Effects of Melatonin Formulations on Caffeine-Evoked Cortical Activity and Pentobarbital-Induced Sleep in Mice

Abstract

Melatonin has chronobiotic, antioxidant, anti-inflammatory, and neuromodulatory properties, and its oral effects may vary according to formulation. This study compared conventional melatonin with a lipid-multiparticulate (LMP) formulation in two acute pharmacological mouse paradigms. Eighty-four male BALB/c mice were assigned to caffeine-evoked cortical activity or pentobarbital-induced sedative-hypnotic experiments. Mice received caffeine (7.5 mg/kg, i.p.) alone or with standard or LMP-melatonin (10 or 20 mg/kg, oral). ECoG recorded cortical electrical activity under urethane anaesthesia. In a separate cohort, latency to and duration of pentobarbital-induced loss of the righting reflex were measured. Circulating neurochemical and redox markers, as well as neurotransmitter- and inflammation-related gene and protein expression, were evaluated. Caffeine increased spike frequency and altered ECoG amplitude, together with unfavorable changes in circulating neurochemical and redox markers and in neurotransmitter receptor- and inflammation-related outcomes. Both melatonin formulations attenuated several of these changes in a dose-dependent manner, with the strongest effects generally observed in the high-dose LMP-melatonin group. Compared with conventional melatonin, LMP-melatonin produced greater modulation of ECoG activity, circulating biochemical markers, neurotransmitter-receptor expression, and IL-6 and TNF-alpha-related outcomes. LMP-melatonin also produced a greater reduction in the latency to and a greater prolongation of the duration of pentobarbital-induced loss of the righting reflex. LMP-melatonin produced greater formulation-dependent effects than conventional melatonin on caffeine-evoked cortical electrical activity, pentobarbital-induced sedative-hypnotic responses, and selected biochemical and molecular outcomes. However, pharmacokinetic exposure, physiological sleep stages, sleep architecture, sleep quality, and direct measures of neuronal injury were not assessed. Therefore, the findings do not directly establish enhanced bioavailability, physiological sleep promotion, or neuroprotection.