Drebrin A expression is altered after pilocarpine‐induced seizures: Time course of changes is consistent for a role in the integrity and stability of dendritic spines of hippocampal granule cells

Abstract

We used a pathophysiological model of temporal lobe epilepsy induced by pilocarpine in adult rats in order to assess the in vivo role of drebrin A (DA), one of the major regulators of F-actin. This model displays a dynamic reorganization of the glutamatergic network including neo-spinogenesis, morphogenesis, and neo-synaptogenesis associated with an aberrant sprouting of granule cell axons in the dentate gyrus (DG). This reactive plasticity contributes in dentate granule-cell hyperexcitability that could lead to the emergence of recurrent spontaneous seizures. We investigated the hippocampal DA expression changes in pilocarpine animals using immunohistochemical, Western blot, and in situ hybridization analyses. We showed that DA immunoreactivity was decreased in the inner molecular layer (IML) and in the hilus (H) of the DG, at latent stage, when spinogenesis and morphogenesis occur. Western blot analysis confirmed these overall hippocampal decreases of DA protein expression. At chronic stage, when newly formed glutamatergic synapses are being established, the levels of immunolabeling for DA in the H and the IML were similar to control rats. This recovery is likely due to the increase of DA mRNA in perikarya of hilar and granule cells. Interestingly, our data showed that the changes pattern of labeling for Bassoon, a specific marker for presynaptic active zone, in the IML of pilocarpine-treated animals paralleled those found for DA at all time points examined. Furthermore, our double and triple immunofluorescence studies showed that the recovery in DA levels in the IML occurred within the dendritic spines involved in glutamatergic active synapses of presumed granule cells. Altogether, our results indicate that in vivo DA is not critical for spinogenesis and morphogenesis but instead is consistent with an involvement in synaptic structural integrity, stabilization, and function. Thus, DA appears as a novel modulator of reactive synaptic plasticity associated with epilepsy.

Potential Role of Drebrin A, an F-Actin Binding Protein, in Reactive Synaptic Plasticity after Pilocarpine-Induced Seizures: Functional Implications in Epilepsy

“…Several other experimental paradigms such as entorhinal cortex lesion or hippocampal deafferentation with severe loss of presynaptic input cause alterations of postsynaptic target structures, including a loss of dendritic spines [68–71]. According to our results, one of the effects of this deinnervation is a significant decrease in the immunolabeling of Bassoon, a specific marker of presynaptic active zones, in the IML 1-2 weeks after pilocarpine treatment [39]. The subsequent recovery of Bassoon immunolabeling in the IML 12 weeks after pilocarpine treatment is likely due to the formation of aberrant sprouting of mossy fibers after status epilepticus [47, 56, 57], which has been shown to be involved in the establishment of functional excitatory synaptic boutons on granule cell dendrites [57, 72, 73].…”

“…The adult isoform of drebrin, drebrin A (DA), a major neuron-specific binding protein of F-actin, emerges as a convincing candidate protein for providing particular characteristics to the actin cytoskeleton of dendritic spines [32–35]. DA is specifically and highly enriched in dendritic spines of mature neurons [36–39] and is shown to inhibit the actin-binding activity of tropomyosin, fascin and α -actinin [40, 41]. In vitro , DA also blocks the interaction between actin and myosin [36, 42], indicating that it modulates actin filament contractility.…”

“…Altogether, these data indicate that in pilocarpine-induced seizures, DA is not critical for spinogenesis and morphogenesis but is rather involved in the structural integrity and stabilization of dendritic spines of hippocampal granule cells. This likely occurs via regulation of the actin cytoskeleton dynamics, and glutamatergic synaptic function that underlies the development of recurrent spontaneous seizures described in the pilocarpine model [39]. …”

“…H: hilus; IML: inner molecular layer; P : probability, NS: not significant. Modified with permission from [39]. …”

Changes in interictal spike features precede the onset of temporal lobe epilepsy

“…In experimental models, ILA precedes by several days the occurrence of SZ1,6, 9–11 and heralds epileptogenesis and the chronic phase of the disease 3, 11, 12. ILA frequency and shape change during epileptogenesis, in keeping with the concurrent modifications within the γ‐aminobutyric acidergic (GABAergic) and glutamatergic circuitry, as predicted by modeling studies 6, 8, 11, 12, 13–16. The impact and function of ILA are still unclear, as both antiepileptic and proepileptic actions have been proposed 17, 18.…”