Olivary climbing fiber alterations in PN40 rat cerebellum following postnatal ethanol exposure

Developmental ethanol exposure in rats during postnatal days (PN) 4–6 is known to cause significant loss of the cerebellar Purkinje cells. It is not known what happens to the surviving neurons as they continue to develop. This study was designed to quantify the interactions between the olivary climbing fibers and the Purkinje cells when the cerebellar circuits have matured. Rat pups were treated with a daily dose of ethanol (4.5 g/kg body weight) delivered by intragastric intubation on PN4, PN4–6, or PN7–9. The interactions between the climbing fibers and the Purkinje cells were examined on PN40 using confocal microscopy. Mid-vermal cerebellar sections were stained with antibodies to calbindin-D28k (to visualize Purkinje cells) and vesicular glutamate transporter 2 (VGluT2, to visualize climbing fibers). Confocal z-stack images were obtained from Lobule 1 and analyzed with Imaris software to quantify the staining of the two antibodies. The VGluT2 immunostaining was significantly reduced and this was associated with alterations in the synaptic integrity, and synaptic number per Purkinje cell with only a single exposure on PN4 enough to cause the alterations. Previously, we demonstrated similar deficits in climbing fiber innervation when analyzed on PN14 (Pierce, Hayar, Williams, and Light, 2010). The present study confirms that these alterations are sustained and further identifies the decreased synaptic density as well as alterations to the general morphology of the molecular layer of the cerebellar cortex that are the result of the binge ethanol exposure.

Research Highlights
► Third trimester binge drinking alters morphology and circuitry in rat cerebellum.
► Loss of Purkinje and climbing fiber innervation due to third trimester ethanol binge.
► Damage is temporally dependent, but can occur from a single ethanol exposure on PN4.
► This is the first evidence that the climbing fiber alterations are permanent.