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Respiratory dysfunction is the leading cause of morbidity and mortality following traumatic spinal cord injury (SCI). Injuries targeting mid-cervical spinal cord regions affect the phrenic motor neuron pool that innervates the diaphragm, the primary respiratory muscle of inspiration. Contusion-type injury in the cervical spinal cord is one of the most common forms of human SCI; however, few studies have evaluated mid-cervical contusion in animal models or characterized consequent histopathological and functional effects of degeneration of phrenic motor neuron-diaphragm circuitry. In an attempt to target the phrenic motor neuron pool, two unilateral contusion injury paradigms were tested, a single injury at level C4 and a double injury both at levels C3 and C4, and animals were followed for up to 6 weeks post-injury. Both unilateral cervical injury paradigms are reproducible with no mortality or need for breathing assistance, and are accompanied by phrenic motor neuron loss, phrenic nerve axon degeneration, diaphragm atrophy, denervation and subsequent partial reinnervation at the diaphragm neuromuscular junction, changes in spontaneous diaphragm EMG recordings, and reduction in phrenic nerve compound muscle action potential amplitude. These findings demonstrate significant and chronically persistent respiratory compromise following mid-cervical SCI due to phrenic motor neuron degeneration. These injury paradigms and accompanying analyses provide important tools both for understanding mechanisms of phrenic motor neuron and diaphragm pathology following SCI and for evaluating therapeutic strategies in clinically relevant cervical SCI models., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The potential role of the cytochromes P-450 in methylcholanthrene (MC)-mediated suppression of cutaneous delayed hypersensitivity (CDH) in C57BL/6J (B6) mice was evaluated indirectly by treating mice with agents known to induce or inhibit hepatic cytochromes P-450 prior to contact sensitization. Subsequent alterations in aryl hydrocarbon hydroxylase (AHH) activity and CDH, as measured by suppression of 2,4-dinitrofluorobenzene (DNFB)-induced ear swelling, were measured. MC administration resulted in a dose-dependent suppression of ear swelling and a concomitant dose-dependent induction of hepatic AHH activity. Treatment of B6 mice with phenobarbital (PB), 80 mg/kg daily X 3, a broad spectrum inducer of P-450, resulted in a 2.5-fold increase in benzo[a]pyrene (B[a]P) hydroxylase activity without affecting CDH. Animals treated with the same PB protocol prior to an ED20 dose of MC showed no difference in suppression of CDH compared to animals treated with MC alone. In contrast, successive treatment with the selective P1-450 inducer, 5,6-benzoflavone (beta NF), prior to and following an ED20 dose of MC significantly increased suppression of CDH (p less than 0.001) usually seen at this MC dose. Treatment with a known inhibitor of cytochrome P1-450 activity, 7,8-benzoflavone (alpha NF), did not prevent AHH induction when administered prior to and following MC (ED100) nor did it suppress CDH when administered alone. However, this alpha NF treatment completely prevented suppression of CDH usually seen at this MC dose. These data provide evidence suggesting that metabolic activation by cytochrome P1-450 is required for the expression of the immunosuppressive activity of MC.