1. OCD

2. Neurochemical dysfunction (abnormalities in serotonin (5-HT), dopamine (DA), and glutamatergic transmitter systems) Neurochemical dysfunction (abnormalities in serotonin (5-HT), dopamine (DA), and glutamatergic transmitter systems) Drug Therapy in OCD Drug Therapy in OCD Strategies targeting these systems Strategies targeting these systems Role of serotonin (5-HT) neurotransmitter system and glutamatergic system Role of serotonin (5-HT) neurotransmitter system and glutamatergic system

4. SSRIs Block action of 5HT transporter (5-HTT) protein Block action of 5HT transporter (5-HTT) protein Responsible for uptake of intrasynaptic 5-HT released following an action potential Responsible for uptake of intrasynaptic 5-HT released following an action potential Prevent reuptake of 5-HT into the pre-synaptic neuron Prevent reuptake of 5-HT into the pre-synaptic neuron More serotonin left in synapse to bind with post- synaptic receptors More serotonin left in synapse to bind with post- synaptic receptors

6. Serotonin receptors are activated by 5-HT Serotonin receptors are activated by 5-HT Receptors modulate the release of many neurotransmitters, including glutamate, GABA, dopamine, epinephrine/norepinephrine, and acetylcholine, as well as many hormones. Receptors modulate the release of many neurotransmitters, including glutamate, GABA, dopamine, epinephrine/norepinephrine, and acetylcholine, as well as many hormones. Influence biological and neurological processes such as aggression, anxiety, appetite, cognition, learning, and memory Influence biological and neurological processes such as aggression, anxiety, appetite, cognition, learning, and memory

8. Targeting 5-HT receptor subtypes Drugs that block the 5-HT 2 family of receptors Augment action of SSRIs or have therapeutic efficacy by themselves Blockade of 5-HT 2A receptors and activation of non-5HT 2A receptors may have similar effects Synergistic treatment with 5-HT 2A antagonist/SSRI combination Synergistic treatment with 5-HT 2A antagonist/SSRI combination

9. Risperidone Risperidone Potent 5-HT 2A antagonist Potent 5-HT 2A antagonist blocks α 2 adrenoreceptors blocks α 2 adrenoreceptors Presynaptic heteroreceptors on 5-HT neurons that regulate release of 5-HT Presynaptic heteroreceptors on 5-HT neurons that regulate release of 5-HT Further enhance SSRI therapy through desensitization of 5-HT 1D terminal autoreceptor Further enhance SSRI therapy through desensitization of 5-HT 1D terminal autoreceptor 5-HT 2C receptor agonism 5-HT 2C receptor agonism Psilocybin; mixed 5-HT 2C/2A/1A receptor agonist Psilocybin; mixed 5-HT 2C/2A/1A receptor agonist

10. 5-H 1D/B receptor Regulate release of 5-HT from presynaptic terminal by reducing 5-HT neurotransmission Regulate release of 5-HT from presynaptic terminal by reducing 5-HT neurotransmission Activation of 5-HT 1D/B receptor by an agonist compound worsen OCD symptoms Activation of 5-HT 1D/B receptor by an agonist compound worsen OCD symptoms Chronic deficits in 5-HT functioning Chronic deficits in 5-HT functioning Agonist m-CPP Agonist m-CPP

11. Silent polymorphism of G861C gene Silent polymorphism of G861C gene 5-HT 1D/B receptors supersensitive, resulting in chronic reductions in synaptic levels of 5-HT 5-HT 1D/B receptors supersensitive, resulting in chronic reductions in synaptic levels of 5-HT 5-HT 1D/B antagonist compounds expected to hasten onset of therapeutic action of SSRIs in OCD 5-HT 1D/B antagonist compounds expected to hasten onset of therapeutic action of SSRIs in OCD rapidly producing state of 5-HT 1D/B receptor insensitivity rapidly producing state of 5-HT 1D/B receptor insensitivity

12. Glutamatergic System Glutamate Glutamate most abundant excitatory neurotransmitter in the vertebrate nervous system. most abundant excitatory neurotransmitter in the vertebrate nervous system. Nerve impulses trigger release of glutamate from pre-synaptic cell Nerve impulses trigger release of glutamate from pre-synaptic cell Opposing post-synaptic cell, glutamate receptors (NMDA receptors) Opposing post-synaptic cell, glutamate receptors (NMDA receptors) Role in synaptic plasticity Role in synaptic plasticity learning and memory in the brain learning and memory in the brain Glutamate transporters rapidly remove glutamate from extracellular space Glutamate transporters rapidly remove glutamate from extracellular space In brain injury or disease, work in reverse and excess glutamate accumulates outside cells In brain injury or disease, work in reverse and excess glutamate accumulates outside cells Causes calcium ions to enter cells via NMDA receptor channels Causes calcium ions to enter cells via NMDA receptor channels Excitotoxicity- overstimulation of receptors leads to neuronal damage and eventual cell death Excitotoxicity- overstimulation of receptors leads to neuronal damage and eventual cell death

15. “The Combined Effects of Memantine and Fluoxetine on an Animal Model of Obsessive Compulsive Disorder”

16. Effective class of drugs used to treat OCD Effective class of drugs used to treat OCD Fluoxetine Fluoxetine First in a generation of SSRIs for treatment of major depressive disorder and anxiety disorders (OCD) First in a generation of SSRIs for treatment of major depressive disorder and anxiety disorders (OCD) Good overall safety and tolerability Good overall safety and tolerability Better than most other antidepressants Better than most other antidepressants Memantine Memantine First used in treatment of Alzheimer’s dementia First used in treatment of Alzheimer’s dementia low-affinity voltage-dependent antagonist at glutamatergic NMDA receptors low-affinity voltage-dependent antagonist at glutamatergic NMDA receptors Uncompetitive antagonist channel blocker Uncompetitive antagonist channel blocker

17. Aim of Study Use mouse model of OCD Use mouse model of OCD Examine whether a synergistic, as opposed to additive relationship between NMDA antagonists and SSRIs in treatment of OCD Examine whether a synergistic, as opposed to additive relationship between NMDA antagonists and SSRIs in treatment of OCD Combining relatively low doses of both drugs Combining relatively low doses of both drugs Low enough where do not decrease compulsive behavior when administered alone Low enough where do not decrease compulsive behavior when administered alone

18. Isobologram Graph of equally effective dose pairs (isoboles) for a single effect level Particular effect level is selected 50% of the maximum Doses of drug A and drug B (each alone) that give this effect are plotted as axial points in a Cartesian plot Straight line connecting A and B is the locus of points (dose pairs) that will produce this effect in a simply additive combination Line of additivity allows a comparison with the actual dose pair that produces this effect level experimentally

19. Isobologram Third point plotted on graph Third point plotted on graph dose combinations of two drugs necessary to produce same effect size dose combinations of two drugs necessary to produce same effect size Combination points below the line of additivity Combination points below the line of additivity Synergism Synergism Combination points along line of additivity Combination points along line of additivity Simply Additive Simply Additive Combination points above line of additivity Combination points above line of additivity Subadditivity Subadditivity

21. Method Male Swiss Webster mice Male Swiss Webster mice 18-63 g depending on age 18-63 g depending on age Kept at 68 to 72 °F in 12h/12h light-dark cycle Kept at 68 to 72 °F in 12h/12h light-dark cycle Ad libitum access to water and food pellets Ad libitum access to water and food pellets

22. Scratching Assay Established as effective model Established as effective model compulsive behavior in dogs with allergic dermatitis compulsive behavior in dogs with allergic dermatitis Intradermal injection in mice Intradermal injection in mice Serotonin Serotonin Compound 48-80 Compound 48-80 Promotes histamine release and mast cell degranulation Promotes histamine release and mast cell degranulation

23. Effect of fluoxetine on serotonin-induced scratching compared to controls Effect of fluoxetine on serotonin-induced scratching compared to controls 5,10,15,30 mg/kg 5,10,15,30 mg/kg Effect of memantine on serotonin-induced scratching compared to controls Effect of memantine on serotonin-induced scratching compared to controls 5,10,15,30 mg/kg 5,10,15,30 mg/kg Effect of combination fluoxetine and memantine on serotonin-induced scratching Effect of combination fluoxetine and memantine on serotonin-induced scratching 5mg/kg fluoxetine 5mg/kg fluoxetine 5mg/kg memantine 5mg/kg memantine Effect of fluoxetine (10 mg/kg) and memantine (5 mg/kg) by compound 48-80 both alone and in combination Effect of fluoxetine (10 mg/kg) and memantine (5 mg/kg) by compound 48-80 both alone and in combination

24. Experimental mice Experimental mice intraperitoneal injection of varying doses of fluoxetine and/or memantine in saline (0.9% NaCl) containing ascorbic acid (1mg/ml) intraperitoneal injection of varying doses of fluoxetine and/or memantine in saline (0.9% NaCl) containing ascorbic acid (1mg/ml) Control mice Control mice Intraperitoneal injection of varying doses of saline and ascorbic acid Intraperitoneal injection of varying doses of saline and ascorbic acid 0.1ml/10g of body weight 0.1ml/10g of body weight

25. 5 minutes later 5 minutes later Control and experimental mice subcutaneously injected behind neck Control and experimental mice subcutaneously injected behind neck 0.1 ml of 0.4 mg/ml serotonin or 0.1 ml of compound 48-80 1 mg/ml in saline and ascorbic acid to induce scratching 0.1 ml of 0.4 mg/ml serotonin or 0.1 ml of compound 48-80 1 mg/ml in saline and ascorbic acid to induce scratching Each mouse then placed individually in separate cage paired with control mouse in separate cage given saline pretreatment Each mouse then placed individually in separate cage paired with control mouse in separate cage given saline pretreatment

26. Cumulative number of scratches counted continuously using manual counter Cumulative number of scratches counted continuously using manual counter Cumulative scratches recorded every 5 minutes for 30 minutes Cumulative scratches recorded every 5 minutes for 30 minutes Other behaviors noted Other behaviors noted motor activity, sedation, licking, and rearing motor activity, sedation, licking, and rearing

27. Statistical Analysis Mean scratching scores for pretreated mice compared to their saline controls Mean scratching scores for pretreated mice compared to their saline controls Cumulative scratches in mice injected with drug were expressed as % of scratches compared to saline controls Cumulative scratches in mice injected with drug were expressed as % of scratches compared to saline controls

28. Results

33. Discussion Combined doses of fluoxetine and memantine required to produce 90% reduction in scratching Combined doses of fluoxetine and memantine required to produce 90% reduction in scratching much lower than doses of either drug alone necessary to produce same effect much lower than doses of either drug alone necessary to produce same effect Synergistic relationship Synergistic relationship

34. Present study mechanisms most likely serotonergic and glutamatergic Basis for synergism between fluoxetine and memantine Basis for synergism between fluoxetine and memantine SSRIs increase amount of serotonin in synapses and NMDA antagonist block glutamate binding at NMDA receptors SSRIs increase amount of serotonin in synapses and NMDA antagonist block glutamate binding at NMDA receptors Both decreased serotonergic activity and increased glutamatergic activity have been linked to the expression of impulsive behaviors Both decreased serotonergic activity and increased glutamatergic activity have been linked to the expression of impulsive behaviors