Is CRF a ganglionic transmitter or modulator in the cat sudomotor pathway?

The presence of corticotrophin releasing factor (CRF)-like immunoreactivity distinguishes a subset of cat sympathetic preganglionic neurons which supplies sweat glands. It is abundant in their terminals in the stellate ganglion. We sought first to determine whether this immunoreactivity is due to true CRF, then to test whether CRF plays any role in ganglionic transmission in the cat sudomotor pathway. CRF-immunoreactive material extracted from cat stellate ganglia and hypothalamus were eluted on HPLC at equivalent retention times, slightly less than that of standard sheep CRF. In chloralose-anaesthetised cats, sheep CRF (0.13, 1.3 and 13 μg/kg, i.v.) raised plasma immunoreactive ACTH levels by between 3- and 300-fold. Submaximal stimulus trains delivered to pre- or postganglionic nerves of the right stellate ganglion evoked electrodermal response (EDR, a measure of sweat gland activity) in the right forepaw pad as well as increases in heart rate and blood pressure. Exogenous sheep CRF (dose range 130 ng/kg to 13 mg/kg) given close-arterially to the stellate ganglion in 5 chloralose-anaesthetised cats had no consistent effect on either baseline or preganglionically-evoked EDR. Given i.v. at 13 μg/kg to four further cats, sheep CRF caused no significant change in mean baseline or mean preganglionically-evoked EDP ( P > 0.05; CUSUM test). Hexamethonium (10 or 30 mg/kg i.v.) abolished the EDR to preganglionic nerve stimulation (7/7 cats). Increasing preganglionic stimulus voltage, frequency and train duration failed to show any hexamethonium-resistant component of the EDR, although such effects were evident in the cardioaccelerator pathway. We conclude that cat preganglionic sudomotor neurons contain true CRF, although the cat peptide is not identical to that of the sheep. Exogenous CRF had no measurable effect on postganglionic neurons or on ganglionic transmission in the cat sudomotor pathway. Ganglionic transmission in the sudomotor pathway, unlike that to the heart, is entirely nicotinic. The function of CRF in cat sudomotor pathway remains unknown.