Presynaptic alpha 2- and dopamine-receptor-mediated inhibitory mechanisms and dopamine nerve terminals in the rat hypothalamus.
Slices of rat hypothalamus were superfused and endogenous release of dopamine was measured. The potassium (20 mM)-evoked release in the presence of tetrodotoxin was Ca2+-dependent. The evoked release was reduced by adrenaline 10(-7) M, with a potent alpha 2-agonist action, and was reduced by a dopamine receptor agonist, apomorphine 10(-7) M, in the presence of yohimbine 10(-6) M. These inhibitory effects were antagonized by an alpha 2-antagonist, yohimbine 10(-6) M, and a dopamine receptor antagonist, (-)-sulpiride 10(-7) M, respectively. The electrically evoked release of DA was enhanced by (-)-sulpiride but not by the (+)-isomer. Taking into consideration that yohimbine at a relatively high concentration (10(-6) M) increases the electrically evoked DA release, it is suggested that DA release in the rat hypothalamus may be mediated not only via autoreceptors but also in part via presynaptic alpha 2-receptors on the DA nerve terminals.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D046508:Culture Techniques; D004558:Electric Stimulation; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009433:Neural Inhibition; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology*; D013469:Sulpiride / Q000494:pharmacology; D013569:Synapses / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D011942:Receptors, Adrenergic, alpha; D011954:Receptors, Dopamine; D015016:Yohimbine; D013779:Tetrodotoxin; D013469:Sulpiride; D001058:Apomorphine; D011188:Potassium