The morphology and distribution of parvalbumin-immunoreactive neurons (PV-ir) were studied in the human claustrum. PV-ir neurons were observed throughout the claustrum, with the highest numbers noted in the central (broadest) portion as compared with the dorsal and ventral aspects. Reaction product was evident in the neuronal perikarya, dendritic processes, and spines. In the majority of these labeled neurons, the cytoplasm was devoid of lipofuscin pigment. Cell bodies varied widely in both shape and size, ranging from oval and small, to multipolar and large. PV-ir neurons were classified into two groups, primarily based on dendritic morphology: spiny neurons with long and straight dendrites, and aspiny neurons with thin and curving dendritic processes. PV-ir fibers were seen throughout the neuropil, with many immuno-positive puncta noted.

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We studied the topographical distribution and morphological characteristics of NADPH-diaphorase-positive neurons and fibers in the human claustrum. These neurons were seen to be heterogeneously distributed throughout the claustrum. Taking into account the size and shape of stained perikarya as well as dendritic and axonal characteristics, Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd)-positive neurons were categorized by diameter into three types: large, medium and small. Large neurons ranged from 25 to 35 μm in diameter and typically displayed elliptical or multipolar cell bodies. Medium neurons ranged from 20 to 25 μm in diameter and displayed multipolar, bipolar and irregular cell bodies. Small neurons ranged from 14 to 20 μm in diameter and most often displayed oval or elliptical cell bodies. Based on dendritic characteristics, these neurons were divided into spiny and aspiny subtypes. Our findings reveal two populations of NADPHd-positive neurons in the human claustrum—one comprised of large and medium cells consistent with a projection neuron phenotype, the other represented by small cells resembling the interneuron phenotype as defined by previous Golgi impregnation studies.

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Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. Nevertheless, there are little data about the neuronal nitric oxide synthase immunoreactivity (nNOS-ir) in the vestibular complex of a cat. In this respect, the aims of this study were to: (1) demonstrate nNOS-ir in the neurons and fibers, from all major and accessory vestibular nuclei; (2) describe their light microscopic morphology and distribution; (3) investigate and analyze the ultrastructure of the NOS I-immunopositive neurons, fibers, and synaptic boutons. For demonstration of the nNOS-ir, the peroxidase-antiperoxidase-diaminobenzidin method was applied. Immunopositive for nNOS neurons and fibers were present in all major and accessory vestibular nuclei. On the light microscope level, the immunopositive neurons were different in shape and size. According to the latter, they were divided into four groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), large type I (with diameter from 30 to 40 microm), and large type II (with diameter greater than 40 microm). On the electron microscope level, the immunoproduct was observed in neurons, dendrites, and terminal boutons. According to the ultrastructural features, the neurons were divided into three groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), and large (with diameter greater than 30 microm). At least two types of nNOS-ir synaptic boutons were easily distinguished. As a conclusion, we hope that this study will contribute to a better understanding of the functioning of the vestibular complex in cat and that some of the data presented could be extrapolated to other mammals, including human.