Colocalization of neuropeptides with calcium-binding proteins in the claustral interneurons during postnatal development of the rat.

The claustrum is a relatively large telencephalic structure, situated close to the border of the neo- and allocortical regions. Its neuronal population consists of glutamatergic, projecting neurons and GABA-ergic interneurons, characterized by occurrence of numerous additional biochemical markers. The postnatal development of these latter neurons has not been extensively studied. Revealing the characteristic patterns of colocalizations between selected markers may shed some light on their function and origin. We investigated the colocalization patterns between three neuropeptides: neuropeptide Y, somatostatin, vasoactive intestinal polypeptide and three calcium-binding proteins: calbindin D28k, calretinin, parvalbumin in the interneurons of the rat claustrum during a four-month postnatal period (P0-P120; P: postnatal day). Our studies revealed the following types of colocalizations: neuropeptide Y with calbindin D28k, calretinin or parvalbumin; somatostatin with calbindin D28k; vasoactive intestinal polypeptide with calretinin. Only vasoactive intestinal polypeptide- and calretinin-containing, double-labeled neurons were present at the day of birth, whereas the other double-labeled neurons appeared at later stages of development. The ratios of colocalizing neurons to single-labeled neurons in each type of colocalization were differentiated and reached the highest value (51%) for vasoactive intestinal polypeptide- and calretinin-double-labeled neurons. In conclusion, the claustral interneurons represent differentiated population in respect to the occurrence of neuropeptides and calcium-binding proteins. The expression of studied substances is changing during the postnatal period.

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.