Effect
of Type 2 Adrenal Receptor Agonist RU28362 on the Radial Arm
Maze Performance of Adrenalectomized Rats by Paul R. Vaher & Bruce S. McEwen
Abstract:
The
effect of the type 2 adrenal steroid receptor activation on
spatial memory was evaluated. Adrenalectomized (ADX) rats were
treated with RU28362, a specific type 2 receptor agonist, and
tested on a task of spatial memory, the radial arm maze (RAM).
Earlier studies in this series have shown that ADX causes lasting
deficits in RAM performance without of marked loss of granule
cell neurons in the dentate gyrus (DG). Sham, ADX, and ADX rats
treated with RU28362 were tested on the RAM 4 times a week for
3 weeks. RU28362 was delivered by osmotic minipump (10 µg/hr
for 7 days, s.c.). Intake of 3% saline was measured as an index
of serum levels of adrenal steroids. ADX rats treated with RU28362
made fewer correct choices in the first eight visits and more
errors in completing the task than sham and ADX controls for
the first week of testing. The effect lasted for two weeks,
one week beyond the supposed life of the pump, and was paralleled
by the suppression of saline intake. Saline intake increased
in RU28362 treated rats during the third week and was accompanied
by a trend towards a reduction in the number of maze errors.
While poorer maze performance was accompanied by a somewhat
decreased saline intake in RU28362 treated rats, a correlation
between saline intake and measures of choice accuracy was not
shown. As in previous studies, ADX did not result in a high
frequency of granule cell pyknosis or a reduction in cross sectional
DO area. Measures of DO morphology were not correlated to behavioral
performance. It was concluded that RU28362 further impaired
spatial memory performance in ADX rats. Thus, the type 2 receptor
works in opposition to the type 1 receptor which was shown in
our earlier study to facilitate spatial memory function in ADX
rats.
