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PSYC62H3 (313)
Chapter 7

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Suzanne Erb

Chapter 7: psychomotor stimulants and antiparkinsonian drugs - Use term psychomotor stimulants: low-moderate doses = motor stimulation, reduced fatigue, increases resistance to sleep, increased vigilance, alertness, heightened mood or anxiety (depending on the individual or the context), enhanced performance on tasks (dose-response functions is inverted U shape), increased sympathetic nervous system activity (increased heart rate, blood pressure) - Aka behavioural stimulants, CNS stimulants - Depending on dose, frequency of behaviour being observed without drug, the individual some behaviours increase in individuals and some decrease; some neurons increase firing and others decrease rate of firing; energy utilization may increase in some areas of the CNS and decrease in other areas - Most commonly used psychostimulant caffeine, nicotine - Nicotine and caffeine (other methylxanthines) grouped in minor stimulants - Amphetamines, methylphenidate (Ritalin), pemoline, cocaine, dopamine agonists grouped in major stimulants Motor Effects of Psychomotor stimulants BEHAVIOURAL NEUROBIOLOGY - Animals stimulants produce rate dependent effects - Forebrain DA systems are critical for expression on responses: effect of drug depends upon the of major psychomotor stimulant effects baseline rate of response generated by the schedule - Study by Susan Iversen: showed a double - Major/Minor stimulants: enhance rates of lever dissociation effect for the motor stimulant effects pressing when animals are responding on of amphetamines (i.e. two distinct brain areas schedules that generate low response rates (fixed mediate two different behaviours and the effects of interval schedules), but decrease lever pressing selective lesions can dissociate these effects) rates when animals are responding on schedules - Rotation model: a unilateral DA depletion is that generate high baseline rates of response produced, and administration of stimulants causes (fixed ratio schedules) an asymmetrical locomotion known as rotation - Low doses: increase in locomotor activity (both and circling. The direction of the rotation is major and minor) + exploration; [switch from one opposite, depending upon whether the stimulant act to another] drug acts presynaptically (amphetamine) or is an - High doses: stereotypy: focused/repetitive agonist that binds to postsynaptic DA receptors (apomophine). Rotation model is used to assess behaviours (head bobbing, nose picking) for extended period of time antiparkinsonian drugs but has limits - Lyon + Robbins: as dose increases, major stimulants increase response frequency [repeat same response over and over] within decreasing response categories [switch from one act to another] - Stereotypy via stimulants = punding CAFFEINE - One of several called methylxanthines - Difficult to determine overall time course and impact of caffeine on individual ADENOSINE - Caffeine effects are related to its ability to act as a nonselective antagonist of adenosine receptors - Neuromodulator that effects neuronal excitability, inhibits presynaptic release of ACh, NE, DA, GABA, 5HT thus, by blocking adenosine receptors = enhanced release of the mentioned neurotransmitters in brain and increases Catecholamines (A re1eptor subtype) - A 2eceptor subtype: caudate/putamen and nucleus 1 accumbens rich in this subtype; caffeine can reverse many of the behavioural effects of DA D 2 antagonists, including the suppression of operant lever pressing and locomotion - Caffeine acts to antagonize receptors (has high affinity for the receptor, but NO intrinsic activity of the receptorit does not produce change in biological activity), but in doing so, their effects interact with DA mechanisms involved in psychomotor stimulant effects - For adenosine antagonists to increase rates of operant responding depends upon blocking adenosine A 2Aceptors adenosine A 2A antagonists are being developed as antiparkinsonian drugs because of interactions with DA systems WHY SO POPULAR? - Unclear - IV administration studies with animals: caffeine has reinforcing effects in some cases, but not in others - Humans: reinforcing effects = variable, sometimes induce dysphoric effects - Rated as having desirable effects in heavy drinkers, especially after several hours of not having coffee - Coffee abstainers more likely to report unpleasant reactions to caffeinethus, reinforcing effects of caffeine stems from ability to terminate caffeine withdrawal EFFECTS OF CAFFEINE - VARY a lot among individuals in terms of wakefulness, psychomotor coordination, mood alterations, and autonomic nervous system response - 2 cups of coffee: mood elevation, reduced fatigue properties of threshold doses of amphetamine (2-5 mg) - 7 10 cups: insomnia, restlessness, mild sensory disturbances, muscle tenseness (caffeinism), anxiety, panic attacks - Blood pressure increase in men and women - Heart rate changes are variable - Increase in GSR and reactivity - Low-moderate doses = dose-dependent improvements in arousal, alertness, vigilance, some aspects of psychomotor performance and cognitive functions (reaction time, attn, info processing), positive mood, increased well being, energy, concentration effects especially when person is tested under condition of caffeine deprivation or total abstinence in regular caffeine users or following partial or total sleep deprivation - Increased capacity for muscle work and sustained intellectual effort
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