Effects of the optical isomers of the narcotic antagonist analgesic pentazocine on brain and heart biogenic amines

Cardiovascular effects of intravenous pentazocine and cyclazocine in conscious, curarized-conscious, and anesthetized dogs

The cardiovascular effects of intravenous pentazocine and cyclazocine in dogs were studied under conscious, curarized-conscious (paralyzed by gallamine), and anesthetized states. In the conscious state, blood pressure and heart rate were dose-dependently increased by pentazocine (1, 2, 3 mg/kg) and to a lesser extent by cyclazocine (0.3 mg/kg). In all subsequent experiments on dogs, the results were obtained using 3 mg/kg pentazocine and 0.3 mg/kg cyclazocine. Pentazocine accelerated breathing, peaking at about 10 min, whereas cyclazocine reduced breathing to a minimum in 1 min, followed by a gradual recovery thereafter. In the curarized-conscious state, the blood pressure response to pentazocine was biphasic, namely an initial decrease followed by an increase; chronotrophic activity was stimulated. Pretreatment with either ganglionic or alpha andrenergic blocking agents not only significantly antagonized the pressory responses to the drug but also potentiated the initial decreases in blood pressure and unmasked a bradycardic component, but these parameters were not altered by 0.3 mg/kg naxalone. In open-chest anesthetized dogs, blood pressure, heart rate, contractility, and mean peripheral vascular resistance were simultaneously decreased by both pentazocine and cyclazocine, initially accompanied by increases in aortic blood flow. During the later stages of drug action, only the blood pressure and contractility were increased above control levels (biphasic effect). A comparison of blood pressure and heart rate responses to pentazocine in dogs kept under differing experimental conditions revealed that conscious dogs were more sensitive than curarized conscious and anesthetized animals to pentazocine action. In isolated guinea pig atria, the effect of adrenaline (0.1, 0.3, or 1 mg/mL) on the spontaneous breathing rate was significantly augmented by 10 mg/mL pentazocine (p < 0.02 for 0.3 g/mL; p < 0.01 for 0.1 g/mL adrenaline). In dogs, however, adrenaline (1 mg/kg)-induced increases in heart contractility, aortic blood flow, and blood pressure remained almost unaltered in the presence of pentazocine. We concluded that the abovementioned cardiovascular responses to pentazocine and cyclazocine are a consequence of the sum of the two following opposing effects: (i) an indirect reflex activation of sympathetic neuromediation in the periphery, and (ii) a direct membrane effect on the heart leading to bradycardia and a depression in myocardial contractility.

The effect of ibogaine on Sigma- and NMDA-receptor-mediated release of [3H]dopamine

The indole alkaloid ibogaine has been suggested to have potential for inhibiting dependency on stimulant drugs. Radioligand binding studies have suggested possible multisite actions of ibogaine: affinity at the kappa-opioid, NMDA, and sigma receptors, with effects on dopamine (DA) release. To further investigate the multiplicity of sites of action of ibogaine and the presynaptic regulation of the DA release, the effect of ibogaine on NMDA- and sigma-receptor-mediated efflux of [3H]DA was measured in striatal tissue from C57BL/6By mice. Striatal tissue was incubated in vitro with [3H]DA and the effect on DA release was measured. Both NMDA (25 microM) alone increased the efflux of DA. (+/)-Pentazocine (100 nM) did not inhibit the NMDA-evoked release. MK-801 (5 microM) completely inhibited the NMDA-evoked release and inhibited the (+/-)-pentazocine-evoked release by 49%. Ibogaine (10 microM) itself increased the efflux of DA; at 1 microM it was without effect. Ibogaine (1 microM) inhibited the NMDA-evoked release of DA by 31% and inhibited the (+/-)-pentazocine-evoked release by 48%. In addition, the level of basal release of DA obtained after the NMDA- or (+/)-pentazocine-evoked-release remained higher in the tissue exposed to ibogaine throughout. The results suggest that sigma receptors can regulate the release of DA, along with an action at the NMDA receptor. We previously reported action of ibogaine at the kappa-opioid site. The elevated basal release of DA in the presence of ibogaine after NMDA- or (+/-)-pentazocine-evoked release may reflect the ibogaine-induced removal of the tonically active kappa-opioid system that acts presynaptically to reduce dopamine release. The kappa-opioid system also appears to be inhibitory on both the NMDA and sigma receptors.

Stimulation of rat striatal tyrosine hydroxylase activity following intranigral administration of sigma receptor ligands

The effects of sigma ligands on turning behavior and striatal tyrosine hydroxylase activity were determined following microinjection of two chemically dissimilar sigma ligands into the rat substantia nigra. Striatal tyrosine hydroxylase activity was monitored by measuring the amount of 3,4-dihydroxyphenylalanine (DOPA) formed following inhibition of DOPA decarboxylase activity with m-hydroxybenzylhydrazine (NSD-1015). The sigma ligands, 1,3-di-o-tolylguanidine (DTG) and (-)-deoxy-N-benzylnormetazocine, produced a significant increase both in contralateral turning and in tyrosine hydroxylase activity. The DTG-induced increase in tyrosine hydroxylase activity was not antagonized by intranigral injection of the NMDA receptor antagonist, 3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP). CPP alone produced significant contralateral turning that was not accompanied by an increase in striatal tyrosine hydroxylase activity, indicating that turning per se is not sufficient to activate striatal tyrosine hydroxylase. The DTG-induced increase in tyrosine hydroxylase activity was antagonized by general anesthetics such as halothane and chloral hydrate. These results indicate that occupancy of sigma receptors in the substantia nigra is associated with an activation of dopamine formation in dopaminergic terminals in the striatum and support the concept that sigma activity in the substantia nigra produces an activation of dopamine-mediated responses in the striatum.

Increases in rat striatal extracellular dopamine and vacuous chewing produced by two sigma receptor ligands

The present studies were carried out to analyze the neurochemical and behavioral effects of peripheral sigma ligand administration in the rat. Based upon previous studies which showed an increase in turning behavior following unilateral intranigral administration of sigma ligands, we determined the effects of two sigma ligands, 1,3-di-o-tolylguanidine (DTG) and (+)-pentazocine, on extracellular dopamine levels in the rat striatum. Dopamine levels were monitored via microdialysis in awake freely moving animals following i.p. injection of the ligands. Both DTG (1 and 3 mg/kg) and (+)-pentazocine (10 mg/kg) produced a significant (30-50%) increase in extracellular dopamine. Given the relatively high concentration of sigma receptors in brain nuclei involved in facial and mouth movements, we have also determined the effects of the two sigma ligands on facial movements. Both ligands produced a significant increase in vacuous chewing movements, suggesting that studies on the consequences of sigma receptor activation may have relevance to animal models of human dystonia and/or dyskinesia.

Effects of 1,3-di-o-tolylguanidine (DTG), a sigma ligand, on local cerebral glucose utilization in rat brain

The 2-deoxy-D-[1-14C]glucose ([14C]DG) method was used to examine the effects of the relatively selective sigma ligand 1,3-di-o-tolylguanidine (DTG) on cerebral metabolism in freely moving rats. Each animal received an i.p. injection of DTG (0.2, 1, or 5 mg/kg) or normal saline 20 min prior to the infusion of [14C]DG. DTG induced dose-dependent changes in local cerebral glucose utilization (LCGU) in several motor and limbic structures. Most structures showed increases in LCGU, with a maximum effect at 1 mg/kg. The most profound increases in LCGU were observed in brain regions that are rich in sigma receptors. These included cerebellar and related nuclei (interpositus, lateral and medial cerebellar n., vestibular n., olivary n.), ambiguus n., superior colliculus (superior layers), hippocampus (CA2, CA3, DG), n. basalis of Meynert interpeduncular n., and the substantia nigra pars compacta and pars reticulata. No significant decreases in glucose utilization were observed at any dose. Although the areas affected by DTG are similar to those previously reported for other sigma ligands, future studies employing a range of doses for additional selective sigma ligands must be carried out in order to confirm whether these changes in LCGU were sigma-mediated.

Lack of involvement of haloperidol-sensitive sigma binding sites in modulation of dopamine neuronal activity and induction of dystonias by antipsychotic drugs

The present studies evaluated previous suggestions that haloperidol-sensitive sigma binding sites are involved in the modulation of dopamine (DA) neuronal activity and in the induction of the dystonic effects of antipsychotic drugs. These issues were addressed by evaluating the effects of compounds that have differing affinities for sigma binding sites, on the firing activity of DA neurons in the substantia nigra in chloral hydrate-anesthetized rats and on the ability to induce extrapyramidal motor dysfunction in squirrel monkeys sensitized to the dystonic effects of haloperidol. The agents studied included haloperidol, DTG (1,3-di-o-tolylguanidine), (+)-pentazocine, (+)-SKF 10,047, BMY 14802, 8-OH-DPAT and sulpiride. There was no relationship between affinity for sigma binding sites and the ability to either alter DA neuronal activity or to induce extrapyramidal motor dysfunction.

Motor effects of two sigma ligands mediated by nigrostriatal dopamine neurons

(+)-Pentazocine, a potent sigma ligand that lacks affinity for PCP receptors, produced dose-dependent contralateral circling behavior following microinjections in the substantia nigra of rats. This effect was attenuated by 6-hydroxydopamine (6-OHDA) lesions of ascending dopamine neurons and enhanced by systemic injections of amphetamine, 6-OHDA lesions also attenuated the circling produced by another selective sigma ligand, 1,3-di-o-tolylguanidine (DTG). These findings suggest that sigma receptors are involved in the neural control of movement and the regulation of the ascending dopamine system. Since all typical antipsychotic drugs tested bind to sigma receptors with Ki values less than 1 microM, these findings further suggest that sigma receptors may mediate some of the motor side effects of antipsychotic drug therapy.

Pentazocine and tripelennamine: a drug abuse epidemic?

The change in illicit drug use from 1975 to 1978 was studied in Chicago veterans. Barbiturates and amphetamine use has decreased significantly. Nearly a sevenfold increase in pentazocine use has occurred. All but one of the pentazocine users added tripelennamine to the intravenous or subcutaneous injections. Sixty-four instances of medical or psychiatric complications including seizures, abscesses, depression, and psychosis occurred in the 69 pentazocine and tripelennamine users. A possible pharmacologic explanation of the seizures and psychiatric complications is advanced. Most users of pentazocine and tripelennamine started the use in an attempt to withdraw from heroin or because of the poor quality of heroin available.