Age- and sex-related characteristics of tonic GABA currents in the rat substantia nigra pars reticulata.

Previous studies have shown that the pharmacologic effects of GABAergic drugs and the postsynaptic phasic GABAAergic inhibitory responses in the anterior part of the rat substantia nigra pars reticulata (SNRA) are age- and sex-specific. Here, we investigate whether there are age- and sex-related differences in the expression of the δ GABAA receptor (GABAAR) subunit and GABAAR mediated tonic currents. We have used δ-specific immunochemistry and whole cell patch clamp to study GABAAR mediated tonic currents in the SNRA of male and female postnatal day (PN) PN5-9, PN11-16, and PN25-32 rats. We observed age-related decline, but no sex-specific changes, in bicuculline (BIM) sensitive GABAAR tonic current density, which correlated with the decline in δ subunit in the SNRA between PN15 and 30. Furthermore, we show that the GABAAR tonic currents can be modified by muscimol (GABAAR agonist; partial GABACR agonist), THIP (4,5,6,7-tetrahydroisoxazolo (5,4-c)pyridin-3-ol: α4ß3δ GABAARs agonist and GABACR antagonist), and zolpidem (α1-subunit selective GABAAR agonist) in age- and sex-dependent manner specific for each drug. We propose that the emergence of the GABAAR-sensitive anticonvulsant effects of the rat SNRA during development may depend upon the developmental decline in tonic GABAergic inhibition of the activity of rat SNRA neurons, although other sex-specific factors are also involved.

Age- and gender-related differences in GABAA receptor-mediated postsynaptic currents in GABAergic neurons of the substantia nigra reticulata in the rat.

The responsiveness of the rat anterior substantia nigra pars reticulata (SNR) GABAergic neurons to GABA(A)ergic drugs changes with age and gender, altering its role in seizure control. To determine whether maturational and gender-specific differences in the properties of spontaneous GABA(A)Rs-mediated inhibitory postsynaptic currents (sIPSCs) underlie these events, we studied sIPSCs at baseline and after application of the alpha1 GABA(A)Rs subunit selective agonist zolpidem, at postnatal days (PN) 5-9, PN12-15, and PN28-32. Results were correlated with the alpha1 and alpha 3 GABA(A)Rs subunit immunoreactivity (-ir) at PN5, PN15, and PN30, using immunochemistry. The mean frequency, amplitude and charge transfer increased whereas the 10-90% rise time and decay time accelerated with age in both genders. The faster sIPSC kinetics in older rats were paralleled by increased alpha1-ir and decreased alpha 3-ir. At PN5-9, males had more robust sIPSCs (frequency, amplitude, charge carried per event and charge transfer) than females. At PN28-32, males exhibited higher amplitudes and faster kinetics than females. The zolpidem-induced increase of decay times, amplitude and charge transfer and alpha1-ir expression were the lowest in PN5-9 males but increased with age, in both genders. Our findings demonstrate that alterations in GABA(A)Rs subunit expression partially underlie age- and gender-specific sIPSC changes in SNR neurons. However, the observation of gender differences in sIPSC kinetics that cannot be attributed to changes in perisomatic alpha1 expression suggests the existence of additional gender-specific factors that control the sIPSC kinetics in rat SNR.