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Biomedical subjects

L C Weaver

Publications and source records attributed to L C Weaver.

115 records · Page 7Linked to original sources
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Role of dorsal medullary reticular formation in maintenance of vasomotor tone in rats.

Recent investigations of central nervous system structures involved in the generation of vasomotor tone have focused on the rostral ventrolateral portion of the medulla, whereas other medullary areas have not been considered to have primary importance. The present study was designed to determine the role of the medullary reticular formation, dorsal to the ventrolateral medulla, in the maintenance of vasomotor tone. The effects of microinjections of the inhibitory amino acid glycine into this medullary region on systemic arterial pressure, heart rate and renal nerve activity were determined in male rats anaesthetized with propofol and treated with atropine to block vagal influences on the heart. Unilateral injections (24 of 57 sites) of glycine into the dorsal medulla caused significant decreases in arterial pressure (-10 +/- 1.0 mmHg) and renal sympathetic nerve activity (-12 +/- 1%) whereas heart rate was not significantly affected. Bilateral injections (12 of 20) of glycine caused significantly greater decreases in heart rate (-10 +/- 1 bpm) and renal nerve activity (-25 +/- 4%) than were elicited by unilateral injections. In contrast, although arterial pressure decreased significantly from control values (-10 +/- 1 mmHg), these responses were not different from the arterial pressure changes caused by unilateral injections. These results demonstrate that, in the propofol anaesthetized rat, neurons in the dorsal medullary reticular formation contribute to the maintenance of vasomotor tone.

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Reflex and morphological changes in spinal preganglionic neurons after cord injury in rats.

Autonomic dysreflexia manifested as episodic hypertension after spinal cord injury may occur because of changes in sympathetic preganglionic neurons (SPNs) in response to loss of bulbospinal inputs. We studied dysreflexia in rats one week after midthoracic spinal cord hemisection or complete transection. After cord hemisection at the fifth thoracic segment all rats had hemiparaplegia and after complete transection they were paraplegic and exhibited dysreflexia characterized by pressor responses to distension of the urinary bladder. Changes in morphology of SPNs retrogradely labelled by cholera toxin and Fluoro Gold were examined and changes also were assessed in expression of the synaptic vesicular protein synaptophysin. A comparison of SPNs rostral and caudal to the lesion revealed significant dendritic degeneration and decreased soma size after the loss of supraspinal input. Expression of synaptophysin was normally observed rostral to a cord hemisection but this immunoreactivity was increased caudal to the lesion. In conclusion significant structural changes in SPNs occur within a week after cord injury. The abnormal cardiovascular control and exaggerated reflex reactions may be due to new synapse formation on these SPNs.

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