Priming of excitatory synapses by alpha1 adrenoceptor-mediated inhibition of group III metabotropic glutamate receptors

J Neurosci. 2003 Jul 16;23(15):6223-31. doi: 10.1523/JNEUROSCI.23-15-06223.2003.

Abstract

Adaptive responses mediated by the hypothalamus require sustained activation until homeostasis is achieved. Increases in excitatory drive to the magnocellular neuroendocrine cells that mediate these responses, however, result in the activation of a presynaptic metabotropic glutamate receptor (mGluR) that curtails synaptic excitability. Recent evidence that group III mGluRs can be inhibited by protein kinase C prompted us to test the hypothesis that activation of PKC by noradrenaline (NA) inhibits group III mGluRs and increases excitatory synaptic input to these cells. To examine the effects of NA on miniature EPSCs (mEPSCs), we obtained whole-cell recordings from magnocellular vasopressin and oxytocin neurons in the paraventricular nucleus of the hypothalamus. All of the neurons tested in the current study displayed an alpha1 adrenoceptor-mediated increase in mEPSC frequency in response to NA (1-200 microm). The excitatory effects of NA were mimicked by the phorbol ester PMA and blocked by the PKC inhibitor calphostin C. The activation of PKC inhibits the efficacy of group III mGluRs, resulting in an increase in mEPSC frequency in response to a subsequent exposure to NA. By removing feedback inhibition, this mechanism effectively primes the synapses such that subsequent activation is more efficacious. The novel form of synaptic rescaling afforded by this cross-talk between distinct metabotropic receptors provides a means by which ascending catecholamine inputs can facilitate the control of homeostasis by hypothalamic networks.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Excitatory Postsynaptic Potentials / drug effects
  • Excitatory Postsynaptic Potentials / physiology
  • Feedback, Physiological / physiology
  • GTP-Binding Protein alpha Subunits, Gq-G11
  • Glutamic Acid / metabolism
  • Heterotrimeric GTP-Binding Proteins / metabolism
  • Hypothalamus / cytology
  • Hypothalamus / drug effects
  • Hypothalamus / physiology
  • In Vitro Techniques
  • Male
  • Neurons / drug effects
  • Neurons / physiology
  • Norepinephrine / pharmacology
  • Paraventricular Hypothalamic Nucleus / cytology
  • Paraventricular Hypothalamic Nucleus / drug effects
  • Paraventricular Hypothalamic Nucleus / physiology
  • Patch-Clamp Techniques
  • Protein Kinase C / drug effects
  • Protein Kinase C / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Receptor Cross-Talk / physiology
  • Receptors, Adrenergic, alpha-1 / metabolism*
  • Receptors, Metabotropic Glutamate / antagonists & inhibitors*
  • Receptors, Metabotropic Glutamate / metabolism
  • Synapses / drug effects
  • Synapses / physiology*
  • Tetradecanoylphorbol Acetate / pharmacology
  • Type C Phospholipases / metabolism

Substances

  • Receptors, Adrenergic, alpha-1
  • Receptors, Metabotropic Glutamate
  • Glutamic Acid
  • Protein Kinase C
  • Type C Phospholipases
  • GTP-Binding Protein alpha Subunits, Gq-G11
  • Heterotrimeric GTP-Binding Proteins
  • Tetradecanoylphorbol Acetate
  • Norepinephrine