Abstract
BackgroundAn opioid peptide neuron/humoral feedback regulation might be involved in changes of intraocular pressure (IOP). The aims of this study are to investigate the effects of arcuate nucleus (ARC) and opioid peptides on intraocular pressure (IOP).MethodsFifty-four healthy purebred New Zealand white rabbits (108eyes) were randomly divided into 4 groups, including control group, electrical stimulation group, [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) group, and [D-Pen 2, D-Pen5]- enkephalin (DPDPE) group. Bilateral IOP was measured after unilateral electrical stimulation of the ARC or unilateral microinjection into the ARC of the selective μ-opioid receptor agonist DAMGO or the selective δ opioid receptor agonist DPDPE, both alone and after pre-administration of either the non-selective opioid receptor antagonist naloxone or saline.ResultsBoth electrical stimulation in ARC and micro-injection either <mu> or <delta> opioid receptor agonists, DAMGO or DPDPE, respectively, caused a significant bilateral reduction in IOP (P<0.05) which was more pronounced in the ipsilateral than in the contralateral eye. Pretreatment with naloxone prevented some, but not all IOP reductions.ConclusionThe ARC takes part in the negative regulation of IOP, an action that may involve opioid neurons.
Highlights
We have not found any published reports describing the following phenomenon, we have observed in our clinical practice that in some patients with open-angle glaucoma, the contralateral intraocular pressure (IOP) increases or decreases after unilateral glaucoma surgery no obvious changes in other influencing factors have occurred
Number of animal used in each of experiments Fifty-four animals were used in this study, 4 in the control group, 21 in the electrical stimulation group, 15 in the DAMGO injection group, and 14 in the DPDPE injection group
In the ipsilateral eye after unilateral stimulation of the arcuate nucleus (ARC), significant group effects were seen on IOP for both the electrical (Figure 2a, P = 0.0004) and antagonist (Figure 2b, P = 0.0002) effects
Summary
We have not found any published reports describing the following phenomenon, we have observed in our clinical practice that in some patients with open-angle glaucoma, the contralateral intraocular pressure (IOP) increases or decreases after unilateral glaucoma surgery no obvious changes in other influencing factors have occurred. Rabbits have a hypothalamic arcuate nucleus with neurons containing b-endorphin, the major endogenous opioid in the brain, and have opioid peptides present in the eye in the iris and ciliary body [1,2,3]. Long-term repeated electrical stimulation of the rabbit hypothalamic ventromedial nucleus increases IOP and the rate of aqueous humor formation, and decreases the aqueous humor outflow rate [4,5,6]. Unilateral topical administration of morphine decreases IOP in both eyes in rabbits [8] These studies indicate a degree of CNS regulation of IOP, but leave many details unanswered. An opioid peptide neuron/humoral feedback regulation might be involved in changes of intraocular pressure (IOP). The aims of this study are to investigate the effects of arcuate nucleus (ARC) and opioid peptides on intraocular pressure (IOP)
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