SFN Poster of the Year 1999

Awarded by ATS at Society for Neuroscience (SFN) Miami, Florida • October 23-28, 1999

474.6 Abolition of cyanide-induced sympathoexcitation by selective lesion of bulbospinal catecholaminergic neurons.
A.M. SCHREIHOFER* and P.G. GUYENET Univ. of Virginia.
Cardiovascular regulation: central control III (POSTER)

The rostral ventrolateral medulla (RVLM) contains BS C1 adrenergic cells and non-CA neurons whose relative importance for the production of sympathetic vasomotor tone and cardiovascular reflexes remains unknown. In the present study we evaluate 2 sympathetic reflexes after selective lesions of BS CA neurons with the neurotoxin saporin-anti-dopamine beta hydroxylase (SAP-DBH). Rats received bilateral microinjections of SAP-DBH (42 ng/200nl/site) into the spinal cord centered at the intermediolateral cell column at T2 & T4 & T6 and were allowed to recover for 3-5 weeks. Arterial pressure (AP), heart rate (HR), and splanchnic nerve activity (SNA) were measured while the rats were chloralose-anesthetized, artificially ventilated, and paralyzed. Baseline AP and HR were comparable between control rats (n-7, 113 +/- 7 mmHg, 426 +/- 12 bpm) and lesioned rats (n=7, 123 +/- 4 mmHg, 448 +/- 7 bpm). In control rats stimulation of the carotid chemoreflex (100 micrograms/kg sodium cyanide, iv) produced a burst in SNA (266 +/- 26%) followed by inhibition (to 18 +/- 3% of base). In contrast, in the SAP-DBH-treated animals cyanide produced only an inhibition of SNA (to 33 +/- 7% of base). Mean AP responses mirrored the SNA responses. In contrast, the Bezold-Jarisch reflex was not diminished in the SAP-DBH-treated rats. Phenyl biguanide (5 micrograms/kg, iv) decreased AP (22 +/- 3 vs. 42 +/- 5 mmHg), SNA (85 +/- 4 vs. 67 +/- 6%), and HR (28 +/- 6 vs. 56 +/- 7 bpm) in control rats and lesioned rats respectively. Histological examination revealed that SAP-DBH depleted the vast majority of BS C1 cells (>70% of the rostral third of the C1 cell group), and >80% of the A5 cell group. These results indicate that sympathetic vasomotor tone persists and rats have a normal mean AP in the absence of most of BS C1 and A5 cells. Although the BS C1 cells may not be required for the Bezold-Jarisch reflex, BS CA cells are essential for the sympathoexcitatory response to cyanide. Work supported by NIH 28785.