Age dependent changes in A 2A receptor expression in PreBotzinger Complex

Abstract

Adenosine is a modulator of respiratory output, and can both increase and decrease respiratory frequency in an age and receptor dependent manner. We have shown an in vivo, age dependent, effect of A2A receptor activation on apneas in rats which is attenuated from postnatal day (P)14 to P21 through adulthood. We hypothesized that the attenuated response to A2A activation was due to decreased A2A receptor expression in the PreBötzinger complex (pBc). To test this hypothesis, we used unbiased stereology to quantify changes in A2A expression in pBc over the first three weeks of life. Sprague Dawley rat pups were perfused at P0, 4, 7, 14, and 21. The brains were cryosectioned and 4 identical sets of slides made from each brain. These slides were immunostained for NK-1R and somatostatin to deliniate the pBc. The remaining slides were stained with A2A, NeuN or S100β antibodies. The number of immunopositive cells in the pBc and the pBc volume were quantified using unbiased stereology (n=5 for each antibody at each age). The number of cells immunopositive for A2A per 1X105μm3 of pBc decreased significantly between P0 and P7 (p < 0.006), and rose again by P21 (P < 0.2). The number of NeuN and S100β immunopositive cells per 1X105μm3 decreased significantly between P0 and P21 (p < 0.001 for both). We conclude that A2A expression changes with age, but these changes are not correlated with the pattern of A2A dependent apneas seen in vivo.