Colocalization of parvalbumin, calretinin and calbindin D-28k in human cortical and subcortical visual structures

Several studies have demonstrated that three calcium-binding proteins parvalbumin (PV), calbindin D-28k (CB) and calretinin (CR) mark distinct subsets of cortical interneurons. This study demonstrates, in cortical and subcortical visual structures, the coexistence of two calcium-binding proteins in some neuronal subpopulations. The human visual cortex (VC), lateral geniculate nucleus (LGN), lateral inferior pulvinar (LIP) and superior colliculus (SC) were examined by a double-labelling immunocytochemical technique. The VC showed mostly separate populations of PV, CB and CR immunoreactive (-ir) interneurons, but also small populations of double-stained PV+CR and CR+CB neurons, while PV+CB neurons were less frequent. An average of 2.5% of the immunoreactive neurons were double-stained for PV+CR and 7.1% for CR+CB in area 17, while this percentage was slightly higher in association area 18 (3.3 and 7.4%, respectively). In the LGN and LIP, double-stained neurons were scarce, but in the fibre capsule of these nuclei, as well as in the optic radiation (OR) and white matter underlying area 17, both double-stained PV+CR or CR+CB and separate populations of PV-ir, CB-ir and CR-ir neurons and fibres were observed. Unlike the thalamic regions, the SC showed some double-stained PV+CR and CR+CB neurons, scattered both in the superficial and deep layers. These findings are discussed in the light of similar observations recently reported from other regions of the human brain.     

Tectorecipient zone of cat lateral posterior nucleus: evidence that collicular afferents contain acetylcholinesterase

Summary The superficial layers of the cat's superior colliculus innervate the medial subdivision of the thalamic lateral posterior nucleus (LPm). LPm is set off from adjoining thalamic zones by its denser staining for acetylcholinesterase (AChE). We sought to learn whether the tectal afferents to LPm might themselves be the source of the enzyme staining by examining the effects of collicular lesions on the thalamic staining pattern. Large excitotoxin lesions of the colliculus largely eliminated AChE staining in the ipsilateral LPm. By contrast, fibersparing lesions of LPm itself left AChE staining nearly unchanged. Destruction of collicular neurons by excitotoxins dramatically reduced AChE staining in fibers of the brachium and superficial gray layer of the superior colliculus. The reduction was especially pronounced in the lower part of the superficial gray layer, in which LP-projecting collicular neurons are located. These results are consistent with the view that LP-projecting collicular neurons synthesize AChE and account for much of the histochemically detectable enzyme present both in the lower superficial gray layer and in LPm. In the colliculus, the excitotoxin lesions spared AChE staining in a thin sheet at the upper border of the superficial gray layer and in the enzyme-positive patches in the intermediate layers. This surviving tectal AChE thus is probably presynaptic and could be contained at least partly in cholinergic afferents from the parabigeminal nucleus and pontomesencephalic tegmentum. The collicular lesions had no obvious effect on AChE staining in the parabigeminal nucleus or in the C-laminae or ventral division of the lateral geniculate nucleus.     

Intrinsic inter- and intralaminar connections and their relationship to the tonotopic map in cat primary auditory cortex

Summary Small iontophoretic injections of the lectin, Phaseolus vulgaris leucoagglutinin (PHA-L), were made into different layers of the primary auditory cortex (AI) of cats. Injections in layer I labeled two types of morphologically distinct fibers in layer I as well as a smaller number of axons in layers II and III. Layer II injections labeled descending axons that produced a dense plexus of terminal fibers in layers I–III of both AI and adjacent auditory fields. Injections in layer III also labeled a dense plexus of axon collaterals at the junction of layers V and VI and labeled patches of terminal fibers in both AI and adjacent auditory fields. These were densest in layers I–III but usually extended into layers IV and V as well. The patches were partly formed by axon collaterals of layer III pyramidal cells that traveled for over 4 mm in the gray matter. Injections confined to layer IV labeled axons in all layers of the cortex but none of these axons appeared to reach the white matter. The axons spread laterally in layer IV and up into the superficial layers and ramified especially layer I. Injections in layers V and VI labeled axons in all layers of the cortex but these were densest in the deep layers where labeling was fairly homogeneous. In the upper layers the labeling was arranged in semi-discrete patches. Large injections involving layers I–III were studied in tangential sections. Between 3 and 8 patches of terminal labeling were observed in AI and these were mainly arranged in a band with its long axis aligned approximately in the dorsoventral direction. However dense patches of terminal labeling also occurred both anterior and posterior to the injection site. In selected experiments portions of the tonotopic map in AI were mapped by single unit recording and subsequently the map was related to patches of anterogradely labeled fibers that surrounded injections of PHA-L. Rows of dorsoventrally oriented patches were among cells with a similar best frequency to those in the injection site. However patches located anterior or posterior to the injection site were among cells with higher or lower best frequencies. Two injections of PHA-L close together produce different patterns of labeling. One of the injections usually produces one or more patches that has no correlate among the patches of fibers labeled by the adjacent injection. This is clearest when one of the injections is made with biotinylated PHA-L that can be visualized directly without the use of primary antibodies. Thus the intrinsic connections of AI arising from nearby cylinders of neurons are not homogenous and clusters of cells can be identified by their unique pattern of connections within AI.     

Calbindin-D28k在出生前人海马本部及下托神经元的表达及其变化

本实验采用免疫组织化学方法研究了１３～３８ 周人胎儿海马本部及下托含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 神经元的分布和发育。结果表明：在１３～１４ 周时,许多含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 锥体细胞可见于ＣＡ１ 区锥体细胞层中部及深部,随着胎龄增大,ＣＡ１ 区含Ｃａｌ－ｂｉｎｄｉｎ－Ｄ２８ｋ 锥体细胞的数量及密度逐渐下降,最终消失,并且这种下降及消失首先从含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 锥体细胞区浅部开始,然后向深部推进;在１３～２８ 周期间,ＣＡ２ 和ＣＡ３ 区也有许多含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 锥体细胞,但至３２ 周以及其后,ＣＡ３ 和ＣＡ２ 区则不见含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 锥体细胞,仅在ＣＡ２ 与ＣＡ１ 交界区见到少量弱染的含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 锥体细胞。此外,在２８～３８ 周期间,ＣＡ３ 和ＣＡ２ 区锥体细胞层周围可见许多含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 的苔藓纤维,其密度随胎龄增大而增加。１４～３８ 周期间,许多含Ｃａｌｂｉｎｄｉｎ－Ｄ２８ｋ 的锥体细胞也出现于下托锥体细胞层全层及前下托锥体细胞层浅部（细胞岛区）及中部。这些区域含Ｃａｌ－ｂｉｎｄｉｎ－Ｄ２８ｋ 锥体细胞的数量及染色强度在１４～２４ 周期间逐渐增     

Morphological details of the projection from the presubiculum to the entorhinal area as shown with the novel PHA-L immunohistochemical tracing method in the rat

Iontophoretic injections of the lectin, phaseolus vulgaris leucoagglutinin (PHA-L) were made into the presubiculum of rats. The anterogradely transported lectin was visualized by using an anti-PHA-L antibody in combination with immunohistochemistry. The PHA-L tracing method revealed morphological details of the projection of the presubiculum to the ipsi- and contralateral medial entorhinal area usually not seen with other anterograde transport techniques. Fine varicose fibers form a dense terminal plexus in the deep parts of layer III. In layer II and deep layer I, the fibers form column-like axonal bundles, terminating in patches in the deep part of layer I. Some fibers reach the outer three layers of the entorhinal area (EA) from collaterals of axons running in the molecular layer, while a majority enter from the deep layers.     

NADPH-diaphorase distribution in the rabbit superior colliculus and co-localization with calcium-binding proteins

Nitric oxide (NO) and calcium‐binding proteins (CaBP) are important neuromodulators implicated in brain plasticity and brain disease. In addition, the mammalian superior colliculus (SC) has one of the highest concentrations of NO within the brain. The present study was designed to determine the distribution of nitric oxide‐synthesizing neurons in the SC of the rabbit by enzyme histochemistry for reduced nicotinamide adenine dinucleotide phosphate‐diaphorase (NADPH‐d), and its degree of co‐localization with CaBP, parvalbumin (PV) and calbindin (CB). NADPH‐d‐labelled fibres formed dense patches of terminal buttons within the intermediate grey layer and streams of fibres within the deepest layers of SC. Cells expressing NOS constitute a subpopulation of neurons in which practically all cell types are represented. Combined PV/NADPH‐d experiments showed a complete lack of co‐localization within individual neurons and fibres. On the contrary, double‐labelled neurons appeared in CB/NADPH‐d‐stained sections, only in the superficial layers, and mostly in the SGS and SO. These cells, which were intermingled with other neurons containing either NADPH‐d or CB, appear to be a subtype of narrow‐field and wide‐field vertical cells, and display an anterior–posterior gradient of density. Owing to the involvement of the superficial layers of the SC in the organization and integration of the visual information, it is suggested that these neurons may play a concrete role within the visual circuits. Our data indicate a clear selectivity in the expression of NADPH‐d, PV and CB in the SC, and that NO and CB probably serve as co‐modulators and/or co‐transmitters in the connectivity of the superficial layers of this midbrain structure.     

Zinc-positive afferents to the rat septum originate from distinct subpopulations of zinc-containing neurons in the hippocampal areas and layers

The purpose of the present study was to examine whether zinc-positive and zinc-negative hippocampal neurons in rats differed with respect to their projections to the septum. By combining retrograde axonal transport of the fluorescent tracer Fluoro-Gold with histochemical demonstration of zinc selenide complexes in zinc-containing neurons after intraperitoneal injection of sodium selenite, we were able to visualize the distribution of retrogradely Fluoro-Gold labeled neurons and zinc-containing neurons in the same sections. After unilateral injection of Fluoro-Gold into the rat septum a few retrogradely labeled cells were observed in layer IV of the ipsilateral medial entorhinal area, and numerous labeled cells were observed mainly in the superficial layers of the ipsilateral subicular areas and throughout the CA1 and CA3 pyramidal cell layers, as well as in the contralateral CA3 pyramidal cell layer. Zinc-containing neurons were observed in layers IV–VI of the medial entorhinal area, layers II and III of the parasubiculum, layers II, III and V of presubiculum, and in the superficial CA1 and deep CA3 pyramidal cell layers. Cells double-labeled with Fluoro-Gold and zinc selenide complexes were primarily located in distal (relative to the area dentata) parts of the superficial CA1 pyramidal cell layer and distal parts of the deep CA3 pyramidal cell layer and in layers II and III of presubiculum. Only a very few double-labeled cells were seen in the contralateral CA3. The result demonstrates that the hippocampo-septal projection of rats is a mixture of zinc-positive and zinc-negative fibers. Where-as zinc-negative fibers originate from neurons throughout the hippocampal and retrohippocampal areas, zinc-positive fibers originate from distinct subgroups of zinc-containing cells in different areas and layers.     

Glycogen phosphorylase reactivity in the entorhinal complex in familiar and novel environments: evidence for labile glycogenolytic modules in the rat

Active and total glycogen phosphorylase were measured histochemically in the entorhinal complex of male Sprague-Dawley rats. Rats were sacrificed from their home cage, or after 5 min in a novel holeboard. Hemispheres from each group were paired, sectioned and processed together. Glycogen phosphorylase reactivity highlighted entorhinal cortex in contrast to less densely stained perirhinal cortex or neocortex. The presubiculum, but not parasubiculum, was strongly reactive for glycogen phosphorylase. Within medial and lateral entorhinal cortex, modularity of active glycogen phosphorylase reactivity was apparent. In inner Layer I there were small ( approximately 50 microm) intense patches of active glycogen phosphorylase. In Layer III there were both small and larger ( approximately 200 microm), patches of active glycogen phosphorylase. Lamina dessicans was reactive. Layers V and VI were relatively unreactive. Exposure to a holeboard intensified the small patches of active glycogen phosphorylase in inner Layer I, while attenuating active glycogen phosphorylase reactivity in Layer III. Total glycogen phosphorylase was unaffected by exposure to the novel environment and exhibited a pattern of continuous dense reactivity suggesting enzyme reserves, particularly in superficial layers of entorhinal cortex. These patterns confirm earlier evidence that glycogenolytic demand in Layers I and III of rat entorhinal cortex is organized in a modular fashion and show that such demand can be modified by brief exposure to a novel holeboard.     

Immunocytochemical Localization of Calbindin D28K,Calretinin, and Parvalbumin in Bat Superior Colliculus

The purpose of this study was to investigate the localization of cells containing the calcium-binding proteins (CBPs) calbindin D28K (CB), calretinin (CR), and parvalbumin (PV) in the superior colliculus (SC) of the bat using immunocytochemistry. CB-immunoreactive (IR) cells formed a laminar tier within the upper superficial gray layer (SGL), while CR-IR cells were widely distributed within the optic layer (OL). Scattered CR-IR cells were also found within the intermediate gray, white, and deep gray layers. By contrast, PV-IR cells formed a laminar tier within the lower SGL and upper OL. Scattered PV-IR cells were also found throughout the intermediate layers, but without a specific laminar pattern. The CBP-IR cells varied in size and morphology: While most of the CB-IR cells in the superficial layers were small round or oval cells, most CR-IR cells in the intermediate and deep layers were large stellate cells. By contrast, PV-IR cells were small to large in size and included round or oval, stellate, vertical fusiform, and horizontal cells. The average diameters of the CB-, CR-, and PV-IR cells were 11.59, 17.17, and 12.60 μm, respectively. Double-immunofluorescence revealed that the percentage of co-localization with GABA-IR cells was 0.0, 0.0, and 10.27% of CB-, CR-, and PV-IR cells, respectively. These results indicate that CBP distribution patterns in the bat SC are unique compared with other mammalian SCs, which suggest functional diversity of these proteins in visually guided behaviors.     

Cluster-and-sheet pattern of enkephalin-like immunoreactivity in the superior colliculus of the cat

The distribution of enkephalin-like immunoreactivity in the superior colliculus has been studied in the cat with the peroxidase-antiperoxidase method. Two striking patterns of immunoreactivity were observed. In the superficial layers there is a thin, dense horizontal band of immunoreactivity in the neuropil of the most dorsal tier of the superficial gray layer (sublamina 1). Because this sublayer corresponds to the zone of densest contralateral retinotectal projection, an intraocular injection of horseradish peroxidase was made in one cat to allow direct comparison of the distributions of opiate-like immunoreactivity and transported tracer in the contralateral superior colliculus. There was a detailed similarity between the two, including the presence of a gap in both at the presumptive site of the optic disc representation. The presence of enkephalin-like immunoreactivity in neural perikarya in and near sublamina 1 of the superficial gray layer, however, raised the possibility that the immunoreactive band is part of an intrinsic opiate system. Deeper in the superficial gray layer there was appreciable but weaker immunoreactivity in the neuropil and fewer immunoreactive neurons. In the intermediate gray layer and, especially medially, even deeper in the superior colliculus, enkephalin-like immunoreactivity was organized into small (100-300 micron wide) patches. In the intermediate gray layer these tended to be arranged periodically, five-seven patches being spaced at 200-600 micron intervals in caudal transverse sections. In some sections adjoining patches appeared to be fused. The patches were absent or difficult to detect in rostral sections. Caudally, they sometimes were adjacent to blood vessels penetrating the intermediate gray layer, but other times were not. Serial section reconstructions suggested that the patches observed in individual sections are part of larger arrays which have the form of anastomotic bands running in longitudinal directions somewhat oblique to the sagittal plane. It is concluded that an opiate mechanism may play a part in controlling the effects of incoming retinal information in the superficial gray layer, directly or indirectly, and that opiate peptides may also act in modulating one or more afferent or efferent systems of the deep collicular layers. Accordingly, from the functional standpoint, enkephalin-like peptides may influence both visual and sensory motor processing in the superior colliculus.     

Localization of Nitric Oxide Synthase-containing Neurons in the Bat Visual Cortex and Co-localization with Calcium-binding Proteins

Microchiroptera (microbats) is a suborder of bats thought to have degenerated vision. However, many recent studies have shown that they have visual ability. In this study, we labeled neuronal nitric oxide synthase (nNOS)—the synthesizing enzyme of the gaseous non-synaptic neurotransmitter nitric oxide—and co-localized it with calbindin D28K (CB), calretinin (CR), and parvalbumin (PV) in the visual cortex of the greater horseshoe bat (Rhinolophus ferrumequinum, a species of microbats). nNOS-immunoreactive (IR) neurons were found in all layers of the visual cortex. Intensely labeled neurons were most common in layer IV, and weakly labeled neurons were most common in layer VI. Majority of the nNOS-IR neurons were round- or oval-type neurons; no pyramidal-type neurons were found. None of these neurons co-localized with CB, CR, or PV. However, the synthesis of nitric oxide in the bat visual cortex by nNOS does not depend on CB, CR, or PV.     

Projections from the hippocampal and parahippocampal regions to the entorhinal cortex. An anterograde and retrograde tract-tracing study in the cat

Projections from the hippocampal and parahippocampal regions to the entorhinal cortex (EC) were examined in the cat by anterograde and retrograde tract-tracing with Phaseolus vulgaris leucoagglutinin and cholera toxin B subunit. CA1 fibers to EC were distributed more densely in the medial EC than in the lateral EC; these were seen in all EC layers, but most densely in layers II and III. The septotemporal axis of the area of origin of CA1-EC fibers corresponded to a caudal-to-rostral axis of the area of their termination in the EC. CA2 and CA4 also sent a small number of fibers to the EC. The subiculum sent fibers mainly to the lateral EC; more densely to layers IV-VI than to layers I-III. The septotemporal axis of the area of origin of subiculum-EC fibers corresponded to a caudolateral-to-rostromedial axis of their termination in the EC. Distribution pattern of fibers from the prosubiculum regions close to CA1 or from prosubiculum regions close to the subiculum was similar to that of CA1 fibers or subiculum fibers, respectively. The presubiculum sent fibers mainly to the medial EC; most densely to layers I and III. The parasubiculum sent fibers mainly to the medial EC; most densely to layer II. Fibers to the contralateral EC were detected only from the presubiculum; they originated from the superficial layers and terminated in layer III of the medial entorhinal area.     

3H]muscimol labels neurons in both the superficial and deep layers of cat superior colliculus

We examined the pattern of [3H]muscimol labeling in cat superior colliculus to determine if it matches that of [3H] gamma-aminobutyric acid ([3H]-GABA) labeling or GABA antibody immunoreactivity. Injections in the superficial layers labeled cell bodies in only the superficial layers. Of 204 labeled cells, 68% were located within the upper 200 microns of the superior colliculus, 31% within the deep superficial gray layer, and only 1% below that layer, a pattern similar to that seen with [3H]GABA labeling. By contrast, an injection in the deep layers of the colliculus resulted in cell labeling in both the superficial and deep layers, including 68% in the superficial gray layer, 24% in the optic layer, and 8% in the intermediate and deep gray layers. This pattern approximates that seen with GABA immunocytochemistry. We conclude that the pattern of accumulation of [3H]muscimol depends critically upon the location of the injection and reasonably matches the pattern of GABA immunoreactivity if the injection involves the deep layers of the colliculus.     

Distribution of calcium binding proteins in visual and auditory cortices of hamsters

The morphology and distribution of neurons immunoreactive (ir) to parvalbumin (PV), calretinin (CR) and calbindin (CB) were studied in the primary visual (V1) and auditory (A1) cortices of hamsters. Cortical cell populations were labelled immunohistochemically using a glucose oxidase-diaminobenzidine-nickel combined revelation method. Quantitative analysis revealed significant differences between V1 and A1 in the density and distribution of their neuronal population. CBir cells exhibited several typologies in both cortical regions. Most cells were multipolar even though many of them had bitufted or bipolar morphologies. These cells were distributed in layers II/III and in layer V of both A1 and V1, but were more numerous in layer V of V1. CRir cells were of the fusiform type with long bipolar dendritic arbours. These were similarly distributed in both cortices with a peak in superficial layers II/III. PVir cells were also found in both cortices and had round or oval-shaped somata with multipolar processes. They were mostly located in layer V for V1 and in layers III/IV for A1. Visual and auditory primary cortices can thus be differentiated on the basis of their immunoreactivity to specific calcium binding proteins.     

Strain differences in the effect of rTMS on cortical expression of calcium-binding proteins in rats

Using a rat model to study the cellular effects of repetitive transcranial magnetic stimulation (rTMS) with regard to changes in cortical excitability, we previously described opposite effects of continuous and intermittent theta-burst stimulation (cTBS, iTBS) on the expression of the calcium-binding proteins (CaBP) parvalbumin (PV), calbindin (CB) and calretinin (CR) in Dark Agouti rats (DA). While iTBS significantly reduced the number of cortical PV+ cells but did not affect the CB+ cells, cTBS resulted in a decrease in CB+ cells with no effects on PV+ cells. We concluded that activity of these classes of cortical interneurons is differently modulated by iTBS and cTBS. When testing two further rat strains, Sprague–Dawley (SD) and Long Evans (LE), we obtained deviating results. In SD, iTBS reduced PV and CB expression, while cTBS only reduced PV expression. In contrast, reanalysed DA showed reduced CB expression after cTBS and reduced PV expression after iTBS, while LE shows an intermediate reaction. CR expression was unaffected in any case. Interestingly, we found significantly different basal expression patterns of the CaBPs for the strains, with DA and LE showing much higher numbers of PV+, CB+ and CR+ cells than SD, and with particularly higher number of CB+ and CR+ cells in DA compared to the other two strains. These findings demonstrate that inhibitory systems may be either differently developed in rats belonging to diverse strains or show different basal levels of activity and CaBP expression and may therefore be differently sensitive to the rTMS protocols.     

Afferents to the seizure-sensitive neurons in layer III of the medial entorhinal area: a tracing study in the rat

Neurons in layer III of the medial entorhinal area (MEA) in the rat are extremely vulnerable to local injections of amino-oxyacetic acid and to exprimentally induced limbic seizures. A comparable specific pathology has been noted in surgical specimens from patients with temporal lobe epilepsy. Efforts to understand this preferential neuronal vulnerability led us to study the neural input to this layer in the rat. Iontophoretic injection of the retrograde tracer fast blue, aimed at layer III of the MEA, resulted in retrogradely labeled neurons in the presubiculum in all the injected hemispheres. The nucleus reuniens thalami, the anteromedial thalamic nucleus, the ventral portion of the claustrum (endopiriform nucleus), the dorsomedial parts of the anteroventral thalamic nucleus, and the septum-diagonal band complex were labeled less frequently. In only one experiment, retrogradely labeled neurons were observed in the ventrolateral hypothalamus and in the brainstem nucleus raphe dorsalis. Since projections from claustrum to the entorhinal cortex has not been studied in the rat with modern sensitive anterograde tracing techniques, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were placed into the ventral portion of the claustrum. Anterogradely labeled fibers in the entorhinal area proved not to be confined to the MEA, since a prominent projection distributed to the lateral entorhinal area as well. In both areas, the densest terminal labeling was present in layers IV–VI, whereas layer III appeared to be only sparsely labeled. The present data indicate that of all potential afferents only those from the presubiculum distribute preferentially to layer III of the MEA. This, in turn, suggests a potentially important role of the presubiculum in the seizure-related degeneration of neurons in layer III of the MEA.     

Dopamine D2 receptors in the rat, monkey and the post-mortem human hippocampus. An autoradiographic study using the novel D2-selective ligand 125I-NCQ 298.

The distribution of dopamine D2 receptors in the hippocampal region of the rat, monkey and the postmortem human brain was studied with in vitro receptor autoradiography using the selective salicylamide ligand 125I-NCQ 298. Specific binding was defined in the presence of the D2-selective compound raclopride. In all 3 species, higher densities of specifically bound 125I-NCQ 298 was found in the retrohippocampal structures than in the hippocampus proper. In the rat, layers 1 and 3 of the entorhinal cortex and layer 2 of the presubiculum were found to be rich in specific binding sites. In the monkey, the highest densities were detected in the deep layers (4 through 6) of the entorhinal cortex (EC) and in layer 2 of the presubiculum. Relatively high density of binding was found in the granule cell layer of area dentata. In the human brain, less specific binding was seen as compared to the other two species; the highest densities occurred in the outer layers of the presubiculum and in the hilus of area dentata. These findings show that D2 receptors are present in the hippocampal region and that the retrohippocampal region, including the entorhinal cortex, is enriched in dopamine D2 receptors.     

Expression of the cannabinoid CB2 receptor in the rat cerebellum: an immunohistochemical study

Reports of cannabinoid CB2 receptor protein in the brain have been ambiguous. We therefore tested for CB2 immunoreactivity in the rat brain using immunofluorescence. We detected CB2 labeling in fine fibers in the granule layer. This CB2 labeling did not co-localise with the astrocyte marker glial fibrillary acidic protein (GFAP) and, therefore, the CB2-positive fibers were not astrocytes and were possibly microglial or neuronal. Additionally, strong CB2 labeling was detected in capillary endothelia in the granule, Purkinje cell, and molecular layers. Our results suggest that the role of CB2 receptors in the brain may have been previously underestimated.     

Organization of interlaminar interactions in the rat superior colliculus

Our previous studies have shown that when slices of the rat superior colliculus (SC) are exposed to a solution containing 10 microM bicuculline and a low concentration of Mg2+ (0.1 mM), most neurons in the intermediate gray layer (stratum griseum intermediale; SGI), wide-field vertical (WFV) cells in the optic layer (stratum opticum; SO), and a minor population of neurons in the superficial gray layer (stratum griseum superficiale; SGS) exhibit spontaneous depolarization and burst firing, which are synchronous among adjacent neurons. These spontaneous and synchronous depolarizations were thought to share common mechanisms with presaccadic burst activity in SGI neurons. In the present study, we explored the site responsible for generation of synchronous depolarization of SGI neurons by performing dual whole cell recordings under different slice conditions. A pair of SGI neurons recorded in a small rectangular piece of the SGI punched out from the SC slice showed synchronous depolarization but far less frequently than those recorded in a small rectangular piece including SGS and SO. This suggests that the superficial layers are needed for triggering synchronous depolarization in the SGI. Furthermore, we recorded spontaneous depolarizations in pairs of neurons belonging to the different layers. Analysis of their synchronicity revealed that WFV cells in the SO exhibit synchronous depolarizations with both SGS and SGI neurons, and the onset of spontaneous depolarization in WFV cells precedes those of neurons in other layers. Further, when SGS and SGI neurons exhibit synchronous depolarizations, SGI neurons usually precede the SGS neurons. These observations give further evidence to the existence of interlaminar interaction between superficial and deeper layers of the SC. In addition, it is suggested that WFV cells can trigger burst activity in other layers of the SC and that there is an excitatory signal transmission from the deeper layers to the superficial layers.     

The calcium binding proteins calbindin, parvalbumin, and calretinin have specific patterns of expression in the gray matter of cat spinal cord

Calcium binding proteins (CBPs) regulate intracellular levels of calcium (Ca²⁺) ions. CBPs are particularly interesting from a morphological standpoint, because they are differentially expressed in certain sub-populations of cells in the nervous system of various species of vertebrate animals. However, knowledge on the cellular regulation governing such cell-specific CBP expression is still incomplete. In this work on the L7 segment of the cat spinal cord, we analyzed the localization and morphology of neurons expressing the CBPs calbindin-28 KD (CB), parvalbumin (PV), and calretinin (CR), and co-expressing CB and PV, CB and CR, and PV and CR. Single CBP-positive (⁺) neurons showed specific distributions: (1) CB was present in small neurons localized in laminae I, II, III and X, in small to medium size neurons in laminae III–VI, and in medium to large neurons in laminae VI–VIII; (2) PV was present in small size neurons in laminae III and IV and in medial portions of laminae V and VI, medium neurons and in lamina X at the border with lamina VII, in medium to large neurons in laminae VII and VIII; (3) CR labeling was detected in small size neurons in laminae I, II, III and VIII, in medium to large size neurons in laminae I and III–VII, and in small to medium size neurons in lamina X. Double labeled neurons were a small minority of the CBP⁺ cells. Co-expression of CB and PV was seen in 1 to 2% of the CBP⁺ cells, and they were detected in the ventral and intermediate portions of lamina VII and in lamina X. Co-localization of CB and CR was present in 0.3% of the cells and these cells were localized in lamina II. Double labeling for PV and CR occurred in 6% of the cells, and the cells were localized in ventral part of lamina VII and in lamina VIII. Overall, these results revealed distinct and reproducible patterns of localization of the neurons expressing single CBPs and co-expressing two of them. Distinct differences of CBP expression between cat and other species are discussed. Possible relations between the cat L7 neurons expressing different CBPs with the neurons previously analyzed in cat and other animals are suggested.