TMS Measures of Plasticity and Excitatory/Inhibitory Ratio as Biomarkers: R-baclofen Effects in Normal Volunteers

Study Overview
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Brief Summary
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Our overall objective is to apply Transcranial Magnetic Stimulation (TMS) to develop measures of human synaptic plasticity and of brain excitatory:inhibitory ratio (E:I ratio), which we propose as novel biomarkers and outcome measures that will expedite clinical trials of treatments for Autism Spectrum Disorder (ASD). One potential therapeutic agent, R-baclofen will be investigated under this protocol. TMS is a safe, inexpensive and noninvasive means to focally stimulate the human brain. Presently, TMS is in extensive use as a means to measure regional brain excitability, which is dependent on local synaptic strength. TMS can be used to temporarily alter synaptic strength as well as to acutely measure levels of cortical excitability and short and long interval inhibition. Since altered synaptic plasticity and an imbalanced inhibitory:excitatory ratio are cited as fundamental abnormalities in ASD, we hypothesize that both severity of ASD-related learning deficits and their improvement after therapy will correlate with TMS measures of synaptic plasticity and E:I ratio. We propose to embed TMS measures of synaptic plasticity and E:I ratio in a 'Proof of Principal' trial of R-baclofen and to examine: Aim 1: Whether R-baclofen (a potential therapeutic agent for ASD) predictably alters TMS measures of synaptic plasticity and E:I ratio as a function of plasma concentration in adult volunteers. We will test the following hypotheses: R-baclofen produces a significant change in TMS measures of LTD and E:I ratio; and R-baclofen plasma levels and TMS measures of LTD and E:I ratio show a predictable exposure-response relationship. Exploratory Aim 1: Whether the presence of genetic polymorphisms of the BDNF and GABA-B receptor genes has a moderating effect on TMS measures and on R-baclofen effects. We will test the following hypotheses: Presence of the BDNF val66met allele will be associated with decreased long-term depression (LTD) of cortical excitability Polymorphisms of GABA-B receptor genes will be associated with altered magnitude of response to R-baclofen as measured by TMS

Detailed Description
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The design is a double-blind placebo controlled 5 way crossover trial of a single dose each of placebo x 2 (0 mg), 3, 10, and 25 mg of R-baclofen followed by plasma levels at 0, 30, 60, 90, and 140 minutes after each dose; and TMS testing at 0, 30, 60, 90 (cTBS application at 90 minute time point), 95, and then periodically every 5-10 minutes until the MEPs return to baseline. There will be a total of 7 visits. Patients will come in for a screening visit, then scheduled to return for 1 baseline visit (cTBS without drug) and 5 crossover visits. At each crossover visit a venous line will be placed for blood sampling and a single dose of study drug at one of the five dose levels will be given orally at time 0. There will be a one-week washout between each of the crossover arms (R-baclofen has a mean Tmax of approximately 80 minutes and a terminal half life of 4.9 hour).

Official Title
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Transcranial Magnetic Stimulation (TMS) Measures of Plasticity and Excitatory/Inhibitory Ratio as Biomarkers for R-baclofen Effects in Normal Volunteers

Conditions
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Autism

Intervention / Treatment
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* Drug: R-baclofen


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age: 18-30 IQ: higher than 85 Normal physical examination Exclusion Criteria significant medical problems ongoing medications All female participants are required to have a negative pregnancy test

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 30 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Placebo Comparator: sugar pill<br>placebo administered under double blind conditions | Drug: R-baclofen<br>* oral R-baclofen at 0x2, 3, 10, and 25 mg<br>* Other names: arbaclofen;|
| Experimental: 3 mg of R-baclofen<br>3 mg of R-Baclofen administered double blind | Drug: R-baclofen<br>* oral R-baclofen at 0x2, 3, 10, and 25 mg<br>* Other names: arbaclofen;|
| Experimental: 10 mg of R-baclofen<br>10 mg of R-baclofen administered double-blind | Drug: R-baclofen<br>* oral R-baclofen at 0x2, 3, 10, and 25 mg<br>* Other names: arbaclofen;|
| Experimental: 25 mg of R-baclofen<br>25 mg of R-baclofen administered double blind | Drug: R-baclofen<br>* oral R-baclofen at 0x2, 3, 10, and 25 mg<br>* Other names: arbaclofen;|
| Placebo Comparator: second sugar pill<br>the second placebo administered double blind | Drug: R-baclofen<br>* oral R-baclofen at 0x2, 3, 10, and 25 mg<br>* Other names: arbaclofen;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| percent of baseline TMS-induced measures of (1) human synaptic plasticity (LTD) | Synaptic plasticity or LTD will be measured using the MEP in response to stimulation set at 80% of the active motor threshold. This MEP will be measured at 90 minutes after study drug dose to establish baseline MEP amplitude then LTD will be induced with the cTBS procedure. The amount of LTD remaining at the different time points, post-cTBS will be quantified by measuring the MEPs and dividing it by the baseline MEP. This will yield a percent of baseline MEP at the various time points. | at 90 minutes after study drug dose | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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plasticity, excitatory, inhibitory, synaptic plasticity, R-Baclofen, TMS, transcranial magnetic stimulation, biomarker, autism