[Characteristics of antagonism between ceruletide and various central-acting drugs: investigation by means of ambulatory activity in mice]

Contrasting effects on methamphetamine sensitization of ceruletide, a cholecystokinin-like decapeptide, and haloperidol

Ceruletide, a cholecystokinin-like decapeptide, and haloperidol show neuroleptic actions through inhibition of dopamine release and blockade of dopamine receptors, respectively. In this study, the effects of both drugs on methamphetamine sensitization were assessed by means of ambulation in mice. The enhancement in ambulation increase caused by five repeated administrations of methamphetamine (2 mg/kg, SC) at 3- to 4-day intervals was dose-dependently reduced when it was administered simultaneously with ceruletide (0.01-0.1 mg/kg, SC) or haloperidol (0.03-0.3 mg/kg, SC). However, only haloperidol could inhibit the induction of methamphetamine sensitization as assessed by challenge with methamphetamine alone. Post-treatment with ceruletide (0.03 mg/kg) 3 h after each methamphetamine accelerated, whereas such post-treatment with ceruletide (0.1 mg/kg) or haloperidol (0.03-0.3 mg/kg) delayed, the induction of methamphetamine sensitization. On the other hand, mice given five pretreatments with ceruletide (0.01-0.1 mg/kg) or haloperidol (0.03-0.3 mg/kg) at 3- to 4-day intervals did not exhibit any significant change in the sensitivity to methamphetamine. The present results suggest that, in contrast to the dose-dependent inhibition of methamphetamine sensitization in the simultaneous administration and post-treatment schedules, although both drugs can antagonize the acute stimulant effect of methamphetamine.

Potentiation of the ambulation-increasing effect induced by combined administration of MK-801 with ethanol in mice

Although both MK-801 (dizocilpine: 0.1 mg/kg, IP) and ethanol (1.6 nd 2.4 g/kg, PO) only slightly increased ambulatory activity in mice, their combination produced a marked enhancement of the ambulation-increasing effect. The combination of MK-801 (0.03 mg/kg) with ethanol (1.6 and 2.4 g/kg) also elicited a significant increase in the mouse's ambulation. A significant enhancement of the effect was produced by the combination of ketamine (3 and 10 mg/kg) with ethanol only (2.4 g/kg). The ambulation increment induced by the combination of MK-801 (0.1 mg/kg) plus ethanol (1.6 g/kg) was dose-dependently inhibited by YM-09151-2 (0.0001-0.01 mg/kg IP), SCH 23390 (0.001-1 mg/kg IP), reserpine (0.1-1 mg/kg, IP) and ceruletide (0.00001-0.001 mg/kg, IP), and the highest dose of each drug was effective for complete inhibition of the ambulation. Naloxone (0.05-5 mg/kg IP), apomorphine (0.001-0.1 mg/kg IP) and alpha-methyl-p-tyrosine (50-200 mg/kg, IP) partially reduced the ambulatory activity induced by the combination of MK-801 with ethanol. These results suggest that the dopaminergic system, particularly via presynaptic changes in the release of stored dopamine, as well as the opioid system, are involved in the interaction of MK-801 with ethanol.