Biology Reference
In-Depth Information
VI.
A
GE
-D
EPENDENCE OF
LA-LTP
AND
LA-LTD
Most patch-clamp and intracellular studies elucidating the mechanisms of plasticity
changes in the LA were performed in brain slices of very young animals. Therefore,
recordings of neuronal activity in brain slices of aged rodents are to our knowledge not
performed yet. Although several studies on aging and hippocampal LTP failed to demonstrate
any age-related deficits using HFS (Lanahan et al. 1997),
TBS revealed age-related deficits in
the induction of LTP (Moore et al. 1993). The type of CA1-LTP induced by HFS seems to be
genuinely different from LTP induced by learning processes or theta-patterned stimulation.
Moreover, TBS-induced LTP in the CA1 region of the hippocampus depends only on
NMDARs (Larson and Lynch 1988) and NMDA receptor-dependent LTP appears to decline
in the CA1 area of aged rats (Shankar et al. 1998).
Recently, we compared changes in the magnitude of LA-LTP with those of CA1-LTP in
24-months-old rats. Since the LA does not have a layered architecture like the hippocampus,
and since TBS was not able to induce stable LA-LTP in aged mice, we used HFS of EC fiber
stimulation to induce LA-LTP. In case of the hippocampal CA1 region, TBS of Schaffer
collateral stimulation was used. In both structures we found an age-dependent decrease in
LTP magnitude (in comparison to 9-months-old rats; unpublished observation).
Concerning LTD in aged rodents it is known that hippocampal slices from very young
animals show robust LTD, whereas slices from adult animals lack, or show attenuated LTD
after LFS (Battistin and Cherubini 1994; Kemp and Bashir 1999). In agreement with these
data we obtained that LA-LTD can be easily induced in 8-week-old mice or 8-16 week old
rats, whereas LFS of fibers within the LA failed to induce LA-LTD in 12-months-old mice as
shown in Fig. 3.
200
150
100
50
2 months [n = 10]
LFS
12 months [n = 6]
0
-20
-10
0
10
20
30
40
50
60
70
min
Figure 3. Age-dependency of LA-LTD. Low frequency stimulation (1 Hz, 15 min; LFS) of afferents
within the LA. Data points represent averaged amplitudes (mean ± SEM) normalized in relation to
baseline values
