Pituitary adenylate cyclase activating polypepetide is expressed by developing rat Purkinje cells and decreases the number of cerebellar gamma-amino butyric acid positive neurons in culture.

The neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) is expressed in various parts of the developing and adult rat brain, including the cerebellum. In situ hybridization was employed to localize the precise site of mRNA expression for PACAP and PACAP receptor I (PRI). During prenatal cerebellar development, PACAP mRNA was present in developing Purkinje cells and some deep cerebellar nuclei, whilst PRI mRNA was expressed by adjacent cells in the Purkinje cell layer (PCL). There was a shift in PRI mRNA expression to the external germinal cell layer around birth. PACAP decreased the number of neurons positive for the inhibitory neurotransmitter gamma-amino butyric acid (GABA) in cultures from embryonic cerebellum, but did not affect overall cell survival. In conclusion, our results show the pattern of PACAP mRNA expression in embryonic cerebellum and suggest a physiological role for PACAP on GABAergic cerebellar neurons.