Peripheral target contact regulates Ca2+ channels in the cell bodies of bullfrog sympathetic ganglion B-neurons

Tyrosine-hydroxyrase immunohistochemistry demonstrated that a single inject ion of 120 mg/kg 6-hydroxydopamine (6-OHDA) reversibly disconnected bullfro g sympathetic ganglia from their peripheral targets. This was correlated wi th a decrease in sympathetic outflow to the eyes and a reversible decrease in pupil diameter. 6-OHDA did not damage the cell bodies of ganglionic neur ons. Calcium channel current in ganglionic B-neurons, (measured at - 10 mV; holding potential -60 mV; Ba2+ as charge carrier; I-BA) was reduced. It re ached a minimum of about 40% of control amplitude 7-14 days after 6-OHDA in jection and recovered to 73% of control amplitude after 63 days. 6-OHDA ind uced loss and recovery of functional sympathetic innervation of peripheral target tissues, as determined by measurement of pupil diameter, occurred at a similar rate. Thus, pupil diameter attained minimum values 7-14 days aft er 6-OHDA treatment and recovered to 81% of control after 63 days. The prop erties of Ca2+ channels in sympathetic neurons are, therefore, determined b y continuity of contact with peripheral target. 6-OHDA also decreased the p eak amplitude and duration of the afterhyperpolarization (a.h.p) that follo ws the action potential (a.p.). The rate of recovery of a.h.p duration was more rapid than the rate of recovery of peak a.h.p. amplitude. This may ref lect known differences in properties of two types of Ca2+-sensitive K+ curr ents, I-C and I-AHP. I-C, which is responsible for the peak amplitude of th e a.h.p has a low affinity for Ca2+, whereas I-AHP, which determines a.h.p. duration, has higher Ca2+ affinity. (C) 2001 Elsevier Science B.V. All rig hts reserved.