Alcohol consumption and gustatory hedonic profiles in Wistar-Kyoto hyper- and normoactive rat strains.

The purpose of the present study was to compare the consummatory behaviour of rats of the Wistar Kyoto Hyperactive (WKHA) strain, selected for their hyperactivity in a novel environment, with the normoactive Wistar-Kyoto (WKY) rats in three choice tasks: between water and increasing concentrations of saccharin, between water and increasing concentrations of quinine, and between water and a 10% (v/v) ethanol solution. The results of the present study show that: (1) WKHA rats exhibited a significantly higher acceptance of a 10% (v/v) alcohol solution than the normoactive control WKY rats when alcohol solution was the only available fluid; (2) WKHA rats also showed significantly larger alcohol intakes during the 15 days of choice between water and alcohol (WKY: 0.39 +/- 0.05; WKHA: 1.72 +/- 0.26 g/kg/day); (3) as frequently cited in the literature for other strains, the higher level of alcohol ingestion of WKHA rats was associated with a higher preference for saccharin; (4) no strain differences were observed in the water-quinine choice test. The discussion is mainly centred on the small alcohol consumption of the two strains, since the intake of WKHA rats is in the normal range for consumption of outbred strains, while the amount of alcohol consumption of WKY rats is very low and in the range of alcohol intake of non-preferring rat strains. It is concluded that the difference in alcohol consumption is mainly due to the low intake of the WKY rats and it is suggested that their different level of consumption might result from the particular behavioural profile of these rats.

Interaction between mu and kappa receptors located in the parabrachial area in the opioid control of preference threshold for saccharin: modulatory role of lateral hypothalamic neurones.

In the course of our previous analyses of gustatory reward processes, we showed that, in normal or sham-lesioned rats, the preference threshold for saccharin over water was observed with a 0.3mM solution of the sweetener. The same solution was neutral for rats whose lateral hypothalamic neurones had been destroyed by ibotenic acid. Furthermore, injection of small dose of morphine (50ng) in the second gustatory relay-station, the parabrachial area, suppressed preference for the 0.3mM saccharin solution in sham-lesioned rats, while the same injection induced preference in lesioned rats. The aim of the present study was to determine if this paradoxical effect of morphine, in particular the suppressive action observed in sham-lesioned rats, could be explained by a differential activation of µ and kappa receptors located in the parabrachial area. Using the choice test between 0.3mM solution of saccharin and water, we compared the effect of intra-parabrachial injection of 50ng of morphine to those obtained with the µ agonist DAGO, the putative endogenous kappa ligand, dynorphin A(1-13) (Dyn A(1-13)) and the kappa antagonist, nor-binaltorphimine (nor-BNI). Increasing doses of each agonist and the antagonist were tested in independent groups of rats including lesioned and sham-lesioned animals. The same doses of DAGO that increased preference in sham-lesioned animals, decreased saccharin and water intakes in lesioned rats. On the contrary, Dyn A(1-13) dose-dependently decreased preference in the control rats and increased preference in lesioned animals. The effects of increasing doses of nor-BNI were more variable. To clarify the respective roles of the µ and kappa receptors, we tested the effect of two mixtures: (1) the simultaneous injection of DAGO and Dyn A(1-13) at doses ineffective when tested separately reproduced the paradoxical effect of morphine in each group of rats; (2) morphine effects were reversed when kappa receptors were blocked by a prior injection of nor-BNI. Taken together, the results suggest that: (1) in the parabrachial area of the normal rat, two opioidergic components, behaving antagonistically to each other, are implicated in the control of gustatory preference, a µ component with rewarding properties and a kappa component with aversive properties; (2) the main effect of the lateral hypothalamic lesion is to invert the properties of these two components; and (3) at least in the parabrachial area, µ and kappa receptors are functionally coupled and must be co-activated to reproduce the full effect of morphine.

Gustatory preference-aversion profiles for saccharin, quinine and alcohol in Roman high- and low-avoidance lines.

Rats of the Roman high-(RHA) and low-avoidance (RLA) lines are known to differ in alcohol preference, since the RHA rats freely consume more ethanol than RLA animals. In order to investigate whether this difference in alcohol intake could be due to an alteration of the gustatory quality of ethanol induced by the selection, we compared taste preference and aversion responses of RHA and RLA rats in four procedures: saccharin-water choice; gustatory negative contrast; quinine-water choice and 10% v/v alcohol-water choice. Our results confirm that RHA rats drink more alcohol than RLA rats. In the saccharin-water choice task, RHA rats tended to show higher preference than RLA rats for the most palatable concentrations, while their aversion to the highest concentration of saccharin (50mM) was smaller than the aversion shown by RLA rats. The negative gustatory contrast test did not clearly differentiate the two lines, although only RHA rats showed significant negative contrast. Lastly, while RLA rats showed only aversion to quinine as the concentration increased, RHA rats did not show any aversion and preferred quinine to water at mid-range concentrations. To explain these results three hypotheses are briefly discussed: first, selective breeding for high avoidance learning could have enhanced brain reinforcement processes implicated in the evaluation of palatability. Secondly, selective breeding could have decreased aversiveness to quinine-adulterated solutions, as well as to saccharin and alcohol solutions which include a quinine-like taste component. Lastly, the present results suggest that the RHA rats may be high sensation-seekers whereas RLA animals are low sensation-seekers.