Barry D. Sawyer

Dopamine deficiency in the weaver mutant mouse.

The dopamine system in weaver mutant mice (B6CBA-Aw-J/A background) was studied. Dopamine was 27% lower in the olfactory tubercle, 77% lower in the frontal cortex, and 75% lower in the striatum of 6-month-old weaver mice compared to control mice of the same age. Norepinephrine and serotonin were not lower in these brain areas. Tyrosine hydroxylase activity in the striatum was measured with a radiometric assay and was 70% lower in weaver mice. Examination of mice from 11 to 180 days of age revealed that the dopamine system failed to develop in weaver mice. Motor activity in individual animals was assessed using circular photocell activity cages with minimal illumination. Apomorphine and pergolide, direct dopamine agonists, increased activity more in weaver mice than in normal littermates. Amphetamine, which releases endogenous stores of dopamine, was less active in mutant mice. These findings provide suggestive evidence that postsynaptic dopamine receptors in weaver mutants might have become supersensitive as a result of lower levels of dopamine in motor areas of the brain. Anatomical evidence of dopamine system abnormalities was found in weaver mice by examination of serial sections cut from the midbrain of mutant and normal mice. The pars compacta of the substantia nigra in weaver mice appeared hypocellular when compared with the corresponding sections from controls. Fewer large neurons were seen in the affected animals. This study illustrates that weaver mice have specific deficiencies in the dopamine system. The weaver mouse might provide a way of examining the biochemical and behavioral effects of long term dopamine deficiency and a way to examine drugs to treat dopamine-deficient states in vivo.

Antipsychotic drugs stimulate prolactin release

Antipsychotic drugs have been found to markedly stimulate prolactin secretion in male and female rats. The amount of prolactin released was greater in females than in males. Most non-antipsychotic phenothiazines failed to alter prolactin. These results imply that the dopamine receptor that inhibits prolactin release may be similar to the dopamine receptor involved in the action of antipsychotic drugs.

Purkinje cell loss and the noradrenergic system in the cerebellum of pcd mutant mice

Purkinje cells in the cerebellum receive inhibitory noradrenergic input from the locus coeruleus. In pcd mutant mice all Purkinje cells degenerate by 45 days of age. The purpose of the present studies was to determine if the loss of these cerebellar neurons affects the amounts of norepinephrine in the cerebellum of mice 25-280 days of age. No significant changes in norepinephrine content were detected during or after Purkinje cell degeneration. However, since degeneration led to a reduction in cerebellar weight, the norepinephrine concentration was increased in pcd mutants. These results indicate that despite the loss of a major postsynaptic target (Purkinje cells), the cerebellar noradrenergic input remains stable.

Inhibition of luteinizing hormone release and ovulation by 6-chloro- and 6-fluoromelatonin.

The effects of 6-chloromelatonin and 6-fluoromelatonin on ovulation and LH and prolactin release in rats were determined. Both halogenated melatonin analogs were more potent ovulation blockers than melatonin. The halogenated melatonin analogs inhibited the ovulatory surge of luteinizing hormone (LH) but did not alter the proestrous prolactin surge, nor did they alter basal serum levels of LH or prolactin. The plasma half-life of 6-chloromelatonin in rats and rhesus monkeys was 27 min compared to 11 min for melatonin. The results indicate that 6-chloromelatonin is a melatonin agonist with greater metabolic stability than melatonin.

Muscarinic M1 receptor agonist actions of muscarinic receptor agonists in rabbit vas deferens

In the electrically field-stimulated rabbit vas deferens, muscarinic receptor agonists increase twitch-height by actions at postjunctional M2 receptors and decrease twitch-height by actions at prejunctional M1 receptors. In the present studies, in contrast to previous reports, muscarinic receptor agonists primarily decreased twitch-height, produced minimal increases in twitch-height, and, produced identical responses in both epididymal and prostatic tissue segments, thus permitting a more detailed investigation of the M1 receptor component of action of muscarinic receptor agonists in the rabbit vas deferens. The nonselective muscarinic receptor agonist carbachol produced biphasic effects on twitch-height in the vas deferens: lower concentrations increased twitch-height to only approximately 25-30% over control, whereas higher concentrations inhibited the twitch. The selective M1 receptor antagonist pirenzepine blocked the inhibitory effects of carbachol, and unmasked carbachol-induced increases in twitch-height. Atropine, 4-DAMP (4-diphenylacetoxy-N-methylpiperidine methiodide) and AF-DX 116 (11-2[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro- 6H-pyrido[2,3-b][1,4]benzodiazepin-6-one) blocked both the inhibitory and stimulatory effects of carbachol, but atropine and 4-DAMP were more potent in blocking the inhibitory than the stimulatory effects of carbachol, whereas the reverse was true for AF-DX 116. McN-A-343 (4-hydroxy-2-butynyl)trimethylammonium chloride, m-chlorocarbanilate) and 12 other muscarinic receptor agonists from a variety of chemical classes also produced concentration-dependent decreases in twitch-height. The log IC50s of the muscarinic receptor agonists for decreasing twitch-height were highly correlated with their log Kis for inhibiting [3H]pirenzepine (r = 0.96) and [3H]oxotremorine-M (r = 0.85) binding in rat hippocampal membranes. The present results demonstrate that the muscarinic M1 receptor mediating inhibition of twitch-height in the rabbit vas deferens has pharmacologic properties similar to the muscarinic M1 receptor in rat hippocampus.

Direct pharmacological comparison of the muscarinic receptors mediating relaxation and contraction in the rabbit thoracic aorta.

The purpose of the present studies was to directly compare the pharmacology of the muscarinic cholinergic receptors coupled to carbachol-induced relaxation and contraction of the intact and the endothelium-denuded rabbit thoracic aorta, respectively. The order of potencies of agonists for producing relaxation in the intact aorta was similar to that for producing contraction in the denuded aorta. In both preparations, the partial agonists pilocarpine, McN-A-343, and RS86 functioned as antagonists, indicating a lack of receptor reserve in both preparations. Further, the pA2 values for antagonists in both tissues were virtually identical and were consistent with the pharmacology of M3 receptors.

Evidence That Methadone Stimulates Prolactin Release by Dopamine Receptor Blockade

This study has shown that methadone shares with phenothiazine and butyrophenone neuroleptics the ability to stimulate prolactin release. Administration of D,L-methadone to male rats resulted in elevated serum prolactin levels of a magnitude similar to those noted in rats treated with chlorpromazine or haloperidol. Simultaneous administration of apomorphine and methadone prevented the rise of serum prolactin. We suggest that methadone can stimulate prolactin release by blockading dopamine receptors.

Synthesis and structure-activity relationships of heterocyclic analogues of the functional M1 selective muscarinic agonist hexyloxy-TZTP

Abstract Isothiazole ( 8a,b ), isoxazole ( 14 ) and thiophene ( 19a,b ) analogues of the potent, M 1 selective muscarinic agonist, hexyloxy-TZTP, 1b , were synthesized and tested |in vitro for muscarinic receptor affinity and M 1 efficacy. All the analogues had lower affinity and efficacy at the M 1 muscarinic receptors than 1b .

Xanomeline: A potent and selective M1 muscarinic agonist in vitro

Xanomeline (3-(4-Hexyloxy-1,2,5-thiadiazole-3-yl)-1,2,5,6-tetrahydro-1- methylpyridine), (hexyloxy-TZTP) was discovered in the course of investigations on the structure activity relationship of a series of thiadiazole based analogs of the muscarinic agonist arecoline. The compound demonstrated functional selectivity for M1 receptors when tested in isolated tissue preparations and in cloned cell lines expressing specific muscarinic receptor subtypes.