1. Clozapine potentiation of GABA mediated cortical inhibition in treatment resistant schizophrenia
Presenter: Tyler Kaster
Supervisor: Zafiris Daskalakis
Co-Authors: Danilo de Jesus, Natasha Radhu, Faranak Farzan, Daniel Blumberger, Tarek Rajji, Paul Fitzgerald,

2. Disclosures TSK, DJ, NR, FF, DM, TKR, PBF ZJD Nothing to disclose
Research and equipment support from Brainsway Inc
Advisory board of Hoffmann-La Roche Limited and Merck
Speaker support from Sepracor and Eli Lilly

3. Schizophrenia Debilitating illness affecting 1% of population
Characterized by delusions, hallucinations, and neurocognitive symptoms
Subset of these patients are treatment resistant (TRS)
minimal response to typical & atypical antipsychotics
Often requires use of antipsychotic clozapine

4. SCZ & Cortical Inhibition
Healthy individuals able to filter emotionally irrelevant stimuli (conversation, noise, thoughts, impulses)
Evidence suggests patients with schizophrenia unable to filter irrelevant stimuli
Deluge of these internal/external stimuli may be final common pathway through which delusions and hallucinations become manifested
Healthy people  hear a noise that’s not important to you, you can not recognize it and ignore it
Schizophrenic  hear a noise, think it’s something extremely important

5. Evidence for CI Deficits in SCZ
Anatomic – Reduced GABA interneurons1
Physiologic – P50 Auditory gating deficits2
Neurophysiology – Previous TMS studies3,4
Multiple converging lines of evidence:
-anatomic (these mediate CI) (del Rio and deFelipe 1997)
-neurophysiology (P50 suppression related to presynaptic GABA-B receptors on excitatory cells that input to pyramidal cells) (Freedman et al. 2000)
-in vitro studies (direct in vitro binding of clozapine to GABA-B) (Wu et al. 2011)
-previous TMS studies ((Daskalakis et al. 2008, Liu et al. 2009))
1. Del Rio and deFelipe 1997, 2. Freedman et al. 2000, 3. Daskalakis et al Liu et al. 2009

6. TMS Schematic
-Transcranial magnetic stimulation involves a moving magnetic field that induces a current inside the brain
-can be used for therapeutic or investigative purposes

7. CI Measurement
If you stimulate motor cortex get various measures of cortical inhibition
To measure cortical inhibition with TMS you attach the EMG monitor to the hand (specifically the Abductor pollicis brevis muscle)
You then place the TMS over the corresponding motor cortex and induce a stimulus causing muscle contraction

8. } } CI Measurement CSP = GABAB (Siebner et al. 1998) SICI = GABAA
1 mV
40 msec
CSP = GABAB
(Siebner et al. 1998) }
10 msec
1 mV }
SICI = GABAA
(Ziemann et al. 1996)
Depending on how the stimulus is applied, it can measure different inhibitory systems
They are connected to the GABA systems because of their IPSP’s
CSP: a strong stimulus is applied which causes suppression of motor activity. Duration of this motor activity is a measure of the amount of GABA-B related cortical inhibition. related to GABAB IPSPs (e.g., Siebner et al. 1998)
SICI: two pulses are applied: a weak one (conditioning) 1-5ms prior to the strong testing stimulus. Ratio of peak amplitudes is a measure of the amount of GABA-A related cortical inhibition. related to GABAA IPSPs (e.g., Ziemann et al. 1996)
ICF: not technically CI measure, but may interact with CI. This is NMDA mediated. same as SICI, except the conditioning stimulus was done 10-20ms prior to testing stimulus
short-interval cortical inhibition means that a ‘conditioning stimulus’ is applied 1-5 ms prior to the test stimulus

9. Previous TMS CI Studies in SCZ
Daskalakis et al. 2008
This study was the first to show that clozapine treated patients significantly longer than healthy patients or unmedicated patients

10. Previous TMS CI Studies in SCZ
Liu et al. 2009
This study looked at multiple medications
Clozapine was significantly greater than other medications and unmedicated
Significantly larger effect size, especially with the CSP

11. Objective
To measure TMS indices of CI in TRS patients before and after clozapine treatment
Determine if change in TMS indices correlates with clinical response
Problem with both prior studies is that they were cross-sectional.
There is the question that patients on clozapine may represent a unique subpopulation neurophysiologically
We designed this study to try and answer the question “Is treatment resistance or clozapine the reason for the increased cortical inhibition seen in previous studies?”
Hypothesis: clozapine itself rather than treatment resistance is responsible for changes in TMS measures

12. Methods – Patients
16 patients with DSM-IV diagnosis of schizophrenia or schizoaffective disorder
Inclusion Criteria:
Between years old
Medication resistance (2 trials of antipsychotics, at least 1 atypical)
Willing to switch to clozapine
Exclusion Criteria:
self-reported comorbid medical illness
history of drug or alcohol abuse/dependence
active suicidal ideation
traumatic brain injury

13. Methods - Controls 15 subjects age and sex matched
Recruited from separate study
TMS indices measured at baseline

14. Methods – Study Design
TMS indices and symptoms were measured at each assessment
Symptoms measured by Positive and Negative Syndrome Scale (PANSS)
Baseline assessment performed prior to starting clozapine
Follow-up assessments at 6 weeks and 6 months after starting clozapine

15. Methods – CI Measurement
Resting motor threshold (RMT):
lowest stimulation intensity that creates MEP peak of 50μV in at least 5 of 10 consecutive trials in relaxed APB muscle
CSP
Motor cortex stimulated at 140% of RMT
Duration defined as MEP onset to return of EMG activity
SICI/ICF
Conditioning stimulus at 80% of RMT
Testing stimulus at 140% of RMT
Ratio defined as conditioned/unconditioned MEP
SICI: Inter-stimulus interval of 2 or 4ms
ICF: Inter-stimulus interval of 10, 15, or 20ms

16. Results - Demographics
SCZ: 11, SCZ-A: 5
Male: 11, Female: 5
Age: 33.3 (±10.9) years
Baseline medications (no data for 1 patient):
14/15 antipsychotics
6/15 antidepressants
5/15 benzodiazepines
2/15 mood stabilizers

17. Results - CSP
-pts: 6 weeks vs baseline – signficant, 6 months vs baseline – not significant, 6 weeks vs 6 months – not significant

18. Results – CSP Change and Symptoms
-no correlation (p>0.05)
-note however that 2/3 responders have change in the CSP >50ms

19. Results – SICI & ICF Not significant.
Possibly increased SICI at 6 months

20. Potential Limitations
Sample size
Medications
CI Measured in motor region
Longitudinal control group
-size: limits conclusions re: significance
-medications: on a variety of medications at baseline. May impact TMS measures differently
-motor: only measured CI in motor region, which may not accurately reflect effect of clozapine on CNS. However previous evidence suggests that the motor region is an acceptable estimate of non-motor region
-control group: ideally we would have a non-medicated schizophrenia group of patients to monitor change in CSP over time, or non-clozapine medicated patients. However the former is ethically not feasible, the latter was technically challenging due to drop-outs

21. Conclusion Supports clozapine mediation of GABAB CI
Consistent with pharmacological studies1
Consistent with previous TMS studies2,3
Potentially reduced SICI with long-term clozapine treatment
GABAB receptor may represent a novel neurotransmitter target for treatment refractory schizophrenia
1. Wu et al. 2011, 2. Daskalakis et al. 2008, 3. Liu et al. 2009

22. Conclusion

23. Results – CLZ Dose & CSP
Extra slide, in case asked questions