Acute cardiorespiratory effects of intracisternal injections of mercuric chloride

AbstractThe present studies were conducted to changes arising from mercury poisoning in the central nervous system (CNS), with a focus on determining the receptors and neurotransmitters involved. Currently, little is known regarding the neurological basis of the cardiopulmonary effects of mercury poisoning. We evaluated changes in systolic arterial pressure (SAP), diastolic arterial pressure (DAP), respiratory rate (RR) and heart rate (HR) following a 5μl intracisternal (i.c) injection of mercuric chloride (HgCl2) and the participation of the autonomic nervous system in these responses. 58 animals were utilized and distributed randomly into 10 groups and administered a 5μL intracisternal injection of 0.68μg/kg HgCl2 (n=7), 1.2μg/kg HgCl2 (n=7), 2.4μg/kg HgCl2 (n=7), 60μg/kg HgCl2 (n=7), 120μg/kg HgCl2 (n=3), saline (control) (n=7), 60μg/kg HgCl2 plus prazosin (n=6), saline plus prazosin (n=6), 60μg/kg HgCl2 plus metilatropina (n=4) or saline plus metilatropina (n=4)HgCl2. Anesthesia was induced with halothane and maintained as needed with urethane (1.2g/kg) administered intravenously (i.v.) through a cannula placed in the left femoral vein. The left femoral artery was also cannulated to record systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and heart rate (HR). A tracheotomy was performed to record respiratory rate. Animals were placed in a stereotaxic frame, and the cisterna magna was exposed. After a stabilization period, solutions (saline or HgCl2) were injected i.c., and cardiopulmonary responses were recorded for 50min. Involvement of the autonomic nervous system was assessed through the i.v. injection of hexamethonium (20mg/kg), prazosin (1mg/kg) and methylatropine (1mg/kg) 10min before the i.c. injection of HgCl2 or saline. Treatment with 0.68, 1.2, 2.4μg/kg HgCl2 or saline did not modify basal cardiorespiratory parameters, whereas the 120μg/kg dose induced acute toxicity, provoking respiratory arrest and death. The administration of 60μg/kg HgCl2, however, induced significant increases (p