2. Amygdala kindled seizures in suspend rats: A reanalysis

Abstract

Background There has been a controversy concerning the motor substrate for kindled convulsions. Dr. Daniel McIntyre of Carlton University has argued that kindled motor seizures are driven from the anterior (motor) neocortex in rats, whereas our group at the University of Toronto has argued that they are driven from the brain-stem core. Neocortical convulsions in rats tend to be clonic in nature, whereas brain-stem convulsions can be either clonic or tonic. Methods Adult, male, Long–Evans rats were suspended in harnesses that allowed visualization of both fore- and hindlimbs. The development of their motor seizures was videotaped as subjects were kindled from the right basolateral amygdala. The question was whether the developing motor seizures would resemble the convulsions triggered from the neocortex or the convulsions triggered from the brain stem. Results All subjects developed motor seizures as a result of daily, low level electrical stimulation of the right amygdala. As previously reported, motor seizures did not develop incrementally, but rather evolved in a stepwise manner - as if separate motor substrates were being recruited. Early in development, motor seizures largely involved face and forelimb clonus, which resembled a “cortical” pattern. Later in kindling, motor seizures developed tonic elements, including forelimb tonic extensions, which resembled a “brain-stem” pattern. Of interest, the clonic convulsions seen early in stimulation were accompanied by stiffening of the body and hindlimbs – which did not resemble a typical tonic hindlimb extension. This stiffening – of unknown substrate – seems to correspond to the “rearing” seen in “Stage 3–5” kindled seizures. Conclusions As they develop, kindled convulsions display elements that resemble both cortical and brain-stem convulsive behavior. Future experiments might use pharmacological tools to investigate the drug response of these convulsions. Kindled convulsions, however, also contain an element of body stiffening (rearing?) which is not traditionally associated with either cortical or brain-stem convulsions.