Elsevier

Neuroscience Research

Volume 22, Issue 4, July 1995, Pages 367-374
Neuroscience Research

Research report
Release of false transmitter serotonin from the dopaminergic nerve terminals of the rat pituitary intermediate lobe

https://doi.org/10.1016/0168-0102(95)00913-EGet rights and content

Abstract

Rat pituitary intermediate lobe contains two types of serotonin-immunoreactive nerve terminals. Most of them are dopaminergic, in which serotonin acts as a false transmitter, while the rest are true serotonergic nerves. In the present study, release of the false transmitter serotonin from the dopaminergic nerve terminals was studied by loading the neurons in vivo with serotonin precursor l-tryptophan and MAO inhibitor pargyline, which results in accumulation of false transmitter serotonin. Subsequently pituitary neurointermediate lobe complexes were incubated in the presence of various agents. Potassium induced dramatic release of serotonin. This release was Ca2+-dependent, as demonstrated by an inhibition by Mg2+, and transporter-independent, since it was unaffected by GBR 12909 (a dopamine transport inhibitor). Tyramine and sodium nitroprusside, a nitric oxide donor, caused slight to remarkable release of serotonin. This release was inhibited by GBR 12909, suggesting that it was transporter-dependent. Presynaptic stimulation with apomorphine or haloperidol, dopamine receptor agonist or antagonist, respectively, or isoproterenol, agonist of the β-adrenergic receptor, did not significantly release serotonin. Thus, it seems that presynaptic receptors per se cannot induce release of significant amounts of serotonin from the IL dopaminergic fibers. Our results suggest that false transmitter serotonin in the IL dopaminergic nerve terminals is released primarily by the classical exocytotic release mechanism, but may also be partly released by the transporter-dependent, non-exocytotic release.

References (46)

  • J.A. Stamford et al.

    Striatal dopamine terminals release serotonin after 5-HTP pretreatment: in vivo voltammetric data

    Brain Res.

    (1990)
  • H.W.M. Steinbusch et al.

    Localization of serotonin in the central nervous system by immunohistochemistry: description of a specific and sensitive technique and some applications

    Neuroscience

    (1978)
  • C.G.J. Sweep et al.

    Isoproterenol-stimulated release of β-endorphin and related peptides from the rat pituitary neurointermediate lobe in vitro: evidence for preferential release of certain molecular forms of β-endorphin

    Neuropeptides

    (1990)
  • S. Vanhatalo et al.

    Pharmacological characterization of serotonin synthesis and uptake suggest a false transmitter role for serotonin in the pituitary intermediate lobe

    Neurosci. Res.

    (1994)
  • H. Vaudry et al.

    Multineuronal control of the intermediate lobe of the pituitary

    Br. Res. Bull.

    (1986)
  • G.J. Augustine et al.

    Calcium action in synaptic transmitter release

    Annu. Rev. Neurosci.

    (1987)
  • R. Bach

    Non-synaptic diffusion neurotransmission (NDN) in the brain

    Neurochem. Int.

    (1993)
  • N. Bäck et al.

    Catecholamine-synthesizing enzymes in the rat pituitary. An immunohistochemical study

    Histochemistry

    (1987)
  • R.D. Blakely et al.

    Cloning and expression of a functional serotonin transporter from rat brain

    Nature

    (1991)
  • J.A. Carr et al.

    In vivo effects of serotonergic agents on α-melanocyte-stimulating hormone secretion

    Neuroendocrinology

    (1991)
  • R.A. Cohen

    Platelet 5-hydroxytryptamine and vascular adrenergic nerves

    News Physiol. Sci.

    (1988)
  • I.S. Fairbrother et al.

    In vivo mechanisms underlying dopamine release from rat nigrostriatal terminals: II. Studies using potassium and tyramine

    J. Neurochem.

    (1990)
  • J.L. Goudreau et al.

    Evidence that hypothalamic periventricular dopamine neurons innervate the intermediate lobe of the rat pituitary

    Neuroendocrinology

    (1992)
  • Cited by (0)

    View full text