Effects
of Aldosterine Replacement on the Radial Arm Maze Performance
of Adrenalectomized Rats by Paul R. Vaher & Bruce S. McEwen Key words: adrenalectomy; spatial memory; radial arm maze; dentate gyrus;
aldosterone; adrenal steroids
Abstract:
Because
our earlier study showed that adrenalectomy (ADX) caused lasting
deficits in radial arm maze (RAM) performance, without a significant
loss of granule cell neurons, we admininistered aldosterone
(ALDO), a selective type 1 adrenal steroid receptor agonist,
in an atempt to reverse RAM deficits in ADX rats. ALDO was delivered
to ADX rats by osmotic minipump (10 mg/hr for 7 days, s.c.).
Intake of 3% saline was measured as an index of serum levels
of adrenal steroids. Sham, ADX and ADX rats receiving ALDO were
tested on the RAM 4 times a week for 3 weeks. ALDO improved
RAM performance in ADX rats as was especially evident in the
number of errors made. Improved performance with ALDO treatment
was correlated with a reduction in saline intake. Performance
deteriorated during the third week in conjunction with an increase
in salt appetite. In this, as well as our previous experiment,
ADX resulted in only a modest increase in apoptotic neuronal
death in the dentate gyrus measured 5 wks after surgery. Cross
sectional dentate gyrus area was not reduced in ADX rats. Thus,
type 1 receptor activation diminished spatial memory deficits
in ADX rats. Our studies suggest that adrenal steroids themselves
exert activational effects on spatial memory in the absence
of pervasive degeneration of dentate gyrus granule cells.
