Yonago Acta medica

Abbreviations: AD, after-discharge; ADD, AD duration; ADT, AD threshold; PS, primary site; PTE, positive transfer effect; SS, secondary site Kindling is the progression of behavioral and electrographical seizure induced by repeated activation of neural pathways with initial subclinical stimulations (Goddard et al., 1969). Once kindling is established, the kindling effect is sustained for a long period without electrical stimulations. In addition, after the establishment of kindling at one site in the brain (primary site, PS), a significantly lower number of stimulations can induce kindling at another site (secondary site, SS), called the “positive transfer effect” (PTE) (Goddard et al., 1969; Racine, 1972; Cain, 1985). These data suggest that the separate secondary epileptic foci can be created with minor stimuli in comparison to the original stimuli required for the induction of the 1st focus. We previously reported that young rats developed amygdaloid kindling with a smaller number of stimulations and had a higher susceptibility than adult rats (Matsuda et al., 1993, 1995). Difference of the PTE between young and adult brains may add the deeper understanding on the age dependency of kindling induction in rat brains, but only reports on 16-day-old rats (Kawawaki et al., 1987) and 20-dayold rats (Chiba et al., 1994) are available to date. No reports are available on the PTE in the younger rats. To shed a light on a working hypothesis that the young rat brain is more susceptible to kindling, we investigated the PTE in rats at various ages, including those before weaning.