Nicotinic acetylcholine receptors control acetylcholine and noradrenaline release in the rodent habenulo-interpeduncular complex

Nicotinic acetylcholine receptors (nACh receptors) play a central role in the habenulo-interpeduncular system. We studied nicotine-induced release of NA and ACh in the habenula and interpeduncular nucleus (IPN). Experimental approach: The habenula and IPN were loaded with [(3) H]-choline or [(3) H]-NA and placed in superfusion chambers. [(3) H]-ACh release was also stimulated using nicotinic agonists, electrical pulses and elevated [KCl]o in hippocampal and cortical slices from rats, wild-type mice and mice lacking α5, α7, β2, or β4 nACh receptor subunits. Finally, we analysed nACh receptor subtypes in the IPN using immunoprecipitation. Key

Nicotinic acetylcholine receptors (nACh receptors) play a central role in the habenulo-interpeduncular system. We studied nicotine-induced release of NA and ACh in the habenula and interpeduncular nucleus (IPN). Experimental approach: The habenula and IPN were loaded with [(3) H]-choline or [(3) H]-NA and placed in superfusion chambers. [(3) H]-ACh release was also stimulated using nicotinic agonists, electrical pulses and elevated [KCl]o in hippocampal and cortical slices from rats, wild-type mice and mice lacking α5, α7, β2, or β4 nACh receptor subunits. Finally, we analysed nACh receptor subtypes in the IPN using immunoprecipitation. Key

Nicotine induced release of [(3) H]-ACh in the IPN of rats and mice. This release was calcium-dependent but not blocked by tetrodotoxin (TTX); moreover, [(3) H]-ACh release was abolished in β4-knockout mice but was unaffected in β2- and α5-knockout mice. In contrast, nicotine-induced release of [(3) H]-NA in the IPN and habenula was blocked by TTX and reduced in both β2-knockout and β4-knockout mice, and dose-response curves were right-shifted in α5-knockout mice. Although electrical stimuli triggered the release of both transmitters, [(3) H]-ACh release required more pulses delivered at a higher frequency. Conclusions and implications: Our results confirm previous findings that β4-containing nACh receptors are critical for [(3) H]-ACh release in the mouse IPN. Experiments using α5-knockout mice also revealed that unlike in the hippocampus, nicotine-induced [(3) H]-NA release in the habenulo-interpeduncular system is altered in this knockout model. As α5-containing nACh receptors play a key role in nicotine intake, our results add NA to the list of transmitters involved in this mechanism.