Transcript pdf Poster - University of Nottingham

ABOLITION OF SENSORY GATING BY THE CANNABINOID
WIN55, 212-2 IN THE RAT HIPPOCAMPUS
Neuronal
Networks
Laboratory
Dissanayake WDN1, Zachariou M2, Marsden CA1 and Mason R1
School of Biomedical Sciences1, School of Mathematical sciences2, University of Nottingham Medical School, QMC, UK.
METHODS
INTRODUCTION
• Sensory gating is a mechanism which allows filtering of irrelevant sensory
information, so enabling efficient information processing within the CNS.
• Male Lister-hooded rats (n=11) were anaesthetised with isoflurane & N2O:O2
(50%:50%).
• Sensory gating can be assessed using an auditory Conditioning-Test paradigm
which measures the reduction in the auditory evoked response (AER) produced
by a test stimulus following an initial conditioning stimulus (Bickford-Wimer et
al, 1990) .
• Stereotactically manipulated 16-channel microwire electrode arrays (2x8 array
running medio-laterally; NB Labs, USA) were centred on the hippocampal CA3
region and dentate gyrus (Paxinos & Watson, 1998).
• Paired auditory stimuli (3kHz tones, intensity 90dB, duration 10ms) separated
by 0.5s were binaurally presented through hollow ear bars repeatedly for 128
trials with an inter-trial interval of 10s.
• Schizophrenic patients demonstrate a lack of attenuation of the test response
measured electrophysiologically by the P50 wave component of the cortical
evoked potential.
• Simultaneous multiple single unit and local field potential (LFP) activity was
recorded using a Plexon Multineuron Acquisition Processor (MAP) system
(Plexon Inc., Texas, USA). Neural signals were split at the Plexon PBX
preamplifier, amplified x1000 and filtered (LFPs: 0.1-170Hz; spikes: 500Hz-5kHz).
• In rats, a similar defect in the N40 wave, recorded from the CA3 region of the
hippocampus, has been observed in pharmacologically-induced -e.g.
amphetamine, phencyclidine(PCP)- models of schizophrenia (Joy et al, 2004;
Dissanayake et al , 2005 ).
• The effect of WIN55,212-2 (1.2mg/kg, i.p) and PCP (1mg/kg,i.p) on sensory
gating were compared.
• Cannabinoids may produce schizophrenic symptoms in human subjects and
cause relevant behavioural changes in rats (Schneider , Koch ,2002).
• Data were analysed using NEX v3 (Neuroexplorer Inc.,USA) and Matlab v7.2.
• Gating was assessed by measuring the ratio of the N40 LFP amplitude of the
test (T) to the conditioning (C) response; a T/C ratio < 50% indicates gating was
present.
• This study examined auditory gating in the rat hippocampus following a single
dose of non selective cannabinoid agonist WIN55,212-2.
FIG 2: Effects of WIN 55,212-2 on gating compared with the effects of PCP
FIG 1: Hippocampal auditory-evoked LFP responses
Stimuli
A
LFP1
LFP2
LFP2 Averaged
over 128 trials
Peri-event rasters
500ms
Basal (WIN-control)
Basal (PCP control)
T/C = 20 ± 8%
T/C = 25 ± 3%
1
B
WIN 1.2mg/kg i.p
Trials
PCP 1mg/Kg i.p
128
N40 (C)
N40 (T)
Amplitude mV
Averaged
LFPS
Time sec
TS
CS
(A) Representative recording of auditory-evoked responses illustrating
local field potentials from dentate gyrus (LFP1) and CA3 (LFP2).
T/C = 114 ± 21%
T/C = 81 ± 3%
p<0.005
p<0.001
(B) Averaged local field potentials recorded from CA3 for 128 stimulus
presentation trials demonstrated a reduction in test (T) response
amplitude compared to conditioning (C) response amplitude;
CS = Conditioning stimulus, TS = Test stimulus.
Averaged LFPs and peri-event LFP rasters recorded from CA3 in gating rats; basal recording compared with effect of WIN 55,212-2 and PCP 45
minutes after administration of each drug. Both averaged LFPS and rasters demonstrated a significant drug induced disruption of gating in CA3 with
N40 responses )
a higher T/C ratio seen after WIN.55,212-2. (
Test Stimulus
Conditioning Stimulus
FIG 4: Effects of (A) WIN 55,212-2 and (B) PCP on
conditioning response (Camp) and test response
(Tamp) amplitudes compared with the T/C ratios
15 and 45mins after drug administration
FIG 3: Effects of WIN 55,212-2 on Non gating rats compared with the effects of PCP
A
Basal (PCP control)
Basal (WIN control)
350
300
Amplitude  V
WIN 1.2mg/kg i.p
PCP 1mg/kg i.p
200
150
**
100
0
400
Amplitude  V
100
*
0
15
0
400
45
300
300
**
**
200
200
***
***
100
T/C ratio
T/C = 94 ± 6%
p>0.05
200
50
B
T/C = 93 ± 7%
250
T/C Ratio
T/C = 87±8%
T/C = 97 ± 9%
300
*
WIN Camp
WIN Tamp
WIN T/C ratio
PCP Camp
PCP Tamp
PCP T/C ratio
100
p>0.05
0
0
0
15
45
Time mins
A There was a significant increase in the Tamp (p<0.05) accompanied with a
significant increase in the T/C ratio 45mins after administration of WIN. There
was no significant change in Camp.
Averaged LFPs and peri-event LFP rasters recorded from CA3 in non-gating rats; basal recording compared with effect of WIN 55,212-2 and PCP,
45 minutes after administration of each drug. Both averaged LFPS and rasters showed no significant drug induced changes in T/C ratios.
B There was a significant increase in the Tamp accompanied with a significant
increase in the T/C ratio both 15 (p<0.01) and 45mins (p<0.01) after
administration of PCP. There was no significant change in Camp.
DISCUSSION
• The CA3 region of the rat hippocampus gates auditory responses. Some rats fail
to gate responses to auditory stimuli under basal conditions.
•Single administration of non selective cannabinoid agonist WIN55,212-2 and PCP
disrupt sensory gating but WIN55,212-2 caused a greater disruption than PCP.
• With both drugs the disruption of gating was brought about by a significant
increase in the test response amplitude with no significant change in the
conditioning response amplitude.
• WIN 55,212-2 had been shown to disrupt Pre Pulse Inhibition (PPI) in rat- a
measure of sensory motor gating (Schneider & Koch, 2002). However the effect
of WIN 55,212-2 on auditory gating has not been examined before.
• The results of this study suggest the possibility of using cannabinoid agonists
to pharmacologically model the gating deficits seen in schizophrenic patients.
• WIN 55,212-2 and PCP failed to show any effect on non-gating rats. Whether or
not non-gating rats represent a sub-population with inherent cognitive deficits,
comparable to those seen in schizophrenia remains to be addressed.
• Single administration of either WIN or PCP failed to induce any significant change
in the T/C ratios in non-gating rats.
REFERENCES
Bickford-Wimer PC, et al (1990) Auditory sensory gating in hippocampal neurons: A model system in the rat. Biol. Psychiatry 27: 183-192.
Joy B, McMahon RP & Sheppard PD (2004) Effects of acute and chronic clozapine on D-amphetamine induced disruption of auditory gating in the rat. Psychopharmacology 174: 274-82
ACKNOWLEDGEMENTS
WDN Dissanayake was supported by the government of Sri Lanka and the University of Nottingham
International Office and M Zachariou by the Institute of Neuroscience University of Nottingham.
Paxinos G & Watson C (1998) The Rat Brain in stereotaxic coordinates, 4th edition, Academic Press.
Dissanayake WDN, Marsden CA & Mason R (2005) Effect of phencyclidine on hippocampal sensory gating under isoflurane anaesthesia in the rat Brit J Pharmacol.
http://www.pa2online.org/abstracts/Vol3Issue4abst163P.pdf
Schneider M, Koch M (2002). The cannabinoid agonist WIN 55,212-2 reduces sensorimotor gating and recognition memory in rats. Behav Pharmacol 13: 29-37
Harvey Wiggins and team at Plexon Inc USA.