C34 There is a growing body of evidence showing that pentoba

There is a growing body of evidence showing that pentobarbital causes memory disorders [3], [4], [5]. Our results that a single injection of pentobarbital into bilateral hippocampus significantly impaired hippocampus-dependent spatial memory retrieval (Fig. 1) add support to that evidence. Previous studies have reported that increasing synaptic γ-aminobutyric C34 type A receptor (GABAAR) activity will lead to memory impairment and LTP suppression in the hippocampus [21]. In contrast, the blockade of GABAAR facilitates the induction of LTP [22]. Our recent study has revealed that pentobarbital, a GABAAR agonist, impairs spatial learning and memory and reduces the induction of LTP in the CA1 area of the hippocampus [5]. Here we have shown that pentobarbital depressed basal synaptic transmission in a dose-dependent manner (Fig. 2). These are similar to the effects of propofol, another highly effective intravenous anesthetic [17]. Synaptic plasticity in the hippocampus is widely believed to be the cellular mechanism underlying certain types of learning and memory [6], [7], [8]. Thus, the pentobarbital-caused memory deficit may be attributed to the dysfunction of hippocampal synaptic plasticity including impaired LTP and facilitated synaptic depression. It has been demonstrated that the expression of LTD, or the decaying of LTP, involves the facilitation of clathrin-dependent endocytosis of postsynaptic AMPARs, through a GluA2 subunit-dependent mechanism [7], [12], [16], [19], [23]. Thus, the synthetic peptide Tat-GluA23Y blocks LTD by interfering with facilitated endocytosis of AMPA receptors, the last step of LTD expression, without affecting any upstream signaling steps [13], [14], [15], [24], [25]. Previously we had shown that the GluA23Y peptide not only rescues the impaired LTP but also prolongs memory retention in both physiological and pathological conditions [16]. Consistent with these studies, we have found that pre-injection of GluA23Y alleviated pentobarbital-caused memory deficits (Fig. 1) and pre-incubation of GluA23Y upregulated pentobarbital-suppressed basal synaptic transmission (Fig. 3). These indicate that the increased inhibitory transmission by pentobarbital can be regulated by inhibiting AMPAR endocytosis. In addition, we here also found that pentobarbital induced GluA2-containing AMPAR endocytosis, and GluA23Y enables to prevent this process (Fig. 4). However, a previous report has shown that a systemic injection of pentobarbital does not alter GluA2 expression of both the surface and total protein levels in mouse striatal and cortical neurons [26]. Discrepancies between that study and our present work need to be resolved. The species variations and the different brain areas used in these studies may account for some of the variations. Notably, in this study we focused on the acute effects of pentobarbital and GluA23Y on memory and synaptic transmission but the long-term or chronic effects will also need to be further investigated in the future. In summary, pentobarbital causes GluA2-containing AMPAR endocytosis and subsequently suppresses hippocampal CA1 synaptic transmission, thereby resulting in spatial memory deficit. An AMPAR endocytosis inhibitor, GluA23Y can rescue the impaired memory retrieval and the suppressed synaptic transmission. These results provide evidence that the side effects of pentobarbital on spatial memory and synaptic plasticity may be involved in AMPAR trafficking.
Conflict of interest
Introduction Progressive functional changes in neural circuitry mediating learning and motivation are known to underlie key behavioral hallmarks of drug addiction (Hyman et al., 2006, Thomas et al., 2008, Volkow and Morales, 2015). A critical component of mesocorticolimbic circuitry governing reward-related learning and motivated behavior, the nucleus accumbens (NAc) is a structure composed principally of medium spiny neurons (MSNs) that receive converging input from midbrain dopaminergic afferents and glutamatergic projections from cortical and limbic areas. Extensive experimental evidence indicates that drugs of abuse engage endogenous mechanisms of neuronal plasticity to drive persistent changes in synaptic transmission at NAc MSNs (Kauer and Malenka, 2007, Lüscher and Malenka, 2011). This maladaptive form of plasticity has been well-demonstrated to underlie the development and persistence of drug-seeking behavior in animal models of addiction (Wolf, 2016).