[Abstract Title]. - Society for Neuroscience

Disclosures: X. Zhang , None; Y. Zhou, None; J.F. Chiu, None; V.K.L. Hung, None; S.M.
Chung, None; S.K. Chung, None.
Poster
293. Startle and Modulation of Startle
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 293.12/SS40
Topic: F.02.f. Fear and aversive learning and memory
Support: Grant-in-Aid for Young Scientists (#16730376) from the MEXT of Japan to TS
Title: Startle response in spontaneously hypertensive rats (SHR): Effects of two different
hypotensive drugs on fear-potentiated startle
Authors: *T. SATO;
Hlth. and Social Services, Tohoku Bunka Gakuen Univ., sendai, Japan
Abstract: Spontaneously hypertensive rats (SHR) show some marked differences in behavioral
reactivity to emotional stimuli. The present study focuses on fear-potentiated startle (FPS). To
determine the relationship between FPS and blood pressure level, the author examined the effects
of blood pressure reduction on the magnitude of FPS, using two hypotensive drugs: vasodilator
hydralazine and ganglionic blocker hexamethonium. FPS training sessions were conducted on 2
consecutive days. Each rat was given 10 light stimuli (conditioned stimulus, CS) for 3.7 s paired
with electric shocks of 0.7 mA for 0.5 s. The rats received a short test for FPS 24 h after the
second session. In this test, the rats were presented with 10 startle-alone trials (5 at 95 dB and 5
at 105 dB, each startle stimulus lasting 50 ms) followed by 8 startle-alone and 8 CS-paired trials
(4 at 95 dB and 4 at 105 dB for both types of trials). The rats were divided into three groups
based on the percentage index of FPS (%FPS) in the test. There was no significant difference in
%FPS in the short test. The rats were intravenously treated with hydralazine (0.6 mg/kg),
hexamethonium (20 mg/kg), or vehicle (saline) 24 h after the short test; blood pressure was
measured 20 min after the treatment, soon after which the post-treatment FPS measurement was
obtained. For this, 4 startle-alone trials were administered, followed by 16 startle-alone and 16
startle-CS paired trials (8 at 95 dB and 8 at 105 dB). An ANOVA and post hoc tests revealed that
systolic blood pressure in the hydralazine- and hexamethonium-treated groups was significantly
lower than that in the saline-treated group; systolic blood pressure in the hydralazine-treated
group was significantly lower than that in the hexamethonium-treated group. Nevertheless, the
hydralazine-treated group also showed higher values with regard to heart rate than the other two
groups, whereas no significant differences were found between the hexamethonium-treated and
saline-treated groups. Further, the %FPS for the 95 dB startle stimuli in the hydralazine- and