Topical cannabinoid agonist, WIN55,212-2, reduces cornea-evoked trigeminal brainstem activity in the rat

D. A. Bereiter, D. F. Bereiter, H. Hirata

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

Cannabinoids act at receptors on peripheral and central neurons to modulate diverse physiological functions and produce analgesia. Corneal sensory nerves express the CB1 cannabinoid receptor and project to two spatially discrete regions of the lower brainstem, the trigeminal interpolaris/caudalis (Vi/Vc) transition and subnucleus caudalis/upper cervical cord (Vc/C1) junction region. The function of CB1 expression on corneal nerves is not known. To determine if cannabinoid receptors in the anterior eye affect the activity of trigeminal brainstem neurons at the Vi/Vc and Vc/C1 the CB1 agonist, WIN55,212-2 (WIN-2), was applied topically prior to chemical excitation of corneal afferent fibers. In the first series of experiments WIN-2 was applied topically prior to excitation of corneal nociceptors by mustard oil (MO). WIN-2 reduced significantly the number of Fos-like immunoreactive neuronal nuclei (Fos-LI) at the Vi/Vc transition (-46.7±8.2%, P<0.05), while smaller non-significant reductions occurred at the Vc/C1 junction region (-20.3±7.6%). The selective CB1 antagonist, SR141716A (1mg/kg, i.v.), prevented WIN-2-evoked reduction in Fos-LI after MO. Systemic administration of WIN-2 (1 or 10mg/kg, i.p.) or SR141716A (1mg/kg, i.v.) or topical corneal application of morphine sulfate did not affect Fos-LI produced by MO. In parallel experiments, topical WIN-2 reduced the magnitude of single unit activity recorded at the Vi/Vc transition (-80±7%, P<0.025), but not at the Vc/C1 junction region (-34±30%) evoked by CO2 pulses applied to the cornea. Topical morphine did not alter CO2-evoked unit activity at either recording location. These results indicated that cannabinoid receptor agonists acted, at least in part, at CB1 receptors in the anterior eye to reduce corneal stimulation-evoked trigeminal brainstem neural activity. Corneal nociceptor-evoked activity at the Vi/Vc transition was reduced significantly by topical WIN-2, while activity at the Vc/C1 junction region displayed only minor decreases. These findings were consistent with the hypothesis that CB1 receptors affect the activity of corneal-responsive neurons that preferentially contribute to homeostasis of the anterior eye and/or reflexive aspects of nociception rather than the sensory-discriminative aspects of corneal nociception.

Original languageEnglish (US)
Pages (from-to)547-556
Number of pages10
JournalPain
Volume99
Issue number3
DOIs
StatePublished - Oct 2002

Bibliographical note

Funding Information:
This study was supported in part by a grant from the National Institute of Neurological Disorders and Stroke (NS26137).

Keywords

  • Cannabinoid receptors
  • Cornea
  • Medullary dorsal horn
  • Nociception

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