Changes in Neurofilament Protein NF‐L and NF‐H Immunoreactivity Following Kainic Acid‐Induced Seizures

Abstract

Postlesion plasticity of neuronal processes might contribute to secondary spontaneous seizures after kainic acid administration . In this study, neurofilament (NF) proteins were examined following intraperitoneal injection of kainic acid, and special reference was given to temporal changes in quantity and quality of the NF light (NF-L) and heavy {NF-H) subunits . A pronounced decrease in phosphorylation-related immunoreactivity of NF-H occurred as early as 1 day after the injection in the amygdala/pyriform cortex, hippocampus, striatum, and dorsal cerebral cortex . A shift of NF-H from the phosphorylated to nonphosphorylated form was evident in immunoblots, suggesting dephosphorylation contributed to the decrease . Decreases in NF-L and phosphorylated NF-H contents in the limbic structure at 3 days were correlated with the increasing kainic acid doses from 2 .5 to 10 mg/kg . The degradation pattern in immunoblots with antibodies against NF-L indicated that the decrease in NF-L was probably due to calcium-activated proteolysis . NF-L and phosphorylated NF-H contents secondarily increased from 9 days onward, with~20% above the control level of phosphorylated NF-H immunoreactivity at 27 days in the amygdala/pyriform cortex and ventral hippocampus . Immunohistochemical examination of the hippocampus revealed that an increase of NF staining in the mossy fiber system may contribute to the NF recovery in this region . Furthermore, the temporal changes of NF-L and phosphorylated NF-H contents were positively correlated with those of the neuronal cell adhesion molecule, a neuritic growth cone marker, substantiating postlesion regenerative reactions of NF proteins . Functional consequences of the NF plasticity remain to be identified .

Activity-Dependent Plasticity in the Adult Auditory Brainstem

“…Again, the phosphorylation state of neurofilament subunits is a major regulatory variable. Following kainic acid-induced lesions, a pronounced dephosphorylation of the neurofilament heavy chain and a decrease in NF-L have been reported [Wang et al, 1994;Vaidya et al, 2000].…”

“…Apart from its role in the mechanical stabilization of neuronal morphology, it may also be involved in the regulation of plastic changes that neurons may undergo in development or even in the adult brain. The NF-L has been implicated in axonal sprouting in the adult brain [Wang et al, 1994;Vaidya et al, 2000]. A genetically induced NF-L deficiency in mice leads to a decline of other neurofilaments as well; at the same time, levels of tubulin and GAP-43 rise in neurons of such animals [Zhu et al, 1997a].…”

Differential expression and localization of the phosphorylated and nonphosphorylated neurofilaments during the early postnatal development of rat hippocampus

“…Consequently, it has been suggested that the phosphorylation of NF-L could be associated with the induction and/or maintenance of neuronal plasticity during the long term potentiation. In pathological situations, such as ischemia (Nakamura et al, 1992;Kaku et al, 1993), kainic acid-induced seizures (Wang et al, 1994;Yang et al, 1995), and traumatic brain injury (Posmantur et al, 2000), phosphorylation/dephosphorylation is thought to be one early sign of cellular damage, the changes in the dendrites preceding those in the axons (Posmantur et al, 2000). Further studies using several different antibodies, which detects various phosphoepitopes will be needed to clarify the role of phosphorylation in the stability of NF proteins.…”

“…NF proteins, in particular NF-M and NF-H, are phosphorylated extensively, with highly conserved phosphorylation sites (Julien and Mushynski, 1983;Carden et al, 1985;Schlaepfer, 1987). It is suggested that the phosphorylation plays an important role in stabilizing and continuously remodeling NF filaments during the axonal growth and might be connected to plasticity of both axons and dendrites (Schlaepfer, 1987;Wang et al, 1994;Hashimoto et al, 2000;Posmantur et al, 2000).…”

“…The pyramidal CA1-CA3 neurons are formed during the embryonic period of ϳ14 -20, whereas granule cells in the dentate gyrus (DG) mainly proliferate postnatally, with the proliferation largely completed within the first 3 postnatal weeks (Schlessinger et al, 1975;Bayer, 1985). Temporal differences in the neurogenesis, together with the observed cellular heterogeneity of NF expression in the immature hippocampus both in vivo (Shetty and Turner, 1995) and in vitro (Holopainen et al, 2001), could be of importance in determining the neuronal reactivity in pathological situations, as shown in adult rats after ischemia (Nakamura et al, 1992), kainic acid-induced seizures (Wang et al, 1994), and traumatic brain injury (Posmantur et al, 2000).…”