N-(2-chloroethyl)- N-ethyl-2-bromobenzylamine reduces intracellular calcium response to noradrenaline in rat visual cortex

Abstract

Using the fluorescent indicator Fura-2, we investigated the effects of N-(2-chloroethyl)- N-ethyl-2-bromobenzylamine (DSP-4), a noradrenergic neurotoxin, on intracellular calcium responses to noradrenaline, N-methyl- D-aspartate, and carbamylcholine chloride in brain slices of the rat visual cortex. Noradrenergic depletion in the visual cortex of young rats was induced by DSP-4, and its selectivity was confirmed by two different methods, i.e., immunostaining with anti-dopamine-β-hydroxylase antibody and biochemical analysis by high-performance liquid chromatography. The treatment with DSP-4 (25 mg/kg i.p., ×2) caused disruption of noradrenergic fibers throughout all cortical layers, and reduced the content of noradrenaline to 6.4% of that in the normal control. In the normal cortex, bath-applied noradrenaline (100 μM) increased the intracellular calcium to 123% of the control in terms of the F 340/ F 380 ratio of Fura-2 fluorescence. Quantitative analysis of the F 340/ F 380 ratio was performed in layers II to IV, since the increase was mainly observed in these layers. The intracellular calcium response to noradrenaline was significantly ( P<0.0001) reduced in the DSP-4-treated animals to 63.2% of that in the normal control. The response to N-methyl- D-aspartate (100 μM) was also reduced, whereas the response to carbamylcholine chloride, a muscarinic cholinergic agonist (100 μM), was not affected by the DSP-4 treatment. From these findings we suggest that noradrenergic denervation by DSP-4 reduces the intracellular calcium response to noradrenaline through changes in the intracellular signal transduction.