Neural Correlates of Ketamine's Anti-suicidal Effects in Bipolar Depression

Ketamine is a fast-acting anesthetic that can have stimulant effects when taken at low doses. It acts as a non-competitive high-affinity N-methyl-d-aspartate (NMDA) receptor antagonist that stimulates synaptic glutamate release and blocks extra-synaptic NMDA receptors. This mechanism of action mediates excitatory synaptic transmission through the central nervous system and therefore results in robust antidepressant effects. Sub-anesthetic doses of ketamine administered intravenously (IV) have shown to produce rapid antidepressant and ant-suicidal effects. Despite this important clinical finding, our understanding of ketamine's neurophysiological mechanism of action for suicidality remains limited. This clinical trial is an open label pilot study that aims to address this limitation by studying the effects of IV ketamine on patients with bipolar depression who are currently experiencing suicidal thoughts. Using a combination of Transcranial Magnetic Stimulation (TMS) neurophysiological tools with electromyography (EMG) and electroencephalography (EEG), this trial aims to explore ketamine's action on NMDA neurotransmission to understand ketamine's anti-suicidal effects. Investigating the impact of ketamine on cortical excitation, cortical inhibition, and resting-state cortical oscillation could provide insight into the role of NMDA receptors in cortical physiology and determine potential predictors of clinical response for suicidality in bipolar depression.

Objective 1: To examine the effect of a series of therapeutic IV ketamine 40-min infusions on neurophysiological markers linked with cortical excitation and inhibition (as indexed via TMS-EMG and TMS-EEG, as a proxy of NMDA-receptor activity in the cortex)

Hypothesis 1: Ketamine will increase intracortical facilitation - a neurophysiological measure of NMDA neurotransmission

Objective 2: To examine the effect of ketamine IV 40-min infusions in sub-anesthetic doses on acute suicidality in patients with BD

Hypothesis 2: Ketamine infusions will result in improvement of suicidality in BD

Objective 3: To examine the safety and tolerability of ketamine IV 40-min infusions in sub-anesthetic doses and its effect on depressive symptoms in patients with BD

Hypothesis 3:

• Ketamine infusions will be safe and well tolerated
• Ketamine infusions will result in improvement of depressive mood symptoms in BD

Objective 4: To examine the effect of ketamine IV 40-min infusions in sub-anesthetic on additional neurophysiological measures and on changes in quality of life measures

Hypothesis 4:

• Ketamine will decrease cortical inhibitory measures as indexed by (SICI) paradigms
• Ketamine will increase cortical excitation measures as indexed by TMS-evoked potential waveform amplitude
• Ketamine infusions will result in improvement in quality of life measures

Inclusion criteria

• Individual meeting DSM-IV diagnostic criteria for Bipolar Disorder, current depressive episode as confirmed by the Mini-International Neuropsychiatric Interview (MINI)
• Individuals capable to provide consent and able to communicate, read and write in English
• Individuals currently depressed defined as scoring 14 and above on the Hamilton Rating Scale for Depression-24 Items (HRSD-24)
• Individuals currently experiencing suicidal ideation as defined by a score of 9 or higher on the scale for suicide ideation (SSI)

Exclusion criteria

• Individuals with history of a DSM-IV substance use disorder (i.e. dependence or abuse) within the past month; and lifetime history of ketamine substance use disorder as confirmed by the MINI
• Concomitant major unstable medical illness such as poorly controlled high blood pressure or patients diagnosed with enlarged prostate or reporting any other urinary related issues
• Stage 2 hypertension defined as a systolic pressure of 140 mm Hg or higher or a diastolic pressure of 90 mm Hg or higher on three consecutive readings taken 5 minutes apart
• Results of liver function tests (ALT, AST) are three times or greater than the upper limit of normal readings
• Pregnancy or the intention to become pregnant and breastfeeding during the study as confirmed by self-report. Female participants of reproductive potential must be willing to use a medically acceptable method of birth control which include highly effective (e.g. approved hormonal contraceptives, IUD, tubal ligation) or double barrier (e.g. male condom with diaphragm, male condom with cervical cap) methods of contraception or abstinence if that is the usual and preferred lifestyle of the participant
• Presence of cardiac decompensation/heart failure
• DSM-IV diagnosis of any primary psychotic disorder, bipolar disorder, obsessive-compulsive disorder, or post-traumatic stress disorder (current) as confirmed by the MINI
• Current episode meeting criteria for mania/hypomania or mixed episode as per DSM-IV criteria on the MINI or as determined by the study team
• Diagnosis of severe personality disorder as assessed during the initial consultation with a physician at the Temerty Centre prior to study entry
• Any significant neurological disorder (e.g., a space occupying brain lesion, a history of stroke, a cerebral aneurysm, a seizure disorder, Parkinson's disease, Huntington's chorea, multiple sclerosis) as assessed through medical history review during the initial consultation with a physician at the Temerty Centre prior to study entry
• Individuals presenting with a medical condition, a medication, or a laboratory abnormality that could cause a major depressive episode or significant cognitive impairment in the opinion of the investigator
• Individuals requiring a benzodiazepine with a dose equivalent to lorazepam 2 mg/day or higher; being on any anticonvulsant(e.g. Lamotrigine) and/or opioid medication due to the potential of these medications to limit the efficacy of ketamine
• Individuals unable to communicate in spoken and written English fluently enough to complete the required study assessments due to a language barrier or a non-correctable clinically significant sensory impairment (i.e., cannot hear or see well enough to complete clinical assessments)
• Individuals with cognitive or physical impairment which may potentially interfere with IN ketamine administration and subject's ability to stay in the same place for a 2-hr monitoring supervision as assessed through medical history review during the initial consultation with a physician at the Temerty Centre prior to study entry
• Any intracranial implant (e.g., aneurysm clips, shunts, cochlear implants) or any other metal object within or near the head, excluding the mouth, that cannot be safely removed given that we will be using TMS-EMG/EEG
• Those unable to secure escort to accompany them back home after ketamine sessions will also be excluded from this study
• Any known allergy to the study medication or any component/ingredient of the ketamine preparation