Spinal cord regulation of sympathetic activity in intact and spinal rats.
Excitatory amino acid (EAA) and cholinergic neurotransmission in the spinal cord of urethan-anesthetized rats was investigated to assess mechanisms regulating sympathetic activity after spinal cord injury. Blockade of EAA transmission by intrathecal injection of kynurenic acid decreased arterial blood pressure by 24 +/- 4 mmHg, heart rate by 15 +/- 10 beats/min, and renal sympathetic nerve activity (RSNA) by 85 +/- 4% in intact rats. In rats with cervical spinal transections, this blockade decreased RSNA by 51 +/- 5% and had no effect on arterial pressure and heart rate. Muscarinic blockade by intrathecal atropine decreased RSNA by 12 +/- 3 and 32 +/- 6% in intact and spinal rats, respectively, and caused no cardiovascular responses in either group. Combined blockade of EAA and muscarinic receptors in spinal rats decreased RSNA by 77 +/- 1%. Intrathecal injections of the EAA agonist D,L-homocysteic acid in spinal rats caused initial increases (335 +/- 28%) in RSNA lasting approximately 3 min and later sustained increases (157 +/- 19%) lasting 36 +/- 8 min. Only the early excitation increased arterial pressure by 17 +/- 3 mmHg, and then pressure returned to baseline values. The EAA agonist kainic acid increased RSNA by 402 +/- 90% in spinal rats, an effect lasting 70 +/- 5 min, and increased arterial pressure by only 8 +/- 2 mmHg for 12 +/- 5 min. These findings suggest that tonic activity of spinal neurons with EAA and cholinergic receptors maintains tonic RSNA after spinal cord transection. However, this activity does not play a major role in maintaining arterial pressure, even if it is increased substantially by EAA receptor stimulation.
Hong
Y
Y
Stroke and Aging Group, John P. Robarts Research Institute, University of Western Ontario, London, Canada.
Cechetto
D F
DF
Weaver
L C
LC
D000818:Animals; D001794:Blood Pressure; D018680:Cholinergic Antagonists; D003655:Decerebrate State; D005728:Ganglia, Sympathetic / Q000502:physiology; D007668:Kidney / Q000294:innervation; D008297:Male; D009407:Nerve Block; D009538:Nicotine / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017459:Receptors, Amino Acid / Q000037:antagonists & inhibitors / Q000378:metabolism; D012016:Reference Values; D013116:Spinal Cord / Q000378:metabolism / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D009435:Synaptic Transmission
D018680:Cholinergic Antagonists; D017459:Receptors, Amino Acid; D009538:Nicotine