CORRELATION OF ELECTROPHYSIOLOGY, NEUROCHEMISTRY AND AXONAL PROJECTIONS OF GUINEA-PIG SPHINCTER OF ODDI NEURONS

Sphincter of Oddi (SO) ganglia are comprised of two main types of neur ones based either on their electrical or neurochemical properties. Thi s study investigated whether any correlation exists between the electr ical and neurochemical properties of these cells. SO neurones were cha racterized electrically as either Tonic or Phasic cells, labelled with neurobiotin, fixed, and processed for B-nicotinamide adenine dinucleo tide phosphate diaphorase (NADPH-DA) staining and choline acetyltransf erase immunoreactivity to identify whether electrically characterized neurones were nitrergic or cholinergic. A total of 119 cells were anal ysed in this manner; 45% of cells were Tonic and 37% were Phasic. An e quivalent number of Tonic (58.1%, 18/31) and Phasic cells (60%, 22/35) were choline acetyltransferase (ChAT) positive. Three of 34 Phasic ce lls were NADPH-DA positive, whereas 11/33 Tonic cells were NADPH-DA po sitive. In none of the preparations was ChAT immunoreactivity and NADP H-DA reactivity ever observed in the same neurone. Calretinin immunore activity was present in a subpopulation of both Tonic and Phasic neuro nes. No correlation was observed between the direction of axon project ions and the electrophysiological or neurochemical properties of the c ell. These results suggest that there is a lack of correlation between the electrical properties and the neurochemical content of SO neurone s. Various explanations for these findings are discussed.