Histone deacetylase inhibition reduces ventral tegmental area dopamine neuronal hyperexcitability involving AKAP150 signaling following maternal deprivation in juvenile male rats

Abstract

Traumatic early life stress (ELS) is linked to dopamine (DA) dysregulation which increases the probability of developing psychiatric disorders in adolescence and adulthood. Our prior studies demonstrated that a severe early life stressor, a 24-hr maternal deprivation (MD) in juvenile male rats, could lead to altered DA signaling from the ventral tegmental area (VTA) due to impairment of GABAergic synaptic plasticity (promoting GABAergic long-term depression, LTD) with concomitant changes in the abundance of synaptic regulators including A-kinase anchoring protein (AKAP150). Importantly, these MD-induced synaptic changes in the VTA were accompanied by upregulation of histone deacetylase 2, histone hypoacetylation, and were reversible by HDAC inhibition. Using cell-attached and whole-cell patch clamp recordings, we found that MD stress also increased spontaneous VTA DA neuronal activity and excitability in juvenile male rats without affecting intrinsic excitability. Postsynaptic chemical disruption of AKAP150 and protein kinase A interaction increased VTA DA neuronal excitability in control non-MD rats mimicking the effects of MD on DA cell excitability with similar changes in membrane properties. Interestingly, this disruption decreased MD-induced VTA DA hyperexcitability. This MD-induced DA neuronal hyperexcitability could also be normalized at 24 hr after injection of the class 1 HDAC inhibitor, CI-994. Altogether, our data suggest that AKAP150 plays a critical role in the regulation of VTA DA neuronal excitability and that HDAC-mediated targeting of AKAP150 signaling could normalize VTA DA dysfunction following ELS thereby providing novel therapeutic targets for prevention of later life psychopathology.

Keywords: AKAP; HDAC; VTA; dopamine; epigenetics; histone acetylation.

Figure 1.. MD increases activity of VTA DA neurons that is dependent on synaptic transmission.

(A) Sample cell-attached voltage clamp AP recordings from VTA DA neurons depicting silent and spontaneously active neurons with proportional distribution of these neurons in non-MD and MD rats displayed as pie charts (57% vs 73% active neurons, respectively) and spike frequency bar graph. (B) AP recordings in response to depolarizing current steps in the presence of fast synaptic transmission antagonists for AMPAR, NMDAR, and GABA_AR with representative AP traces in response to 200pA depolarizing current step. In all recordings in this graph and the subsequent graphs only one cell/rat was recorded, therefore the n-value represents total number of animals used.

Figure 2.. Disruption of AKAP150-PKA complex increases VTA DA neuronal excitability in non-MD rats.

(A) All recordings in this graph were performed with intact synaptic transmission. Graph shows AP recordings in response to depolarizing step currents with representative AP traces (in response to a 200pA depolarizing current step) with intra-pipette inclusion of either control peptide Ht31p (1μM) or active AKAP150 inhibitor peptide Ht31 (1μM). (B) Average bar graphs of Rin, threshold potential, and the amplitude of fAHP, and mAHP derived from recordings in Figure 2A.

Figure 3.. Disruption of AKAP150-PKA complex decreases VTA DA neuronal excitability in MD rats.

(A) All recordings in this graph were performed with intact synaptic transmission. Graph shows AP recordings in response to depolarizing step currents with representative AP traces (in response to a 200pA depolarizing current step) with intra-pipette inclusion of either control peptide Ht31p (1μM) or active AKAP150 inhibitor peptide Ht31 (1μM). (B) Average bar graphs of Rin, threshold potential, and the amplitude of fAHP, and mAHP derived from recordings in Figure 3A.

Figure 4.. In vivo HDAC inhibition reverses MD-induced increases in VTA DA neuronal excitability.

(A) Representative timeline of experimental design for HDACi experiments.(B) AP recordings in response to depolarizing current steps with representative AP traces (in response to a 200pA current step) in intact synaptic transmission from non-MD or MD rats that were either: naïve, injected with vehicle, or CI-994. Rats were sacrificed 24hr after the injection. Data from naïve and vehicle-injected rats were pooled and averaged. (C) Average bar graphs of Rin, threshold potential, and the amplitude of fAHP, and mAHP derived from recordings in Figure 4B.