Visual thalamic afferents to area 29 of the rat limbic cortex

Afferent connections of the retrosplenial area of the rat limbic cortex were investigated by the retrograde horseradish peroxidase axon transport method. After injection of horseradish peroxidase (HRP) into area 29 of the cortex, HRP-labeled cells were found in the dorsal part of the lateral geniculate body and the posterolateral, pretectal, and anterior dorsal thalamic nuclei. Connections were found between cortical area 29 and visual projection areas (areas 17 and 18a) and with area 29 on the contralateral side of the brain. The results are evidence that all the principal visual structures of the thalamus and the visual cortical projection area form direct projections to the retrosplenial cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 135–139, March–April, 1982.     

Thalamic inputs to the motor cortex studied in cats by retrograde axonal horseradish peroxidase transport

Thalamic afferent inputs of the motor cortex (area 4) were studied in cats by retrograde axonal transport of horseradish peroxidase (HRP). The main concentration of HRP-labeled neurons was found in rostral zones of the relay nuclei (of the ventrolateral and ventrobasal complex). A few labeled neurons were found in the mediodorsal association nucleus, where their distribution is quite local. HRP-labeled neurons of nonspecific intralaminar nuclei, projecting into the motor cortex, are present only in single numbers and show no tendency toward grouping in any parts of these nuclei. The results are evidence that the motor cortex receives heterogeneous afferentation from various thalamic nuclei, and it is evidently this which guarantees the reliability of transmission of incoming information.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 250–255, March–April, 1985.     

Medial temporal lobe projections to the retrosplenial cortex of the macaque monkey

The projections to the retrosplenial cortex (areas 29 and 30) from the hippocampal formation, the entorhinal cortex, perirhinal cortex, and amygdala were examined in two species of macaque monkey by tracking the anterograde transport of amino acids. Hippocampal projections arose from the subiculum and presubiculum to terminate principally in area 29. Label was found in layer I and layer III(IV), the former seemingly reflecting both fibers of passage and termination. While the rostral subiculum mainly projects to the ventral retrosplenial cortex, mid and caudal levels of the subiculum have denser projections to both the caudal and dorsal retrosplenial cortex. Appreciable projections to dorsal area 30 [layer III(IV)] were only seen following an extensive injection involving both the caudal subiculum and presubiculum. This same case provided the only example of a light projection from the hippocampal formation to posterior cingulate area 23 (layer III). Anterograde label from the entorhinal cortex injections was typically concentrated in layer I of 29a-c, though the very caudal entorhinal cortex appeared to provide more widespread retrosplenial projections. In this study, neither the amygdala nor the perirhinal cortex were found to have appreciable projections to the retrosplenial cortex, although injections in either medial temporal region revealed efferent fibers that pass very close or even within this cortical area. Finally, light projections to area 30V, which is adjacent to the calcarine sulcus, were seen in those cases with rostral subiculum and entorhinal injections. The results reveal a particular affinity between the hippocampal formation and the retrosplenial cortex, and so distinguish areas 29 and 30 from area 23 within the posterior cingulate region. The findings also suggest further functional differences within retrosplenial subregions as area 29 received the large majority of efferents from the subiculum. ? 2012 Wiley Periodicals, Inc.     

Sources of direct afferents of the rostral field CA3 in the rat dorsal hippocampus

Afferents to the rostral field CA₃ of the dorsal hippocampus were investigated using horseradish peroxidase retrograde transport techniques. By iontophoretic injection of horseradish peroxidase into this area of the hippocampus cells stained with this enzyme could be identified in the anterior nuclei of the thalamus, the supramillary and submamillothalamic nuclei of the hypothalamus, and the midbrain central gray matter, as well as the parietal, insular, temporal, retrosplenial, and pyriform areas of the neocortex. The findings obtained complete the picture of connections between one of the least explored sections of the rat hippocampus and other brain structures.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 469–475, July–August, 1986.     

Retrosplenial and hippocampal projections of structures of the thalamoparietal associative system in rats

Afferent connections of the nucleus lateralis posterior (NLP) of the thalamus and area 7 of the parietal cortex with the retrosplenial region of the limbic cortex and hippocampus were studied in rats with retrograde axon transport of horseradish peroxidase. It was shown that the NLP receives ipsilateral projections from area 29d neurons, while area 7 receives ipsilateral axons from area 29d and 29c neurons. It was found that associations of the retrosplenial region with associative cortex are far more pronounced than with associative thalamus. Moreover, the afferent connections of area 7 with area 29d are more numerous than with area 29c. We disclosed no projections of areas 29a and 29b to thalamoparietal system structures. In addition to neocortical input from the limbic cortex, area 7 receives afferent fibers from the archicortex; neurons situated in hippocampus area CA1 are the source of these projections.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy Academy of Sciences, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 647–655, November–December, 1991.     

Corticocortical projections to the monkey temporal lobe with particular reference to the visual processing pathways

Cortico-cortical connections occurring within the temporal lobe and afferent projections to the temporal cortex particularly from the prefrontal and parahippocampal areas were studied in the monkey by means of retrograde axonal transport of horseradish peroxidase (HRP) or wheat-germ-agglutinin-conjugated HRP (WGA-HRP). In particular, 0.1-0.3 microliter of 50% HRP or 5% WGA-HRP was injected into various parts of the temporal cortex, i.e. the rostral (TEr), the caudal (TEc), and the most caudal (TEO) parts of the inferotemporal cortex, the superior temporal gyrus, and the temporal pole (TG), and in the upper bank of the inferior arcuate sulcus in the frontal lobe. Labeled cells, which represent cells of origin of association fibers projecting to the injection site, appeared in various cortical regions. The main findings of the present study are the following. The temporal pole (TG) receives fibers almost exclusively from the most rostral part of the TE. The rostral part of the TE receives many fibers from both the caudal part of the TE and the TEO. The caudal part of the TE receives fibers from the TEO, and the TEO from the prestriate cortex (OA and OB). Taking these findings together, the morphological basis of the "step-wise" progression of visual impulses from the prestriate cortex to the TEO, TE and finally to the TG is clearly presented. The superior temporal gyrus (TA or area 22) receives most fibers from the dorsolateral frontal gyrus, while the inferotemporal cortex (TE or areas 21 and 20) receives most fibers from the ventrolateral frontal gyrus (inferior frontal convexity). Both the temporal pole (TG) and the inferotemporal cortex (TE) receives a fair number of fibers from the parahippocampal region (TH and TF).     

Neuronal responses of the reticular and anterior ventral thalamic nuclei to stimulation of the thalamic ventrolateral nucleus and motor cortex

Responses of 137 neurons of the rostral pole of the reticular and anterior ventral thalamic nuclei to electrical stimulation of the ventrolateral nucleus and motor cortex were studied in 17 cats immobilized with D-tubocurarine. The number of neurons responding antidromically to stimulation of the ventrolateral nucleus was 10.5% of all cells tested (latent period of response 0.7–3.0 msec), whereas to stimulation of the motor cortex it was 11.0% (latent period of response 0.4–4.0 msec). Neurons with a dividing axon, one branch of which terminated in the thalamic ventrolateral nuclei, the other in the motor cortex, were found. Orthodromic excitation was observed in 78.9% of neurons tested during stimulation of the ventrolateral nucleus and in 52.5% of neurons during stimulation of the motor cortex. Altogether 55.6% of cells responded to stimulation of the ventrolateral nucleus with a discharge of 3 to 20 action potentials with a frequency of 130–350 Hz. Similar discharges in response to stimulation of the motor cortex were observed in 30.5% of neurons tested. An inhibitory response was recorded in only 6.8% of cells. Convergence of influences from the thalamic ventrolateral nucleus and motor cortex was observed in 55.7% of neurons. The corticofugal influence of the motor cortex on responses arising in these cells to testing stimulation of the ventrolateral nucleus could be either inhibitory or facilitatory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 460–468, September–October, 1978.     

Uptake of horseradish peroxidase from CSF into the choroid plexus of the rat,with special reference to transepithelial transport

Summary Protein uptake from cerebral ventricles into the epithelium of the choroid plexus, and transport across the epithelium were studied ultrastructurally in rats. Horseradish peroxidase (HRP, MW 40,000) was used as protein tracer. Steady-state ventriculo-cisternal perfusion with subatmospheric pressure (-10cm of water) in the ventricular system was applied. HRP dissolved in artificial CSF was perfused from the lateral ventricles to cisterna magna for various times, and ventriculo-cisternal perfusion, vascular perfusion or immersion fixation with a formaldehyde-glutaraldehyde solution was performed.Coated micropinocytic vesicles containing HRP were seen both connected with the apical, lateral and basal epithelial surface and within the cells. Heavily HRP-labeled vesicles were often fused with the lining membrane of slightly labeled or unlabeled intercellular spaces. Since the apical tight junctions of the epithelium never appeared open or never contained HRP in the spaces between the fusion points, and since the intercellular spaces between adjacent epithelial cells below the junctions only infrequently contained tracer after 5 min, by increasing amounts after 15–60 min of HRP perfusion, a vesicular transport of HRP from the apical epithelial surface to the intercellular spaces, bypassing the tight junctions, is suggested.In addition to the transepithelial transport, micropinocytic vesicles also transported HRP to the lysosomal apparatus of the epithelial cells. With increasing length of exposure to HRP, a sequence of HRP-labeled structures could be evaluated, from slightly labeled apical vacuoles and multivesicular bodies to very heavily labeled dense bodies.     

The distribution of respiration-related and swallowing-related motoneurons innervating the rat genioglossus muscle

The present study was an attempt to identify the location of genioglossal respiratory and swallowing motoneuron cell bodies within the hypoglossal (XII) nucleus using both electrophysiological and morphological studies. The genioglossus muscle is innervated by the genioglossal branch of the medial XII nerve. At the entrance to the muscle, the genioglossal branch divides in the directions of the mandible and tongue. Five of five rats displayed both respiratory-related and swallowing-related bursts in the medial XII branch towards the mandible. All five rats also displayed swallowing-related bursts in the medial XII branch towards the tongue. In addition, horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) was injected into the proximal cut ends of each branch. When HRP:WGA was injected into the branch in the direction of the mandible, HRP-labeled cells were detected in the lateral region of the ventromedial subnucleus in the XII nucleus, extending from 0.7 to 1.2 mm rostral to the obex. On the other hand, after injection into the branch in the direction of the mandible, HRP-labeled cells were detected in the ventromedial subnucleus of the XII nucleus, extending from 0.3 to 1.2 mm rostral to the obex. These results provide evidence that genioglossal respiration-related and swallowing-related motoneurons are located in different portions within the ventromedial subnucleus of the XII nucleus.     

The distribution of respiration-related and swallowing-related motoneurons innervating the rat genioglossus muscle

The present study was an attempt to identify the location of genioglossal respiratory and swallowing motoneuron cell bodies within the hypoglossal (XII) nucleus using both electrophysiological and morphological studies. The genioglossus muscle is innervated by the genioglossal branch of the medial XII nerve. At the entrance to the muscle, the genioglossal branch divides in the directions of the mandible and tongue. Five of five rats displayed both respiratory-related and swallowing-related bursts in the medial XII branch towards the mandible. All five rats also displayed swallowing-related bursts in the medial XII branch towards the tongue. In addition, horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) was injected into the proximal cut ends of each branch. When HRP:WGA was injected into the branch in the direction of the mandible, HRP-labeled cells were detected in the lateral region of the ventromedial subnucleus in the XII nucleus, extending from 0.7 to 1.2 mm rostral to the obex. On the other hand, after injection into the branch in the direction of the mandible, HRP-labeled cells were detected in the ventromedial subnucleus of the XII nucleus, extending from 0.3 to 1.2 mm rostral to the obex. These results provide evidence that genioglossal respiration-related and swallowing-related motoneurons are located in different portions within the ventromedial subnucleus of the XII nucleus.     

Cortico-cortical projections from the prefrontal cortex to the superior temporal sulcal area (STs) in the monkey studied by means of HRP method.

Cortico-cortical connections from the prefrontal cortex to the superior temporal sulcal cortex (STs area) were studied in the monkey by means of retrograde axonal transport of horseradish peroxidase (HRP). After injections of 0.15-0.6 microliter of 50% HRP into the STs area, labeled cells were found in various cortical regions. In the prefrontal-STs projections, main features of topographic correlation were revealed; the posterior part of the STs area receives fibers from the superior frontal convexity (areas dorsal to the principal sulcus) and areas 8 and 6, whereas the anterior part of the STs area receives fibers from the inferior frontal convexity (areas ventral to the principal sulcus) and the frontal pole (area FD). The principal sulcus sends fibers to the entire STs area except for its ventral wall of the posterior part. A small cortical area adjacent to the inferior ramus of the arcuate sulcus (area 45 of ref. 41) sends fibers to the entire STs area. In addition, the orbitofrontal cortex projects mainly to the rostral part of the STs area, and the parahippocampal gyrus (areas TF and TH) projects to the deeper part of the entire STs area.     

Horseradish peroxidase localization of sympathetic postganglionic and parasympathetic preganglionic neurons innervating the monkey heart

The localization of the sympathetic postganglionic and parasympathetic preganglionic neurons innervating the monkey heart were investigated through retrograde axonal transport with horseradish peroxidase (HRP). HRP (4 mg or 30 mg) was injected into the subepicardial and myocardial layers in four different cardiac regions. The animals were euthanized 84-96 hours later and fixed by paraformaldehyde perfusion via the left ventricle. The brain stem and the paravertebral sympathetic ganglia from the superior cervical, middle cervical, and stellate ganglia down to the T9 ganglia were removed and processed for HRP identification. Following injection of HRP into the apex of the heart, the sinoatrial nodal region, or the right ventricle, HRP-labeled sympathetic neurons were found exclusively in the right superior cervical ganglion (64.8%) or in the left superior cervical ganglion (35%). Fewer labeled cells were found in the right stellate ganglia. After HRP injection into the left ventricle, labeled sympathetic cells were found chiefly in the left superior cervical ganglion (51%) or in the right superior cervical ganglion (38.6%); a few labeled cells were seen in the stellate ganglion bilaterally and in the left middle cervical ganglion. Also, in response to administration of HRP into the anterior part of the apex, anterior middle part of the right ventricle, posterior upper part of the left ventricle, or sinoatrial nodal region, HRP-labeled parasympathetic neurons were found in the nucleus ambiguus on both the right (74.8%) and left (25.2%) sides. No HRP-labeled cells were found in the dorsal motor nucleus of the vagus on either side.     

Sources of thalamic projections in the region of vibrissal representation in the rat somatosensory cortex studied by horseradish peroxide labeling

The retrograde horseradish peroxidase (HRP) transport method was used to study the location and morphology of neuron groups in the ventrobasal complex of the thalamus projecting to the region of vibrissal representation in the somatosensory cortex in rats. Injection of HRP into a circumscribed region of the somatosensory cortex revealed the following pattern of organization of the thalamocortical relay groups of neurons. Labeled neurons were located in the ventroposterolateral nucleus of the ventrobasal complex and were associated in groups 100–120 µ in diameter. Staining of several groups, even after minimal injections of HRP, and an increase in the number of labeled cells in each group with an increase in the zone of injection of HRP in the cortex suggest the presence of both convergence and divergence of specific thalamocortical pathways. The different shapes of the relay neurons and differences in the degree of HRP accumulation by them may indicate differences in their functional role in thalamocortical integration.Research Institute of Neurocybernetics, Rostov State University. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 631–635, November–December, 1982.     

Serotonin receptor expression along the dorsal–ventral axis of mouse hippocampus

Using in situ hybridization, we describe, for the first time, the profiles of expression of serotonin receptors (Htr/5-HTR) along the dorsal–ventral axis of mouse hippocampus. cRNA probes for most Htrs, excluding Htr6, were used. All hippocampal subregions and the entorhinal cortex cells providing input into the hippocampus were examined. The study shows that some, but not all, Htrs are expressed in the cells of the hippocampal circuitry. At both the subfield and the cell type levels, a somewhat overlapping pattern is observed. Four serotonin receptors, Htr1a, Htr2a, Htr2c and Htr7, display an expression pattern that changes along the dorsal–ventral axis of the hippocampus. Given the proposed functional differentiation of the hippocampus along its long axis, with the dorsal pole more involved in cognitive functions and the ventral pole more involved in mood and anxiety, our results suggest that serotonin receptors enriched in the ventral pole probably contribute to mood- and anxiety-related behaviours.     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 μm in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V–VI; some were also present in layers I–III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

Small lesions in the primary visual cortex of rats cause a specific reorganization of associational connections

Summary Neuroplastic changes in associational connections were investigated 3 weeks after the intrinsic organization of the visual cortex of rats had been partially damaged by small cylindrical lesions (type I). These lesions caused the degeneration of short intracortical connections and associational connections that form patches in the primary and secondary visual areas. The resulting terminal degeneration disappeared within 20 days p.o. after which only some fiber degeneration was evident in the infragranular layers.Patches of terminal degeneration reappeared in the vicinity of the stab wounds, when the associational connections between the retrosplenial and the primary visual cortex had been secondarily interrupted by elongated lesions (type II), which penetrated the paramedian cortex and subcortical white matter. When type-II lesions were made in the intact cortex, patches of degeneration were absent, although in both cases some terminal degeneration was diffusely distributed in the primary visual cortex.Horseradish peroxidase (HRP) was applied to sites similar to those where type-I lesions were applied. In the intact cortex, HRP caused a granular labeling of numerous neurons in various positions including the retrosplenial cortex and patches of the postero-median visual cortex. HRP was also applied to type-I lesions that had been made 3 weeks earlier. In these cases, apparently HRP labeled the same subpopulations of neurons as it did in the intact cortex. However, a fraction of the labeled neurons showed a Golgilike staining (e.g., 27% of the labeled neurons in the retrosplenial cortex) only when HRP was applied to stab wounds.These results suggest that the breakdown of corticocortical connections in foci of the primary visual cortex causes a focal augmentation of specific associational connections, which are weak and diffusely distributed in the intact adult cortex of rats. Re-innervation originates from subpopulations of associative neurons in the retrosplenial and postero-median visual cortex. Preliminary experiments indicate that the failure of neonatal treatment with 6-OHDA to suppress this lesion-induced plasticity is not dependent on an intact noradrenergic innervation.     

Diencephalic afferents of the rat hippocampus

Connection between diencephalic structures and the hippocampus were investigated in albino rats by the retrograde horseradish peroxidase axon transport method in albino rats. After injection of horseradish peroxidase into the dorsocaudal zone of hippocampal area CA₁, cells labeled with the enzyme were found in nuclei of the thalamus and hypothalamus. The sources of hippocampal afferents were found to be both nonspecific (n. reuniens, n. centralis lateralis, n. centralis medialis) and specific (n. anterodorsalis, n. anteroventralis, n. lateralis anterior, n. lateralis) thalamic nuclei. Axons to the hippocampus also are sent by neurons of n. paraventricularis and n. perifornicalis of the hypothalamus. The results are evidence that direct pathways from structures with sensory inputs run to the hippocampus from the thalamus.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 359–364, July–August, 1981.     

Effect of stimulation of neocortical regions and the subiculum on hippocampal neurons in rabbits

In chronic experiments on rabbits using extracellular recording of unit activity in hippocampal area CA₁ the effects of stimulation of the subiculum, posterior cingulate cortex, and anterior and posterior nonprimary areas of the neocortex were investigated. The effects of such stimulation were compared in the intact and chronically isolated hippocampus. It is concluded from the results that direct two-way connections exist between CA₁ and the subiculum. Polysynaptic influences of the subiculum on CA₁ are realized through the entorhinal cortex, for they are not present in the isolated hippocampus. Influences of the neocortical areas studied on CA₁ are transmitted to some extent through a relay in the subiculum. The entorhinal cortex plays no part in the realization of polysynaptic effects. The effectiveness of these influences increases with removal of the principal hippocampal afferent systems.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 315–323, May–June, 1982.     

Electrophysiological analysis of corticopontine connections

In acute experiments on cats anesthetized with pentobarbital and chloralose, the method of recording focal responses was used to study projections of various parts of the orbito-frontal and basal temporal cortex and also of the hippocampus in the region of the pons. Different formations of the fronto-basal zones of the neocortex were shown to have local projections in the rostral zones of the pons and relatively diffuse projections in its caudal zones. Projections of the hippocampus in structures of the pons are less well marked than those of the fronto-basal zones of the neocortex and their focal responses are more diffuse in character. Representation of all the structures studied is found only in the nuclei of the gray matter of the pons. The orbito-insular zone of the orbito-frontal cortex is not represented in the caudal zones of the reticular formation; the basal temporal cortex has no projection in the middle cerebellar peduncles.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 347–354, July–August, 1977.     

Spontaneous unit activity in the rabbit limbic cortex

Spontaneous unit activity in different parts of the limbic cortex, recorded extracellularly in waking rabbits during chronic experiments, was analyzed. Attention was paid particularly to unit activity in theta- and delta-rhythms. Theta-modulation was found in a small proportion (5–12%) of neurons in all parts except the lateral entorhinal cortex. Delta-activity was found in all structures tested but its characteristics varied. In the subiculum (45% of neurons) it consists of short, high-frequency discharges with long pauses, in the entorhinal cortex (22%) opposite characteristics were found (long loosely packed bursts with short intervals between them). Activating influences raised the frequency and increased the resistance of the theta component and desynchronized the delta volleys in the subiculum and most other structures; in the entorhinal cortex under these circumstances the density of the volleys of spikes was increased but without any change in their frequency or regularity. The spectral composition of unit activity in the presubiculum was mixed. The nature of rhythmic modulation of unit activity in areas of the limbic cortex is discussed.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 753–760, November–December, 1984.