Galanin and neuropeptide Y reduce cholinergic transmission in the heart of the anaesthetised mouse

1 This study investigated the effects of galanin (GAL) on inhibition of cholinergic (vagal) activity in the mouse heart using control galanin knockout (GAL-KO) and GAL-1R receptor knockout (GAL-1R-KO) mice. 2 In pentobarbitone anaesthetised mice, supramaximal stimulation every 30s of the vagus nerve innervating the heart, increased pulse interval (PI) by approximately 50 ms or decreased heart rate by approximately 100 beats min(-1). This response was attenuated by intravenous administration of GAL (dose ranged from 0.8 to 13 nmol kg(-1)) in a dose-dependent manner. 3 In GAL-KO mice, the magnitude of inhibition of the increase in PI (DeltaPI) following a bolus dose of GAL was not different from the DeltaPI in control mice, and neuropeptide Y (NPY), previously shown to attenuate vagal inhibitory activity in mice, evoked a comparative inhibition of DeltaPI in GAL-KO mice. 4 In GAL-1R-KO mice, an intravenous, bolus injection of GAL had no inhibitory effect on vagal activity. 5 In control mice, stimulation of the sympathetic nerve at 25 V, 10 Hz for 2 min in the presence of propranolol evoked a long-lasting attenuation of DeltaPI. The inhibitory effect on DeltaPI was reduced in the presence of the NPY Y-2 antagonist, BIIE0246. 6 In GAL-1R-KO mice, stimulation of the sympathetic nerve in the presence of propranolol evoked an attenuation of DeltaPI not significantly different from the response in control mice in the presence of BIIE0246. Following administration of BlIE0246 in GAL-1R-KO mice, the inhibition of DeltaPI that followed stimulation of the sympathetic nerve was abolished. 7 These findings support the view that the nerve terminals of parasympathetic neurons in the mouse heart possess both GAL-1R and NPY Y-2 receptors which, when activated, reduce acetylcholine release.