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At least 37 records · Page 2Linked to original sources
PubMed1976

Central dopaminergic neurons: effects of alterations in impulse flow on the accumulation of dihydroxyphenylacetic acid.

Stimulation of the nigro-neostriatal or mesolimbic dopamine pathway results in a stimulus dependent increase in the accumulation of dihydroxyphenylacetic acid (DOPAC) in the neostriatum and olfactory tubercles, respectively. A block of impulse flow induced pharamacologically by administration of gamma-butyrolactone or by placement of a lesion in the dopamine pathway results in a decrease in the steady state levels of DOPAC. Drugs which have previously been shown to alter impulse flow in central dopaminergic neurons also produce a predictable change in the brain levels of DOPAC. Drugs which increase impulse flow in nigro-neostriatal or mesolimbic dopamine neurons increase DOPAC levels in the striatum and olfactory tubercles and drugs which reduce impulse flow cause a reduction in DOPAC. Pargyline, a monoamine oxidase inhibitor, causes a rapid depletion of striatal DOPAC suggesting that this metabolite is rapidly cleared from the brain. Administration of benztropine, a potent inhibitor of dopamine reuptake, causes a significant decrease in striatal DOPAC and partially prevents the stimulus-induced increase in the accumulation of DOPAC. These observations together with the finding that about 85% of the DOPAC in the striatum disappears when the dopamine neurons in the nigro-neostriatal pathway are destroyed suggests that the majority of striatal DOPAC is formed within the dopaminergic neurons and may reflect the metabolism of dopamine which has been released and recaptured. We conclude that short-term changes in brain levels of DOPAC appear to provide a useful index of alterations in the functional activity of central dopaminergic neurons.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1977

The effect of LSD and 2-bromo LSD on the striatal DOPA accumulation after decarboxylase inhibition in rats.

LSD and BOL (0.125-0.5 mg/kg) were equipotent in increasing the in vivo tyrosine hydroxylation in the striatum as measured by the accumulation of DOPA after inhibition of neuronal decarboxylase. However, with 2--4 mg/kg doses, the maximum effect of BOL was larger than that of LSD. LSD and BOL antagonized the apomorphine-induced decrease of DOPA accumulation, without affecting the haloperidol-induced increase. LSD like apomorphine inhibited the increase of DOPA accumulation seen after reserpine, cerebral hemisection and after gamma-butyrolactone (GBL). The effect of apomorphine in rats given GBL was blocked by haloperidol, but not by BOL and promethazine, whereas that of LSD was inhibited by haloperidol, BOL, and promethazine. These findings suggest that LSD and BOL directly affect nigro-neostriatal dopamine neurons. LSD therefore appears to be a partial agonist and BOL a pure antagonist at dopamine autoreceptors. It is proposed in addition that LSD activates and BOL blocks 5-HT receptors that control DOPA formation.

4-Butyrolactone↗
PubMed1978

Significance of dopamine metabolites in the evaluation of drugs acting on dopaminergic neurons.

The effect of various drugs was studied on 3-methoxytyramine (3-MT) concentrations in rat striatum. The drugs were chosen for their ability to interfere with the dopaminergic system at different levels. Dopamine (DA) acidic metabolites, i.e. homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), were also measured. Changes of 3-MT, unlike those of DOPAC and HVA, seem to reflect the functional activity of dopaminergic neurons. In fact drugs believed to increase or decrease DA content in the synaptic cleft produce predictable changes of striatal 3-MT. Thus cocaine, nomifensine and d-amphetamine increase 3-MT concentrations while gamma-butyrolactone, alpha-methyltyrosine and apomorphine decrease it.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1979

Effect of morphine on the accumulation of DOPA after decarboxylase inhibition in the rat.

Acute systemic administration of morphine (10 mg/kg s.c.) to rats increased in vivo tyrosine hydroxylation in the striatum measured as the accumulation of DOPA after decarboxylase inhibition. DOPA accumulation reached a maximum 30-60 min after morphine. The morphine antagonist naloxone (1, 10 or 100 mg/kg s.c.) did not significantly after DOPA accumulation. However, naloxone completely antagonized the effect of morphine. The DA agonist apomorphine decreased and the DA antagonist haloperidol increased DOPA accumulation. The effect of apomorphine (0.05 mg/kg) was counteracted by morphine. Naloxone did not significantly change the accumulation of DOPA after apomorphine or after haloperidol. In rats treated with gamma-butyrolactone (GBL) or with reserpine DOPA accumulation was not altered by treatment with morphine or naloxone. However, the inhibiting effect of apomorphine (0.5 mg/kg) on the accumulation of DOPA in rats treated with reserpine was weakly counteracted by morphine (0.5 mg/kg) on the accumulation of DOPA in rats treated with reserpine was weakly counteracted by morphine (10 mg/kg s.c.). Since the effects of morphine on the apomorphine-induced inhibition of DOPA accumulation were antagonized by naloxone, we suggest that the effects on striatal DOPA accumulation produced by morphine were mediated via opioid receptors and not directly via DA receptors.

4-Butyrolactone↗
PubMed1979

Repeated exposure to butenolide vapour: subacute study in Syrian golden hamsters.

The subacute inhalation toxicity of butenolide was examined in hamsters by repeated exposure of 4 groups of 10 males and 10 females to butenolide vapour at concentrations of 0, 5.4, 25 and 130 ppm respectively (6 h/day, 5 days/week) for a period of 13 weeks. The effects found at 130 ppm included eye irritation, salivation, nasal discharge, growth retardation, decreased number of eosinophils, increased liver weight, and hyper- and metaplastic epithelium in the nasal cavity. At the 5.4 and 25 ppm levels no changes were observed which could be attributed to butenolide; 25 ppm was, therefore, considered the highest no-toxic effect level observed. The actual no-adverse effect level was placed at 75 ppm.

4-Butyrolactone↗