Cholinergic modulation of dopamine release in corpus striatum and substantia nigra of the rat

The selective m1 muscarinic antagonist MT-7 blocks pilocarpine-induced striatal Fos expression

Systemic administration of the nonselective muscarinic agonist pilocarpine induces pronounced striatal Fos expression. Intrastriatal injections of the mamba snake toxin MT-7, a highly selective and irreversible m1 muscarinic antagonist, drastically attenuated this response when given 2, but not 8, days before pilocarpine. In contrast, MT-7 did not alter the response to amphetamine (5 mg/kg). These results suggest that pilocarpine induces Fos expression in the striatum as a result of stimulating m1 muscarinic receptors located within this structure and demonstrate the utility of the MT-7 for in vivo studies of cholinergic function.

Role of dopamine D1 receptors in the striatal and cortical fos expression induced by the muscarinic agonist pilocarpine

Injections of the muscarinic cholinergic receptor agonist pilocarpine (50 mg/kg) induced pronounced expression of the immediate early gene (IEG) product Fos in the striatum and cortex of rats. Pretreatment with the dopamine D1 receptor antagonist 7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-H-3-benzazepine hydrochloride (SCH-23390; 0.2-2.0 mg/kg) drastically attenuated the pilocarpine response in the striatum, but had no effect in the cortex. In contrast, the muscarinic receptor antagonist scopolamine (0.75-3.00 mg/kg) virtually abolished the Fos response at both sites. These results suggest that stimulation of dopamine D1 receptors may mediate the effects of muscarinic agonists on Fos expression in the striatum, but not the cortex.

Effects of in utero and lactational exposure of the laboratory rat to 2,4,2',4'- and 3,4,3',4'-tetrachlorobiphenyl on dopamine function

Offspring of Sprague-Dawley derived dams were exposed to either 2,4, 2',4'-tetrachlorobiphenyl (TCB) (1, 10, or 20 mg/(kg.day)) or 3,4,3', 4'-TCB (0.1 or 1 mg/(kg.day)) from gestational Day 6 through weaning by providing the dams with cookies adulterated with the appropriate amount and type of PCB. Male and female offspring were sacrificed on postnatal Days 35, 60, and 90, and brain concentrations of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, were determined in the frontal cortex, caudate nucleus and substantia nigra by high-performance liquid chromatography with electrochemical detection. In utero and lactational exposure to 3,4,3',4'-TCB resulted in significant elevations in concentrations of dopamine in the frontal cortex, and of dopamine and its metabolites in the substantia nigra that persisted into adulthood. In contrast, in utero and lactational exposure to 2,4,2',4'-TCB resulted in significant decreases in concentrations of dopamine in the frontal cortex and caudate nucleus that also persisted into adulthood. We suggest that the reductions in brain dopamine concentrations are a consequence of ortho-substituted PCB congener-induced inhibition of the synthesis of dopamine during critical periods of development acting, perhaps, in concert with PCB-induced changes in cholinergic receptor function. On the other hand, the persistent elevations in brain dopamine and metabolite concentrations following perinatal exposure to 3,4,3',4'-TCB may be mediated by alterations in steroid hormone function during key developmental periods.

Pre- and postsynaptic M3 muscarinic receptor mRNAs in the rodent peripheral auditory system

The medial and lateral efferent innervations originate from distinct parts of the superior olivary complex. Both use acetylcholine, respectively, to modulate the activity of outer hair cells (OHC), and spiral ganglion neurons (SGN) which are postsynaptic to the inner hair cells (IHC). Besides predominantly activating nicotinic receptors, acetylcholine recognizes muscarinic M3 receptors, whose the role(s) and cellular localization(s) are not yet firmly established. We used reverse transcription and polymerase chain reaction to amplify the M3 receptor cDNA in the rat and guinea pig organ of Corti and spiral ganglion. Then, we localized the M3 receptor mRNAs in cochleas and superior olivary complex of both species. The M3 receptor cDNA was amplified from samples of brain, organ of Corti and spiral ganglion. Indeed, its corresponding mRNA was localized in SGNs, OHCs and IHCs. However, in the apical turns, OHCs were often found unlabeled. In the superior olivary complex, M3 mRNAs were colocalized with choline acetyltransferase mRNAs in neurons of the lateral superior olive and ventral nucleus of the trapezoid body. These results suggest that the M3 receptor-induced inositol phosphate formation described in previous studies [21] takes place in both postsynaptic (SGNs, OHCs) and presynaptic components of efferent cochlear synapses, and in cells that are not contacted by efferents in the adult cochlea (IHCs).

Effect of vinconate on the extracellular levels of dopamine and its metabolites in the rat striatum: microdialysis studies

The effects of (+/-)-methyl-3-ethyl-2,3,3 alpha, 4-tetrahydro-1H- indolo[3,2,1-de][1,5]naphthyridine-6-carboxylate hydrochloride (vinconate), an indolonaphthyridine derivative, on the extracellular levels of dopamine and its metabolites in the rat striatum were examined using brain microdialysis. Single administration of vinconate (10, 100 mg/kg i.p.) increased the extracellular level of dopamine and its metabolites. This enhancing effect of vinconate was antagonized by scopolamine (10 microM), a muscarinic receptor antagonist, which was added to the perfusate from 30 min before vinconate treatment. These findings suggest that vinconate, even when systemically administered, enhances the endogenous release of dopamine in the striatum, probably via the stimulation of presynaptic muscarinic receptors.