Enhancement of acoustic evoked potentials and impairment of startle reflex induced by reduction of GABAergic control of the neural substrates of aversion in the inferior colliculus.
The neural network of the inferior colliculus (IC), implicated in the generation of defensive behavior to aversive acoustic stimuli, is under tonic GABAergic control. Dopamine also seems to have a modulatory role in these neural circuits. It is still unclear how such changes in transmission of acoustic information influence the motor expression of the defensive behavior. Startle reaction to a sudden noise has been used as an effective way to measure the motor reactivity of rats to fearful acoustic stimuli. In this work we examined the processing of sensorial information--assessed by the recording of auditory evoked potentials (AEP)--and the behavioral effects--evaluated by the freezing and startle responses--during the reduction of GABA levels caused by microinjections of semicarbazide (SMC, 6 microg/0.2 microl), a glutamic acid decarboxylase inhibitor, into the IC. These data were compared to the effects of the overall arousal elicited by apomorphine (APO, 0.5 mg/kg, i.p.). The results obtained show that IC microinjections of SMC induced freezing behavior, enhanced the AEP and impaired the startle reaction to a loud sound. On the other hand, APO changed neither the AEP nor the startle in the same experimental conditions. These results suggest that the release of GABAergic control of the neural substrates of aversion in the IC results in an increased processing of auditory information along with an inhibitory influence on the motor pathways responsible for the startle response.
Nobre
Manoel Jorge
MJ
Laboratório de Psicobiologia, F.F.C.L.R.P., Campus USP, 3900, Av. Bandeirantes, 14040-901 Ribeirão Preto, SP, Brazil.
Sandner
Guy
G
Brandão
Marcus Lira
ML
D000161:Acoustic Stimulation / Q000379:methods; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001143:Arousal; D001362:Avoidance Learning / Q000502:physiology*; D001522:Behavior, Animal / Q000187:drug effects; D001931:Brain Mapping; D018491:Dopamine Agonists / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D005072:Evoked Potentials, Auditory / Q000187:drug effects; D005968:Glutamate Decarboxylase / Q000494:pharmacology; D007245:Inferior Colliculi / Q000502:physiology*; D008297:Male; D008845:Microinjections; D051381:Rats; D017208:Rats, Wistar; D013216:Reflex, Startle / Q000187:drug effects / Q000502:physiology*; D012663:Semicarbazides / Q000008:administration & dosage; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D018491:Dopamine Agonists; D004791:Enzyme Inhibitors; D012663:Semicarbazides; C010059:carbamylhydrazine; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; D001058:Apomorphine