Specific patterns of immunoreactivity in neuronal elements of the anterior major pelvic ganglion of the male guinea-pig.

The anterior major pelvic ganglion (AMPG) of the male guinea-pig has been found to consist of three principal components. The presence of a cholinergic component was determined by the demonstration of cytoplasmic and nerve fibre acetylcholinesterase activity. A noradrenergic component was demonstrated by immunoreactivity (IR) of the catecholamine-synthesising enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) in neuronal perikarya. The AMPG also had a peptidergic component which may or may not sub-classify the cholinergic and noradrenergic components. Neuropeptide Y (NPY)-, vasoactive intestinal peptide (VIP)-, and atrial natriuretic factor (ANF)-immunoreactivities were seen in neuronal perikarya, nerve fibres and nerve terminals/varicosities, while somatostatin (SOM)-IR was restricted to neuronal perikarya. Substance P (SP)-IR was present in a dense network of varicose nerve fibres. However, on a rare occasion SP-IR was observed in neuronal perikarya. Enkephalin (ENK)-IR occurred in a sparsely distributed plexus of varicose nerve fibres. The analysis of adjacent serial sections demonstrated distinct patterns of neuropeptide coexistence in AMPG neurons. NPY-IR was colocalised to a subpopulation of TH-IR neuronal perikarya. NPY-IR was also colocalised with VIP-IR in non-TH-IR neuronal perikarya. VIP-IR occurred together with AChE in particular neuronal perikarya. The relationship between immunoreactive neuronal perikarya and immunoreactive nerve terminals was investigated. SP-IR nerve terminals were closely related to neuronal perikarya exhibiting VIP-, NPY-, or TH-IR. TH-IR neuronal perikarya were also abutted by ENK-IR nerve terminals. VIP- and NPY-immunoreactive neuronal perikarya were abutted by two nerve terminal types: one immunoreactive for VIP, the other for NPY. DBH-IR neuronal perikarya received AChE-positive varicosities while AChE-positive neurons were abutted by DBH-IR varicose nerve fibres. AChE-positive varicosities were also closely related to neuronal perikarya possessing VIP-IR and AChE activity.