Endogenous neurosteroids modulate GABAA receptor synaptic transmission in neonatal mouse cortical neurones

Adam R Brown, Dianne R Peden, David JK Balfour, Jeremy J Lambert, Delia Belelli. University of Dundee, Dundee, Scotland, United Kingdom.

Certain brain-derived pregnane neurosteroids enhance the function of GABAA receptors (GABAARs). At GABA-ergic synapses this effect is manifest as a prolongation of the decay time of the miniature inhibitory postsynaptic current (mIPSC). Neurosteroids may play an important physiological role during neuronal development (Belelli & Lambert, 2005). Here, we investigated the influence of the 5α-reductase inhibitor finasteride (which inhibits neurosteroid synthesis) and γ-cyclodextrin (γ−CD), a steroid-scavenger molecule, (Shu et al., 2007) on synaptic inhibition during neonatal development of mouse cortex. Coronal brain slices (post-natal (P) day 7-24) were prepared from wild-type (WT) and α1 ‘knockout’ (α10/0) mice of either sex. The whole-cell patch clamp technique was used to record mIPSCs from cortical layer II/III pyramidal neurones (35°C, in the presence 0.5 μM TTX and 2 mM kynurenic acid; holding potential, -60 mV). With maturation the mIPSC decay time constant (τw) decreased (WT, P7/8 = 11.8 ± 0.5 ms; P15 = 6.8 ± 0.2 ms; P20-24 = 4.7 ± 0.2 ms, n = 29-31). In certain brain regions incorporation of the α1-subunit may cause a developmental reduction in the duration of GABAAR-mediated mIPSCs. Although the decay kinetics of cortical mIPSCs recorded from α10/0 were slower than WT at all ages examined, they exhibited a similar developmental change to WT (α10/0, P7/8 = 17.0 ± 1.1 ms; P15 = 10.9 ± 0.5 ms; P20-24 = 8.3 ± 0.4 ms, n = 8-13). Pre-incubation of WT cortical slices with either 50 μM finasteride, or 1 mM γ-CD, significantly (P < 0.05 vs non-treated, unpaired Student’s t-test) reduced the τw of P7/8 mIPSCs (P7/8: γ-CD-treated = 8.3 ± 0.2 ms, n = 18; finasteride-treated = 8.8 ± 0.4 ms, n = 10). These data reveal that during neonatal development endogenous neurosteroids prolong the duration of cortical mIPSCs, an effect which may be important for neuronal maturation.

Belelli D and Lambert JJ (2005) Nat Neurosci Rev 6: 565-575.
Shu HJ et al. (2007) Br J Pharmacol 150: 164-175.

BPS A J Clark studentship to ARB; Dr Thomas Rosahl for providing the α10/0 mice.