Post-stress facilitation of serotonergic, but not noradrenergic, neurotransmission in the dorsal hippocampus prevents learned helplessness development in rats.
Recent pieces of evidence suggest that the dorsal hippocampus may mediate adaptation to severe and inescapable stress, possibly by the facilitation of serotonergic and/or noradrenergic neurotransmission. Chronic social stress and high corticosteroid levels would impair this coping mechanism, predisposing animals to learned helplessness. To test the hypothesis that increasing serotonin or noradrenaline levels in the dorsal hippocampus would attenuate the development of learned helplessness (LH), rats received inescapable foot shock (IS) and were tested in a shuttle box 24 h latter. Prestressed animals showed impairment of escape responses. This effect was prevented by bilateral intrahippocampal injections of zimelidine (100 nmol/0.5 microl), a serotonin reuptake blocker, immediately after IS. This effect was not observed when zimelidine was administered before or 2 h after IS. Bilateral intrahippocampal injections of desipramine (3 or 30 nmol/0.5 microl), a noradrenaline reuptake blocker, before IS or immediately after it did not prevent LH development. Desipramine (30 nmol) enhanced LH development when injected before IS. These data suggest that poststress facilitation of hippocampal serotonergic, but not noradrenergic, neurotransmission in the dorsal hippocampus facilitates adaptation to severe inescapable stress. Antidepressant effects of noradrenaline-selective drugs seem to depend on other structures than the dorsal hippocampus.
Joca
Sâmia Regiane Lourenço
SR
Department of Pharmacology, Faculty of Medicine of Ribeirão Preto, University of São Paulo, 14049-900, Ribeirão Preto, SP, Brazil. samia@usp.br
Zanelati
Tatiane
T
Guimarães
Francisco Silveira
FS
D018759:Adrenergic Uptake Inhibitors / Q000008:administration & dosage; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003891:Desipramine / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D004597:Electroshock / Q000009:adverse effects; D004924:Escape Reaction / Q000187:drug effects; D007839:Functional Laterality; D006380:Helplessness, Learned; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects; D012701:Serotonin / Q000502:physiology*; D017367:Selective Serotonin Reuptake Inhibitors / Q000008:administration & dosage; D013312:Stress, Physiological / Q000150:complications / Q000378:metabolism / Q000473:pathology*; D015031:Zimeldine / Q000008:administration & dosage
D018759:Adrenergic Uptake Inhibitors; D003891:Desipramine; D009638:Norepinephrine; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors; D015031:Zimeldine