Transcript No Slide Title

Antagonists of neural nitric oxide synthase affect auditory behaviours in mice: A study of the acoustic startle reflex
(ASR) and its inhibition by gaps in noise and a change in sound source location.
ARO 2009
#429
James Ison1,2, Nathaniel Housel1, Paul Allen2, Conny Kopp-Scheinpflug3 and Ian Forsythe4
and 2NB&A, Univ. Rochester, Rochester, NY USA; 3Biology II, Univ. Leipzig, Leipzig, Saxony, Germany; 4MRC Toxicol. Unit, U.Leicester, Leicester, Leicestershire, UK
Fig 1: The apparatus for testing
sensitivity to a change in sound
source location. The ES speaker
above the test cage elicits the ASR,
which is modified by the noise
moving from one to the other of the
PS speakers facing the mouse. The
ASR sensor is below the cage.
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Fig. 3: There was a small but significant positive
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Fig. 2: The normal increase on the ASR with an
increasing ES level and the masking effect of noise at
low ES levels were unaffected by 7-NI administration,
showing that NOS inhibition has little effect on these
auditory measures, and a small effect on activity.
effect of 7-NI dose levels from 0 up to 100 mg/kg in an
ANOVA that included both 1800 and 450. This ANOVA
found also a significant initial faster increase in
performance for the 1800 shift in location, but a
significant second rise in performance at 450. The
ANOVA of the 450 shift data showed the highly
significant positive effect of 7-NI especially at 160
mg/kg between lead times of 20 and 100 ms. High
levels of 7-NI also depressed “restless” background
activity, but did not significantly affect ASR vigour.
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Methods Stimulus detection was measured by prestimulus inhibition of
the acoustic startle reflex (ASR), the prestimuli being a spatial change in
sound location and a gap in noise. Fig. 1 shows the spatial apparatus:
the mouse in a test cage, an overhead speaker that presents the eliciting
stimulus (ES) for the ASR and two prestimulus speakers on the left and
right of the mouse (PS-L and PS-R). WBN moved from PS-R to PS-L at
lead times of 1 to 300 ms before the ES. Design: Exp. 1 tested the
effect of 7-NI (IP, in a peanut oil suspension) on the ASR in noise vs.
quiet for ES between 80 and 130 dB SPL. Exp. 2 tested the effect of 7NI on the response to shifts in sound location of 1800 and 450, presented
1 to 300 ms before the ES. Exp. 3 examined the effects of 7-NI on the
response to gaps in WBN of 0.5 to 15 ms in duration, ending 60 ms
before the ES. 7 CBA mice (6-mo. old) were used in Exps. 1, 2 and 3,
and 7 more mice tested in Exp. 3. The data are given as Mean (SEM).
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Background Activity in Quiet and in Noise
The data on motor and sensory effects of blocking
nNOS in rodents are limited: Wiley et al. (Eur.J.Physiol,
1997) found no effect on ASR amplitudes or prepulse
inhibition in rats with 7-NI doses up to 100 mg/kg.
Araki et al. (Eur.NeuroPsychPharmacol, 2001) found
catalepsy in mice with 7-NI doses up to 160 mg/kg.
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Experiment 1: Effect of 7-NI on ASR and
ACT (aV-units)
Introduction The impetus for this study was the report
of Steinert et al. (Neuron, 2008) that the generation of
nitric oxide in the principle cells of the MNTB following
stimulation of the Calyx of Held reduces their
excitability, via an adaptation-like regulation of postsynaptic Kv3 voltage-gated K+ ion channel currents.
These effects were obtained from in vitro and in vivo
preparations of wild-type mice and were blocked by
administration of nNOS inhibitors, such as 7nitroindazole (7-NI). The intent of the present research
was to determine whether nitric oxide signaling
influences auditory processing in the awake behaving
mouse. The behaviour agreed with predictions derived
from the physiology data in showing that systemic 7-NI
injection improved spatial location and gap detection.
ASR (aVu)
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Fig. 4: The high dose of 7-NI increased the
inhibitory effect of gaps beyond 3 ms in duration, but
did not significantly affect behaviour for the 3 ms or
smaller gaps. The insert shows the depressant effect
of 160 mg/kg 7-NI on activity, but no effect on ASR
vigour. This activity effect may be related to the 7-NI
induced catalepsy observed by Araki et al. (2001).
Experiment 2: Effect of 7-NI on the response to Experiment 3: Effect of 7-NI on gap detection
Conclusions: These data are consistent with in
1800 and 450 degree changes in sound location.
The MNTB is the critical intermediary in progressing
from the VCN monaural to SOC binaural processing for
sound localization in mice: and so, given Steinert et al.,
it might be expected the 7-NI would improve this ability.
The mice began with a 1800 shift and 7-NI levels of 0,
50, and 100 mg/kg. The second test used a smaller 450
shift and 7-NI levels of 0, 50, 100, and 160 mg/kg. The
data presented in Fig. 3 show the positive effect of the
higher drug levels, especially for the 450 shift.
vitro and in vivo effects reported by Steinert et al.
(2008), that the normal use-related generation of NO
produces an adaptation of Kv3 K+ ion channels that
are sensitive to nNOS inhibition by 7-NI. The proposed
relationship between behaviour and the physiological
data could be further tested by contrasting the effects
seen here with prospective studies in Kv3 -/- mice.
The intent here was to determine if 7-NI might affect
gap detection, a monaural task that does not require
the MNTB but is likely to involve other brainstem nuclei
expressing neuronal NOS and Kv3 channels. Seven
additional mice were used to ensure that the
experiment would have sufficient power to detect small
changes and to ensure that any negative effects were
not due to repeated 7-NI exposure. Only two 7-NI
levels were used, 0 and 160 mg/kg. Gaps of 0.5 to 15
ms in duration were used, ending 60 ms before the ES.
Research support from NIH (AG09524, DC05409) and
the Schmitt Foundation for Integrative Brain Research
[email protected]