Repeated intermittent alcohol exposure during the third trimester-equivalent increases expression of the GABAA receptor δ subunit in cerebellar granule neurons and delays motor development in rats

Abstract

Exposure to ethanol (EtOH) during fetal development can lead to long-lasting alterations, including deficits in fine motor skills and motor learning. Studies suggest that these are, in part, a consequence of cerebellar damage. Cerebellar granule neurons (CGNs) are the gateway of information into the cerebellar cortex. Functionally, CGNs are heavily regulated by phasic and tonic GABAergic inhibition from Golgi cell interneurons; however, the effect of EtOH exposure on the development of GABAergic transmission in immature CGNs has not been investigated. To model EtOH exposure during the 3rd trimester-equivalent of human pregnancy, neonatal pups were exposed intermittently to high levels of vaporized EtOH from postnatal day (P) 2 to P12. This exposure gradually increased pup serum EtOH concentrations (SECs) to ~60 mM (~0.28 g/dl) during the 4 hours of exposure. EtOH levels gradually decreased to baseline 8 hrs after the end of exposure. Surprisingly, basal tonic and phasic GABAergic currents in CGNs were not significantly affected by postnatal alcohol exposure (PAE). However, PAE increased the expression of δ subunit expression at P28 as detected by immunohistochemical and western blot analyses. Also, electrophysiological studies with an agonist that is highly selective for δ-containing GABAA receptors, 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridine-3-ol (THIP), showed an increase in THIP-induced tonic current. Behavioral studies of PAE rats did not reveal any deficits in motor coordination, except for a delay in the acquisition of the mid-air righting reflex that was apparent at P15 to P18. These findings demonstrate that repeated intermittent exposure to high levels of EtOH during the equivalent of the last trimester of human pregnancy has significant but relatively subtle effects on motor coordination and GABAergic transmission in CGNs in rats.

Third trimester-equivalent ethanol exposure increases anxiety-like behavior and glutamatergic transmission in the basolateral amygdala

“…In addition, we previously found that exposure to lower levels of ethanol (i.e., 0.1 g/dl) during the 3 rd trimester equivalent have relatively subtle effects on synaptic transmission in the amygdala (Diaz et al, 2014a) and wished to test a higher dose of ethanol that was comparable to that used in other studies of the effect of exposure during this period on anxiety-like behavior in mature rats (Roskam and Koch, 2009). In general agreement with previous studies (Puglia and Valenzuela, 2010, Everett et al, 2012, Diaz et al, 2014b), the paradigm minimally affected pup weight gain or nursing ability. Maternal care was also minimally altered, consistent with the finding that serum ethanol concentrations in the dam were less than 10% of the levels found in the pup, which is likely due to increased ability to metabolize ethanol in the dams.…”

Dihydromyricetin Prevents Fetal Alcohol Exposure-Induced Behavioral and Physiological Deficits: The Roles of GABAA Receptors in Adolescence

“…Studies have also demonstrated FAE-induced decreases in allopregnanolone potentiation of [ 3 H]flunitrazepam binding to hippocampal GABA A Rs in guinea pigs [100], age-dependent changes in a5 GABA A R subunit expression in mice [101], and increased d GABA A R subunit expression and sensitivity to THIP in cerebellar granule neurons of rats after early postnatal (P2-12) EtOH vapor exposure [102]. Neurosteroids, such as 3a,5a-3-hydroxypregnan-20-one (3a,5a-THP or allopregnanolone) and 3a;5a-tetrahydrodeoxycorticosterone (THDOC), are potent endogenous modulators of d subunitcontaining GABA A Rs [103].…”

Third trimester-equivalent ethanol exposure causes micro-hemorrhages in the rat brain

“…Although the Catwalk test only revealed subtle deficits in locomotion and gait, it is possible that the rats were able to compensate for the damage caused by the third trimester-ethanol exposure-induced micro-hemorrhages or that this test lacks sufficient sensitivity to detect motor alterations secondary to the brain micro-hemorrhages. We previously found that ethanol vapor exposure for 4 hr/day during P2-P12 (peak pup blood ethanol levels near 0.3 g/dl) delayed the acquisition of the air-righting reflex, which was evident at P14-P18 (Diaz et al, 2014). Consequently, a more detailed assessment of sensorimotor and cognitive functions in these animals is clearly warranted, including an in-depth characterization of these across different developmental time points.…”