Movement- and behavioral state-dependent activity of pontine reticulospinal neurons.

Forty-five years ago Shik and colleagues were the first to demonstrate that electrical stimulation of the dorsal pontine reticular formation induced fictive locomotion in decerebrate cats. This supraspinal motor site was subsequently termed the "mesencephalic locomotor region (MLR)". Cholinergic neurons of the pedunculopontine tegmental nucleus (PPT) have been suggested to form, or at least comprise in part, the neuroanatomical basis for the MLR, but direct evidence is lacking. In an effort to clarify the location and activity profiles of pontine reticulospinal neurons supporting locomotor behaviors, we employed in the present study a retrograde tracing method in combination with single-unit recordings and antidromic spinal cord stimulation as well as characterized the locomotor- and behavioral state-dependent activities of both reticulospinal and non-reticulospinal neurons. The retrograde labeling and antidromic stimulation responses suggested a candidate group of reticulospinal neurons that were non-cholinergic and located just medial to the PPT cholinergic neurons and ventral to the cuneiform nucleus (CnF). Unit recordings from these reticulospinal neurons in freely behaving animals revealed that the preponderance of neurons fired in relation to motor behaviors and that some of these neurons were also active during rapid eye movement sleep. By contrast, non-reticulospinal neurons, which likely included cholinergic neurons, did not exhibit firing activity in relation to motor behaviors. In summary, the present study provides neuroanatomical and electrophysiological evidence that non-cholinergic, pontine reticulospinal neurons may constitute the major component of the long-sought neuroanatomic MLR in mammals.

Inducible clocks: living in an unpredictable world.

All mammals have daily cycles of behavior (e.g., wake-sleep and feeding), and physiology (e.g., hormone secretion and body temperature). These cycles are typically entrained to the external light/dark cycle, but they can be altered dramatically under conditions of restricted food availability, changes in ambient temperature, or the presence of external stimuli such as predators. During the past 30 years, one of the best studied of these responses has been the entrainment of circadian rhythms to food availability. Experiments in rats and other rodents have provided evidence for a food-entrainable oscillator (FEO) in the mammalian circadian timing system (CTS). Until recently, however, very little was understood about the locus subserving the FEO or the functional interrelationship between the FEO and the master CTS pacemaker, the suprachiasmatic nucleus (SCN). We discuss here new data on the location of the FEO and suggest that it may involve an oscillator mechanism that is "induced" by starvation and refeeding.

Evidence for macular gravity receptor modulation of hypothalamic, limbic and autonomic nuclei.

Mice lacking normal vestibular gravity reception show altered homeostatic, circadian and autonomic responses to hypergravity (+G) exposure. Using c-Fos as a marker of neuronal activation, the current study identifies CNS nuclei that may be critical for initiating and integrating such responses to changes in vestibular signaling. This experiment utilized the mutant C57BL/6JEi-het mouse (het), which lacks macular otoconia and thus gravity receptor function. Following 2 h of 2G (2x Earth's gravity) exposure (via centrifugation) the neuronal responses of the het mice were compared with wildtype mice similarly exposed to 2G, as well as het and wildtype 1G controls. Wildtype mice exposed to 2G demonstrated robust c-Fos expression in multiple autonomic, hypothalamic and limbic nuclei, including: the lateral septum, bed nucleus of the stria terminalis, amygdala, paraventricular hypothalamus, dorsomedial hypothalamus, arcuate, suprachiasmatic hypothalamus, intergeniculate leaflet, dorsal raphe, parabrachial and locus coeruleus. The het mice exposed to 2G demonstrated little to null c-Fos expression in these nuclei with a few exceptions and, in general, a similar pattern of c-Fos to 1G controls. Data from this study further support the existence of a complex and extensive influence of the neurovestibular system on homeostatic, circadian and possibly autonomic regulatory systems.

Effects of 2-G exposure on temperature regulation, circadian rhythms, and adiposity in UCP2/3 transgenic mice.

Altered ambient force environments affect energy expenditure via changes in thermoregulation, metabolism, and body composition. Uncoupling proteins (UCPs) have been implicated as potential enhancers of energy expenditure and may participate in some of the adaptations to a hyperdynamic environment. To test this hypothesis, this study examined the homeostatic and circadian profiles of body temperature (T(b)) and activity and adiposity in wild-type and UCP2/3 transgenic mice exposed to 1 and 2 G. There were no significant differences between the groups in the means, amplitudes, or phases of T(b) and activity rhythms at either the 1- or 2-G level. Percent body fat was significantly lower in transgenic (5.2 +/- 0. 2%) relative to the wild-type mice (6.2 +/- 0.1%) after 2-G exposure; mass-adjusted mesenteric and epididymal fat pads in transgenic mice were also significantly lower (P < 0.05). The data suggest that 1) the actions of two UCPs (UCP2 and UCP3) do not contribute to an altered energy balance at 2 G, although 2) UCP2 and UCP3 do contribute to the utilization of lipids as a fuel substrate at 2 G.

Development of circadian rhythms in rat pups exposed to microgravity during gestation.

Ten pregnant Sprague Dawley rat dams were exposed to spaceflight aboard the Space Shuttle (STS-70) for gestational days 11-20 (G 11-20; FLT group). Control dams were maintained in either a flight-like (FDS group) or vivarium cage environment (VIV group) on earth. All dams had ad lib access to food and water and were exposed to a light-dark cycle consisting of 12 hours of light (approximately 30 lux) followed by 12 hours of darkness. The dams were closely monitored from G 22 until parturition. All pups were cross-fostered at birth; each foster dam had a litter of 10 pups. Pups remained with their foster dam until post natal day 21 (PN 21). Pup body mass was measured twice weekly. At PN 14 FLT pups had a smaller body mass than did the VIV pups (p < 0.01). Circadian rhythms of body temperature and activity of pups from two FLT dams (n = 8), two FDS dams (n = 9) and two VIV dams (n = 7) were studied starting from age PN 21. All pups had circadian rhythms of temperature and activity at this age. There were no significant differences in rhythms between groups that could be attributed to microgravity exposure. These results indicate that exposure to the microgravity environment of spaceflight during this embryonic development period does not affect the development of the circadian rhythms of body temperature and activity.

Production of spiral fractures in human cadaver long bones by use of a simple torsion machine.

A simple machine was developed so that long bones could be torqued to failure in order to estimate applied moment and study the resulting spiral fracture pattern. Detailed study of the fragments enabled the postulation of an orderly manner of fracture propagation. Twenty-seven embalmed human cadaver femurs were studied. The machine held one end of the bone in a fixed vise and the other in a rotating vise. Spring scales were used to apply force to a bar connected to the rotating vise which allowed for a crude estimation of torsional moment. Male femurs (72.8 yrs old sigma = 11.4) fractured at a mean torque of 106.7 N-m (sigma = 23.8), while female femurs (78.0 yrs old sigma = 6.7) failed at a mean torque of 96.7 N-m (sigma = 39.4). There were no statistically significant differences between the ages (p = 0.20) or the torsional moments at fracture (p = 0.41) for the male and female femurs. Given the similarities in this study population, an eye was turned towards anthropomorphic measurements in order to determine factors that might be indicative of bone strength. Several measurements were made on the fragments especially in the midshaft region. These included six cortex thicknesses, bone depth, width and circumference. Simple statistical analyses were performed.

Fractures of experimentally traumatized embalmed versus unembalmed cadaver legs.

Intact legs from six geriatric cadavers were fractured in a self-controlled study aimed at documenting the effects of embalming on both the soft and hard tissues of cadaver specimens subjected to biomechanical impact research. Upon bequeathal, one leg was removed and frozen while the other remained with the cadaver for embalming. The embalmed legs were amputated later and pre-test radiographs were made. For testing, a rod was inserted in the upright leg such that simulated upper body mass could be applied. A 50 kg cart propelled by a pneumatic accelerator to 7.5 m/s struck the anterior leg midway between the knee and ankle. The cart was headed by an instrumented steel pipe (4.75 cm dia.) coupled to a transducer which relayed impact force data to a Hewlett Packard 3562 A signal analyzer. Testing was captured on standard VHS video (30 frames/s) and 16 mm Color High Speed Film (1,000 frames/s). Post-test analyses included radiographs and thorough dissection. Peak forces were comparable for matched pairs. The unembalmed legs showed greater soft tissue damage (muscle and skin) but generally less bone fragmentation than their embalmed counterparts. Neurovascular components were virtually unharmed in most legs.

Airbag-induced eye injuries: a report of 25 cases.

OBJECTIVE: To acquire a better understanding of airbag-induced eye injuries, 25 cases are reviewed and an attempt is made to identify the causal mechanisms associated with each injury. DESIGN AND METHODS: The National Highway Traffic Safety Administration's National Accident Sampling System for the years 1984-1994 was accessed to identify automobile accidents that included airbag deployment and injury to the ocular region. The search provided 25 such cases with detailed studies of the accident scene and medical records of the injuries. The cases were comprehensively reviewed to determine the casual mechanisms associated with each group of injuries. RESULTS: The study determined that the injuries range from mild corneal abrasions to retinal detachment. Causation for each injury was determined and is detailed. The injuries were grouped according to location within the ocular region, and the distribution is shown. CONCLUSIONS: Most of the injuries were induced by impact with the fully deployed airbag, but the more severe ocular trauma resulted from the actively deploying airbag striking the occupant. Thus, ocular trauma from airbags can occur in very minor impacts. Additionally, the left eye seemed more vulnerable to injury than the right. Nontethered airbags have greater inflation distances that tend to increase the probability of injury. External parameters that may also increase the severity of eye injury include an unfastened seat belt, sitting too close to the steering wheel, or wearing glasses.

The forensic pathologist and the determination of driver versus passenger in motor vehicle collisions. The need to examine injury mechanisms, occupant kinematics, vehicle dynamics, and trace evidence.

Five cases of vehicular homicide are presented in which the determination of an occupant's role in a motor vehicle collision was an important medicolegal question. The identification of the occupant's role in a motor vehicle collision can be determined by the forensic pathologist. The investigation that coordinates an examination of injury mechanisms, occupant kinematics, vehicle dynamics, and trace evidence will facilitate such a determination. This determination protects the innocent passenger, when faced with criminal or civil charges, from being falsely prosecuted as the driver. The examination of the above-mentioned components in a multi-occupant collision takes on particular forensic importance when a surviving driver claims to be a passenger: the victim rather than the assailant.

Accessory innervation of mandibular anterior teeth in cats: a horseradish peroxidase study.

In 10 cats, an ipsilateral section of the inferior alveolar nerve was performed following which horseradish peroxidase was deposited in cavity preparations of either ipsicentral incisors (8) or canines (2). The animals were sacrificed in 24 h, and the ipsilateral nerve to mylohyoid and both semilunar ganglia were prepared histochemically for observation. Labeled axons were found in 6 of 8 cats, whose incisors were prepared, and 4 of the 6 had labeled ganglion cells. In the two remaining cats with incisor preparations, no labeled ganglion cells were found; however, labeled axons were found in the mylohyoid nerve. Neither labeled axons or cells were found in those cats whose canines were prepared. One case of cross-innervation was noted. These results suggest that in addition to the inferior alveolar nerve, the nerve to mylohyoid and possibly other accessory neural pathways are involved in incisor innervation in cats.

The inferior alveolar and mylohyoid nerves: an anatomic study and relationship to local anesthesia of the anterior mandibular teeth.

The distance between the branching point of the mylohyoid nerve to the entrance of the inferior alveolar nerve into the mandibular canal was studied in 37 adult human cadavers. On the average, this branching distance was 14.7 mm, which is greater than previously reported. Also found was a 43% incidence of extension of the mylohyoid nerve beyond the muscle to foramina on the lingual aspect of the mandible. If the mylohyoid nerve mediates sensory information from the anterior incisors, then the factor of an increased branching distance may become important in terms of the dilution of the anesthetic agent during diffusion and the amount of nerve length exposed to the anesthetic agent. These findings may also account in part for the purported greater success of the so-called Gow-Gates type of injection technique compared with that of the conventional mandibular block.

A self-instructional approach to gross anatomy: evaluation of five years experience.

A largely self-instructional teaching method in gross anatomy for dental students, developed and tested over five years at the University of Louisville, is presented and evaluated. The merits of the method include reduced faculty teaching load, the potential to accommodate increased numbers of students without comparable increases in faculty or physical plant, apparent improvement in the quality of instruction, student satisfaction, early identification of marginal students, and conservation of cadavers.

Afferent and efferent components of the facial nerve in the bullfrog (Rana catesbeiana).

The afferent and efferent components of the facial nerve were traced within the brain stem of Rana catesbeiana, using three different neuroanatomical techniques. Primary afferent fibers could be traced to the spinal tract of trigeminal nerve and to fasciculus solitarius as far caudally as the first or second spinal segment, using silver degeneration methods. Cobalt filling of of the entire nerve showed the same distribution of afferent fibers, as well as the filling of the cells within the mesencephalic nucleus of trigeminal, indicating the origin of a proprioceptive component of the facial nerve. Cobalt iontophoresis and horseradish perioxidase experiments showed that the motor nucleus of the facial nerve was located just ventral to the fourth ventricle, and caudal to the motor nucleus of trigeminal. The distribution of afferent fibers to fasciculus solitarius and the spinal tract of trigeminal is similar in some respects to the distribution of afferent fibers from the trigeminal and vagal nerves in the bullfrog. The afferent fibers from the three cranial nerves are found as far caudally in the brain stem as the second spinal segment.

Origin and course of an afferent component of the facial nerve within the central nervous system.

The mesencephalic nucleus of trigeminal gives rise to an afferent component of the facial nerve. This nucleus contains large unipolar afferent cell bodies which give rise to an axon which courses caudally through the brainstem and exists via the facial nerve to terminate distal to the stylomastoid foramen.