Activation of mu opioid receptors in the ventrolateral periaqueductal gray inhibits reflex micturition in anesthetized rats

• Published in: Neuroscience letters 2004-06, Vol.363 (2), p.116-119
• Main Authors: Matsumoto, Seiji, Levendusky, Mark C., Longhurst, Penelope A., Levin, Robert M., Millington, William R.
• Format: Article
• Language: English
• Subjects: Administration, Intravesical; Anesthetics - pharmacology; Animals; Benzeneacetamides - pharmacology; Biological and medical sciences; Bladder; Enkephalin, Ala-MePhe-Gly- - pharmacology; Enkephalin, D-Penicillamine (2,5)- - pharmacology; Female; Fundamental and applied biological sciences. Psychology; Kappa receptor; Medical sciences; Microinjections; Micturition; Morphine - pharmacology; Mu receptor; Muscle Contraction - drug effects; Muscle Contraction - physiology; Narcotics - pharmacology; Nephrology. Urinary tract diseases; Opioid; Periaqueductal gray; Periaqueductal Gray - drug effects; Periaqueductal Gray - metabolism; Pyrrolidines - pharmacology; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa - drug effects; Receptors, Opioid, kappa - metabolism; Receptors, Opioid, mu - drug effects; Receptors, Opioid, mu - metabolism; Reflex - drug effects; Reflex - physiology; Sodium Chloride - administration & dosage; Urinary Bladder - innervation; Urinary Bladder - physiopathology; Urinary retention; Urinary system involvement in other diseases. Miscellaneous; Urinary tract. Prostate gland; Urination - drug effects; Urination - physiology; Vertebrates: nervous system and sense organs
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2004.03.055

This study tested the hypothesis that morphine and other opiates cause urinary retention by activating mu opioid receptors in the midbrain periaqueductal gray (PAG) region. Selective mu, delta and kappa receptor agonists were microinjected into the PAG of urethane-anesthetized rats and the amplitude and incidence of bladder contractions were recorded during continuous saline infusion. Arterial pressure was monitored through a femoral artery catheter. Microinjection of the mu receptor agonist DAMGO into the ventrolateral PAG (vlPAG) suppressed volume-evoked bladder contractions completely. Bladder contractions ceased within 5 min of DAMGO injection and remained essentially undetectable for the rest of the 20 min recording period. Microinjection of the delta receptor agonist DPDPE into the vlPAG did not significantly affect either the amplitude of bladder contractions or the time interval separating contractions. The kappa receptor agonist U-69593 caused no discernible change in amplitude but increased the interval between bladder contractions significantly. Microinjection of DAMGO, DPDPE or U-69593 into the lateral or dorsolateral PAG columns was ineffective. DAMGO injection into the vlPAG increased arterial pressure whereas DPDPE and U-69593 produced a small but significant depressor response. These data support the hypothesis that mu and kappa receptors in the vlPAG participate in the micturition reflex.