Muscarinic cholinergic receptor blockade impairs free fatty acid mobilization during fasting in pigeons ( Columba livia )

Abstract

The effects of intracerebroventricular pretreatment with muscarinic (scopolamine or methylscopolamine; 2.7 nmol or 5.4 nmol) or nicotinic (mecamylamine, 2.7 nmol or 5.4 nmol) cholinergic receptor antagonists on plasma free fatty acid increases induced by intracerebroventricular injections of carbachol in conscious resting pigeons (Columba livia) were examined. Plasma glucose levels were also measured throughout the experiments. Pretreatment with methylscopolamine suppressed the lipolytic effect of carbachol injections, while mecamylamine left this response unchanged. Neither carbachol treatment alone, nor the pretreatments with cholinergic agents affected glucose levels. Subsequently, the effects of intracerebroventricular injections of methylscopolamine were investigated in 24-h food-deprived pigeons. The increase in free fatty acid levels after fasting was of a magnitude similar to that observed after carbachol treatment; intracerebroventricular injections of methylscopolamine (5.4 nmol) transiently but powerfully decreased plasma free fatty acids in 24-h food-deprived pigeons to levels comparable to those of free-feeding animals. The fasting-induced decrease in glucose levels was not affected by this treatment. These data indicate that the lipolytic response induced by carbachol may be mediated by central muscarinic cholinergic receptors and that this central cholinergic mechanism partially contributes to plasma free fatty acid increases observed during fasting. Furthermore, the absence of effects on glucose levels suggests that these cholinergic mechanisms participate selectively in the lipolytic component of the metabolic response to fasting.

Avian Muscarinic Receptors: An Update

“…In birds, fundamental pharmacological studies indicate that mAChRs located in the CNS are associated with vision, navigation, metabolism, and central thermoregulation [35]. However, the role of each of the mAChRs subtypes has not been established in either the CNS or peripheral nervous system [36].…”

Muscarinic acetylcholine receptor subtype expression in avian vestibular hair cells, nerve terminals and ganglion cells

“…In birds, preliminary pharmacological studies indicate that mAChRs located in the central nervous system are associated with vision, homing, navigation, metabolism and central thermoregulation (de Azevedo et al, 2002;Kohler et al, 1996;Chawla et al, 1975). However, the role of each of the mAChR subtypes has not been clearly established in either the central or peripheral nervous systems (Kohler et al, 1995;Dietl et al, 1988).…”