Changes in synaptic transmission and protein expression in the brains of adult offspring after prenatal inhibition of the kynurenine pathway

Abstract

Highlights-An inhibitor of kynurenine-3-monoxygenase was administered to pregnant female rats-Adult offspring at postnatal day 60 (P60) showed alterations in synaptic plasticity-Expression of GluN2A, sonic hedgehog and other developmental proteins were changed-Most earlier protein changes had disappeared with no changes in RNA or learning tasks-Prenatal kynurenine pathway inhibition produces persistent synaptic and protein changes 3 Abstract During early brain development, NMDA receptors are involved in cell migration, neuritogenesis, axon guidance and synapse formation, but the mechanisms which regulate NMDA receptor density and function remain unclear. The kynurenine pathway of tryptophan metabolism includes an agonist (quinolinic acid) and an antagonist (kynurenic acid) at NMDA receptors and we have previously shown that inhibition of the pathway using the kynurenine-3-monoxygenase inhibitor Ro61-8048 in late gestation produces rapid changes in protein expression in the embryos and effects on synaptic transmission lasting until postnatal day 21 (P21). The present study sought to determine whether any of these effects are maintained into adulthood. After prenatal injections of Ro61-8048 the litter was allowed to develop to P60 when some offspring were euthanised and the brains removed for examination. Analysis of protein expression by western blotting revealed significantly reduced expression of the GluN2A subunit (32%) and the morphogenetic protein sonic hedgehog (31%), with a 29% increase in expression of doublecortin, a protein associated with neurogenesis. No changes were seen in mRNA abundance using qRT-PCR. Neuronal excitability was normal in the CA1 region of hippocampal slices but paired-pulse stimulation revealed less inhibition at short interpulse intervals. The amount of long-term potentiation was decreased by 49% in treated pups and recovery after low frequency stimulation was delayed. The results not only strengthen the view that basal, constitutive kynurenine metabolism is involved in normal brain development, but also show that changes induced prenatally can affect the brains of adult offspring and those changes are quite different from those seen previously at weaning (P21). Those changes may be mediated by altered expression of NMDAR subunits and sonic hedgehog.

Preferential Disruption of Prefrontal GABAergic Function by Nanomolar Concentrations of the α7nACh Negative Modulator Kynurenic Acid

“…All LFP recordings were conducted in the medial PFC (prelimbic and infralimbic regions) using a concentric bipolar electrode (SNE-100x 50 mm; Rhodes Medical Instruments) attached to a 28-gauge cannula to enable local administration of artificial CSF (aCSF)-containing agonists and antagonists as described previously (Thomases et al, 2013). Here, single infusions of 0.8 l of aCSF alone (control) or in combination with one of the following neuromodulators were delivered into the PFC at 0.1 l/min: (1) KYNA (100-300 nM), (2) methyllycaconitine (MLA; 300 nM), (3) 7-chlorokynurenic acid (7Cl-KYNA; 300 nM), (4) Indiplon (10 M), (5) KYNA ϩ Indiplon, or (6) MLA ϩ Indiplon.…”

“…The functional maturation of GABAergic circuits in the prefrontal cortex (PFC) is one key mechanism for enabling proper processing of ventral hippocampal afferent information (Thomases et al, 2013;Caballero et al, 2014) and for supporting PFCdependent cognitive functions (Floresco, 2013;Tse et al, 2015). It is thought that a disruption of such GABAergic control in the PFC underlies the onset of cognitive deficits seen in a variety of psychiatric disorders including schizophrenia (Tseng et al, 2009;Tse et al, 2015;Caballero et al, 2016).…”

“…It is thought that a disruption of such GABAergic control in the PFC underlies the onset of cognitive deficits seen in a variety of psychiatric disorders including schizophrenia (Tseng et al, 2009;Tse et al, 2015;Caballero et al, 2016). Further understanding of the different synaptic mechanisms that enable proper regulation of GABAergic function in the PFC is therefore a critical step toward gaining insights on how to restore normal cognition in schizophrenia and related psychiatric syndromes (Caballero and Tseng, 2016).…”

“…Therefore, the increased PFC levels of KYNA observed in schizophrenia may be clinically relevant and mechanistically linked to the onset of cognitive impairments as a result of deficits in ␣7nAChR and/or NMDAR function in cortical circuits (Robbins and Murphy, 2006;Timofeeva and Levin, 2011). Accordingly, studies from animal models converge to indicate that increased cortical levels of KYNA can lead to deficits in executive function (Chess et al, 2007;Akagbosu et al, 2012;Alexander et al, , 2013Pershing et al, 2015;Pershing et al, 2016). However, the precise mechanism underlying the disrupting action of KYNA in cortical circuits remains elusive despite the fact that fluctuations in endogenous KYNA levels in the PFC are known to modulate bidirectionally the extracellular concentrations of glutamate (Konradsson-Geuken et al, 2010;, GABA (Beggiato et al, 2014), dopamine , and acetylcholine (Zmarowski et al, 2009).…”

“…We used local field potential (LFP) recordings to assess disruptions in the pattern of PFC response to ventral hippocampal train stimulation (10, 20, and 40 Hz) following PFC infusions of KYNA in vivo. This protocol of train stimulation was chosen because of its sensitivity in revealing changes in the relative contribution of excitatory and inhibitory transmission in the PFC Thomases et al, 2013). At the cellular level, whole-cell patch-clamp recordings in brain slices were then used to identify the mechanisms by which nanomolar concentrations of KYNA regulate synaptic transmission onto pyramidal output neurons in the PFC.…”