Four hours of paradoxical sleep deprivation impairs alternation performance in a water maze in the rat.

Sixteen rats were deprived of paradoxical sleep (PS) for 4 h using the "flower pot" technique and 16 other served as yoked controls. PS-deprived and control rats then had to learn a water maze using either a standard allocentric configuration (i.e., finding the submerged platform using external cues; n = 6/group) or an alternation version (goal platform alternating between two locations; n 10/group). Rats were submitted to six trials with a cutoff time of 60 s and an intertrial interval of 5 min. Criterion was set as two consecutive successful completions. PS-deprived rats made more quadrant entries and took more time to reach criterion on the alternation task than control rats while both groups were equal on the allocentric task. Based on lesion studies (Ethier et al., this issue) we propose that tasks that require an intact medial prefrontal cortex are particularly sensitive to PS deprivation.

Spatial learning on the Morris Water Maze Test after a short-term paradoxical sleep deprivation in the rat.

Twelve rats were deprived of paradoxical sleep (PS) for eight hours using the small platform method. PS-deprived and control rats then learned either the standard allocentric version (using external cues) of the Morris Water Maze (MWM) or a delayed alternation version (changing the platform location between trials: MWM(DA)). Overall, rats learning the MWM(DA) made more quadrant entries than rats learning the allocentric version. Compared to other rats, PS-deprived rats crossed more quadrants only in the MWM(DA). These results show that MWM(DA) is a more complex task to learn and is more vulnerable to PS deprivation than allocentric spatial orientation. Since delayed alternation is dependent upon frontal structures, we propose that tasks involving the frontal cortex are more sensitive to short-term PS deprivation than tasks related to hippocampal structures.

[Interactive multimedia learning systems in oral medicine: experiences at the Faculty of Oral Medicine of Laval University]. / Les systèmes d'apprentissage multimédiatisé interactif en médecine dentaire: expérience à la Faculté de médecine dentaire de l'Université Laval.

Dental teaching must keep in stride with the latest trends. Evolution and challenge are very much a part of every day life for both students and dentists. At the University of Laval, the faculty of dentistry has developed an interactive multimedia apprenticeship system. This system will be incorporated into the curriculum of Laval's doctor of dental medicine degree, as well as the organizational framework of its continuing education program. It will only be a first step for the faculty's department of oral rehabilitation, which ultimately hopes to see the system used by dental schools across Canada. Known as "Médent," the prototype system is designed to teach the principles of osseointegration, and the rehabilitation of oral function using osseointegrated implants.

Hypothalamic versus pituitary dysfunction in Down's syndrome as cause of growth retardation.

We have found that some children with Down's syndrome (DS) have growth retardation secondary to growth hormone (GH) deficiency. To test the hypothesis that hypothalamic dysfunction is the primary cause for GH deficiency and growth retardation, hypothalamic-pituitary responses of serum GH concentrations to levodopa and clonidine as well as pituitary responses in serum GH concentrations to growth-hormone-releasing hormone (GHRH) were analysed in 14 prepubertal children with DS. Levodopa and clonidine were given, and blood was drawn for determining serum GH levels. Seven prepubertal control children had both levodopa and clonidine tests done. The delta serum GH during levodopa was 5.7 +/- 6.3 ng ml-1 in DS and 13.1 +/- 9.8 ng ml-1 in controls. The delta serum GH during clonidine administration was 3.0 +/- 3.2 ng ml-1 in DS and 17.3 +/- 5.6 ng ml-1 in controls. Children with DS had a significantly lower response to levodopa and clonidine, compared with controls by the Mann-Whitney U-test (P < 0.03 and P < 0.009, respectively). Growth-hormone-releasing hormone was given at 1 microgram kg-1 i.v. bolus and bloods for GH were drawn at-15, 0, 15, 30, 60, 90 and 120 min in 14 subjects with DS and 24 normal controls, both groups prepubertal. The mean delta serum GH concentration in DS was 53.6 +/- 38.3 ng ml-1, and it was 35.6 +/- 25.1 ng ml-1 in controls with P < 0.23 non-significant by the Mann-Whitney U-test. These results indicate that levodopa and clonidine (drugs stimulating hypothalamic GHRH release and secondary pituitary GH release in normal individuals) do not stimulate GH release in DS. Furthermore, normal GH response to GHRH in DS indicates normal pituitary function (normal somatotroph response to GHRH) and supports hypothalamic dysfunction in DS.