Developmental profile of cholinergic and purinergic traits and receptors in peripheral chemoreflex pathway in cats

This study describes the developmental profile of specific aspects of cholinergic and purinergic neurotransmission in key organs of the peripheral chemoreflex: the carotid body (CB), petrosal ganglion (PG) and superior cervical ganglion (SCG). Using real time RT-PCR and Western blot analyses, we assessed both mRNA and protein expression levels for choline-acetyl-transferase (ChAT), nicotinic receptor (subunits alpha 3, alpha 4, alpha 7, and beta 2), ATP and purinergic receptors (P2X(2) and P2X(3)). These analyses were performed on tissue from 1- and 15-day-old, 2-month-old, and adult cats. During development, ChAT protein expression level increased slightly in CB; however, this increase was more important in PG and SCG. In CB, mRNA level for alpha(4) nicotinic receptor subunit decreased during development (90% higher in 1-day-old cats than in adults). In the PG, mRNA level for beta(2) nicotinic receptor subunit increased during development (80% higher in adults than in 1-day-old cats). In SCG, mRNA for a7 nicotinic receptor levels increased (400% higher in adults vs. 1-day-old cats). Conversely, P2X(2) receptor protein level was not altered during development in CB and decreased slightly in PG; a similar pattern was observed for the P2X(3) receptor. Our findings suggest that in cats, age-related changes in cholinergic and purinergic systems (such as physiological expression of receptor function) are significant within the afferent chemoreceptor pathway and likely contribute to the temporal changes of O-2-chemosensitivity during development. (C) 2007 IBRO. Published by Elsevier Ltd. All rights reserved.