547.15
DEHYDROEPIANDROSTERONE SULFATE*AFFECTS LTP IN AREA CAI
Antidromically-ConditbnedE-SPotentiation is not Blocked by GABAA
O F THE RAT HIPPOCAMPUS. LH. Mever . 0.
andaL.Gruol.Dept. of Neurophannacology and
Inhibitors. Lee W. ~amnbell*,Jennlfer M. Jester, Terrence J Se!nowskk
Computatronal Neuroblology Laboratory, Salk Insutute, La Jolla, CA
Long-term potenmuon (LTP) of the populaUon splke m excess of that
predicted by Increase m the slope of the field excltatov post-synapuc potential
(EPSP) has been described as a component of theta-burstLTP (Exp B w n Res
79 633-641) An lncrease m the ratro of excmuon to mhlbluon, n reductton of
are Illought to conu~buteto lhis
tonic ~nhlhitlon,and a dccreasc In spike d~rml~old
BI'SP-to-snikc (E-S) notentiation Assoc~utiveI.TP using antidrom~cstimulation
as the condlhonrng strmulus produces a stable mcrease m thepopulatlon splke
ampltbde, but no change m the slope of the EPSP (Soc Neuro Abstr 17 533 15)
Do changes m tonlc or synapuc lnhlbluon underhe the assoctauve form of E-S
potentratlon as they are thought to do m theta-burstE-S potentlatlon?
The EPSP and populaUon spike were recorded from the CAI layer of rat
h~ppocampalshces The ant~dromlccondluonlng stlmulus was 50 bursts of 5
pulses at 100 Hz wlth an mterburst interval of 200 ms dehvered to the alveus The
Schaffer-collateralpathway was stimulated once per burst In some sllces the
GABAA blockers plcrotoxln (10 HM) and/or btcuculhne (10 pM) were added to
the bath prlor to tesung When pared together, the ant~dromlcand orthodromlc
sumull produced a potentlauon of the popolauon sp~ke,even m the presence of the
GABAA blockers (138% 16 7, mean s e m) In conuast. the E-S potentlauon
component of U~eta-burstLTP a blocked by GABAA tnhlhttors
Intracellular recordmgs from the CAI layer reveal an Increase m
excltab~htyf0llowlng assoclatlve E-S poteouabon Pwed t-tests suggest that a
depolarlzatlonof the restlng membrane potent~al(RMP) accounts for the Increased
excltababllrty (ctrl -63 7 0 326 mV, 15 mm post tetanus -61 2 mV 0 438, mean
RMP s e m, P = 0 04, F1= 9 08) Splke threshold, Input tes~stance.and m e
constant of the membrane were not effectedby assoclauveE-S potentlatlon
*
*
*
The Scripps Research Institute, La Jolla CA. 92037
~euroiteroidssuch as dehydroepiandrosterone sulfate (DHEAS) affect bolll
GABAA-mediated IPSPs as well as excitatory neumtransrnission. We have
explored whether DHEAS can influence paired-pulse facilitation and long-tern,
potentiation (LTP) in a rat hippocampal slice preparation.
Hippocampal slices from Sprague-Dawley rats were placed in an interlace
type slice chamber and perfused with artificial cerebrospinal fluid ( A q ,
Extracellular synaptic field potentials i n response to Schaffer collateral
stimulation were recorded from the CAI stratum radiatum. Paired pulse
stimulation (inter-pulse interval 20-200 ms) was used during baseline
recordings. Slices were then perfused with either ACSF (control slices) or 10
DHEAS (experimental slices) and paired pulse responses again Obtained
after a 112 hour period. Changes in synaptic responses of control slices we,
compared to changes noted in DHEAS-exposed slices. Subsequently, single
pulse responses were recorded at 1 minute intervals in each slice both before
and after induction of LTP. LTP responses noted in control slices were then
compared to LTP responses seen in DHEAS-exposed slices. Analysis of ule
paired pulse responses indicated that DHEAS had no effect upon facilitation at
any inter-pulse interval, arguing against any pre-synpatic effect of the steroid,
DHEAS, however, did significantly augment the nragnitude of LTP induced in
area CAI. Such results may account for behavioral effects of DHEAS in whicll
this neurosteroid has been noted to enhance memory (SOC.Neurosci Abstr 18;
1160). Supported by AA6420 and AA0756.
*
*
THE EFFECTS O F A NITRIC OXIDE SYNTHASE INHIBITOR ON
DENDRITIC V C A L I Z A T I O N OF LTP A N D LTD
C o u s s e n s & ~ ~ , N e u r o b i o l o g Ny E, Ohio
Col. o f M e d . , R o o t s t o w n , OH 44272.
LONG TERM POTENTIATION IN AREA CAI O F RAT HIPPOCAMPUS
S. M. Nicola. J. A. Cumminas and R. C. Malenka' Neuroscience Graduate
-.. 94141
. . ..Program, University of California. San Francisco-,CA
The search for a retrograde messenger thought to be necessary for LTP
has focused recently on nitric oxide (NO). T o test the hypothesis that NO
production is required for LTP, we attempted to obtain LTP in area CAI
of hippocampal slices that had been incubated in the NO synthase inhibitor
N"-nitro-L-arginine (NOArg, 100-500 pM) for 1.5-1 1 hr at mom temperature (21-23°C). The LTP induction protocol, given at 27-29°C. consisted
of two 100 Hz, 1 s tetani at increased stimulus intensity. No significant
reduction in LTP magnitude was observed in NOArg-treated (n=14) vs
control (n=ll) slices (LTP at 5 0 6 0 min post-tetanus: contml=I62f16%,
NOArg=135f14%, P>.2). The study was then repeated in a blind manncr,
such that the experimenters did not know whether slices had been incubiitcd
in NOArg (100 pM) until after data analysis was complete. The induction
protocol used in the blind study (four 100 Hz, 1 s tetani at control stimulus
intensity, temperature 25-29T, slices from 14-18 day old rats) resullcd
in LTP that was identical in magnitude in both control (n=ll) and NOArgtreated (n=12) slices (control LTP=149f9%. NOArg LTP=148*12%, b.5).
T o assess whether the NOArg was effective in permeating cells and
inhibiting NO synlllase, we incubated slices from 14 or 15 day old ma
blindly in 100 pM NOArg or in control medium exactly as previously.
applied 100 pM NMDA for 10 rnin at 27-2g°C, and determined the level
of cGMP per mg protein. Consistent with others' findings. NOArg completely blocked the NMDA-stimulated increase in cGMP observed in
control slices (n=3). Our results suggest that NO synthase activity is not
required for the induction of LTP under these experimental conditions.
This e x p e r i m e n t a n a l y z e d t h e d i s t r i b u t i o n of LTP a n d
LTD in dendrites o f CAI h i p o c a m p u s . A " r a k e "
s t i m u l a t i n g e l e c t r o d e w a s pfaced o r t h o g o n a l to t h e
S c h a f f e r c o l l a t e r a l s and a r e c o r d i n g e l e c t r o d e w a s p l a c e d
in t h e cell b o d y l a y e r . B a s e l i n e r e c o r d i n g s w e r e o b t a m e d
f r o m each o f t h e 6 s t i m u l a t i n g e l e c t r o d e s s a n n i n g
stratum radiatum/ stratum lacunosum-mofeculare (every
1 0 0 g m ) . T h e n , a 50 Hz t e t a n u s w a s delivered t o a m i d point e l e c t r o d e - 3 0 0 g m f r o m t h e f i s s u r e . A t 20 m i n
p o s t - t e t a n u s , LTP w a s s e e n a t the t e t a n u s s i t e and at
d i s t a l s y n a p s e s , w h e r e a s LTP t o w a r d the c e l l b o d y was
r a r e l y n o t e d . LTD was s e e n in 4 o u t o f 10 s l i c e s at s i t e s
a d j a c e n t t o the b o u n d a r y o f p o t e n t i a t e d s y n a p s e s .
W h e n d e p o t e n t i a t i n g s t i m u l a t i o n (3-5 H z f o r 900
pulses) was given t o t h e p r e v i o u s l y t e t a n i z e d site,
d e p o t e n t i a t i o n was o b s e r v e d there and, to a lesser degree,
a t adjacent previously potentiated synapses. T h e s e
results s h o w t h a t LTP 1s d i s t r i b u t e d over a large e x t e n t o f
the d e n d r i t e , b u t d e p o t e n t i a t i o n 1s a m o r e f o c a l
phenomenon. These results m a y r e f l e c t the a n a t o m y o f
t h e a f f e r e n t s a c t i v a t e d , d i f f u s i o n o f s e c o n d messengers, or
a c t i v a t i o n o f v o l t a g e d e p e n d e n t p r o c e s s e s along t h e
dendrite.
S u p p o r t e d by NZNDS #28698
-
THE SIGN OF LONG-LASTING EAP MODIFICATIONS IN THE DENTATB
GYRUS IS PREDICTED BY THE SEQUENCE OF ISO-CCK APPLICATION
The
TO THE RAT HIPPOCAMPAL SLICE..!University of Texas at Dallas, Richardson, TX 7.5083.
Cholecystokinin (CCK) and baclofen (BAC, a y-aminobutyric acid, [GABAJ
agonist) similarly potentiate paired-pulse facihtation in the dentate gyms @G),
suggestingthe involvement of s common substrate. Given the synergy of BACisoproterenol (ISO-a 0-adrenergic agonlsl) m induction of long-lasting potentiation
m the DG, CCK-IS0 modulation of neuronal responses may also be expected.
In the hippocampal slice preparation, application of 75 nM IS0 for 15-30 min
induced a potentiation of EAPs that reversed to baseline upon a 30 min wash with
ISO-free artificial cerebrospinal fluid (ACSF). However, when the wssh was
followed by n IS min application of I FM CCK, potentlationof the EAP
reoccurred that persisted through a second 30 min of wash with drug-free ACSF.
When 1 .UM CCK was added after 1.5 min of ISO, such that there was a
concutrent application of ISO-CCK, then the ISO-induced potentration reversed to
a long-lasting depression that persisted through 30 nnn of wash with dmg-free
ACSF.
Concurrent apphcation of IS0 and a 0-adrenergic antagonist (1 pM propranolol
or I WM timolol) or the N-methyl-D-aspartateantagonist APV (10 pd) blocked the
reversible ISO-mduced potentiation and also the postwash potentiation associated ,
w~thCCK. The depression associated with concurrent ISO-CCK was also blocked
by application of the antagonists.
These results suggest an interaction between 0-adrenergic receptors and CCK in
the mod~ficationof DG granule cell responses.
(Supported by a grant from the Whitehall Foundation to D.D.)
.
547.20
THE INVOLVHvlFHT OF a-TOCOPHEROLIN LONG-TERMPOTENTIATION.
Q
,Neuroscience Research Laboratory, DcPt. of
Pharmacology and Therapeutics, The University of British Columbia, Vancouver,
B. C., Canada, V6T 123.
An increase in lipid peroxide content in hippocampus has been implicated in IhC
impairment of learning ability in vitamin E-deficient rats. In the present studies. (1s
ability of a-tocopherol phosphate (0.2 mM, applied for 5 min), a major antioxidant,
to induce lohg-term potentiation (LTP) of the stratum radiatum stimulation-induced
excitatory postsynaptic potentials (£!PSPs) in CAI neurons in guinea Pig
hippocampal slices was examined, a-Tocopherol induced a slowly developing
of thb EPSP without changing the membrane potential and the input resistance
(n=16), or the fast and the slow inhibitory postsynaptic potentials (IPSPs)
a.
Tocopherol failed to induce a funher potentiation of the EPSP during a PrDestablished tetanus-induced LTP (rl=10). The chelation of postsynaptic CaZt
BAPTA (n=6) or the inhibition of protein kinase C (PKC) by sflingosine (nz6) Or
K-252b (n=6) prevented the a-tocopherol-induced LTP. AP3 (100 @, n=8), but
not APV (40 pM, n=6), blocked h e a-tocopherol-indnckdLTP. a-~ocophcrol
did not significantly alter the depolarization of CAI neurons induced by ~ 1 u " ~ ~ ~ ~
(applied in normal medium containing APV, n=6) or by NMDA (applied In MgZ'.
free medium containing CNQX, n=6). Tetanic stimulation of the stratum radialum
failed to induce LTP of the EPSP in hippocampal slices of v i m i n %deficient
(n=IO); application of a-tocopherol also did not induce LTP in these slices (nZ6),
These results indicate that vitamin E is involved in LTP in the hippocampal
neumns. The activation of the membouopic glutamate receptors, postsynaptic
and the activation of PKC may be required for this LTP. It appears that In
E-deficient rats LTP-induction is compromised not only because a - t o c 0 ~ ~ ~is" '
depleted but also since something else is adversely affected.
~*
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