Kainic acid-induced seizures in aged rats: neurochemical correlates

This study was conducted to assess the functional integrity of the kainate receptor-mediated seizure response in aged rats. Kainic acid was administered systemically to aged female Long-Evans (LE) rats and aged male F344 rats and the proconvulsant actions of kainic acid was compared to adult controls. The effects of kainic acid on brain regional content of monoamines and amino acids was also determined in the aged female LE and adult control rats. The latency to full clonic-tonic seizures was significantly reduced in aged female LE rats, and the number of seizures was significantly increased above that of the controls. There was increased mortality and a reduction in the latency to exhibit wet dog shakes in the aged F344 rats. Studies were also conducted to evaluate the role of ovarian hormones, route of administration, and dose of kainic acid in mediating the enhanced proconvulsant actions of kainic acid in aged rats. The neurochemical studies suggested that kainic acid significantly enhanced the release of ASP, GLU, and norepinephrine (NE) in the aged rats exhibiting clonic-tonic seizures. The adult rats given the same dose of kainic acid (15 mg/kg, IP) did not exhibit any significant change in brain content of monoamines or amino acids except for a reduction in mediobasal hypothalamic NE. An in vitro study was also conducted using brain slices from adult and aged F344 and it was found that aged rats released significantly more ASP than adults in response to kainic acid. These neurochemical findings were discussed in relation to previous studies of age-related alterations in excitatory amino acids (EAAs) and the role of EAA and NE in modulating limbic seizures. This study has clearly demonstrated that aged rats may be more susceptible to the excitotoxic action of EEAs acting through kainetic receptors.