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L M Pubols

Publications and source records attributed to L M Pubols.

14 recordsLinked to original sources
PubMed1992

Distribution of 5-HT1 binding sites in cat spinal cord.

Quantitative analysis of high affinity [3H]5-HT binding to 5-HT1 receptors in the cervical, thoracic, lumbar, and sacral spinal cord of the cat revealed specific binding throughout the grey matter, with the highest levels of binding in laminae II and III, and the lowest levels in laminae I and VII. Relatively high levels were also observed in the thoracic intermediolateral cell column. There were no significant differences in the degree of binding between various segmental levels. Comparison of these data with published maps of 5-HT immunoreactivity reveals--with the exception of lamina I--a close correspondence between the degree of immunoreactivity and the degree of 5-HT binding. These results suggest that 5-HT plays an important role in a variety of spinal cord sensory, motor and autonomic functions.

Animals↗
PubMed1991

Anesthetic blockade of the dorsolateral funiculus enhances evoked activity of spinal cord dorsal horn neurons.

1. A previous study of cat lumbar dorsal horn neurons found reduced responsiveness to A-fiber stimulation 1.5-12 h after thoracic dorsolateral funiculus (DLF) lesions. The present study was undertaken to determine whether this was due to the loss of descending activity or to factors specifically associated with injury by examining the response properties of dorsal horn cells before and during lidocaine blockade of the ipsilateral DLF. Electric shocks applied to the dorsal columns were used to search for dorsal horn cells. Noxious and nonnoxious cutaneous mechanical stimuli and graded electrical stimuli applied to the tibial nerve were used to activate peripheral afferent fibers. Cells were classed as low threshold (LT), high threshold (HT), or multireceptive (MR), according to their responses to natural stimuli. Baseline data were collected from a total of 58 cells. Twelve of these were further studied after lidocaine injection of the DLF. All cells examined with lidocaine were in dorsal horn laminae III-V. 2. All cells responded to activation of tibial nerve A fibers. However, the median threshold for the HT and MR cells (200 microA) was significantly higher than that of the LT cells (75 microA). Some cells in each class were also activated by C fibers (10, 70, and 64% of the LT, HT, and MR cells, respectively). 3. For the cells that were further characterized by lidocaine blockade of the DLF, all LT cells (n = 3) responded only to A-fiber stimulation, and all HT (n = 3) and MR cells (n = 6) responded to both A- and C-fiber stimulation. 4. For LT cells, responses evoked by mechanical and electrical stimuli were unaltered by lidocaine blockade. 5. HT and MR cells showed enhanced responses to electrical stimulation of C fibers during DLF blockade. There was no consistent effect of the blockade on A-fiber-evoked responses. 6. Two of three HT and four of six MR cells studied with lidocaine had spontaneous activity, which exhibited a small but significant increase during DLF blockade. 7. Receptive fields for noxious stimulation expanded in two of six MR cells during DLF blockade. Two of three HT cells developed responses to tactile stimuli during the blockade. 8. In two additional cells (1 HT and 1 MR), spontaneous activity and responses to C-fiber input increased after the DLF was cut.(ABSTRACT TRUNCATED AT 400 WORDS)

Anesthesia, Spinal↗
PubMed1991

Influence of map scale on primary afferent terminal field geometry in cat dorsal horn.

1. Thirty-one physiologically identified primary afferent fibers were labeled intracellularly with horseradish peroxidase (HRP). 2. A computer analysis was used to determine whether the distribution of cutaneous mechanoreceptive afferent terminals varies as a function of location within the dorsal horn somatotopic map. 3. An analysis of the geometry of the projections of these afferents has shown that 1) terminal arbors have a greater mediolateral width within the region of the foot representation than lateral to it, 2) terminal arbors have larger length-to-width ratios outside the foot representation than within it, and 3) the orientation of terminal arbors near the boundary of the foot representation reflects the angle of the boundary. Previous attribution of mediolateral width variations to primary afferent type are probably in error, although there appear to be genuine variations of longitudinal extent as a function of primary afferent type. 4. Nonuniform terminal distributions represent the first of a three-component process underlying assembly of the monosynaptic portions of cell receptive fields (RFs) and the somatotopic map. The other two components consist of the elaboration of cell dendritic trees and the establishment of selective connections. 5. The variation of primary afferent terminal distributions with map location is not an absolute requirement for development of the map; for example, the RFs of postsynaptic cells could be assembled with the use of a uniform terminal distribution for all afferents, everywhere in the map, as long as cell dendrites penetrate the appropriate portions of the presynaptic neuropil and receive connections only from afferent axons contributing to their RFs.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1991

Somatotopic organization of single primary afferent axon projections to cat spinal cord dorsal horn.

Horseradish peroxidase injection of identified low threshold cutaneous mechanoreceptor (LTCM) primary afferent axons was used to assess the somatotopic organization of hindlimb projections to laminae III and IV of cat dorsal horn. Multiple injections in the same animals were used to assess bilateral symmetry and precision. Thirty-one axons were injected, with more than 1 axon injected in each of 8 animals (25 axons). Somatotopic relations between their receptive field (RF) centers and the centers of their dorsal horn projections were similar to the somatotopic relations between dorsal horn cell RF centers and cell locations. Very few reversals of mediolateral somatotopic gradients (proximodistal RF location as a function of mediolateral projection center) were observed. Two afferents with nearly identical RFs in 1 animal had nearly identical projections. These observations held for many different combinations of receptor types. A simple mathematical model was used to demonstrate that assembly of dorsal horn cell RFs via passive sampling of the presynaptic neuropil by dorsal horn cell dendrites cannot account for the sizes of dorsal horn cell LTCM RFs. Hypothesized mechanisms for assembly of dorsal horn cell RFs must take into account the functional selectivity of connections required to produce RFs smaller than those predicted by the passive assembly model.

Afferent Pathways↗
PubMed1990

Characteristics of dorsal horn neurons expressing subliminal responses to sural nerve stimulation.

The present study was designed (1) to characterize the subliminal responses of dorsal horn neurons to stimulation of the sural nerve, and (2) to correlate the type of response to this stimulus with the responses to natural mechanical stimulation of the skin. To accomplish this, intracellular and extracellular recordings were carried out in L6 and L7 dorsal horn neurons in the cat. The excitatory responses of each cell to electrical stimulation of the sural nerve and to mechanical stimulation of the skin were noted. Of 35 dorsal horn cells recorded intracellularly, 11 responded with impulses to sural nerve stimulation, 9 responded with excitatory postsynaptic potentials (EPSPs) but not impulses, and 15 had no excitatory responses to this stimulus. The type of response to sural nerve stimulation was strongly correlated with receptive field modality. Most cells receiving an input from high-threshold cutaneous mechanoreceptors responded with impulses or gave no excitatory response to sural nerve stimulation, whereas most cells that had only low-threshold mechanoreceptor input responded with EPSPs only or gave no response. In cells with only low-threshold (LT) mechanoreceptive input, response to sural nerve stimulation was highly correlated with receptive field locus. Those LT cells with no excitatory responses to sural nerve stimulation had receptive fields confined to the foot and/or toes, whereas those that gave EPSPs had more proximal receptive fields. The possible significance of these data with reference to changes observed after lesions, such as increased response to sural nerve stimulation, increased receptive field size, and somatotopic reorganization, is discussed.

Afferent Pathways↗
PubMed1988

Acute and chronic effects of the neurolytic agent ricin on dorsal root ganglia, spinal cord, and nerves.

The short- and long-term effects of ricin injections into nerves have been evaluated with light microscopy in the dorsal root ganglia, spinal cord, and peripheral nerves in rats and cats. Dorsal root ganglion cells initially exhibited chromatolysis, followed by gliosis and cell death. These changes were associated with Fink-Heimer degeneration in the somatotopically appropriate region of the dorsal horn. There were no signs of chromatolysis in dorsal horn neurons in ricin-injected animals, but chromatolytic motoneurons were observed. Ricin produced acute necrosis of injected nerves and dissolution of axoplasm. At long survival times (greater than 4 weeks) some apparently regenerating axons were seen in the injection sites of rats. Cell counts indicated that a substantial percentage of dorsal root ganglion neurons associated with the injected nerves were killed, but the presence of regenerating axons suggested that some cells survived the ricin treatment. Although the lesion may not always be complete, even with maximum sublethal doses, this method appears to be useful for specifically destroying afferent fibers associated with a particular nerve without transynaptic destruction of dorsal horn neurons.

Animals↗
PubMed1988

Lack of central sprouting of primary afferent fibers after ricin deafferentation.

A new deafferentation technique, the application of ricin to peripheral nerves, was used to test for collateral sprouting of undamaged primary afferent fibers within the adult mammalian spinal cord dorsal horn. The right sciatic nerves in rats were injected with ricin 14 to 57 days prior to bilateral labelling of dorsal rootlets with horseradish peroxidase. To equate the number of surviving dorsal root fibers on the two sides, the left sciatic nerves were injected 5 days prior to labelling. In each animal, horseradish peroxidase was applied to a bilateral pair of lumbar or low thoracic dorsal rootlets 18 hours prior to sacrifice to test for sprouting by labelling primary afferent fibers and terminals in the right (experimental) and left (control) dorsal horns. Although there is overlap of degenerated and intact primary afferent fields in this preparation, a postulated precondition for sprouting (Murray and Goldberger: J. Neurosci. 6:3205-3217, '86), we found no evidence for sprouting of undamaged, myelinated afferent fibers in the experimental dorsal horns. The pattern of labelling was symmetrical in all animals, and the density of labelling was not consistently greater on the experimental side. These results support the conclusions of Rodin et al. (J. Comp. Neurol. 215:187-198, '83) and Rodin and Kruger (Somatosens. Res. 2:171-192, '84), who also found no sprouting in the rat's dorsal horn after surgical deafferentation, and do not support the assertion that the difference between the results of those studies and earlier studies in cats was due to a lack of overlap of degenerated and intact dorsal roots in the rat.

Animals↗
PubMed1988

Temporally dependent changes in response properties of dorsal horn neurons after dorsolateral funiculus lesions.

Previous studies in this laboratory have shown 1) that 19% of L6 and L7 dorsal horn cells in normal cats respond only with excitatory postsynaptic potentials (EPSPs) to sural nerve stimulation, and 2) that the distribution of dorsal horn neurons responding with impulses to sural nerve stimulation is increased in cats with chronic lateral funiculus lesions. The present study was undertaken to determine whether strengthening of subliminal sural nerve projections could account for the changes seen after lateral funiculus lesions and to explore the nature of these changes in greater detail. Ipsilateral L6 and L7 dorsal horn cells of cats with T12 dorsolateral funiculus (DLF) lesions were studied electrophysiologically at less than 1-30 days postoperatively (DPO) and were compared with similar cells recorded in normal cats. The major results were as follows. 1. Responsiveness to peripheral stimulation was depressed for up to 3 DPO following the lesions. 2. The percentage of L6 and L7 dorsal horn cells showing spontaneous activity was elevated at 3 DPO and declined to normal levels by 28 DPO. 3. The percentage of cells that responded to sural nerve stimulation increased over 3-30 DPO and was significantly greater than normal at 28-30 DPO. The increase in the percentage of cells giving impulses to sural nerve stimulation at 28-30 DPO was similar to the percentage of cells with subliminal responses to sural nerve stimulation in normal cats. A subpopulation of identified postsynaptic dorsal column neurons also showed a significant increase in the percentage that responded to sural nerve stimulation after DLF lesions. 4. The percentage of cells that had a cutaneous receptive field (RF) overlapping the region of skin innervated by the sural nerve also increased over time and was significantly greater than normal at 28-30 DPO. 5. Median low-threshold or high-threshold RF areas were not significantly greater than normal ipsilateral to DLF lesions at any survival time. 6. The proportions of low-threshold (LT), high-threshold (HT), and multireceptive (MR) cells were not significantly different from normal at any survival time from less than 1 to 30 DPO.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Electrical stimulation reveals relatively ineffective sural nerve projections to dorsal horn neurons in the cat.

Electrical stimulation of the sural nerve (SN) revealed input from sural nerve afferents to L6 and L7 dorsal horn neurons that were not apparent using natural mechanical stimuli, especially in cells with variable latency responses to SN stimulation. Nearly all (31/32) cells that had reliable, fixed latency responses to SN stimulation also had an excitatory receptive field (RF) in the region of skin innervated by the sural nerve (SN region). About one-third (20/57) of the cells with variable latency responses to SN stimulation, however, had an RF outside the SN region. Most (130/146) cells with no response to SN stimulation had RFs outside the SN region. There were no obvious differences between variable latency cells with RFs in the SN region vs those with RFs outside it in latency of response to SN stimulation, recording depth, RF sizes or modality properties. In a subsample of 31 postsynaptic dorsal column neurons all cells responding to SN stimulation also had an RF in the SN region. Strengthening of relatively ineffective projections from the sural nerve by lesions might be expected to lead to an increase in the proportion of cells responding with impulses to natural stimulation of the skin innervated by the sural nerve, and, hence, to an increase in average RF size.

Animals↗
PubMed1979

Variations in the fissural pattern of the cerebral neocortex of the spider monkey (Ateles).

Data are reported on the range and variety of fissural patterning in 40 cerebral hemispheres from 22 specimens of spider monkeys (Ateles). The hemispheres are categorized according to a number of criteria, including proximity of the central sulcus to neighboring sulci, whether certain other sulci are joined or separated from each other, and the presence and location of idiosyncratic fissures. Interhemispheric variability was found to be as pronounced within as between specimens. The study revealed a wide variability in fissural patterns of primate brain specimens and a topological significance of many sulci in that they demarcate functional subdivisions of either somatosensory or somatomotor cortex.

Animals↗
PubMed1977

Orientation detectors in the primary somatosensory neocortex of the raccoon.

An analysis of response properties of single neurons in the forepaw region of the primary somatosensory neocortex (SI) of the raccoon was undertaken to gain a better understanding of the neural bases of tactile form discrimination. In the course of this investigation a new type of feature detector neuron which responded preferentially to tactile stimulus orientation was discovered. Within a sample of 110 neurons responding to light touch, two categories of cells were noted in terms of the type of stimulation best able to excite them. One category (linear units) was preferentially responsive to indentations of the skin using a narrow elongated stimulus probe applied in a particular orientation. The other category (round field units) gave a maximum response to stimulation with a round stimulus probe applied anywhere within a roughly circular receptive field. The response pattern of some SI neurons to a maintained indentation of the skin consisted of early and late excitatory responses, separated by a depression in responding. The second excitatory response appeared to be more influenced by variations in stimulus parameters than was the first.

Action Potentials↗
PubMed1976

Opossum somatic sensory cortex: a microelectrode mapping study.

Organization of opossum somatic sensory cortex has been investigated utilizing closely spaced microelectrode penetrations (0.25-0.5 mm apart) and delicate mechanical stimulation of body surfaces including the facial vibrissae. Results may be summarized as follows: (1) the general organization of somatic sensory cortex, as originally defined by Lende ('63a) has been confirmed; (2) a double representation of the contralateral mystacial vibrissae and rhinarium, implicit in Lende's original data, was revealed in detail, the two representations being orderly, adjacent, mirror-images of each other; (3) units at a given cortical locus responded to deflection of between one and five mystacial vibrissae, about half responding to movement of a single vibrissa only; (4) about 40% of mystacial vibrissa units showed a directional specificity to the extent that they responded to deflections in only one or two cardinal directions; (5) units located in the medial vibrissa area showed a greater directional specificity than did units located in the lateral vibrissa area; (6) the surface area of rhinarial receptive fields was about ten times the area of first-order rhinarial unit receptive fields (B. Pubols et al., '73); (7) representation of the contralateral forelimb, especially the ventral surface of the forepaw, is extensive, orderly, and precise; (8) representation of the contralateral hindlimb, foot, and tail is minimal, and is confined to the midline convexity; (9) the presence of a small region of bilateral representation, lateral to the regions of contralateral representation, was confirmed. It is suggested that the region of contralateral postcranial representation plus the medial rhinarium and mystacial vibrissa areas are the homologue of SmI in placental mammals, and the region of bilateral representation is homologous to SmII of placental mammals, but that the lateral vibrissa and rhinarium areas are a specialization of somatic sensory cortex unique to the Virginia opossum.

Animals↗
PubMed1976

Coding of mechanical stimulus velocity and indentation depth by squirrel monkey and raccoon glabrous skin mechanoreceptors.

1. A sample of 113 large, myelinated first-order afferent fibers innervating the glabrous skin of the squirrel monkey's hand proved to consist primarily of two basic types. In a sample where the only known source of sampling bias is a greater likelihood to record from larger diameter fibers, 40% of the fibers were rapidly adapting (RA) and 60% were very slowly adapting (VSA). Two units were moderately slowly adapting (MSA), and one had the properties of a Pacinian afferent (Pc). 2. The RA and VSA resemble those in the glabrous skin of other mammalian species in terms of thresholds, receptive-field areas, conduction velocities, and the coding of velocity of mechanical displacement of the skin. Mean instantaneous frequency during ramp stimulation is a power function of ramp velocity for both RA and VSA, with exponents generally less than 1.00. However, ramp discharge patterns differ for RA and VSA. 3. The VSA exhibit a wide range of coefficients of variation (CV) of their interspike-interval distributions, but form a continuous distribution with respect to this statistic. In other respects the VSA are more similar to slowly adapting type I than to slowly adapting type II. They lack spontaneous activity, have restricted receptive fields, and are relatively insensitive to skin stretch. 4. Effects of mechanical stimulus velocity and static indentation depth on static discharge rate were examined in 23 squirrel monkey and 22 raccoon SA units having receptive fields on glabrous skin of the hand. 5. Discharge rate during static indentation is a monotonic, increasing function of identation depth. However, the nature of the best-fitting function (highest r) varies from unit to unit. Using a set of standard conditions (milliseconds 100-500 of static displacements up to 960 mum, following a ramp velocity of 100 mum/ms, interstimulus interval of at least 10 s), the ratio of units for which linear, as opposed to logarithmic, functions provided the best fit was 4:3 for squirrel monkeys and 1:3 for raccoons. Few units had power functions as best fits in either species. Differences between fits for different functions within the same unit, however, were often trivial and insignificant. 6. Response rate during static skin displacement is also strongly influenced by prior stimulus ramp velocity. For at least the first 500 ms, discharge rate is positively related to onset velocity but, in many units, within the first 1 s of static displacement, this relationship reverses itself, and the inverse relationship may persist for at least 5 s.

Adaptation, Physiological↗