ABSTRACT
Nicotine improves endotoxic manifestations of hypotension and cardiac autonomic dysfunction in rats. Here, we test the hypothesis that brainstem antiinflammatory pathways of α7/α4ß2 nicotinic acetylcholine receptors (nAChRs) modulate endotoxic cardiovascular derangements. Pharmacologic and molecular studies were performed to determine the influence of nicotine or selective α7/α4ß2-nAChR ligands on cardiovascular derangements and brainstem neuroinflammation caused by endotoxemia in conscious rats. The i.v. administration of nicotine (50⯵g/kg) abolished the lipopolysaccharide (LPS, 10â¯mg/kg i.v.)-evoked: (i) falls in blood pressure and spectral measure of cardiac sympathovagal balance (ratio of the low-frequency to high-frequency power, LF/HF), (ii) elevations in immunohistochemical protein expressions of NFκB and α4ß2-nAChR in medullary neurons of the nucleus tractus solitarius (NTS) and rostral ventrolateral medulla (RVLM), and (iii) decreases in medullary α7-nAChR protein expression. These favorable nicotine influences were replicated in rats treated intracisternally (i.c.) with PHA-543613 (selective α7-nAChR agonist) or 5-iodo-A-85380 (5IA, selective α4ß2-nAChRs agonist). Measurement of arterial baroreflex activity by the vasoactive method revealed that nicotine, PHA, or 5IA reversed the LPS depression of reflex bradycardic, but not tachycardic, activity. Moreover, the counteraction by nicotine of LPS hypotension was mostly inhibited after treatment with i.c. methyllycaconitine (MLA, α7-nAChR antagonist) in contrast to a smaller effect for dihydro-ß-erythroidine (DHßE, α4ß2-nAChR antagonist), whereas the associated increases in LF/HF ratio remained unaltered. The data signifies the importance of brainstem α7, and to a lesser extent α4ß2, receptors in the nicotine counteraction of detrimental cardiovascular and neuroinflammatory consequences of endotoxemia.