Background and purpose
Domoic acid (DA), a potent neurotoxin, is structurally related to glutamate analogue kainic acid, called excitotoxins. Administration of DA evokes seizures accompanied by neuronal damage especially in the CA3 hippocampal area. The hippocampus has an important role for memory and learning. Therefore, the injury of this hippocampal area causes memory and learning disturbunce, resulting dementia. In the present study, we examined neuronal damage and neurogenesis following administration of DA in the hippocampus in rats.
Methods
Adult male Wistar rats (6 week) were treated intraperitoneally with DA at dose of 3.5 mg/kg. Rats were perfused with 4% paraformaldehyde and decapitated at 48, 72 hours for TUNEL staining, and at 7 days for HE staining after DA injection. On the regeneration study, BrdU was intraperitoneally administered 24, 48 hours and weekly after DA injection (3.5 mg/kg). 10 weeks after DA injection, rats were sacrificed for BrdU immunohistochemical staining. Double labelling for Neu N, GFAP, MAP2 were also performed.
Results
DA can more easily transfuse through the blood-brain barrier than glutamate. Several peculiar behavioral effects such as epileptic seizures, scratching and autophagia were observed after DA injection. On the histological study, the most extensive damage was observed in the CA3 area of the hippocampus (approximately 60–80%). In the other regions of hippocampus, lesser damage were observed at 7 days postinjection (CA4>CA1>CA2>DG). TUNEL positive cells were observed throughout the hippocampus, especially in the DA area. The distribution of BrdU positive cells was not correlated to the degree of neuronal damage. The BrdU positive cell proliferation was marked in the dentate gyrus subgranular layer. Double staining for NeuN, a marker for mature nerve cells, and BrdU labelling showed that some newly born cells changed to mature neuron. Double staining for GFAP, a marker for glial cells, and BrdU labelling was also observed in the same regions.
Conclusions
The most extensive neuronal damage was observed in the CA3, with lesser damage observed in the other regions (CA4>CA1>CA2>DG) on the HE stained sections at 7 days after DA injection. TUNEL positive cells did not proceed parallel with neuronal loss. The distribution of the BrdU positive cells were most abundant in dentate gyrus subgranular layer and not correlated to the degree of the neuronal damage.