Rapid dephosphorylation of microtubule‐associated protein 2 in the rat brain hippocampus after pentylenetetrazole‐induced seizures

Abstract

We have studied the effect of Pentylenetetrazole (PTZ)-induced seizures on the state of phosphorylation of microtubule-associated protein 2 (MAP-2) from rat hippocampus. A method for the in vivo 32P-labeling of hippocampal proteins has been established, consisting of intracerebro-ventricular injection of "PO, of high specific activity. The results obtained indicate that PTZ induces a rapid and transient dephosphorylation of high-molecular-mass MAP-2, which is prevented when the Nmethyl+-aspartate receptor antagonist MK-801 is previously administered. Phosphopeptide mapping of 32P-labeled MAP-2 obtained from hippocampi of PTZ-treated rats reveals a pattern of phosphorylation distinct from that obtained from control saline-treated rats or MK-801 plus PTZ treated rats. We discuss the possible implications of N-methyl-D-aspartate-receptor activation and MAP-2 dephosphorylation on the plastic changes induced in rat brain hippocampus after induced epileptiform activity.It has been long recognized that experimental paradigms such as kindling or chemically induced seizures profoundly alter the pattern of synaptic connectivity within the limbic system [l -41. The hippocampal formation constitutes a clear target for the plastic changes associated with sustained stimulation of limbic pathways and development of generalized convulsions. There have been reported alterations in the content and release of different neurotransmitters [5 -81, the expression of a variety of neuropeptides [9-131, neurotrophic factors [14-161 and the activity of several enzymes [17-211 after experimentally induced seizures. In the longer term, morphological alterations such as aberrant axon sprouting and de novo formation of synaptic contacts appear [22-261. The alterations in neuronal morphology have to be based on changes in the neuronal cytoskeleton, which is responsible for the initiation and stabilization of the new fibers and synaptic contacts. In this respect, modifications on microtubuleassociated protein 2 (MAP-2) may play a role in such changes 1271. These modifications could include phosphorylation-dephosphorylation since this mechanism has been implicated in neural transmission [28]. High-molecular-mass MAP-2 is a neuron-specific protein which promotes the assembly of microtubules in v i m , localizes in the dendritic compartment of the neuron and is also present in the dendritic spines [ suggested that the phosphorylation state of MAP-2 is related to its ability to promote microtubule assembly [36, 371. More recently, it has been indicated that activation of N-methyl-Daspartate receptors induces a rapid dephosphorylation of MAP-2 in hippocampal slices [38].Pentylenetetrazole (PTZ) is a drug with potent convulsant effects. Its effects seem to be mediated by inhibition of 4-aminobutyric-acid-A receptors, since PTZ has been shown to block 4-aminobutyric-acid-dependent chloride influx [39]. Intraperitoneally (ip) administered PTZ quickly evokes the appearance of strong seizures which are accompanied by a dramatic increase in the express...

Biomarkers Improve Clinical Outcome Predictors of Mortality Following Non-Penetrating Severe Traumatic Brain Injury

“…MAP-2 is a relatively novel biomarker in human TBI and is a major component of cytoskeleton family proteins. It is localized predominantly in dendrites and is associated with promoting microtubule assembly and stability [49,50]. It has been shown to be altered following TBI in animal models and is associated with dendritic damage [51,52].…”

Early Changes in MAP2 Protein in the Rat Hippocampus Following Soman Intoxication

“…The authors suggest that the quantitative loss of this sensitive neuron-specific protein is, likewise to other neuropathologies, [20][21][22][23][24][25][26][27][28] a reliable marker of seizure-induced neuronal necrosis. Conversely, our present biochemical approach supports the hypothesis that, as soon as the first hour of seizure activity, the intrahippocampal content of MAP2 increases dramatically.…”

“…The intracerebroventricular injection of 32 PO 4 was performed as previously described. [26,27] Briefly, about 0.5 mCi 32 PO 4 (9.1 mCi/mmol, Amersham) was microinjected (1 mL; 0.5 mL/min) in the right cerebral ventricle (stereotaxic coordinates from bregma: AP À0.9 mm; L À1.6 mm; DV À4.5 mm). After surgery, animals were kept for three days in a plexiglas cage especially designed to shield radiation to the outside.…”

“…The protein extraction protocol has been previously described. [26,27] Briefly, the homogenates from frozen hippocampi were boiled for 5 min and centrifuged at 100,000 g for 60 min (4 C). Supernatants were used as a source of MAP2 protein for SDS/PAGE.…”

“…[17][18][19] Finally, MAP2 is considered as a sensitive marker of neuronal damage in various pathophysiological states [20][21][22][23][24][25] including epileptic seizures. [26][27][28][29][30] Therefore, we carried out a biochemical study in order to measure the both hippocampal content of MAP2 and its phosphorylation degree during the first 90 min of soman-elicited seizures, i.e., during the previously described period of dendritic spine regression and glutamatergic receptor overstimulation.…”