Reciprocal circuits involved in nitroglycerin-induced neuronal activation of autonomic regions and pain pathways: a double immunolabeling and tract-tracing study

This study uses tract-tracing protocols to determine the circuitry of speci fic nuclei involved in nitroglycerin-induced activation. Combined retrograd e and anterograde tracers were injected into nuclei which consistently demo nstrate robust Fos expression following our systemic nitroglycerin injectio n paradigm. The nuclei, which conform to these criteria, that we have evalu ated in this study ate the locus coeruleus, parabrachial nucleus and parave ntricular nucleus of the hypothalamus. Dual Fos/tracer immunocytochemistry in treated animals documented the existence of a subset of autonomic nuclei which are activated by nitroglycerin injection and have reciprocal connect ions. From the nature of this rich interconnection we suggest that nitrogly cerin activates autonomic responses involved in cardiovascular presser mech anisms. Nuclei which show strong Fos labeling following nitroglycerin admin istration, but not traced in this study, include the nucleus trigeminalis c audalis and the ventrolateral column of the periaqueductal gray, both of wh ich mediate nociceptive modalities. These data confirm and expand on our pr evious findings and demonstrate that nitroglycerin activates a complex set of structures that: are functionally and structurally interconnected to art iculate an integrated response. (C) 1999 Elsevier Science B.V. All rights r eserved.