Immunohistochemical localization of calcium-binding proteins, parvalbumin and calbindin-D 28k, in the adult and developing visual cortex of cats: a light and electron microscopic study

Early postnatal development of the primary visual areas 17 and 18 of the cat cerebral cortex: An SMI-32 study

Using anti-neurofilament H non-phosphorylated antibodies (SMI-32) as markers for the neuronal maturation level and Y channel responsible for motion processing, we investigated early postnatal development of the primary visual areas 17 and 18 in cats aged 0, 10, 14, and 34 days and in adults. Two analyzed parameters of SMI-32-immunolabeling were used: the total proportion of SMI-32-labeling and the density of labeled neurons. (i) The developmental time course of the total proportion of SMI-32-labeling shows the general increase in the accumulation of heavy-chain neurofilaments. This parameter showed a different time course for cortical layer development; the maximal increment in the total labeling in layer V occurred between the second and fifth postnatal weeks and in layers II-III and VI after the fifth postnatal week. In addition, the delay in accumulation of SMI-32-labeling was shown in layer V of the area 17 periphery representation during the first two postnatal weeks. (ii) The density of SMI-32-labeled neurons decreased in all layers of area 18, but was increased, decreased, or had a transient peak in layers II-III, V, and VI of area 17, respectively. The transient peak is in good correspondence with some transient neurochemical features previously revealed for different classes of cortical and thalamic neurons and reflects the time course of the early development of the thalamocortical circuitry. Some similarities between the time courses for the development of SMI-32-labeling in areas 17/18 and in A- and C-laminae of the LGNd allow us to propose heterochronous postnatal development of two Y sub-channels.

Parvalbumin - Positive Neurons in the Neocortex: A Review

The calcium binding protein parvalbumin (PV) in the mammalian neocortex is expressed in a subpopulation of cortical GABAergic inhibitory interneurons. PV - producing interneurons represent the largest subpopulation of neocortical inhibitory cells, exhibit mutual chemical and electrical synaptic contacts and are well known to generate gamma oscillation. This review summarizes basic data of the distribution, afferent and efferent connections and physiological properties of parvalbumin expressing neurons in the neocortex. Basic data about participation of PV-positive neurons in cortical microcircuits are presented. Autaptic connections, metabolism and perineuronal nets (PNN) of PV positive neurons are also discussed.

What Is Parvalbumin for?

Parvalbumin (PA) is a small, acidic, mostly cytosolic Ca2+-binding protein of the EF-hand superfamily. Structural and physical properties of PA are well studied but recently two highly conserved structural motifs consisting of three amino acids each (clusters I and II), which contribute to the hydrophobic core of the EF-hand domains, have been revealed. Despite several decades of studies, physiological functions of PA are still poorly known. Since no target proteins have been revealed for PA so far, it is believed that PA acts as a slow calcium buffer. Numerous experiments on various muscle systems have shown that PA accelerates the relaxation of fast skeletal muscles. It has been found that oxidation of PA by reactive oxygen species (ROS) is conformation-dependent and one more physiological function of PA in fast muscles could be a protection of these cells from ROS. PA is thought to regulate calcium-dependent metabolic and electric processes within the population of gamma-aminobutyric acid (GABA) neurons. Genetic elimination of PA results in changes in GABAergic synaptic transmission. Mammalian oncomodulin (OM), the β isoform of PA, is expressed mostly in cochlear outer hair cells and in vestibular hair cells. OM knockout mice lose their hearing after 3–4 months. It was suggested that, in sensory cells, OM maintains auditory function, most likely affecting outer hair cells’ motility mechanisms.

Neuronal Calcium and cAMP Cross-Talk Mediated by Cannabinoid CB1 Receptor and EF-Hand Calcium Sensor Interactions

Endocannabinoids are important players in neural development and function. They act via receptors, whose activation inhibits cAMP production. The aim of the paper was to look for calcium- and cAMP-signaling cross-talk mediated by cannabinoid CB₁ receptors (CB₁R) and to assess the relevance of EF-hand CaM-like calcium sensors in this regard. Using a heterologous expression system, we demonstrated that CB₁R interacts with calneuron-1 and NCS1 but not with caldendrin. Furthermore, interaction motives were identified in both calcium binding proteins and the receptor, and we showed that the first two sensors competed for binding to the receptor in a Ca²⁺-dependent manner. Assays in neuronal primary cultures showed that, CB₁R-NCS1 complexes predominate at basal Ca²⁺ levels, whereas in the presence of ionomycin, a calcium ionophore, CB₁R-calneuron-1 complexes were more abundant. Signaling assays following forskolin-induced intracellular cAMP levels showed in mouse striatal neurons that binding of CB₁R to NCS1 is required for CB₁R-mediated signaling, while the binding of CB₁R to calneuron-1 completely blocked G_i-mediated signaling in response to a selective receptor agonist, arachidonyl-2-chloroethylamide. Calcium levels and interaction with calcium sensors may even lead to apparent Gs coupling after CB₁R agonist challenge.

Compartmental organization of synaptic inputs to parvalbumin-expressing GABAergic neurons in mouse primary somatosensory cortex

Parvalbumin (PV)-positive fast-spiking cells in the neocortex are known to generate gamma oscillations by mutual chemical and electrical connections. Recent findings suggest that this rhythm might be responsible for higher-order brain functions, and related to psychiatric disorders. To elucidate the precise structural rules of the connections of PV neurons, we first produced genetic tools. Using a lentiviral expression system, we developed neuron-specific promoters and a new reporter protein that labels the somatodendritic membrane of neurons. We applied the reporter protein to the generation of transgenic mice, and succeeded in visualizing the dendrites and cell bodies of PV neurons efficiently. Then we analyzed excitatory and inhibitory inputs to PV neurons in the primary somatosensory cortex using the mice. Corticocortical glutamatergic inputs were more frequently found on the distal dendrites than on the soma, whereas thalamocortical inputs did not differ between the proximal and distal portions. Corticocortical inhibitory inputs were more densely distributed on the soma than on the dendrites. We further investigated which types of neocortical GABAergic neurons preferred the PV soma over their dendrites. We revealed that the somatic and dendritic compartments principally received GABAergic inputs from vasoactive intestinal polypeptide (VIP)-positive and PV neurons, respectively. This compartmental organization suggests that PV neurons communicate with each other mainly via the dendrites, and that their activity is effectively controlled by the somatic inputs of VIP neurons. These findings provide new insights into the neuronal circuits involving PV neurons, and contribute to a better understanding of brain functions and mental disorders.

Perineuronal nets affect parvalbumin expression in GABAergic neurons of the mouse hippocampus

Recent studies have suggested that the perineuronal net (PNN), a specialised extracellular matrix structure, and parvalbumin (PV), an EF-hand calcium-binding protein, are involved in the regulation of plasticity of neural circuits. Here, we aimed to quantitatively estimate the relationship between the two plasticity regulators, PV and PNNs, in the hippocampus of young adult mice. Dual fluorescence staining for PV and Wisteria floribunda agglutinin (a broad PNN marker) showed that a substantial population of PV-expressing (PV(+) ) GABAergic neurons lacked PNNs. Optical disector analysis demonstrated that there were fewer PNN(+) neurons than PV(+) neurons. The ratio of PNN expression in PV(+) neurons was generally lower in the dendritic layers than in the principal cell layers, whereas the ratio of PV expression in PNN(+) neurons was effectively 100%. The mean PV fluorescence was significantly higher in PNN(+) /PV(+) neurons than in PNN(-) /PV(+) neurons. Cumulative frequencies for single-cell PV fluorescence indicated that intensely stained PV(+) neurons tend to be enwrapped by PNNs, whereas weakly stained PV(+) neurons are likely to lack PNNs. We digested the PNNs by a unilateral injection of chondroitinase ABC (chABC) into the dorsal CA1 region. Although the densities of PV(+) neurons remained unchanged, the PV fluorescence declined 7 days after chABC injection. Quantitative real-time polymerase chain reaction analysis demonstrated a reduction in PV mRNA expression following chABC injection. These findings indicate that the presence or absence of PNNs affects the relative PV expression in GABAergic neurons in the hippocampus.

New insights into the regulation of synaptic plasticity from an unexpected place: hippocampal area CA2

The search for molecules that restrict synaptic plasticity in the brain has focused primarily on sensory systems during early postnatal development, as critical periods for inducing plasticity in sensory regions are easily defined. The recent discovery that Schaffer collateral inputs to hippocampal area CA2 do not readily support canonical activity-dependent long-term potentiation (LTP) serves as a reminder that the capacity for synaptic modification is also regulated anatomically across different brain regions. Hippocampal CA2 shares features with other similarly "LTP-resistant" brain areas in that many of the genes linked to synaptic function and the associated proteins known to restrict synaptic plasticity are expressed there. Add to this a rich complement of receptors and signaling molecules permissive for induction of atypical forms of synaptic potentiation, and area CA2 becomes an ideal model system for studying specific modulators of brain plasticity. Additionally, recent evidence suggests that hippocampal CA2 is instrumental for certain forms of learning, memory, and social behavior, but the links between CA2-enriched molecules and putative CA2-dependent behaviors are only just beginning to be made. In this review, we offer a detailed look at what is currently known about the synaptic plasticity in this important, yet largely overlooked component of the hippocampus and consider how the study of CA2 may provide clues to understanding the molecular signals critical to the modulation of synaptic function in different brain regions and across different stages of development.

Fewer GABAergic interneurons, heightened anxiety and decreased high-frequency electroencephalogram components in Bronx waltzer mice, a model of hereditary deafness

The homozygous Bronx waltzer mutation (bv/bv) results in the degeneration of most but not all of the primary auditory receptors, the inner hair cells and their afferent neurons, and leads to perceptive deafness. However, the influence of the mutation on the central nervous system (CNS) remains largely unclear. In this study, we have conducted behavioral, morphological and electrophysiological investigations to clarify the CNS dysfunction in bv/bv mice. These mutant mice exhibited heightened levels of anxiety with normal levels of motor activity. Immunohistochemical analysis revealed a significant reduction in parvalbumin-containing GABAergic interneurons in the anterior cingulate, somatosensory and auditory cortices of bv/bv mice. The current results suggest that interneuron development may be disrupted in the bv/bv cerebrum. Moreover, the high-frequency electroencephalogram components of the cortical activity, including the frequency range containing high gamma, were markedly decreased in bv/bv mice compared with controls, probably indicating a disturbance in cortical inhibitory function. Together, these results suggest that the cortical development of interneurons and their electrophysiological profiles are altered in bv/bv mice. We propose that these novel phenotypes identified in bv/bv mice provide new perspectives on the basic neuronal mechanisms of developmental disorders.

Parvalbumin-, calbindin-, and calretinin-immunoreactive hippocampal interneuron density in autism

BACKGROUND

There has been a long-standing interest in the possible role of the hippocampus in autism and both postmortem brain and neuroimaging studies have documented varying abnormalities in this limbic system structure.

AIMS

This study investigates the density of subsets of hippocampal interneurons, immunostained with the calcium binding proteins, calbindin (CB), calretinin (CR) and parvalbumin (PV) to determine whether specific subpopulations of interneurons are impacted in autism.

MATERIALS AND METHODS

Unbiased stereological techniques were used to quantify the neuronal density of these immunoreactive subpopulations of gamma-aminobutyric acid-ergic (GABAergic) interneurons analyzed in the CA and subicular fields in postmortem brain material obtained from five autistic and five age-, gender- and postmortem interval-matched control cases.

RESULTS

Results indicate a selective increase in the density of CB-immunoreactive interneurons in the dentate gyrus, an increase in CR-immunoreactive interneurons in area CA1, and an increase in PV-immunoreactive interneurons in areas CA1 and CA3 in the hippocampus of individuals with autism when compared with controls.

DISCUSSION/CONCLUSIONS

Although our sample size is small, these findings suggest that GABAergic interneurons may represent a vulnerable target in the brains of individuals with autism, potentially impacting upon their key role in learning and information processing. These preliminary findings further suggest the need for future more expanded studies in a larger number of postmortem brain samples from cases of autism and controls.

Brain development and susceptibility to damage; ion levels and movements

Responses of immature brains to physiological and pathological stimuli often differ from those in the adult. Because CNS function critically depends on ion movements, this chapter evaluates ion levels and gradients during ontogeny and their alterations in response to adverse conditions. Total brain Na(+) and Cl(-) content decreases during development, but K(+) content rises, reflecting shrinkage of the extracellular and increase in the intracellular water spaces and a reduction in total brain water volume. Unexpectedly, [K(+)](i) seems to fall during the first postnatal week, which should reduce [K(+)](i)/ [K(+)](e) and result in a lower V(m), consistent with experimental observations. Neuronal [Cl(-)](i) is high during early postnatal development, hence the opening of Cl(-) conduction pathways may lead to plasma membrane depolarization. Equivalent loss of K(+)(i) into a relatively large extracellular space leads to a smaller increase in [K(+)](e) in immature animals, while the larger reservoir of Ca(2+)(e) may result in a greater [Ca(2+)](i) rise. In vivo and in vitro studies show that compared with adult, developing brains are more resistant to hypoxic/ischemic ion leakage: increases in [K(+)](e) and decreases in [Ca(2+)](e) are slower and smaller, consistent with the known low level of energy utilization and better maintenance of [ATP]. Severe hypoxia/ischemia may, however, lead to large Ca(2+)(i) overload. Rises in [K(+)](e) during epileptogenesis in vivo are smaller and take longer to manifest themselves in immature brains, although the rate of K(+) clearance is slower. By contrast, in vitro studies suggest the existence of a period of enhanced vulnerability sometime during the developmental period. This chapter concludes that there is a great need for more information on ion changes during ontogeny and poses the question whether the rat is the most appropriate model for investigation of mechanisms of pathological changes in human neonates.

Doublecortin expression in adult cat and primate cerebral cortex relates to immature neurons that develop into GABAergic subgroups

DCX-immunoreactive (DCX+) cells occur in the piriform cortex in adult mice and rats, but also in the neocortex in adult guinea pigs and rabbits. Here we describe these cells in adult domestic cats and primates. In cats and rhesus monkeys, DCX+ cells existed across the allo- and neocortex, with an overall ventrodorsal high to low gradient at a given frontal plane. Labeled cells formed a cellular band in layers II and upper III, exhibiting dramatic differences in somal size (5-20 microm), shape (unipolar, bipolar, multipolar and irregular), neuritic complexity and labeling intensity. Cell clusters were also seen in this band, and those in the entorhinal cortex extended into deeper layers as chain-like structures. Densitometry revealed a parallel decline of the cells across regions with age in cats. Besides the cellular band, medium-sized cells with weak DCX reactivity resided sparsely in other layers. Throughout the cortex, virtually all DCX+ cells co-expressed polysialylated neural cell adhesion molecule. Medium to large mature-looking DCX+ cells frequently colocalized with neuron-specific nuclear protein and gamma-aminobutyric acid (GABA), and those with a reduced DCX expression also partially co-labeled for glutamic acid decarboxylase, parvalbumin, calbindin, beta-nicotinamide adenine dinucleotide phosphate diaphorase and neuronal nitric oxide synthase. Similar to cats and monkeys, small and larger DCX+ cells were detected in surgically removed human frontal and temporal cortices. These data suggest that immature neurons persist into adulthood in many cortical areas in cats and primates, and that these cells appear to undergo development and differentiation to become functional subgroups of GABAergic interneurons.

Molecular markers distinguishing supragranular and infragranular layers in the human prefrontal cortex

The human neocortex is organized into six layers that are differentiated by the size and packing density of their constituent neurons. The gene products that guide the establishment of this lamination have been studied extensively, but the gene expression gradients present across the layers of the adult human neocortex are mostly unknown. As the supragranular (SG) and infragranular (IG) layers of the human prefrontal cortex (PFC) differ in their connectivity and developmental time course, we hypothesized that the SG and IG layers will show distinct differences in their transcriptomes. To test this prediction, we used laser capture microdissection coupled with DNA microarray transcriptome profiling. Sixty-nine genes exhibited robust and highly consistent expression differences between the SG and IG layers. For six selected markers, in addition to validating the microarray findings, in situ hybridization revealed a complex, subpopulation-specific neuronal distribution. The markers we identified are likely to be related to the functional differences between the SG and IG layers of the human PFC and can be used for assessing alterations in structure and function of this cortical region in human brain disorders.

Parvalbumin in the cat claustrum: ultrastructure, distribution and functional implications

The presence of the calcium-binding protein (CaBP) parvalbumin (PV) in the neuronal elements of the cat's dorsal claustrum was studied by immunohistochemistry at the light- and electron-microscopic level. PV-immunoreactive neurons and fibers were detected in all parts of the claustrum. The PV-immunoreactive neurons were divided into several subtypes according to their size and shape. Approximately 7% of all PV-immunoreactive neurons were classified as large, while approximately half of the labeled neurons were medium-sized. The small PV-immunoreactive neurons were 45% of the total PV-immunoreactive neuronal population. Ultrastructurally, many spiny and aspiny dendrites were heavily immunolabeled, and the reaction product was present in dendritic spines as well. Several types of synaptic boutons containing reaction product were also found. These boutons terminated on both labeled and unlabeled postsynaptic targets (soma, dendrites, etc.), forming asymmetric or symmetric synapses. Approximately 70% of all PV-immunoreactive terminals contained round synaptic vesicles and formed asymmetric synapses. The majority of these boutons were of the ''large round'' type. A lesser percentage were of the ''small round'' type. This paper represents the first study demonstrating the existence of PV, a CaBP, in the cat claustrum, and its distribution at the light and electron microscope level. Beyond the relevance of this research from the standpoint of adding to the paucity of literature on PV immunoreactivity in the claustrum of various other mammals (e.g. monkey, rabbit, rat, mouse), it is of particular significance that the cat claustrum is more similar to the rabbit claustrum than to any other mammalian species studied thus far, noted by the existence of four distinct morphologic subtypes. We also demonstrate a lack of intrinsic, and possibly functional, heterogeneity as evidenced by the uniform distribution of PV throughout the cat claustrum, across the four cell subtypes (i.e. inhibitory interneurons as well as projection neurons). Indeed, the association with, and influence of, the cat claustrum on diverse multisensory mechanisms may have more to do with its afferent than efferent relationships, which speaks strongly for its importance in the sensory hierarchy. Exactly what role PV plays in the claustrum is subject to discussion, but it can be postulated that, since CaBP is associated with GABAergic interneurons, synaptogenesis and neuronal maturation, it may also serve as a neuroprotectant, particularly with regard to pathologies associated with the aging process, such as in Alzheimer's disease.

Chemoarchitecture of the middle temporal visual area in the marmoset monkey (Callithrix jacchus): laminar distribution of calcium-binding proteins (calbindin, parvalbumin) and nonphosphorylated neurofilament

We studied the distributions of interneurons containing the calcium-binding proteins parvalbumin and calbindin D-28k, as well as that of pyramidal neurons containing nonphosphorylated neurofilament (NNF), in the middle temporal visual area (MT) of marmoset monkeys. The distributions of these classes of cells in MT are distinct from those found in adjacent areas. Similar to the primary visual area (V1), in MT, calbindin-immunopositive neurons can be objectively classified into "dark" and "light" subtypes based on optical density of stained cell bodies. Calbindin-positive dark neurons are particularly concentrated in layers 2 and 3, whereas light neurons have a more widespread distribution. In addition, a subcategory of calbindin-positive dark neuron, characterized by a "halo" of stained processes surrounding the cell body, is found within and around layer 4 of MT and V1. These cells are rare in most other visual areas. In comparison, parvalbumin-immunopositive cells in area MT have a relatively homogeneous distribution, although with a trend toward higher spatial density in lower layer 3, and are relatively uniform in terms of density of staining. Finally, MT shows a characteristic trilaminar distribution of NNF-immunopositive pyramidal cells, with stained cell bodies evident in layers 3, 5, and 6. Although the laminar distribution of cells stained for the three markers overlap to some extent, these subcategories can be readily distinguished in terms of morphology, including cell body size. Chemoarchitectural parallels observed between MT and V1 suggest comparable physiological requirements and neuronal circuitry.

Ionotropic glutamate receptor GluR1 in the visual cortex of hamster: distribution and co-localization with calcium-binding proteins and GABA

The subunit composition of the AMPA receptor is critical to its function. AMPA receptors that display very low calcium permeability include the GluR2 subunit, while AMPA receptors that contain other subunits, such as GluR1, display high calcium permeability. We have studied the distribution and morphology of neurons containing GluR1 in the hamster visual cortex with antibody immunocytochemistry. We compared this labeling to that for calbindin D28K, parvalbumin, and GABA. Anti-GluR1-immunoreactive (IR) neurons were located in all layers. The highest density of GluR1-IR neurons was found in layers II/III. The labeled neurons were non-pyramidal neurons, but were varied in morphology. The majority of the labeled neurons were round or oval cells. However, stellate, vertical fusiform, pyriform, and horizontal neurons were also labeled with the anti-GluR1 antibody. Two-color immunofluorescence revealed that many of the GluR1-IR neurons in the hamster visual cortex were double-labeled with either calbindin D28K (31.50%), or parvalbumin (22.91%), or GABA (63.89%). These results indicate that neurons in the hamster visual cortex express GluR1 differently according to different layers and selective cell types, and that many of the GluR1-IR neurons are limited to neurons that express calbindin D28K, parvalbumin, or GABA. The present study elucidates the neurochemical structure of GluR1, a useful clue in understanding the differential vulnerability of GluR1-containing neurons with regard to calcium-dependent excitotoxic mechanisms.

Topography and connections of the telencephalon in a chondrostean,Acipenser baeri: An experimental study

Sturgeons belong to an ancient group of the extant actinopterygian fishes. Accordingly, the study of their brain connections is important to understand brain evolution in the line leading to teleosts. We examined the topography and connections of the various telencephalic regions of the Siberian sturgeon (Acipenser baeri). The telencephalic regions were characterized on the basis of acetylcholinesterase histochemistry and calbindin-D28k and calretinin immunohistochemistry. The telencephalic connections were investigated by using the fluorescent dye DiI (1,1'-dioctadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate) in fixed brains. Application of DiI to different areas of the pallial (dorsal) regions of the telencephalic lobes showed that they have mostly intratelencephalic connections. A posterior pallial region is characterized by its similar hodology to that of the posterior zone of the teleosts dorsal telencephalon and those described in other ancient groups. Extratelencephalic connections of the pallium are scarce, although a few afferent and efferent connections with the diencephalon, mesencephalon, and rostral rhombencephalon were observed. DiI application to subpallial regions showed both intratelencephalic connections and connections with different brain regions. Afferents to the subpallium originate from the olfactory bulbs, preoptic area, thalamus, posterior tuberculum, hypothalamus, secondary gustatory nucleus, and raphe nuclei. Some of these connections are quite similar to those described for other vertebrates.

Suppression of expression of muscle-associated proteins by PPARalpha in brown adipose tissue

Peroxisome proliferator-activated receptor alpha (PPARalpha) belongs to the steroid/nuclear receptor superfamily. Two-dimensional (2D) SDS-PAGE analysis of brown adipose tissue (BAT) unexpectedly revealed six spots that were present only in PPARalpha-null mice. Proteomic analysis indicated that these proteins were tropomyosin-1 alpha chain, tropomyosin beta chain, myosin regulatory light chain 2, myosin light chain 3, and parvalbumin alpha. Analyses of mRNA have revealed that PPARalpha suppressed the genes encoding these proteins in a synchronous manner in adult wild-type mice. Histological and physiological analyses of BAT showed in adult wild-type mice, a marked suppression of BAT growth concurrent with a prominent decrease in lipolytic and thermogenesis activities. These results suggest that in adult mice, PPARalpha functions to suppress the expression of the proteins that may be involved in the architecture of BAT, and thus may function in keeping BAT in a quiescent state.

Embryonic and postnatal development of GABA, calbindin, calretinin, and parvalbumin in the mouse claustral complex

We analyzed the development of immunoreactive expression patterns for the neurotransmitter gamma-aminobutyric acid (GABA) and the calcium-binding proteins calbindin, calretinin, and parvalbumin in the embryonic and postnatal mouse claustral complex. Each calcium-binding protein shows a different temporal and spatial pattern of development. Calbindin-positive cells start to be seen very early during embryogenesis and increase dramatically until birth, thus becoming the most abundant cell type during embryonic development, especially in the ventral pallial part of the claustrum. The distribution of calbindin neurons throughout the claustrum during embryonic development partly parallels that of GABA neurons, suggesting that at least part of the calbindin neurons of the claustral complex are GABAergic and originate in the subpallium. Parvalbumin cells, on the other hand, start to be seen only postnatally, and their number then increases while the density of calbindin neurons decreases. Based on calretinin expression in axons, the core/shell compartments of the dorsal claustrum start to be clearly seen at embryonic day 18.5 and may be related to the development of the thalamoclaustral input. Comparison with the expression of Cadherin 8, a marker of the developing dorsolateral claustrum, indicates that the core includes a central part of the dorsolateral claustrum, whereas the shell includes a peripheral area of the dorsolateral claustrum, plus the adjacent ventromedial claustrum. The present data on the spatiotemporal developmental patterns of several subtypes of GABAergic neurons in the claustral complex may help for future studies on temporal lobe epilepsies, which have been related to an alteration of the GABAergic activity.

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.

Parvalbumin is expressed in glutamatergic and GABAergic corticostriatal pathway in mice

The connections between the cortex and the striatum are critically involved in control and execution of voluntary movements. Here we focused on the expression of calcium binding protein parvalbumin (PV) in the corticostriatal pathway. Injections of Fluorogold into the striatum gave rise to retrograde labeling of PV-positive neurons in the retrosplenial cortex and somatosensory cortex. The PV-positive corticostriatal projection neurons were mainly found in layer V, but occasionally seen in layers II, III, and VI. The PV immunoreactivity of retrogradely labeled cells was weaker than that of nonlabeled cells. Although it was rather difficult to analyze the morphology of Fluorogold-labeled neurons that exhibited PV immunoreactivity, some of them showed distinct apical dendrites and were considered pyramidal cells. The main target of PV-positive cortical afferents was the caudal striatum on the ipsilateral side. Next, we tested whether PV-positive corticostriatal projection neurons were GABAergic or not, because previous studies emphasized that PV was an important marker for cortical GABAergic neurons. Unexpectedly, we found that the majority of PV-positive corticostriatal projection neurons were glutamic acid decarboxylase (GAD)-negative, while some of them were GAD-positive. Finally, an anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) injection into the somatosensory cortex resulted in many PV-positive corticostriatal terminals that were vesicular glutamate transporter 1-positive, whereas some of the PV-positive PHA-L-labeled terminals were GAD-positive. Our results provide anatomical evidence for expression of PV in glutamatergic and GABAergic corticostriatal pathway in mice and suggest that a subset of cortical afferents may exert some inhibitory influence on striatal activity.

Ultrastructural study of gap junctions between dendrites of parvalbumin-containing GABAergic neurons in various neocortical areas of the adult rat

Parvalbumin (PV)-containing GABAergic neurons in the hippocampus form dual networks linked by both dendrodendritic gap junctions and mutual inhibitory synapses. Recent physiological studies have demonstrated similar functional connectivity among cortical GABAergic neurons, but the corresponding structures have not been fully analyzed at the electron microscopic level. In this study we examined detailed ultrastructural features of gap junctions between PV neurons in the mature neocortex. Light microscopic observations and confocal laser scanning microscopy revealed frequent dendrodendritic contacts between PV neurons. Electron microscopic analysis provided direct morphological evidence for the existence of gap junctions between 22 pairs of PV-immunoreactive dendrites in the visual, auditory, and somatosensory cortices. Their ultrastructural features that were characteristic of immunolabeled profiles were consistent with the general structure of gap junctions. In one case a gap junction coexisted with a dendrodendritic chemical synapse, making a mixed synapse. Importantly, we also encountered a gap junction between PV positive and negative, presumptive non-principal cell-derived, dendrites. Quantitative analysis was made in 16 pairs of PV positive dendrites forming gap junctions in the infragranular layers of the somatosensory cortex. Diameters of these dendrites ranged from 0.3 to 2.7 microm, suggesting diverse locations of gap junctions along the proximal-distal axis of dendritic trees, but the majority (81%) were less than 1 microm. The mean size of gap junctions along apposing membranes was 0.22+/-0.09 microm. By using this size, the theoretical value of a junctional conductance was estimated to be 2.1-5.3 nS. Dendrites of PV neurons in the infragranular layers of the somatosensory cortex were reconstructed light microscopically and the sites of contacts with other PV neurons were mapped. Although these contacts do not necessarily imply gap junctional coupling, their number (5.3+/-2.3 per cell, n=11) suggested the degree of connectivity of less than 10 coupling from single PV neurons with others. Sholl analysis revealed that only 38% of their dendrites occurred within 200 microm from the soma. The present study demonstrated detailed ultrastructural features of gap junctions between mature cortical PV neurons. These features will facilitate not only identification of gap junctions in variously labeled neurons but also analysis of their functional aspects by enabling theoretical estimate of their junctional conductances.

Abnormal neuronal expression of the calcium-binding proteins, parvalbumin and calbindin D-28k, in aged dogs

Disturbances of the gamma-aminobutyric acid (GABA) neurotransmitter system have been implicated in chronic degenerative neurological disease. Cognitive dysfunction and neuron loss are features in older dogs. GABAergic neurons also show immunoreactivity for specific calcium-binding proteins. Immunohistochemistry was used to study the neuronal expression of calbindin D-28k and parvalbumin in different areas of the brain in 13 dogs, aged between 2 and 13.5 years. Calbindin expression was found only in the cerebellum. There were significant differences in the quantity and distribution of neurons expressing these proteins between geriatric and adult brains. Parvalbumin- and calbindin-expressing neurons are relatively sensitive to degeneration in the cerebellum of older dogs. Parvalbumin labelling was associated with dystrophic structures that are commonly associated with ageing.

Postnatal development of parvalbumin and calbindin D-28k immunoreactivities in the canine anterior cingulate cortex: transient expression in layer V pyramidal cells

We have examined the ontogeny of parvalbumin (PV) and calbindin D-28k (CB) immunoreactivities in the canine anterior cingulate cortex (ACC) from the day of birth (P0) through P180. At P7, PV immunoreactivity first appeared in layer VI multipolar cells. The PV immunoreactivity in GABAergic nonpyramidal cells appeared to follow an inside-out gradient of radial emergence. Although immunoreaction was limited mainly to the developing nonpyramidal cells, pyramid-like PV immunoreactive cells were transitorily observed in layer V from P14 to P90. The developmental pattern of CB immunoreactivity differed from that of PV immunoreactivity. CB immunoreactivity first developed in layer V pyramidal cells from P0, which continued through P90. CB immunoreactive nonpyramidal cells were located in the infragranular layers and white matter at P0 and matured in both the supragranular and infragranular layers without clear inside-out gradient. This developmental study revealed the comparable belated expression of PV immunoreactivity and the transient expression of both calcium-binding proteins in layer V pyramidal cells. These results suggest that the transient expression of calcium-binding proteins in layer V pyramidal cells might be related to the critical period of early postnatal development.

Differential expression of c-fos in subtypes of GABAergic cells following sensory stimulation in the cat primary visual cortex

Recent immunocytochemical stainings on cat visual cortex, visually stimulated for 1 h, showed a strong induction of Fos expression in cortical neurons. We initiated immunocytochemical double staining experiments with different cytochemical markers to investigate the neurochemical and morphological character of these activated neurons showing Fos induction after sensory stimulation. Double staining with Fos and glutamic acid decarboxylase (GAD) demonstrated the presence of Fos in the nuclei of GABAergic neurons of the primary visual cortex. To further subdivide this Fos/GABAergic cell population we investigated whether Fos colocalized with parvalbumin, calbindin or calretinin. Colocalization of Fos with these calcium-binding proteins delineated distinct neuronal subclasses of Fos-immunoreactive neurons in supra- and infragranular layers of cat area 17. Quantitative analysis of the proportion of immunoreactive local circuit neurons revealed that 35% of the GABAergic neurons showed Fos induction in supragranular layers, whereas in infragranular layers a mere 10% of the GABAergic cells revealed Fos expression. Fos coexisted in about 24% of the calbindin-immunopositive cells within supra- and infragranular layers, but only a minority of the parvalbumin and the calretinin neuronal subgroups were immunopositive for Fos in the corresponding layers of area 17. These findings suggest that visual stimulation induces Fos expression in distinct subsets of inhibitory neurons in cat primary visual cortex.

Distribution of calbindin D-28k in the entorhinal, perirhinal, and parahippocampal cortices of the macaque monkey

We examined the distribution of calbindin D-28k-immunoreactive (CB-IR) neurons, fibers, and neuropil in the entorhinal (area 28), perirhinal (areas 35 and 36), and parahippocampal (areas TH and TF) cortices in the macaque monkey. Two main findings are reported. First, except for CB-IR neurogliaform cells that are only observed in the parahippocampal cortex, the morphology of CB-stained pyramidal and nonpyramidal cells were similar across the three cortical areas examined. Second, we find that the topography of CB staining differed between the three areas. The entorhinal cortex exhibits the most striking gradient of CB staining such that the most anterior and medial portions are most strongly labeled, whereas posterior and lateral areas exhibit only weak labeling. The labeling throughout the perirhinal and parahippocampal cortices is more homogeneous. Area 35 contains only lightly stained neuropil and few CB-IR cells. Area 36 and areas TH and TF of the parahippocampal cortex contain a moderate to high density of CB-IR cells and fibers throughout their full rostrocaudal extents, although each area exhibits unique laminar patterns of staining. In all areas examined, the highest density of CB-positive cells and fibers is observed in superficial layers with lower densities of CB-positive cells and fibers present in deep layers. These findings, taken together with our current understanding of the connections of these areas may have implications for understanding the circuit properties of the entorhinal, perirhinal, and parahippocampal cortices areas in both normal and disease states.

Relation Between Putative Transmitter Phenotypes and Connectivity of Subplate Neurons During Cerebral Cortical Development

During development, the earliest generated neurons of the mammalian telencephalon reside in a region of the white matter, the subplate, just beneath the cortical plate. Neurons in the subplate are only transiently present in the telencephalon: shortly after birth in the cat the majority have disappeared. During their brief life, however, subplate neurons mature; they extend long-distance and local projections, and express immunoreactivity for GABA and several neuropeptides. In the present study we examined the relation between possible transmitter phenotypes of subplate neurons and their connectivity. To do so, we used a double-label technique in which immunohistochemistry for neuropeptide Y (NPY), somatostatin (SRIF) or calbindin (CaBP) was combined with retrograde tracing. Experiments were performed in neonatal cats and in ferret kits at equivalent postconceptional ages, times when subplate neurons are numerous. Subplate neurons immunoreactive for neuropeptides and CaBP could be double-labelled by an injection of retrograde tracer either into the cortical plate or the white matter, indicating that this particular subset of subplate neurons can make local circuit projections. In contrast, peptide or CaBP immunoreactive subplate neurons could never be retrogradely labelled from a tracer injection into the thalamus. Taken together, these observations indicate that subplate neurons immunoreactive for NPY, SRIF and CaBP are likely to be interneurons exclusively. On the other hand, subplate neurons with long-distance projections to the thalamus or the contralateral hemisphere could be labelled by the retrograde transport of d-[3H]aspartate, suggesting that at least some projection subplate neurons might use an excitatory amino acid as a neurotransmitter. These results indicate that there is a defined relationship between the putative transmitter phenotypes of subplate neurons and their patterns of projection. Interneurons of the subplate express peptidergic properties while projection neurons to the thalamus may use an excitatory amino acid. Thus, these basic organizational features of the transient subplate are reminiscent of those found in the adult cortical layers.

Expression of calbindin-D28k and parvalbumin during development of rat's basolateral amygdaloid complex

Parvalbumin and calbindin-D28k are calcium-binding proteins, which are considered to be markers for certain populations of GABAergic neurons. Their correct development in the basolateral amygdaloid complex is critical for the proper emotional functioning in adult live of human and animals. Therefore, in this paper we describe the pattern of the morphological differentiation and distribution of immunoreactive elements of the parvalbumin and calbindin-D28k in this complex on the basis of immunohistochemically stained material obtained from embryonic (E20) and postnatal (P0-P90) rat brains. Calbindin-D28k appeared early in the development, already in the prenatal life. At this time immunopositive reaction was visible only in cell bodies. However, during development the population of immunopositive neurons was divided into four types: (1) polygonal; (2) piriform-like; (3) bipolar; and (4) pyramidal-like. Two weeks after birth calbindin-D28k immunoreactivity also appeared in neuropil. First, there were visible calbindin-D28k positive fibers and granules that encircled unstained cell bodies and formed basket-like structures. Subsequently, these granules appeared along proximal parts of unstained dendrites forming, so called 'cartridges'. The distribution of calbindin-D28k positive cells during postnatal life was rather homogenous throughout whole basolateral complex. Intensity of calbindin-D28k immunoreactivity reached mature level on the 21st day after birth.The maturation pattern of parvalbumin immunopositive elements followed the same sequence as calbindin-D28k, but it started much later - since the 17th day after birth and reached mature appearance on the 30th day of life. Contrary to calbindin-D28k, parvalbumin was not homogeneously distributed in the basolateral complex. Originally, parvalbumin was restricted to the magnocellular part of basolateral nucleus but it was finally expressed also in the parvicellular part of basolateral nucleus and the dorsolateral part of lateral nucleus. The differences in development of these two calcium-binding proteins indicate that parvalbumin and calbindin-D28k play diverse roles during development and maturation of the basolateral amygdala.

Characterization of neuronal migration disorders in neocortical structures: loss or preservation of inhibitory interneurons?

PURPOSE

Neuronal migration disorders (NMD) are often associated with therapy-resistant epilepsy. In human cerebral cortex, this hyperexcitability has been correlated with a loss of inhibitory interneurons. We used a rat model of focal cortical NMD (microgyria) to determine whether the expression of epileptiform activity in this model coincides with a decrease in inhibitory interneurons.

METHODS

In 2-to 4-month-old rats, the density of interneurons immunoreactive for gamma-aminobutyric acid (GABA), calbindin, and parvalbumin was determined in fronto-parietal cortex in nine 200-microm-wide sectors located up to 2.5 mm lateral and 2.0 mm medial from the lesion center in primary parietal cortex (Par1). Quantitative measurements in homotopic areas of age-matched sham-operated rats served as controls.

RESULTS

The freeze lesion performed in newborn rat cortex resulted in adult rats with a microgyrus extending in a rostro-caudal direction from frontal to occipital cortex. The density of GABA-and parvalbumin-positive neurons in fronto-parietal cortex was not significantly different between lesioned and control animals. Only the density of calbindin-immunoreactive neurons located 1.0 mm lateral and 0.5 mm medial from the lesion was significantly (Student t test, p < 0.05) larger in freeze-lesioned rats (5,817 +/- 562 and 6,400 +/- 795 cells per mm3, respectively; n = 12) compared with measurements in homotopic regions in Par1 cortex of controls (4,507 +/- 281 and 4, 061 +/- 319 cells per mm3, respectively; n = 5).

CONCLUSIONS

The previously reported widespread functional changes in this model of cortical NMD are not related to a general loss of inhibitory interneurons. Other factors, such as a decrease in GABA receptor density, modifications in GABAA receptor subunit composition, or alterations in the excitatory network, e.g., an increase in the density of calbindin-immunoreactive pyramidal cells, more likely contribute to the global disinhibition and widespread expression of pathophysiological activity in this model of cortical NMD.

Development of inhibitory circuitry in visual and auditory cortex of postnatal ferrets: immunocytochemical localization of calbindin- and parvalbumin-containing neurons

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is thought to play an important role in activity-dependent stages of brain development. Previous studies have shown that different functional subclasses of cortical GABA-containing neurons can be distinguished by antibodies to the calcium-binding proteins parvalbumin and calbindin. Thus insight into the development of distinct subsets of inhibitory cortical circuits can be gained by studying the development of these calcium-binding protein-containing neurons. Previous studies in several mammalian species have suggested that calcium-binding proteins are upregulated in sensory cortex when thalamocortical afferents arrive. In ferrets, the ingrowth of thalamic axons into cortex occurs well into postnatal development, allowing access to early stages of cortical development and calcium-binding protein expression. We find in ferrets that both parvalbumin- and calbindin-immunoreactivity are present in primary visual and primary auditory cortex long before thalamocortical synapse formation, but that there is a sharp decline in immunoreactivity by postnatal day 20. Day 20 in ferrets corresponds to postnatal day 1 in cats, and thus previous studies in postnatal cats would have missed this early pattern of calcium-binding protein distribution. Another surprising finding is that the proportion of parvalbumin- and calbindin-immunoreactive neurons peaks secondarily late in development, between P60 and adulthood. This result suggests that the parvalbumin- and calbindin-containing subclasses of nonpyramidal neurons remain immature until late in the critical period for cortical plasticity, and that they are positioned to play an important role in experience-dependent modification of cortical circuits.

Does the visual system of the flying fox resemble that of primates? The distribution of calcium-binding proteins in the primary visual pathway of Pteropus poliocephalus

It has been proposed that flying foxes and echolocating bats evolved independently from early mammalian ancestors in such a way that flying foxes form one of the suborders most closely related to primates. A major piece of evidence offered in support of a flying fox-primate link is the highly developed visual system of flying foxes, which is theorized to be primate-like in several different ways. Because the calcium-binding proteins parvalbumin (PV) and calbindin (CB) show distinct and consistent distributions in the primate visual system, the distribution of these same proteins was examined in the flying fox (Pteropus poliocephalus) visual system. Standard immunocytochemical techniques reveal that PV labeling within the lateral geniculate nucleus (LGN) of the flying fox is sparse, with clearly labeled cells located only within layer 1, adjacent to the optic tract. CB labeling in the LGN is profuse, with cells labeled in all layers throughout the nucleus. Double labeling reveals that all PV+ cells also contain CB, and that these cells are among the largest in the LGN. In primary visual cortex (V1) PV and CB label different classes of non-pyramidal neurons. PV+ cells are found in all cortical layers, although labeled cells are found only rarely in layer I. CB+ cells are found primarily in layers II and III. The density of PV+ neuropil correlates with the density of cytochrome oxidase staining; however, no CO+ or PV+ or CB+ patches or blobs are found in V1. These results show that the distribution of calcium-binding proteins in the flying fox LGN is unlike that found in primates, in which antibodies for PV and CB label specific separate populations of relay cells that exist in different layers. Indeed, the pattern of calcium-binding protein distribution in the flying fox LGN is different from that reported in any other terrestrial mammal. Within V1 no PV+ patches, CO blobs, or patchy distribution of CB+ neuropil that might reveal interblobs characteristic of primate V1 are found; however, PV and CB are found in separate populations of non-pyramidal neurons. The types of V1 cells labeled with antibodies to PV and CB in all mammals examined including the flying fox suggest that the similarities in the cellular distribution of these proteins in cortex reflect the fact that this feature is common to all mammals.

Calcium-binding protein-immunoreactive projection neurons in the caudal subnucleus of the spinal trigeminal nucleus of the rat

It has been reported that calcium-binding proteins are good markers for different sets of neurons in various brain regions. We examined expression of the main calcium-binding proteins in projection neurons in the rat medullary dorsal horn (MDH) by combining immunofluorescence histochemistry for calbindin D28k (CB), calretinin (CR) and parvalbumin (PV) with the retrograde tract-tracing method. A fluorescence tracer, tetramethylrhodamine-dextran amine (TMR-DA), was injected into the parabrachial, thalamic or hypothalamic region. After such injections, a number of PV-, CR-, and/or CB-immunoreactive MDH neurons were labeled retrogradely with TMR-DA. Triple-immunofluorescence histochemistry further revealed that a number of CB-, CR-, or PV-immunoreactive TMR-DA-labeled MDH neurons showed immunoreactivity for substance P receptor (NK1), and that they expressed immunoreactivity for c-fos protein in the rats which were injected with formalin into the lips. Thus, it was indicated that some of CB-, CR-, or PV-containing projection neurons in the MDH might be involved in the transmission of nociceptive stimuli.

Calbindin immunoreactivity in the developing and adult human cerebellum

Calbindin (CALB), a calcium-binding protein, is known to be expressed in the embryonic nervous system. In this study, we have examined its distribution in the cerebellum of human fetuses (11-25 weeks of gestation) and adult by immunohistochemistry. At the gestational age of 11-12 weeks. CALB immunoreactivity was present in granule and Purkinje cells throughout the cerebellum. By 16-21 weeks of gestation, immunoreactive Purkinje cells were well-differentiated in the vermis and flocculus, and their axons ran towards the deep cerebellar nuclei area, while the axon collaterals were seen to be distributed into adjacent folia. At the gestational period of 24-25 weeks, most Purkinje cells of the flocculus and vermis were arranged in one to two rows, while those of the hemispheres were still undifferentiated. A few Golgi cells of the vermis showed immunoreactivity. The neurons of the deep nuclei were immunonegative right from the gestational age of 11 weeks although a fine stippled staining of fibers was present throughout the body of all nuclei. The fibers lying close to the hilum of the dentate nucleus were strongly CALB-positive. The vestibulocerebellar fibers, being traced at the level of lower pons and upper medulla oblongata were stained as early as 11 weeks of gestation, whereas the olivocerebellar fibers were stained from 16 weeks onward. In the adult cerebellum, Purkinje cells were moderately immunopositive while granule cells were faintly stained; no other cells, including those of the deep nuclei were stained. In the medulla oblongata, the inferior olivary nucleus and olivocerebellar fibers were strongly CALB-positive. Our results indicate that CALB is expressed in early migratory Purkinje cells, and their maturation occurs in a vermal-to-hemisphere gradient. It is likely that CALB plays a significant role in the regulation of Ca2+-dependent activities in the developing cerebellum.

Development of inhibitory circuitry in visual and auditory cortex of postnatal ferrets: immunocytochemical localization of GABAergic neurons

The goal of this study was to describe the development of gamma-aminobutyric acid (GABA)-containing neurons in visual and auditory cortex of ferrets. The laminar and tangential distribution of neurons containing excitatory, inhibitory, and neuromodulatory substances constrain the potential circuits which can form during development. Ferrets are born at an early stage of brain development, allowing examination of inhibitory circuit formation in cerebral cortex prior to thalamocortical ingrowth and cortical plate differentiation. Immunocytochemically labelled nonpyramidal GABA neurons were present from postnatal day 1 throughout development, in all cortical layers, and generally followed the inside-out pattern of neuronal migration into the cortical plate. Prior to postnatal day 14, pyramidal neurons with transient GABA immunoreactivity were also observed. The density of Nissl-stained and GABA-immunoreactive neurons was high early in development, declined markedly by postnatal day 20, then remained relatively constant until adulthood. However, examination of the proportion of GABA neurons revealed an unexpected late peak at postnatal day 60, then a decrease in adulthood. Visual and auditory cortex were similar in most respects, but the peak at postnatal day 60 and the final proportion of GABA neurons was higher in auditory cortex. The late peak suggests that inhibitory circuitry is stabilized relatively late in sensory cortical development, and thus that GABA neurons could provide an important substrate for experience-dependent plasticity at late stages of development.

Developmental expression of calretinin immunoreactivity in the human retina and a comparison with two other EF-hand calcium binding proteins

This paper reports the localization pattern of calretinin, a calcium-binding protein, in the human retina during development, as studied by immunohistochemistry. A comparison is made of the cellular distribution of calretinin with two other calcium-binding proteins, calbindin and parvalbumin, recently reported by us in the human retina, and by parallel labeling with both antisera in the same tissues. At 11-12 weeks of gestation, calretinin immunoreactivity was expressed in many prospective ganglion cells of the central inner neuroblastic zone. At 16-17 weeks of gestation, the immunoreactivity was localized in the ganglion cell layer, inner plexiform layer, and in most differentiated amacrine, horizontal and cone cells located in the central (1-2 mm temporal from optic disc) to midperipheral parts of the retina. By midgestation (20-21 weeks), calretinin immunoreactivity was strongly developed in the cone photoreceptors. Parallel labeling with calbindin and parvalbumin antisera revealed that the calretinin-positive horizontal cells were somewhat smaller and less frequent and less intense than the calbindin- and parvalbumin-positive counterparts, at 16-21 weeks of gestation. No horizontal cells were calretinin immunopositive in the postnatal (four-month-old infant) and adult retinas examined. Also, at both stages, a few bipolar and cone cells were weakly immunoreactive. These observations suggest a critical role for calretinin in the development and maturation of a select class of horizontal cells. The widespread expression of immunoreactivity in the early ganglion cells indicates that calretinin may be involved in their differentiation. The weak immunoreactivity pattern noted in the adult photoreceptor and bipolar cells, and an apparent lack of immunoreactivity in the mature horizontal cells, tends to indicate that, unlike calbindin and parvalbumin, calretinin plays little role in the transport and physiological buffering of Ca2+ in these neurons of the human retina. It appears, however, that calretinin is predominantly involved in both processes in amacrine cells.

Illusive transience of parvalbumin expression during embryonic development of the primate spinal cord

Parvalbumin has been located by pre-embedding light- and electron microscopic immunohistochemical techniques in the spinal cords of monkey fetuses (Macaca fasciculata), ranging from E70 to E 123, and in young (P20) and young adult (3 years) Macaque monkeys. During the time window investigated, the main developmental events of parvalbumin-containing neural elements are that parvalbumin-positive dorsal root collaterals establish intercellular networks first around nerve cells of Clarke's nucleus, then in the motoneuron pool and finally in the upper dorsal horn. In each of these areas, location of the parvalbumin-positive network is gradually shifted from medial to lateral. Whenever an intercellular network is established, nerve cells innervated by parvalbumin-positive terminals of dorsal root collaterals start to express parvalbumin. Immunoreactivity of dorsal root axons is transient; it disappears first from the intercellular networks and, afterwards, also from the dorsal columns. However, the pericellular synaptic terminals and their post-synaptic nerve cells express parvalbumin into adulthood. It is concluded that some of the large (Type A) dorsal root ganglion cells are the first ones in the spinal reflex pathway to express parvalbumin, which is elicited and gradually increased in nerve cells synaptically innervated by parvalbumin-positive axon terminals. This seems to represent a specific case of activation (or desinhibiton) of the genome. Apparent "transience" of parvalbumin is due to the specific geometry of primary sensory neurons equipped with extremely long axonal processes, and the consequent specialities of axonal transport characteristics.

Cellular distribution of the calcium-binding proteins parvalbumin, calbindin, and calretinin in the neocortex of mammals: phylogenetic and developmental patterns

The three calcium-binding proteins parvalbumin, calbindin, and calretinin are found in morphologically distinct classes of inhibitory interneurons as well as in some pyramidal neurons in the mammalian neocortex. Although there is a wide variability in the qualitative and quantitative characteristics of the neocortical subpopulations of calcium-binding protein-immunoreactive neurons in mammals, most of the available data show that there is a fundamental similarity among the mammalian species investigated so far, in terms of the distribution of parvalbumin, calbindin, and calretinin across the depth of the neocortex. Thus, calbindin- and calretinin-immunoreactive neurons are predominant in layers II and III, but are present across all cortical layers, whereas parvalbumin-immunoreactive neurons are more prevalent in the middle and lower cortical layers. These different neuronal populations have well defined regional and laminar distribution, neurochemical characteristics and synaptic connections, and each of these cell types displays a particular developmental sequence. Most of the available data on the development, distribution and morphological characteristics of these calcium-binding proteins are from studies in common laboratory animals such as the rat, mouse, cat, macaque monkey, as well as from postmortem analyses in humans, but there are virtually no data on other species aside of a few incidental reports. In the context of the evolution of mammalian neocortex, the distribution and morphological characteristics of calcium-binding protein-immunoreactive neurons may help defining taxon-specific patterns that may be used as reliable phylogenetic traits. It would be interesting to extend such neurochemical analyses of neuronal subpopulations to other species to assess the degree to which neurochemical specialization of particular neuronal subtypes, as well as their regional and laminar distribution in the cerebral cortex, may represent sets of derived features in any given mammalian order. This could be particularly interesting in view of the consistent differences in neurochemical typology observed in considerably divergent orders such as cetaceans and certain families of insectivores and metatherians, as well as in monotremes. The present article provides an overview of calcium-binding protein distribution across a large number of representative mammalian species and a review of their developmental patterns in the species where data are available. This analysis demonstrates that while it is likely that the developmental patterns are quite consistent across species, at least based on the limited number of species for which ontogenetic data exist, the distribution and morphology of calcium-binding protein-containingneurons varies substantially among mammalian orders and that certain species show highly divergent patterns compared to closely related taxa. Interestingly, primates, carnivores, rodents and tree shrews appear closely related on the basis of the observed patterns, marsupials show some affinities with that group, whereas prototherians have unique patterns. Our findings also support the relationships of cetaceans and ungulates, and demonstrates possible affinities between carnivores and ungulates, as well as the existence of common, probably primitive, traits in cetaceans and insectivores.

Spatiotemporal patterns of ontogenetic expression of parvalbumin in the superior colliculi of rats and rabbits

We have examined the development of parvalbumin immunoreactivity in the superior colliculi (SC) of the perinatal and mature rats and rabbits. In mature animals, parvalbumin-expressing cells (PECs) and neuropil in the retinorecipient layers were distributed in a continuous single band extending throughout the entire extent of the colliculus, whereas those in the intermediate layers formed distinct, radially oriented patches. Parvalbumin was expressed for the first time on postconceptional day 34 (PCD 34, postnatal day 12) and PCD 42 (postnatal day 11) in the SC of rat and rabbit, respectively. During ensuing development, both the thickness of the parvalbumin-expressing band in the retinorecipient layers and the numbers of PECs in this band gradually increased, reaching adultlike values by PCD 44 and PCD 50 in the rat and rabbit, respectively. In the rat, monocular eye enucleations on PCD 23 resulted in approximately 55% reduction in the number of PECs in the retinorecipient layers of the contralateral colliculi examined on PCD 44 or PCD 50. Unilateral ablations of the entire visual cortex on PCD 23 (before the first corticotectal fibers from visual cortices reach the SC) or on PCD 28 (when about half of the corticotectal fibers have reached colliculus) resulted in, respectively, approximately 55% and approximately 25% relative reduction in the number of PECs in the retinorecipient layers of the ipsilateral colliculi examined on PCD 44 or PCD 50. We conclude that the ontogenetic expression of parvalbumin in most of PECs in the retinorecipient collicular layers is induced by the activity of the contralateral retinotectal and/or the activity of the ipsilateral corticotectal afferents.

The onset of parvalbumin-expression in interneurons of the rat parietal cortex depends upon extrinsic factor(s)

Parvalbumin (PV) belongs to the large family of EF-hand calcium-binding proteins and is an excellent marker for a subpopulation of GABAergic neocortical interneurons. During cortical development, PV first appears on postnatal day (P)8, in the infragranular layers; after P14, it also becomes apparent within the supragranular layers. However, nothing is known about the factors controlling its expression, which could involve functional activity, neuronal connectivity and/or neurotrophic factors. It being difficult to manipulate these parameters in vivo, their role may be more readily assessed in organotypic cultures, which are deprived of their subcortical afferents and efferents, and hence of subcortically derived neurotrophic factors and extrinsic functional activity. We prepared slices of the rat brain on P3, P5, P7 and P9, maintained them in culture for 2-5 weeks, and compared the temporal and spatial distribution pattern of PV-immunoreactivity within these slices with the in vivo situation. We found, first, that during late postnatal in vivo development and ageing, the number of PV-immunoreactive neurons in the parietal cortex decreases significantly, and second, that the expression of PV-immunoreactivity in the parietal cortex was markedly influenced by the phase of postnatal development at which slice cultures were explanted. In those removed on P7 and P9, the number of PV-immunoreactive cells, as well as the temporal and spatial distribution pattern of PV-immunoreactivity corresponded to the in vivo situation, but in explants obtained on P3 or P5, PV-immunoreactivity remained confined to layer V of the cortex, reminiscent of the expression profile manifested at the end of the second postnatal week in vivo. Also, the number of PV-immunoreactive cells in these cultures was significantly lower than in explants at the later stages. Our results indicate that the onset of PV-expression in the parietal cortex depends upon extrinsic cortical factors subsisting prior to P7. Once the production of this protein has been initiated, such influences are no longer required.

Calbindin-D28k in nerve cell nuclei

Calbindin-D28k is a member of the large EF-hand family of calcium-binding proteins, that is believed to function, in part as a cytosolic calcium buffer. Recent studies have demonstrated that cells containing Calbindin-D28k are protected from degeneration caused by conditions that elevate intracellular calcium concentrations. Since its initial discovery in 1966, Calbindin-D28k has been localized in the cytoplasm of many neuronal populations, but its nuclear localization has been uncertain. Using light and electron microscopic immunohistochemistry, and nuclear fractionation methods, we demonstrate localization of Calbindin-D28k not only in the cytoplasm, but also in the nucleus of rodent midbrain dopaminergic neurons and cerebellar Purkinje cells. The Calbindin-D28k immunoreactive staining intensity in the nucleus was routinely equal or greater than that in the cytoplasm. Since calcium signals are propagated to the nucleus, where they can regulate gene expression, the existence of nuclear Calbindin-D28k has important implications for cellular function.

Parvalbumin-immunoreactive neurons in the hippocampal formation of Alzheimer's diseased brain

The number and topographic distribution of immunocytochemically stained parvalbumin interneurons was determined in the hippocampal formation of control and Alzheimer's diseased brain. In control hippocampus, parvalbumin interneurons were aspiny and pleomorphic, with extensive dendritic arbors. In dentate gyrus, parvalbumin cells, as well as a dense plexus of fibers and puncta, were associated with the granule cell layer. A few cells also occupied the molecular layer. In strata oriens and pyramidale of CA1-CA3 subfields, parvalbumin neurons gave rise to dendrites that extended into adjacent strata. Densely stained puncta and beaded fibers occupied stratum pyramidale, with less dense staining in adjacent strata oriens and radiatum. Virtually no parvalbumin profiles were observed in stratum lacunosum-moleculare or the alveus. Numerous polymorphic parvalbumin neurons and a dense plexus of fibers and puncta characterized the deep layer of the subiculum and the lamina principalis externa of the presubiculum. In Alzheimer's diseased hippocampus, there was an approximate 60% decrease in the number of parvalbumin interneurons in the dentate gyrus/CA4 subfield (P<0.01) and subfields CA1-CA2 (P<0.01). In contrast, parvalbumin neurons did not statistically decline in subfields CA3, subiculum or presubiculum in Alzheimer's diseased brains relative to controls. Concurrent staining with Thioflavin-S histochemistry did not reveal degenerative changes within parvalbumin-stained profiles. These findings reveal that parvalbumin interneurons within specific hippocampal subfields are selectively vulnerable in Alzheimer's disease. This vulnerability may be related to their differential connectivity, e.g., those regions connectionally related to the cerebral cortex (dentate gyrus and CA1) are more vulnerable than those regions connectionally related to subcortical loci (subiculum and presubiculum).

Neurofilament and calcium-binding proteins in the human cingulate cortex

Functional imaging studies of the human brain have suggested the involvement of the cingulate gyrus in a wide variety of affective, cognitive, motor, and sensory functions. These studies highlighted the need for detailed anatomic analyses to delineate its many cortical fields more clearly. In the present study, neurofilament protein, and the calcium-binding proteins parvalbumin, calbindin, and calretinin were used as neurochemical markers to study the differences among areas and subareas in the distributions of particular cell types or neuropil staining patterns. The most rostral parts of the anterior cingulate cortex were marked by a lower density of neurofilament protein-containing neurons, which were virtually restricted to layers V and VI. Immunoreactive layer III neurons, in contrast, were sparse in the anterior cingulate cortex, and reached maximal densities in the posterior cingulate cortex. These neurons were more prevalent in dorsal than in ventral portions of the gyrus. Parvalbumin-immunoreactive neurons generally had the same distribution. Calbindin- and calretinin-immunoreactive nonpyramidal neurons had a more uniform distribution along the gyrus. Calbindin-immunoreactive pyramidal neurons were more abundant anteriorly than posteriorly, and a population of calretinin-immunoreactive pyramidal-like neurons in layer V was found largely in the most anterior and ventral portions of the gyrus. Neuropil labeling with parvalbumin and calbindin was most dense in layer III of the anterior cingulate cortex. In addition, parvalbumin-immunoreactive axonal cartridges were most dense in layer V of area 24a. Calretinin immunoreactivity showed less regional specificity, with the exception of areas 29 and 30. These chemoarchitectonic features may represent cellular reflections of functional specializations in distinct domains of the cingulate cortex.