Opioids dopaminergic system

In rodents, PCP produces not only ataxia, but also stereotyped behavior and hyperactivity. The PCP-induced stereotyped behavior is thought to be due to changes in serotonergic and dopaminergic systems (Nabeshima et al. 1983 Martin et al. 1979 Sturgeon et al. 1981). It is not known whether PCP receptors mediate PCP-induced hyperactivity or stereotyped behavior or even the effect on neurotransmitter systems. It is also possible that mu, kappa, or sigma opioid receptors are involved (Castellani et al. 1982). 

Morphine generally has sedative effects, reducing overall activity. But local injections into dopaminergic systems can increase locomotor activity, and daily administration can also sensitize one to the locomotor effect (Kalivas and Duffy 1987). High does of opioids create muscle rigidity and catalepsy. 

The precise functions of the opioid receptor subtypes remain to be delineated. In many studies, it has been established that they modulate the functions of the dopaminergic system. For example, administration of morphine into the area 10 region results in a dopamine-dependent increase in locomotor activity. Electiophysiological studies of area 9 neurons suggest that p and k opioids have opposite effects on motor behaviors activation or sedation, respectively. The k and p agonists have also been found to exert opposite actions with respect to fluid regulation diuretic and... 

ROLE OF DELTA OPIOID RECEPTORS IN THE BEHAVIORAL EFFECTS OF DUAL INHIBITORS— INTERACTION WITH THE DOPAMINERGIC SYSTEM... 

Spanagel R., Herz A., Shippenberg T. Opposing tonically active endogenous opioid systems modulate the mesolimbic dopaminergic pathway. Proc. Natl. Acad. Sci. U.S.A. 89 2046, 1992. 

Nicotinic cholinergic receptors are located on cells that release a wide variety of transmitters (see chapter by Barik and Wonnacott, in this volume), so that nicotine interacts with multiple neurochemical pathways. The roles of cholinergic, dopaminergic, and endogenous opioid systems in physical dependence and withdrawal have been most thoroughly studied and documented. Research on the role of other transmitters and neurochemical mechanisms is rather scattered. Overall, however, research with rodent models of physical dependence has provided a wealth of potential targets for experimental treatments to aid smoking cessation. 

Opioids have been shown to increase the release of dopamine in the nucleus accumbens but they also subserve reinforcement in animals by a non-dopaminergic mechanism (Di Chiara 8c North,1992 Koob, 1992). Physiologically the opioid system appears to be largely involved in the con-sumatory rewards of feeding, drinking, sexual and maternal behaviour (Koob, 1992 Di Chiara 8c North, 1992) and certain types of social behaviour (Panksepp, 1981 Bolles 8c Fanselow, 1982). 

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