Distribution of PACAP in the Mammalian Nervous System

PACAP is widely distributed in the central and peripheral nervous systems of various mammalian species. To demonstrate PACAP or its mRNA several methods were used: immunohistochemistry, radioimmunoassay, sandwich-enzyme immunoassay, in situ hybridization, and reverse transcription polymerase chain reaction. High levels of PACAP measured by radioimmunoassay are due to the great number of PACAP containing cell bodies or dense fiber network. PACAP immunoreactive cell bodies were observed in several hypothalamic nuclei and in various extrahypothalamic structures, mainly in the limbic system. PACAP is also present in the retinohypothalamic tract and in the centrifugal visual system. In the periphery, PACAP was demonstrated in the sensory, motor, and autonomic nervous systems. Autonomic PACAP immunoreactive fibers innervate glands and smooth muscle layers of viscera and vessels. This chapter summarizes the most important data available in the literature up to now.