| pA2 online © Copyright 2004 The British Pharmacological Society |
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University of Bath Summer Meeting July 2004 |
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The J.A. Dickinson, I.W. Jones, J.N.C. Kew* C. Roberts* & S. Wonnacott. Dept. Biology & Biochemistry, University of Bath, Bath, BA2 7AY and *Psychiatry CEDD, GlaxoSmithKline, Harlow, Essex, CM19 5AW |
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7 nicotinic acetylcholine receptor modulates [3H]D-aspartate release from rat prefrontal cortex synaptosomes
Print abstractPresynaptic nicotinic acetylcholine receptors (nAChR) modulate the release of several neurotransmitters, including dopamine and glutamate (Wonnacott, 1997). In this study, the nAChR modulation of [3H]D-aspartate (D-asp) release from prefrontal cortex (PFC) synaptosomes has been pharmacologically characterised using the technique of open-chamber superfusion. D-asp serves as a surrogate for glutamate (Rousseau et al., 2002).
PFC synaptosomes from 2 male Sprague-Dawley rats (250 -350 g) were loaded with 0.2 µM D-asp at 37°C for 15 min. Aliquots were added to superfusion chambers and perfused with Krebs-bicarbonate buffer ± antagonist (0.75 ml min-1) for 24 min to remove excess D-asp before fractions were sequentially collected (2 min fractions). D-asp release was evoked by the application of a nAChR agonist (90 s). Release was calculated as a percentage of the total radioactivity present at the point of stimulation .
Nicotine and the α 7 nAChR selective agonists, choline and AR-R17779, evoked D-asp release in a concentration-dependent manner. Cd2+ (100 µM) blocked nicotine (10 µM) and choline (10 mM)-evoked release by 78.1 ± 3.1% (n=3) and 77.7 ± 11.7% (n=3) respectively, consistent with release by Ca2+-dependent exocytosis. The non-selective nAChR antagonist mecamylamine (20 µM) and 
7 nAChR selective antagonist -bungarotoxin ( 40 nM) significantly inhibited nicotine (10 µM) and choline (10 µM)-evoked D-asp release (Figure 1).
These data suggest the presence of 7 nAChR on excitatory amino acid terminals within the rat PFC. This was substantiated by immunocytochemical evidence for the colocalisation of the 7 nAChR with glutamatergic terminals identified by antibodies to the vesicular glutamate transporters 1 and 2.
FIGURE 1: [3H]D-aspartate release in response to nAChR agonists, nicotine (n=4) and choline (n=3), in the presence or absence of antagonists, mecamylamine (mec, 20 µM) or - bungarotoxin ( α bgt, 40 nM). *P<0.05, significantly different from its respective control in the absence of antagonist (Student’s paired t-test).
Wonnacott S. (1997) Trends Neurosci. 20; 92-98
Rousseau S. J. et al. (2002) BJP ( Proceedings Supplement ) 136; 55P
Supported by BBSRC CASE studentship with GlaxoSmithKline