Repeated treatment in ontogeny with the dopamine (DA) D2/D3 receptor agonist quinpirole is associated with enhanced quinpirole-induced yawning and other behaviors such as vacuous chewing, vertical jumping, and antinociception. To determine if the reputedly DA D3 agonist (±)-2-(dipropylamino)-7-hydroxy-1,2,3,4-tetrahydronaphthalene (7-OH-DPAT) would prime for yawning in a manner analogous to that for quinpirole, rats were treated for the first 11 days after birth with an equimolar dose of either quinpirole or 7-OH-DPAT (195.4 nmol/kg/day) and tested for agonist-induced yawning in adulthood. While enhanced quinpirole-induced and 7-OH-DPAT-induced yawning was observed in quinpirole-primed rats, acute treatments with quinpirole and 7-OH-DPAT did not produce an enhanced yawing response in 7-OH-DPAT-'primed' rats. Our findings indicate that 7-OH-DPAT, unlike quinpirole, does not prime for quinpirole- or 7-OH-DPAT-induced yawning in rats.

On the morning of the first day of pregnancy, Wistar rats were administered a single IP injection of either zinc sulfate (10.0 mg/kg) or saline. For the remainder of pregnancy, half the rats in each group then consumed filtered tap water while the other half consumed filtered tap water with 50 ppm of cadmium (CdCl2). At eight weeks after birth, the behavioral profile of male offspring was assessed in the following way: Apomorphine (non-selective dopamine receptor agonist), (+)-7-hydroxy-2-(di-n-propylamino) tetralin (7-OH-DPAT) (D3 agonist) and (+/-)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol (SKF 38393) (D1 agonist) were used to evaluate stereotyped behavior, yawning activity and oral movements - indices for these respective agonists. In addition, two dopamine receptor antagonists, haloperidol (D2 antagonist) and 7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzapine (SCH 23390) (D1 antagonist) were used to evaluate cataleptogenic activity. Additional behavioral parameters studied were locomotor activity, irritability and reaction to a painful stimulus. Dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3-MT) were quantified in the striatum, hippocampus and in the frontal cortex of the brain by means of HPLC/ED technique. In addition, cadmium levels were analyzed in the brain, liver, kidney and bone of newborn rats. Our results indicate that prenatal exposure of pregnant rats to cadmium produced alterations in the reactivity of central dopamine receptors and modulated the level of dopamine and its metabolites in the offsprings' brains. A single injection of zinc, preceding cadmium consumption, attenuated some of the effects of cadmium on the offsprings' dopaminergic system. Zinc also reduced cadmium deposition in the brain, kidney and bone, but enhanced its accumulation in liver. In summary, zinc may exert some neuroprotective effects against cadmium neurotoxicity.

Nitric acid has been implicated in a variety of physiological functions of the mammalian brain, and in a large number of its pathologies. Recently we have demonstrated that a nitric oxide donor (L-arginine) and a nitric-oxide-synthase-inhibitor (nitro-L-arginine-methyl-ester) modified the response of central al dopamine D 1 and D 3 receptors to some of their agonists. In the present study we demonstrate the modulatory effect of L-arginine, nitro-L-arginine-methyl-ester and molsidomine (another nitric oxide donor) on the reactivity of the central dopamine receptors to specific agonists and antagonists. The agonists tested were SKF-38393, 7-OH-DPAT and quinpirole, and the antagonists - SCH-23390 and haloperidol. They were evaluated in the rat by the following behavioral methods: locomotor activity, locomotor coordination, rearings and cataleptogenic activity (D 2 modulation); grooming time (D 1 activation); yawning (D 3 activation) and ethanol- and phenobarbital-sleeping-time parameters after SKF-38393 or quinpirole pretreatment. Our results suggest that nitro-L-arginine-methyl-ester is effective in modulating the reactivity of the central dopamine receptors D 2, D 1 and D 3, to their agonists and antagonists, and that it is much more effective than L-arginine in regulating the righting reflex after ethanol and phenobarbital, in both female and male mature rats.