Proceedings of The Physiological Society
AstraZeneca (2010) Proc Physiol Soc 18, C16 and PC16
CCK-stimulation of GLP-1 neurons involves α2 adrenergic receptor activation
K. Hisadome1, F. Reimann2, F. M. Gribble2, S. Trapp1
1. Department of Surgery and Cancer, Biophysics Section, Imperial College London, London, United Kingdom. 2. Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom.
Cholecystokinin-octapeptide (CCK-8) is released from the gut postprandially and inhibits food intake. Peripheral application of CCK-8 activates c-FOS in the vagal complex. Immunohistochemical characterisation of these c-FOS-positive cells revealed that these include catecholaminergic and glucagon-like-peptide 1 (GLP-1) producing pre-proglucagon (PPG) neurons. Hindbrain catecholaminergic neurons have been implicated in glucoprivic feeding and GLP-1 injected into the brain causes satiety. In order to analyze functional effects of CCK-8 and catecholamines on PPG neurons we used transgenic mice expressing YFP under PPG promoter control, thus allowing patch-clamp recordings from PPG cells identified by fluorescence. Coronal slices (200μm) were obtained from adult transgenic mice after halothane anaesthesia. Perforated patch-clamp (current clamp) and conventional whole-cell (voltage clamp) recordings were performed on PPG neurons under visual control at 32°C. In current-clamp, 10 μM adrenaline (AD) and 100 μM noradrenaline (NA) increased action potential firing rate (by 58±14 % and 85±37 %, respectively), but had no effect on membrane potential and conductance. In voltage-clamp, AD and NA increased the frequency of spontaneous excitatory synaptic currents (sEPSCs). Kynurenic acid (1mM) reduced the frequency of sEPSCs from 2.4±0.5 Hz to 0.2±0.04 Hz and blocked the AD-induced increase in sEPSC frequency (n=5). The AD effect was also prevented by the α2 receptor antagonist yohimbine (n=5). TTX reduced sEPSC frequency from 3.0±0.6 Hz to 0.7±0.1 Hz in 15 out of 24 PPG cells and blocked the effect of AD. In the remaining 9 PPG neurons TTX did not affect sEPSC frequency and the AD effect remained in 5 of these cells. 100 nM CCK-8 increased the frequency of sEPSCs by 79±1 % in 3 out of 8 cells tested. Yohimbine (10 μM) blocked this response in all 3 cells. PPG neurons do not receive a direct adrenergic input, but their glutamatergic input is modulated by α2-adrenergic receptor activation. This modulation takes place at either of two sites: at the glutamatergic synapse (TTX-resistant) or distant from the synapse (TTX-sensitive). CCK-8 stimulation of PPG neurons is indirect and involves activation of α2-adrenergic receptors, thus suggesting that catecholaminergic neurons are essential for the effect of CCK on PPG neurons.
Where applicable, experiments conform with Society ethical requirements