Chapter 4 Summary & Outline

Many Chemical Neurotransmitters Have Been Identified

• The major categories of neurotransmitters are amine, amino acid, peptide, and soluble gas neurotransmitters. Review Table 4.1, Web Activity 4.1
• Because many drugs work by acting on receptor molecules, investigators search for the receptor molecules and for the endogenous substances that work on the receptors. A given neurotransmitter may normally bind several different subtypes of receptors. Review Figure 4.1
• A ligand is any substance that binds to a receptor. Agonists activate transmitter pathways, antagonists block transmitter pathways, and inverse agonists have active effects that are opposite to a transmitter’s normal effects. Review Web Activity 4.2

Study questions: 1 | 2 | 3

Neurotransmitter Systems Form a Complex Array in the Brain

• The classic neurotransmitters are found in segregated regions that project widely throughout the brain. Review Figures 4.2 – 4.5, Web Activity 4.3

Study questions: 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17

Research on Drugs Ranges from Molecular Processes to Effects on Behavior

• Drugs vary in their binding affinity for different types of receptors, as well as in efficacy—their ability to produce effects—once they are bound. Review Figure 4.6
• The relationship between concentrations of a drug and its physiological effects is formally studied by use of a dose-response curve. Dose-response relationships reveal a drug’s activity, specificity, potency, and safety. Review Figure 4.8
• Repeated treatments with a drug can produce tolerance to its effects, often through the up- or down-regulation of receptors. This compensatory mechanism is responsible for withdrawal symptoms. However, repeated use of some drugs produces sensitization, in which the drug’s effects increase with use of the same dosage.

Study questions: 18 | 19 | 20 | 21 | 22

Drugs Affect Each Stage of Neural Conduction and Synaptic Transmission

• Most CNS drugs alter neural transmission, such as by inhibiting axonal transport, affecting transmitter reuptake, or acting on postsynaptic receptors. Neuromodulators such as caffeine may affect the release of the transmitter or the receptor’s response to the transmitter. Review Figure 4.9

Study questions: 23 | 24

Drugs That Affect the Brain Can Be Divided into Functional Classes

• Effective drug treatments revolutionized the management of schizophrenia. Most antipsychotic medications block dopamine D₂ receptors, but some also block serotonin receptors. Review Figure 4.10
• The main categories of antidepressants are MAO inhibitors, tricyclics, and selective serotonin reuptake inhibitors. All share the basic action of increasing the availability of monoamine transmitters in synapses.
• Substances that are used to combat anxiety, such as the benzodiazepines, are called anxiolytic drugs. The benzodiazepines synergize the activity of the inhibitory transmitter GABA at some of its receptors. Review Figure 4.11
• Alcohol acts on GABA receptors to produce some of its effects. Alcohol in moderation has beneficial effects; but in higher doses it is very harmful, damaging neurons in many areas of the brain. Review Figure 4.12
• Opiates are potent painkillers; endogenous opioids include the endorphins, and exogenous opiates include morphine and heroin.
• The active ingredient in marijuana, THC, acts on cannabinoid receptors to produce its effects. An endogenous cannabinoid, anandamide, serves as a retrograde transmitter in some synapses. Review Figure 4.16
• Some stimulants, such as nicotine, imitate an excitatory synaptic transmitter. Others, such as amphetamine, cause the release of excitatory synaptic transmitters and block the reuptake of transmitters. Still others, such as caffeine, block the activity of an inhibitory neuromodulator.
• Some drugs are called hallucinogens because they alter sensory perception and produce peculiar experiences. Different hallucinogens act on different kinds of synaptic receptors, and it is not yet clear what causes the hallucinogenic effects.

Study questions: 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44

Drug Abuse Is Pervasive

• Drug abuse and addiction are being studied intensively, and several models have been proposed: the moral model, the disease model, the physical dependence model, and the positive reward model. Review Figure 4.21
• People differ in their vulnerability to drug abuse according to several factors: genetic predisposition, personality characteristics, and family and social context. Environmental stimuli can be associated with drug effects and potently cue subsequent drug use.
• There are several medicinal approaches to treating drug addiction, including antiwithdrawal and anticraving medication and immunization.

Study questions: 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59