Quantitative assessment of respiratory function following contusion injury of the cervical spinal cord

Patterns of gene expression reveal a temporally orchestrated wound healing response in the injured spinal cord

Spinal cord injury (SCI) induces a progressive pathophysiology affecting cell survival and neurological integrity via complex and evolving molecular cascades whose interrelationships are not fully understood. The present experiments were designed to: (1) determine potential functional interactions within transcriptional expression profiles obtained after a clinically relevant SCI and (2) test the consistency of transcript expression after SCI in two genetically and immunologically diverse rat strains characterized by differences in T cell competence and associated inflammatory responses. By interrogating Affymetrix U34A rat genome GeneChip microarrays, we defined the transcriptional expression patterns in midcervical contusion lesion sites between 1 and 90 d postinjury of athymic nude (AN) and Sprague Dawley (SD) strains. Stringent statistical analyses detected significant changes in 3638 probe sets, with 80 genes differing between the AN and SD groups. Subsequent detailed functional categorization of these transcripts unveiled an overall tissue remodeling response that was common to both strains. The functionally organized gene profiles were temporally distinct and correlated with repair indices observed microscopically and by magnetic resonance microimaging. Our molecular and anatomical observations have identified a novel, longitudinal perspective of the post-SCI response, namely, that of a highly orchestrated tissue repair and remodeling repertoire with a prominent cutaneous wound healing signature that is conserved between two widely differing rat strains. These results have significant bearing on the continuing development of cellular and pharmacological therapeutics directed at tissue rescue and neuronal regeneration in the injured spinal cord.

Severe Respiratory Compromise Secondary to Cervical Disk Herniation in Two Dogs

Two dogs presented with acute tetraparesis, hypoventilation, and bradycardia with a second-degree atrioventricular heart block. Neurological examination localized both lesions to the cervical spine. Diagnostic imaging revealed a ventral extradural compression at the second to third cervical (C2–C3) region in one dog and at the third to fourth cervical (C3–C4) region in the other. Following surgical correction of the extruded disk, the hypoventilation and bradycardia resolved. Cervical disk extrusions are a common cause of acute tetraparesis in the dog. This report shows that respiratory and cardiac complications may occur concurrently. The authors recommend screening dogs with cervical myelopathies for respiratory and cardiac dysfunctions and treating appropriately. Prompt surgical intervention and supportive care can improve the prognosis.

Transient post-traumatic hemidiaphragmatic paralysis in two cats

A diagnosis of post-traumatic hemidiaphragmatic paralysis was made in two cats. Both cats had a history of trauma and paradoxical inward movement of the abdominal wall at inspiration. Thoracic radiographs were taken at inspiration and expiration. Although the images were suggestive of hemidiaphragmatic paralysis, definitive diagnosis was reached by fluoroscopy in one cat and by ultrasonography in the second. Both cases resolved spontaneously and diaphragmatic function was normal at follow-up.

Cervical spinal cord injury alters the pattern of breathing in anesthetized rats

The mechanisms by which chronic cervical spinal cord injury alters respiratory function and plasticity are not well understood. We speculated that spinal hemisection at C(2) would alter the respiratory pattern controlled by vagal mechanisms. Expired volume (V(E)) and respiratory rate (RR) were measured in anesthetized control and C(2)-hemisected rats at 1 and 2 mo postinjury. C(2) hemisection altered the pattern of breathing at both postinjury time intervals. Injured rats utilized a higher RR and lower V(E) to maintain the same minute ventilation as control rats. After bilateral vagotomy, the pattern of breathing in injured rats was not different from controls. The frequency of augmented breaths was higher in injured rats at 2 mo postinjury before vagotomy; however, the V(E) of augmented breaths was not different between groups. In conclusion, C(2) hemisection alters the pattern of breathing at 1 and 2 mo postinjury via vagal mechanisms.

Ventilatory failure, ventilator management, and outcome in dogs with cervical spinal disorders: 14 cases (1991-1999)

OBJECTIVE

To determine the incidence of and risk factors for ventilatory failure in dogs undergoing surgery for treatment of cervical spinal disorders and to document ventilator management, clinical course, and long-term outcome of dogs that experienced ventilatory failure in association with cervical spinal disorders or their management.

DESIGN

Retrospective study.

ANIMALS

14 dogs.

PROCEDURE

Dogs with cervical spinal disorders that required positive-pressure ventilation (PPV) were identified, and signalment, concurrent diseases, neurologic status at initial examination, clinical course, pulmonary function before, during, and after PPV, management techniques, complications, and outcome were recorded. Dogs that underwent surgery and required PPV were compared with dogs that underwent cervical spinal surgery during the same period that did not require PPV.

RESULTS

14 dogs with cervical spinal disorders required PPV to treat hypoventilation, including 13 of 263 (4.9%) dogs that underwent surgery for cervical spinal disorders. Lesions between the second and fourth cervical vertebrae and treatment by means of a dorsal decompressive laminectomy were associated with a significantly increased risk of perioperative hypoventilation. Pulmonary gas exchange function was normal or nearly normal throughout the course of PPV in dogs that survived. Ten dogs survived, and 9 of the 10 regained neurologic function. All 9 dogs that regained neurologic function had deep pain perception on initial examination at the veterinary teaching hospital.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that a small percentage of dogs with cervical spinal disorders may require perioperative ventilatory support. With prolonged PPV and aggressive management, a good outcome may be achieved in dogs similar to those described in the present study.

Alkylxanthine-induced recovery of respiratory function following cervical spinal cord injury in adult rats

Previous investigations from our laboratory have demonstrated qualitatively that a latent respiratory pathway can be activated by systemic theophylline administration to restore function to a hemidiaphragm paralyzed by an upper (C2) cervical spinal cord hemisection in adult rats. The present study seeks to extend the previous investigations by contrasting and quantitating the actions of theophylline, 8-phenyltheophylline, enprofylline, and 8(p-Sulfophenyl)theophylline in restoring function 24 h after hemidiaphragm paralysis. The alkylxanthines were selected based on their diverse pharmacologic profiles to elucidate the mechanisms that underlie functional recovery after spinal cord injury. To quantitatively assess the magnitude of recovery, electrophysiological experiments were conducted on pancuronium-paralyzed, hemisected animals under standardized recording conditions. The total absence of respiratory-related activity in the phrenic nerve ipsilateral to the hemisection and paralyzed hemidiaphragm was used as the index of a functionally complete hemisection. Thereafter, drug-induced recovered activity in the phrenic nerve ipsilateral to hemisection was quantified and expressed either as a percentage of contralateral phrenic nerve activity in the same animal prior to drug administration or as a percentage of predrug activity in the homolateral nerve in noninjured animals. With either approach, theophylline (5-15 mg/kg) and 8-phenyltheophylline (5-10 mg/kg) dose-dependently induced respiratory-related recovered activity. Enprofylline, a potent bronchodilator, and 8(p-Sulfophenyl)theophylline, an adenosine receptor antagonist with limited access to the central nervous system, were ineffective. Maximal recovery was attained with theophylline (15 mg/kg) and 8-phenyltheophylline (10 mg/kg). At these doses, theophylline and 8-phenyltheophylline induced recovery that was 70.0 +/- 2.5 and 69.3 +/- 4.1% of predrug contralateral nerve activity respectively. When expressed as a percentage of activity in the homolateral nerve in noninjured animals, the magnitude changed to 32.9 +/- 4.9 and 35.7 +/- 6.9%, respectively. Involvement of adenosine receptors in the alkylxanthine-induced actions was confirmed in experiments with the adenosine analog, N6 (l-2-phenylisopropyl) adenosine (L-PIA). It is concluded that central adenosine receptor-mediated mechanisms are implicated in the recovery of respiratory-related activity after spinal cord injury. Furthermore, our results suggest a potential for a new therapeutic approach in the rehabilitation of spinal cord patients with respiratory deficits.

Basic fibroblast growth factor increases long-term survival of spinal motor neurons and improves respiratory function after experimental spinal cord injury

Acute focal injection of basic fibroblast growth factor (FGF2) protects ventral horn (VH) neurons from death after experimental contusive spinal cord injury (SCI) at T8. Because these neurons innervate respiratory muscles, we hypothesized that respiratory deficits resulting from SCI would be attenuated by FGF2 treatment. To test this hypothesis we used a head-out plethysmograph system to evaluate respiratory parameters in conscious rats before and at 24 hr and 7, 28, and 35 d after SCI. Two groups of rats (n = 8 per group) received either FGF2 (3 microg) beginning 5 min after injury or vehicle (VEH) solution alone. We found significantly increased respiratory rate and decreased tidal volume at 24 hr and 7 d after SCI in the VEH-treated group. Ventilatory response to breathing 5 or 7% CO(2) was also significantly reduced. Recovery took place over time. Respiration remained normal in the FGF2-treated group. At 35 d after injury, histological analyses were used to compare long-term neuron survival. FGF2 treatment doubled the survival of VH neurons adjacent to the injury site. Because the number of surviving VH neurons rostral to the injury epicenter was significantly correlated to the ventilatory response to CO(2), it is likely that the absence of respiratory deficits in FGF2-treated rats was caused by its neuroprotective effect. Our results demonstrate that FGF2 treatment prevents the respiratory deficits produced by thoracic SCI. Because FGF2 also reduced the loss of preganglionic sympathetic motoneurons after injury, this neurotrophic factor may have broad therapeutic potential for SCI.

Comparing deficits following excitotoxic and contusion injuries in the thoracic and lumbar spinal cord of the adult rat

The majority of human spinal cord injuries involve gray matter loss from the cervical or lumbar enlargements. However, the deficits that arise from gray matter damage are largely masked by the severe deficits due to associated white matter damage. We have developed a model to examine gray matter-specific deficits and therapeutic strategies that uses intraspinal injections of the excitotoxin kainic acid into the T9 and L2 regions of the spinal cord. The resulting deficits have been compared to those from standard contusion injuries at the same levels. Injuries were assessed histologically and functional deficits were determined using the Basso, Beattie, and Bresnahan (BBB) 21-point open field locomotor scale and transcranial magnetic motor evoked potentials (tcMMEPs). Kainic acid injections into T9 resulted in substantial gray matter damage; however, BBB scores and tcMMEP response latencies were not different from those of controls. In contrast, kainic acid injections into L2 resulted in paraplegia with BBB scores similar to those following contusion injuries at either T9 or L2, without affecting tcMMEP response latencies. These observations demonstrate that gray matter loss can result in significant functional deficits, including paraplegia, in the absence of a disruption of major descending pathways.