Scopolamine impairs spatial working memory in the radial maze: an analysis by error type and arm choice.

The effects of scopolamine hydrobromide on performance in uninterrupted and delayed radial maze trials were studied in the rat. In addition to defining errors as incorrect arm entries, errors were defined by incorrect nose pokes in a food trough and were summed across the number of correct choices remaining. The average time elapsed from arm entry to nose poke was also calculated as a new measure of motivation and mobility. Working memory errors increased significantly following scopolamine injection in the uninterrupted trials and occurred significantly more often before the last correct choice. Errors in nonbaited arms during the last portion of a 3-h delay task increased significantly following scopolamine injection both before and after the first portion of the task and occurred more often before the last correct choice. However, nonbaited errors occurred more readily and at lower doses when scopolamine was injected 20 min before the onset of the task than when scopolamine was injected immediately after the completion of the first portion of the task. These data indicate that scopolamine affects current working memory and specifically affects acquisition more than consolidation of working memory.

rco-3, a gene involved in glucose transport and conidiation in Neurospora crassa.

Macroconidiation in Neurospora crassa is influenced by a number of environmental cues, including the nutritional status of the growing organism. Conidia formation is normally observed when the fungus is exposed to air. However, carbon limitation can induce conidiation in mycclia submerged in an aerated liquid medium. A mutant was previously isolated that could conidiate in submerged culture without imposing nutrient limitation and the gene responsible for this phenotype (rco-3) has now been cloned. RCO3 exhibits sequence similarity to members of the sugar transporter gene superfamily, with greatest similarity to glucose transporters of yeast. Consistent with this structural similarity, we find that glucose transport activity is altered in the mutant. However, growth of the mutant in media containing alternate carbon sources does not suppress conidiation in submerged culture. The properties of the mutant suggest that RCO3 is required for expression of glucose transport activity, glucose regulation of gene expression, and general carbon repression of development.

The olfactory thalamocortical system and odor reversal learning examined using an asymmetrical lesion paradigm in rats.

The olfactory thalamocortical system was disrupted bilaterally in rats using (a) unilateral mediodorsal thalamic (MD) lesions plus contralateral bulbectomy and transection of the anterior commissure (AC), (b) unilateral MD lesions plus contralateral lesions of the frontal cortex, or (c) bilateral MD lesions. Rats were trained on an odor discrimination task and on the reversal of that task. Experimental groups performed as well as controls on the initial discrimination task but made more errors on the reversal problem. Rats with asymmetrical disruption of the olfactory thalamocortical system performed as poorly as those with bilateral MD lesions. These outcomes indicate that odor reversal learning deficits in rats with bilateral MD lesions stem from interruption of the olfactory thalamic-neocortical system and also provide evidence that the AC mediates significant interhemispheric transfer of olfactory information.

An eight-alternative concurrent schedule: foraging in a radial maze.

In two experiments conducted in an eight-arm radial maze, food pellets were delivered when a photocell beam was broken at the end of each arm via a nose poke, according to either fixed-interval or random-interval schedules of reinforcement, with each arm providing a different frequency of reinforcement. The behavior of rats exposed to these procedures was well described by the generalized matching law; that is, the relationships between log behavior ratios and log pellet ratios were approximated by linear functions. The slopes of these log-log functions, an index of sensitivity to reinforcement frequency, were greatest for nose pokes, intermediate for time spent in an arm, and least for arm entries. Similar results were obtained with both fixed-interval and random-interval schedules. Addition of a 10-s changeover delay in both experiments eliminated the slope differentials between nose pokes and time spent in an arm by reducing the slopes of the nose-poke functions. These results suggest that different aspects of foraging may be differentially sensitive to reinforcement frequency. With concurrent fixed-interval schedules, the degree of temporal control exerted by individual fixed-interval schedules was directly related to reinforcement frequency.

Finding the base of the brain.

An electrode carrier mounted in a T-slot holder is described. An electronic circuit detects the vertical displacement of the carrier in the T-slot when an electrode encounters the base of the skull. Use of this vertical coordinate can reduce errors in locating structures at or close to the base of the brain.

Zinc deficiency decreases the activity of calmodulin regulated cyclic nucleotide phosphodiesterases in vivo in selected rat tissues.

The effect of zinc deficiency on calmodulin function was investigated by assessing the in vivo activity of two calmodulin regulated enzymes, adenosine 3',5'-monophosphate (c-AMP) and guanosine 3',5'-monophosphate (c-GMP) phosphodiesterase (PDE) in several rat tissues. Enzymatic activities in brain, heart, and testis of rats fed a zinc deficient diet were compared with activities in these tissues from pair fed, zinc supplemented rats. In testis, a tissue in which zinc concentration decreased with zinc deficient diet, enzyme activities were significantly decreased over those in rats who were pair fed zinc supplemented diets. In brain and heart, tissues in which zinc concentrations did not change with either diet, enzymatic activities between the groups were not different. These results indicate that zinc deficiency influences the activity of calmodulin-regulated phosphodiesterases in vivo supporting the hypothesis that zinc plays a role in calmodulin function in vivo in zinc sensitive tissues.

In vivo effects of zinc deficiency on calmodulin concentrations in selected rat tissues.

Two groups of male Sprague-Dawley rats, one fed zinc-deficient diet, ad libitum, the other, pair-fed with the same diet, but given supplemental zinc in the drinking water (8 mg Zn++/ml) were studied. After ten weeks of diet, rats were exsanguinated and zinc and calmodulin concentrations in brain and testis were measured. Mean zinc concentration in testis was significantly decreased in rats fed zinc-deficient diet without supplemental Zn++, but mean zinc concentration in brain was not different. Similarly, mean calmodulin concentration in testis was decreased in rats fed zinc-deficient diet without supplemental Zn++ whereas mean calmodulin concentration in brain was not different. Distribution studies of zinc and calmodulin showed that both zinc and calmodulin were released more freely into soluble fractions of testis in rats fed zinc-deficient diet without supplemental Zn++. These results indicate, for the first time in in vivo studies, that zinc influences the calmodulin content of testis.

The horizontal-vertical illusion: independence of line bisection and a comparison line.

Undergraduate students in social science and architecture did not differ in their accuracy of adjusting the vertical lines of L and inverted-T figures to be equal to a 1-in. horizontal line (the adjustment task) or in producing a 1 in. long line in the vertical or horizontal plane on a blank sheet of paper (the production task). In the adjustment task vertical lines were made significantly shorter than the horizontal comparison line and the shortening of the vertical line was significantly greater for the inverted-T than for the L-figure. In the production task lines drawn in the horizontal plane did not differ significantly from 1 inch but those drawn in the vertical plane were significantly shorter than 1 inch. Further, the magnitude of this error was equal to that obtained with the inverted-T figure. These results demonstrate that, while line bisection (the bisection of the horizontal by the vertical in the inverted-T figure) contributes to the horizontal-vertical illusion, the illusion clearly exists in the absence of a comparison line and can be accounted for as an overestimation of the vertical line.