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  • Title: Involvement of GABAergic transmission in the midbrain ventral tegmental area in the regulation of hippocampal theta rhythm.
    Author: Orzeł-Gryglewska J, Kuśmierczak M, Jurkowlaniec E.
    Journal: Brain Res Bull; 2010 Nov 20; 83(6):310-20. PubMed ID: 20851748.
    Abstract:
    Previously we indicated that the ventral tegmental area (VTA) may belong to the system regulating hippocampal theta rhythm. In the present study, we aimed at assessing the role of the GABAergic system of the VTA in regulation of hippocampal electric activity. Male Wistar rats received unilateral intra-VTA microinjection of either bicuculline (50ng/0.5μl, n=9), muscimol (100ng/0.5μl, n=10) or phaclofen (500ng/0.5μl, n=9). 1-min tail pinch stimulations were applied at 10-min intervals to evoke theta rhythm episodes in hippocampus. We analysed peak power (P(max)) and corresponding frequency (F(max)) of EEG signal at delta and theta bands. Bicuculline induced theta rhythm in both hippocampi with 0 latency, continuous for ca. 33min. Phaclofen also induced theta but in this group it appeared with latency (17.45±3.16min on average), lasted for ca. 33.6min and during this time was interrupted by periods of irregular activity of variable length. Tail pinch was not applied in these groups. Muscimol induced an opposite effect: depression of theta P(max) with simultaneous increase in delta P(max) and a decrease in F(max) delta during episodes of tail pinch-evoked theta. This effect had variable latency and no return to the control EEG could be observed. We propose that GABA activity in the VTA is of tonic character, so that abolition of this mechanism produces immediate effect, i.e. theta induction (strong by GABA(A) and weak by GABA(B) receptors blockade), whereas enhancing the already present GABAergic inhibition causes delayed, prolonged changes expressed as gradual loss of theta synchronisation.
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