Properties of tachykinin receptors examined by intracellular recording from chick sympathetic ganglia.

The physiological and pharmacological properties of tachykinin receptors have been examined by intracellular recording from intact chick lumbar sympathetic ganglia in vitro. In these ganglia, both substance P and eledoisin are potent agonists, producing a slowly developing depolarization in ganglion neurons which is associated with an increase in input resistance and inhibition of the M-current. In contrast, physalaemin is a considerably less potent tachykinin in chick ganglia, and kassinin is without activity even at high doses. The rank order of potencies of tachykinin agonists is consistent from cell to cell, indicating that a single type of tachykinin receptor may be responsible for the observed responses. A putative tachykinin antagonist, (D-Arg1,D-Pro2,D-Trp7,9,Leu11)-substance P, exhibits no intrinsic activity in the ganglia but does block the responses to subsequently applied substance P and eledoisin. This tachykinin antagonist also inhibits a portion of the slow excitatory postsynaptic potential (EPSP) elicited in ganglion neurons by repetitive nerve stimulation. Since substance P has been identified within nerve fibers in the ganglia, it appears that this or another endogenous tachykinin mediates a portion of the slow EPSPs observed in the ganglia. Acetylcholine acting via muscarinic receptors is also capable of producing slow EPSPs in the ganglia, since perfusion with atropine can reduce the size of some slow EPSPs. It is concluded that chick sympathetic neurons contain both tachykinin and muscarinic receptors, and that these receptors are involved in slow synaptic responses in the ganglion neurons which increase the excitability of the cells.