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Related Experiment Videos

Decrease in neuronal uptake of noradrenaline simply explains the supersensitivity after sympathectomy in the rat iris

K Shibata1, S Takei, T Kawai

  • 1Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.

Japanese Journal of Pharmacology
|May 1, 1989
PubMed
Summary
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Sympathetic denervation of rat iris dilator muscle caused supersensitivity to noradrenaline (NA). This effect was attributed to impaired neuronal uptake, not postsynaptic changes, highlighting a presynaptic mechanism.

Area of Science:

  • Pharmacology
  • Neuroscience
  • Ophthalmology

Background:

  • The sympathetic nervous system regulates iris dilator muscle function.
  • Understanding denervation effects on receptor sensitivity is crucial for ocular pharmacology.

Purpose of the Study:

  • To investigate the impact of sympathetic denervation on the mechanical response of the rat iris dilator muscle.
  • To determine the specific mechanisms underlying supersensitivity to noradrenaline (NA) after denervation.

Main Methods:

  • Superior cervical ganglionectomy (surgical denervation) and long-term guanethidine treatment (chemical denervation) in rats.
  • Measurement of mechanical responses of the iris dilator muscle to various stimulants, including noradrenaline (NA), methoxamine (Meth), acetylcholine (ACh), and calcium ions (Ca2+).

Related Experiment Videos

  • Assessment of cocaine's effect on muscle sensitivity to NA and Meth in both normal and denervated muscles.

    • Main Results:

    • Denervation (surgical or chemical) significantly shifted the NA dose-response curve leftward, indicating supersensitivity.
    • Methoxamine and acetylcholine responses remained unchanged, suggesting specificity.
    • Cocaine sensitized normal muscle to NA similarly to denervation, but did not affect denervated muscle sensitivity.
    • Maximum response to NA decreased post-denervation, while responses to Meth, ACh, and Ca2+ were unaffected.

    Conclusions:

    • Sympathetic denervation of the iris dilator muscle induces specific supersensitivity to noradrenaline (NA).
    • This supersensitivity is primarily explained by a presynaptic mechanism, specifically impaired neuronal uptake of NA.
    • Postsynaptic mechanisms do not appear to contribute significantly to the observed supersensitivity.