Journal
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
Volume 279, Issue 2, Pages R729-R742Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpregu.2000.279.2.R729
Keywords
cyanide; phenyl biguanide; tyrosine hydroxylase; phenylethanolamine-N-methyltransferase; tryptophan hydroxylase; splanchnic nerve activity
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Funding
- NHLBI NIH HHS [HL-28785] Funding Source: Medline
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We examined the effects of destroying bulbospinal catecholaminergic neurons with the immunotoxin anti-dopamine beta-hydroxylase- saporin (anti-D beta H-Sap) on splanchnic nerve activity (SNA) and selected sympathetic reflexes in rats. Anti-D beta H- Sap was administered into the thoracic spinal cord with the retrograde tracer fast blue. After 3-5 wk, anti-D beta H-Sap eliminated most bulbospinal C1 (>74%), C3 (similar to 84%), A5 (similar to 98%), and A6 cells. Noncatecholaminergic bulbospinal neurons of the rostral ventrolateral medulla and serotonergic neurons were spared. Under chloralose anesthesia, mean arterial pressure and heart rate of anti-D beta H-Sap-treated rats (3-5 wk) were normal. Resting SNA was not detectably altered, but the baroreflex range and gain were reduced similar to 40% (P< 0.05). Phenyl biguanide-induced decreases in mean arterial pressure, heart rate, and SNA were unchanged by anti-D beta H-Sap, but the sympathoexcitatory response to intravenous cyanide was virtually abolished (P< 0.05). Rats that received spinal injections of saporin conjugated to an anti-mouse IgG had intact bulbospinal C1 and A5 cells and normal physiological responses. These data suggest that C1 and A5 neurons contribute modestly to resting SNA and cardiopulmonary reflexes. However, bulbospinal catecholaminergic neurons appear to play a prominent sympathoexcitatory role during stimulation of chemoreceptors.
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