The distribution and colocalization of neuropeptides in perivascular nerves innervating the large arteries and veins of the snake, Elaphe obsoleta.

Single- and dual-labelling immunohistochemistry were used to determine the distribution and coexistence of neuropeptides in perivascular nerves of the large arteries and veins of the snake, Elaphe obsoleta, using antibodies for vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide, neuropeptide Y, galanin, somatostatin, and leu-enkephalin. Blood vessels were sampled from four regions along the body of the snake: region 1, arteries and veins anterior to the heart; region 2, central vasculature 5 cm anterior and 10 cm posterior to the heart; region 3, arteries and veins in a 30-cm region posterior to the liver; and region 4, dorsal aorta and renal arteries, renal and intestinal veins, 5-30 cm cephalad of the vent. A moderate to dense distribution of vasoactive intestinal polypeptide-like immunoreactive fibres was found in most arteries and veins of regions 1-3, but fibres were absent from the vessels of region 4. The majority of vasoactive intestinal polypeptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were unaffected by either capsaicin or 6-hydroxydopamine (6-OHDA) pretreatment. In the anterior section of the snake, the vagal trunks contained many cell bodies with colocalized vasoactive intestinal polypeptide and substance P-like immunoreactivity. It is suggested that the vasoactive intestinal polypeptide/substance P-like immunoreactive cell bodies and fibres are parasympathetic postganglionic nerves. Neuropeptide Y-like immunoreactive fibres were observed in all arteries and veins, being most dense in regions 3 and 4. The majority of these fibres also contained colocalized galanin-like immunoreactivity, and were absent in tissues from 6-OHDA pretreated snakes, suggesting that neuropeptide Y and galanin are colocalized in adrenergic nerves. A small number of neuropeptide Y-like immunoreactive fibres contained vasoactive intestinal polypeptide but not galanin, and were unaffected by 6-OHDA treatment. All calcitonin gene-related peptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were observed in all vessels, being particularly dense in the carotid artery and jugular veins. All calcitonin gene-related peptide/substance P-like immunoreactive fibres appeared damaged after capsaicin treatment suggesting they represent fibres from afferent sensory neurons. A sparse plexus of somatostatin-like immunoreactive fibres was observed in the vessels only from region 4. No enkephalin-like immunoreactive fibres were found in any blood vessels from any region. This study provides morphological evidence to suggest that there is considerable functional specialization within the components of the rat snake peripheral autonomic system controlling the circulation, in particular the regulation of venous capacitance.