Nicotinic receptors mediate increased GABA release in brain through a tetrodotoxin-insensitive mechanism during prolonged exposure to nicotine

Neuroscience. 2002;115(1):137-44. doi: 10.1016/s0306-4522(02)00371-8.

Abstract

The effects of nicotine on the spontaneous release of GABA from nerve terminals in the chick lateral spiriform nucleus were examined using whole cell patch-clamp recording in brain slices. Exposure to 1 microM nicotine produced an early immediate increase in the frequency of spontaneous postsynaptic GABAergic currents. This effect was blocked in the presence of 0.5 microM tetrodotoxin. However, a prolonged application of 0.1-1 microM nicotine (>3 min) caused a tetrodotoxin-insensitive increase in the frequency of spontaneous GABAergic currents. This late tetrodotoxin-insensitive effect was blocked by the nicotinic antagonists dihydro-beta-erythroidine (30 microM) and mecamylamine (10 microM), but not by methyllycaconitine (50-100 nM), indicating that activation of high affinity nicotine receptors was mainly responsible for this effect. This enhancement was inhibited by the high threshold Ca(2+) channel blocker Cd(2+) (100 microM), but not by dantrolene or ryanodine. The tetrodotoxin-insensitive enhancement of the frequency of GABA currents by nicotine was reduced by inhibition of cAMP-dependent protein kinase with HA1004 (30 microM), but not by inhibition of protein kinase C with staurosporine (1 microM), and was facilitated by forskolin (10 microM) or bromo-cAMP (50 microM). The results indicate that nicotine-enhanced GABA release can operate through both tetrodotoxin-sensitive and -insensitive mechanisms in a single brain region and that a second messenger cascade may be involved in the tetrodotoxin-insensitive enhancement by nicotine.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Brain / drug effects*
  • Brain / metabolism*
  • Chick Embryo
  • In Vitro Techniques
  • Nicotine / toxicity*
  • Receptors, Nicotinic / physiology*
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology
  • Tetrodotoxin / pharmacology*
  • gamma-Aminobutyric Acid / biosynthesis
  • gamma-Aminobutyric Acid / metabolism*

Substances

  • Receptors, Nicotinic
  • Tetrodotoxin
  • gamma-Aminobutyric Acid
  • Nicotine