Characterization of pretentorial periaqueductal gray matter neurons mediating intraspecific defensive behaviors in the rat by microinjections of kainic acid.
Unilateral microinjections of 40 pmol of kainic acid (KA; in 0.2 microliter) within the periaqueductal gray matter (PAG) evoked intraspecific defensive postures (defensive uprights, defensive alterting, defensive sideways, backing) in rats confronted with a conspecific. These reactions, which lasted for up to 30 min, were seemingly identical to the rat's natural defensive reaction to attacks by a conspecific although they were evoked by the investigatory approach, rather than the attack, of another rat. Histological analysis revealed that the strongest defensive reactions were evoked from sites within a restricted part of the pretentorial periaqueductal gray matter. Lower doses of KA induced fewer (20 pmol) or non-significant increases (4 pmol) in defensive reactions. Higher doses (100 and 200 pmol) increased the percentage of defensive behavior and also induced oriented jumps out of the test cage. In tests with a conspecific, defensive reactions were elicited most frequently when investigation by the partner was localized to the side of the body contralateral to the injection site. This was confirmed in a sensory reactivity test in which tactile stimulation by the experimenter elicited most defensive reactions when applied on the side of the body contralateral to the injection side. This test also revealed a somatotopic gradient in the animal's reaction: tactile stimulation of the contralateral head and the forelimb evoked the strongest reactions, whereas no responses were observed upon tactile stimulation of the contralateral flank or hindlimb. Measurement of electroencephalographic activity at the cortical, hippocampal, amygdala and PAG levels indicated that the evoked defensive reactions were not secondary to epileptogenic effects. Finally, quantitative analysis of an autoradiographic study found that [3H]KA diffused within a diameter of 1.0-1.2 mm around the cannula tip. Taken together, these results indicate the existence of a population of neurons within a restricted part of the pretentorial PAG of the rat, the excitation of which produces defensive responses and demonstrate that these defensive reactions have a socially adaptive value.
Depaulis
A
A
Département de Neurophysiologie et Biologie des Comportements, Centre de Neurochimie CNRS/INSERM, Strasbourg, France.
Bandler
R
R
Vergnes
M
M
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001931:Brain Mapping; D004305:Dose-Response Relationship, Drug; D007839:Functional Laterality / Q000187:drug effects / Q000502:physiology; D007608:Kainic Acid / Q000494:pharmacology*; D008297:Male; D008845:Microinjections; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D007608:Kainic Acid