RESUMO
Findings by our group have shown that the dorsolateral telencephalon of Gymnotus carapo sends efferents to the mesencephalic torus semicircularis dorsalis (TSd) and that presumably this connection is involved in the changes in electric organ discharge (EOD) and in skeletomotor responses observed following microinjections of GABA A antagonist bicuculline into this telencephalic region. Other studies have implicated the TSd or its mammalian homologue, the inferior colliculus, in defensive responses. In the present study, we explore the possible involvement of the TSd and of the GABA-ergic system in the modulation of the electric and skeletomotor displays. For this purpose, different doses of bicuculline (0.98, 0.49, 0.245, and 0.015 mM) and muscimol (15.35 mM) were microinjected (0.1 microL) in the TSd of the awake G. carapo. Microinjection of bicuculline induced dose-dependent interruptions of EOD and increased skeletomotor activity resembling defense displays. The effects of the two highest doses showed maximum values at 5 min (4.3 +/- 2.7 and 3.8 +/- 2.0 Hz, P < 0.05) and persisted until 10 min (11 +/- 5.7 and 8.7 +/- 5.2 Hz, P < 0.05). Microinjections of muscimol were ineffective. During the interruptions of EOD, the novelty response (increased frequency in response to sensory novelties) induced by an electric stimulus delivered by a pair of electrodes placed in the water of the experimental cuvette was reduced or abolished. These data suggest that the GABA-ergic mechanisms of the TSd inhibit the neural substrate of the defense reaction at this midbrain level.
Assuntos
Comportamento Animal/efeitos dos fármacos , Bicuculina/farmacologia , Gimnotiformes/fisiologia , Mesencéfalo/efeitos dos fármacos , Muscimol/farmacologia , Animais , Comportamento Animal/fisiologia , Bicuculina/administração & dosagem , Mecanismos de Defesa , Interações Medicamentosas/fisiologia , Órgão Elétrico/efeitos dos fármacos , Órgão Elétrico/fisiologia , Estimulação Elétrica , Agonistas GABAérgicos/farmacologia , Antagonistas GABAérgicos/farmacologia , Mesencéfalo/fisiologia , Microinjeções , Movimento/efeitos dos fármacos , Movimento/fisiologia , Muscimol/administração & dosagem , Vias Neurais/efeitos dos fármacos , Vias Neurais/fisiologiaRESUMO
Findings by our group have shown that the dorsolateral telencephalon of Gymnotus carapo sends efferents to the mesencephalic torus semicircularis dorsalis (TSd) and that presumably this connection is involved in the changes in electric organ discharge (EOD) and in skeletomotor responses observed following microinjections of GABA A antagonist bicuculline into this telencephalic region. Other studies have implicated the TSd or its mammalian homologue, the inferior colliculus, in defensive responses. In the present study, we explore the possible involvement of the TSd and of the GABA-ergic system in the modulation of the electric and skeletomotor displays. For this purpose, different doses of bicuculline (0.98, 0.49, 0.245, and 0.015 mM) and muscimol (15.35 mM) were microinjected (0.1 æL) in the TSd of the awake G. carapo. Microinjection of bicuculline induced dose-dependent interruptions of EOD and increased skeletomotor activity resembling defense displays. The effects of the two highest doses showed maximum values at 5 min (4.3 ± 2.7 and 3.8 ± 2.0 Hz, P < 0.05) and persisted until 10 min (11 ± 5.7 and 8.7 ± 5.2 Hz, P < 0.05). Microinjections of muscimol were ineffective. During the interruptions of EOD, the novelty response (increased frequency in response to sensory novelties) induced by an electric stimulus delivered by a pair of electrodes placed in the water of the experimental cuvette was reduced or abolished. These data suggest that the GABA-ergic mechanisms of the TSd inhibit the neural substrate of the defense reaction at this midbrain level.
Assuntos
Animais , Comportamento Animal/fisiologia , Bicuculina/farmacologia , Gimnotiformes/fisiologia , Mesencéfalo/fisiologia , Muscimol/farmacologia , Comportamento Animal/efeitos dos fármacos , Bicuculina/administração & dosagem , Mecanismos de Defesa , Interações Medicamentosas/fisiologia , Estimulação Elétrica , Órgão Elétrico/efeitos dos fármacos , Órgão Elétrico/fisiologia , Agonistas GABAérgicos/farmacologia , Antagonistas GABAérgicos/farmacologia , Microinjeções , Mesencéfalo/efeitos dos fármacos , Movimento/efeitos dos fármacos , Movimento/fisiologia , Muscimol/administração & dosagem , Vias Neurais/efeitos dos fármacos , Vias Neurais/fisiologiaRESUMO
The functional role of the dorsal portions of dorsolateral telencephalon in modulating the stable electric organ discharge was determined by microinjection of an agonist or antagonist GABAergic drug in the awake weak electric fish, Gymnotus carapo. The dorsolateral telencephalon, which is interconnected with the preglomerular complex and the dorsocentral telencephalic area was microinjected through a guide cannula previously implanted, with different doses of bicuculline, muscimol and saline. Microinjection of bicuculline into the dorsolateral telencephalon induced a complex response consisting of increase, decrease and abrupt interruptions in the frequency of electric organ discharges and an increase in motor activity. Motor activity and modulations in the electric organ discharge are dose dependent. The somatic, but not the electric, effect is abolished under anesthesia by urethane, suggesting that the two responses are parallel but unrelated in terms of occurrence. These data, together with former neuroanatomical findings by this laboratory, suggest two parallel pathways by which the blockage of GABAA receptors in the dorsolateral telencephalon causes modulations in the firing of the medullary pacemaker nucleus. A possible route for the motor effect through reticular projection from the torus semicircularis dorsalis is discussed.