CORTISTATIN IS EXPRESSED IN A DISTINCT SUBSET OF CORTICAL INTERNEURONS

Cortistatin is a presumptive neuropeptide that shares 11 of its 14 ami no acids with somatostatin. In contrast to somatostatin, administratio n of cortistatin into the rat brain ventricles specifically enhances s low wave sleep, apparently by antagonizing the effects of acetylcholin e on cortical excitability, Here we show that preprocortistatin mRNA i s expressed in a subset of GABAergic cells in the cortex and hippocamp us that partially overlap with those containing somatostatin. A signif icant percentage of cortistatin-positive neurons is also positive for parvalbumin, In contrast, no colocalization was found between cortista tin and calretinin, cholecystokinin, or vasoactive intestinal peptide. During development there is a transient increase in cortistatin-expre ssing cells in the second postnatal week in all cortical areas and in the dentate gyrus. A transient expression of preprocortistatin mRNA in the hilar region at P16 is paralleled by electrophysiological changes in dentate granule cells, Together, these observations suggest mechan isms by which cortistatin may regulate cortical activity.