The hypothalamohypophyseal system in vitro: electrophysiology of the pars intermedia and evidence for both excitatory and inhibitory inputs.
The purpose of this study was to better assess the function of catecholamine-containing nerve terminals in the pituitary pars intermedia lobe. Hypothalamohypophyseal explants, which included the intact mediobasal hypothalamus (MBH), median eminence, infundibular stalk and the neurointermediate lobe, were obtained from 2-3-week-old male and female albino rats. The tissue was placed in a perfusion chamber and maintained under physiological conditions for up to 12 h. A set of bipolar stimulating electrodes was positioned on the surface of the median eminence, infundibular stalk or the rostroventral arcuate nucleus of the MBH. A microelectrode recorded electrical activity in the pars intermedia gland. Two types of spontaneous action potentials were found; fast 2-4 ms duration neural fiber type spikes and slower 7-10 ms duration spikes probably derived from non-neural endocrine cells. Single-pulse electrical stimulation at all 3 sites evoked both kinds of potentials, while trains of stimuli (0.1-20 Hz) decreased or completely inhibited the basal firing rate of the slower ones. Application of the neuroleptic. L-sulpiride (0.01, 0.1 or 1.0 mumol), to the perfusion medium increased the spontaneous endocrine cell activity and blocked the stimulus-induced inhibition in the explants but had no effect on the activity in isolated pituitaries. Dopamine (0.1 mumol), which is known to inhibit the secretion of pro-opiomelanocortin peptides, reversibly suppressed the spontaneous endocrine cell potentials. These observations support a hypothesis for the presence of a functional tuberohypophyseal dopamine inhibitory system and a possible, but as yet unidentifiable, excitatory system in the pars intermedia. Thus, hypothalamohypophyseal explants can be used to elucidate specific information on this type of neuroendocrine axis.
Davis
M D
MD
Haas
H L
HL
Lichtensteiger
W
W
D000200:Action Potentials; D000320:Adrenergic Fibers / Q000502:physiology; D000818:Animals; D004298:Dopamine / Q000502:physiology*; D005260:Female; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009431:Neural Conduction; D009433:Neural Inhibition; D009434:Neural Pathways / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D009435:Synaptic Transmission
D004298:Dopamine