Search

A previous published assay method for tyrosine hydroxylase by the evolution of 14CO2 was modified to a two-step procedure to allow reliable measurement of large numbers of samples containing low tyrosine hydroxylase activity. The reliability of the method was examined in detail. Properties of rat brain and pineal tyrosine hydroxylase solubilized with 0.2% Triton X-100 were as follows. The apparent Km values of the brain enzyme for L-tyrosine with 1 mM-(6-DL)-5,6,7,8-tetrahydro-L-erythro-biopterin (BPH4) as cofactor and for BPH4 with 62 microM-L-tyrosine as substrate were approximately 25 microM and 85 microM, respectively. The Km's for L-tyrosine with 1 mM-(6-DL)-5,6,7,8-tetrahydro-6-methylpterin (6MPH4) as cofactor and for 6MPH4 with 210 microM-L-tyrosine as substrate were 68 microM and 270 microM, respectively. The marked substrate inhibition by high concentrations of L-tyrosine was observed only when BPH4 was used as cofactor. High concentrations of BPH4 inhibited the reaction slightly. The kinetic properties of tyrosine hydroxylase in the pineal extract were similar to those of the brain enzyme, except that a Lineweaver-Burk plot of reciprocal velocity versus the reciprocal concentration of BPH4 with 62 microM-L-tyrosine as substrate deviated downward at a BPH4 concentration of about 100 microM. Analyses of the plot indicated that the peculiar kinetic property may represent either the reaction occurring at two independent sites or with two forms (6L- and 6D-isomers) of the tetrahydrobiopterin cofactor, with apparent Km for BPH4 of 23 microM and 1025 microM, respectively, or the negatively cooperative ligand binding with a Hill coefficient of 0.72. Based on the results obtained as reported above the standard assay conditions of tyrosine hydroxylase in tissue extracts were established. Using the assay method and conditions, the absence of the daily rhythmicity of tyrosine hydroxylase in rat pineal glands and three discrete brain areas was demonstrated. The findings, especially on pineal tyrosine hydroxylase, are discussed in relation to the daily change of noradrenaline turnover.

The neurochemical basis for the clinical observation that some patients receiving a large dose of haloperidol exhibit no extrapyramidal side effects was investigated in rats. Haloperidol at doses of 1, 2.5, 5, 7.5 and 10 mg kg (i.p.) caused a dose-dependent decrease in the duration of catalepsy. Haloperidol at a dose of 10 mg kg induced catalepsy lasting for only 20% ofthat obtained with 1 mg kg . Haloperidol decreased the content of noradrenaline in the frontal cortex and thalamus in a dose-dependent manner, while the content of 3-methoxy-4-hydroxyphenylglycol (MHPG) showed a dose-dependent increase in the same areas of the brain. Thus, there was an inverse relationship between the duration of catalepsy and the ratio of 3-methoxy-4-hydroxyphenylglycol to noradrenaline in the frontal cortex or thalamus. The concomitant administration of 20 mg kg of phenoxybenzamine with 10 mg kg of haloperidol induced a long-lasting catalepsy. The result may indicate that the increased metabolism of noradrenaline by large doses of haloperidol was not secondary to the blocking of dopaminergic receptors. In contrast, haloperidol caused a dose-dependent decrease in the content of homovanillic acid and 3,4-dihydroxyphenylacetic acid in the striatum and mesolimbic area. These results indicate that noradrenergic hyperfunction in the frontal cortex or thalamus induced by large doses of haloperidol may reduce the cataleptogenic effect of the drug via indirect stimulation of a dopaminoceptive neuron in the striatum or mesolimbic area.

The neurochemical background of clinical experiences that the patients receiving high dosage haloperidol showed no extrapyramidal side effects was investigated by using rats. Haloperidol at doses of 1, 2.5, 5, 7.5 and 10 mg/kg, ip caused a dose-dependent decrease in the duration of catalepsy. Haloperidol at a dose of 10 mg/kg induced catalepsy lasting only 20% of that by 1 mg/kg. Haloperidol decreased noradrenaline content in the frontal cortex and thalamus in a dose-dependent manner while 3-methoxy-4-hydroxyphenylglycol content showed a dose-dependent increase in the same brain areas. Thus, there is an inverse relationship between the duration of catalepsy and the ratio of 3-methoxy-4-hydroxyphenylglycol to noradrenaline in the frontal cortex or thalamus. In contrast, haloperidol caused a dose-dependent decrease in homovanillic acid and 3, 4-dihydroxyphenylacetic acid content in the striatum and mesolimbic area. These results indicate that noradrenergic hyperfunction in the frontal cortex or thalamus induced by high dosage haloperidol may reduce cataleptogenic effect of the drug via indirect stimulation of dopaminoceptive neuron in the striatum or mesolimbic area.

To assess the roles of substance P in neurologic or psychiatric illnesses, effects of acute or chronic (40- or 80-day dietary) treatment with trihexyphenidyl and carbamazepine alone or in combination with haloperidol on substance P content were investigated in the rat brain. Either acute or chronic trihexyphenidyl administration did not alter substance P content when administered alone and did not prevent the haloperidol-induced substance P decrease in the striatum and substantia nigra when coadministered with haloperidol. Chronic dietary carbamazepine administration dose-dependently increased substance P content in the striatum and substantia nigra, but not in the raphe area, in a haloperidol-reversible manner. Carbamazepine also dose-dependently increased gamma-aminobutyric acid levels in the substantia nigra without altering the striatal dopamine turnover rate. The lack of effect of trihexyphenidyl, an anticholinergic drug used to treat antipsychotic drug-induced extrapyramidal (Parkinson) syndromes, suggests that antipsychotic drug-induced reduction in substance P content is not involved in the extrapyramidal side effects. Since the effects of carbamazepine on substance P content are identical with previously described effects of lithium, an alteration in substance P neurotransmission may be one of the neurochemical bases of common clinical and behavioral effects of carbamazepine and lithium on affective disorders.

Eine stark verbesserte Methode zur Extraktion und damit zur Bestimmung von Acetylcholin in der weissen Substanz von Ratten- und Meerschweinchengehirn, die bis zu 20–40% hohere Werte ergibt als die bisherigen Verfahren, wird beschrieben.