Rapid axonal transport in trigeminal nerve of rat.

The rat trigeminal nerve was investigated as a model system for axonal transport to identifiable sensory nerve endings. Following stereotaxic injection of [3-H]proline into the ganglion, the distribution of label in protein and other extracts of ligated or unligated infraorbital nerve was measured in replicates at various time intervals from 30 min to 3 days. In unligated nerves the average maximum velocity of somatofugal protein transport was 228 mm/day. Light microscope autoradiography demonstrated rapid intraaxonal transport of radioactive material to nerve endings in molar teeth and vibrissae. The system appears suitable for investigating the fate of axonally transported material at peripheral receptors.

Fourth Daniel C. Baker, Jr. memorial lecture. Energy and the larynx.

Review of the logistics of energy supply in animals indicates that the advent of the larynx was part of a response to an earlier energy crisis. It permitted a major increase in the flow of energy available to the organism and became the mechanical control point and rate-limiting factor of the increased inflow. Phylogenetically, a succession of structural innovations steadily enhanced the flow capacity of the larynx and rendered the mechanism more versatile, most recently with the accrual of phonation (in mammals), pressurized closure (in primates and odontocetes), and vocal formants and efficiency (in man). The larynx is thus a marker of the animal's capabilities for energy intake, energy utilization and information emmission and, apparently, of the size and complexity of the brain. Today's energy crises appear to continue those of the past.

Quantification of intralaryngeal pressure exerted by endotracheal tubes.

Prolonged endotracheal intubation in critically ill patients has become an accepted routine. One notable consequence of this form of management is injury to the posterior aspect of the glottis, apparently an injury caused by the presence of an endotracheal tube. Utilizing two types of sensing devices, the pressure exerted by endotracheal tubes was measured in the canine larynx via a laryngofissure approach. Pressure in excess of 200 mm Hg was consistently noted in the region of the arytenoid cartilage. A variety of tubes were tested with similar results.

Biomechanics of the human epiglottis.

The mechanism that folds the epiglottis down over the closed larynx in the course of swallowing has been unclear. Measurements of the force needed to fold the epiglottis in cadaver specimens exceed the estimated force available from the aryepiglottic muscle. Frame-by-frame analysis of cinefluorograms reveals that deglutitional epiglottic downfolding occurs at the time of maximal elongation of the hyoepiglottic ligament. The observations lead us to propose a conical model of epiglottic downfolding which also explains the conical shape of the epiglottis usual in early infancy. The infant shape may be part of a protective partially closed entrance adaptive to suckling, while maturational widening of the opening adapts to the growing respiratory demands of increasing physical exertion.

Chondroblastoma of the foot.

A total of 322 cases of chondroblastoma were referred to the Armed Forces Institute of Pathology between 1960 and 1990. Ten additional cases of chondroblastoma were treated at Walter Reed Army Medical Center between 1985 and 1993. Forty-two of these involved the foot, two of which were treated at Walter Reed Army Medical Center. Patients with chondroblastoma of the foot were male in 35 (81%) cases, with a mean age of 25.5 years, which was significantly different from the mean age of 17.3 years in patients with chondroblastoma of the long bones (P < 0.0001). Chondroblastoma of the foot is most commonly found in the posterior subchondral areas of the talus and calcaneus as well as in the calcaneal apophysis. Radiographically, the lesion was associated with an articular surface or apophyseal area in all cases and appeared radiolucent, with little to no matrix production. The margins were generally well defined. Cystic features were noted grossly and histologically in 24 (57%) specimens, a feature seen in only 21% of all chondroblastomas overall. Treatment consists of thorough curetting and bone grafting with good oncologic and functional results.

Differential effects of glucose and potassium lack in conduction block of myelinated and unmyelinated axons.

The effect of potassium on conduction in myelinated and unmyelinated axons lacking glucose was investigated in vitro. In the presence of ambient potassium neural excitability was lost after the same period of time in both myelinated and unmyelinated fibers. In the absence of potassium in the incubation solution however, the extinction times of the unmyelinated axons only (p less than 0.01), but not those of the myelinated ones were delayed. It is suggested that unmyelinated C fibers are more energy efficient than myelinated A axons.