Glutamate and GABA levels and glutamate decarboxylase activity in brain regions of rats after prolonged treatment with alkali cations

Sodium p-Aminosalicylic Acid Reverses Sub-Chronic Manganese-Induced Impairments of Spatial Learning and Memory Abilities in Rats, but Fails to Restore γ-Aminobutyric Acid Levels

Excessive manganese (Mn) exposure is not only a health risk for occupational workers, but also for the general population. Sodium para-aminosalicylic acid (PAS-Na) has been successfully used in the treatment of manganism, but the involved molecular mechanisms have yet to be determined. The present study aimed to investigate the effects of PAS-Na on sub-chronic Mn exposure-induced impairments of spatial learning and memory, and determine the possible involvements of γ-aminobutyric acid (GABA) metabolism in vivo. Sprague-Dawley male rats received daily intraperitoneal injections MnCl₂ (as 6.55 mg/kg Mn body weight, five days per week for 12 weeks), followed by daily subcutaneous injections of 100, 200, or 300 mg/kg PAS-Na for an additional six weeks. Mn exposure significantly impaired spatial learning and memory ability, as noted in the Morris water maze test, and the following PAS-Na treatment successfully restored these adverse effects to levels indistinguishable from controls. Unexpectedly, PAS-Na failed to recover the Mn-induced decrease in the overall GABA levels, although PAS-Na treatment reversed Mn-induced alterations in the enzyme activities directly responsible for the synthesis and degradation of GABA (glutamate decarboxylase and GABA-transaminase, respectively). Moreover, Mn exposure caused an increase of GABA transporter 1 (GAT-1) and decrease of GABA A receptor (GABA_A) in transcriptional levels, which could be reverted by the highest dose of 300 mg/kg PAS-Na treatment. In conclusion, the GABA metabolism was interrupted by sub-chronic Mn exposure. However, the PAS-Na treatment mediated protection from sub-chronic Mn exposure-induced neurotoxicity, which may not be dependent on the GABA metabolism.

Acute and chronic effects of lithium chloride on GABA-ergic function in the rat corpus striatum and frontal cerebral cortex

The acute (1 h, i.p.) and chronic (14 days, p.o.) effects of LiCl treatment upon GABA-ergic neurons were studied in the rat corpus striatum and frontal cerebral cortex. One hour after a single injection of LiCl the activity of glutamic acid decarboxylase (GAD) was reduced by 29% in the striatum (2 meq/kg LiCl) and by 38% in the cerebral cortex (10 meq/kg LiCl). In contrast, striatal GAD was activated by 34% 1 h after the injection of 10 meq/kg of LiCl; this dose also reduced the endogenous striatal GABA level by 24%. After 14 days of oral LiCl administration (2 meq/kg/day): a) cortical GAD activity was enhanced by 50% and GABA concentration was decreased by 28%; b) no changes were observed in the striatum. These findings suggest that: LiCl administration stimulates GABA-ergic function in specific areas (depending on the dose and length of treatment) increasing both GAD activity and probably GABA release. This occurs in the striatum after acute treatment only with a high dose, and in the frontal cerebral cortex after chronic treatment with a low dose.

Effect of lithium and other alkali metals on brain chemistry and behavior. I. Glutamic acid and GABA in brain regions

Glutamic acid and GABA concentrations were measured in brain areas of rats injected with the chloride salts of Li+, Na+, K", Rb+ or Cs+ for 5 days. Regional changes in brain glutamic acid and GABA were found in animals after lithium, rubidium or cesium, but not potassium, compared to sodium treatments. Increased glutamic acid and GABA levels, caused by lithium and rubidium, were found in brain structures (hypothalamus and amygdala) known to be involved in emotional behavior. Whether these changes are associated with the effective use of lithium and, perhaps, of rubidium in affective disorders remains obscure.