Resumo

Objectives: The NTS, located in the brainstem, is one of the main nuclei responsible for integrating different signals from other brain areas or organs. This nucleus contains the greatest density of adenosine uptake sites in the CNS. Adenosine A1 receptors have been especially reported to modulate α2-adrenoceptors, an important receptor in neural control of arterial pressure in the NTS, in hippocampus, spinal cord and brainstem. This modulation, however, is still poorly understood. Thus, the main objective of this study was to evaluate the modulation of the α2-adrenoceptor by adenosine in cell cultures of the brainstem of newborn rats.

Methods: All the procedures and protocols were performed in accordance with the Institutional Guidelines for Animal Experimentation. Cell culture was prepared from the dorsomedial brainstem and cortex of newborn rats Rattus norvegicus (n=30). Cells were enzymatically and mechanically dissociated, and plated in culture dishes pre-treated with Poly-D-Lisine and maintained for seven days in appropriated culture medium. The effect of different concentrations of CPA, an adenosine A1 receptor agonist, on [3H]RX821002, an α2-adrenoceptor antagonist, was evaluated on the brainstem and cortex cell cultures by means of binding assay. All data were evaluated by one-way analysis of variance (ANOVA) followed by Bonferroni post test.

Results: Results were expressed as percentage of control +- standard error. Treatment with 10uM CPA induced a significant increase in alpha2-adrenoceptors binding as compared with the control in dorsomedial brainstem cell cultures. The adenosine A1 receptor antagonist blocked the increase promoted by CPA on α2-adrenoceptor binding (Control: 100..5 ± 6.3; 5*10-6 CPA: 102.8 ± 6.8; 10-5 CPA: 130.4 ± 6.15*10-5 CPA: 113.8 ± 5.4; 10-5 CPA+Antag.: 94.9 ± 8.1; Antag.: 96.5 ± 7.5).CPA did not induce any changes in alpha2-adrenoceptor binding in cortex neuronal cultures (Control: 163,5 ± 9,8; 10-7 CPA: 173,8 ± 8,3; 10-6 CPA: 166,2 ± 9,7; 10-5 CPA: 174,3 ± 10,3; 10-4 CPA: 165 ± 10,8; Antag.: 176,8 ± 8).

Conclusions: We showed that adenosine is able to modulate α2 adrenoceptor binding affinity specifically in cells from the dorsomedial brainstem of newborn rats, We suggest that this modulation might be important to the neural mechanisms of blood pressure control. This study was supported by grants from FAPESP and CNPq.