Postnatal maturation in the cochlea of the cat

At birth, the cochlea of the cat, though generally developed, is still immature. Maturation of the organ of Corti begins at the base and gradually reaches the apex. In two weeks the process is complete. The most significant morphological criteria of the epithelial maturation are the formation of the tunnel of Corti and of the space of Nuel, the lengthening of the outer hair cells and the freeing of the internal spiral sulcus. On the third day after birth, the appearance of these criteria at the level of the first coil of the lamina spiralis coincides with the general physiological awakening of the auditory systems, as testified by the recording of evoked potentials from the cerebral cortex. Since such responses can be provoked by electrical stimulation of the nerve from birth onwards, the maturation of the organ of Corti appears to be the final stage in the development of the auditory system.     

The callosal connexions of the primary somatic sensory cortex in the monkey

The callosal connexions of the primary somatic sensory cortex, SI, of the monkey have been studied with axonal degeneration methods after the placement of lesions of varying size in the cortex of one hemisphere and after section of the corpus callosum. For the correlation of the distribution of the degeneration with the cytoarchitectonic subdivisions of SI and with their boundaries, planar reconstructions of the extents of the subdivisions and of area 5 were made. The extent of area 5 is surprisingly large, being about the same as SI, and area 3a can be recognized as a distinct subdivision along the entire medio-lateral extent of SI. The callosal fibres end in narrow, irregular bands aligned in the medio-lateral dimension and there are accentuations at the boundaries of the cytoarchitectural subdivisions. In the representations of the trunk and face, the bands of degeneration are present across the entire antero-posterior extent of SI and with increases at the boundaries, while in the limb regions the degeneration becomes restricted to the boundaries. It is suggested that the callosal connexions of the somatic sensory cortex, like those in the visual and auditory areas, are connecting those parts of the cortex in the two hemispheres that are concurrently activated by a peripheral stimulus. The parts of SI that are devoid of callosal connexions are related to the distal limbs. The callosal connexions are homo- and heterotopical; an architectonic subdivision within the callosally connected regions projects to the same and other architectonic subdivisions at the same medio-lateral level in the opposite hemisphere; the cortex containing the representation of the caudal trunk near the post-central dimple is connected with the same region in the other hemisphere and with that of the separate representation of the caudal trunk in the posterior part of the cingulate sulcus, while the representation of the occipital region at the post-central dimple is connected both with the homotopical site in the other hemisphere and with the other representation of this part of the periphery at the level of the lower end of the intraparietal sulcus.     

Representation of the cecum in the lateral dorsal motor nucleus of the vagus nerve and commissural subnucleus of the nucleus tractus solitarii in rat.

Motor fibers of the accessory celiac and celiac vagal branches are derived from the lateral columns of the dorsal motor nucleus of the vagus nerve. These branches also contain sensory fibers that terminate within the nucleus of the tractus solitarii. This study traces the innervation of the intestines by using the tracer cholera toxin-horseradish peroxidase. In 53 rats, the tracer was injected into either the stomach, duodenum, jejunum, terminal ileum, cecum, or ascending colon. With all cecal injections, prominent retrograde labeling of cell bodies occurred bilaterally in the lateral columns of the dorsal motor nucleus of the vagus nerve above, at, and below the level of the area postrema. Dendrites of laterally positioned neurons projected medially and rostrocaudally within the dorsal motor nucleus of the vagus nerve and dorsomedially into both the medial subnucleus and parts of the commissural subnucleus of the nucleus of the tractus solitarii. Sensory terminal labeling occurred in the dorsolateral commissural subnucleus at the level of the rostral area postrema and the medial commissural subnucleus caudal to the area postrema. Additionally, there was sensory terminal labeling within a small confined area of the dorsomedial zone of the nucleus of the tractus solitarii immediately adjacent to the fourth ventricle at a level just anterior to the area postrema. Stomach injections labeled motoneurons of the medial column of the entire rostrocaudal extent of the dorsal motor nucleus of the vagus nerve and a sensory terminal field primarily in the subnucleus gelatinosus, with less intense labeling extending caudally into the medial and ventral commissural subnuclei. Dendrites of gastric motoneurons project rostrocaudally and mediolaterally within the dorsal motor nucleus of the vagus nerve and dorsolaterally within the nucleus of the tractus solitarii. They are most pronounced at the level of the rostral area postrema where many dendrites course dorsolaterally terminating primarily within the subnucleus gelatinosus. Injections of the duodenum labeled a small number of the cells within the medial aspects of the dorsal motor nucleus of the vagus nerve. Jejunal, ileal, and ascending colon injections labeled cells sparsely within the lateral aspects of the dorsal motor nucleus of the vagus nerve bilaterally. No afferent terminal labeling was evident after injection of these areas of the bowel.(ABSTRACT TRUNCATED AT 400 WORDS)     

Projection from the nucleus reuniens thalami to the hippocampal region: light and electron microscopic tracing study in the rat with the anterograde tracer Phaseolus vulgaris-leucoagglutinin

In order to study the morphological substrate of possible thalamic influence on the cells of origin and area of termination of the projection from the entorhinal cortex to the hippocampal formation, we examined the pathways, terminal distribution, and ultrastructure of the innervation of the hippocampal formation and parahippocampal region by the nucleus reuniens of the thalamus (NRT). We employed anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Injections of PHA-L in the NRT produce fiber and terminal labeling in the stratum lacunosum-moleculare of field CA1 of the hippocampus, the molecular layer of the subiculum, layers I and III/IV of the dorsal subdivision of the lateral entorhinal area (DLEA), and layers I and III-VI of the ventral lateral (VLEA) and medial (MEA) divisions of the entorhinal cortex. Terminal labeling is most dense in the stratum lacunosum-moleculare of field CA1, the molecular layer of the ventral part of the subiculum, MEA, and layer I of the perirhinal cortex. In layer I of the caudal part of DLEA and in MEA, terminal labeling is present in clusters. Injections in the rostral half of the NRT produce the same distribution in the hippocampal region as those in the caudal half of the NRT, although the projections from the rostral half of the NRT are much stronger. A topographical organization is present in the projections from the head of the NRT, so that the dorsal part projects predominantly to dorsal parts of field CA1 and the subiculum and to lateral parts of the entorhinal cortex, whereas the ventral part projects in greatest volume to ventral parts of field CA1 and the subiculum and to medial parts of the entorhinal cortex. The distribution of the reuniens fibers coursing in the cingulate bundle was determined by comparing cases with and without transections of this bundle. The fibers carried by the cingulate bundle exclusively innervate field CA1 of the hippocampus, the dorsal part of the subiculum, and the presubiculum and parasubiculum. They participate in the innervation of the ventral part of the subiculum and MEA. Electron microscopy was used to visualize the axon terminals of PHA-L-labeled reuniens fibers. These terminals possess spherical synaptic vesicles and form asymmetric synaptic contacts with dendritic spines or with thin shafts of spinous dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)     

Two distinct strio-nigral substance P pathways in the rat: An experimental immunohistochemical study

Re-examination of the strio-nigral substance P (SP) tract by means of an experimental immunohistochemical method in the rats demonstrated the presence of two distinct pathways from the nucleus caudatus putamen (CP) to the substantia nigra (SN). Destruction of the posterior portion of the CP resulted in the disappearance of SP-positive fibers in the SN pars lateralis but not in the SN pars compacta or reticulata. On the other hand, destruction of the ventrolateral portion of the anterior portion of the CP caused the disappearance of SP-positive fibers in the SN pars compacta and pars reticulata but not in the SN pars lateralis. In addition, destruction of the dorsal portion of the anterior portion of the CP, where 3-6 cell islets of SP-positive cells are located, failed to decrease SP-positive fibers in any of the subdivisions of the SN. These findings strongly suggest that SP-positive neurons in the posterior portion of the CP project to the SN pars lateralis (posterior strio-nigral SP tract), SP-positive cells in the lateroventral part of the anterior portion of the CP extend to the SN pars compacta and pars reticulata, but SP-positive cells in the dorsal part of the anterior portion of the CP do not innervate the SN.     

Pathogenesis of early phase experimental allergic neuritis: DAILY MONITORING OF HUMORAL AND CELLULAR IMMUNE RESPONSE TO PERIPHERAL NERVE ANTIGEN

The role of humoral factors in the mechanism of demyelination has been the object of continuous interest. In the present study the role of the antibodies against a peripheral nerve antigenic protein fraction (PN-APF) was studied in the pathogenesis of experimental allergic neuritis (EAN). Blood samples were taken daily starting on the third day after the inoculation of the rabbits and control animals. The titers of anti-PN-APF antibodies were determined by the ELISA method from each sample. The stimulation response of the lymphocytes in a whole blood microculture to the same antigenic protein was also studied and the results are correlated to each other and to the severity of the clinical signs of the disease. At the time of the manifestation of the disease all of the 11 rabbits had measurable levels of antibodies against PN-APF. The stimulation response of the lymphocytes declined at the same time. However, the level of antibody titers and the rate of lymphocyte stimulation response during observation showed no correlation with the severity of the clinical signs. On the basis of the results obtained it seems probable that the antibodies against myelin antigens and lymphocyte stimulation constitute only two of the factors involved in demyelination in EAN.     

Processus psychopathologique, sentiment et syndrome de vulnérabilité

The aim of this paper is to show the interest of taking into account, in the psychological reflection, the feeling of vulnerability met by a patient at the beginning of the psychopathological process. The authors attempt to specify the diverse modalities of the vulnerability, the nature of the predisposition and of its factors, the differences between the deeply lived feeling and the syndrome, revealed into the identitary weakening itself. They examine the way from the feeling to the syndrome of vulnerability, being like a terrifying waiting of a internal disintegration, from extreme situations, intentional or imposed. The clinical approach of psychical weakness of the elderly people and of the inaugural experiences of the schizophrenia (particularly the case of Suzanne Urban), permits to precise the processual nature of the syndrome of vulnerability. It proposes a new reading of some syndromes of acute psychic disorganization.     

Rearrangements of efferent activity parameters in generators of cyclic motor reactions during electric stimulation of cerebellum inputs and outputs in the cat]

Rearrangements of the activity parameters of scratching and locomotor generators conditioned by electric stimulation of the inferior olive, nucleus reticularis lateralis as well as of the fastigial nucleus and nucleus interpositus of the cerebellum were investigated on decerebrate immobilized animals. Scratching and locomotor generators were characterized by the ability to effectively rearrange the time structure of their activity in response to certain changes in phase and amplitude characteristics of signals arriving both by the mossy and climbing inputs of the cerebellum. The flexor half-centre of the locomotor generator and aiming half-centre of the scratching generator increased both the period and intensity of their activity under influence of signals arriving to the cerebellum from the inferior olive and nucleus reticularis lateralis at the first half of the working phase of these half-centres. Stimulation of the inferior olive and nucleus reticularis lateralis during the second half of the flexor and aiming phases evoked somewhat different changes in correlation of activity for half-centres of the locomotor and scratching generators. A slight shortening of the activity period of the aiming half-centre during scratching and a decrease of the activity period of the extensor half-centre during locomotion were observed. Stimulation of the structures mentioned above during the working phase of half-centres controlling limb extensor movements evoked shortening of the extensor half-centres activity period during locomotion and exerted no effect on the scratching jerk half-centre activity period during scratching. The scratching generator, unlike the locomotor generator is characterized by a significant degree of resemblance of the rearrangement of generator efferent activity parameters evoked by electric stimulation of the cerebellum nuclei and its afferent inputs. Possible mechanisms of forming the correcting influences on scratching and locomotor generators from the cerebellum during changes in phase and amplitude characteristics of its input signals are discussed.     

Olivary projections from the mesodiencephalic structures in the cat studied by means of axonal transport of horseradish peroxidase and tritiated amino acids

By means of horseradish peroxidase (HRP) and autoradiographic methods, olivary projections from mesodiencephalic structures were studied in the cat. Following HRP injections in various parts of the inferior olive, many cells were labeled ipsilaterally in the nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, the nucleus of the fields of Forel, and the subnucleus dorsomedialis and ventrolateralis of the parvocellular red nucleus. Some labeled cells also occurred ipsilaterally in the suprarubral reticular formation and a few labeled cells in the interstitial nucleus of Cajal. After injection of tritiated amino acids in different parts of the mesodiencephalic region mentioned above, labeled fibers were found in different parts of the inferior olive, presenting a high degree of the topographic correlation within the mesodiencephalo-olivary projection, which was exclusively ipsilateral. That is, the nucleus of Darkschewitsch was found to project to the rostral half of the medial accessory olive and the dorsomedial cell column. There was mediolateral topographic relation in this projection. The nucleus accessorius medialis of Bechterew was found to project to the ventral lamella and the lateral part of the dorsal lamella as well as to a small rostromedial part of the caudal half of the medial accessory olive. The subnucleus dorsomedialis and ventrolateralis of the parvocellular red nucleus projected to the rostral and caudal halves, respectively, of the medial part of the dorsal lamella. The subnucleus ventrolateralis of the parvocellular red nucleus also sent fibers to the lateral part of the ventrolateral outgrowth. The nucleus of the fields of Forel, suprarubral reticular formation, and interstitial nucleus of Cajal appeared to project to the caudal half of the medial accessory olive, the medial part of the ventrolateral outgrowth, the rostral part of the dorsal cap, and the caudal part of the dorsal accessory olive.     

Effects of intra-accumbens dopaminergic grafts on behavioral deficits induced by 6-OHDA lesions of the nucleus accumbens or A10 dopaminergic neurons: a comparison

Local lesion of the dopaminergic (DA) terminals of the nucleus accumbens have been described to reproduce part of the behavioral deficits evoked by the lesion of the whole mesocorticolimbic DA system. The most straightforward interpretation of these results would be that the DA innervation of the nucleus accumbens is necessary for and critically involved in the normal performance of the given behaviors. However, while giving some indication as to the necessity of the integrity of this DA innervation for normal behaviors, such an approach cannot reveal whether the presence of the DA innervation of other mesocorticolimbic areas (e.g. amygdala, septum, etc.) is also required. In order to approach this question, the behavioral effects of DA grafts implanted into the nucleus accumbens of rats were evaluated following two different 6-hydroxydopamine-induced lesions: a lesion restricted to the anterior DA field (DA terminals of the nucleus accumbens and to a lesser degree the frontal cortex and anteromedial striatum) or a lesion of the whole mesocorticolimbic DA system. The latter lesion induces a disappearance of the DA innervation of the nucleus accumbens as well as the amygdala, septum, etc. Both kinds of lesions led to locomotor hypoactivity, loss of locomotor activation by amphetamine, increased locomotor stimulation to apomorphine, decrease of exploratory activity and loss of hoarding behavior. These deficits were not seen in grafted animals bearing a local lesion of the DA innervation of this structure. For some of these recoveries, however, a pharmacological stimulation of the grafted neurons was required to reveal the effect of the graft. In the case of the total lesion of the mesocorticolimbic DA system, only locomotor dysfunctions were compensated by the intra-accumbens DA implants, while the other deficits remained intact, irrespective of a stimulation of the graft. These results indicate that the re-establishment of the DA innervation of the nucleus accumbens is a sufficient condition for the compensation of locomotor deficits, irrespective of the presence of the DA terminals in more posterior limbic structures, while for deficits of more complex behaviors the simultaneous presence of posterior DA innervations is also required. This latter requirement suggests the existence of some cooperativity between the different central DA terminal areas for the normal performance of behaviors.     

The role of the pineal gland in stress

Summary A short survey of the results of our previous research into the protective role of the pineal gland against stress is given. The neuroendocrine aspect of a chronic auditory stress and the neuroendocrine aspect of ulcer disease in man were studied. Auditory stress: hypertrophy and hyperplasia of pinealocytes, hyperplasia of the STH, FSH, LTH and TSH cells, hypertrophy of the nuclei and nucleoli of the neuroglandular cells of the supraoptic and paraventricular nuclei, pronounced hyperplasia of the cells of the reticular zone of the adrenal gland, involution of the seminal epithelium, hyperplasia of the Leydig cells. Ulcer disease: numerous glial plates, cavities and acervuli in the pineal gland, numerous granules and vacuoles in the FSH cells, large and eccentrical nuclei in the LH cells, hyperplasia of the cells of the reticular zone of the adrenal gland, presence of the seminal tubules marked by signs of involution, hyperplasia of the Leydig cells. The results obtained point to the secretion of androgens and the insufficiency of the antiandrogenic function of the pineal gland both in auditory stress and ulcer disease. The anticancerogenic effect of the pineal gland would be based on its antiandrogenic function.     

Distribution of neurotensin-immunoreactivity within baroreceptive portions of the nucleus of the tractus solitarius and the dorsal vagal nucleus of the rat

We have examined the distribution of neurotensin immunoreactivity within subnuclear regions of the nucleus of the tractus solitarius (NTS) and the dorsal motor nucleus of the vagus nerve (DVN) in the rat. In order to determine which regions of the NTS were involved in the regulation of baroreceptor reflexes, we mapped the central distribution of the aortic branch of the vagus nerve using transganglionic transport of horseradish peroxidase. Comparison of the pattern of aortic nerve innervation with that of the distribution of neurotensin-immunoreactive cells and fibers shows the dorsomedial nucleus of the NTS both to be the primary site of aortic baroreceptor termination and to contain the highest concentration of neurotensin-immunoreactive elements within the NTS. Neurotensin-immunoreactive fibers are also present in medial regions of the NTS adjacent to the area postrema where they may be involved in the modulation of vagal gastric afferents. Double-label experiments, in which, on the same tissue sections, neurotensin immunohistochemistry was combined with retrograde horseradish peroxidase labeling of DVN neurons, reveal a topographic innervation of vagal preganglionic motoneurons by neurotensin-immunoreactive fibers. The heaviest innervation is of lateral portions of the DVN and adjacent ventral portions of the NTS at the level of the obex, an area which may contain cardiac motoneurons. In this region neurotensin-immunoreactive fibers can be observed in close proximity to retrogradely labeled cells. The concentration of neurotensin elements in a region of the NTS which is involved in the control of baroreceptor reflexes provides a morphological basis for the cardiovascular effects produced by central administration of the peptide. Additional control may be exerted at the level of the motoneuron, as evidenced by apparent neurotensin fiber innervation of presumptive cardiac preganglionic neurons. Similarly, the distribution of neurotensin fibers suggests that the peptide may be acting in gastric regulatory areas of the NTS or on vagal secretomotor neurons to regulate gastric acid secretion.     

Ascending projections of the inferior colliculus in the cat: An autoradiographic study

The ascending projections of the inferior colliculus (IC) in the cat were traced by the autoradiographic method, with special reference to the differential projections of each subnucleus of IC. The laminated ventrolateral part of the central nucleus of IC (CNv) projects to the ventral and medial divisions of the ipsilateral medial geniculate body (MGB). The projections to the ventral division are topographically organized in the mediolateral direction, the terminals being arranged in the form of lamina, while those to the medial division are diffuse. The unlaminated dorsomedial part of the central nucleus of IC (CNd) sends fibers to every division of the ipsilateral MGB, particularly to the dorsal division and the ventromedial portion of the ventral division. It is noteworthy that the external nucleus of IC (EN) projects to the superior colliculus, part of the pretectum, and the anterior extremity of MGB ipsilaterally, in addition to the ventral and medial divisions of MGB. The posterior cap of IC, regarded as the pericentral nucleus of IC (PC), projects ipsilaterally to the ventral part of the caudal tip of MGB and the posterior part of the suprapeduncular nucleus. In addition to these projections, the parabrachial region and interstitial nucleus of the brachium of IC (BIC) are identified as common targets of projections of each nucleus of IC on the ipsilateral side. Contralaterally, every subnucleus of IC except for PC projects via the commissure of IC to areas corresponding to the targets of the ipsilateral projections, such as the ventral and medial divisions of MGB and the parabrachial region and the interstitial nucleus of BIC, although these contralateral projections are in general much sparser than those ipsilateral. Intrinsic and commissural connections within IC are also revealed in this study, providing characteristic configurations of each subnucleus of IC. It is concluded that the ascending projections of IC in the cat are highly differentially organized according to its subnucleus.     

Corticocortical connections of frontal oculomotor areas in the cat

The corticocortical connections of the frontal 'oculomotor' areas related to eye movements of the cat were studied using the retrograde horseradish peroxidase (HRP) tracing method combined with electrophysiological techniques. The following results were obtained. (1) The medial wall of the hemisphere under the cruciate sulcus (CRU), where contralateral conjugate eye deviation was elicited, received fibers from the medial bank of the presylvian sulcus (PRE). The fundus of the coronal sulcus (COR), where monocular movement of the contralateral eye was evoked, received fibers from the lateral bank of the PRE. (2) All the frontal oculomotor areas, the medial wall of the hemisphere under the CRU, the fundus of the COR, and both banks of the PRE, received fibers from the ipsilateral ventral bank of the anterior ectosylvian sulcus (AES). (3) The ventral bank of the AES received fibers from the caudal part of the lateral suprasylvian visual areas. On the basis of the fiber connections, the frontal oculomotor areas can be subdivided into a 'medial' area, the medial wall of the hemisphere under the CRU and the medial bank of the PRE, and a 'lateral' area, the lateral bank of the PRE and the fundus of the COR. Moreover, we found evidence of fiber projections from the ventral bank of the AES to the frontal oculomotor areas that were physiologically identified.     

The development of the isthmo-optic nucleus.

The nucleus of origin of centrifugal fibers to the retina (the so-called isthmo-optic nucleus - ION) has been used as a model for the study of the major features of neural development, from the period of cell proliferation until after the formation of its afferent and efferent connections. 3H-thymidine autoradiography has established that in the chick cells of the ION are generated (i.e., become post-mitotic) between the middle of the 5th and the end of the 7th days of incubation. The first-formed cells are found in the ventrolateral part of the nucleus, while those that are generated at successively later stages come to occupy progressively more medial and dorsal positions within the nucleus. The anlage of the ION can be identified on the 8th day of incubation, and by the 11th day, when it is numerically complete, it occupies a prominent position in the caudo-dorsal part of the midbrain tegmentum at the level of the IVth nerve nucleus. At this stage the nucleus contains about 22,000 neurons, and shows no signs of cytoarchitectonic differentiation. Between the 13th and 17th days of incubation, about 60% of the neurons in the nucleus degenerate; as a result of this degeneration, the arrival of afferent fibers, and the growth of the cells' processes, the nucleus comes to have its characteristic adult form of a complex, folded, bilaminar sheet, in which each part of the retina is precisely represented. Experiments based on the retrograde transport of horseradish peroxidase (HRP) from the eye indicate that the first centrifugal fibers, in the isthmo-optic tract (IOT), reach the retina on the 10 day of incubation, and by the 12th day all but about 5% of the neurons in the ION can be retrogradely labeled in this way...     

Ascending connections of the anterior ventral cochlear nucleus in the rat

The purpose of the experiment was to determine the connections of the three regions of the anterior ventral cochlear nucleus in the rat. Lesions were placed in the regions of the nucleus in 11 rats. After 25 days each animal was sacrificed and its brain impregnated by the protargol method of Bodian. The superior olivary complex, the lateral lemniscus and the dorsal acoustic stria were examined for diminution of synaptic endings, thinning of neuropil and debris of degeneration. Complete destruction of region III of the anterior ventral cochlear nucleus produced degeneration in the ipsilateral lateral superior olive and in the medial superior olive of both sides. Destruction of other regions of the anterior ventral cochlear nucleus, region III remaining intact, had no effect upon the lateral or medial superior olive. Destruction of region II of the anterior ventral cochlear nucleus produced degeneration in the anterior halves of the ipsilateral lateral nucleus of the trapezoid body and the contralateral medial nucleus of the trapezoid body. Complete destruction of other regions of the anterior ventral cochlear nucleus, region II remaining intact, was without effect upon the lateral and medial nuclei of the trapezoid body. No degeneration was detected following destruction of region I of the anterior ventral cochlear nucleus.     

Absence of impairments or recovery mediated by the uncrossed pyramidal tract in the rat versus enduring deficits produced by the crossed pyramidal tract

The pyramidal tract of the rat consists of at least two components. A majority of the fibers cross in the lower medulla and descend through the spinal cord in the ventral portion of the dorsal funiculus. The remaining 5% of the corticospinal projection does not cross and descends in the ipsilateral ventral funiculus into the cervical spinal region where its projections terminate in the internuncial portions of the spinal gray matter. The anatomical origin and terminal distribution of the ipsilateral component suggests that it may be involved in the control of the ipsilateral limb, but the possible contribution of the ipsilateral corticospinal tract has not been systematically examined. To determine whether the ipsilateral corticospinal tract makes a contribution to skilled movement, the corticospinal tract was severed unilaterally at the medullary level rostral to the decussation, thus severing both the crossed component of the tract as well as the ipsilateral component. Performance of the ipsilateral and the contralateral limbs of rats were then evaluated on tests of limb posture, preference, placing, and use in two skilled reaching tasks. No impairments on any quantitative or qualitative measure of performance were detected in the use of the limb ipsilateral to the lesion but severe, enduring impairments on all qualitative and quantitative measures were obtained in use of the limb contralateral to the lesion. Thus, the study finds: (1) no evidence that the ipsilateral portion of the corticospinal tract makes a contribution to skilled movement of the kind made by the contralateral portion of the corticospinal tract, and (2) no evidence that the remaining uncrossed portion of the tract contributes to recovery of symptoms produced by severing the crossed portion of the tract.     

Possible pathways through which neurons of the shell of the nucleus accumbens influence the outflow of the core of the nucleus accumbens

The nucleus accumbens (Acb), a major sector of the ventral striatum, is considered to be an integral part of the striatal complex. The Acb has been shown to be composed of two subdivisions, core and shell, which are distinguishable in several aspects, suggesting that these two subdivisions play different functional roles. The aim of this study was to identify pathways of the efferents of the shell of the Acb to influence the outflow of the core of the Acb. Potential disynaptic projections of the shell to the core of the Acb were investigated in chloral hydrate-anesthetized male Sprague-Dawley rats. Following ipsilateral injections of biotinylated dextran amine (BDA) into the shell of the Acb and cholera toxin B subunit (CT-B) into the core, strong overlapping distributions of BDA-labeled terminals and CT-B-labeled neuronal cell somata were found in the medial part of the ventral tegmental area, medial part of the lateral hypothalamic area, and dorsolateral part of the basolateral amygdaloid nucleus. The significance of multiple sites of relay between the efferents of the shell and the afferents of the core of the Acb at different levels of the neuraxis may be related to the functional specificity of each relay site.     

The physiological basis of transcranial motor cortex stimulation in conscious humans.

Transcranial stimulation of the human motor cortex can evoke several different kinds of descending activity depending on the type of stimulation, the intensity of stimulation and the area of the cortex being stimulated. Thus, transcranial magnetic stimulation preferentially activates different structures than transcranial electrical stimulation. In addition, the response to magnetic stimulation depends on the direction of the induced current in the brain, the waveform of the stimulating current, and the shape of the coil. Stimulation of the lower limb area of motor cortex recruits different elements than stimulation of the upper limb area. These differences occur because different structures in the motor cortex have a differential threshold to the different techniques of stimulation. We have had the opportunity to perform a series of direct recordings of the corticospinal volley evoked by the different techniques of transcranial stimulation from the epidural space of conscious patients with chronically implanted spinal electrodes. These recordings provide insights about the physiological basis of the excitatory and inhibitory phenomena produced by transcranial stimulation.