Medial Part Of Laminae Research Articles

DISTRIBUTION OF PARVALBUMIN-EXPRESSING NEURONAL POPULATIONS IN THE CAT CERVICAL AND LUMBAR SPINAL CORD GRAY MATTER

Parvalbumin is a classical marker of interneuronal populations in the central nervous system. Analyzing the cervical and lumbar spinal cord segments of cats (Felis catus), both individual cells and entire populations of neurons expressing parvalbumin were identified in most of the gray matter laminae. These populations have strict laminar and nuclear localization. Numerous neuronal clusters are located in the medial part of lamina V–VI and in laminae VII of cervical and lumbar enlargements. We believe that the first one located in segments C4–C8 and L4–L7 may participate in the modulatory mechanisms of locomotor activity via the convergence of cutaneous and proprioceptive afferentation from the limbs. Neuronal populations in lamina VII consist of Ia interneurons and Renshaw interneurons that participate in the motoneuron inhibition. Less numerous populations of parvalbumin-immunopositive cells found in laminae III possibly participated in the regulation of cutaneous sensitivity. Another population located in lamina VIII possibly forms commissural and propriospinal connections and participates in modulating the activity of motoneurons. Immunopositive interneurons also revealed in the precerebellar nuclei: central cervical nucleus and Clarke’s nucleus; unlike the general population of these nuclei, neurons revealed are interneurons. Scarce immunopositive cells are found in lamina I of L6–L7 segments, as well as in laminae II, IV, and X of all segments investigated.

Possible Role of the Myelinated Neural Network in the Parietal Peritoneum in Rats as a Mechanoreceptor.

A network of myelinated nerve fibers in the peritoneum covers the abdominal wall. We studied the topographic distribution of this network, explored the fibers' destination in the central nervous system, and examined the markers in these fibers in order to identify the nature of the sensation conveyed by the network of nerve fibers in rats. We used Sihler's method, which stains myelinated fibers in whole mount materials, and observed a dense nerve network and endings toward the peritoneal cavity in the peritoneum that covers the abdomen's lateral bulge. We studied the axonal transport of cholera toxin subunit B to investigate the central projections of this network in order to identify its function. After applying the tracer in the peritoneum, we observed many labeled terminals in the medial part of laminae 3-5 of the spinal cord. A small number of labeled terminals was observed in the dorsal nucleus of Clarke and gracile nucleus. Labeled somata were observed in the dorsal root ganglia (DRG). Most (96%) were larger than 35 μm. We performed immunohistochemistry of the abdominal wall, using antiserum against the 200-kD neurofilament (a marker for mechanosensory neurons). We observed many positive nerve fibers in the peritoneum. Because cell bodies in the DRG were large, their nerve terminals ended in the base of the dorsal horn, which is known to transmit proprioceptive information, and the network possesses the marker for mechanosensitive fibers; therefore, it appears that the myelinated nerve network conveys information about distension and/or contraction of the abdominal wall. Anat Rec, 300:1662-1669, 2017. © 2017 Wiley Periodicals, Inc.

Neuroanatomical Basis for Acupuncture Point Pc8 in the Rat: Neural Tracing Study with Cholera Toxin Subunit B

This study was performed to investigate the innervations related to acupuncture point PC8 in rats using a neural tracing technique. After 6 μL of 1% cholera toxin subunit B (CTB) was injected into the site between the second and third metacarpal bone in rats, a corresponding site to acupuncture point PC8 in the human body, CTB labelling was examined with immunofluorescence and immunohistochemistry in the dorsal root ganglia (DRG), spinal cord and brainstem. All CTB labelling appeared on the ipsilateral side of the injection. The labelled sensory neurons distributed from cervical (C)6 to thoracic (T)1 DRG, while the labelled motor neurons were located on the dorsolateral part of the spinal ventral horn ranging from the C6 to T1 segments. In addition, the transganglionically-labelled axonal terminals were found to be dense in the medial part of laminae 3-4 from C6 to the T1 spinal dorsal horn, as far as in the cuneate nucleus. These results indicate that sensory and motor neurons associated with PC8 distribute in a distinct segmental pattern. The sensory information from PC8 could be transganglionically transported to the spinal dorsal horn and cuneate nucleus.

Projections from the insular cortex to pain-receptive trigeminal caudal subnucleus (medullary dorsal horn) and other lower brainstem areas in rats

This study examined the projections from the rat insular cortex (Ins) to lower brainstem areas which are possibly involved in orofacial pain processing. We first examined distributions of Ins neurons projecting directly to the trigeminal caudal subnucleus (Vc, medullary dorsal horn) and oral subnucleus (Vo) which are known to receive orofacial nociceptive inputs. After injections of a retrograde tracer, Fluorogold (FG), into the medial part and lateral part of laminae I/II of Vc, many neurons were labeled bilaterally with a contralateral predominance in the rostral level of granular Ins (GI) and dysgranular Ins (DI) and the caudal level of GI/DI, respectively, but none in the agranular Ins (AI). After FG injections into laminae III–V of Vc, no Ins neurons were labeled. After FG injections into the Vo, many neurons were labeled bilaterally with a contralateral predominance in the rostral and caudal GI/DI, but none in the AI. We then examined descending projections from the GI/DI to the lower brainstem. After injections of an anterograde tracer, biotinylated dextranamine (BDA), into the rostral GI/DI, many BDA-labeled axons and terminals were seen bilaterally with a contralateral predominance in the medial part of laminae I/II of Vc, dorsomedial Vo, juxtatrigeminal region, rostral ventromedial medulla (RVM), and nucleus of the solitary tract, and with an ipsilateral predominance in the parabrachial nucleus (Pb), Kölliker–Fuse nucleus (KF) and trigeminal mesencephalic nucleus. After BDA injections into the caudal GI/DI, they were seen bilaterally with a contralateral predominance in the lateral part of laminae I/II of Vc, ventrolateral Vo, juxtatrigeminal region and RVM, and with an ipsilateral dominance in the lateral zone (PAGl) of periaqueductal gray, Pb and KF. These results suggest that orofacial nociceptive processing of Vc and Vo neurons may be regulated by GI/DI directly or indirectly through brainstem nuclei such as PAGl, Pb, KF and RVM.

Propriospinal pathways in the dorsal horn (laminae I–IV) of the rat lumbar spinal cord

The spinal dorsal horn is regarded as a unit that executes the function of sensory information processing without any significant communication with other regions of the spinal gray matter. Within the spinal dorsal horn, however, the different rostro-caudal and medio-lateral subdivisions intensively communicate with each other through propriospinal pathways. This review gives an overview about these propriospinal systems, and emphasizes that the medial and lateral parts of the spinal dorsal horn show the following distinct features in their propriospinal interconnectivities: (a) A 100-300μm long section of the medial aspects of laminae I-IV projects to and receives afferent fibers from a three segment long compartment of the spinal dorsal gray matter, whereas the same length of the lateral aspects of laminae I-IV projects to and receives afferent fibers from the entire rostro-caudal extent of the lumbar spinal cord. (b) The medial aspects of laminae I-IV project extensively to the lateral areas of the dorsal horn. In contrast to this, the lateral areas of laminae I-IV, with the exception of a few fibers at the segmental level, do not project back to the medial territories. (c) There is a substantial direct commissural connection between the lateral aspects of laminae I-IV on the two sides of the lumbar spinal cord. The medial part of laminae I-IV, however, establishes only a minor commissural propriospinal connection with the gray matter on the opposite side.

Cytoarchitecture of the Spinal Cord of the Postnatal (P4) Mouse

Interpretation of the new wealth of gene expression and molecular mechanisms in the developing mouse spinal cord requires an accurate anatomical base on which data can be mapped. Therefore, we have assembled a spinal cord atlas of the P4 mouse to facilitate direct comparison with the adult specimens and to contribute to studies of the development of the mouse spinal cord. This study presents the anatomy of the spinal cord of the P4 C57Bl/6J mouse using Nissl and acetyl cholinesterase-stained sections. It includes a detailed map of the laminar organization of selected spinal cord segments and a description of named cell groups of the spinal cord such as the central cervical (CeCv), lateral spinal nucleus, lateral cervical, and dorsal nuclei. The motor neuron groups have also been identified according to the muscle groups they are likely to supply. General features of Rexed's laminae of the P4 spinal cord showed similarities to that of the adult (P56). However, certain differences were observed with regard to the extent of laminae and location of certain cell groups, such as the dorsal nucleus having a more dispersed structure and a more ventral and medial position or the CeCv being located in the medial part of lamina 5 in contrast to the adult where it is located in lamina 7. Motor neuron pools appeared to be more tightly packed in the P4 spinal cord. The dorsal horn was relatively larger and there was more white matter in the P56 spinal cord.

P boutons in lamina IX of the rodent spinal cord express high levels of glutamic acid decarboxylase-65 and originate from cells in deep medial dorsal horn.

Presynaptic inhibition of primary muscle spindle (group Ia) afferent terminals in motor nuclei of the spinal cord plays an important role in regulating motor output and is produced by a population of GABAergic axon terminals known as P boutons. Despite extensive investigation, the cells that mediate this control have not yet been identified. In this work, we use immunocytochemistry with confocal microscopy and EM to demonstrate that P boutons can be distinguished from other GABAergic terminals in the ventral horn of rat and mouse spinal cord by their high level of the glutamic acid decarboxylase (GAD) 65 isoform of GAD. By carrying out retrograde labeling from lamina IX in mice that express green fluorescent protein under the control of the GAD65 promoter, we provide evidence that the cells of origin of the P boutons are located in the medial part of laminae V and VI. Our results suggest that P boutons represent the major output of these cells within the ventral horn and are consistent with the view that presynaptic inhibition of proprioceptive afferents is mediated by specific populations of interneurons. They also provide a means of identifying P boutons that will be important in studies of the organization of presynaptic control of Ia afferents.

Propriospinal afferent and efferent connections of the lateral and medial areas of the dorsal horn (laminae I-IV) in the rat lumbar spinal cord.

The different subdivisions along the mediolateral extent of the superficial dorsal horn of the spinal cord are generally regarded as identical structures that execute the function of sensory information processing without any significant communication with other regions of the spinal gray matter. In contrast to this standing, here we endeavor to show that neural assemblies along the mediolateral extent of laminae I-IV cannot be regarded as identical structures. After injecting Phaseolus vulgaris leucoagglutinin and biotinylated dextran amine into various areas of the superficial dorsal horn (laminae I-IV) at the level of the lumbar spinal cord in rats, we have demonstrated that the medial and lateral areas of the superficial dorsal horn show the following distinct features in their propriospinal afferent and efferent connections: 1) A 300- to 400-microm-long section of the medial aspects of laminae I-IV projects to and receives afferent fibers from a three segment long compartment of the spinal dorsal gray matter, whereas the same length of the lateral aspects of laminae I-IV projects to and receives afferent fibers from the entire rostrocaudal extent of the lumbar spinal cord. 2) The medial aspects of laminae I-IV project extensively to the lateral areas of the superficial dorsal horn. In contrast to this, the lateral areas of laminae I-IV, with the exception of a few fibers at the segmental level, do not project back to the medial territories. 3) There is a substantial direct commissural connection between the lateral aspects of laminae I-IV on the two sides of the lumbar spinal cord. The medial part of laminae I-IV, however, does not establish any direct connection with the gray matter on the opposite side. 4) The lateral aspects of laminae I-IV appear to be the primary source of fibers projecting to the ipsi- and contralateral ventral horns and supraspinal brain centers. Projecting fibers arise from the medial subdivision of laminae I-IV in a substantially lower number. The findings indicate that the medial and lateral areas of the superficial spinal dorsal horn of rats may play different roles in sensory information processing.

Localization and controls of aromatase in the quail spinal cord.

In adult male and female Japanese quail, aromatase-immunoreactive cells were identified in the spinal dorsal horns from the upper cervical segments to the lower caudal area. These immunoreactive cells are located mostly in laminae I-III, with additional sparse cells being present in the medial part of lamina V and, at the cervical level exclusively, in lamina X around the central canal. Radioenzyme assays based on the measurement of tritiated water release confirmed the presence of substantial levels of aromatase activity throughout the rostrocaudal extent of the spinal cord. Contrary to what is observed in the brain, this enzyme activity and the number of aromatase-immunoreactive cells in five representative segments of the spinal cord are not different in sexually mature males or females and are not influenced in males by castration with or without testosterone treatment. The aromatase activity and the numbers of aromatase-immunoreactive cells per section are higher at the brachial and thoracic levels than in the cervical and lumbar segments. These experiments demonstrate for the first time the presence of local estrogen production in the spinal cord of a higher vertebrate. This production was localized in the sensory fields of the dorsal horn, where estrogen receptors have been identified previously in several avian and mammalian species, suggesting an implication of aromatase in the modulation of sensory (particularly nociceptive) processes.

Neurons lying in the white matter of the upper cervical spinal cord project to the intermediolateral cell column.

Neurons lying in the white matter of the upper cervical spinal cord become transneuronally labelled following pseudorabies virus injections into the kidney or stellate ganglion, suggesting that they project directly to sympathetic preganglionic neurons. In the present study, we extend these findings and report here that i) neurons in both the lateral spinal nucleus and lateral funiculus become transneuronally labelled after pseudorabies virus injections into the superior cervical ganglion, stellate ganglion, celiac ganglion, or adrenal gland and ii) both of these two cell groups project directly to the sympathetic preganglionic neurons as demonstrated with the Phaseolus vulgaris leuco-agglutinin axonal tracing method. In addition, lateral funiculus neurons project to the cervical and upper thoracic dorsal horn (lamina V), intermediate gray matter (laminae VII and X), and ventral horn. The lateral spinal nucleus also projects to the medial part of laminae I and II, V, VII. To verify that pseudorabies virus-infected lateral funiculus and lateral spinal nucleus cells have a neuronal phenotype, we demonstrated that these cells also can be immunostained with antibodies directed against a neuron specific marker, neuronal nuclear protein called NeuN, but not with antibodies against glial acidic fibrillary protein or oligodendroglia. In summary, this report provides the first evidence that two descending sympathetic projection systems arise from neurons lying within the white matter of the cervical spinal cord.

Neuronal expression of Fos-like protein along the afferent pathway of the milk-ejection reflex in the sheep

This study was designed to reveal the relay stations of the afferent branch of the milk-ejection reflex in the sheep, by examining the effect of nipple stimulation on the expression of Fos protein along the spino-hypothalamic axis. Immunocytochemical detection of Fos protein after manual nipple stimulation in nonlactating ewes revealed intmunolabeled neurons located exclusively ipsilaterally in the 3rd and4th lumbar spinal ganglia, the medial part of laminae I–III of the 3rd and 4th lumbar spinal segments, the lateral cervical nucleus, the dorsal column nuclei, and bilaterally in the hypothalamic paraventricular nucleus. These findings selectively demonstrate for the first time those cell groups mediating the neuroendocrine effects of nipple stimulation.

Peripheral nerve stimulation increases fos immunoreactivity without affecting type II Ca2+/calmodulin-dependent protein kinase, glutamic acid decarboxylase, or GABAA receptor gene expression in cat spinal cord

Expression patterns of the immediate early gene c-fos and of other genes including those for the alpha-subunit of type II Ca2+/calmodulin-dependent protein kinase (CaMKII alpha), 67-kDa glutamic acid decarboxylase (GAD), and the alpha 1-, beta 2-, and gamma 2-subunits of the GABAA receptor were described in the spinal cord of normal cats and following peripheral nerve stimulation. As revealed by in situ hybridization histochemistry, CaMKII alpha messenger RNA (mRNA) is normally distributed only in cells of Rexed's laminae I-IV, whereas GAD mRNA is expressed by subpopulations of cells in all laminae, with the heaviest hybridization signal found in laminae I-III and medial parts of laminae V and VI. The three GABAA receptor subunits have varying expression patterns in the laminae. All of them are expressed by many cells located in the base of the dorsal horn and the intermediate zone, but only the gamma 2-subunit is intensely expressed by motoneurons. Single-pulse, electrical stimulation of the sciatic or median and ulnar nerve of anesthetized cats at a pulse rate of 1/s for 6-8 h failed to induce observable changes in gene expression for CaMKII alpha, GAD, or for the three subunits of the GABAA receptor; although immunoreactivity for the protein products of c-fos (or c-fos-related genes) was markedly upregulated in some neurons of the dorsal horn and the intermediate zone. Therefore, under the present experimental conditions, upregulation of the immediate early gene c-fos (or c-fos-related genes) is not associated with changes in expression of late-effector genes potentially involved in central nervous system plasticity.

Walking evokes a distinctive pattern of Fos-like immunoreactivity in the caudal brainstem and spinal cord of the rat

We have evaluated the pattern of c-fos expression induced in the rat spinal cord, caudal brainstem and cerebellum by a behavior that is associated with non-noxious inputs transmitted over large-diameter primary afferent fibers, namely walking for 1 h on a rotating rod. Walking on the rotating rod induced a large increase in the number of Fos-like immunoreactive neurons in regions of the cervical and lumbar spinal cord gray matter that contain neurons that respond to non-noxious stimuli: the inner part of the substantia gelatinosa (lamina IIi), the nucleus proprius and the medial parts of laminae V and VI. We also observed considerable labeling in lamina VII and in ventral horn motoneurons. We did not record an increased number of Fos-like immunoreactive neurons in lamina I, in the outer substantia gelatinosa (lamina IIo), or in the lateral, reticulated portion of lamina V, regions that contain neurons predominantly responsive to noxious stimulation. Unilateral sensory deafferentation of the forelimb, by multiple dorsal rhizotomies, significantly decreased the number of Fos-like immunoreactive neurons in the ipsilateral spinal cord, suggesting that afferent input contributed to the walking-induced pattern of labeling. In rats that walked on the Rota-Rod, we also recorded increased labeling in the dorsal column nuclei. Unilateral cervical deafferentation reduced the labeling in the cuneate nucleus; this reduction was paralleled by decreased cytochrome oxidase activity. Finally, we found that there was a significant increase in the number of Fos-like immunoreactive neurons in the cerebellum of rats that walked on the Rota-Rod. Northern blot analysis revealed that the increase in Fos-like immunoreactivity was associated with an increase in c-fos messenger RNA. The pattern of labeling observed in the rats that walked on the Rota-Rod was distinct from that observed when rats are exposed to a noxious stimulus [Presley et al. (1990) J. Neurosci. 10, 323–335]. This result reinforces the conclusion that by monitoring the evoked expression of the c-fos proto-oncogene, it is possible to identify unique populations of neurons that are specifically related to the modality of the stimulus or to behaviour occurring during the stimulus presentation.

Spinal distribution of extracellular field potentials generated by electrical stimulation of pudendal and perineal afferents in the cat.

Electrical stimulation of sensory pudendal and superficial perineal nerves evokes focal synaptic potentials produced by activation of spinal neurons in the lumbosacral gray matter in chloralose anesthetized or decerebrate cats. The field potentials evoked by sensory pudendal nerve stimulation were located in medial parts of laminae V and VI, and lamina X in the S1 to S3 spinal segments. The superficial perineal cutaneous field potentials partially overlapped with those produced by the pudendal nerve, but in general were localized more laterally in laminae V and VI. The central latencies of the earliest portion of the field potentials evoked by either sensory pudendal or superficial perineal nerves were less than 0.9 ms suggesting that monosynaptic activation of neurons contributed to the potentials.

Immunohistochemical study of tyrosine-hydroxylase-positive cells and fibers in the chicken spinal cord

Tyrosine hydroxylase (TH)-positive cells and fibers were examined by immunohistochemistry in the chick spinal cord. TH-positive cells, which were located in laminae I, V and X, were most frequently found in the rostral part of the cervical spinal cord, with fewer cells being found in more caudal levels of the spinal cord. TH-positive cells located in lamina X, which were bipolar in shape, were mainly found in regions lateral as well as just ventral to the central canal. They had processes reaching to the central canal. The terminals of these cerebrospinal-fluid-contacting cells were oval in shape, and were most frequently found at the ventral wall of the central canal. There were dense clusters of TH-positive fibers in lamina X. A meshwork-like structure of TH-positive fibers was found over the lateral wall of the central canal. A high density of TH-positive fibers was also found in the medial part of laminae V–VII. In lamina IX, small numbers of TH-positive fibers were observed in the lateral motor column of the brachial spinal cord, and in the medial and lateral motor columns of the lumbosacral spinal cord. However, within the medial motor column of the brachial spinal cord TH-positive fibers were densely distributed around somal as well as dendritic profiles. Similar to our previous observations on serotoninergic fibers, TH-positive fibers were also differentially distributed in the ventral horn of the chicken spinal cord: a high density of TH-positive fibers was localized to specific regions of the spinal motor nucleus.

Propriospinal neurons with ascending collaterals to the dorsal medulla, the thalamus and the tectum: a retrograde fluorescent double-labeling study of the cervical cord of the rat

Branching neurons with descending propriospinal collaterals and ascending collaterals to the dorsal medulla, the thalamus and the tectum were studied in the rat's cervical spinal cord (C1-C8), using the retrograde fluorescent double-labeling technique: Diamidino Yellow Dihydrochloride (DY) was injected in the cord at T2, True Blue (TB) was injected in the brain stem. DY-labeled descending propriospinal neurons were present in all laminae, except lamina IX. They were concentrated in lamina I, laminae IV to VIII, and in the lateral spinal nucleus, LSN. TB-labeled neurons projecting to the dorsal medulla were concentrated in lamina IV and the medial parts of laminae V and VI (probably representing postsynaptic dorsal column--PSDC--neurons), but were also present in lamina I, the LSN, the lateral dorsal horn, and in laminae VII and VIII. DY-TB double-labeled neurons giving rise to both a descending propriospinal collateral and an ascending collateral to the dorsal medulla were intermingled with the TB single-labeled neurons. About 4% of the descending propriospinal neurons gave rise to an ascending collateral to the dorsal column nuclei; these double-labeled cells constitute a sizable fraction (10%) of the PSDC neurons. TB-labeled spinothalamic and spinotectal neurons were located in lamina I, the lateral cervical nucleus (LCN), and LSN, the lateral lamina V, lamina VII and VIII, lamina X and in the spinal extensions of the dorsal column nuclei, predominantly contralateral to the TB injections. DY-TB double-labeled neurons were present throughout C1-C8 in the LSN, lateral lamina V, lamina VIII, ventromedial lamina VII, and lamina X. Only very few were observed in lamina I and the LCN, and none in the spinal extensions of the dorsal column nuclei. The double-labeled neurons constituted only a minor fraction of all labeled neurons; 3-5% of the spinothalamic neurons and about 1-7% of the spinotectal neurons were double-labeled. Conversely, only about 1% of the labeled descending propriospinal neurons gave rise to an ascending spinothalamic collateral, and even fewer (0.1 to 0.6%) to a collateral to the dorsal midbrain. The LSN displayed the highest relative content of branching neurons. Up to 20% of its ascending spinothalamic and spinotectal neurons and up to 8% of its descending propriospinal neurons were found to be branching neurons, indicating that the LSN constitutes an unique cell-group in the rat spinal cord.

Cytoplasmic laminated bodies in the lateral geniculate nucleus of normal and dark reared cats

AbstractThe postnatal development of cytoplasmic laminated bodies in lamina A cells of the lateral geniculate nucleus in normal and dark reared cats has been studied quantitatively with light microscopy. In the normal cat laminated bodies develop between the sixth and eighth postnatal week and increase steadily in number thereafter. These inclusion bodies are found chiefly in medium size cells and are distributed more densely in the medial part of lamina A than laterally. Laminated bodies appear not to be a general feature of the visual pathways since they are not found in cells of the visual cortex, superior colliculus, or ventral lateral geniculate. In the dark reared cat laminated bodies develop at about the same time as in the normal animal, but approximately twice as many of them are seen at all ages investigated.Our experiments indicate that dark rearing does not cause a proliferation of multiple laminated bodies within single neurons, but rather induces the formation of a laminated body in cells that normally would not acquire one. This effect appears to be permanent since it is not reversed by long term dark rearing nor by periods of normal visual experience following deprivation.Physiological experiments (Sherman et al., '72) have shown that fewer Y‐cells are recorded in binocularly deprived cats than in normally reared animals. On the basis of the present results, it is suggested that dark rearing influences the functional specificity of developing lateral geniculate neurons. In this view, deprivation prevents normal numbers of Y‐cells from developing. Neurons which would have become Y‐cells develop instead as X‐cells; a change in functional organization which is associated structurally with an increase in the number of cells that contain cytoplasmic laminated bodies.

Connections of the corticospinal and rubrospinal tracts with neurons of the cervical spinal cord in cats

The distribution of focal potentials over the cross section of the 7th cervical segment of the spinal cord was studied during stimulation of the pyramids, the red nucleus, and a peripheral nerve (ulnar) in adult cats anesthetized with chloralose and Nembutal. The earliest focal potentials in the fasciculus dorsolateralis were recorded 1.4–1.5 msec after stimulation of the pyramids and 0.8–0.9 msec after stimulation of the red nucleus. These times correspond to maximal condution velocities of 56–68 and 105–124 m/sec respectively. The earliest post-synaptic activity in response to pyramidal stimulation was found in the lateral areas of laminae V and VI, and in response to stimulation of the red nucleus in laminae VI and VII in Rexed's classification. The pyramidal wave also evoked considerable postsynaptic activity in medial areas of the dorsal horn. In response to stimulation of peripheral afferents activity was evoked in neurons in the central and medial parts of laminae V and VI. It is postulated on the basis of these results that corticospinal and rubrospinal fibers may be connected monosynaptically with specialized interneurons, free from peripheral influences, in the lateral areas of laminae V and VII respectively; in the lateral part of lamina VI convergence of both types of influences on the same cells is possible. Interaction between descending and afferent influences possibly takes place on more medially located neurons.

Projections of the visual cortex to the lateral geniculate and posterior thalamic nuclei in the cat.

AbstractFiber degeneration in the cat following lesions of various parts of areas 17, 18 and 19 was traced to the lateral geniculate and posterior thalamic nuclei by the method of Nauta and Gygax. Area 17 lying in the lateral and posterolateral gyri projects to the most medial parts of laminae A, A1 and central interlaminar nucleus (NIC). Area 17 in the suprasplenial gyrus sends fibers to the medial and middle parts of laminae A and A1 and the underlying part of NIC, while that in the splenial gyrus gives off fibers to the dorsolateral and ventrolateral parts of laminae A, A1 and NIC. These data indicate that there is a mediolateral organization in the projection from area 17 to the dorsal lateral geniculate nucleus. A topical organization exists also in the anteroposterior direction; the anterior, middle and posterior parts of area 17 project to the corresponding portion of the dorsal nucleus. Area 18 gives rise to fibers that pass between the medial interlaminar nucleus (NIM) and lamina A1 into the dorsolateral part of NIM, the medial part of NIC and the medial ends of laminae A and A1. The projections of area 18 to the dorsal nucleus are also organized in the anteroposterior dimension. Area 19 sends fibers to the major part of NIM, except to its most ventral and dorsolateral parts, and to the medialmost parts of NIC and lamina B. The majority of these fibers run along the medial aspect of NIM, but a few fibers pass ventrolaterally between NIM and lamina A1. It should be mentioned that NIM receives fibers not only from area 19 in the lateral and the posterior suprasylvian gyri, but also from area 19 in the medial cortex. As with areas 17 and 18, the corticogeniculate projections of area 19 are organized in an anteroposterior dimension.The ventral lateral geniculate nucleus also receives fibers from areas 17 and 19. The anterior part of area 17 projects only very few fibers to the ventral nucleus, but the posterior part gives off many fibers to the external layer of the nucleus. Area 17 fibers from the posterolateral gyrus are distributed in the dorso‐medial part of the external layer and those from the suprasplenial gyrus enter the ventral and medial portion of the layer. In contrast most of area 18 and that part of area 19 in the lateral gyrus project no fibers to the ventral nucleus. The other parts of area 19 give off fibers to the internal layer and the adjoining portion of the external layer of the ventral nucleus. There appears to be an anteroposterior organization of the projection of the visual cortex on the ventral nucleus. The posterior thalamic nucleus receives fibers from areas 18 and 19 and part of area 17. Area 18 sends fibers to the medial and ventromedial part of the posterior nucleus, while most of area 19 projects fibers to the dorsal and middle part of the nucleus. Area 17 lying in the upper portion of the posterolateral gyrus and the suprasplenial and splenial gyri projects to the dorsomedial and medial part of the posterior nucleus.