Behavioral disturbances induced in rats via the intranigral injection of leptin

Abstract

Introduction: Leptin action on brain structures might be helpful for better understanding of mechanism of this hormone neurotropic effects realization. Experiments have been carried out on Wistar rats (250-320 g) with the help of the EEG-, actometry recording and "open field" indices registration after microinjection of leptin (5-50 ng) into reticular part of substantia nigra (SNR). Besides, severity of picrtoxon-induced generalized seizures (2 mg/kg, i.p.) have been estimated after intra-SNR leptin administration. It was shown that bilateral intraSNR leptin injection (50 ng) resulted in oligo-akinesia, muscle tonus enhancement, decrease of wakefulness period and increase of deep slow-wave sleep and paradoxal sleep. Unilateral leptin administration (5; 25 and 50 ng) into SNR resulted in the appearance of dosedependent contralateral circlings, which were blocked by naloxone (1.0 mg/kg). Haloperidol (1.0 mg/kg) caused the potentiation on keeping of uncomfortable position in animals with bilateral intraSNR leptin administration, while naloxone (1.0 mg/kg) markedly reduced this index. Analogous leptin intrastriatal injection failed to induce the same behavioral disturbances. Intranigral leptin administration was followed by decreasing of seizure susceptibility to i.p. picrotoxin administration (2,0 mg/kg).