Levels of several amino acids in the cerebellar peduncles and four medullary nuclei of control and 3-acetylpyridine-treated rats

Regulatory role of cysteine dioxygenase in cerebral biosynthesis of taurine. Analysis using cerebellum from 3-acetylpyridine-treated rat

The effect of 3-acetylpyridine (3-AP) administration on the biosynthesis of taurine in the rat brain has been studied. Treatment with 3-AP induced a significant decrease in the cerebellar contents of taurine and its metabolic precursors, cysteine sulfinic acid (CSA) and cysteic acid (CA), as well as a selective degeneration of climbing fibers in the molecular layer of the cerebellum. It was found that the activity of cerebral cysteine dioxygenase, the enzyme catalyzing the formation of CSA from cysteine, consisted of two systems with low and high Km values. The 3-AP-induced attenuation of cysteine dioxygenase activity with a low Km value was noted only in the cerebellum, while that with a high Km value was detected not only in the cerebellum but also in other brain areas such as the medulla oblongata, striatum and cerebral cortex. In contrast, no alteration in the activity of cysteine sulfinic acid decarboxylase (CSD) was observed in any brain areas examined following the administration of 3-AP. Furthermore, it was found that essentially no cystamine as well as a very low activity of cysteamine dioxygenase is present in the brain. The present results suggest that taurine in the brain is synthesized from cysteine, mainly by the CSA and CA pathways, and the observed decline of cerebellar taurine in 3-AP-treated rats may be due to an attenuation of the biosynthesis, possibly at the step of cysteine dioxygenase. A possible regulatory role of cysteine dioxygenase with a low Km value in the biosynthesis of cerebral taurine is also suggested.

Oxidative metabolism and acetylcholine synthesis during acetylpyridine treatment

In order to clarify the mechanisms by which nicotinic acid deficiency impairs brain function, the effects of the nicotinic acid antimetabolite, 3-acetylpyridine, have been investigated on behavior, cerebral oxidative metabolism, and acetylcholine synthesis. In young rats (21-23 days old), 3-acetylpyridine caused dose- and time-related deficits in behavior, as measured by a neurological scale and by "tight-rope" performance, loss of body weight, and decreased survival. An intermediate dosage decreased cerebral glucose utilization in the inferior olivary nuclei, but increased it in the fastigial, interpositus, red, dentate, vestibular, posterior mamillary, and habenular nuclei. Selective alteration of metabolism was also observed in brain slices from 3-acetylpyridine-treated rats. Although forebrain slices were unaffected, in brainstem slices the synthesis of acetylcholine decreased by 34% with depolarizing (31 mM) concentrations of K+ (P less than 0.05). This dose of 3-acetylpyridine did not deplete the total pool of NAD in any of the 7 brain regions examined. Thus, the nicotinic acid deficiency which results from 3-acetylpyridine treatment appears to be yet another metabolic encephalopathy in which cholinergic systems are impaired.

Effects of injection of 3-acetylpyridine on the levels of taurine in the cerebellum and medulla of the rat: a reappraisal

Values for taurine in a 5% TCA extract of whole rat medulla were decreased by 19% after acid hydrolysis of samples. Values for taurine in a similar extract of rat cerebellum were unaffected by hydrolysis. The values for taurine were lower in the medulla and cerebellum of 3-acetylpyridine treated rat (65 mg/kp i.p.) when the unhydrolyzed TCA extract was assayed. However, when the hydrolyzed TCA extract was assayed, the level of taurine in the medulla was not lower in the 3-AP treatment rat but it was reduced in the cerebella of the drug-treated group. 3-Acetylpyridine appeared to reduce the levels in the medulla of acid-labile compounds which can interfere with the estimation of taurine.