Optoactivation of parvalbumin neurons in the spinal dorsal horn evokes GABA release that is regulated by presynaptic GABAB receptors

Neurosci Lett. 2015 May 6;594:55-9. doi: 10.1016/j.neulet.2015.03.050. Epub 2015 Mar 26.

Abstract

Among heterogeneous neural cells in the spinal dorsal horn, parvalbumin (PV)-positive neurons are one subtype of GABA (γ-aminobutyric acid)-containing interneurons. Using an optogenetic approach, we expressed blue light-sensitive cation channel channelrhodopsin-2 (ChR2) via a viral vector on PV neurons in the spinal dorsal horn. Combined with in vitro whole-cell recordings, we activated ChR2 expressed on PV neurons by blue light and recorded GABAA receptor-mediated light-evoked inhibitory postsynaptic currents (L-IPSCs). The L-IPSCs were action potential-dependent and abolished by the GABAA receptor antagonist picrotoxin, indicating a synchronic GABA release from presynaptic terminals. Activation of GABAB receptors (the metabotropic receptors of GABA) on presynaptic terminals by a putative agonist, baclofen, depressed the amplitude of L-IPSCs. This depression was largely occluded by pretreatment with the highly selective Cav2.1 (P/Q-type) Ca(2+) channel blocker ω-agatoxin IVA. N-type Ca(2+) channel blocker ω-conotoxin GVIA showed less effects on either L-IPSCs or baclofen depression. We conclude that optoactivation of PV-ChR2 neurons in the spinal dorsal horn induces GABA release from presynaptic terminals, which is modulated by presynaptic GABAB receptors that are coupled to P/Q-type Ca(2+) channels. Importantly, our studies provide a simple and reliable optogenetic approach to study dorsal horn neural circuits.

Keywords: GABA; Optogenetics; Pain; Spinal cord; Whole-cell recordings.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Channelrhodopsins
  • Female
  • Male
  • Mice, Transgenic
  • Optogenetics
  • Parvalbumins / metabolism*
  • Posterior Horn Cells / metabolism*
  • Receptors, GABA-B / metabolism*
  • Receptors, Presynaptic / metabolism*
  • Substantia Gelatinosa / metabolism
  • gamma-Aminobutyric Acid / metabolism*

Substances

  • Channelrhodopsins
  • Parvalbumins
  • Receptors, GABA-B
  • Receptors, Presynaptic
  • gamma-Aminobutyric Acid