Activation of GABAA and GABAB receptors in the lateral septum increases sucrose intake by differential stimulation of sucrose licking activity.

The present study was aimed to determine how direct injections into the lateral septum (LS) of muscimol and baclofen, GABAA and GABAB receptor agonists, respectively, affect intake of 10% sucrose and sucrose licking activity in rats. The effects of muscimol and baclofen on the 1-h intake of sucrose and sucrose licking activity were tested at low (350pmol), medium (876pmol), and high (1752pmol) doses. The medium and high doses of muscimol and the high dose of baclofen significantly increased 1-h sucrose intake. The total sucrose lick number was significantly increased by the medium dose of muscimol and the high dose of baclofen. An increase in sucrose licking activity induced by muscimol but not baclofen occurred in the first 15min after injections. The medium and high doses of muscimol but not baclofen significantly decreased latency to initiate the first lick of sucrose. The total licking time calculated as the sum of the duration of all sucrose lick clusters showed a significant increase by the high dose of baclofen but not by any dose of muscimol. Therefore, the GABAA and GABAB LS mechanisms appear to be involved in stimulating sucrose intake, but this stimulation occurs by differential regulation of the sucrose licking activity. Muscimol intra-LS administration led to a short-latency rapid increase in sucrose licking. In contrast, baclofen did not decrease latency to initiate licking, but significantly increased total licking duration.