Alpha2-adrenergic receptor distribution and density within the nucleus tractus solitarii of normotensive and hypertensive rats during development

The nucleus tractus solitarii (NTS), located in the brainstem, is one of the main nuclei responsible for integrating different signals in order to originate a specific and orchestrated autonomic response. Antihypertensive drugs are well known to stimulate alpha2-adrenoceptor (alpha2R) in brainstem cardiovascular regions to induce reduction in blood pressure. Because alpha2R impairment is present in several models of hypertension, the aim of the present study was to investigate the distribution and density of alpha2R binding within the NTS of Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats during development (1,15,30 and 90 day-old) by an in vitro autoradiographical study. The NTS shows heterogeneous distribution of alpha2R in dorsomedial/dorsolateral, subpostremal and medial/intermediate subnuclei. Alpha2R increased from rostral to caudal dorsomedial/dorsolateral subnuclei in 30 and 90 day-old SHR but not in WKY. Alpha2R decreased from rostral to caudal subpostremal subnucleus in 15, 30 and 90 day-old SHR but not in WKY. Medial/intermediate subnuclei did not show any changes in alpha2R according to NTS levels. Furthermore, alpha2R are decreased in SHR as compared with WKY in all NTS subnuclei and in different ages. Surprisingly, alpha2R impairment was also found in pre-hypertensive stages, specifically in subpostremal subnucleus of 15 day-old rats. Finally, alpha2R decrease from 1 to 90 day-old rats in all subnuclei analyzed. This decrease is different between strains in rostral dorsomedial/dorsolateral and caudal subpostremal subnuclei within the NTS. In summary, our results highlight the importance of alpha2R distribution within the NTS regarding the neural control of blood pressure and the development of hypertension.