Development of transient myasthenia-like symptoms in chickens injected with acetylcholine receptor from Torpedo marmorata [proceedings].

Tyrosine hydroxylase activity was determined in eight brain regions: cerebral cortex, tuberculum olfactorium, nucleus accumbens, hypothalamus, amygdala, striatum, pons and medulla. Tyrosine hydroxylase activity was measured by the radiometric method of Hendry & Iversen (1971). After 30 days of chronic treatment, the specific activity of tyrosine hydroxylase was decreased t o a value below the sensitivity of the assay in all eight brain regions analysed. Within 36 h after withdrawing treatment, the activity of this enzyme had returned to control values in three brain regions, but was still significantly below control in another four (Fig. 1). Only the activity in the cerebral cortex remained undetectable, but this could be misleading, since control enzyme activity in this region was only 3 % of the striatal activity, and in control samples of cortex radioactivity was only twice blank values. The results of Fig. I suggest that the regions with the highest control activity recover more rapidly on withdrawal of the drug. Our results on the changes in tyrosine hydroxylase activity have been compared with catecholamine concentrations in the same regions. The results indicate that there appears to be no significant cell loss in the striatum, amygdala and nucleus accumbens after chronically treating rats with methamphetamine on the aforementioned drug regime. However, a direct comparison with the observations of Seiden e t a / . (1976) has not been made, since there may be species differences between rat and monkey, and until it has been determined whether the activity of tyrosine hydroxylase returns to control values in all regions after a longer period of withdrawal.