Neurofilament expression in the rat brain after cerebral infarction: effect of age
Introduction
Brain injury leads to neuronal degeneration with loss of synaptic connectivity. In response, compensatory axonal sprouting in the surviving deafferented neurons [6] leads to the establishment of new synaptic contacts with other nerve cells [12]. In this context, cytoskeletal elements such as neurofilament proteins play an important role in the response of the brain to damage.
Neurofilaments (NFs) are neuron-specific intermediate filaments that are composed of three major subunits designated NF-L (68 kDa), NF-M (160 kDa) and NF-H (200 kDa). These neurofilament proteins are involved in multiple plasticity processes; NF-68 is expressed in axonal growth cones [13]. NF-M and NF-H are involved in the stabilization of newly-sprouted axonal processes [20], [28] while NF-H is thought to play an important role primarily in the stabilization and maturation of pre-existing connections [14], [16]. Neurofilament proteins, especially NF-160 and NF-200, are among the most phosphorylated proteins in the brain. Maybe the extent and localization of phosphorylation are involved in the distribution and biological functions of neurofilaments in neurons [8], [15].
The aim of the present study was to investigate the involvement of different phosphorylated NFs in the cerebral response to stroke in young and aged rats. We focused especially on the border zone, or penumbra, of the infarct because the persistence of viable neuronal elements in this region makes it an important site for potential therapeutic interventions. If protection is not achieved in the penumbra, the neurons there will die and become part of the infarct core [24].
Most experimental studies on cerebral ischemia have been performed with young animals, whereas in humans, stroke occurs mainly in the elderly. Consequently, there is little information on whether the cytoskeletal response to ischemia differs between young and old subjects. We found previously that the response of microtubule-associated proteins to stroke is blunted in aged animals [19]. We therefore hypothesized that neurofilament expression would be similarly attenuated in aged animals. To that end, we examined the effects of aging on the response of neurofilaments to focal brain ischemia in rats.
Section snippets
Materials and methods
Eighteen hours prior to surgery, male Sprague–Dawley rats (n=12 for 3-month-old rats, weighing 300–360 g, and n=11 for 20-month-old rats, weighing 440–480 g) were deprived of food to minimize variability in ischemic damage that can result from varying plasma glucose levels [11]. Water remained available ad libitum. In all cases, surgery was performed between 8:00 and 13:00 h.
The experiments reported in this study were conducted in accordance with the statement regarding the care and use of
Results
There was no apparent difference in the clinical status of young and aged rats during the 7-day post-surgical survival time. One 3-month-old rat and two 20-month-old rats died in the first 24 h after MCA occlusion. At the time of perfusion, one young (3 months) and one old (20 months) animal had pronounced inflammation at the infarct site. All of these animals were excluded from further evaluation.
Although some blood parameters showed some age-associated variation, notably blood pressure, the
Discussion
The results of this study show that NF-mRNA synthesis is significantly increased in the penumbra of old and young rats following temporary, 3 h occlusion of the middle cerebral artery. The infarct-induced upregulation of NF-mRNA was significantly greater in young animals than in old animals. Our data thus indicate that neurofilament protein biosynthesis is augmented in reaction to the inflicted trauma, similar to the upregulation of NF-mRNA seen in the peripheral nervous system following axotomy
Acknowledgements
We extend our thanks to Lary C. Walker for many enlightening discussions and critical review of the manuscript. This research was supported by a grant from the Deutsche Forschungsgemeinschaft (DFG) [Ke 599/1-1].
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