Serotoninergic innervation of nonprincipal cells in the cerebral cortex of the lizard Podarcis hispanica

The mechanism of serotoninergic transmission in the neo- and archicortex of mammals kis complex, including both synaptic and nonsynaptic components, direct actions on principal cells, and indirect effects mediated by GABAergic interneurons. Here we studied the termination pattern and synaptic organization of the serotoninergic afferents in the cerebral cortex of the lizard, Podarcis hispanica, which is considered to correspond in part to the mammalian hippocampal formation, with the aim of unraveling basic, phylogenetically preserved rules in the connectivity of this pathway. We demonstrate that serotoninergic afferents, visualized by immunostaining for serotonin itself, establish multiple synaptic contacts with different subpopulations of nonprincipal cells containing parvalbumin, neuropeptide Y, and opioid peptides. The former two subpopulations contain GABA, whereas the opioid- immunoreactive neurons are most likely GABA-negative cells. Evidence is provided at the electron microscopic level that serotonin-immunoreactive varicosities establish conventional asymmetric synaptic contacts with their nonprincipal targets, but nonsynaptic varicosities also exist. We conclude that, similarly to mammals, a selective synaptic innervation of nonprincipal, possibly inhibitory, neurons is among the mechanisms of serotoninergic modulation of cerebral cortical activity in the lizard. © 1994 Wiley-Liss, Inc.     

Parvalbumin immunocytochemistry and calcium deposition in muscle fiber necrosis and subsequent regeneration following intramuscular injection of metoclopramide

We have studied the sequential change of parvalbumin immunocytochemistry and its correlation with intracellular Ca24²⁺ deposition in an animal model of muscle fiber necrosis and regeneration induced by intramuscular injection of metoclopramide. Twenty-four hours after the drug's injection, extensive muscle fiber necrosis, together with dramatic loss of parvalbumin immunoreactivity and intracellular Ca²⁺ deposition, was observed. Muscle fiber regeneration began on day 4 after the injection and was complete by the end of the third week. Parvalbumin was not detected in the regenerating fibers, but gradually emerged during the second week as muscle fibers increased in size. It can be suggested that loss of parvalbumin in necrotic fibers is secondary to the loss in integrity of the sarcolemma. Alternatively, loss of parvalbumin in degenerating fibers may impair calcium buffering and act as a contributory factor in the necrotic process. The progressive appearance of parvalbumin immunoreactivity in regenerating fibers parallels that found in normal myogenesis. © 1994 John & Sons, Inc.     

Differential Foci and Synaptic Organization of the Principal and Spinal Trigeminal Projections to the Thalamus in the Rat

The thalamus is known to receive single-whisker ‘lemniscal’ inputs from the trigeminal nucleus principalis (Prv) and multiwhisker ‘paralemniscal’ inputs from the spinal trigeminal nucleus (Spv), yet the responses of cells in the thalamic ventroposteromedial nucleus (VPM) are most similar to and contingent upon inputs from PrV. This may reflect a differential termination pattern, density and/or synaptic organization of PrV and SpV projections. This hypothesis was tested in adult rats using anterograde double-labelling with fluorescent dextrans, horseradish peroxidase (HRP) and choleragenoid, referenced against parvalbumin and calbindin immunoreactivity. The results indicated that Prv's most robust thalamic projection is to the whisker-related barreloids of VPM. The SpV had robust projections to non-barreloid thalamic regions, including the VPM ‘shell’ encapsulating the barreloid area, a caudal and ventral region of VPM that lacks barreloids and PrV inputs, the posterior thalamic nucleus, nucleus submedius and zona incerta. Within the barreloid portion of VPM, SpV projections were sparse relative to those from PrV, and most terminal labelling occurred in the peripheral fringes of whisker-related patches and in inter-barreloid septae. Thus, PrV and SpV have largely complementary projection foci in the thalamus. Intra-axonal staining of a small sample of trigeminothalamic axons with whisker or guard hair receptive fields revealed highly localized and somatotopic terminal aggregates in VPM that spanned areas no larger than that of a single barreloid. In the electron microscopic component of this study, HRP transport to the barreloid region of VPM from left SpV and right PrV in the same cases revealed PrV terminals contacting dendrites with a broad range of minor axis diameters (mean ± SD: 1. 51 ± 0. 10 μm). SpV terminals were indistinguishable from those of PrV, but they had a disproportionate number of contacts on narrow dendrites (1. 27 ± 0. 07 μm, P 0. 01). PrV endings were also more likely to contact VPM somata (11. 0 ± 4. 2% of all labelled terminals) than those from SpV (3. 0 ± 1. O%, P 0. 01). Insofar as primary dendrites are thicker than distal dendrites in VPM, these data suggest a differential distribution of PrV and SpV inputs onto VPM cells that may account for their relative efficacies in dictating the responses of VPM cells to whisker stimulation. Multiwhisker receptive fields in VPM may also reflect direct transmission of convergent inputs from PrV.     

Neurochemical development of the hippocampal region in the fetal rhesus monkey. II. Immunocytochemistry of peptides,calcium-binding proteins,DARPP-32, and monoamine innervation in the entorhinal cortex by the end of gestation

Material for the study came from one 126 day-old rhesus monkey fetus and two 3 day-old neonates. The immunocytochemical detection of somatostatin, neurotensin (NT), parvalbumin, calbindin D-28K, DARPP-32 as well as tyrosine hydroxylase (TH), dopamine-β-hydroxylase and serotonin (5-HT), was carried out on serial cryostat sections of the entorhinal cortex. The authors reported in a previous paper the precocious differentiation of the entorhinal cortex in rhesus monkey fetuses and featured the conspicuous expression of calbindin D-28K, somatostatin, neurotensin, and the monoaminergic innervation during the first half of gestation. The present study shows distinct temporal profiles of neurochemical development during the second half of gestation: the dense neuropeptidergic innervation remained a constant feature; the three aminergic systems gradually increased in density; parvalbumin, unlike calbindin D-28K, was primarily expressed during the last quarter of gestation. Three othe prominent features of the last quarter of gestation are illustrated: the refinement of the modular neurochemical organization of the lamina principalis externa, the delayed chemoanatomical development of the rhinal sulcus area, and the establishment of a distinct rostrocaudal pattern of neurochemical distribution. In correspondence with the cluster-like organization of the lamina principalis externa, the authors observed in the olfactory, rostral, and intermediate fields of the neonate monkey entorhinal cortex, a particular subset of pyramidal-shaped neurons: located in layer III, they were characterized by fasciculated apical dendrites ascending between the cellular islands of the discontinuous layer II and the coexpression of calbindin D-28K and DARPP-32. Besides, most of the other chemical systems displayed a distinct, area-specific, patcy distribution, except for the homogeneously distributed noradrenergic innervation. In the olfactory and rostral fields, TH positive dopaminergic fibers accumulated on the neuronal islands of layers II-III, and parvalbumin labeled fibers on those of layer III, whereas patches of 5-HT and NT-like reactive terminals were segregated between the cellular islands, overlapping the DARPP-32/calbindin D-28 K labeled dendritic bundles. At the opposite, in the intermediate field, 5-HT positive terminals overlapped the cellular islands of layer II and thin fascicles of dopaminergic fibers ran in the inter island spaces. The somatostatin-LIR innervation was apparently too dense to reveal a patchy distribution that existed at earlier developmental stages. In the cadual field, the patchy pattern was replaced by a predominant bilaminar type of distribution of NT, 5-HT, and TH-like positive afferents. Numerous parvalbumin positive multipolar neurons and basket cells participated to a dense parvalbumin labeled network, extending through layers II-V, whose partial extrinsic origin is open to discussion. The rhinal sulcus, still reduced to a small dimple at E126, appeared fully developed at birth. The fundus of the sulcus was marked by a sharp decrease of the neurotensin and parvalbumin-LIR innervations whereas the density of somatostatin and aminergic terminals increased markedly in the perirhinal cortex. Although a transitory overexpression of some of the neurochemical systems under study might occur during development, their modular organization in the lamina principalis externa of the neonate represents a basic feature of the entorhinal cortex and adds further support to the evidence that neurons of layers II-III that project to different parts of the hippocampal formation, belong to distinct heterogeneous systems. This extensive prenatal development is in line with recent data emphasizing the critical role of limbic structures in early recognition memory in infant monkeys. The question arises, however, in view of the delayed development of the rhinal sulcus area, as to whether the preferential connections of the lateral entohinal and perirhinal cortex with regions of polymodal sensory convergence such as the prefrontal cortex and superior temporal gyrus might be established later than the connections of the rest of the entorhinal cortex.     

Region-specific and Age-related Decrease of Parvalbumin Gene Expression in the Prefrontal Cortex of Elderly Patients with Schizophrenia

Background: Multiple studies on schizophrenia have suggested a dysfunction of γ-aminobutyric acid (GABA) transmission in the prefrontal cortex (PFC) and some vulnerability of the central nervous system to the aging process. Since one of the calcium-binding proteins, parvalbumin (PV) is a useful marker for a subpopulation of GABAergic local circuit neurons, we determined the PV gene expression in the PFC in schizophrenic brains to study a possible involvement of GABAergic system and its vulnerability, if any, to the aging process.

Methods:

Methods: We attempted a detailed in situ hybridization to determine the PV gene expression throughout the three PFC subregions (Brodmann areas; BAs 9, 10, and 11) from six elderly patients with schizophrenia and five age-matched normal individuals.

Results:

Results: The regional levels of PV messenger RNA (mRNA) were significantly decreased in BAs 9 and 10 of schizophrenics compared with controls. The cellular levels were significantly decreased in layers III, IV, and V in BAs 9 and 10 of schizophrenics. However, in BA 11 of schizophrenics, the cellular level was significantly decreased in layer in alone. There were significant reverse correlations between the PV mRNA levels in those areas and the age at death in the schizophrenic group, but not in the controls.

Conclusion:

Conclusion: The present results not only provide further evidence of a disturbance in GABA transmission in the PFC of schizophrenics, but also suggest that such dysfunction may be region-specific and vulnerable to the aging process.     

Cell‐specific and developmental expression of lectican‐cleaving proteases in mouse hippocampus and neocortex

Mounting evidence has demonstrated that a specialized extracellular matrix exists in the mammalian brain and that this glycoprotein‐rich matrix contributes to many aspects of brain development and function. The most prominent supramolecular assemblies of these extracellular matrix glycoproteins are perineuronal nets, specialized lattice‐like structures that surround the cell bodies and proximal neurites of select classes of interneurons. Perineuronal nets are composed of lecticans, a family of chondroitin sulfate proteoglycans that includes aggrecan, brevican, neurocan, and versican. These lattice‐like structures emerge late in postnatal brain development, coinciding with the ending of critical periods of brain development. Despite our knowledge of the presence of lecticans in perineuronal nets and their importance in regulating synaptic plasticity, we know little about the development or distribution of the extracellular proteases that are responsible for their cleavage and turnover. A subset of a large family of extracellular proteases (called a disintegrin and metalloproteinase with thrombospondin motifs [ADAMTS]) is responsible for endogenously cleaving lecticans. We therefore explored the expression pattern of two aggrecan‐degrading ADAMTS family members, ADAMTS15 and ADAMTS4, in the hippocampus and neocortex. Here, we show that both lectican‐degrading metalloproteases are present in these brain regions and that each exhibits a distinct temporal and spatial expression pattern. Adamts15 mRNA is expressed exclusively by parvalbumin‐expressing interneurons during synaptogenesis, whereas Adamts4 mRNA is exclusively generated by telencephalic oligodendrocytes during myelination. Thus, ADAMTS15 and ADAMTS4 not only exhibit unique cellular expression patterns but their developmental upregulation by these cell types coincides with critical aspects of neural development. J. Comp. Neurol. 523:629–648, 2015. © 2014 Wiley Periodicals, Inc.     

Fine structure of rat septohippocampal neurons: I. Identification of septohippocampal projection neurons by retrograde tracing combined with electron microscopic immunocytochemistry and intracellular staining.

In this report the normal dendritic organization and fine structure of identified septohippocampal projection neurons is described as a prerequisite for a time course analysis of retrograde changes in these neurons following axotomy (see Naumann et al., J. Comp. Neurol. 325:219-242, 1992). Septohippocampal projection neurons were retrogradely labeled by injection of the fluorescent tracer Fluoro-Gold into the hippocampus. Next, retrogradely labeled cells in Vibratome sections of the medial septum/diagonal band complex were intracellularly stained with the fluorescent dye Lucifer Yellow (LY). Photooxidation of LY resulted in a stable electron-dense reaction product, which allowed us to study these double-labeled neurons by electron microscopy. Another series of sections containing retrogradely labeled neurons were immunostained for choline acetyltransferase (ChAT) or parvalbumin (PARV). In this way the fine structure of two different chemically characterized subpopulations of septohippocampal neurons could be compared with that of the LY-injected neurons. Intracellular filling of retrogradely labeled neurons with LY stained the cell body and the entire dendritic arbor. Essentially, three classes of neurons could be distinguished, i.e., bipolar cells, multipolar neurons, and an intermediate group. All these neurons displayed smooth, often varicose dendrites lacking spines. Mainly located close to the midline, there was a group of cells with only very few if any LY-stained dendrites. In the electron microscope, the double-labeled neurons were easily identified by numerous electron-dense lysosomes associated with transported Fluoro-Gold and the diffuse reaction product resulting from photooxidation. They displayed fine-structural characteristics as previously described for cholinergic neurons. In fact, our fine-structural analysis of ChAT-positive Fluoro-Gold-labeled neurons, but also of back-filled PARV-positive cells, gave very similar results. All these neurons had infolded nuclei, abundant cytoplasmic organelles, and a few axosomatic synapses. Thus, a plain electron microscopic study does not allow one to distinguish between subpopulations of septohippocampal projection neurons.