Benzodiazepine effects on licking responses for sodium chloride solutions in water-deprived male rats

The aim of this study was to investigate, for the first time, the effects of a centrally active benzodiazepine receptor agonist, midazolam maleate, on the microstructure of licking responses for a range of sodium chloride (NaCl) solutions in mildly water-deprived male rats. Doses of midazolam were chosen (0.3-3.0 mg/kg. i.p.) which have been characterised in studies of licking responses for several different kinds of nutrients. NaCl concentrations (0.075 M-0.45 M) were chosen to cover a range of taste preferences and acceptability. A brief-contact testing session was employed to focus on the initial determinants of licking responses (i.e. taste palatability), and to minimise any contribution of post-ingestional effects. The results indicate the midazolam significantly increased the total number of licks recorded across all salt concentrations, but that it had no effect on the number of bouts of licking. Instead, midazolam specifically enhanced the mean duration of licking bouts, an effect that was most evident at the weaker but more acceptable NaCl concentrations (0.075 M and 0.15 M). In addition, midazolam diminished the intrabout rate of licking across all salt concentrations. These results confirm that benzodiazepines can exert a specific pattern of effects on the microstructure of licking for salt solutions. They are discussed in terms of the oropharyngeal stimulation controlling intake and the palatability or "liking" hypothesis for the effects of benzodiazepines on taste stimuli, and indicate that the hypothesis is applicable to salt solution ingestive behaviour.