Chromogranin/secretogranins are a family of acidic, soluble proteins with a widespread distribution in secretory vesicles of endocrine and nervous tissues. The effects of experimental stimuli of differing duration and intensity on chromogranin B and secretogranin II mRNA levels in relevant areas of the rat brain were examined by in situ hybridization histochemistry using 35S-labelled oligonucleotides. Effects of two 'chronic stimulation' paradigms were studied - the effect of 4 days of water or food deprivation on mRNA levels in the hypothalamus and the effect of unilateral cervical vagotomy on transcript levels in the dorsal vagal complex 1, 2 and 7 days after surgery. After 4 days of water deprivation secretogranin II mRNA was significantly increased in supraoptic nucleus (366 +/- 21% of control, P < 0.01), the magnocellular paraventricular nucleus (209 +/- 20% of control, P < 0.01) and the parvocellular paraventricular nucleus (147 +/- 6% of control, P < 0. 05) after 4 days of food deprivation. Seven days after unilateral cervical vagotomy, secretogranin II and chromogranin B mRNA levels were markedly decreased in the ipsilateral dorsal motor nucleus of the vagus (25 +/- 4 and 47 +/- 8% of contralateral values respectively, P < 0.01). Rapid changes in chromogranin mRNA were also detected following shorter duration 'acute stimulation' - in the hypothalamus after hypertonic saline injection, in the hippocampus after electrical stimulation-induced kindled seizures, and in the cerebral cortex after unilateral craniotomy. A large increase in secretogranin II mRNA was detected in the supraoptic nucleus (202 +/- 25% of control, P < 0.01) and the magnocellular paraventricular nucleus (168 +/- 29% of control, P < 0.05) 3 h after a single intraperitoneal injection of hypertonic (1.8 M) saline. Markedly increased levels of secretogranin II (125-160% of control) and chromogranin B (140-230% of control) mRNA were observed in granule cells of the dentate gyrus 0.5-2 h after amygdaloid stimulation-induced seizures. A moderate increase in secretogranin II mRNA (144 +/- 11% of contralateral side, P < 0.01) was found in the underlying cerebral cortex 2.5 h after unilateral craniotomy. These results indicate that measurement of changes in chromogranin mRNA, particularly secretogranin II, is a useful means of assessing both rapid and long-lasting increases and decreases in neuronal activity and, in contrast to immediate early gene mRNA levels, may better reflect specific changes in neuronal secretory activity associated with transmitter/peptide release.