Tylš F., Páleníček T., Fujáková M., Kadeřábek L., Nováková P

THE COMPARISON OF SENSORIMOTOR GATING AND QUANTITATIVE EEG
IN RATS IN SEROTONERGIC MODELS OF PSYCHOSIS
Tylš F., Páleníček T., Fujáková M., Kadeřábek L., Nováková P., Kubešová A., Krajča V., Horáček J.
Psychiatric centre Prague, Czech Republic
3rd. Medical Faculty, Charles University in Prague
INTRODUCTION
Animals:
Adult male Wistar rats, 250-300g, 8-12 rats per group
Substances:
Drug Full name
Psilocin 4-hydroxy dimethyltryptamine
LSD fumarate D-lysegid acid diethylamide
Mescaline hydrochloride3,4,5-trimethoxy phenethylamine
DOB 4-Bromo-2,5-dimethoxy-amphetamine
The representatives of main classes of serotonergic hallucinogens - tryptamines (Psilocin, LSD) and phenylethyamines
(mescaline, DOB) were used as pharmacological models of
psychosis in rats. Regarding the fact, that psychotic state is
characterized by impaired processing of information (1), we
measured behavioral parameter prepulse inhibition (PPI)
of startle reaction in order to asses these changes in rats.
However, the main interest of the study was to explore the
eletrophysiological mechanisms underlying the behavioral
changes using quantitative EEG.
METHODS
Dose + administration
0.25, 1, 4 mg/kg s.c.
5, 50, 200 μg/kg s.c.
10, 20, 100 mg/kg s.c.
1, 5 mg/kg i.p.
Substances were dissolved in saline (or acidified saline in
case of psilocin) and applied in a volume of 2ml/kg of animal
weight. Saline was administrated to controls.
PPI ASR:
Sensimotor gating was assessed in the test of prepulse inhibition of acoustic startle reaction (PPI ASR) (SR-LAB San
Diego Instruments, USA) 15 minutes after drug administration. The scheme of PPI experiment: 5 minutes of acclimatization with background noise was followed by 15 minutes of
PPI registration, where initially 5 isolated pulse alone trials
were presented, subsequently followed a pseudo-random
sequence of pulse alone, prepulse, prepulse-pulse and
no stimulus trials (5 presentation of each). The intensity of
stimuli is included in Figure 1.
RESULTS - PPI
Prepulse inhibition of ASR (Figure 6)
LSD and psilocin tended to evoke deficit in PPI ASR, but the
only significant effect was observed after the intermediate doses.
Mescaline evoked PPI deficit in all doses used. The PPI disruption after DOB did not reach significance level.
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Surgery:
The rats were stereotactically implanted under isoflurane anesthesia with 14
electrodes (12 active) on the surface of the frontal, parietal and temporal cortex. Locations of the electrodes (Figure 2) were established based on the stereotactic atlas (2), and electrodes were fixed to the rat’s skull with dental cement.
Connectors enabling linkage to the registration system were joined to the electrodes under short-lasting isoflurane anesthesia one day before registration
(Figure 3,4).
EEG registration:
The EEG was recorded using a 21 channel BrainScope amplifier system 7
days after the implantation of the electrodes. Initially, a baseline recording of
10 minutes was obtained, and subsequently the substances were administrated and registration continued for another 40 minutes. Along with the EEG
registration, we manually co-registered behavioral activity and inactivity using
the Activities program (Figure 5).
EEG analysis:
The data was digitally filtered (0.5 – 40 Hz) and pre-processed in WaveFinder
v.2.3 (separation of EEG signal to parts corresponding to behavioral activity
and inactivity). Only signals corresponding to inactivity were used in the further analysis. The length of the selected data for analysis was approximately
1-3 minutes from each part of the signal (baseline and 20-30 minutes after
administration). Data were transformed by Fast Fourier Transformation (FFT)
and spectral and coherence analyses were performed in Neuroguide Deluxe
software v.2.6.
60,00
50,00
40,00
% PPI
30,00
*
*
*
*
*
20,00
Figure 5. The scheme of EEG experiment
Figure 1 (top). The intensity of PPI stimuli.
10,00
0,00
psilocin (mg/kg)
0
-10,00
0.25
1
LSD (μg/kg)
4
0
5
50
mescaline (mg/kg)
200
0
10
20
100
DOB (mg/kg)
0
1
5
Figure 3,4 (top). Fixation of electrodes,
connector
Figure 2 (right). Location of electrodes
on the rat skull.
Figure 6. The diagram of PPI ASR. * = p < 0.05
Statistics:
For behavioral experiments a one-way ANOVA with Bonferroni correction was
performed. The impact of substances on EEG signal was evaluated using a
pair T-test. The significance level was established as p < 0.05. Each animal
served as a control (10 minutes of baseline record versus 20-30 minutes after
substance administration).
RESULTS - QEEG
20
beta
high beta
gamma
**
***
***
***
***
***
-10
-20
-30
-50
0
gamma
***
***
***
***
***
***
-20
-30
Figure 7 (left). The diagram of EEG spetra after psilocin, LSD, mescaline and DOB.
* = p < 0.05, ** = p < 0.01, *** = p < 0.001
***
**
alpha
beta
high beta
gamma
**
**
*
-20
-30
0
***
theta
alpha
beta
high beta
gamma
**
***
***
***
-10
-20
EEG coherences (Figure 8)
The inter- and intra-hemispherical coherences were prominently decreased with the maximum in delta (all substances) and theta band (psilocin and LSD). The decrement of intrer-hemispherical coherences was
observed in all frequency bands.
-30
Figure 8 (down). The diagram of EEG coherences after psilocin, LSD, mescaline and DOB.
-40
LSD 200 μg/kg
-50
DOB 5 mg/kg
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MESCALINE 100
MESCALINE 100 mg/kg
PSILOCIN 4 mg/kg
20
EEG spectral power (Figure 7)
The EEG power spectral analysis revealed general decrease in absolute
EEG power in all frequency bands in all drug conditions. After mescaline,
the decrease was less pronounced and was mainly in the delta band (for
both mescaline and DOB), while the effects of the psilocin and LSD were
more widespread within the spectrum.
CONCLUSION
Serotonergic drugs produced profound electrophysiological changes in rat brain characterized generally by local desynchronization and disconnection of long projections. The decrement of functional
connectivity is common finding in patients suffering from schizophrenia (3), indicating the validity of
serotonergic models of psychosis. Described EEG changes could be an underlying factor of observed
impairment of information processing (disrupted PPI). The experiments also revealed slightly different
EEG and PPI pattern of indolamine and phenylethylamine hallucinogens, which can be related to the
lack of affinity of phenylethylamines to 5HT1A receptors (4,5).
REFERENCES
1. Swerdlow NR et al., 1992. The neural substrates of sensorimotor gating of the startle reflex: a review of recent findings and their implications. Psychopharmacology 6, 176-190.
2. Paxinos G and Watson Ch, 1998. The rat brain in stereotactic coordi-
nates, 4th ed.
3. Friston KJ and Firth CD, 1995. Schizophrenia: a disconnection syn
drome? Clin. Neurosci. 3, 89-97.
4. Nichols DE, 2004. Hallucinogens. Pharmacol Ther 101(2): 131-81.
5. Halberstadt AL and Geyer M, 2011. Multiple receptor contributes to the behavioral effects of indoleamine hallucinogens. Neuropharmacology 61(3):364-81.
This poster is financially supported by grants VG20122015080, VG20122015075,
NT/13897, MH CZ - DRO (PCP, 00023752), ECGA 278006 and PRVOUK P34.