Alterations in somatostatin and proenkephalin mRNA in response to a single amygdaloid stimulation versus kindling

Previous studies have shown changes in both somatostatin (SS)- and proenkephalin(PE)-derived peptides in the brains of amygdaloid-kindled rats, suggesting possible roles for the peptides in the kindling process. In this study, we have extended this analysis by looking at the time course of changes in SS and PE mRNAs at various times after kindling, in comparison with a single non-convulsive stimulation. Blot analysis of total RNA showed increases in SS mRNA in striatum, frontal cortex and hippocampus of animals receiving only a single stimulation as well as kindled animals--the increase occurred 1-3 days following stimulation and levels were back to basal by 1 week. PE mRNA did not change. In situ hybridization analysis, one day after the last kindling stimulation, showed significant elevations of SS mRNA in CA1, CA2 and dentate gyrus of hippocampus and of PE mRNA in olfactory cortex that were specific to kindling. However, both a single stimulation and kindling increased PE mRNA in olfactory tubercle and arcuate nucleus. In contrast, a single electrical stimulus increased PE mRNA in ventral striatum and SS mRNA in cingulate cortex and olfactory tubercle. These data support the idea that changes of SS mRNA in hippocampus and of PE mRNA in olfactory cortex may be related to kindling, and point out the importance of using animals which receive a single electrical stimulus, rather than sham-operated animals, as controls.