n-methylnaloxone and Catatonia

Alfentanil, a short-acting and powerful analgesic, when injected peripherally to rats (0.5 mg/kg) produced a catatonic state characterized by a rigid akinesia. The present study was designed to explore the neuroanatomical location of the opiate receptors mediating the alfentanil induced catatonia. The catatonic effect of alfentanil was measured using a bar test and depression of locomotor activity in rats tested in photocell cages during an active nocturnal phase of their cycle. Methylnaloxonium HCl (MN), a quaternary derivative of naloxone which does not readily cross the blood-brain barrier, injected into the lateral ventricle significantly reduced the catatonia at doses of 0.125-2.0 micrograms as measured in both the locomotor and bar test. MN perfusion of similar doses directly into the nucleus raphe pontis, but not in the caudate nucleus significantly antagonized the catatonia. These data complement results on alfentanil-induced muscular rigidity (Blasco et al., see companion paper) where EMG indices of rigidity in rats were reversed by microinjections of low doses of MN (0.125 and 0.5 microgram) in the nucleus raphe pontis, but not the caudate nucleus even at a high dose (4.0 micrograms). Together these results suggest that the region of the nucleus raphe pontis is an important neural substrate for opiate-induced muscular rigidity, and that the catatonic state produced by opiates depends on more diffuse opiate receptor activation of which one important component may be the nucleus raphe pontis.

Topics: Alfentanil; Animals; Brain; Catatonia; Fentanyl; Male; Motor Activity; Naloxone; Quaternary Ammonium Compounds; Rats; Rats, Inbred Strains; Receptors, Opioid

Attempts to eliminate or reduce the rigidity induced with high-dose narcotic anesthesia in the operating room have been only partially successful. Previous investigations of opioid receptor sites mediating this rigidity have implicated two central regions: the nucleus raphe pontis (NRP) within the reticular formation and the caudate nucleus (CN) within the basal ganglia. The present study used systemically administered alfentanil (ALF), a potent, short-acting fentanyl analog, and intracerebrally infused methylnaloxonium (MN), a quaternary derivative of naloxone, to elucidate further the functional role of the NRP and CN in rigidity. ALF (0.5 mg/kg s.c.) produced a reliable model of rigidity, as documented by gastrocnemius electromyography. The onset of this rigidity was within 60 s of ALF administration, with a total duration of approximately 40-50 min. Intracerebroventricular (i.c.v.) injections of 2.0 or 4.0 micrograms of MN 15 min prior to ALF treatment prevented rigidity, while 0.125 or 0.5 microgram had no significant effect on rigidity. MN injected directly into the NRP at doses as low as 0.125 microgram significantly antagonized ALF-induced rigidity, while injections of MN into the caudate nucleus at doses as high as 4.0 micrograms failed to antagonize ALF-induced rigidity. These observations demonstrate that injection of MN into the NRP is at least 16-fold more effective in blocking ALF-induced rigidity than MN injected into the ventricle and, more importantly, at least 32-fold more effective than MN injected into the CN. The results suggest that the NRP may be an important site for the neural control of muscular rigidity associated with high-dose narcotic administration.

Topics: Alfentanil; Animals; Catatonia; Caudate Nucleus; Electromyography; Fentanyl; Male; Muscle Rigidity; Naloxone; Pons; Quaternary Ammonium Compounds; Raphe Nuclei; Rats; Rats, Inbred Strains