A study on preganglionic connections and possible viscerofugal projections from urinary bladder intramural ganglia to the caudal mesenteric ganglion in the pig

The present study was designed to (1) ascertain the distribution and immunohistochemical characteristics of sympathetic preganglionic neurons supplying the caudal mesenteric ganglion (CaMG) and (2) verify the existence of viscerofugal projections from the urinary bladder trigone intramural ganglia (UBT-IG) to the CaMG in female pigs (n = 6). Combined retrograde tracing and immunofluorescence methods were used. Injections of the neuronal tracer Fast Blue (FB) into the right CaMG revealed no retrogradely labelled (FB-positive; FB+) nerve cells in the intramural ganglia; however, many FB+ neurons were found in the spinal cord sympathetic nuclei. Double-labelling immunohistochemistry revealed that nearly all (99.4 +/- 0.6%) retrogradely labelled neurons were cholinergic (choline acetyltransferase-positive; ChAT(+)) in nature. Many FB+/ChAT(+) perikarya stained positive for vesicular acetylcholine transporter (63.11 +/- 5.34%), neuronal nitric oxide synthase (53.48 +/- 9.62%) or cocaine- and amphetamine-regulated transcript peptide (41.13 +/- 4.77%). A small number of the retrogradely labelled cells revealed immunoreactivity for calcitonin gene-related peptide (7.60 +/- 1.34%) or pituitary adenylate cyclase-activating polypeptide (4.57 +/- 1.43%). The present study provides the first detailed information on the arrangement and chemical features of preganglionic neurons projecting to the porcine CaMG and, importantly, strong evidence suggesting the absence of viscerofugal projections from the UBT-IG.