Endogenous dopamine and serotonin release from the explanted rat tuberohypophyseal system: effects of electrical stimulation and neurotensin.

Excised blocks of brain tissue encompassing the hypothalamic periventricular nucleus, arcuate nucleus, infundibular stalk and attached pituitary neurointermediate lobe (NIL) were obtained from rats and perifused in vitro. The intact tuberohypophyseal dopaminergic pathway projecting from cell bodies in the hypothalamus to terminations in the pars intermedia and posterior lobes was thus isolated. An electrode placed in the explant delivered electrical pulses at various frequencies to hypothalamic targets. Products released in the immediate vicinity of the NIL were continuously collected and assayed for dopamine and serotonin content. Electrical stimulation of the arcuate nucleus from 1.0 - 10.0 Hz produced a frequency-dependent increase in dopamine, but not serotonin, release from the NIL. Stimulation of the infundibular stalk, however, elevated the release of both neurotransmitters. Addition of neurotensin (0.001 - 1.0 microM) to the bathing media produced a concentration-dependent increase in dopamine, but not serotonin, release. These experiments demonstrate the utility of the tuberohypophyseal explant as a model for use in the study of dopaminergic neuronal function in this neuroendocrine axis.