Some Autonomic Deficits of Acute or Chronic Cervical Spinal Contusion Reversed by Interim Brainstem Stimulation

Prolonged electrical stimulation of the hindbrain's nucleus raphe magnus (NRM) or of its major midbrain input region, the periaqueductal gray (PAG), was previously found in rats to promote recovery from sensory-motor and histological deficits of acute thoracic spinal cord injury (SCI). Here, some visceral deficits of acute and chronic midline cervical (C5) contusion are similarly examined. Cranially implanted wireless stimulators delivered intermittent 8 Hz, 30-70 μA cathodal pulse trains to a brainstem microelectrode. Injured controls were given inactive stimulators; rats without injuries or implants were also compared. Rectal distension or squeezing of the forepaws caused an exaggerated rise in mean arterial pressure in injured, untreated rats under anesthesia on post-injury week 6, probably reflecting autonomic dysreflexia (AD). These pressor responses became normal when 7 days of unilateral PAG stimulation was started on the injury day. Older untreated injuries (weeks 18-19) showed normal pressor responses, but unexpectedly had significant resting and nociceptive bradycardia, which was reversed by 3 weeks of PAG stimulation started on weeks 7 or 12. Subsequent chronic studies examined gastric emptying (GE), as indicated by intestinal transit of gavaged dye, and serum chemistry. GE and fasting serum insulin were reduced on injury weeks 14-15, and were both normalized by ∼5 weeks of PAG stimulation begun in weeks 7-8. Increases in calcitonin gene-related peptide, a prominent visceral afferent neurotransmitter, measured near untreated injuries (first thoracic segment) in superficial dorsal laminae were reversed by acutely or chronically initiated PAG stimulation. The NRM, given 2-3 weeks of stimulation beginning 2 days after SCI, prevented abnormalities in both pressor responses and GE on post-injury week 9, consistent with its relaying of repair commands from the PAG. The descending PAG-NRM axis thus exhibits broadly restorative influences on visceral as well as sensory-motor deficits, improving chronic as well as acute signs of injury

Prolonged stimulation of a brainstem raphe region attenuates experimental autoimmune encephalomyelitis

•We proposed that brainstem activity can reverse experimental autoimmune encephalomyelitis, a model of multiple sclerosis.•The nucleus raphe magnus of the mouse’s hindbrain was wirelessly stimulated for up to several weeks.•The stimulation reduced overt symptoms and lastingly increased myelination.•After stimulation, immune cell invasion and some inflammatory cytokines were lower for at least several days.•These findings confirm the restorative role for raphe nuclei suggested by prior studies of neurotrauma. Multiple sclerosis (MS), a neuroinflammatory disease, has few treatment options, none entirely adequate. We studied whether prolonged electrical microstimulation of a hindbrain region (the nucleus raphe magnus) can attenuate experimental autoimmune encephalomyelitis, a murine model of MS induced by MOG35-55 injection. Eight days after symptoms emerged, a wireless electrical stimulator with an attached microelectrode was implanted cranially, and daily intermittent stimulation was begun in awake, unrestrained mice. The thoracic spinal cord was analyzed for changes in histology (on day 29) and gene expression (on day 37), with a focus on myelination and cytokine production. Controls, with inactive implants, showed a phase of disease exacerbation on days 19–25 that stimulation for >16days eliminated. Prolonged stimulation also reduced numbers of infiltrating immune cells and increased numbers of myelinated axons. It additionally lowered genetic expression of some pro-inflammatory cytokines (interferon gamma and tumor necrosis factor) and platelet-derived growth factor receptor alpha, a marker of oligodendrocyte precursors, while raising expression of myelin basic protein. Studies of restorative treatments for MS might profitably consider ways to stimulate the raphe magnus, directly or via its inputs, or to emulate its serotonergic and peptidergic output