Noradrenergic responses of spinal neurons in locus coeruleus-spinal cord co-cultures.

Locus coeruleus (LC) explants were co-cultured with dissociated spinal neurons of mice. Nerve fibers exhibiting catecholamine fluorescence radiated from the explants and frequently invested spinal cord (SC) neurons close to the explants. Electrical stimulation of the explant and iontophoretic application of norepinephrine evoked a spectrum of slow depolarizing, hyperpolarizing, and biphasic responses in the SC cells. The responses to LC stimulation and to application of norepinephrine were usually similar in a given cell. The depolarizing responses were associated with an increase in apparent input resistance and pharmacologic tests indicated that the responses were mediated by alpha-receptors. Neurons in regions innervated by catecholamine-containing fibers usually gave depolarizing responses to LC stimulation and such neurons had a very high probability of exhibiting depolarizing responses to applied norepinephrine. It would appear that either locus coeruleus explants favored the survival of cells with alpha-receptors or expression of these receptors in SC neurons was induced by innervation of the neurons by locus coeruleus axons.