Heat-shock proteins expression in fish central nervous system and its possible relation with water acidosis resistance.

The expression of 70 and 60-kDa heat-shock proteins (HSP70 and HSP60) and glial fibrillary acidic protein (GFAP), determined by immunoblotting and immunohistochemical methods, was studied in fish neural tissue; moreover the possible correlation between the expression of these proteins in neural tissue and fish acidosis resistance was also examined. The HSP GFAP content was analyzed in four different teleostean fish species (gourami, carp, goldfish and trout) under control conditions and in carp under experimental conditions to induce HSPs expression. Under control conditions, HSP70 and HSP60 expression was similar in gourami, carp and goldfish, but gourami had the highest acidosis resistance; trout had the lowest HSP70 and 60 expression and lowest acidosis resistance. The HSP expression pattern was mainly neuronal under control conditions. HSP expression was induced in carp and the effect of this induction on acidosis resistance was studied. Two methods were used for HSP induction in carp: acid shock (2 h at 4.5 pH) and heat shock (2 h at 33 degrees C). A high acidosis resistance, although non-significant, was observed after heat pretreatment. An important HSP expression was detected in glial cells after induction. GFAP expression showed no association with acidosis resistance under either control or experimental conditions.

High ammonia diet: its effect on the glial fibrillary acidic protein (GFAP).

The effect of a recent hyperammonemic model, consisting of a high ammonia diet for 3, 7, 15, 45, and 90 days, on glial fibrillary acidic protein (GFAP) in the rat spinal cord and on blood ammonia levels has been studied. The high ammonia diet was prepared by mixing a standard diet with ammonium acetate (20% wt/wt); in addition, 5 mM of ammonium acetate was added to the water supply. GFAP contents were determined by means of immunoblotting analysis. The results demonstrated that this high ammonia diet model neither induces significant changes in GFAP immunoreactivity, nor modifies total protein concentration, and only induces significant blood hyperammonemic levels in the first days of treatment. An adaptive response to the diet is suggested and discussed to explain these results. A relation between ammonia and GFAP expression is suggested because transient hyperammonemia induces transient, although no significant, changes on GFAP expression.

Effect of ammonium acetate on the somatostatinergic system in the rat frontoparietal cortex.

Short (90 min)-, mid (5 days)-, and long-term (15 days) ammonium acetate (5 mmol/kg IP) administration decreased the number of specific [125I][Tyr11]somatostatin receptors in synaptosomes from the frontoparietal cortex without changing the affinity constant. Administration of ammonium acetate did no affect the levels of somatostatin-like immunoreactivity in the frontoparietal cortex. The administration of a single dose of N-carbamyl-L-glutamate (1 mmol/kg) plus L-arginine (1 mmol/kg) 1 h before the last administration of ammonium acetate totally blocked the inhibitory effects of the latter on somatostatin receptor number in the frontoparietal cortex synaptosomes. N-Carbamyl-L-glutamate plus L-arginine alone had no observable effect on the somatostatinergic system. The decrease in the number of somatostatin receptors induced by ammonium acetate might reflect decreased target cell sensitivity to somatostatin, a phenomenon that could contribute to the depressed neuronal excitability induced by ammonia in the rat frontoparietal cortex.

Somatostatin binding reduced by ammonium acetate in the rat hippocampus can be reversed by treatment with N-carbamyl-L-glutamate plus L-arginine.

The effects of short-term (90 min), mid-term (5 days), and long-term (15 days) administration of ammonium acetate (5 mmol/Kg day i.p.) on the somatostatinergic neurotransmitter system of the rat hippocampus have been studied. Scatchard analysis of the binding of 125I-Tyr11-somatostatin to hippocampal dissociated cells indicated that administration of ammonium acetate at the times studied were associated with a decrease in the number of somatostatin receptors in this brain area, whereas the affinity of the same receptors remained unchanged. Administration of ammonium acetate did not affect the levels of somatostatin-like immunoreactivity in the hippocampus. Treatment with N-carbamyl-L-glutamate (1 mmol/Kg, i.p.) plus L-arginine (1 mmol/kg), which lead to the conversion of ammonia into urea, prevented the ammonium acetate-induced changes in somatostatin binding in this brain area. N-carbamyl-L-glutamate plus L-arginine alone had no observable effect on the somatostatinergic system. The decrease in the number of somatostatin receptors induced by ammonium acetate might reflect a decreased sensitivity of the target cells to somatostatin, a phenomenon that could contribute to the depressed neuronal excitability induced by ammonia in the rat hippocampus.