Intro
Agonistic Drug Effects:
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6
Antagonist Drug Effects:
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11
Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test
Neuropharmacology is the study of drugs that affect the nervous system. These drugs include anesthetics (eliminate sensation), anticonvulsants (used to treat epilepsy), analgesics (relieve pain), and a variety of drugs that affect the autonomic nervous system. Of particular interest, however, to the student of psychology is the subfield of psychopharmacology. Psychopharmacology studies the effects of psychotropic drugs, those that affect particular moods and behaviors, sedatives (calming), analeptics (stimulants), and hypnotics (sleep-inducing).
Psychotropic drugs exert their effects by altering a synaptic event. These alterations ultimately change the activity of a neurotransmitter. Some psychotropic drugs facilitate the effects of a neurotransmitter, and are called agonistic. While other psychotropic drugs inhibit the effects of particular neurotransmitters, and are called antagonistic. Tutorial 13 focuses on the variety of mechanisms altered by drugs, and provides examples for each. Figure 13 illustrates the synaptic mechanisms affected by drug use.
Knowledge of the synaptic event altered by a drug does not lead to an automatic understanding of the drug's effects on mood or behavior. Even knowledge of the particular neurons whose activity is affected by a particular drug does not lead to such clarification. In a network as complex as the nervous system there are likely hundreds of intermediary reactions between the drug's effects and the ultimate behavior. Knowledge of local drug effects nonetheless has enriched our understanding of both normal and abnormal neurochemistry and neurophysiology.
| Advanced |
There is often more than one receptor responsive to a given neurotransmitter. These vary based on the shape of the site that binds the neurotransmitter, the portion of the receptor that changes in response to neurotransmitter binding, the function and location within the nervous system, and the substances that may act as agonists or antagonists with the receptor. For example, three different dopamine receptor types have been studied extensively (there are more, however). The two major types of dopamine postsynaptic receptors are called D1 and D2 receptors (Baldessarini & Tarazi, 1996; Picetti, Saiardi, Abdel Samad, Bozzi, Baik & Borrelli, 1997). Both are located in the striatum, a region of the brain important in motor control (Sedvall, Pauli, Farde, Karlsson, Nyberg & Nordstrom, 1995). Although general effects of inducing hyperactivity, stereotyped movements, psychosis, and vomiting are similar for both D1 and D2 receptors, only one (D1) uses adenylate cyclase to mediate the receptor response (Undie, Berki & Beardsley, 2000) and the agents that serve as antagonists for each differ. In addition, D1 receptors are inhibitory, whereas D2 receptors are excitatory. D3 receptors are presynaptic autoreceptors that inhibit the dopamine neuron. Much research effort sponsored by the pharmaceutical companies involves the identification and localization of new neurotransmitter receptor variants, and the discovery of compounds that may serve as selective agonists or antagonists of each. With this added detail, it is hoped that drugs may be developed to inhibit or excite regions of the brain more selectively, yielding improved treatment.
| References |
Baldessarini, R.J. & Tarazi, F.I. (1996). Brain dopamine receptors: a primer on their current status, basic and clinical. Harvard Review of Psychiatry, 3(6), 301-325.
Sedvall, G., Pauli, S., Farde, L., Karlsson, P., Nyberg, S. & Nordstrom AL. (1995). Recent developments in PET scan imaging of neuroreceptors in schizophrenia. Israel Journal of Psychiatry and Related Sciences, 32(1), 22-29.
Picetti, R., Saiardi, A., Abdel Samad, T., Bozzi, Y., Baik, J.H. & Borrelli E. (1997). Dopamine D2 receptors in signal transduction and behavior. Critical Reviews in Neurobiology, 11(2-3), 121-142.
Undie, A.S., Berki, A.C. & Beardsley, K. (2000). Dopaminergic behaviors and signal transduction mediated through adenylate cyclase and phospholipase C pathways. Neuropharmacology, 39(1), 75-87.
| Suggestions for further study |
Beardsley, T.M. (1990, October). Cannabis comprehended. The "assassin of youth" points to a new pharmacology. Scientific American, 263(4), 38.
Beardsley, T. (1996, August). Paying attention. The controversy over ADHD and the drug Ritalin is obscuring a real look at the disorder and its underpinnings. Scientific American, 275(2), 12, 14.
Bugg, C.E., Carson, W.M. & Montgomery, J.A. (1991, November). Brain, food. Drugs based on neuropeptides may soon treat eating disorders. Scientific American, 265(5), 124, 126.
Cox, P.A. & Balick, M.J. (1992, June). The estrogen factor. Scientific American, 266(6), 26.
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http://micro.magnet.fsu.edu/micro/gallery/neurotrans/neurotrans.html
(The Neurotransmitter Collection)
M.W. Davidson, Florida State University, Photos of neurotransmitter in
crystallized form
http://www-rci.rutgers.edu/~lwh/drugs/chap03.htm
(Drugs, Brains and Behavior)
C. Robin Timmons & Leonard W. Hamilton, an on-line textbook