Norepinephrine and acetylcholine release in guinea pig thalamus (VL).

Abstract

The release of 3H-NE and 3H-ACh from isolated guinea pig thalamic slices was investigated to determine the possible neurotransmitter role of these substances. Thalamic slices preloaded with 3H-NE or 3H-choline were impaled with bipolar electrodes and superfused at 0.2 ml/min with Krebs solution. Electrical stimulation increased the efflux of 3H-NE from these tissues in a current- and frequency-dependent fashion. The release of 3H-NE induced by stimulation of up to 1 mA was inhibited by TTX (10−6 M) or Ca-free medium containing EGTA (10−4 M). The stimulated 3H-NE release was enhanced by yohimbine (10−8 to 10−6 M) and reduced by Clonidine (10−5 M). These findings provide evidence for the neurotransmitter role of NE in this nucleus. The excitatory effect of yohimbine or the inhibitory effect of Clonidine on this 3H-NE release suggests the presence of presynaptic α2-receptors on the noradrenergic nerve terminals. The release of 3H-ACh was slightly increased by electrical stimulation. The stimulated 3H-ACh release was one fourth of the 3H-NE release evoked by the same stimulus parameters. Therefore, innervation of the cholinergic neuron may be less extensive than that of the noradrenergic neuron, in this nucleus.