Defense reaction elicited by microinjection of kainic acid into the medial hypothalamus of the rat: antagonism by a GABAA receptor agonist.
Electrical stimulation of either the midbrain central gray or the medial hypothalamus induces a defense reaction in the rat, characterized mainly by increased locomotion, rearing, and leaping. However, microinjection of the excitatory amino acid glutamate was effective only in the former region. Because excitatory amino acids do not depolarize axons of passage, it was suggested that the hypothalamus is devoid of soma/dendrites of neurons commanding the defense reaction. In the present study, we show that a subtoxic dose (60 pmol) of another excitatory amino acid, kainic acid, injected into the medial hypothalamus significantly enhanced locomotion and rearing of Wistar rats systematically observed in an open field. Similar behavioral changes have been reported following microinjection of drugs impairing GABAergic neurotransmission. Local pretreatment with the GABAA receptor agonist THIP (2 nmol) blocked the effect of kainic acid. Therefore, the medial hypothalamus of the rat seems to contain a population of neuronal cell bodies commanding the defense reaction, which is activated by excitatory amino acids and tonically inhibited by GABAergic fibers.
Silveira
M C
MC
Laboratory of Psychobiology, FFCLRP, Ribeirão Preto, SP, Brazil.
Graeff
F G
FG
D000378:Agonistic Behavior / Q000187:drug effects*; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D001143:Arousal / Q000187:drug effects*; D001931:Brain Mapping; D004305:Dose-Response Relationship, Drug; D005106:Exploratory Behavior / Q000187:drug effects*; D007033:Hypothalamus, Middle / Q000187:drug effects*; D007555:Isoxazoles / Q000494:pharmacology*; D007608:Kainic Acid / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D011963:Receptors, GABA-A / Q000187:drug effects*; D012934:Social Isolation
D000927:Anticonvulsants; D007555:Isoxazoles; D011963:Receptors, GABA-A; C015542:gaboxadol; D007608:Kainic Acid