Growth-associated phosphoprotein expression is increased in the supragranular regions of the dentate gyrus following pilocarpine-induced seizures in rats.

Neuroplasticity has been investigated considering the neuronal growth-associated phosphoprotein as a marker of neuronal adaptive capabilities. In the present work, studying the hippocampal reorganization observed in the epilepsy model induced by pilocarpine, we carried out quantitative western blotting associated with immunohistochemistry to determine the distribution of growth-associated phosphoprotein in the hippocampus of rats in acute, silent and chronic periods of this epilepsy model. The fibers and punctate elements from the inner molecular layer of the dentate gyrus were strongly immunostained in animals killed 5 h after status epilepticus, compared with the same region in control animals. Rats presenting partial seizures showed no alterations in the immunostaining pattern compared with saline-treated animals. The hippocampal dentate gyrus of animals during the seizure-free period and presenting spontaneous recurrent seizures was also characterized by strong growth-associated phosphoprotein immunostaining of fibers and punctate elements in the inner molecular layer, contrasting with the control group. As determined by western blotting analysis, growth-associated phosphoprotein levels increased following status epilepticus and remained elevated at the later time-points, both during the silent period and during the period of chronic recurring seizures. Pilocarpine-treated animals, which did not develop status epilepticus, showed no change in growth-associated phosphoprotein levels, indicating that status epilepticus is important to induce growth-associated phosphoprotein overexpression. The measurement of this overexpression could represent one of the early signals of hippocampal reorganization due to status epilepticus-induced damage.

Mitogen-activated protein kinase is increased in the limbic structures of the rat brain during the early stages of status epilepticus.

Systemic administration of pilocarpine (PILO) in adult rat produces acute limbic seizures leading to status epilepticus. Recent studies have shown the activation of mitogen-activated protein kinase (MAPK) cascades during experimentally induced seizures. MAPK activation may be triggered by glutamatergic stimulation and may play a key role in signal transduction pathways. In the present study, immunocytochemistry was used to analyze the spatiotemporal distribution pattern of the MAPK protein and its active form (A-MAPK) following PILO-induced status epilepticus. MAPK and A-MAPK immunoreactivities exhibited different patterns of distribution in the brain of normal and epileptic rats. The saline-treated rats, as well as the animals that received PILO but did not evolve to status epilepticus, showed a weak but selective MAPK immunoreactivity, detected in the hippocampal pyramidal neurons, dentate gyrus, hilus, CA3, CA1, and entorhinal, piriform, and cingulate cortices. A-MAPK immunoreactivity was instead observed only in neurites of the CA3 and hilus and in cells of the entorhinal and piriform cortices. In PILO-treated rats, between 30 and 60 min after status epilepticus there was an increase of the immunoreactivity to both antibodies, which were differently distributed throughout several structures of the limbic system. The immunostaining showed a slight decrease after 5 h of status epilepticus. However, MAPK and A-MAPK immunopositivities decreased markedly after 12 h of status epilepticus, returning almost to the basal expression. These findings are consistent with a spatial and time-dependent MAPK expression in selected limbic structures, and its activation could represent an initial trigger for neuronal modifications that may take part in the mechanism underlying acute epileptogenesis and in long-lasting neuropathological changes of the PILO model of epilepsy.

Tyrosine phosphorylation is increased in the rat hippocampus during the status epilepticus induced by pilocarpine.

Phosphorylation of tyrosine residue in proteins is an important modulatory process for membrane transduction and cell signaling and for several cellular functions. The concentration and distribution of phosphotyrosine proteins were analyzed in the hippocampi of rats in the model of epilepsy induced by pilocarpine using Western blotting and immunohistochemistry. The concentration of several phosphotyrosine proteins increased during status epilepticus. During the seizure-free period and the chronic period of this epilepsy model, the hippocampi of rats did not exhibit changes in the expression of these proteins. Immunohistochemistry showed an increased immunoreactivity throughout the hippocampal formation of rats 1 h after status epilepticus that was acutely induced by pilocarpine. Animals killed after 3 h of status epilepticus showed an increased expression of phosphotyrosine in the hippocampal hilus and CA3 regions. After 5 h of status epilepticus, phosphotyrosine immunoreactivity persisted only in the CA3 region. After 12 h of status epilepticus, the hippocampal formation exhibited a normal phosphotyrosine immunostaining, showing that the increased expression of these proteins is related to the acute phase and that several intracellular events could undergo modifications during the status epilepticus induced by pilocarpine.

Neuromodulin (GAP-43): a protein related to chronic diseases

The important of a large number of proteins involved in chronic diseases has been reported. In the present study the phosphoprotein GAP-43 was focused due to its relationship with chronic diseases such as epilepsy Alzheimer's disease, cerebral ischemia and phusiological events like long-term potentiation (LTP).