Developmental pattern of M 1 and M 2 muscarinic gene expression and receptor levels in cat carotid body, petrosal and superior cervical ganglion

Abstract

Using real-time reverse transcriptase polymerase chain reaction, Northern blot, and Western blot analyses, we evaluated the developmental pattern of mRNA and protein expression level of muscarinic M 1 and M 2 receptors in the carotid body, petrosal ganglion and superior cervical ganglion of 1-day, 15-day, 2-month-old and adult cats. mRNA expression and protein levels of tyrosine hydroxylase, the rate limiting enzyme for dopamine synthesis, were also assessed. Carotid body M 1 receptor mRNA, increased significantly by ∼100% and 300% in 2-month and adult vs. 1- and 15-day-old cats, but protein level decreased gradually being ∼50% lower compared with 1-day-old cats. In the petrosal ganglion, muscarinic M 1 receptor mRNA level was higher in 15-day-old cats vs. 1-day-old, 2-month-old and adult cats and protein levels were about 30% lower than in 1- and 15-day-old cats. In the superior cervical ganglion, muscarinic M 1 receptor mRNA was ∼50% and 80% higher in 2-month-old and adult cats than 1- and 15-day-old, but no changes in the protein level except in 15-day-old cats which was ∼40% higher than 1-day-old. There was no change of muscarinic M 2 receptor mRNA or protein level in the carotid body or petrosal ganglion. However, in the superior cervical ganglion, the significant increase of mRNA of 30% and 50% in 2-month-olds and adults, respectively was not associated with an increase in receptor protein. Tyrosine hydroxylase mRNA and protein level decreased significantly with age in the carotid body and petrosal ganglion. In the superior cervical ganglion, the age dependent increase in tyrosine hydroxylase mRNA was not associated with any changes in the protein level. These results show that the expression of muscarinic M 1 and M 2 receptors are age and organ-dependent in cats. Consequently, these changes may modulate chemosensory activity during development since muscarinic M 1 receptor is predominantly involved in postsynaptic chemosensory activity, while muscarinic M 2 receptor modulates acetylcholine and dopamine release from chemosensitive cells.