Altered respiratory motor drive after spinal cord injury: supraspinal and bilateral effects of a unilateral lesion.
Because some bulbospinal respiratory premotor neurons have bilateral projections to the phrenic nuclei, we investigated whether changes in contralateral phrenic motoneuron function would occur after unilateral axotomy via C(2) hemisection. Phrenic neurograms were recorded under baseline conditions and during hypercapnic and hypoxic challenge in C(2) hemisected, normal, and sham-operated rats at 1 and 2 months after injury. The rats were anesthetized, vagotomized, and mechanically ventilated. No group differences were seen in contralateral neurograms at 1 month after injury. At 2 months, however, there was a statistically significant decrease in respiratory rate (RR) at normocapnia, an elevated RR during hypoxia, and an attenuated increase in phrenic neurogram amplitude during hypercapnia in the C(2)-hemisected animals. To test whether C(2) hemisection had induced a supraspinal change in respiratory motor drive, we recorded ipsilateral and contralateral hypoglossal neurograms during hypercapnia. As with the phrenic motor function data, no change in hypoglossal output was evident until 2 months had elapsed when hypoglossal amplitudes were significantly decreased bilaterally. Last, the influence of serotonin-containing neurons on the injury-induced change in phrenic motoneuron function was examined in rats treated with the serotonin neurotoxin, 5,7-dihydroxytryptamine. Pretreatment with 5,7-dihydroxytryptamine prevented the effects of C(2) hemisection on contralateral phrenic neurogram amplitude and normalized the change in RR during hypoxia. The results of this study show novel neuroplastic changes in segmental and brainstem respiratory motor output after C(2) hemisection that coincided with the spontaneous recovery of some ipsilateral phrenic function. Some of these effects may be modulated by serotonin-containing neurons.
Golder
F J
FJ
Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida 32610, USA. golderf@mail.vetmed.ufl.edu
Reier
P J
PJ
Bolser
D C
DC
D015116:5,7-Dihydroxytryptamine / Q000008:administration & dosage; D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D000818:Animals; D019771:Axotomy; D001933:Brain Stem / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology*; D004195:Disease Models, Animal; D005260:Female; D007839:Functional Laterality; D006935:Hypercapnia / Q000503:physiopathology; D007002:Hypoglossal Nerve / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology; D007276:Injections, Intraventricular; D009046:Motor Neurons / Q000187:drug effects; D009473:Neuronal Plasticity / Q000187:drug effects; D010791:Phrenic Nerve / Q000187:drug effects / Q000503:physiopathology; D051381:Rats; D012119:Respiration / Q000187:drug effects; D012121:Respiration, Artificial; D012137:Respiratory System / Q000187:drug effects / Q000294:innervation / Q000503:physiopathology*; D018490:Serotonin Agents / Q000008:administration & dosage; D013047:Specific Pathogen-Free Organisms; D013116:Spinal Cord / Q000473:pathology / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000473:pathology / Q000503:physiopathology*; D014628:Vagotomy
D018759:Adrenergic Uptake Inhibitors; D018490:Serotonin Agents; D015116:5,7-Dihydroxytryptamine