Biomedical subjects

A Rustioni

Publications and source records attributed to A Rustioni.

At least 55 records · Page 3Linked to original sources

PubMed1990

Antibodies to glutamate and aspartate recognize non-endogenous ligands for excitatory amino acid receptors.

Antisera raised against glutaraldehyde conjugates of glutamate (Glu) and aspartate (Asp) with hemocyanin proved highly specific for their respective unconjugated amino acid haptens when tested in immunocytochemical blocking experiments on sections of the rat spinal cord. In addition, immunocytochemical staining by the Glu antiserum was effectively blocked by quisqualate but not by kainate or N-methyl-D-aspartate (NMDA); staining with the Asp antiserum was effectively blocked by kainate, to a lesser extent by quisqualate, and was not affected by NMDA. These results may be explained by assuming that the specific binding regions of the antibodies tested share certain recognition characteristics with endogenous binding sites or receptors for excitatory amino acids and their agonists.

Animals↗

PubMed1990

Single fiber studies of ascending input to the cuneate nucleus of cats: I. Morphometry of primary afferent fibers.

The morphology of afferent fibers ascending to the cuneate nucleus has been examined in this and the subsequent paper in order to quantify the pattern of arborization and bouton arrangement of selected classes of primary afferents and to compare these data with data from postsynaptic fibers ascending to the cuneate nucleus. Electrophysiologically identified G hair and Ia muscle afferent fibers in the cuneate fasciculus were intraaxonally injected with horseradish peroxidase. Cutaneous afferents terminated dorsal to proprioceptive afferents, especially at middle levels of the cuneate nucleus. The spacing of collaterals along G hair fibers was variable, but averaged 1.46 collaterals per mm; collateral density was higher at middle cuneate levels than in the rest of the nucleus. Collateral density of Ia fibers was lower than for G hair fibers and was lowest at caudal levels of the nucleus. Branches of G hair collaterals, though often initially diverging, usually converged to terminate in a single focus in the dorsal part of the nucleus. The probability of bifurcation of Ia collaterals decreased steadily at successive branch points. These collaterals branched less symmetrically than G hair collaterals, and terminated in the ventral cuneate with less dense arbors, stretched mediolaterally, but of comparable cross-sectional area. Individual G hair collaterals gave rise to more boutons than Ia collaterals; in both cases they were mostly of the en passant type. Boutons were restricted to distal branches of G hair collaterals, whereas boutons of Ia collaterals were also located on proximal branches. Bouton size was similar for the two classes of collaterals. The data reported here, in combination with the published literature, suggest that the collaterals of roughly 300 G hair fibers overlap at any given point at middle levels of the cuneate nucleus. This high degree of anatomical convergence is not predicted by the functional segregation described with electrophysiological mapping, implying the presence of intrinsic nuclear mechanisms enhancing response specificity.

Afferent Pathways↗

PubMed1990

Single fiber studies of ascending input to the cuneate nucleus of cats: II. Postsynaptic afferents.

The morphology of single postsynaptic afferent fibers terminating in the feline cuneate nucleus was investigated by using transport of Phasolus vulgaris leucoagglutinin from the cervical spinal cord and intraaxonal injections of horseradish peroxidase into identified postsynaptic fibers in the cuneate fasciculus. Injections of Phaseolus in C5 and C6 of both rhizotomized and non-rhizotomized cats gave similar results and confirmed previous observations with other techniques. In one animal with the smallest injection and the fewest labeled fibers in the cuneate nucleus, ten individual collaterals were reconstructed from serial sections. Most of these collaterals were at middle levels of the cuneate (from obex to about 4 mm caudal to it); they were largely confined to the rim and ventral regions of the nucleus, and their terminal fields were restricted rostrocaudally. Electrophysiologically identified fibers stained with horseradish peroxidase had large receptive fields on the ipsilateral forepaw, and latencies suggesting an oligosynaptic link to the periphery. Most of the collaterals from these fibers were also at middle cuneate levels and terminated mainly at the periphery of the nucleus but gave rise to larger terminal arbors, including sparse terminal branches to the core of the nucleus. Individual postsynaptic fibers differed in several respects from primary afferent fibers. While the spacing of collaterals of postsynaptic fibers was intermediate between that of G hair and Ia fibers, their arbors were larger than either, and could extend through the dorsoventral extent of the cuneate nucleus. The pattern of bifurcation of postsynaptic fibers resulted in stringier arbors which encompassed larger and less dense terminal fields than those of primary afferents. The number of boutons per collateral was intermediate between G hair and Ia fibers, but boutons of postsynaptic fibers were substantially smaller. These morphological differences are consistent with distinct functional roles for the two main ascending afferent systems, as suggested by electrophysiological data.

Afferent Pathways↗

PubMed1990

Extracellular labeling of unmyelinated dorsal root terminals after WGA-HRP injections in spinal ganglia.

Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) is a widely used neuroanatomical tracer. When compared with other tracers, WGA-HRP may preferentially label unmyelinated fibers. In agreement with this hypothesis, injections of WGA-HRP in cervical and lumbar dorsal root ganglia resulted in more prominent light microscopical labeling in superficial than deep laminae of the dorsal horn. However, ultrastructural examination of these laminae reveals a paucity of terminal labeling in contrast to the abundance of extracellular tracer in the space surrounding unmyelinated fibers and their terminals, and to the widespread occurrence of transneuronal labeling. These results bear upon the mechanism of preferential labeling in the spinal cord and have implications for the interpretation of the labeling obtained when using WGA-HRP.

Animals↗

PubMed1990

Substance P-containing projections in the dorsal columns of rats and cats.

Light and electron microscopic immunocytochemical methods were used to study the distribution and the morphology of substance P-positive fibers and axon terminals in the dorsal column nuclei of rats and cats, and to determine whether they are part of an ascending input to these nuclei. In rats, substance P-positive fibers and axon terminals are present throughout the rostrocaudal extent of the dorsal column nuclei. In cats, immunostained fibers and terminals are mostly confined to the ventral region of the caudal and middle portions of these nuclei but they are more homogeneously distributed at rostral levels. In both species, substance P-positive neurons are not present in the same nuclear complex. At the electron microscope level, substance P-positive terminals are small- to medium-sized and dome-shaped; they form asymmetric contacts on dendrites and contain many round, agranular vesicles and sparse dense core vesicles. In double-labeling experiments, visualization of substance P-immunoreactivity in the dorsal root ganglia and dorsal horn of the spinal cord was combined with the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase or of colloidal gold-labeled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase. These experiments show that substance P-positive axon terminals may originate from both small dorsal root ganglion neurons and from spinodorsal column nuclei neurons in lamina IV. Although quantitative evaluation of the contribution of these two pathways to the substance P innervation of the dorsal column nuclei has not been performed and other sources cannot be discarded on the basis of the present evidence, it is proposed that non-primary afferents to the dorsal column nuclei account for most of the substance P-positive fibers and terminals in the dorsal column nuclei. The experiments support previous findings suggesting that nociceptive input may access the dorsal column nuclei and that this may be mediated, though to a very limited extent, directly by way of small dorsal root ganglion neurons.

Animals↗

PubMed1990

Ultrastructural immunocytochemical localization of excitatory amino acids in the somatosensory system.

We studied the ultrastructure and the synaptic arrangement of glutamate-immunoreactive terminals in rats, in the superficial laminae of the spinal cord, the brainstem cuneate nucleus, and the thalamic ventroposterolateral nucleus, where a role for glutamate as neurotransmitter has been suggested by biochemical, physiological and pharmacological approaches. The antiserum employed was raised against glutaramate conjugated to keyhole limpet hemocyanin with glutaraldehyde, and was used for pre-embedding staining with an avidin-biotin-peroxidase method and for post-embedding staining with an immunogold procedure. Both methods yielded similar results, consisting of labeling of selected terminals in all the areas examined. Double immunogold labeling on the same thin section using antisera against gamma-amino-butyric acid (GABA) or substance P (SP), in combination with the anti-glutamate serum, showed that staining for glutamate and GABA was present in different terminals in all the regions examined; glutamate and SP were co-localized in a few terminals only in the superficial laminae of the spinal cord. By performing immunogold staining in combination with anterograde tracing, glutamate immunoreactivity could be localized in identified primary afferents to the dorsal spinal cord and cuneate nucleus, and in lemniscal afferents to the thalamus.

Animals↗

PubMed1989

Glutamate and aspartate immunoreactivity in corticospinal neurons of rats.

A combination of retrograde tracers and immunostaining was employed to test whether corticospinal tract (CST) neurons in rats may use amino acid excitatory neurotransmitters. CST neurons were identified following injections of either Diamidino Yellow (DY) or colloidal gold-labeled enzymatically inactive horseradish peroxidase conjugated to wheat germ agglutinin (WGAapoHRP-Au) in the spinal cord. As retrograde tracers, the two substances seemed to be equally effective, but WGAapoHRP-Au was better suited than DY as a tracer to use in combination with immunocytochemistry. Sections through the primary sensorimotor cortex, which contained the bulk of identified CST neurons, and the secondary somatosensory cortex were processed with antisera raised in rabbits against glutamate (Glu) or aspartate (Asp) conjugated by glutaraldehyde to hemocyanin. In rats with DY injections, about 60-75% of the CST neurons were Glu-immunopositive, with higher ratios in SI and MI than in SII. Similar results were obtained in all areas examined from the rats with injections of WGAapoHRP-Au. Only sections from rats with injections of WGAapoHRP-Au were processed for Asp immunostaining. In this material, between 65 and 75% of the CST neurons were Asp-immunopositive, with a slightly higher ratio in SI and MI than in SII. The possibility that these results might reflect limited penetration of the antiserum and/or staining of the same population of CST neurons by either antiserum was addressed in sections processed with both the Glu and Asp antisera. In sections incubated in a mixture of the two antisera, the percentage of immunostained CST neurons was higher, about 90%, than in sections processed for only one of the two antisera. Furthermore, in rats in which Glu and Asp antibodies were visualized by two distinguishable immunostainings, four populations of CST neurons were identifiable: 1) neurons only immunopositive for Glu, 2) neurons only immunopositive for Asp, 3) neurons likely to be stained by both, and 4) neurons immunonegative for both antisera. Twenty-five to 30% of CST neurons were positive for only one antiserum, and about 50% were positive for both. No preferential distribution was evident for any one of these populations of neurons. However, perikaryal cross-sectional areas were larger for the double-stained than for the single-stained CST neurons. Glutamergic and aspartergic transmission in CST neurons has been proposed in several publications in which methods other than immunocytochemistry were employed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Brainstem projections to the rat cuneate nucleus.

Neurons in the pontomedullary tegmentum have been proposed as a final common pathway subserving descending inhibition in the dorsal column nuclei. To investigate the anatomical substrate for these descending effects, brainstem projections to the cuneate nucleus of rats were studied with injections of lectin-conjugated horseradish peroxidase. In rats with iontophoretic tracer injections in this nucleus, many labeled neurons were detected near the injection site, especially ventral and caudal to it. Intrinsic reciprocal projections were observed after injections in caudal, middle, or rostral levels of the cuneate nucleus. Neurons were labeled in the red nucleus, in agreement with previous anatomical studies, and also in the trigeminal, vestibular, and cochlear nuclei. An ipsilateral dorsomedial group of neurons was labeled in the upper cervical segments and scattered neurons were also labeled bilaterally near the central canal. Sparse retrograde labeling in the tegmentum was focused in the lateral paragigantocellular nucleus and caudal raphe. Consistent with the retrograde experiments, anterograde labeling after pressure injections of lectin-conjugated horseradish peroxidase in the pontomedullary tegmentum was very sparse within the dorsal column nuclei; labeling was dense, however, in the region immediately ventral to these nuclei. These results confirm previous work indicating that the activity of cuneate neurons is modulated by brainstem sensory nuclei. However, it appears that direct projections to the cuneate nucleus from pontine and rostral medullary regions are sparser than previously suggested. The last link of a polysynaptic descending inhibitory pathway may include GABAergic neurons immediately adjacent to the dorsal column nuclei and/or intrinsic to these nuclei.

Animals↗

PubMed1989

Glutamate and aspartate immunoreactivity in cortico-cortical neurons of the sensorimotor cortex of rats.

Retrograde transport of tracers and immunocytochemistry have been used to determine if association and callosal neurons in the primary motor and somatosensory cortex of rats contain high levels of glutamate or aspartate and may, thus, use these amino acids as neurotransmitter. After tracer injections in these areas, about 65% of the retrogradely labeled neurons in layer V in the ipsilateral or contralateral hemisphere are immunopositive for glutamate. Lower percentages of double-labeled neurons are found in layers III, VI, and II. Similar results are obtained when sections are processed for aspartate immunoreactivity. About 90% of retrogradely labeled neurons are immunopositive in sections incubated with a mixture of both glutamate-and aspartate antisera. These results suggest that a large fraction of cortico-cortical neurons are immunoreactive for either one amino acid but not for both. It is proposed that neurons with high levels of one amino acid use this as neurotransmitter; high levels of glutamate and aspartate are likely to be present in a fraction of neurons which may release both amino acids or a substance closely related to these.

Amidines↗

PubMed1988

Direct projection of the corticospinal tract to the superficial laminae of the spinal cord in the rat.

The anterograde transport of both wheat germ agglutinin conjugated to horseradish peroxidase and the kidney bean lectin Phaseolus vulgaris leucoagglutinin was utilized to investigate the projection of primary sensorimotor corticospinal tract axons to the superficial laminae of the spinal dorsal horn in the rat. Both methods yielded qualitatively similar patterns of connectivity. Corticospinal tract axons were found to terminate within all laminae on the side contralateral to the injection site. Labeling was most dense within laminae III and IV and medial portions of laminae I, II, and V in the cervical and lumbar enlargements. Labeling in the ventral horn, though present, was relatively less dense. P. vulgaris leucoagglutinin-labeled axons within laminae I and II exhibited boutons en passant and terminaux; many of these axons also terminated or were collaterals of axons that terminated in deeper dorsal horn laminae. Results are discussed with reference to the somatotopic organization of the spinal cord and to a possible role for the cortex in the modulation of nociception within the spinal cord.

Animals↗

PubMed1988

Coexistence of glutamate and substance P in dorsal root ganglion neurons of the rat and monkey.

Antisera to a glutamate (Glu) conjugate, to glutaminase (GLN), and to substance P (SP) have been used to investigate the issue of putative glutamergic neurons in the dorsal root ganglia (DRG) and the possible coexistence in these neurons of Glu and SP. The Glu antiserum, characterized by immunoadsorption and immunoblot tests, is highly selective for Glu out of a number of other amino acids including aspartate. Quantitative data were gathered from consecutive 4-microns-thick paraffin sections from cervical ganglia of rats with or without spinal injections of colchicine and from one monkey not treated with colchicine. Neurons containing more than one antigen could be identified on adjacent sections tested with the three different antisera. Neurons labeled by the Glu-antiserum represent 15-30% of the DRG population in untreated rats. They include most of the small neurons (with mean perikaryal area around 300-400 microns) but also larger neurons (with perikaryal area greater than 600 microns). DRG neurons labeled by either the GLN or the SP antiserum are small (mean area 335-375 microns and 356-374 microns, respectively) and account for approximately 40 and 15%, respectively, of the sampled neurons. In colchicine-treated rats the number of Glu-positive neurons increases up to about 70%. The same treatment also increases the number of SP-positive neurons but not that of GLN-positive neurons. In the monkey about half of the DRG neurons are Glu positive and, as in rats, they are mostly small. GLN-positive neurons in the same species account for about half of the DRG population and are only small. In rats, about 60-80% of Glu-positive neurons are also GLN-positive and most GLN-positive neurons are Glu positive. In colchicine-treated rats, close to 90% of SP-positive neurons are also positive for Glu and about 60% of SP-positive neurons are triple labeled. In the monkey's DRGs, whose sections were not processed for SP, most Glu- or GLN-positive neurons are also positive for the other antiserum used. Several considerations argue against the possibility that, under the present experimental conditions, the Glu antiserum is a metabolic marker. It is therefore suggested that Glu-positive neurons may use Glu as neurotransmitter. Coexistence of Glu and SP in some DRG neurons suggests that both agents may be released by terminals of primary afferents from the same DRG neuron.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Glutamate and substance P coexist in primary afferent terminals in the superficial laminae of spinal cord.

By light microscopic immunocytochemistry it has been previously shown that approximately equal to 70% of the neurons in rat dorsal root ganglia are labeled with an antiserum for glutamate conjugated to hemocyanin; the smaller among these neurons are also positive for substance P. By using a postembedding ImmunoGold method and electron microscopy, it is shown here that synaptic terminals in the superficial laminae of the spinal cord of rats selectively stain for the same glutamate antiserum. Immunolabeling is in small dome-shaped and in large scalloped synaptic terminals. Scalloped terminals are of two types. One type consists of dark terminals with many agranular vesicles of different size and a few large granular vesicles; these are probably endings of unmyelinated and small myelinated primary afferent fibers. The other type consists of light terminals with small agranular vesicles homogeneous in size with neurofilaments and many mitochondria; these are probably endings of larger myelinated primary afferent fibers. By means of double-labeling electron microscopic immunocytochemistry with colloidal gold particles of two different sizes, it is also shown here that substance P is present in only the dark type of glutamate-labeled scalloped terminals. The primary afferent origin of the terminals labeled by the antisera for glutamate and for substance P is demonstrated by a triple-labeling strategy: immunocytochemistry for both antisera on sections from rats in which dorsal rhizotomy or dorsal root ganglion injection of horseradish peroxidase conjugated to wheat germ agglutinin was performed. It is proposed that glutamate is the neurotransmitter in primary afferents mediating input from different peripheral receptor classes, including nociceptors. Effects of glutamate and substance P on spinal dorsal horn neurons may result from co-release of these two mediators from the same dorsal root afferent terminal.

Animals↗

PubMed1988

Characterization of antisera to glutamate and aspartate.

Antisera were raised in rabbits against glutamate (Glu) and aspartate (Asp) conjugated to the invertebrate carrier protein hemocyanin (HC) with glutaraldehyde (GA). The antisera were characterized by testing their immunocytochemical staining properties on sections cut at the level of the ventral cochlear nucleus (VCN) from fixed brains of normal rats after absorption with conjugates of compounds structurally similar and biologically relevant to Glu and Asp. Optimal staining with Glu antiserum was obtained at a dilution of 1:10,000 and was completely blocked by 303 micrograms/ml of the Glu-HC conjugate. No crossreactivity with any of 11 compounds tested was observed. Optimal staining with the Asp antiserum was obtained at 1:8000 dilution and was completely blocked by 225 micrograms/ml of the Asp-HC conjugate. Of 10 compounds tested for crossreactivity, only L-asparagine demonstrated a measurable (about 10%) crossreactivity with the Asp antiserum. The specificity of the two antisera was also tested by immunoblot analysis against 11 compounds conjugated to HC with GA. Listed in order of staining intensity, from greatest to least, conjugates that reacted with the Glu antiserum were Glu greater than Gly-Glu greater than Asp-Glu = Asp greater than N-carbamyl (NC)-Glu greater than Asn = Gln = GABA. Conjugates that reacted with the Asp antiserum, in order of decreasing staining intensity, were Asp greater than Glu-Asp = Asn greater than Gly-Asp greater than Glu. No other compounds tested for crossreactivity reacted with the two antisera in the immunoblot analysis. Glu-like immunoreactivity in rat dorsal root ganglia and somatosensory cortex, and the comparative distribution of Glu- and Asp-like immunoreactivities in the latter tissue, are presented as examples of staining patterns obtained with the two antisera.

Animals↗

PubMed1987

A cuneocochlear pathway in the rat.

Following injections of wheat germ agglutinin-conjugated horseradish peroxidase into the cuneate nucleus of anesthetized rats, retrograde and anterograde label was observed in the cochlear nucleus. Labeled cochlear neurons were found mostly in the ipsilateral dorsal cochlear nucleus and in the contralateral ventral cochlear nucleus. Anterograde label was found primarily ipsilateral to the injection site, and was restricted mainly to the dorsal cochlear nucleus, although label was also observed in the anteroventral cochlear nucleus. Horseradish peroxidase injections were made in the dorsal cochlear nucleus to investigate the source of this pathway. Retrogradely labeled cells in the region of the dorsal column nuclei were located mainly in a shell on the dorsal edge of the cuneate nucleus extending into the white matter of the cuneate fasciculus. The cuneocochlear pathway could provide a direct link between the auditory and somatosensory systems; connections between these two sensory systems may be explained on phylogenetic grounds.

Animals↗

PubMed1987

SII-projecting neurons in the rat thalamus: a single- and double-retrograde-tracing study.

Experiments were performed on adult albino rats, using single-labeling (free horseradish peroxidase [HRP] or wheatgerm agglutinin conjugated to HRP [WGA:HRP]) and double-labeling (fluorescent dyes) techniques to investigate the thalamic projections to the secondary somatosensory cortex (SII) and to demonstrate the presence and location of thalamic neurons projecting to both the primary somatosensory cortex (SI) and SII by way of branching axons. In single-labeling experiments, the tracer was injected in SI or SII with or without electrophysiological control; in double-labeling experiments, fast blue and diamidino yellow were injected into the electrophysiologically identified forelimb areas of SI and SII. Single-tracer experiments showed that after injections in SI, focused in the forelimb representation area, retrogradely labeled neurons were present mainly in the ventral third of the nucleus ventralis posterolateralis (VPL) and in the anterior part of the posterior nuclear complex (PO); labeled neurons were also present consistently in the caudal portion of PO. Injection of tracers in the forelimb or forelimb and hindlimb representation areas of SII resulted in labeling of neurons in the posterior part of PO and in the caudal part of VPL. Double-labeling experiments confirmed the distribution of neurons projecting to SI or to SII, as observed in single-labeling experiments. Some neurons labeled with both tracers were also present. These neurons are interpreted as projecting to both SI and SII by means of axon collaterals and were observed in areas of overlap of the two single-labeled population of neurons--that is, at the border between PO and the ventroposterior complex, and in the medial part of caudal PO. Comparison of these data with those obtained after injections of tracers in SI and SII of cats (Spreafico et al., 1981b) suggests that in both species thalamic neurons projecting to these two areas are largely segregated, though partially overlapping; and that thalamic neurons projecting simultaneously to SI and SII, modest in number in cats, are even sparser in rats.

Afferent Pathways↗

PubMed1987

Glutamate-positive neurons in the somatic sensory cortex of rats and monkeys.

The morphology and laminar distribution of neurons labeled with an antiserum prepared against glutamic acid (Glu) conjugated to keyhole limpet hemocyanin have been studied in the somatic sensory cortex of rats and monkeys. In both species, the vast majority of immunostained neurons are pyramidal; some nonpyramidal neurons are also present. Positive neurons are observed in all cortical layers, although variations are found in the percentage of Glu-positive neurons in the different layers. In rats they are most numerous in layer V (36%), followed by layer II (33%), layer III (32%), and layer VI (29%). In layer IV, 13% of all neurons are positive. Immunoreactive neurons are very sparse in layer I. In monkeys, Glu-positive neurons represent 51% of all neurons in layer V, 49% in layer III, 40% in layers II and VI, and 19% in layer IV. No differences are evident in the laminar distribution of Glu-positive neurons among cytoarchitectonic areas 3a, 3b, 1, and 2. As in rats, Glu-positive neurons are very sparse in layer I. Since Glu and GABA metabolisms are closely related, double-labeling experiments were performed in which thin, adjacent paraffin sections were stained alternately with the anti-Glu serum and with an anti-GABA serum. The 2 populations are almost completely segregated, even though a small fraction of neurons (less than 5%) are labeled by the antisera against both antigens.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Corticospinal neurons with branching axons to the dorsal column nuclei in the monkey.

Previous work in cats has shown that cells of origin of the corticospinal tract give rise to collateral branches to the dorsal column nuclei (DCN). The present experiments were performed in monkeys (Macaca fascicularis) in which 2% fast blue and 2% diamidino yellow were delivered to infiltrate the dorsolateral funiculus at levels between C2 and C6 and the cuneate nucleus on the same side. Retrograde labelling in the cortex allows simultaneous visualization of three classes of neurons: corticospinal tract (CST) neurons, corticocuneate tract (CCT) neurons, and double-labelled neurons. The morphological features and distribution of CST and CCT neurons are similar to those previously reported from investigations based mainly upon the retrograde transport of horseradish peroxidase (HRP). CST neurons occur in layer V in the pre- and postcentral gyri, except for the lateral part (face representation), in the supplementary motor and sensory cortex, and in SII. CCT neurons are present in layer V largely in the postcentral gyrus and in SII. Double-labelled neurons are present wherever CST and CCT neurons are found. Reconstruction and quantitative data from the pericentral cortex show that up to 60% of CCT neurons are double-labelled and are found predominantly in areas 1 and 2, and that their perikarya are in the size range of the larger CCT neurons. Comparison of these results with those obtained previously in cats by using HRP and tritiated, enzymatically inactive HRP (3H-apo-HRP, Rustioni and Hayes: Exp. Brain Res. 43:237-245, 1981) suggests that CST neurons with branching axons to the DCN are considerably more numerous in monkeys than in cats. To determine whether this difference is caused by the different tracers used in the two species. 2% fast blue and 2% diamidino yellow were delivered in cats to infiltrate the dorsolateral funiculus at C2-C3 and the cuneate nucleus on the same side. The results in these cats are remarkably similar to those obtained in the previous study, which used HRP and 3H-apo-HRP: double-labelled neurons occur predominantly in area 3a and constitute 14-16% of the CCT neurons in the pericruciate area. The results bear upon mechanisms of descending control and tuning of performances that characterize the dorsal column-medial lemniscal system, e.g., discrimination of discrete spatiotemporal cues. The species differences may be related to the higher degree of tactile resolution and synchronous control of sensory inflow at the DCN and spinal cord in monkeys relative to cats.

Afferent Pathways↗

PubMed1986

GABAergic neurons are present in the dorsal column nuclei but not in the ventroposterior complex of rats.

Neurons containing glutamatic acid decarboxylase (GAD) are known to exist in the spinal dorsal horn, dorsal column nuclei (DCN), n. ventralis posterior (VP), and somatosensory cortex of cats. Recent work suggested that species differences exist concerning the presence and/or density of GAD-positive neurons in VP. The present experiments demonstrate that, in contrast with carnivores and primates, the rat's VP contains virtually no GAD-positive neurons and that virtually all neurons in it project to the cortex. This conclusion is supported by the failure to find, in Golgi-impregnated material, neurons with characteristics commonly attributed to Golgi type II neurons in VP of cats. The lack of GAD-positive neurons in VP of rats contrasts also with the presence of such neurons in the DCN in the same species. As in cats, about one third of the neurons in the cuneate n. are GAD-positive; these have mostly small perikarya and they are present throughout the nucleus. It is likely that these are intrinsic neurons, i.e. non-projecting beyond the limits of the DCN since a comparable percentage of neurons are unlabeled by simultaneous injections of horseradish peroxidase in multiple targets of the DCN. Like GAD-positive neurons, neurons unlabeled by the retrograde transport of HRP have, for the most part, small perikarya. It is possible that inhibitory mechanisms necessary for basic transfer functions in VP of rats are sustained through projections to this nucleus from the n. reticularis thalami. Extrinsic source of GABAergic input to the DCN seem to be absent or very weak. From this and previous evidence it may be proposed that intrinsic inhibitory interneurons have gradually developed in VP of rabbits, carnivores, and primates in parallel with more elaborate levels of thalamic integration of somatosensation.

Animals↗