Electrophysiological and Immunohistochemical Evidence for an Increase in GABAergic Inputs and HCN Channels in Purkinje Cells that Survive Developmental Ethanol Exposure

Abstract

Ethanol exposures during the early postnatal period of the rat result in significant death of Purkinje cells (PCs). The magnitude, time-course, and lobular specificity of PC death have been well characterized in several studies. Additionally, significant reduction of climbing fiber inputs to the surviving PCs has been characterized. This study investigates whether further alterations to the cerebellar cortical circuits might occur as a result of developmental ethanol exposures. We first examined the firing pattern of PCs in acute slice preparations on postnatal days 13–15. While the basic firing frequency was not significantly altered, PCs from rat pups treated with ethanol on postnatal days 4–6 showed a significantly increased number of inhibitory postsynaptic potentials (IPSCs) and a larger Ih current. We conducted immunofluorescent studies to identify the probable cause of the increased IPSCs. We found a significant 21 % increase in the number of basket cells per PC and a near doubling of the volume of colocalized basket cell axonal membrane with PC. In addition, we identified a significant (~147 %) increase in HCN1 channel volume co-localized to PC volume. Therefore, the cerebellar cortex that survives targeted postnatal ethanol exposure is dramatically altered in development subsequent to PC death. The cerebellar cortical circuit that results is one that operates under a significant degree of increased resting inhibition. The alterations in the development of cerebellar circuitry following ethanol exposure, and the significant loss of PCs, could result in modifications of the structure and function of other brain regions that receive cerebellar inputs.

Eyeblink Classical Conditioning in Alcoholism and Fetal Alcohol Spectrum Disorders

“…These exposed mice also exhibited impaired EBC, further supporting the hypothesis that cerebellar LTD in Purkinje cells is crucial for the timing of eyeblink CRs ( 39 ). Interestingly, other in vitro electrophysiology experiments showed that alcohol exposure led to relatively greater inhibitory inputs to the Purkinje cells in the vermis ( 40 ). In the cerebellar deep nuclei, activity in the interpositus nucleus of the cerebellum was diminished and did not develop as rapidly in neonatal alcohol-exposed rats relative to controls during EBC ( 41 , 42 ).…”

GLP-1 enhances hyperpolarization-activated currents of mouse cerebellar Purkinje cell in vitro

“…In addition to climbing fibers and parallel fibers, cerebellar PCs also receive adrenocorticotropic, monoaminergic and preglucagonergic projections, which are involved in the regulation of PC spike firing activity ( Larsen et al, 1997 ; Merchenthaler et al, 1999 ). PCs exhibit intrinsic simple spike activity, which is dependent on activation of the persistent sodium current, IH, and voltage-dependent potassium current ( Ito, 1984 , 2006 ; Libster et al, 2015 ; Light et al, 2015 ). Activation of G protein-coupled receptors can increase the IH in mouse cerebellar PCs, resulting in an increased simple spike firing rate in vitro ( Libster et al, 2015 ).…”

White matter abnormalities in fetal alcohol spectrum disorders: Focus on axon growth and guidance

“…Alcohol targeting of L1CAM or its interacting partners could explain abnormalities in brain morphology that are evident at the cerebellar midline in severe cases of FASD. 52 Developmental alcohol exposure increases basket cells and their innervation of Purkinje cells, altering cerebellar output 54 which could also result from effects on Semaphorin signaling. Further study of the effects of alcohol on molecular players driving these connections is warranted.…”