Interaction of morphine, etorphine and enkephalins with dopamine-stimulated adenylate cyclase of monkey amygdala.

Adenylate cyclase activity (AC) of homogenates of monkey amygdaloid nucleus was approximately doubled in the presence of dopamine (10 micrometer). Morphine, etorphine, and several enkephalin analogs (met-enkephalin, D-ala2-met-enkephalin, and D-met2, pro5-enkephalinamide) were capable of inhibiting the stimulation of AC produced by dopamine (90-100% with etorphine or D-ala2-met-enkephalin). Unlike morphine and etorphine, the peptides exhibited bell-shaped dose-response curves for this inhibition with maximal effects at approximately 1 X 10(-7) M, but negligible effects at 1 X 10(-5) M. Under the conditions studied, only etorphine inhibited basal AC. Naloxone antagonized the inhibitory effects of each of the opioids tested, and dextrorphan, an inactive L-(+)-opiate, failed to inhibit the dopamine response. Together these data indicate that the effects were mediated via the classically described stereospecific opiate receptor. The relative order of potency (etorphine greater than enkephalins greater than morphine) was similar to that previously reported for the binding affinities of these drugs in rat brain homogenates. The influence of narcotic agents on dopamine stimulated AC was eliminated by either freezing the amygdaloid tissue or preincubating the homogenate at 4 degrees C; the dopamine responses, however, could still be elicited. The narcotic receptor interaction with the adenylate cyclase thus appears to be distinct from and more labile than that of the dopamine receptor. Gpp(NH)p-stimulated AC was not inhibited by morphine. It is postulated that the inhibition involves interaction of opiate receptors with catalytic units of dopamine-stimulated AC, but not with other cyclase species which may provide the major component of Gpp(NH)p-stimulated activity in amygdala.

Control of opiate receptor-adenylate cyclase interactions by calcium ions and guanosine-5'-triphosphate.

Adenylate cyclase of homogenates of NG108-15 neuroblastoma x glioma hybrid cells is activated by low concentrations of Ca2+ ions and is inhibited by higher (greater than 0.1 mM) concentrations of Ca2+ ions. Activation of either opiate receptors by 10 microM morphine or alpha-adrenergic receptors by 10 microM norepinephrine inhibits adenylate cyclase by 55% in the absence of Ca2+ ions, and inhibits the Ca2+-dependent activation of adenylate cyclase by more than 90%. Concentrations of Ca2+ ions greater than 0.1 mM inhibit adenylate cyclase and also reduce the extent inhibition of adenylate cyclase by morphine but not by norepinephrine. Guanosine-5'-triphosphate (0.1-1 microM) is required for inhibition of adenylate cyclase by morphine. The results show that morphine inhibits adenylate cyclase by a guanosine-5-triphosphate-dependent process and that the extent of inhibition of adenylate cyclase by morphine or norepinephrine is a function of the Ca2+ ion concentration and the proportion of adenylate cyclase molecules that are activated or inhibited by Ca2+ ions.

Catecholamine-stimulated cyclic AMP formation in phenylethanolamine N-methyltransferase containing brain stem nuclei of normal rats and of rats with spontaneous genetic hypertension.

Stimultaion of cyclic AMP formation by epinephrine and norepinephrine has been studied in discrete areas of rat brain that include the epinephrine-containing brain stem nuclei C-1 and C-2. In the C-1 area, epinephrine-stimulated cyclic AMP formation was partially reversed by 100 microM phentolamine and by 10--100 microM propranolol or alprenolol and hence appeared to involve activation of a mixture of both alpha- and beta-adrenergic receptors as has been reported for other rat brain areas such as the cerebral cortex. However, in the C-2-area, the epinephrine and norepinephrine stimulated cyclic AMP formation involved the activation of a single receptor type which was alpha-like in character. Stimulation of cyclic AMP formation by epinephrine in the C-2 area was antagonized by nanomolar concentrations of both phentolamine and yohimbine. The epinephrine-stimulated formation of cyclic AMP in the C-2 but not in the C-1 area was augmented in a strains of rats which exhibit spontaneous genetic hypertension (SHR) vs. Wistar-Kyoto controls. It is suggested that the enhanced epinephrine-stimulated cyclic AMP formation in the C-2 area of SHR rats could be a physiological compensatory response to some other hypertension-causing lesion which, for example, results in chronically reduced epinephrine release or in ruduced availability of epinephrine at its postsynaptic receptor thereby leading to receptor supersensitivity. Supporting this possibility was the finding that treatment of SHRs and control animals and reserpine resulted in enhancement of epinephrine-stimulated cyclic AMP formation in the C-2 area of control rats, essentially obliterating the difference between control and SHR. The findings are also interepreted as supporting the involvement of epinephrine neurons in central vaso-depressor mechanisms.

A Parkinson-like neurologic deficit in primates is caused by a novel 4-substituted piperidine.

A neurologic deficit characterized by hypokinesia, postural flexion, and to a lesser extent, rigidity, tremor and myoclonus, has been observed in cynomolgus monkeys following administration of 1-methyl-4-(1-methylpyrrol-2-yl)-4-piperidinol (MMPP), a novel 4-substituted piperidine. The syndrome, similar to that described for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), developed within 3-7 days after oral or i.v. dosing, and was accompanied by lesions in the substantia nigra. The behavioral syndrome was seen to a lesser extent in dogs but not in rats. MMPP contains a hydroxyl group on the 4-position of the pyridine ring; the corresponding dehydration product was inactive.