Cannabinoid receptor agonist disrupts behavioral and neuroendocrine responses during lactation.

It has been shown that the endocannabinoid system is involved in the neurohypophyseal hormone secretion produced by exposure to several different stimuli; however, the influence of this system on neuroendocrine responses during lactation is unclear. Therefore, the aim of our study was to investigate the influence of an acute peripheral administration of WIN55,212-2 (cannabinoid receptor agonist) on behavioral and neuroendocrine responses during lactation. On day 6 of lactation, female rats were treated with vehicle or WIN55,212-2 30 min before the start of our experiments. To evaluate maternal behavior, the pups were returned to their home cages to the side of the cage opposite the previous nest, and the resulting behavior of the lactating rats was recorded for the next 30 min. Aggressive behavior was evaluated for 10 min following the placement of an intruder male rat in the home cage. The plasma level of oxytocin and the amount of milk consumption by the pups were evaluated 15 min after the onset of suckling. In addition, double-labelled c-Fos/oxytocin neurons in the medial magnocellular subdivision of the paraventricular nucleus and in the supraoptic nucleus were quantified for each lactating rat. The results show that WIN decreased maternal care, decreased aggressive behaviors, suppressed maternal anxiolysis, decreased plasma oxytocin levels and milk consumption by pups and decreased activation of oxytocinergic neurons in hypothalamic nuclei. Our results indicate that the changes in the behavioral responses of lactating rats treated with WIN maybe can be related to disruption in the neuroendocrine control of oxytocin secretion.