Introduction
We have recently demonstrated that generalized convulsive seizures (GCS) induced by cholinergic stimulation of the thalamus provoke a focal post-seizures amygdaloallocortical neurovascular injury characterized by neuronal loss, microvascular TNFα and IL-1β expression and gliosis, followed by atrophy 1 . Here we report the temporal progression and spatial specificity of the seizures-induced neurovascular amygdaloallocortical injury.
Methods
Adult Wistar rats were injected stereotaxically with carbachol (55 nmol in 100nl PBS) under halothane anesthesia unilaterally in the ventroposterolateral and reticular thalamic nuclei as previously described 2 . Behavioral alterations were observed for 2 hours. After at least one episode of GCS, animals were sacrificed at 3 h (n=2), 6 h (n=3), 12 h (n=2), 24 h (n=3), and 72 h (n=3). Brain sections immunohistochemically processed for COX-2, TNFα and IL-1β staining were examined with a camera lucida. Edema and microhemorrhage sites were estimated on digital photographs of fresh frozen tissue using an image analyser.
Results
Three hours after the initial GCS, neuronal COX-2 induction was observed bilaterally throughout the brain. However, as compared to the contralateral side, the ipsilateral side was devoid of neuronal COX-2 expression in the insular and perirhinal cortices, in the amygdaloid complex including the basolateral, the posteromedial cortical amygdaloid nuclei and the amygdalohippocampal area. At approximately 6 h after the initial GCS, the TNF-α and Il-1β staining was clustered in the COX-2 devoid area including the rostral part of the amygdaloallocortical area, the claustrum and the dorsal endopiriform nucleus, the piriform cortex and the basolateral, central and medial amygdaloid nuclei, as well as in the internal capsule. Between 12 h and 24 h, Il-1β induction was also seen in microglia/macrophage-like cells throughout the allocortex and amygdala, particularly the insular cortex, the perirhinal cortex, the upper layer of the piriform cortex, the posteromedial, posterolateral cortical amygdaloid nuclei and the amygdalopiriform transition. Edema, seen as a gray area on fresh frozen tissue coronal sections, appeared at 24 h after the initial GCS along the rostro-caudal amygdaloallocortical axis and remained relatively unchanged up to 72 h. Rostrally to the anterior commissure, edema was observed in the insular cortex, the piriform cortex, the dorsal endopiriform nucleus and the claustrum representing 6±0.2% (n=5) of the total coronal surface area. Caudally, edema was observed in the perirhinal cortex, the basolateral and the centromedial amygdala, the anterior cortical amygdaloid nucleus and amygdalopiriform transition reaching 11±0.1% (n=5) of the total coronal surface area. Edema was associated with multifocal microhemorrhage scattered along the rostro-caudal amygdaloallocortical axis.
Conclusion
We conclude that generalized convulsive seizures elicited by cholinergic stimulation of the thalamus are at the origin of amygdaloallocortical microvascular inflammatory processes leading to edema and multifocal microhemorrhage. The spatial distribution of multifocal microhemorrhages was shown to correlate with microvascular and glial-like cells expressing TNF-α and IL-1β within the amygdaloallocortical area characterized by reduced and/or absent neuronal COX-2 expression.