Pharmacology of lobeline, a nicotinic receptor ligand

In this study we investigated the pharmacology of lobeline, a high affinity nicotinic ligand with a unique pharmacological profile, in different in vitro and in vivo tests. Although lobeline displaced [3H]-nicotine binding sites in the rat brain with a Ki of 4.4 nM, it did not activate alpha4beta2 expressed receptors in frog oocytes. The in vivo pharmacological effects of lobeline were highly complex. Lobeline, at the time of maximal effect, dose-dependently produced motor impairment and decreased locomotor activity and body temperature in mice after s.c. treatment. However, antinociception was present after intrathecal but not after s.c. administration of lobeline in the tail-flick tests. The behavioral effects of lobeline were not blocked by pretreatment with either mecamylamine or dihydro-beta-erythroidine. In addition, lobeline given s.c. enhanced nicotine-induced antinociception in a dose-related manner. No acute tolerance developed to either lobeline's behavioral or antinociceptive effect after s.c. or intrathecal administration, respectively. However, tolerance developed to lobeline's pharmacological effects after chronic treatment with the drug for 10 days (15 mg/kg, s.c. twice a day). Furthermore, cross-tolerance between lobeline and nicotine developed after chronic treatment with either drug. Although the alpha4beta2 receptor is unlikely to mediate the agonist effects of lobeline, our results indicate that lobeline does interact with the nicotinic receptor in a novel fashion.