X-Message-Number: 26366 From: "Basie" <> Subject: GABAA action Date: Tue, 21 Jun 2005 21:10:59 -0400 I came across this interesting presentation. Start of quote: Oral 2. Use-dependent shift from inhibitory to excitatory GABAA action in interneurons induces beta-gamma oscillations in the hippocampus K.L ms and T.Taira Department of Biosciences, and Institute of Biotechnology, University of Helsinki, FIN-00014. Background: Glutamatergic excitation has a critical role in the generation and maintenance of fast network oscillations in the hippocampus. In addition to glutamatergic input, excitatory drive to hippocampal neurons can also be provided by synaptic activation of GABAA receptors (GABAARs). However, the physiological relevance and the generation mechanisms of this "paradoxical" GABAA action in different cell types are largely unknown. Results: We now show that in the absence of glutamatergic transmission a fast switch from inhibitory to excitatory GABAA action induces bursts of synchronous beta (15-30 Hz) and low gamma frequency (30-40 Hz) oscillations in the CA3 interneuronal network. The GABAAR-mediated postsynaptic potentials (PSPs) in the interneurons were typically hyperpolarizing, but by an increase in the GABAAR-mediated conductance the PSPs became depolarizing and excitatory. During mutual excitation of interneurons, GABAAR-mediated currents displayed beta-gamma oscillations. A shift of GABAAR-mediated PSPs to depolarizing by the GABAAR permeant weak acid anion formate (20-30 mM) or by up-modulation of the GABAA conductance with pentobarbital (100 M) provoked interneuronal population bursting. The synchronous beta-gamma rhytmicity, however, was dependent on electrotonic coupling, since it was abolished by gap-junction blockers, although the population discharges were preserved. Conclusions: We conclude that the use-dependent switch from inhibitory to excitatory GABAA action provides a mechanism for the generation of synchronous b-g bursts in the interneuron network. Further, it provides an alternative mechanism for short-term plasticity in excitatory synapses in interneurons. End of quote. Basie http://www.agingtheory.com/pages/1/index.htm Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=26366