Estrogen Treatment Protects GABA_B Inhibition in the Dentate Gyrus of Female Rats after Kainic Acid–Induced Status Epilepticus

Abstract

Summary: Purpose:We used the paired-pulse inhibition paradigm to determine whether the cell loss in the hilus of the dentate gyrus of female rats after kainic acid (KA)-induced status epilepticus (SE) is associated with functional changes in the dentate gyrus. Additionally, we determined whether the lost function could be preserved by using estrogen neuroprotection.Methods: Female rats were ovariectomized and treated either with estrogen replacement (four doses of 2 g of estradiol every 24 h: two doses before SE, two doses after) or oil. SE was induced by I.P. administration of KA (16 mg/kg) and terminated after 5 h with pentobarbital. After 2 days, hippocampal/ dentate gyrus slices were prepared. Population spikes were recorded in the granule cell layer as a response to mixed perforant-path stimulation (10-to 1,000-ms interstimulus intervals). Ratios of the test response to conditioning response were evaluated. ␥-Aminobutyric acid type B (GABA B ) receptors were blocked with 400 M CGP 35348. Results:In slices from oil-treated rats, SE induced a loss of paired-pulse inhibition in the dentate gyrus at the interstimulus intervals marking intermediate facilitation and late depression. There was no such loss of paired-pulse inhibition in estrogentreated rats. CGP 35348 was unable to alter paired-pulse inhibition in slices form oil-treated rats. In slices from estrogen-treated rats, CGP decreased paired-pulse inhibition at 50-150-ms interstimulus intervals. Comparison of paired-pulse inhibition in slices from oil-treated rats with slices from estrogen-treated rats with CGP 35348 revealed a GABA B -independent difference at interstimulus intervals >300 ms.Conclusions: Our study demonstrated that there is a complete loss of GABA B receptor-mediated inhibition after KAinduced SE in the dentate gyrus. Pretreatment with estrogen can save GABA B -receptor function, probably by neuroprotection of neurons containing the postsynaptic GABA B receptors.

β-Estradiol Increases Dentate Gyrus Inhibition in Female Rats via Augmentation of Hilar Neuropeptide Y

“…Horizontal slices (4ϫ oil, n ϭ 22; 4ϫ ␤-estradiol, n ϭ 22; 1ϫ oil, n ϭ 18; 1ϫ ␤-estradiol, n ϭ 8) containing the dorsal hippocampus (400 m thick) were cut on a vibratome in ice-cold artificial CSF (ACSF) (in mM: 126 NaCl, 5 KCl, 1.25 NaH 2 PO 4 , 2 MgCl 2 , 2 CaCl 2 , 26 NaHCO 3 , and 10 glucose, pH 7.36). The slices were preincubated in an interface chamber in warmed (34 -35°C) and oxygenated ACSF (5% CO 2 /95% O 2 ) for at least 1 h. Paired square pulses (50 -400 A, 150 s duration) were delivered via a stainless steel bipolar stimulating electrode (Frederick Haer Company, Bowdoinham, ME) positioned over the outer and middle third of the molecular layer (mixed perforant path stimulation) (Velíšek and Velíšková, 2002) using a stimulator coupled to a stimulus isolation unit (A.M.P.I., Jerusalem, Israel). Interstimulus intervals between the paired stimuli ranged from 10 to 1000 ms, corresponding to frequencies of 100 to 1 Hz.…”

“…To determine the role of Y 1 , Y 2 , and Y 5 NPY receptors, the following specific antagonists to individual NPY receptors were bath applied for at least 30 min before recording: 100 (El Bahh et al, 2002;Tu et al, 2005) (Y 2 receptor antagonist; 30 nM, n ϭ 8; 100 nM, n ϭ 6), and 250 nM 5,5-dimethyl-2-(2,3,4,9-tetrahydro-3,3-dimethyl-1 oxo-1H-xanthen-9-yl)-1,3-cyclohexanedione (L-152,804) (Woldbye et al, 2005) (Y 5 receptor antagonist; n ϭ 5). To determine the role of GABA B receptors in the ␤-estradiol-induced enhancement of the late paired-pulse inhibition, 400 M (3-aminopropyl)(diethoxymethyl)phosphinic acid (CGP 35348) (Velíšek and Velíšková, 2002) was bath applied for at least 30 min before recordings (n ϭ 10). LY 341495 [(2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid] was bath applied for at least 30 min before recordings at 20 M (n ϭ 8) or 200 nM (n ϭ 7) to determine the role of metabotropic glutamate receptors (mGluRs) in the effects of ␤-estradiol pretreatment.…”

“…␤-Estradiol enhances the late paired-pulse inhibition in the dentate gyrus We used the in vitro paired-pulse paradigm by stimulating the mixed perforant pathway to assess changes in the dentate granule cell network excitability (Velíšek and Velíšková, 2002). The paired-pulse curve was constructed by calculating population spike amplitude ratio (R 2 /R 1 ) at increasing interstimulus intervals.…”

“…The paired-pulse curve was constructed by calculating population spike amplitude ratio (R 2 /R 1 ) at increasing interstimulus intervals. The curve consisted of three components (Haas et al, 1996;Velíšek and Velíšková, 2002) referred to here as (1) early inhibition (10 -50 ms), (2) intermediate facilitation (70 -125 ms), and (3) late inhibition (150 -1000 ms). Slices from OVX females treated with four daily doses of ␤-estradiol (2 g/rat; n ϭ 22) displayed significant enhancement of late paired-pulse inhibition at interstimulus intervals 125-1000 ms compared with slices from OVX controls (n ϭ 22) receiving oil (two-way ANOVA; main effect of treatment, F (1,42) ϭ 15.871; *p Ͻ 0.001).…”

Effect of Intrahippocampal γ Aminobutyrate B Receptor on Pain Sensitivity during Estrous Cycle

“…Baclofen has long been known to have antinociceptive activity in acute and chronic pain models (Hwang and Yaksh, 1997). On the other hand, pretreatment with estrogen can save GABA B receptor function, probably by neuroprotection of neurons containing postsynaptic GABA B receptors (Velisek and Veliskova, 2002). Noriega et al (2010) reported that estrogen decreases the functional coupling of the mu-opioid and GABA B receptors to the inwardly rectifying K + channel, possibly through an action on the G-protein (Noriega et al, 2010).…”