Assessment of dopamine (DA) synthesis rate in selected parts of the rat brain with central noradrenergic lesion after administration of 5-HT3 receptor ligands

Abstract

The study objective was to determine the effect of central noradrenergic system lesions performed in the early extrafetal life period on dopamine synthesis in the rat brain. The content of L-dihydroxyphenylalanine (L-DOPA) was assessed in the frontal lobe, thalamus, hypothalamus and brain stem of rats by high-pressure chromatography with electrochemical detection (HPLC/ED) after administration of 5-HT3 receptor ligands. Adult male Wistar rats which underwent central noradrenergic lesions by DSP-4 administration (50 mg/kg m.c. i.p.) on day 1 and 3 of life received i.p. injections of the aromatic amino acid decarboxylase inhibitor (NSD-1050) in a dose of 100 mg/kg b.w. Next, 30 min after NSD-1050 injection, the animals were decapitated by guillotine. Selected brain structures were dissected and L-DOPA content was determined by HPLC/ED. A statistically significant reduction was found in DA synthesis in the group of animals with DSP-4 lesions induced by PBG (1-phenylbiguanide, 7.5 mg/kg b.w. i.p.) and ondansetron (1.0 mg/kg b.w. i.p.). Morphine and PBG had no major effect on DA synthesis in the cerebral cortex of both control animals and in rats with noradrenergic lesions. The assessment of the effect of DSP-4 lesions on L-DOPA content in the brain stem after administration of morphine (7.5 mg/kg b.w. s.c.), PBG (7.5 mg/kg b.w. i.p.) or ondansetron (1.0 mg/kg b.w. i.p.) separately or jointly showed a statistically significant increase in the synthesis of DA in animals with DSP-4 lesions, as compared to the control group exposed to 0.9% NaCl and morphine. The analysis of the effect of DSP-4 lesions on L-DOPA content in the thalamus and hypothalamus revealed no statistically significant differences between the control groups of rats and those with DSP-4 lesions. As shown by this model, permanent noradrenergic lesions in animals in the early extra-fetal period result in increased reactivity of the central dopamine system.