A longitudinal study of the effects of prenatal ethanol exposure on neuronal acquisition and death in the principal sensory nucleus of the trigeminal nerve: interaction with changes induced by transection of the infraorbital nerve.

The present study determines (1) whether ethanol-induced microencephaly results from reductions in neuronal acquisition (i.e., cell proliferation and neuronal migration) and/or increases in neuronal death and (2) whether ethanol exacerbates death by the same mode as that for naturally occurring or lesion-induced neuronal death. Pregnant rats were exposed to a diet containing 6.7% (v/v) ethanol or an isocaloric control diet during the last two weeks of gestation. At birth, the right infraorbital nerves of the pups were transected. The numbers of neurons in the principal sensory nucleus of the trigeminal nerve (PSN) on both sides of the pons were examined at various prenatal and early postnatal timepoints. The numbers of pyknotic and argyrophilic PSN cells were also counted. Ethanol delayed and reduced (19.9%) the prenatal acquisition of PSN neurons. The postnatal decline in neuronal number (indicative of neuronal death) was significantly increased (10.6%) by ethanol. Likewise, the numbers of pyknotic and silver-stained cells were significantly higher in ethanol-treated rats. Lesion of the infraorbital nerve induced significant transsynaptic neuronal death in the control rats. Ethanol increased the amount of death caused by the lesion; however, it altered neither the timing of the neuronal loss nor the incidence of pyknosis or silver-staining. Therefore, ethanol affects both neuronal acquisition and survival; the greater effect being on neuronal acquisition. The timing and morphology of dying cells indicate that regardless of the cause (natural processes, ethanol-induced, or lesion-induced), neurons die in the developing PSN by the same mode.