“Inside-Out” Mechanisms in Neuropharmacology
“Inside-out” neuropharmacology also arose in our approach to an inadvertent therapeutic effect of smoking: the inverse correlation between a person's history of smoking and his/her susceptibility to Parkinson's disease, in which dopaminergic neurons degenerate. There will never be a medical justification for the use of smoked tobacco. However, the organism's responses to chronic nicotine probably also underlie this apparent neuroprotection.
The field of psychiatric drugs seems ripe for testing “inside-out” ideas, because nobody understands the events that occur during the two to three week “therapeutic lag” in the actions of antidepressant and antipsychotic drugs.
Recently our lab has shifted from focusing on the immediate effects of nicotine binding to receptors on the surface of nerve cells to what happens when that nicotine infiltrates deep into the cell. Nicotine receptors entering the endoplasmic reticulum increase its output of these same nicotine receptors which then travel to the cell's surface. In other words, nicotine acts "inside out," directing actions that ultimately fuel and support the body's addiction to nicotine. These longer-term changes deep within the cell may also explain why the beneficial actions of antidepressants and antischizophrenic drugs require several weeks to develop.
We hope to define the action of the novel antidepressant ketamine which has useful properties as an antidepressant but undesirable side effects.
We are now in the process to design and discover novel protein based biosensors and engineer them to detect nicotine. This nicotine biosensor will then help in studying inside-out neuropharmacology.
Evidence Supporting Inside-out pharmacology of nicotine and nicotinic ligands. (1) Nicotine permeates lung epithelium, blood brain barrier and permeates cell membranes to enter intracellular organelles. (2) Nicotine enhances maturation of pentameric nAChRs, increasing assembly in the ER. (3) ER retention is necessary for up-regulation. (4) Cycling between the Golgi and ER is necessary for up-regulation. (5) Nicotinic ligands change the area of the peripheral ER. (6) The changes in nAChR stoichiometry have occurred by the time nAChRs have reached the Golgi. (7) Nicotine enhances the PM insertion rate of vesicles carrying α4β2 and α6β2β3 nAChRs. (8) Nicotinic ligands have differential effects on PM stoichiometry. (9) Nicotine and cytisine up-regulate α4β2 and α6β2β3 nAChRs at concentrations that activate ≤0.4% of PM nAChRs. (10) Quaternary ammonium nicotinic ligands that permeate membranes poorly up-regulate nAChRs more slowly than nicotine and other tertiary ammonium ligands. (11) Nicotine increases the number of trans-Golgi network bodies. (12) Nicotine enhances α4β2 nAChR glycosylation. (13) β2 nAChR subunit mutations that enhance ER exit change stoichiometry, similar to nicotine. (14) Blocking proteasome activity up-regulates nAChRs. (14) Nicotine enhances the number of ER exit sites. (15) ER exit sites are increased by α4 nAChR subunit M3-M4 loop mutations that introduce ER exit motifs. (16) ER exit sites are increased by β2 nAChR subunit M3-M4 loop mutations that eliminate ER retention motifs. (17) Nicotinic ligands decrease ATF6 translocation to the nucleus. (18) Nicotinic ligands decrease eIF2α phosphorylation. (19) Nicotinic ligands reduce ER stress at concentrations that activate ≤0.4% of PM α4β2 nAChRs. Brown font denotes events involved with up-regulation of PM nAChRs; Blue font denotes events involved with up-regulation and the reduced unfolded protein response.