Baclofen and adenosine inhibition of synaptic transmission at CA3-CA1 synapses display differential sensitivity to K+ channel blockade

Academic Article

Abstract

  • The metabotropic GABAB and adenosine A1 receptors mediate presynaptic inhibition through regulation of voltage-dependent Ca 2+ channels, whereas K+ channel regulation is believed to have no role at the CA3-CA1 synapse. We show here that the inhibitory effect of baclofen (20 μM) and adenosine (300 μM) on field EPSPs are differentially sensitive to Cs+ (3.5 mM) and Ba2+ (200 μM), but not 4-aminopyridine (100 μM). Barium had no effect on paired-pulse facilitation (PPF) in itself, but gave significant reduction (14 ± 5%) when applied in the presence of baclofen, but not adenosine, suggesting that the effect is presynaptic and selective on the GABAB receptor-mediated response. The effect of Ba2+ on PPF was not mimicked by tertiapin (30 nM), indicating that the underlying mechanism does not involve GIRK channels. Barium did not affect PPF in slices from young rats (P7-P8), suggesting developmental regulation. The above effects of Ba2+ on adult tissue were reproduced when measuring evoked whole-cell EPSCs from CA1 pyramidal neurons: PPF was reduced by 22 ± 3% in the presence of baclofen and unaltered in adenosine. In contrast, Ba2+ caused no significant change in frequency or amplitude of miniature EPSCs. The Ba2+-induced reduction of PPF was antagonized by LY341495, suggesting metabotropic glutamate receptor involvement. We propose that these novel effects of Ba2+ and Cs + are exerted through blockade of inwardly rectifying K+ channels in glial cells, which are functionally interacting with the GABA B receptor-dependent glutamate release that generates heterosynaptic depression. © 2011 Springer Science+Business Media, LLC.
  • Authors

    Digital Object Identifier (doi)

    Author List

  • Skov J; Andreasen M; Hablitz JJ; Nedergaard S
  • Start Page

  • 587
  • End Page

  • 596
  • Volume

  • 31
  • Issue

  • 4