Conditioning method determines patterns of c-fos expression following novel taste-illness pairing.

Conditioned taste aversions (CTAs) can be established by exposing rats to a novel taste CS through a bottle or through intra-oral (IO) infusion. Lesion studies suggest differences between the two methods in their engagement of brain circuits, as excitotoxic amygdala lesions have no effect on bottle-conditioned CTAs, but eliminate CTAs produced using IO infusion. Fos-like immunoreactivity (FLI) was used to compare patterns of brain activation after pairing CS taste and US drug using bottle and IO methods. Conditioning rats using the bottle method was associated with widespread elevations in FLI throughout the putative CTA circuit (basolateral and central nuclei of amygdala, insular cortex and nucleus of the solitary tract). In contrast, IO conditioning led to activation only in the central nucleus of amygdala. This supports the suggestion of differences in aversion processing as a function of conditioning method and may explain the greater reliance on amygdala of IO-conditioned CTAs due to engagement of a less distributed neural network.

Losartan blocks drinking and cFos expression induced by central ornithine vasotocin in rats.

We previously reported that an intracerebroventricular (icv) injection of the oxytocin receptor antagonist ornithine vasotocin (OVT) caused water and saline intakes, a pressor response, and Fos-like immunoreactivity (Fos-IR) in the median preoptic nucleus of the rat brain. In the present report, rats receiving an icv injection of isotonic saline vehicle followed by an icv injection of 10 microg of OVT 20 min later drank 5.5+/-1.1 ml of total water and saline intake in 60 min after the OVT; rats receiving 10 microg of losartan before the OVT drank only 0.9+/-0.3 ml of total fluid. In a separate study, rats were treated as above except that they were not allowed to drink and were perfused for analysis of Fos-IR in the median preoptic nucleus at 90 min. Fos-IR in the dorsal part of the median preoptic nucleus was significantly suppressed from 2.69+/-0.57 cells per 10,000 square mum in vehicle-treated rats to 0.89+/-0.20 in losartan-treated rats. Losartan alone had no effect on Fos-IR. Losartan did not reduce intake of saccharin in a dessert test. This suggests that the OVT-induced drinking may result from an activation or disinhibition of angiotensin type AT1 receptors in the median preoptic nucleus.

Novel tastes elevate c-fos expression in the central amygdala and insular cortex: implication for taste aversion learning.

Taste novelty strongly modulates the speed and strength of taste aversion conditioning. To identify molecular signals responsive to novel tastes, immunostaining for c-fos protein (Fos-like immunoreactivity [FLI]) was used to mark neurons that responded differentially to taste novelty. Novel saccharin induced larger increases in FLI than familiar saccharin. This pattern was seen in central amygdala and insular cortex, but not in basolateral amygdala, parabrachial nucleus, or nucleus of the solitary tract. Other parameters known to influence aversion learning were tested for effects on FLI. Manipulations known to reduce the strength of learning blunted the FLI response, supporting the idea that FLI marks neural pathways critical to taste processing during acquisition, and that c-fos expression is a key transcriptional event underlying this plasticity.