naltrindole and Epilepsy

Postictal movement dysfunction is a common symptom in patients with epilepsy. We investigated the involvement of opioid receptors in the nucleus accumbens (NAC) in amygdaloid kindling-induced postictal decrease in locomotion (PDL) in rats. Seizures were induced by daily electrical stimulation of the basolateral amygdala until four consecutive stage 5 seizures were elicited. Locomotion was quantified before and after infusion of an opioid receptor antagonist or saline into the NAC. Whereas PDL was induced after a stage 5 seizure in saline-infused rats, pre-infusion of the mu opioid receptor antagonist H-D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP, 5 microg/1 microL/side) into the NAC prevented PDL. Pre-infusion of delta (naltrindole, 30 microg/1 microL/side), kappa (nor-binaltorphimine, 1.8 microg/1 microL/side), or nonselective (naloxone, 10 microg/1 microL/side) opioid receptor antagonists did not block PDL, but late postictal hyperactivity was blocked by naltrindole. None of the antagonists affected amygdaloid evoked afterdischarge duration. It is suggested that mu opioid receptors in the NAC participate in amygdaloid seizure-induced PDL without affecting seizure duration.

Topics: Amygdala; Animals; Epilepsy; Kindling, Neurologic; Locomotion; Male; Naloxone; Naltrexone; Narcotic Antagonists; Nucleus Accumbens; Rats; Rats, Long-Evans; Receptors, Opioid, mu; Seizures

In vivo and in vitro binding studies with natural thebaine and its enantiomer, (+)-thebaine were conducted to elucidate further their interactions with the opioid system. (-)-Thebaine a key intermediate in the biosynthesis of morphine in the poppy plant (Papaver somniferum) and in mammalian tissue, was poorly effective antinociceptively in mice at doses to 30 mg/kg. Its principal behavioral manifestation was lethal convulsions. Naltrindole, at doses of 1 and 10 mg/kg did not block either the convulsions or lethal effects, suggesting that the delta-opioid receptor system was not involved in this action. Surprisingly, the dextrorotatory isomer exhibited significant antinociceptive activity in the tail-flick [ED50 = 8.9 (3.4-22.1) mg/kg], hot-plate [ED50 = 22.9 (10.9-48.1) mg/kg] and phenylquinone [ED50) = 1.9 (1.6-9.5) mg/kg] assays. Studies with opioid receptor-subtype antagonists, beta-funaltrexamine, nor-binaltorphimine and naltrindole, indicated that antinociception was associated with mu- and delta-opioid receptors. Results of displacement experiments supported the in vivo data. Significant competition for [3H]diprenorphine binding with both isomers for cloned mu- and delta-opioid receptors was observed. However, (-)-thebaine was more effective at the delta-opioid receptor (Ki = 1.02+/-0.01 microM) whereas (+)-thebaine was more effective at the mu-opioid receptor ( Ki = 2.75+/-0.01 microM). Opioid-induced antinociception associated with unnatural thebaine raises the possibility of additional mu- and delta-opioid receptor sites.

Topics: Analgesics; Animals; Binding, Competitive; Cells, Cultured; Epilepsy; Male; Mice; Mice, Inbred ICR; Naltrexone; Narcotic Antagonists; Pain Measurement; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Stereoisomerism; Thebaine