LOCALIZATION OF ANGIOTENSIN-II AT(1) RECEPTOR-LIKE IMMUNOREACTIVITY IN CATECHOLAMINERGIC NEURONS OF THE RAT MEDULLA-OBLONGATA

There exist at least two distinct subtypes of angiotensin II receptors in the brain, namely the AT(1) and AT(2) subtypes. The high density o f angiotensin II AT(1) receptors is present in the medulla oblongata. The AT(1) subtype of angiotensin II receptors mainly mediates central cardiovascular events. In the present study a polyclonal antibody agai nst the angiotensin II AT(1) receptor and a monoclonal antibody agains t tyrosine hydroxylase were employed to evaluate the possible presence of angiotensin II AT(1) receptor-like immunoreactivity in the catecho laminergic neurons of the rat medulla oblongata by means of the double colour immunofluorescence technique. A weak, diffuse cytoplasmic angi otensin II AT(1) receptor-like immunoreactivity was observed in almost all the catecholaminergic cell bodies of the A2, C1, C2 and C3 cell g roups, except those of the Al cell group containing moderately intense ; diffuse cytoplasmic angiotensin II AT(1) receptor-like immunoreactiv ity, occasionally found in the noradrenergic dendrites of the Al cell group. There was a higher density of the angiotensin II AT(1) receptor -like immunoreactive profiles in the A2 cell group area than in other catecholaminergic cell group areas. In addition, the angiotensin II AT (1) receptor-like immunoreactivity was seen in non-catecholaminergic n eurons. The present results provide evidence for the existence of the specific angiotensin II AT(1) receptor-like immunoreactivity in the no radrenergic and adrenergic neurons of the rat medulla oblongata known to have a cardiovascular role. Thus, the findings support the view tha t angiotensin II AT(1) receptors in the medulla oblongata participate in cardiovascular control and indicate a cellular substrate for the do cumented interaction between the angiotensin II and adrenergic transmi ssion lines in cardiovascular function at the level of the nucleus tra ctus solitarii. (C) 1997 IBRO. Published by Elsevier Science Ltd.