A perfusion-fixation procedure for the concurrent demonstration of Timm's, horseradish peroxidase (HRP), and acethycholinesterase (AChE) histochemistry

The sulfide-silver method of Timm has been a widely used histochemical technique to demonstrate the presence of heavy metals in biological tissue, particularly in the central nervous system. However, the use of this method or its several modifications results in less than optimal morphological preservation and requires embedding the tissue in paraffin or freezing it and cutting it directly onto slides with a cryostat. These procedures can decrease the sensitivity and limit the application of other histochemical procedures, particularly when experiments necessitate processing large specimens or reaction procedures require techniques using free-floating sections. A perfusion-fixation protocol is described that yields sufficient fixation to cut whole frozen blocks of tissue with a sliding microtome, permits the use of free-floating sections, and allows the concurrent demonstration of horseradish peroxidase and acetylcholinesterase histochemistry without loss of sensitivity. The method consists of a short initial exposure to a sodium sulfide solution followed by a prolonged exposure to a combined sulfide-aldehyde fixative solution.     

Orienting responses and vocalizations produced by microstimulation in the superior colliculus of the echolocating bat, Eptesicus fuscus

An echolocating bat actively controls the spatial acoustic information that drives its behavior by directing its head and ears and by modulating the spectro-temporal structure of its outgoing sonar emissions. The superior colliculus may function in the coordination of these orienting components of the bat's echolocation system. To test this hypothesis, chemical and electrical microstimulation experiments were carried out in the superior colliculus of the echolocating bat, Eptesicus fuscus, a species that uses frequency modulated sonar signals. Microstimulation elicited pinna and head movements, similar to those reported in other vertebrate species, and the direction of the evoked behaviors corresponded to the site of stimulation, yielding a map of orienting movements in the superior colliculus. Microstimulation of the bat superior colliculus also elicited sonar vocalizations, a motor behavior specific to the bat's acoustic orientation by echolocation. Electrical stimulation of the adjacent periaqueductal gray, shown to be involved in vocal production in other mammalian species, elicited vocal signals resembling acoustic communication calls of E. fuscus. The control of vocal signals in the bat is an integral part of its acoustic orienting system, and our findings suggest that the superior colliculus supports diverse and species-relevant sensorimotor behaviors, including those used for echolocation.     

Growth of the human mandibular angular process: A functional cranial analysis

The angular process of the human mandible alters its inclination with age, changing from a medial to a lateral flare during the transition from the neonatal to the adult stages. The morphological change in this mandibular skeletal unit is shown to be associated with a change in orientation of a portion of the related functional matrix, the masseter muscle. This change to an oblique line of action from an originally vertical one is associated with an increase in the functional movement of protraction at the temporo-mandibular joint. No other physiological parameters of muscle function seemingly are associated with this skeletal alteration. The processes of interaction between the functional matrix and its related skeletal are as yet unknown.     

Errors in calculating cardiac output due to administration of perfluorochemicals

Intravenous administration of perfluorochemicals (PFC) will alter the density (rho)B, the gravimetric specific heat (c)B, and the volumetric specific heat (rho c)B of blood. Changes in hematocrit also influence (rho c)B. The calibration constant employed in the determination of cardiac output (CO) by thermal dilution depends inversely on (rho c)B. We estimate the effect of addition of PFC and changes in hematocrit on (rho c)B. Consider blood to be a mixture of red cells, emulsified PFC particles, and plasma. This leads to the equation: (rho c)cB = 0.96 - 0.11Hct - 0.48Fct. Here Hct and Fct are the fractional volume concentrations of red blood cells and PFC, and (rho c)cB is the calculated specific heat based on the actual composition of blood. CO can be corrected for changes in (rho c)B by the equation: (CO)c = [(rho c)sB/(rho c)cB](CO)o. Here (CO)o is the observed cardiac output, (rho c)sB is the standard specific heat of blood used in the calculation of (CO)o, and (CO)c is the corrected cardiac output. We have observed laboratory situations where the correction factors have been as high as 10%.