In order to adapt to their environment animals need to anticipate when and to what extent food will be available. Using c-Fos-like immunoreactivity (Fos-ir) we have previously shown that a variety of rat brain regions are activated before and during access to bland food under a restricted feeding schedule. Here we conditioned rats to expect a palatable food reward in addition to their normal bland food. We mapped neural activity using Fos-ir in two experimental groups – a group that received the expected reward and one that did not. Two groups of adult male Sprague Dawley rats were conditioned to expect daily restricted access to a palatable food reward. The temporary removal of normal food and water 30 min prior acted as a cue for the reward. Rats had access to the reward for 30 min then bland food and water was replaced 30 min after the reward was removed. This protocol was repeated daily for 10 days. On the 11th day, group 1 received the expected reward and group 2 did not. 60 min after receipt or non-receipt of the reward, the rats were anaesthetised (sodium pentobarbitol, 400mg/kg ip) and perfused transcardially with histological fixative. Brains were removed, post-fixed, sectioned and processed for identification of Fos-ir. In the expectation-receipt group, Fos-ir was observed in brain regions involved in the control of food intake, reward and spatial memory. Fos-ir was observed in the hypothalamus, specifically in the supraoptic nucleus (SON), the arcuate nucleus, the lateral hypothalamus and the ventromedial hypothalamus, but not the paraventricular nucleus (PVN). In regions associated with reward detection and processing, Fos-ir was observed in the substantia nigra, the nucleus accumbens, the medial forebrain bundle, the Islands of Calleja, olfactory tubercle and the medial amygdala. In regions associated with memory, Fos-ir was observed in the mammillary bodies and the dentate gyrus. In rats expecting but not receiving the reward the distribution of Fos-ir was similar to that observed in rats receiving the reward. However, in the SON and mammillary bodies of these rats there was a trend to a reduction in Fos-ir compared to rats that received the expected reward (SON: 26.9±13.8 v. 4.8±3.3 Fos-ir cells/section, p = 0.16; mammillary bodies: 53.6±20.4 v. 19.2±5.7 Fos-ir cells/section, p = 0.14, both n = 5). In summary, rats anticipating a palatable food reward in addition to their normal bland food show widespread neural activity in brain regions associated with the control of feeding, reward and memory. Furthermore, receipt of the reward results in increase in Fos-ir in brain regions associated with satiety and memory.
Physiology 2012 (Edinburgh) (2012) Proc Physiol Soc 27, PC329
Poster Communications: Brain c-Fos-like immunoreactivity in rats anticipating a palatable food reward
J. Menzies1, N. Sabatier1, G. Leng1
1. University of Edinburgh, Edinburgh, United Kingdom.
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Where applicable, experiments conform with Society ethical requirements.