DISSOCIATION BETWEEN MOSSY FIBER SPROUTING AND RAPID KINDLING WITH LOW-FREQUENCY STIMULATION OF THE AMYGDALA

In an attempt to determine whether sprouting of mossy fibers is invari ably correlated with kindling of seizures, we subjected rats to rapid kindling with long trains of low-frequency stimulation of the amygdala that resulted in development of generalized seizures within a mean of five stimulations. For comparison, we subjected other rats to convent ional kindling with short trains of high-frequency stimulation of the amygdala that resulted in development of generalized seizures within a mean of 13 stimulations. We found no evidence of mossy fiber sproutin g in the dentate gyrus of rats killed one day after completion of rapi d kindling, as compared to yoked controls, although significant sprout ing was seen in rats killed one day after completion of conventional k indling. When we examined tissue from rats killed 20 days after rapid kindling, however, we did find significant sprouting, suggesting that messy fiber sprouting can be triggered by rapid kindling if sufficient survival time is allowed. The observed disparity between completion o f rapid low-frequency kindling and detection of messy fiber sprouting suggests that messy fiber sprouting may be associated more with sustai ned survival time after neuronal activation than with kindling per se. Furthermore, the similar time course of conventional kindling and of messy fiber sprouting obscures the determination of a causal role of m essy fiber sprouting in conventional kindling. (C) 1998 Elsevier Scien ce B.V.