Extra-lemniscal afferent projections of dorsal spinal cord nuclei to the ventrobasal nuclear complex structure in the contralateral optic thalamus

It has been found that section of half the midbrain tegmentum in cats failed to prevent the afferent somatosensory projections from the foreleg to the ventrobasal nuclear complex of the contralateral thalamus. Specific evoked responses to the stimulation of the contralateral foreleg were recorded in this structure. These specific EP have the same latency as "lemniscal responses" (4-5 ms) and diminish the amplitude and duration of both components of the responses. Simultaneously, we have observed terminal axonal degeneration into the ventrobasal nuclear complex of the thalamus 5-7 days after the section of the contralateral midbrain tegmentum, using the electron microscopy method. All the results obtained indicate that the dorsal column nuclei have extra-lemniscal afferent connections with ventrolateral nuclear complex of the contralateral thalamus. These connections ascend in the back parts of the brainstem ipsilaterally to the corresponding pair of the dorsal column nuclei and rostrally to the midbrain on the contralateral side.     

Electrophysiological study of locus ceruleus projections to central cerebellar nuclei

Evoked response (field potentials) were recorded in all cerebellar nuclei when stimulating the locus ceruleus (LC). Response occurring in the dentate and fastigial nuclei were of considerably greater amplitude and were repeated at a higher rate than in the interstitial nucleus. Blockade of beta-adrenoreceptors led to clear-cut depression of response in the dentate and fastigial nuclei and increased response in the interstitial nucleus. Neuronal response to LC stimulation in the nuclei mainly took the form of inhibition of spontaneous discharges. A less pronounced response was observed in the interstitial nucleus. The findings obtained would indicate the presence of noradrenergic afferents reaching the cerebellar nuclei, where they are unevenly distributed.Kh. Anovyan Pedagogical Institute, Armenia SSR, Erevan. L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 1, pp. 39–44, January–February, 1989.     

Motor cortex projections to the thalamus. An autoradiographic study in the cat

Adult cats received tritiated proline-leucine injections into the pericruciate cortex (areas 4 gamma and 3a) unilaterally and the projections to the thalamus were analyzed. Ipsilateral projections were found in the following nuclei, from rostral to caudal: ventral anterior, reticular, ventral lateral, central medial, paracentral, central lateral, ventral medial, mediodorsal, ventral posterolateral, ventral posteroinferior, centre median, parafascicular and posterior complex. In the contralateral hemithalamus sparse projections were found within the paracentral, central lateral and ventral medial nuclei.     

Convergence between projections from different thalamic nuclei to columns of the rat somatosensory cortex

Primuline fluorochrome retrograde transport technique was used to investigate sources of thalamocortical projections to a single rat somatosensory cortex column connected with the projection of the C₃ vibrissa. Labeled cells were identified in eight different thalamic nuclei: two specific, five nonspecific, and one association nucleus. Labeled neurons differed in the degree of stain accumulated as well as cell numbers and density of distribution from one nucleus to another, indicative of the different arborization patterns of their axons within the cortex. Highest numbers of heavily stained cells as well as highest density of distribution were observed in the ventral thalamic nucleus. The convergence seen between different thalamocortical inputs on to a single somatosensory cortex column explains the functional differences observed between neurons belonging to the same column and makes the formation of functionally distinct neuronal groupings appear possible on this structural basis.Neurocybernetics Research Institute, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 168–174, March–April, 1989.     

Differential expression of acetylcholinesterase in the brainstem, ventrobasal thalamus and primary somatosensory cortex of perinatal rats, mice, and hamsters

Acetylcholinesterase (AChE) is transiently expressed by thalamocortical axons in the rat, and staining for this enzyme has been used extensively to study the development of thalamocortical projections. In the present study, patterns of AChE staining were compared in the trigeminal brainstem, thalami and primary somatosensory cortices of perinatal rats, mice, and hamsters. As previously reported, the ventral posteromedial nucleus (VPM) of rats showed dense AChE staining from P-0 at least through P-8. The ventral posterolateral nucleus (VPL) contained heavy AChE staining at least through P-60. In the cortex, there was also dense AChE staining which was organized somatotopically in patches similar to those observed with other methods such as cytochrome oxidase (CO) staining. However, by adulthood, AChE staining revealed a negative image of the CO staining pattern in lamina IV. In the mouse and hamster, there was dense AChE staining inVPL from P-0 through adulthood, but VPM was much less heavily stained for this enzyme. Moreover, the staining in VPL of mice was markedly reduced after transection of axons that travel to the thalamus in the medial lemniscus, suggesting that much of it was contained in these afferent fibers. In the cortices of both perinatal and adult mice and hamsters, AChE staining yielded a negative image of the somatotopically organized patches demonstrable with CO staining. This negative image was apparent by P-2 in the mouse and P-4 in the hamster. These results document a dramatic species difference with respect to the expression of AChE in the thalami and cortices of developing rodents. The differences between the patterns observed in rats vs mice and hamsters probably reflect the fact that cortical AChE in the latter species is not contained in thalamocortical afferents arising from either VPM or VPL.     

Craniofacial sequelae of lesions to facial and trigeminal motor nuclei in growing rats

Unilateral electrolytic lesions were made in the left-side facial motor nucleus (FMNu) of six Sprague-Dawley rats at 35 days of age in order to correlate craniofacial sequelae with changed motoneuron function. Experimental and control rats were killed at 22, 32, 42, and 52 days postoperatively to provide muscle weight, brain histology, and dry skull preparations for analyses. Dissection, muscle weight, motoneuron count, and osteometric data revealed that lesion-side facial and masticatory muscles were affected by the lesions. Paired t-tests indicated that significant differences existed between weights of experimental lesion- and nonlesion-side anterior digastric, temporalis, masseteric complex, and medial pterygoid muscles, numbers of facial and trigeminal motoneurons, and several skeletal dimensions of the skull. Basi-cranial dimensions of experimental animals were least affected by the lesion, whereas zygomatic arch, dorsal facial region, and mandibular condyle dimensions were most affected. Statistical analyses also detected significant differences between experimental and control groups for several skeletal dimensions of the skull. Data indicated that damage to the trigeminal motor nucleus (TMNu) was secondary to the primary lesion in the FMNu. Motoneurons within the facial and trigeminal neuromuscular complexes (FNC and TNC) play an important role in craniofacial growth and development.     

Distribution of afferents from the association nuclei of the thalamus in the projection and association cortex in cats

Patterns of distribution of terminal degeneration in the parietal cortex (field 7) and in the occipital cortex (field 17) were studied after ultrasonic destruction of the pulvinar by the Fink-Heimer and electron microscopy methods. Degenerating fibers and their terminals were observed in the parietal cortex within all the layers; the greatest amount of degeneration was found in the III--V layers. In the occipital cortex the fibers from the pulvinar end predominantly in the IV layer. Degenerating axons end on the dendritic spines and thin dendritic branches both in the parietal and occipital cortex.     

Quantitative morphological characteristics of developing neurons of the sensory trigeminal nuclei in kittens

Five types of neurons were distinguished in the sensory nuclei of the trigeminal nerve, stained by Golgi's method, in kittens aged 1–5 days and 30 days: reticular and short-dendritic cells (with few branches), and multipolar giant cells, arborescent, and bushy neurons (densely branching). Yet another special type of cell, with a few short dendrites and one long dendrite, was distinguished in preparations from the brain of newborn kittens. Analysis of the dimensions of the bodies, the number, length, and ramification of the dendrites, and the total ramification of the cell yielded quantitative morphological characteristics of these neurons at different times of development. These types of neurons differed in their qualitative and quantitative parameters and in the features of their maturation.Bushy neurons underwent regressive changes during development. Foci of maximal ramification of dendrites of densely branched neurons changed their location during the first months of life relative to the cell body, moving into the more distal regions of the dendrites. Differences in orientation of dendrites with foci of maximal ramification were found relative to neighboring brain formations, which depended on the types of cells and the animal's age. The high level of maturity of trigeminal neurons at birth was demonstrated.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 592–600, November–December, 1982.     

Opiocortin and catecholamine projections to raphe nuclei

Afferent projections to the nucleus raphe magnus (NRM) and dorsal raphe nucleus (DRN) were identified using retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin (HRP-WGA). Neurons were labeled in important nociceptive regions including periaqueductal gray (PAG), arcuate nucleus, lateral hypothalamus and medial thalamic nuclei following both injections. We have immunocytochemically identified opiocortin/WGA neurons in the arcuate nucleus following NRM and DRN injections. Dual stained catecholamine/WGA perikarya were found in zona incerta, locus coeruleus, substantia nigra, nucleus tractus solitarius and adjacent A2, C2 and C3, lateral paragigantocellular reticular nucleus/C1 and lateral reticular nucleus/A1 following DRN injections and in zona incerta, substantia nigra, nucleus tractus solitarius/A2 and lateral reticular nucleus/A1 after NRM injections. These results provide further evidence for opiocortin and catecholamine modulation of analgesia.     

小脑-下丘脑投射在小脑顶核调节淋巴细胞数量与功能中的介导作用

目的:探讨小脑顶核对淋巴细胞功能的调节作用及其作用途径。方法:用海人酸(KA)损毁大鼠双侧小脑顶核,术后第8d用血细胞计数法和酶联免疫吸附试验(ELISA)分别检测动物外周血中淋巴细胞数和血清中抗绵羊红细胞(SRBC)特异性IgM抗体水平。用电损毁小脑上脚交叉中顶核投射至下丘脑的神经纤维,检测动物淋巴细胞数和抗SRBC特异性IgM抗体水平的变化。结果:KA注入双侧小脑顶核后第8d,在Nissl染色的小脑切片,呈现双侧顶核内神经元胞体破坏。作为对照,在生理盐水注入顶核的动物脑片上,可见正常的Nissl小体。小脑顶核损毁后第8d,动物外周血中淋巴细胞数占白细胞总数的百分比以及血清中抗SRBC特异性IgM抗体水平均明显高于顶核注射生理盐水的对照动物。电损毁小脑上脚交叉处顶核投射至下丘脑的神经纤维后第8d,外周血中淋巴细胞的百分比及抗SRBC特异性IgM抗体水平均明显高于假损毁小脑上脚交叉的对照动物。结论:小脑顶核的神经元胞体损毁导致淋巴细胞功能增强,小脑顶核投射至下丘脑的神经纤维损毁同样引起淋巴细胞功能增强,这些结果提示小脑顶核至下丘脑的神经投射参与介导小脑顶核对淋巴细胞功能的调节作用。     

Somatotopic organization and cortical projections of the ventrobasal complex of the flying fox: an "inverted" wing representation in the thalamus

The present study investigates the somatotopic representation in the somatosensory thalamus of a megachiropteran bat. Using standard microelectrode mapping techniques, representational maps were generated for the ventrobasal (Vb) and posterior (Po) thalamic complexes of the Grey-headed flying fox. Anatomical tracing from neocortical injections provided additional data confirming the somatotopy found physiologically. A full representation of the body surface innervated by the trigeminal and spinal nerves was found. However, in contrast with other mammals, the representations of the forelimb and adjacent thoracic trunk within the thalamus were inverted. This means that the distal portions of the wing membrane and the tips of the digits were represented dorsally in Vb, and the thoracic trunk was represented ventrally. In Po the digit tips were represented in the ventral most portion and the thoracic trunk in the dorsal portion of the nucleus. These results are discussed in relation to similarities of megachiropteran somatosensory thalamic nuclei to those of other mammalian species and in relation to the formation of thalamic somatotopic maps and fiber sorting.     

Properties of thalamocortical cells identified by antidromic stimulation in the ventrolateral and ventrobasal thalamic nuclei in rats

The physiological and pharmacological properties of thalamocortical neurons, identified by electrical antidromic stimulation of the frontoparietal cortex, were studied in the ventrobasal and ventrolateral thalamic nuclei in urethane anaesthetized rats. The spontaneous activity and conduction velocity of these neurons were similar in both nuclei. At both sites, thalamocortical neurons could be excited through iontophoretic application of acetylcholine and muscarinic or nicotinic agonists. Despite the known differences in thalamic organization of the two species, these properties are quite similar to those described in cat by other authors.     

Somatotopic organization and cortical projections of the ventrobasal complex of the flying fox: an "inverted" wing representation in the thalamus

The present study investigates the somatotopic representation in the somatosensory thalamus of a megachiropteran bat. Using standard microelectrode mapping techniques, representational maps were generated for the ventrobasal (Vb) and posterior (Po) thalamic complexes of the Grey-headed flying fox. Anatomical tracing from neocortical injections provided additional data confirming the somatotopy found physiologically. A full representation of the body surface innervated by the trigeminal and spinal nerves was found. However, in contrast with other mammals, the representations of the forelimb and adjacent thoracic trunk within the thalamus were inverted. This means that the distal portions of the wing membrane and the tips of the digits were represented dorsally in Vb, and the thoracic trunk was represented ventrally. In Po the digit tips were represented in the ventral most portion and the thoracic trunk in the dorsal portion of the nucleus.These results are discussed in relation to similarities of megachiropteran somatosensory thalamic nuclei to those of other mammalian species and in relation to the formation of thalamic somatotopic maps and fiber sorting.     

Postnatal development of thalamic reticular nucleus projections to the anterior thalamic nuclei in rats

The thalamic reticular nucleus (TRN) projects inhibitory signals to the thalamus, thereby controlling thalamocortical connections. Few studies have examined the development of TRN projections to the anterior thalamic nuclei with regard to axon course and the axon terminal distributions. In the present study, we used parvalbumin (PV) immunostaining to investigate inhibitory projections from the TRN to the thalamus in postnatal (P) 2- to 5-week-old rats (P14–35). The distribution of PV-positive (+) nerve fibers and nerve terminals markedly differed among the anterior thalamic nuclei at P14. Small, beaded nerve terminals were more distributed throughout the anterodorsal nucleus (AD) than in the anteroventral nucleus (AV) and anteromedial nucleus (AM). PV+ fibers traveling from the TRN to the AD were observed in the AV and AM. Nodular nerve terminals, spindle or en passant terminals, were identified on the axons passing through the AV and AM. At P21, axon bundles traveling without nodular terminals were observed, and nerve terminals were distributed throughout the AV and AM similar to the AD. At P28 and P35, the nerve terminals were evenly distributed throughout each nucleus. In addition, DiI tracer injections into the retrosplenial cortex revealed retrogradely-labeled projection neurons in the 3 nuclei at P14. At P14, the AD received abundant projections from the TRN and then projected to the retrosplenial cortex. The AV and AM seem to receive projections with distinct nodular nerve terminals from the TRN and project to the retrosplenial cortex. The projections from TRN to the AV and AM with nodular nerve terminals at P14 are probably developmental-period specific. In comparison, the TRN projections to the AD at P14 might be related to the development of spatial navigation as part of the head orientation system.Key words: Thalamic reticular nucleus, parvalbumin, axon terminal, development, anterior thalamic nucleus, rat     

Reorganization of the vestibular-thalamic projections following injury of the cerebellar interpositus and deiters vestibuar nuclei

Plastic reorganization of the vestibular-thalamic system was studied in adult cats. It was shown, that preliminary (3 months before) injury of the cerebellar contralateral nucleus interpositus or lateral vestibular nucleus of Deiters leads to reorganization of vestibular-thalamic projections. Ipsilateral projections to the ventrolateral nucleus of thalamus arised from vestibular nuclear complex since the pattern of normal representations to mentioned thalamic nucleus were changed. The peculiarities of distribution and morphological structure of vestibular neurons forming new projections to the ventrolateral thalamic nucleus were studied as well.