Localization of ornithine decarboxylase (ODC) in the cochlea of the immature rat.

Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis, is important in cochlear development. Whereas tissue specific differences in cochlear ODC activity have been demonstrated, cellular localization of ODC protein in the inner ear of the immature rat has not. ODC was localized in inner ear structures using an ODC polyclonal antibody and the effects of cycloheximide on ODC immunoreactivity and enzymatic activity were determined. Tissues demonstrating elevated enzymatic activity contained cells with the strong immunoreactivity. ODC activity was highest in the organ of Corti and lateral wall followed by the cochlear nerve. Immunoreactivity was demonstrated throughout the cochlea with intense staining of the hair cells, pillar cells, Deiter's cells, inner sulcus cells, basilar membrane, stria vascularis, spiral ganglion cell bodies and cochlear nerve fibers. Cycloheximide rapidly diminished cochlear ODC activity and expression of ODC protein. The half-life of cochlear ODC was 30 min. Localization of cellular sites of ODC is important in understanding the role of the ODC-polyamine pathway in cochlear development and will be a valuable marker for tissue damage from ototoxic agents.

Polyamine changes in the vestibular nuclei of guinea pigs following labyrinthectomy.

Vestibular compensation is a process of behavioral recovery from ocular, motor and postural disorders following unilateral damage to the vestibular end-organ. Although restoration of the normal resting discharge rate in the ipsilateral vestibular nuclei is important in compensation, the biochemical and molecular mechanisms mediating recovery are largely unknown. The ornithine decarboxylase polyamine pathway is activated in the nervous system following axotomy or denervation. The authors postulate that changes in polyamines mediate vestibular compensation. Within 150-micron brain stem coronal section micropunches analyzed by high performance liquid chromatography techniques, the polyamine spermidine was significantly increased in the ipsilateral lateral vestibular nucleus 8 hours following labyrinthectomy in the guinea pig model. Because naturally occurring polyamines modulate excitatory amino acid receptors (N-methyl-D-aspartate [NMDA]) which in turn mediate neurotransmission between primary afferents and second order vestibular neurons, stimulation of polyamine pathways following neural injury may play a critical role in compensation.

Transconjunctival approach vs subciliary skin-muscle flap approach for orbital fracture repair.

OBJECTIVE: To compare the transcutaneous and transconjunctival approaches for repair of orbital rim and floor fractures. DESIGN: We conducted a retrospective study of the occurrence of eyelid retraction following the repair of 63 orbital fracture, 27 with the subciliary skin-muscle flap approach and 36 with the transconjunctival preseptal approach. SETTING: Academic tertiary referral medical center. PARTICIPANTS: Fifty-nine patients underwent 63 orbital explorations. INTERVENTIONS: Of the 27 transcutaneous explorations, 24 were done early within the first 2 weeks of injury and three were performed for correction of late posttraumatic enophthalmos. Of the 36 transconjunctival explorations, 25 were done early and 11 were performed for correction of late posttraumatic enophthalmos. OUTCOME MEASURE: Clinically noted complications. RESULTS: We found a 12% rate of transient ectropion and a 28% rate of permanent scleral show with the subciliary skin-muscle flap approach compared with no transient ectropion and a 3% rate of permanent scleral show with the transconjunctival approach. CONCLUSIONS: We believe that the transconjunctival approach provides excellent exposure with less risk of postoperative eyelid retraction and ectropion.

Stimulation variables in electroneurography of the facial nerve.

Electroneurography is an electrophysiologic measurement of compound action potentials elicited by the supramaximal stimulation of a peripheral nerve. The stimulus intensity-response function was examined in the cat facial nerve following stimulation over two different sites of the facial nerve: the main trunk and the buccal branches. Thresholds were achieved at lower current settings, the resultant compound action potential exhibited a greater amplitude, and masseter muscle excitation was more evident following stimulation over the buccal region. The use of concurrent facial- and masseter-evoked electromyographic monitoring allows more sensitive detection of masseter excitation and a more accurate determination of the current level necessary for supramaximal stimulation.

The use of masseter electromyography with electroneurography in the evaluation of facial paralysis.

In the evaluation of facial paralysis, electroneurography provides a quantitative assessment of the degree of degeneration. Near the endpoint of degeneration, the facial musculature compound action potential may be contaminated by masseter artifact resulting from supramaximal stimulation. We propose the use of both masseter electromyography and electroneurography in the evaluation of advanced degeneration to better define the current level for supramaximal stimulation, to eliminate masseter artifact, and to more accurately assess the degree of facial nerve degeneration.