Effects of prenatal exposure to the CB-1 receptor agonist WIN 55212-2 or CO on the GABAergic neuronal systems of rat cerebellar cortex
The aim of this study was to assess the effects of prenatal exposures to cannabinoids or carbon monoxide (CO) in an animal experimental model reproducing the environmental conditions in which a fetus develops whose mother, during pregnancy, ingests by smoking low doses of cannabinoids or CO. Particular attention was devoted to analyses of the long-term effects of the exposures at the level of the cerebellar cortex, where already during prenatal development the GABAergic neuronal systems may be modulated by both cannabinoids and CO. Three groups of rats were subjected to the following experimental conditions: exposure to cannabinoids by maternal treatment during pregnancy with the cannabinoid CB-1 receptor agonist WIN 55212-2 (WIN) (0.5 mg/kg/day, s.c.); exposure to CO by maternal exposure during pregnancy to CO (75 parts per million, by inhalation); and exposure to WIN+CO at the above doses and means of administration; a fourth group was used as control. The body weight of dams, length of pregnancy, litter size at birth, body weight and postnatal mortality of pups were monitored in order to evaluate possible effects of the exposures on reproduction and on prenatal and postnatal development. In the different groups, the long-term effects of the exposures were studied in adult rats (120-150 days) by light microscopy analyses of the structure of the cerebellar cortex and of the distribution in the cortex of markers of GABAergic neurons, such as GAD and GABA itself. Results. Exposures to WIN or CO did not affect reproduction or prenatal/postnatal development. Moreover, the exposed rats showed no structural alterations of the cerebellar cortex and displayed qualitative distribution patterns of GAD and GABA immunoreactivities similar to those of the controls. However, quantitative analyses indicated significant changes of both of these immunoreactivities: in comparison with the controls, they were significantly increased in WIN-exposed rats and reduced in CO-exposed rats, but not significantly different in WIN+CO-exposed rats. The changes were detected in the molecular and Purkinje neuron layers, but not in the granular layer. Prenatal exposures of rats to WIN or CO, at doses that do not affect reproduction, general processes of development and histomorphogenesis of the cerebellar cortex, cause significant changes of GAD and GABA immunoreactivities in some GABAergic neuronal systems of the adult rat cerebellar cortex, indicating selective up-regulation of GABA-mediated neurotransmission as a long-term consequence of chronic prenatal exposures to cannabinoids or CO. Because the changes consist of overexpression or, vice versa, underexpression of these immunoreactivities, functional alterations of opposite types in the GABAergic systems of the cerebellum following exposure to WIN or CO can be postulated, in agreement with the results of behavioral and clinical studies. No changes in immunoreactivities were detected after prenatal exposure to WIN and CO in association.
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