Neocortical connections with perihippocampal and periamygdalar regions in the hedgehog tenrec

The perihippocampal fields represent the most important regions connecting the neocortex and the hippocampus in rat, cat and monkey but little is known about their presence and connectivity in species with poorly differentiated brain. Using axonal tracer substances we have recently studied the distribution of cortical cells projecting to the hippocampus in the hedgehog tenrec. In the present study we determined the regions of the paleocortex and the rhinal cortex connected with the neocortex, and provide a tentative view of the site and the extent of the tenrecs entorhinal, perirhinal and postrhinal/parahippocampal fields. It is shown that only the dorsal portions of the posterior rhinal cortex may be considered equivalent to the perirhinal and postrhinal fields of higher mammals, while a considerable expanse of the ventral rhinal cortex may be part of the entorhinal area (its so-called dorsal portion) connected with both the dentate gyrus and the neocortex. A few cells projecting to the neocortex were also noted in the dorsal-most portion of the three-layered paleocortex (ventral entorhinal portion). These cells were linearly arranged and reminiscent of the neocortical projecting cells in the entorhinal layer 4/5 in more differentiated mammals. The main portion of the paleocortex caudal to the corpus callosum remained unlabeled following neocortical and hippocampal tracer injections. Unexpectedly, the area in the most ventral paleocortex adjacent to the amygdala also projected to the neocortex, particularly the tenrecs somatosensorimotor cortex.Abbreviations Ay amygdala - BDA biotinylated dextran amine - CA cornu ammonis - Cbl cerebellum - cc corpus callosum - ERhD/V dorsal/ventral portion of entorhinal cortex - Et Echinops telfairi - Hip hippocampus - M cell group M - NCx neocortex - OfB olfactory bulb - PCx subrhinal paleocortex (D, I, P, V refer to dorsal, intermediate, posterior and ventral portions of PCx, the numbers to the zones involved) - pⁱ, p^m, p^s perikarya labeled in superficial (s) and intermediate (i) positions of PCx or the multiform (m) layer of RCx - ppc proportional prosencephalic coordinates - PRh perirhinal cortex (possibly including equivalents of the postrhinal cortex in more differentiated species) - PSbE presubiculum - RCx rhinal cortex (additional numbers refer to zones) - Sbi subiculum - Tu tuberculum olfactorium - XCx poorly characterized area caudally adjacent to RCx - WGA-HRP wheat germ agglutinin conjugated to horseradish peroxidase     

Neocortical areas, layers, connections, and gene expression

Cortical patterns of gene expression provide a new approach to long standing issues of lamination, and area identity and formation. In this review, we summarize recent findings where molecular biological techniques have revealed a small number of area-specific genes in the nonhuman primate cortex. One of these (occ1) is strongly expressed in primary visual cortex and is associated with thalamocortical connections. Another gene, RBP, is more strongly expressed in association areas. It is not clear whether RBP might be linked with any particular connectional system, but several possibilities are raised. We also discuss possible roles of area-specific genes in postnatal development, and conclude with a brief sketch of future directions.     

Electrophysiological investigation of hippocampo-pallidal connections in cats

Evoked potentials in the hippocampus to stimulation of the pallidum and vice versa were studied in unanesthetized and anesthetized (pentobarbital 40 mg/kg) cats with permanently implanted electrodes. Hippocampal and pallidal evoked potentials in waking cats consisted of an initial positive deflection (latent period 15–20 msec) followed by a positive-negative wave (latent period 40–50 msec) both of considerable amplitude and duration. Under pentobarbital anesthesia the fast initial short-latency components of the evoked potentials remained unchanged, subsequent long-latency components of the responses were modified, and thresholds of onset of the responses also became appreciably higher. These results suggest a functional connection between the globus pallidus and hippo-campus in cats.     

Investigation of the cortico-reticulo-spinal connections in cats

Stimulation of the motor cortex evoked postsynaptic potentials in bulbar reticulo-spinal neurons of anaesthetized cats. In 72.4% of reticulo-spinal neurons they were identified as monosynaptic. According to the time characteristics they were classified into two groups (‘fast’ and ‘slow’). Corticobulbar fibres projecting to reticulospinal neurons could be also differentiated as ‘fast’ (conduction velocities above 20 m/s) and ‘slow’ (condition velocities below 20 m/s). Evidence was obtained that ‘fast’ cortico-fugal excitatory postsynaptic potentials are mediated by ‘fast’ cortico-bulbar fibres, and ‘slow’ excitatory postsynaptic potentials by the ‘slow’ ones. It was found that reticulo-spinal neurons with axon conduction velocities of 10.8–65 m/s can be activated by both ‘fast’ and ‘slow’ cortico-bulbar fibres, and the neurons with conduction velocities above 65 m/s only by the ‘slow’ ones. The background activity of reticulo-spinal neurons with slow conducting axons can be characterized as ‘tonic’ (with relatively uniform interspike interval distribution) while the activity of ‘fast’ neurons as ‘phasic’ (with significant grouping of discharges).The possible functional role of the differentiated cortico-reticulo-spinal connections is discussed.     

Interhemisphere connections of the visual cortex in cats with bilateral strabismus

The distribution of retrograde labeled callosal cells after microiontophoretic application of horseradish peroxidase into individual cortical columns in fields 17 and 18 was studied in cats reared with bilateral strabismus (with an angle of eye deviation of 10–35°). The area containing labeled cells was located asymmetrically in relation to the position of the injected column in the opposite hemisphere. Some of the cells were located in those parts of the transitional zone between fields 17 and 18 whose retinotopic coordinates corresponded to the column coordinates (as in intact cats). Other labeled cells were located in fields 17 and 18 and were grouped into clusters located at distances of about 1000 μm from the marginal clusters of the transitional zone. The locations of labeled cells in the lateral geniculate body showed that most columns receive inputs from the ipsilateral eye. Evidence for eye specificity of these monosynaptic interhemisphere connections is presented. The functional significance of changes in these connections in bilateral strabismus is discussed. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 91, No. 8, pp. 949–955, August, 2005.     

Neocortical layers I and II of the hedgehog (Erinaceus europaeus). II. Thalamo-cortical connections

Summary This study examines the thalamo-cortical projections to the most superficial neocortical layers in the hedgehog (Erinaceus europaeus) after small injections of horseradish peroxidase and horseradish peroxidase conjugated to wheat germ agglutinin in the somato-sensory cortex. The injections were limited to layers I, II and upper parts of layer III/IV. Retrogradely labeled cells were plotted in serial sections through the thalamus. Injections in the somato-sensory cortex gave a pattern of elongated columns of labeled cells, extending rostro-caudally in the nucleus ventralis thalami. In the neocortex, labeled fibers extended for considerable distances running horizontally in layer I. Complementary observations demonstrate the thalamic origin of certain, coarse ascending bundles observed previously in Golgi preparations of the hedgehog. It is concluded that a major cortical input to layer I originates in the hedgehog in the principal thalamic (relay) nuclei. After injections in the somato-sensory cortex, retrogradely labeled cells were also found in the nucleus ventro-medialis thalami and very few in a zone medial to the nucleus ventralis thalami corresponding to the intralaminar thalamic nuclei. The contributions of this latter system seem to be limited in comparison with other mammals.Abbreviations A hucleus amygdaloideus - Abol bulbus olfactorius accessorius - Al nucleus amygdaloideus lateralis - Am nucleus anterior medialis thalami - Av nucleus anterior ventralis thalami - Bol bulbus olfactorius - Bst nucleus interstitialis striae terminalis - Ca commissura anterior - Cc corpus callosum - Cen cortex entorhinalis - Ch Chiasma opticum - Ci capsula interna - Cp commissura posterior - Cpu nucleus caudatus putamen - Cs colliculus superior - Fmp fasciculus medialis prosencephali - Fmt fasciculus mamillothalamicus - For formatio reticularis - Fr fasciculus retroflexus - Fx columna fornicis - Gd gyrus dentatus - Gla nucleus geniculatus lateralis, pars dorsalis - Glv nucleus geniculatus lateralis, pars ventralis - Gm nucleus geniculatus medialis - Ha nucleus anterior hypothalami - Hb nucleus habenulae - Hdv nucleus dorsomedialis hypothalami - Hia hippocampus, pars anterior - Hip hippocampus - Hl nucleus lateralis hypothalami - Hvm nucleus ventromedialis hypothalami - Lm lemniscus medialis - Noa nucleus olfactorius anterior - Npm nucleus preopticus medialis - Ped crus cerebri - Pf nucleus parafascicularis - Pre pretectum - Pt nucleus paratenialis - Pv nucleus periventricularis - R nucleus reticularis thalami - Rcn regio cingularis (Brodmann) - Re nucleus reuniens - Rhi regio hippocampica (Brodmann) - Re nucleus reuniens - Rhi regio hippocampica (Brodmann) - Ro regio occipitalis (Brodmann) - Rol regio olfactoria (Brodmann) - Rpc regio precentralis (Brodmann) - Rrs regio retrosplenialis (Brodmann) - Rt regio temporalis (Brodmann) - Rti radiatio thalamica - Rt regio temporalis (Brodmann) - Rti radiatio thalamica - Rtn regio insularis (Brodmann) - S subiculum - Sf sulcus frontalis - Sm stria medullaris thalami - Sn substantia nigra - Srh sulcus rhinalis - St stria terminalis - Td tractus diagonalis (Broca) - Tl nucleus lateralis thalami - Tlp nucleus lateralis thalami, pars posterior - Tm nucleus medialis thalami - To tractus opticus - Tol tractus olfactorius lateralis - Tuo tuberculum olfactorium - Tv nucleus ventralis thalami - Tvd nucleus ventralis thalami, pars dorsalis - Tvm nucleus ventromedialis thalami - wm white matter of the cerebral cortex     

Functional interneuronal connections in the motor cortex of alert and anesthetized cats

Neuronal interconnections in the motor cortex of alert and anesthetized cats were investigated. It is shown that the number of connections between neurons did not decrease within microareas of the cortex during deepening of anesthesia, but their reorganization occurred in the form of leveling of the input and output properties of all cells of the microareas. The number of interneuronal connections of various microareas with deepening of anesthesia considerably decreased and those neurons which were relatively inert in the cortex of alert cats were considerably activated during restructuring of the functional interconnections between microareas. The results of the investigations permitted the assumption of differentiated participation of neurons of the cat motor cortex generating spikes of various amplitude in information processing at the level of microareas when alert and under anesthesia.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 74, No. 7, pp. 913–919, July, 1988.     

Pathological effects of maternal hypoglycemia on fetal development in cats.

The pathogenesis of fetal brain damage caused by acute maternal hypoglycemia was investigated experimentally in cats: profound hypoglycemia (blood glucose concentration: less than 30 mg/dl) was induced in 12 pregnant cats at various stages of gestation by intravenous bolus injections of insulin. Maximal hypoglycemia was attained within 2-3 h, although the grade and duration in individual cats varied. The EEGs of all of seven maternal cats examined showed an increased frequency of slow high-voltage waves as hypoglycemia progressed, eventually becoming flat in 3 for a maximum period of 20 min. Some fetuses showed severe neuropathological changes, such as infarction or intrauterine death. Subventricular softening, cortical hemorrhage and ischemic neuronal changes also occurred, being distributed symmetrically in the parasagittal areas of the cerebrum, basal ganglia, thalamus and tegmentum of the brainstem. In general, these pathological changes were more marked in fetuses and neonates than in the maternal cats, in which only ischemic neuronal changes were present, and may have been due to fetal systemic hypotension and cerebral ischemia induced by hypoglycemia. In maternal cats, the distribution of neurons showing ischemic changes was widest in the cerebral cortex, and some were also present in the dentate gyri of the hippocampus. Moreover, ultrastructural examination of the ischemic neurons in maternal cats, unlike those of the fetuses, showed no mitochondrial swelling. Therefore, the distribution and ultrastructural nature of the ischemic neurons found in the maternal cats were considered to be characteristic of hypoglycemia, as proposed by Agardh et al. (1980).     

Interhemispheric connections of areas 17 and 18 in the cortical columns of cats with unilateral strabismus

The interhemispheric connections of areas 17 and 18 of the cerebral cortex were investigated in cats with experimental unilateral strabismus. Single cortical columns were microiontophoretically injected with horseradish peroxidase, and retrogradelly labeled cells were demonstrated in the opposite brain hemisphere. After tracer injection in area 18 columns, the labeled callosal cells were located in area 17/18 transitional zone, similar to what was found in normal cats. However, in some cases the expansion of the region of callosally labeled cells distribution, was found. It is proposed that the extent of the region of callosally-connected cells may vary depending on whether the cells receive their input from intact or strabismic eye.     

Neocortical glial cell numbers in human brains

Stereological cell counting was applied to post-mortem neocortices of human brains from 31 normal individuals, age 18-93 years, 18 females (average age 65 years, range 18-93) and 13 males (average age 57 years, range 19-87). The cells were differentiated in astrocytes, oligodendrocytes, microglia and neurons and counting were done in each of the four lobes. The study showed that the different subpopulations of glial cells behave differently as a function of age; the number of oligodendrocytes showed a significant 27% decrease over adult life and a strong correlation to the total number of neurons while the total astrocyte number is constant through life; finally males have a 28% higher number of neocortical glial cells and a 19% higher neocortical neuron number than females. The overall total number of neocortical neurons and glial cells was 49.3 billion in females and 65.2 billion in males, a difference of 24% with a high biological variance. These numbers can serve as reference values in quantitative studies of the human neocortex.     

Neocortical Lateralization of NK Activity in Mice

The natural killer (NK) reactivity of mouse spleen cells is controlled by the left brain neocortex and not by the right symmetrical brain area. The finding strongly suggests direct relationships between the central nervous system and the immune system, both involved in biological adaptation for the maintenance of homeostasis and body integrity in relation to the external environment.     

舌快反应传入神经终末与三叉神经脊束核的突触联系

目的：研究舌感觉快反应传入纤维终止于三叉神经脊束核形成的突触类型及各类型突触出现的频率,为神经生理学和神经解剖学研究提供参考资料。方法：采用细胞内注射,电镜连续切片技术。结果：猫舌感觉传入快反应纤维投射到三叉神经脊束核形成的突触类型分单纯型、中间型、和复杂型3种,以中间型突触出现率最多。形成突触的各组成部分以轴-树及轴-轴突触形式为主,未见轴-体突触。结论：中间型突触和轴-树及轴-轴突触是三叉神经脊束核处理感觉信息的形态学基础。