Differential sensitivity of various temporal lobe structures in the rat to kindling and status epilepticus induction

Using focal brain stimulation (kindling), discrete seizures can be triggered from many neuroanatomic sites with varying degrees of facility. From several of these sites, protracted seizures or status epilepticus (SE) also can be triggered. To date, no comparison has been made between different brain sites in their sensitivity both to kindling and to SE development. In this report, we have compared the kindling profiles of three amygdala nuclei, namely the basal (BL), central (CE), and medial (ME) nuclei, to the adjacent piriform (PIR) and perirhinal (PRH) cortices. In addition, three weeks following kindling, the susceptibility of each kindled site to status epilepticus (SE) was assessed by exposing the site to 60 min of electrical stimulation. We observed that (a) during the course of daily kindling, the afterdischarge threshold dropped progressively and significantly in all structures, (b) the rate of kindling in the PRH and PIR cortices and the CE amygdala was significantly faster than either the BL or ME amygdala, (c) when discrete convulsions were triggered, the latency to forelimb clonus in the PRH cortex and CE amygdala was significantly shorter than the other three structures, and (d) despite being slower to kindle than most other sites, stimulation of the BL nucleus most readily triggered SE. The kindling data suggest that discharges triggered from the PRH and CE more readily access motor systems supporting limbic convulsions than discharges triggered from the BL, ME nuclei or the PIR cortex. On the other hand, the SE data indicate that the mechanisms and circuits associated with the development of discrete kindled seizures are not identical to those associated with the induction of limbic SE.