Colocalization of prosomatostatin‐derived peptides in the caudate‐putamen of the rat

Abstract

In the striatum of rat, somatostatin 14, somatostatin 28, and somatostatin 28(1-12) have previously been localized within a small population of medium aspiny local circuit neurons. Because all three peptide fragments are generated through the cleavage of prosomatostatin by different converting enzymes, the possibility for differential expression of these peptides exists. In order to investigate this possibility, frozen sections were collected from the brains of adult female Wistar rats fixed with 4% paraformaldehyde and double labelled using immunocytochemistry and in situ hybridization. Sections were first processed for somatostatin 14, somatostatin 28, or somatostatin 28(1-12) by using the avidin-biotin complex immunocytochemical technique followed by in situ hybridization using 35S-labelled antisense riboprobes to somatostatin mRNA. The results of such analysis revealed that somatostatin 28 and somatostatin mRNA are 100% colocalized. Somatostatin 14 and somatostatin 28(1-12), in contrast, are only present within 66% of the neurons that express somatostatin mRNA. Examination of the anatomical distribution of neurons that express both somatostatin mRNA and somatostatin 14 or somatostatin 28(1-12) protein reveals that these neurons are present throughout the caudate-putamen of rat but are more prevalent in the ventromedial regions. Neurons that express somatostatin mRNA but not somatostatin 14 or somatostatin 28(1-12) are also present throughout the caudate-putamen but are most numerous within a dorsolateral strip just beneath the corpus callosum. These results suggest that the somatostatin neuron population within the rat caudate-putamen is actually composed of two smaller subpopulations based on neuropeptide content. The first subpopulation contains somatostatin 28 and constitutes one-third of the total somatostatin population, whereas the other contains somatostatin 28, somatostatin 14, and somatostatin 28(1-12) and represents the remaining two-thirds of the cells that express somatostatin mRNA.

Neurogenesis in the mammalian neostriatum and nucleus accumbens: Parvalbumin-immunoreactive GABAergic interneurons

“…Unlike PV-positive and cholinergic interneurons, somatostatin-containing neurons do not show a clear dorsoventral, rostrocaudal, or mediolateral gradient of neurogenesis . This suggests the existence of multiple subtypes of somatostatin-positive striatal neurons (Rushlow et al, 1994(Rushlow et al, , 1996, which may undergo final mitosis at different ages and display diverse neurogenetic gradients. Neurogenesis of CR-immunoreactive GABAergic striatal interneurons (Bennett and Bolam, 1993;Hussain et al, 1996;Sadikot et al, 1996) has not been studied in detail.…”

Somatostatin and the patch/matrix compartments of the rat caudate-putamen

“…Previously, we have demonstrated heterogeneity in the striatum with respect to the localization of pro-SOMderived peptides (Rushlow et al, 1994). SOM neurons that contain SOM 14, SOM 28, and SOM 2 N -1 2 ) are located orimarilv in the more ventral and medial asneck of t h e CPu.…”

“…Recently, we have demonstrated that different SOM peptides are distributed heterogeneously in the rat CPu (Rushlow et al, 1994). SOM 28 and SOM mRNA are 100% colocalized, whereas SOM 14 and SOM 28(1-12) are present within only 64% of the neurons that contain SOM mRNA.…”