoventral modular organization of forelimb representation in the dorsal horn. These wedge-shaped modules from larger aggregates which represent major body subdivisions and which course sinuously in the rostrocaudal dimension.

Afferent Pathways↗
PubMed1989

Spinocervical tract neurons responsive to light mechanical stimulation of the raccoon forepaw.

1. The extracellular activity of 45 antidromically identified spinocervical tract (SCT) neurons responsive to light mechanical stimulation of the glabrous surfaces of the forepaw was examined in raccoons anesthetized with pentobarbital sodium. An additional seven neurons had peripheral receptive fields (RFs) located on hairy skin of the forelimb, and three had deep RFs. 2. All recording sites were histologically verified as falling within Rexed's laminae III and IV in spinal cord segments C6-T1. Antidromic conduction velocities of the 55 neurons ranged between 8.3 and 64.2 m/s. 3. Units with glabrous skin RFs were classified according to their response to a maintained mechanical stimulus as either rapidly adapting (n = 39) or slowly adapting (n = 6). Of 11 cells tested, 2 displayed enhanced responses to noxious stimuli and were classed as multireceptive. 4. RF areas were significantly smaller on digits (range = 0.4-45.0 mm2) than on palm pads (range = 5.6-76.0 mm2), and comparable in size to RF areas previously reported in raccoon cuneate nuclear cells (32). 5. RA neurons fell into three distinct categories with respect to the relationship between instantaneous spike frequency during displacement ramp stimulation, and ramp velocity, steep functions (as defined by the value of power function exponents), flat functions, and discontinuous functions; SA neurons fell into two categories, continuous, and discontinuous. 6. The results, in conjunction with those of previous studies, lead to two major conclusions: 1) raccoon and primate spinocervicothalamic systems are more similar to each other than either is to that of the cat and 2) the ability of the raccoon SCT to convey information from the glabrous skin of the forepaw regarding characteristics of light mechanical stimuli is at least as precise as that of neurons of the dorsal column-medial lemniscal system.

Afferent Pathways↗
PubMed1989

Patterns of resting discharge in neurons of the raccoon main cuneate nucleus.

1. The presence and pattern of resting discharge were examined in 100 single neurons of the raccoon main cuneate nucleus (MCN). Of these, 66 were activated, either antidromically or synaptically, by electrical stimulation of the contralateral thalamic ventrobasal complex (VB), and 34 were activated by stimulation of the ipsilateral cerebellum (CB). 2. Forty-one percent of VB-activated neurons displayed a resting discharge, whereas 32% of CB-activated neurons did. Most neurons activated from VB and showing a resting discharge fired in bursts of 2-5 spikes, whereas those activated from CB and showing a resting discharge generally fired as single, irregularly spaced spikes, with occasional bursts in some neurons. 3. All neurons antidromically activated from VB were histologically localized within the clusters region of the MCN, whereas those antidromically activated from CB were confined to its polymorphic region. Neurons synaptically activated from either VB or CB were located in either of these regions. 4. Differences in the proportions of neurons displaying a resting discharge did not vary significantly as a function of type of preparation: methoxyflurane anesthesia, pentobarbital sodium anesthesia, decerebrate (the latter CB-activated only). 5. Although the sample sizes were too small to demonstrate statistical significance, neurons exhibiting a resting discharge were more likely to show a bursting pattern in methoxyflurane-anesthetized preparations than were neurons in pentobarbital sodium-anesthetized preparations. 6. The probability of having no resting discharge, firing in bursts, or firing in single spikes was not related to cutaneous submodality [rapidly adapting (RA), slowly adapting (SA), Pacinian (Pc)], or to receptive field (RF) locus (glabrous versus hairy skin). 7. The overall mean rate of firing (11.8 Hz) was not significantly different for bursting versus nonbursting neurons. 8. In bursting neurons, median interspike intervals (ISIs) varied between 1.3 and 2.3 ms. Most bursting neurons also had a range of short or minimal interburst intervals (MIBIs), characteristic for each neuron, whose medians varied from neuron to neuron between 34 and 90 ms. Distributions of within-burst ISIs and MIBIs had comparable coefficients of variation, varying between 0.031 and 0.223. 9. The application of a mechanical stimulus to a neuron's peripheral RF led to a decrease in interburst intervals, accompanied, depending upon the unit, by either an increase or a decrease in the number of spikes per burst. 10. Results are discussed in terms of the functional significance of resting discharge, including bursting, and possible roles in somatosensory information

Animals↗
PubMed1987

Effect of mechanical stimulus spread across glabrous skin of raccoon and squirrel monkey hand on tactile primary afferent fiber discharge.

The role of spread of skin deformation in activating cutaneous mechanoreceptors at a distance from their threshold receptive fields (RFs) was examined in glabrous skin of the North American raccoon and the squirrel monkey. One feedback-controlled mechanical stimulus probe was used to indent the skin to a controlled depth at a constant velocity, at varying distances from a second probe, which was used to monitor vertical displacement depth and velocity at this distant site. In many instances, the monitor probe was positioned over the RF of a cutaneous mechanoreceptor, and single-unit action potentials were simultaneously recorded from individual fibers of the median or ulnar nerve. With distance from the site of stimulation, there was a systematic, monotonic decline in indentation depth and velocity; velocity fell off with distance more rapidly than depth. The degree of diminution with distance varied with the size, shape, and curvature of the digital or palm pad stimulated. Spread of indentation was more restricted on digital than on palm pads, and was more restricted across monkey skin than across raccoon skin. Spread was less with higher-velocity than with lower-velocity indentations, but was seemingly unaffected by indentation depth. As expected from the findings noted above, the number of spikes discharged by slowly adapting mechanoreceptive afferent fibers declined more rapidly with distance between stimulus site and RF for digital than for palmar RFs, in squirrel monkey than in raccoon skin, and with higher-velocity than with lower-velocity stimuli. Furthermore, the number of spikes occurring during either ramp or early static indentation phases of stimulation dropped to zero more rapidly with distance than did either vertical indentation depth or velocity. Decreases with distance in both indentation depth and velocity acted to restrict the size of suprathreshold RFs. For most units, horizontal components of mechanical stimulation subtracted from the effects of vertical components. It is suggested, on the basis of this and other studies, that many neural and perceptual phenomena usually attributed to central mechanisms of afferent inhibition may be attributable, at least in part, to mechanical properties of the skin. In addition, the present data suggest that regional variations in the two-point limen may be associated with variations in spread of mechanical deformation. The conclusion that glabrous skin and subjacent soft tissues act as a low-pass filter system provides a mechanical basis for the relative efficacy of high-frequency vibratory stimuli in tactile pattern perception.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1986

Relations between stimulus force, skin displacement, and discharge characteristics of slowly adapting type I cutaneous mechanoreceptors in glabrous skin of squirrel monkey hand.

The contributions of viscoelastic properties of squirrel monkey glabrous skin to slowly adapting Type I (SAI) mechanoreceptive afferent fiber discharge were examined in the present study. Individual fibers of the median and ulnar nerves were isolated by microdissection in six monkeys anesthetized with pentobarbital sodium. Utilizing mechanical stimulation and data analysis techniques identical to those of a previous study of raccoon glabrous skin and its mechanoreceptors (Pubols, 1982a; Pubols and Maliniak, 1984), we studied and compared responses to punctate mechanical stimuli controlled with respect to force or displacement. Squirrel monkey glabrous skin was found to be more compliant than raccoon glabrous skin, in that a given force applied to either a digital or a palmar skin pad produced a greater displacement of squirrel monkey skin. Skin displacement increased approximately linearly with increasing forces at the beginning of static stimulation, but over time (at least up to 20 sec), the relationship became negatively accelerated. Absolute-force thresholds of individual SAI units were significantly lower in squirrel monkey (mean = 122 mg, range = 48-340 mg) than in raccoon (mean = 484 mg, range = 70-1,290 mg). However, absolute-displacement thresholds were insignificantly lower (squirrel monkey: mean = 17.24 microns, range = 5-30 microns; raccoon: mean = 30 microns, range = 5-185 microns). Application of suprathreshold forces (range = 1-20 g) and displacements (range = 500-1,000 microns) revealed greater interunit variability in response to maintained stimulation than previously found in raccoon. In 8 out of 15 fibers, the rate of adaptation was significantly greater during constant-displacement than during constant-force stimulation; in 4 cases there was no significant difference; and in 3 cases the rate of adaptation was significantly greater during constant-force stimulation. Potential sources of interunit variability include surface topography of the hand, properties of cutaneous and subcutaneous tissues in the vicinity of the receptor, and experimental variables such as stimulus amplitude and rate of stimulus onset. It is suggested that both regional and species differences in functional properties of cutaneous mechanoreceptors are more likely attributable to differences in mechanical properties of skin and subjacent tissues than to any inherent differences in receptor properties.

Adaptation, Physiological↗
PubMed1986

The somatosensory thalamus of the raccoon: properties of single neurons responsive to light mechanical stimulation of the forepaw.

These studies were undertaken to characterize the discharge properties of single neurons of the raccoon thalamic ventrobasal complex (VB) that respond to light mechanical stimulation of the glabrous surfaces of the forepaw. Microelectrodes were used to record the extracellular activity of 146 cells in anesthetized raccoons, and all neurons were histologically verified as falling within or along the boundaries of VB. Sixty-one neurons were tested for activation by electrical stimulaton of primarily somatosensory cortex. Of these, 88% were antidromically activated, 5% were synaptically activated, and the remaining 7% were unresponsive. Out of the total sample of 146 neurons, 136 had peripheral receptive fields (RFs) that were restricted to glabrous skin and revealed properties of modality and place-specificity predictable through knowledge of properties of primary mechanoreceptive afferents. Rapidly adapting (RA) neurons accounted for 77% of this modality-place-specific sample, while 19% were slowly adapting (SA), and 4% revealed properties indicative of input from Pacinian afferents (Pc). Absolute displacement thresholds were comparable for RA and SA neurons (range = 6-415 micron). Palmar RF areas (range = 3.3-328 mm2) were significantly larger than digital RF areas (range = 0.5-98.2 mm2). As defined by exponents (b) of power functions relating instantaneous discharge frequency to displacement ramp velocity, SA neurons formed a single, homogeneous group (range of values of b = 0.633-0.720). However, RA neurons fell into three distinct groups: those showing relatively steep functions (b = 0.559-0.938), those showing relatively flat functions (b = 0.146-0.334), and those showing discontinuous, or step, functions. A small number of neurons (7% of total sample) revealed "complex" properties, not predictable from knowledge of properties of primary afferents. These included five neurons whose RFs encompassed both glabrous and hairy skin, and several linear orientation, or "tactile edge," detectors. The present results, in conjunction with those of earlier studies of the raccoon dorsal column-medial lemniscal system, lead to the conclusion that different types of information transformation are emphasized at different levels of the system. Intramodality convergences (increases in RF area) occur primarily within the cuneothalamic relay, while changes in the coding of quantitative information are primarily a function of VB neurons. The appearance of linear orientation detectors--a type of tactile "feature detector"--indicates that the synthesis of information regarding complex spatial properties of stimuli has its beginnings within the somatosensory thalamus.

Animals↗
PubMed1985

Response properties of raccoon cuneothalamic neurons.

Microelectrodes were used to record the extracellular activity of 80 single neurons of the main cuneate nucleus (MCN) of raccoons anesthetized with either methoxyflurane or pentobarbital sodium. All 80 MCN neurons had peripheral receptive fields (RFs) that lay entirely on the glabrous surfaces of the forepaw and were responsive to light mechanical stimulation. Neurons were characterized according to the nature of their response to mechanical stimulation of their RFs, as well as to their response to electrical stimulation of the contralateral thalamic ventrobasal complex (VB). All antidromically activated neurons (64% of sample) were histologically verified as falling within the clusters region of the MCN, while synaptically activated neurons (19% of sample), as well as neurons not responsive to VB stimulation (17% of sample), were located in both the clusters and the polymorphic regions. Antidromically activated neurons typically responded with a single fixed-latency spike, although a few responded with a burst of 3 or more spikes. Others responded with a single antidromic spike followed by a train of synaptically activated spikes. In these latter neurons, it was often possible to block the synaptic spikes selectively. MCN neurons were classed according to their response to controlled mechanical stimuli as rapidly adapting (RA), slowly adapting (SA), or Pacinian (Pc). The proportions of neurons falling into these categories did not vary significantly with the type of response to thalamic stimulation, and the overall percentages were 56% RA, 24% SA, and 20% Pc. These figures are very similar to those previously obtained in a sample of primary afferent fibers of the raccoon cervical cuneate fasciculus (L. M. Pubols and Pubols, 1973). Absolute displacement, displacement velocity, and force thresholds, which ranged between 4 and 326 micron, 0.01 and 16.3 micron/msec, and 120 and 3600 mg, respectively, are comparable to those previously found for primary afferents supplying mechanoreceptors of the glabrous surfaces of the raccoon's forepaw. Neither displacement nor force thresholds differed for RA versus SA neurons; however, displacement velocity thresholds were significantly lower for SA than for RA neurons.

Afferent Pathways↗
PubMed1984

Somatosensory thalamocortical connections in the raccoon: an HRP study.

In the North American raccoon (Procyon lotor), representations of the glabrous surfaces of the hand digits are found within separate subnuclei of the thalamic ventrobasal complex (VB) and on separate subgyri of the somatosensory cortex (SmI). In the present study, the retrograde transport of horseradish peroxidase from SmI to VB was utilized to study relationships between physiologically identified cortical subgyri and somatotopically corresponding thalamic subnuclei. Single large or multiple small injections confined to a single gyral crown led to retrograde labeling of large groupings of cells filling the entire VB subnucleus for the appropriate digit. In the aggregate, the regions of label appeared as thin, wedge-shaped sheets extended in the dorsoventral and anteroposterior dimensions, but flattened mediolaterally, and curving to form a laterally directed convexity; these appear to correspond to the lamellae of monkey VB described by others. These large injections led to labeling of approximately 80% of all large (18-30-micron diameter) cells within the lamella. Single, small, focal injections of a gyral crown led to variable amounts of labeling, ranging from an entire digital lamella to only a small focal cluster of cells. No evidence was obtained for the existence of anteroposteriorly extending "rods" of cells, as reported in primates. Finally, there was a sparse, but consistent labeling of cells of the posterior nuclear group (Po) following gyral crown injections. These results are in agreement with expectations based on prior electrophysiological studies of raccoon VB and SmI, as well as prior anatomical studies of thalamocortical relationships.

Animals↗
PubMed1984

Electrophysiology of raccoon cuneocerebellar neurons.

Electrophysiological experiments were undertaken in order to locate and functionally characterize cells of the raccoon main cuneate nucleus (MCN) that can be activated by electrical stimulation of the cerebellum. A total of 98 such units were studied in pentobarbital sodium-anesthetized, methoxyflurane-anesthetized, or decerebrate preparations. Aside from a greater likelihood of resting discharge in the decerebrate preparations, no appreciable variability in physiological properties of the neurons could be attributed to differences in the type of preparation. Using constant latency of response and ability to be blocked by collision as principal criteria, both antidromically (n = 31) and synaptically (n = 67) activated neurons of the main cuneate nucleus could be identified. A small number of MCN neurons could be activated by both cerebellar and thalamic stimulation, but no unit was antidromically activated from both locations. MCN neurons projecting to the cerebellum are located primarily in the ventral polymorphic cell region of the nucleus at and rostral to the obex, corresponding to the "medial tongue" region of Johnson et al. (1968). In contrast, neurons synaptically activated from the cerebellum are found throughout the dorsoventral extent of the rostral MCN, including the "clusters" region. The majority of antidromically activated units responded to mechanical stimulation of deeper tissues, and most of these were activated by muscle stretch. Only a small portion (13-15%) of either antidromically or synaptically activated units were classed as light touch units with peripheral receptive fields (RFs) restricted to glabrous surfaces of the forepaw. Glabrous skin RFs located on the digital surfaces are smaller than those located on the palm pads. In both cases, RFs are larger than those associated with primary afferent fibers, but toward the low end of the distribution for MCN neurons not activated by cerebellar stimulation. All MCN units activated by cerebellar stimulation, regardless of modality, respond to mechanical stimulation with trains of irregularly spaced single spikes. Glabrous skin cutaneous mechanoreceptive MCN neurons, whether rapidly or slowly adapting, respond to ramp indentations with an instantaneous frequency which may be described as a power function of ramp velocity, with exponents less than one. These values are in the same range as those previously reported for primary afferents of the cuneate fasciculus (Pubols and Pubols, 1973).

Adaptation, Physiological↗
PubMed1983

Tactile receptor discharge and mechanical properties of glabrous skin.

Current knowledge of the functional properties of mammalian cutaneous mechanoreceptors is reviewed with special reference to receptors associated with the glabrous skin of the raccoon and squirrel monkey hand. Four physiologically defined mechanoreceptor types are recognized: Pacinian afferents, rapidly adapting (RA), and slowly adapting type I (SAI), and slowly adapting type II (SAII). The SAI category is divided into moderately slowly adapting and very slowly adapting (VSA) types in terms of the duration of their response to a prolonged mechanical displacement of skin. Although both RA and SA units are capable of signaling displacement ramp velocity, the pattern of discharge during ramp stimulation may vary widely among units. SAI units also code the depth of skin displacement, but there is no best-fitting function describing the relationship. Static discharge is also markedly influenced by prior ramp velocity. Both raccoon and squirrel monkey VSA units show wide variation in the regularity of their discharge during static displacement. The rate of adaptation of SAI units is less when constant force stimuli are applied to the skin than when constant displacement stimuli are applied. This is partly attributable to mechanical properties of the skin. When either constant force or constant displacement stimuli are spaced too closely in time, there is a progressive (trial-to-trial) decrement in response rate, accounted for in part by failure of the skin to recover to its initial resting level.

Afferent Pathways↗