Enhanced 5-HT(2A) receptor status in the hypothalamus and corpus striatum of ethanol-treated rats

Abstract

Aim: Brain is the major target for the actions of ethanol and it can affect the brain in a variety of ways. In the present study we have investigated the changes in 5-HT level and the 5-HT(2A) receptors in the ethanol-treated rats.

Methods: Wistar adult male rats of 180-200 g body weight were given free access to 15% (v/v) (approx.7.5 g/Kg body wt./day) ethanol for 15 days. Controls were given free access to water for 15 days. Brain 5-HT and its metabolites were assayed by high performance liquid chromatography (HPLC) integrated with an electrochemical detector (ECD) fitted with C-18-CLS-ODS reverse phase column. 5-HT(2A) receptor binding assay was done with different concentrations of [3H] MDL 100907.

Results: The hypothalamic 5-HT content significantly increased (P < 0.001) with a decreased (P < 0.001) 5-HIAA/5-HT turnover in the ethanol-treated rats when compared to control. The corpus striatum 5-HT content significantly decreased (P < 0.01) with increased (P < 0.01) 5-HIAA/5- HT turnovers in the ethanol-treated rats when compared to control. Scatchard analysis of [(3)H] MDL 100907 against ketanserin in hypothalamus showed a significant increase (P < 0.001) in B(max )with a decreased affinity (P < 0.001) in ethanol-treated rats when compared to control. The competition curve for [3H] MDL 100907 against ketanserin fitted one-site model in all the groups with unity as Hill slope value. An increased K(i) and log (EC(50)) value were also observed in ethanol-treated rats when compared to control. Scatchard analysis of [3H] MDL 100907 against ketanserin in the corpus striatum of ethanol-treated rats showed a significant increase (P < 0.001) in B(max) and in affinity (P < 0.01) when compared to control. The change in affinity of the receptor protein in both corpus striatum and hypothalamus shows an altered receptor. The competition curve for [(3)H] MDL 100907 against ketanserin fitted one-site model in all the groups with unity as Hill slope value. There was no significant change in K(i) and log (EC (50)) value in ethanol-treated rats when compared to control.

Conclusion: The present study demonstrated the enhanced 5-HT(2A) receptor status in hypothalamus and corpus striatum. The ethanol-induced enhanced 5-HT(2A) receptors in the hypothalamus and corpus striatum has clinical significance in the better management of ethanol addiction. This will have therapeutic application.

Fig. 1

Scatchard analysis of [³H] MDL 100907 against ketanserin in the hypothalamus of control- and ethanol-treated rats. Crude synaptic membrane preparation was suspended in 50 mM Tris HCl buffer pH 7.7 and used for assay. 0.25–2.0nM of [³H] MDL 100907 was incubated with and without excess of unlabelled ketanserin (100 mM). Tubes were incubated at 37 °C for 30 min and filtered rapidly through GF/B filters (Whatman). Bound radioactivity was determined with cocktail-T in a Wallac 1409 liquid scintillation counter. Specific binding was determined by subtracting non-specific binding from total binding

Fig. 2

Displacement of [³H] MDL 100907 against ketanserin in the hypothalamus of control- and ethanol-treated rats. Competition studies were carried out with 0.5 nM [³H] MDL 100907 in each tube with the unlabelled ketanserin concentrations varying from 10–12 to 10–3 M. The tubes were incubated at 370 °C for 30 min and filtered rapidly through GF/B filters (Whatman). The filters were washed quickly by three successive washing with 3.0 ml of ice-cold buffer containing 50 mM Tris buffer, pH 7.7. Values are representation of 4–6 separate experiments

Fig. 3

Scatchard analysis of [³H] MDL 100907 against ketanserin in the corpus striatum of control- and ethanol-treated rats. Crude synaptic membrane preparation was suspended in 50 mM Tris HCl buffer pH 7.7 and used for assay. 0.25–2.0nM of [³H] MDL 100907 was incubated with and without excess of unlabelled ketanserin (100 mM). Tubes were incubated at 37 °C for 30 min and filtered rapidly through GF/B filters (Whatman). Bound radioactivity was determined with cocktail-T in a Wallac 1409 liquid scintillation counter. Specific binding was determined by subtracting non-specific binding from total binding

Fig. 4

Displacement of [³H] MDL 100907 against ketanserin in the corpus striatum of control- and ethanol-treated rats. Competition studies were carried out with 0.5 nM [³H] MDL 100907 in each tube with the unlabelled ketanserin concentrations varying from 10–12 to 10–3 M. The tubes were incubated at 370 °C for 30 min and filtered rapidly through GF/B filters (Whatman). The filters were washed quickly by three successive washing with 3.0 ml of ice-cold buffer containing 50 mM Tris buffer, pH 7.7. Values are representation of 4–6 separate experiments