Differential Expression of Adenosine A₁and A_2AReceptors After Upper Cervical (C2) Spinal Cord Hemisection in Adult Rats

Abstract

Background: In an animal model of spinal cord injury, a latent respiratory motor pathway can be pharmacologically activated via adenosine receptors to restore respiratory function after cervical (C2) spinal cord hemisection that paralyzes the hemidiaphragm ipsilateral to injury. Although spinal phrenic motoneurons immunopositive for adenosine receptors have been demonstrated (C3-C5), it is unclear if adenosine receptor protein levels are altered after C2 hemisection and theophylline administration.Objective: To assess the effects of C2 spinal cord hemisection and theophylline administration on the expression of adenosine receptor proteins.Methods: Adenosine A 1 and A 2A receptor protein levels were assessed in adult rats classified as (a) noninjured and theophylline treated, (b) C2 hemisected, (c) C2 hemisected and administered theophylline orally (33 daily) for 3 days only, and (d) C2 hemisected and administered theophylline (33 daily for 3 days) and assessed 12 days after drug administration. Assessment of A 1 protein levels was carried out via immunohistochemistry and A 2A protein levels by densitometry.Results: Adenosine A 1 protein levels decreased significantly (both ipsilateral and contralateral to injury) after C2 hemisection; however, the decrease was attenuated in hemisected and theophylline-treated animals. Attenuation in adenosine A 1 receptor protein levels persisted when theophylline administration was stopped for 12 days prior to assessment. Adenosine A 2A protein levels were unchanged by C2 hemisection; however, theophylline reduced the levels within the phrenic motoneurons. Furthermore, the decrease in A 2A levels persisted 12 days after theophylline was withdrawn.Conclusion: Our findings suggest that theophylline mitigates the effects of C2 hemisection by attenuating the C2 hemisection-induced decrease in A 1 protein levels. Furthermore, A 2A protein levels are unaltered by C2 hemisection but decrease after continuous or interrupted theophylline administration. The effects on protein levels may underlie the stimulant actions of theophylline.

Recovery of respiratory activity after C2 hemisection (C2HS): Involvement of adenosinergic mechanisms

“…This was an important study towards identifying whether levels of adenosine A 1 and A 2 receptor protein changes correlate with persistent functional recovery even after drug cessation as had been previously demonstrated (Nantwi et al, 2003a). It appears that changes in adenosine A 1 and A 2 receptor protein changes reported by Petrov and colleagues (2007) support the findings reported by Saharan and Nantwi (2006) of the unmasking of a second site similar in pharmacologic profile with the A 2 receptor. Ongoing studies will characterize the functional significance of A 2 receptors to identify the putative role(s).…”

“…Petrov and colleagues (2007) reasoned that changes in mRNA and or protein levels in the A 2 receptor may be involved in the persistent and sustained actions of theophylline. Petrov and colleagues sought to ascertain whether adenosine receptor proteins may be altered by C2 hemisection and subsequent theophylline administration.…”

“…Weaning from theophylline resulted in levels of 62.0 ± 1.5 and 55.0 ± 0.8 (Fig 6). Petrov and colleagues concluded that theophylline mitigates the effects of C2 hemisection by attenuating the C2 hemisection-induced decrease in A 1 protein levels and that A 2 receptor protein levels are unaltered by C2HS but decrease after theophylline withdrawal (Petrov et al, 2007). The author is aware of the limitations of quantitation by counting immuno-labeled cells.…”

“…To summarize, Petrov and colleagues used immunocytochemistry and semi-quantitative densitometry and showed for the first time (1) differential changes in expression of adenosine A 1 and A 2 receptor proteins in C2 hemisected animals, (2) changes in adenosine A 1 and A 2 receptor levels after continuous chronic (3 days) administration of theophylline by oral gavage and (3) changes in the receptor protein levels after weaning from theophylline for 12 days (Petrov et al, 2007). This was an important study towards identifying whether levels of adenosine A 1 and A 2 receptor protein changes correlate with persistent functional recovery even after drug cessation as had been previously demonstrated (Nantwi et al, 2003a).…”

A1 adenosine receptor modulation of chemically and electrically evoked lumbar locomotor network activity in isolated newborn rat spinal cords

“…by inhibiting voltage-gated Ca 2+ channels (Greene and Haas, 1991;Dunwiddie and Masino, 2001;Fredholm et al 2001;Latini and Pedata, 2001). Such electrophysiological analyses can be combined with (immunohistochemical) analysis of the expression in presumptive CPG versus motoneuron areas of different ADO receptor subtypes that have been described in some studies on rat and human spinal cord (Reppert et al, 1991;Schindler et al, 2001;Petrov et al, 2007).…”