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.

Parvalbumin-like immunostaining in the cat inferior colliculus. Light and electron microscopic investigation.

The presence of the calcium-binding protein parvalbumin (PV) was studied in neuronal elements of the cat's inferior colliculus (IC) by means of light and electron microscopic immunocytochemistry. Immunostaining of PV was detected in all three main parts of the IC. Several subtypes of large neurons that differed in size and shape were immunostained, comprising approx. 15% of the total number of PV-containing neurons. Approx. half of the labeled neurons were medium sized. Two types of small neurons were found to be PV synthesizing, and comprised approx. 35% of the total PV-containing population. Ultrastructurally, many dendrites were heavily immunolabeled, and the reaction product was present in dendritic spines as well. Several types of synaptic boutons contained reaction product, and terminated on both labeled and unlabeled postsynaptic targets forming asymmetric and symmetric synapses. Approx. 70% of all PV-immunolabeled terminals contained round synaptic vesicles and formed asymmetric synapses. The majority of these boutons were of the "large round" type and corresponded to the terminals of cochlear nuclei. A lower number were of the "small round" type, and were probably corticotectal terminals. The remaining 30% of PV-containing terminals contained pleomorphic or elongated vesicles and formed symmetric synapses. These terminals corresponded with "P" and "F1" bouton types. Part of these boutons appeared to arise from nuclei of the lateral lemniscus and the superior olive, and a certain percentage likely represented endings of inhibitory interneurons.