Abstract 324 Poster Session I, Saturday, 5/1 (poster 159)

Pituitary adenylate cyclase activating peptide (PACAP) is a member of the secretin, glucagon and vasoactive intestinal peptide (VIP) family of peptides which act as neuroendocrine hormones and neurotransmitters. There are two types of PACAP receptors and five splice variants of the Type 1 PACAP receptor. These splice variants differ in the length of the third intracellular loop with differential signal transduction mechanisms. Type 1 PACAP receptors have been shown to be present in the embryonic brain by PCR but the cellular localization and subtype differentiation have yet to be examined.

Oligonucleotide probes for the Type 1 PACAP receptors as well as for the short, hip and hop2 splice variants were designed and synthesized. In situ hybridization was performed on embryonic day 7 (E7) through postnatal day 0 (P0) tissues as well as postnatal day 7 (P7) and adult mouse brains. Type 1 PACAP receptors were not apparent until E9 when they appeared in the floor plate of the developing neuroepithelium. By E13, moderate expression was observed in all CNS tissues with greatest abundance in the floor plate and the circumventricular germinal epithelium. Between E18 and P0, additional expression was detected in the superficial cortical layers and hypothalamic nuclei. By P7, the expression remained moderate in all CNS tissues but the adult pattern was becoming apparent. In the adult CNS, the expression was abundant in the olfactory bulb, hippocampus, hypothalamus, cortex and cerebellum. The short PACAP splice variant was shown to be responsible for the signal in the floor plate and the germinative neuroepithelium. Expression of the hip and hop2 splice variants was not apparent until E13, after which time, they were expressed throughout the CNS but not in the floor plate.

Splice variants of the PACAP 1 receptor are expressed early in the postimplantation embryo with differential regulation and ontogenic localization. The presence of PACAP receptors in the floor plate and germinative neuroepithelium indicates an important role for PACAP in the regulation of growth and development of the nervous system. Differential expression of PACAP splice variants with alternative mechanisms of signal transduction may be important for controlling neuronal differentiation.

Supported by the NICHD Intramural Program