The action of reserpine and α-methyl-m-tyrosine on the analgesic effect of morphine in rats and mice

The actions of α-methyl-m-tyrosine (mmt) and reserpine upon the analgesic effect of morphine has been studied in rats and mice. In rats, reserpine antagonised the effect of morphine, while mmt did not cause any appreciable change of the effect of morphine, injected either 2 or 24 hr after mmt. Reserpine also produced its antagonistic action to morphine in rats which were previously (24 hr) treated with mmt. Both mmt and reserpine potentiated the effect of morphine in rats pretreated (24 hr previously) with iproniazid. In mice, both mmt and reserpine antagonised the effect of morphine. Reserpine failed to do so in mmt pretreated animals. The effect of morphine was restored 24 hr after the injection of mmt. It is suggested that the inhibitory action of reserpine upon the analgesic effect of morphine is due to the antagonistic action of brain 5-ht, which is activated after being released from its stores by reserpine. The pattern of reserpine—mmt—morphine interactions in rats probably differs from that in mice.

Cocaine: excitatory effects on sensorimotor reactivity measured with acoustic startle

Cocaine (2.5-10 mg/kg) caused a dose-related increase in the amplitude of the acoustic startle reflex in rats. In contrast, procaine (5-40 mg/kg) caused a dose-related decrease in startle, indicating that the effects of cocaine could not be ascribed to its local anesthetic effects. Cocaine's excitatory effects were blocked by pretreatment with haloperidol (0.5 mg/kg) but not by cyproheptadine or prazosin. The excitatory effects of cocaine (10 mg/kg) were markedly attenuated by pretreatment with reserpine (5 mg/kg 24 and 18 h earlier) but not by alpha-methyl-p-tyrosine (100 mg/kg 1 h earlier). In contrast, comparably sized excitatory effects of d-amphetamine were blocked by alpha-methyl-p-tyrosine and greatly enhanced by pretreatment with reserpine. Neither pretreatment blocked excitatory effects of apomorphine on startle. The data indicate that cocaine increases startle by acting through reserpine-sensitive pools of dopamine and provide further support for the conclusion that acoustic startle is enhanced by activation of dopamine receptors.

Some pharmacological actions of 2,5-dimethoxy-4-ethylamphetamine (DOET) in rats and mice

DOET, like DOM, exhibited pressor action in rats. This increase of blood pressure was blocked by pretreatment with cinanserin. DOET at high doses decreased the spontaneous locomotor activity of mice at the first hour but increased the activity at the second hour; a low dose was less effective. DOET also increased the rectal temperature of rats and this hyperthermic action was suppressed by pretreating the animals with cinanserin or methysergide. These actions of DOET were compared with those of DOM.