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Behavioral and neuroendocrine actions of the Met-enkephalin-related peptide MERF

E Bujdosó1, M Jászberényi, J Farkas

  • 1Department of Pathophysiology, University of Szeged, Neurohumoral Research Group, Hungarian Academy of Sciences, Szeged, Hungary.

Hormones and Behavior
|April 16, 2003
PubMed

Insights

Met(5)-enkephalin-Arg(6)-Phe(7) (MERF) activates the hypothalamo-pituitary-adrenal (HPA) system and influences behavior in mice. Opioid and kappa-receptors mediate these neuroendocrine and behavioral effects, with corticotropin-releasing hormone (CRH) involvement.

Area of Science:

  • Neuroendocrinology
  • Behavioral Neuroscience
  • Opioid Peptides

Background:

  • Proenkephalin derivatives like Met(5)-enkephalin-Arg(6)-Phe(7) (MERF) are implicated in regulating physiological and behavioral processes.
  • The hypothalamo-pituitary-adrenal (HPA) axis is a key neuroendocrine system involved in stress response and behavior.
  • Understanding the receptor mechanisms underlying MERF's actions is crucial for elucidating its neurobiological roles.

Purpose of the Study:

  • To investigate the effects of MERF on the HPA system and open-field behavior in mice.
  • To identify the specific opioid and other receptor systems mediating MERF's neuroendocrine and behavioral actions.
  • To explore the role of corticotropin-releasing hormone (CRH) and dopaminergic pathways in MERF's effects.

Main Methods:

  • Intracerebroventricular (ICV) injection of MERF in mice.
  • Administration of opioid antagonists (naloxone, nor-binaltorphimine) and dopamine/CRH antagonists prior to MERF.
  • Measurement of plasma corticosterone levels.
  • Assessment of open-field behavior (square crossing, rearing).
  • In vitro superfusion of striatal slices to measure dopamine release.

Main Results:

  • ICV injection of MERF increased locomotor activity, rearing, and plasma corticosterone levels.
  • Both naloxone and nor-binaltorphimine dose-dependently attenuated MERF-induced HPA activation.
  • Naloxone blocked MERF's behavioral effects, while nor-binaltorphimine showed no significant inhibition.
  • CRH antagonist diminished both HPA activation and motor responses; haloperidol only affected motor activity.
  • MERF did not alter basal or evoked dopamine release from striatal slices.

Conclusions:

  • Opioid receptor mediation is predominant in MERF's neuroendocrine effects.
  • MERF's action on the HPA system appears to be mediated by kappa-receptors.
  • MERF-evoked behavioral responses involve CRH release and dopaminergic neurons.
  • MERF activates paraventricular CRH neurons, but dopaminergic transmission is not critical for its hypothalamic action.

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