Degeneration of cholinergic basal forebrain nuclei after focally evoked status epilepticus
Status epilepticus (SE) of limbic onset might cause degenerative phenomena in different brain structures, and may be associated with chronic cognitive and EEG effects.
In the present study SE was evoked focally by microinfusing picomolar doses of cyclothiazide+bicuculline into the anterior extent of the piriform cortex (APC) in rats, the so-called area tempestas, an approach which allows to evaluate selectively the effects of seizure spreading through the natural anatomical circuitries up to secondary generalization.
In the brain of rats we analyzed neuronal density and expression of heat shock protein-70 in the piriform cortex, the hippocampus and thalamus.
We further analyzed in detail, the loss of cholinergic neurons, and the presence of FJB- and HSP-70 positive neurons in basal forebrain cholinergic areas, i.e. the medial septal nucleus (MSN, Ch1), the diagonal band of Broca (DBB, Ch2 and Ch3) and the Nucleus basalis of Meynert (NBM, Ch4). In fact, these nuclei are strictly connected with limbic structures, and play a key pivotal role in different cognitive functions and vigilance.
Although recent studies begun to investigate these nuclei in experimental epilepsy and in persons with epilepsy, conflicting results were obtained so far.
In parallel, these nuclei show also FJB and heat shock protein-70 expression. Those effects vary depending on the single nucleus assessed and on the severity of the SE seizure score. We also showed the occurrence of cell loss and degenerative phenomena in limbic cortex, hippocampus and limbic thalamic areas.
These novel findings show direct evidence of SE-induced neuronal damage which is solely due to seizure activity ruling out potential confounding effects produced by systemic pro-convulsant neurotoxins.
A damage to basal forebrain cholinergic nuclei, which may underlie cognitive alterations, is documented for the first time in a model of SE triggered focally.