An iontophoretic survey of opioid peptide actions in the rat limbic system

In search of opiate epileptogenic mechanisms

Edward D French, G. R. Siggins

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Iontophoretic and micropressure drug application and lesion techniques were used to investigate the cellular source of rat limbic system epileptiform responses to opioid peptides. Iontophoretically applied morphine, methionine enkephalin or β-endorphin inhibited the spontaneous or glutamate-activated firing of the great majority of single neurons in medial and lateral septum, amygdala and cingulate cortex. These inhibitions in firing were antagonized by iontophoresis of naloxone. In contrast to inhibitory effects in other limbic areas, morphine and the opioid peptides predominantly excited CA1 and CA3 pyramidal neurons in a naloxone-sensitive manner, as previously reported. On rare occasions, iontophoretically applied β-endorphin evoked repetitive waveforms similar to interictal population EPSPs or spikes. Micropressure application of opiates and peptides also excited hippocampal neurons indicating such responses were not current-induced artefacts. The possible role of the excitatory cholinergic septal hippocampal pathway in the facilitatory response of hippocampal units to the opiates was tested with iontophoretically applied atropine and scopolamine, or lesions of septal nuclei. None of these manipulations reduced the opioid-induced excitations; rather, septal lesions enhanced excitatory and epileptiform responses to the opiates. These results support the hypothesis that opiate-evoked epileptiform activity in the limbic system arises from enhanced pyramidal cell activity in the hippocampal formation, probably by a non-cholinergic mechanism.

Original languageEnglish (US)
Pages (from-to)127-146
Number of pages20
JournalRegulatory Peptides
Volume1
Issue number2
DOIs
StatePublished - 1980
Externally publishedYes

Fingerprint

Opiate Alkaloids
Limbic System
Opioid Peptides
Neurons
Endorphins
Rats
Pyramidal Cells
Naloxone
Morphine
Iontophoresis
Septal Nuclei
Methionine Enkephalin
Scopolamine Hydrobromide
Excitatory Postsynaptic Potentials
Gyrus Cinguli
Induced currents
Amygdala
Atropine
Artifacts
Cholinergic Agents

ASJC Scopus subject areas

  • Biochemistry
  • Endocrinology
  • Physiology
  • Neuroscience(all)

Cite this

An iontophoretic survey of opioid peptide actions in the rat limbic system : In search of opiate epileptogenic mechanisms. / French, Edward D; Siggins, G. R.

In: Regulatory Peptides, Vol. 1, No. 2, 1980, p. 127-146.

Research output: Contribution to journalArticle

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