Developmental and behavioral effects of medetomidine following in ovo injection in chicks

Developmental and behavioral effects of medetomidine were assessed in chicks following in ovo exposure on incubation day 4. Medetomidine at 25 and 50 μg/egg injected once into the air cell on incubation day 4, dose-dependently decreased the number of viable chick embryos starting on day 10 of the incubation. The percentages of successful hatching in the control and medetomidine treated groups were 93, 60 and 47%, respectively. Embryo lethalities in these groups were 7, 40 and 53%, respectively. In ovo exposure of the chicks to medetomidine at 25 and 50 μg/egg did not significantly affect the body weight of the chicks as well as their morphometric measurements. In another experiment, 3- and 8-day old chicks exposed to medetomidine in ovo (25 μg/egg) were monitored in the open-field for 5 min. Medetomidine suppressed the open-field activity of both 3- and 8-day old chicks. This was manifested by a significant increase in the latency to move from the central square of the open-field arena and a decrease in the number of lines crossed (ambulation) with an additional decrease in vocalizations of the 3-day old chicks when compared with respective age-matched control values. In the same medetomidine-exposed chicks the duration of tonic immobility significantly increased in comparison with respective control values. Pharmacological challenge of the medetomidine-exposed chicks (8-day old) with medetomidine at 25 μg/kg, intramuscularly significantly increased the latencies to onset of sedation and loss of righting reflex and decreased the duration of sleep when compared with the saline-control group challenged in the same manner. The data suggest that medetomidine could be a behavioral teratogen in chicks following in ovo exposure.