neuropharmacology

1. Dauphin Island Sea Lab 2014 neuropharmacology

2. neuropharmacology… • ….is that branch of neuroscience, which deals with the study of drug-induced changes in the functioning of cells in the nervous system (Wikipedia 2009). • “Since a drug is broadly defined as any chemical agent that affects any living process, the subject of pharmacology is obviously quite extensive” (Goodman & Gilman, 1980). • At DISL we will largely be concerned with drugs acting at membrane receptors, ion channels, pumps and transporters. • Drugs don’t produce new functions they only modify the rates of existing biological processes.

3. neurotransmitters & receptors

4. drug-receptor history (1850-now) • from drugs to enzymes to pharmacology…… • Bernard (1850’s): curare makes nerves unexcitable • Fischer (1894): lock and key hypothesis for enzyme-substrate interaction • Langley (1900’s): drugs interact with “receptive substance” • Erlich (1900’s): side chains of drug interact with “receptor” atom groups • Dale (1900’s): sympathomimetic action of drugs on nerves • Loewi (1920’s): vago-stuff

5. locks & keys • 2 steps in transmitter-receptor interaction • binding - insert correct key • action (gating) - turn key to open door

6. response log[A] how do we study drugs? • concentration-(dose)-response relationships • drug binding to a population of receptors should be a saturable process (think Michaelis-Menton enzyme kinetics)

7. A.V. Hill • drug-receptor interaction theory (1909;1910;1913) • Hill equation…. • first quantitative description of drug responses • kinetics of drug response onset and offset • explanation for shape of dose-response curve • haemoglobin (a recurring theme……..)

8. k+1 R + A <=> AR k-1 mass action and reaction rates at equilibrium forward & backward rates are equal: d[y] = (1-y)[A]k+1 - yk-1 = 0 dt on rearrangement: y = [A] / ([A] + k-1/k+1) let kD’ = k-1/k+1 (dissociation equilibrium constant): y = [A] / ([A] + kD’) ÷ [A] when [A] = kD’ 50 % max, EC50 Hill (Langmuir) isotherm: y = 1 / (1 + EC50/[A]) let AR = y, R = 1-y the rate of change of y: d[y] = (1-y)[A]k+1 - yk-1 dt

9. ….provides a good fit I / Imax = 1 / (1 + EC50/[A]) Imax response log[A] EC50

10. more than 1 agonist molecule • generalized Hill equation • what does nH mean? • Hill (1910) “just a constant” • can’t be interpreted in terms of any precise mechanism, e.g. number of agonist molecules • co-operative binding (e.g., haemoglobin) • efficacy y = 1 / (1 + (EC50/[A])nH)

11. effects of antagonist on d-r curves • antagonist alone (basal response?) • competitive antagonist + agonist • NMDA versus APV • non-competitive antagonist • NMDA versus glycine-site antagonist • uncompetitive antagonist • NMDA versus MK-801 • partial agonists/antagonists • Clark, Stevenson, Katz • allosteric potentiators

12. uncompetitive antagonists • Drugs action inside a channel • Use-dependence (increased block at increased agonist concentration) • Voltage-dependent (if charged) • Mg++ in NMDA channels • (Mayer & Westbrook, 1985) • Local anesthetics (TTX) at Na channels • experiment idea (permanently charged molecule from inside only - Hille)

13. how does binding lead to outcome? • Channel • binding-gating (most direct relationship between drug binding and effect (efficacy) • structural mechanism • 2 step model (del Castillo & Katz, 1957) • G-protein coupled receptors • same principle • more intermediate steps between binding and effect (whatever is being assayed) • spare receptors • inverse agonists (basal activity) • Desensization?

14. Schild analysis (antagonist affinity) • Agonist dose-ratio (r) in the presence vs absence of antagonist • Linear plot • Competitive drugs (Wyllie& Chen, 2007) log(r-1) = log[B] – logKB