Chapter 4 Psychopharmacolog y OUTLINE Life cycle of a Neurotransmitter Types of Neurotransmitters Life Cycle of a Neurotransmitter Synthesis from precursor chemicals Storage into synaptic vesicles Release Exocytosis from presynaptic terminal Triggered by action potentials and the opening of voltage gated Ca2 channels Modulated by presynaptic facilitation and inhibition Receptor binding Ionotropic or metabotropic Deactivation Diffusion reuptake or enzymatic degradation Categories of Chemical Messengers Neurotransmitters communicate locally across the synapse Neuromodulators communicate with target cells more distant than the synapse by diffusing away from the point of release Neurotransmitter Classification Neuromodulators Categories of Chemical Messengers Neurotransmitters communicate locally across the synapse Neuromodulators communicate with target cells more distant than the synapse by diffusing away from the point of release Neurohormones communicate with target cells at great distance often by traveling through circulation The Endocrine System Inactivation Hormones are secreted into bloodstream by the endocrine glands Gonads Inactivation Secrete sex steroid hormones estrogen and progesterone in females and androgens in males Puberty secondary sexual characteristics Neurotransmitter Defined Must be synthesized within neuron Released in response to AP and has measurable effect on postsynaptic cell Can duplicate action experimentally Mechanism must exist for termination of effect Neurotransmitter Classification Table 4 1 Features of Small Molecule Transmitters and Neuropeptides Single axon terminal may release a small molecule NT and neuropeptide Neurotransmitter Classification Acetylcholine Nicotinic receptor Ionotropic Gates Na excitatory Found at the neuromuscular junction autonomic nervous system Nicotine Acetylcholine Nicotinic receptor Ionotropic Gates Na excitatory Found at the neuromuscular junction autonomic nervous system Muscle Nicotine Acetylcholine Muscarinic receptor Metabotropic Found predominantly in the brain Can be excitatory or inhibitory Amanita muscaria Cholinergic system Acetylcholine Functions Attention Learning and memory Deterioration implicated in Alzheimer s disease Neurotransmitter Classification Catecholamine Synthesis Dopamine Receptors Metabotropic Can be excitatory or inhibitory Dopaminergic system Dopamine Limbic system Systems of Dopaminergic Neurons Mesolimbic system projections from ventral tegmental area VTA to nucleus accumbens hippocampus and amygdala Function reward Implicated in Addiction Mesocortical system projections from VTA to prefrontal cortex Functions planning problem solving Implicated in Schizophrenia Nigrostriatal System projections from substantia nigra to basal ganglia Function control of movement Implicated in Parkinson s disease Neurotransmitter Classification Serotonin 5 HT Synthesis Receptors Metabotropic Can be excitatory or inhibitory Serotonergic system Serotonin Functions Sleep arousal appetite mood Implicated in anxiety and depression Neurotransmitter Classification Glutamate Principle excitatory transmitter in the CNS Ionotropic or Metabotropic postsynaptic receptors Two principle ionotropic receptors AMPA NMDA AMPA receptor activation Glutamate AMPA receptor gates Na excitatory NMDA receptor is unique among receptors requiring both ligand NT binding and membrane depolarization aka valtage gated Important for learning memory NMDA receptor activation Glutamate AMPA receptor gates Na excitatory NMDA receptor is unique among receptors requiring both ligand NT binding and membrane depolarization GABA Principle inhibitory NT in the CNS GABAA Ionotropic Gates Cl inhibitory influx Multiple binding sites GABAB Metabotropic Gates K inhibitory efflux Neurotransmitter Classification Pituitary peptides Oxytocin maternal care bonding Opioid peptides endorphin reduces pain produces feelings of well being e g runner s high Neurotransmitter Classification Gas Rare Nitric Oxide Diffuses through membrane independent of vesicle Retrograde transmitter influencing presynaptic neuron s release Clarifications Questions