Transient expression of GAP-43 within the hippocampus after global brain ischemia in rat

Abstract

Neuroanatomical methods have been used to study selective vulnerability after global brain ischemia. A consistent pattern of ischemic neuronal damage is found in the rodent hippocampus with loss of CA1 neurons and of some cells in the hilus of the dentate gyrus. Very little is known about plastic changes that would be expected in ischemia-resistant areas such as CA3 neurons and granule cells. Neuronal plasticity after lesions may be indicated by changes in labeling with antibodies to the growth-associated protein 43 (GAP-43). Expression of GAP-43 as a marker for neuronal plasticity was studied here in the hippocampus after global brain ischemia. Halothane-anesthetized rats were subjected to 20 min of transient forebrain ischemia using four-vessel occlusion. In situ hybridization was used to study GAP-43 mRNA at 1, 3, 6, and 12 h and at 1, 3, and 7 days after ischemia. Immunostaining was carried out with two different antibodies to GAP-43 in brains which were perfusion-fixed after 1, 2, 4, and 7/8 days. In the control hippocampus, GAP-43 mRNA was localized to CA1-CA3 and the hilus. Moderate increases in cellular signals were seen in hilar cells and granule cells early after ischemia, and some changes occurred in CA3 at late stages. Hybridization was lost in CA1 due to cell death. With immunostaining, GAP-43 was not seen in the cytoplasm of neurons, whereas dense labeling occurred in a differentiated pattern in the axonal and dendritic layers. At 1 day after ischemia, neurons in the hilus of the dentate gyrus and in the stratum pyramidale and lucidum of CA3 showed strong cytoplasmic labeling for GAP-43. Few cells were labeled in these regions at 2 days, and none at later stages. Pyramidal cells in CA1 and CA3 areas and granule cells were never labeled. These studies demonstrate a transient expression of GAP-43 mRNA and protein in a subset of vulnerable neurons after transient brain ischemia. The cytoplasmic localization in hilar neurons could be due to increased synthesis of GAP-43 or to changes in axoplasmic transport. It is suggested that axonal damage occurs in hilar cells which stimulates GAP-43 expression. The increased production of trophic factors after ischemia in granule cells could also cause plastic changes in hilar cells. Since hilar neurons are in a strategic position to control the excitability of the dentate area, increased expression of GAP-43 may indicate an important pathophysiological process. In seizure experiments, strong expression of GAP-43 mRNA in granule cells was associated with abnormal mossy fiber sprouting and development of chronic epilepsy. The relevance of the minor GAP-43 mRNA upregulation after ischemia must be considered. The changes in CA3 neurons at several days after ischemia might represent a plastic response to a loss of CA1 neurons.

Calpains and neuronal damage in the ischemic brain: The swiss knife in synaptic injury

“…Conversely, an upregulation of GAP-43 was observed in different models of brain ischemia: (i) in spontaneously hypertensive rats 1 week after permanent occlusion of the distal middle cerebral artery and ipsilateral common carotid artery (Stroemer et al, 1993); (ii) in transient MCAO in rats (which upregulated the expression of both GAP-43 mRNA and protein levels in the ischemic penumbra, when determined 2 and 14 days after injury) ; (iii) in transient global brain ischemia (which induced a modest increase in GAP-43 mRNA and protein levels in different regions of the hippocampus) (Schmidt-Kastner et al, 1997). The effect of MCAO on GAP-43 protein levels is mediated by activation of NMDAR (Luque et al, 2001).…”

Developmental changes of synaptic proteins expression within the hippocampal formation of the rat

“…Neurons with a potential to respond quickly to the synthesis and activation of GAP-43 are known to be vital for synaptic modifications, as has been observed in seizure experiments that have been used as a memory process model (Sutula et al 1988;Davenport et al 1990;Meberg and Routtenberg 1991;Meberg et al 1993;Bendotti et al 1994;Meberg et al 1996;Schmidt-Kastner et al 1997;Sutula et al 1998).…”

Ischemic Cerebral Damage

“…60 Selective structural damage of presynaptic components as a result of transient focal ischemia has been shown in a few studies and comprises isolated loss of synaptic buttons 61 and a decreased density of presynaptic projections. 62 Elevated levels of proteins involved in synaptogenesis, such as growthassociated protein 63,64 or synaptophysin, 65 and an increase in the density of dendritic spines within hours to days after brief ischemia 62,66,67 suggest efforts to normalize these structural changes. However, complete functional recovery is mostly not achieved.…”