Guinea pig mu opioid receptor: brainstem expression in the morphine-exposed neonate

• Published in: Neurotoxicology and teratology Vol. 26; no. 1; pp. 121 - 129
• Main Authors: Smith, Sue Ann, Stupfel, James T, Ilias, Nasreen A, Olsen, George D
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.01.2004; Elsevier Science
• Subjects: Animals; Animals, Newborn; Binding Sites; Biological and medical sciences; Brain Stem - anatomy & histology; Brain Stem - drug effects; Brain Stem - growth & development; Brain Stem - metabolism; CHO Cells; Cloning, Molecular - methods; Cricetinae; Cricetulus; Development; Female; Gene Expression Regulation, Developmental - drug effects; Guinea pig; Guinea Pigs; Humans; Immunohistochemistry - methods; In Situ Hybridization - methods; In Vitro Techniques; Male; Medical sciences; Mice; Morphine - toxicity; Mu opioid receptor; Narcotics - toxicity; Pregnancy; Prenatal morphine; Rats; Receptors, Opioid, mu - genetics; Receptors, Opioid, mu - metabolism; Reverse Transcriptase Polymerase Chain Reaction - methods; RNA, Messenger - metabolism; Sequence Alignment; Time Factors; Toxicology; Transfection - methods; Development; Guinea pig; Mu opioid receptor; Prenatal morphine; Human; Opioid receptor; Rodentia; Opiates; Morphine; Narcotic analgesic; Development: Prenatal morphine; Prenatal; Vertebrata; Mammalia; Newborn; Animal
• ISSN: 0892-0362; 1872-9738
• DOI: 10.1016/j.ntt.2003.09.004

The mu opioid receptor (MOR) has been characterized in the mouse and rat. The guinea pig has several advantages as a model for in utero exposure to morphine; the placental structure is similar to the human; and the guinea pig metabolizes morphine to its active metabolite, morphine-6-glucuronide, at similar rates as humans. Guinea pig MOR cDNA was sequenced. To evaluate expression in respiratory control areas, a guinea pig specific cRNA probe was prepared and utilized for in situ hybridization in brainstem slices. In situ results were compared with immunohistochemistry to determine a correlation between mRNA expression and MOR protein expression. Neonatal animals exposed in utero to chronic intermittent morphine were compared with saline-exposed controls. Quantitative RT-PCR comparison of mRNA expression levels in brainstem regions was also performed. No differences were found in brainstem areas expressing mRNA or amount of mRNA expression between treatment and neonatal age groups. Immunohistochemistry showed that protein expression correlates anatomically with mRNA expression and no difference in protein levels could be detected between treatment groups. Lack of difference in mRNA or protein levels of MOR following in utero exposure to morphine suggests that differences seen between these groups with DAMGO-stimulated 35S-GTPγS binding involve a change in efficiency of coupling to G-proteins when MOR is activated.