title: NMDA receptor involvement in imipramine withdrawal-associated effects on swim stress, GABA levels and NMDA receptor binding in rat hippocampus.
abstract: Abrupt antidepressant withdrawal after chronic treatment is associated with a stress response that may negatively affect the long-term outcome of depression, the neurochemical correlates, of which, remain undetermined. Prolonged depression involves the stress-related release of glucocorticoids and glutamate, while response to antidepressants involves gamma-amino butyric acid (GABA) and the glutamate N-methyl-D-aspartate (NMDA) receptor. Here, imipramine (IMI) was administered to rats for three weeks followed by acute withdrawal for seven days. Levels of GABA in the hippocampus (HC), and effects on swim stress immobility (SSI), were determined. Furthermore, glutamate/NMDA receptor binding properties were determined using [(3)H]-CGP-39653. Finally, the ability of dizocilpine (MK801), a glutamate NMDA antagonist, to reverse IMI withdrawal was determined. Chronic IMI (15 mg/kg ip) significantly reduced SSI together with a slight but insignificant decrease in HC GABA levels. However, IMI significantly reduced specific binding (B(max)) of [(3)H]-CGP-39653. Withdrawal of IMI for 7 days resulted in a loss of efficacy on SSI, a slight increase in GABA and a significant reversal of IMI effects on [(3)H]-CGP-39653 binding. MK801 (0.2 mg/kg ip) alone for seven days caused a significant decrease in SSI, a significant suppression of HC GABA, and significantly decreased [(3)H]-CGP-39653 B(max). MK801 during IMI-withdrawal significantly decreased GABA, prompted recovery on SSI, though not significantly, but significantly reversed withdrawal effects on [(3)H]-CGP-39653 B(max). In conclusion, acute antidepressant discontinuation is associated with subtle changes on HC GABA, a resurgence of NMDA receptor density and a loss of its anti-immobility response. These responses are reversed by a NMDA antagonist suggesting that abrupt antidepressant discontinuation mobilises glutamate activity.
authors.affiliation: Department of Pharmacology, School of Pharmacy, Potchefstroom University for Christian Higher Education, Potchefstroom, North Province 2520, South Africa. fklbhh@puknet.puk.ac.za
authors.forename: Brian H
authors.initials: BH
authors.lastname: Harvey
authors.forename: Lucy P
authors.initials: LP
authors.lastname: Jonker
authors.forename: Linda
authors.initials: L
authors.lastname: Brand
authors.forename: Marietha
authors.initials: M
authors.lastname: Heenop
authors.forename: Dan J
authors.initials: DJ
authors.lastname: Stein
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000009:adverse effects*; D001522:Behavior, Animal / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000737:chemistry / Q000378:metabolism*; D007099:Imipramine / Q000009:adverse effects*; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D013315:Stress, Psychological / Q000378:metabolism / Q000503:physiopathology* / Q000523:psychology*; D013375:Substance Withdrawal Syndrome / Q000378:metabolism / Q000503:physiopathology* / Q000523:psychology*; D013550:Swimming / Q000502:physiology* / Q000523:psychology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D000929:Antidepressive Agents, Tricyclic; D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; C069052:CGP 39653; D005680:gamma-Aminobutyric Acid; D016291:Dizocilpine Maleate; D015763:2-Amino-5-phosphonovalerate; D007099:Imipramine