Date of Award
1994
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
To reveal central nervous system (CNS) structures involved in the reflex control of the cardiovascular system, the distribution of Fos protein-like immunoreactivity (FLI) was examined in the brains of urethane anesthetized rats following stimulation of the aortic depressor (ADN) and femoral (FN) nerves. First, the ADN was cut bilaterally in 13 rats, the central ends were placed on stimulating electrodes and stimulated for 1 h. CNS sections were incubated in anti-Fos antibody and prepared immunohistochemically for visualization of FLI. Label was found on the side ipsilateral to the side of stimulation in discrete nuclei in the hindbrain, midbrain and forebrain which have been previously implicated in mediating the baroreceptor reflex, as well as in the ipsilateral islands of Calleja (iC) which have no previously described role in mediating the baroreceptor reflex. These results suggest the organization of central pathways involved in the baroreceptor reflex and suggest the involvement of sites not previously implicated in this reflex. Second, the central end of the right FN was stimulated for 1 h in 17 rats. Following immunohistochemical techniques for the detection of FLI, label appeared in regions of the ipsilateral and contralateral lumbar and thoracic spinal cord and medulla previously implicated in mediating somatosympathetic reflexes and bilaterally in regions of the midbrain and forebrain implicated in mediating the defense reaction. These results suggest pathways in the medulla and spinal cord involved in somatosympathetic reflexes and demonstrate the activation of regions which mediate the defense reaction by these reflexes. Finally, to determine whether activation of an area of the CNS not previously known to be involved in mediating the baroreceptor reflex influences arterial pressure and heart rate, microinjection of L-glutamic acid, an excitatory amino acid, was done in 11 histologically verified sites in the iC. GLU microinjection elicited a decrease in mean arterial pressure and heart rate of 24.5 {dollar}\pm{dollar} 1.5 mmHg and 16.6 {dollar}\pm{dollar} 1.6 bpm indicating an influence of the iC on cardiovascular function. To determine the involvement of the sympathetic nervous system in this response, GLU microinjection was preceded by i.v. injection of the {dollar}\beta{dollar}-adrenergic antagonist propranolol (2.2 mg/kg) or by transection of the spinal cord at the C{dollar}\sb1{dollar} level. Both propranolol and spinal transection eliminated both the HR and AP responses, suggesting the cardiovascular responses to stimulation of the iC was due to an influence of the iC on sympathetic nervous system control of heart rate and contractility. Taken together, these results suggest the organization of central neuronal circuits involved in the reflex control of the cardiovascular system and support the usefulness of the Fos technique in revealing central sites, including novel sites in the CNS, involved in mediating specific autonomic reflexes.
Recommended Citation
McKitrick, Douglas James, "Central Neuronal Circuits Involved In The Reflex Control Of The Cardiovascular System" (1994). Digitized Theses. 2354.
https://ir.lib.uwo.ca/digitizedtheses/2354