Quantitative scanning transmission electron microscopy of ultrathin cryosections: subcellular organelles in rapidly frozen liver and cerebellar cortex.

Freeze-dried, ultrathin cryosections of directly frozen mouse liver and brain have been prepared and characterized by low-dose dark-field scanning transmission electron microscopy (STEM). These improved cryosections gave images comparable to those from conventional plastic sections. They were thin enough (< < 1.0 elastic mean free path) to use established dark-field techniques, modified for thickness-dependent nonlinearities, to measure the dry mass fraction of individual organelles, and hence to deduce their water content. Digital STEM imaging in combination with electron and X-ray spectroscopy has important biological applications, as illustrated by studies on calcium regulation in Purkinje neurons. Calcium concentrations per unit dry weight of dendritic compartments were determined by the peak/continuum method of energy-dispersive X-ray spectroscopy (EDXS), which necessarily overstates elemental concentrations because of beam-induced mass loss. The dry mass content of organelles at low dose and the percentage of dry mass retained after analysis at high dose were as follows: mitochondria (46.0 g dry mass/100 g hydrated mass, 67% mass retained); endoplasmic reticulum (27.9 g/100 g, 57%); and cytoplasm (16.3 g/100 g, 41%). These values were used to correct elemental concentrations for mass loss. Results indicated that the major calcium storage organelle in Purkinje cell dendrites is the endoplasmic reticulum, of which there are two types distinguished by their levels of calcium. Parallel electron energy loss spectroscopy of dendritic organelles corroborated EDXS measurements, with an improved sensitivity that indicates the feasibility of quantitative calcium mapping.

Facial electromyography as a predictor of treatment outcome in depression.

Electromyograms (EMGs) from the corrugator, zygomatic and splenius capitis muscle sites and Beck depression inventory scores were obtained from 21 depressed in-patients shortly after admission and after two weeks in hospital. Contrary to the result of a previous study by other investigators, significant covariaton between depressive symptoms and corrugator EMG levels was not seen. However, consistent with a second finding of the previous study, initial corrugator EMG levels were shown to be significantly predictive of treatment outcome. Further, initial EMG from the zygomatic was also found to predict changes in depression. The explanation is unclear and further research is needed.

Autoshaping and food acquisition in mice: a genetic analysis.

A genetic analysis was undertaken for a number of quantitative behavioral characters that were hypothesized to be components in a generalized feeding pattern. These measures included open-field activity, rate of food ingestion, and rate of development of an autoshaped operant response. Four strains of inbred laboratory mice were used as subjects in a diallel cross design. Standard analytical procedures, including the Hayman analysis of variance and the Jinks variance-covariance diagram, were used to interpret the data. The results were evaluated in terms of the contribution of fitness provided by each of the measured characters. It is concluded that both the various open-field measures and the food-consumption measure were of some importance in the evolutionary history of the mouse. The autoshaping measures, on the other hand, showed a pattern of inheritance that differed from the other measures and offered no clear interpretation of their evolutionary significance.

Temporal distributions of responding during discrete-trial omission training in rats.

Within-session temporal distributions of responding were investigated in three experiments using rats pressing a lever in a discrete-trial omission procedure. This schedule entailed 60, one-minute trials, and a sucrose solution was made available at the end of each trial in which no lever press occurred. In Experiment I, nonnaive rats acquired and maintained responding during this training. Moreover, the probability of a response during any session showed a strong and reliable tendency to increase from the beginning to the end of the session. These results were replicated in Experiment II, using naive animals. In Experiment III, alterations were made in the training procedure, including elimination of response-contingent and noncontingent stimulus changes. Results indicate that stimulus change may be sufficient to maintain low levels of responding whether or not this change is contingent on responding.