Neonatal GABAergic transmission primes vestibular gating of output for adult spatial navigation.

GABAergic interneurons are poised with the capacity to shape circuit output via inhibitory gating. How early in the development of medial vestibular nucleus (MVN) are GABAergic neurons recruited for feedforward shaping of outputs to higher centers for spatial navigation? The role of early GABAergic transmission in assembling vestibular circuits for spatial navigation was explored by neonatal perturbation. Immunohistochemistry and confocal imaging were utilized to reveal the expression of parvalbumin (PV)-expressing MVN neurons and their perineuronal nets. Whole-cell patch-clamp recording, coupled with optogenetics, was conducted in vitro to examine the synaptic function of MVN circuitry. Chemogenetic targeting strategy was also employed in vivo to manipulate neuronal activity during navigational tests. We found in rats a neonatal critical period before postnatal day (P) 8 in which competitive antagonization of GABAergic transmission in the MVN retarded maturation of inhibitory neurotransmission, as evidenced by deranged developmental trajectory for excitation/inhibition ratio and an extended period of critical period-like plasticity in GABAergic transmission. Despite increased number of PV-expressing GABAergic interneurons in the MVN, optogenetic-coupled patch-clamp recording indicated null-recruitment of these neurons in tuning outputs along the ascending vestibular pathway. Such perturbation not only offset output dynamics of ascending MVN output neurons, but was further accompanied by impaired vestibular-dependent navigation in adulthood. The same perturbations were however non-consequential when applied after P8. Results highlight neonatal GABAergic transmission as key to establishing feedforward output dynamics to higher brain centers for spatial cognition and navigation.

Impairments of GABAergic transmission in hippocampus mediate increased susceptibility of epilepsy in the early stage of Alzheimer's disease.

BACKGROUND: Patients with Alzheimer's disease (AD) are often co-morbid with unprovoked seizures, making clinical diagnosis and management difficult. Although it has an important role in both AD and epilepsy, abnormal γ-aminobutyric acid (GABA)ergic transmission is recognized only as a compensative change for glutamatergic damage. Neuregulin 1 (NRG1)-ErbB4 signaling can promote GABA release and suppress epileptogenesis, but its effects on cognition in AD are still controversial. METHODS: Four-month-old APPswe/PS1dE9 mice (APP mice) were used as animal models in the early stage of AD in this study. Acute/chronic chemical-kindling epilepsy models were established with pentylenetetrazol. Electroencephalogram and Racine scores were performed to assess seizures. Behavioral tests were used to assess cognition and emotion. Electrophysiology, western blot and immunofluorescence were performed to detect the alterations in synapses, GABAergic system components and NRG1-ErbB4 signaling. Furthermore, NRG1 was administrated intracerebroventricularly into APP mice and then its antiepileptic and cognitive effects were evaluated. RESULTS: APP mice had increased susceptibility to epilepsy and resulting hippocampal synaptic damage and cognitive impairment. Electrophysiological analysis revealed decreased GABAergic transmission in the hippocampus. This abnormal GABAergic transmission involved a reduction in the number of parvalbumin interneurons (PV+ Ins) and decreased levels of GABA synthesis and transport. We also found impaired NRG1-ErbB4 signaling which mediated by PV+ Ins loss. And NRG1 administration could effectively reduce seizures and improve cognition in four-month-old APP mice. CONCLUSION: Our results indicated that abnormal GABAergic transmission mediated hippocampal hyperexcitability, further excitation/inhibition imbalance, and promoted epileptogenesis in the early stage of AD. Appropriate NRG1 administration could down-regulate seizure susceptibility and rescue cognitive function. Our study provided a potential direction for intervening in the co-morbidity of AD and epilepsy.

ErbB4 deficiency exacerbates olfactory dysfunction in an early-stage Alzheimer's disease mouse model.

Olfactory dysfunction is increasingly recognized as an early indicator of Alzheimer's disease (AD). Aberrations in GABAergic function and the excitatory/inhibitory (E/I) balance within the olfactory bulb (OB) have been implicated in olfactory impairment during the initial stages of AD. While the neuregulin 1 (NRG1)/ErbB4 signaling pathway is known to regulate GABAergic transmission in the brain and is associated with various neuropsychiatric disorders, its specific role in early AD-related olfactory impairment remains incompletely understood. This study demonstrated that olfactory dysfunction preceded cognitive decline in young adult APP/PS1 mice and was characterized by reduced levels of NRG1 and ErbB4 in the OB. Further investigation revealed that deletion of ErbB4 in parvalbumin interneurons reduced GABAergic transmission and increased hyperexcitability in mitral and tufted cells (M/Ts) in the OB, thereby accelerating olfactory dysfunction in young adult APP/PS1 mice. Additionally, ErbB4 deficiency was associated with increased accumulation of Aß and BACE1-mediated cleavage of APP, along with enhanced CDK5 signaling in the OB. NRG1 infusion into the OB was found to enhance GABAergic transmission in M/Ts and alleviate olfactory dysfunction in young adult APP/PS1 mice. These findings underscore the critical role of NRG1/ErbB4 signaling in regulating GABAergic transmission and E/I balance within the OB, contributing to olfactory impairment in young adult APP/PS1 mice, and provide novel insights for early intervention strategies in AD. This work has shown that ErbB4 deficiency increased the burden of Aß, impaired GABAergic transmission, and disrupted the E/I balance of mitral and tufted cells (M/Ts) in the OB, ultimately resulting in olfactory dysfunction in young adult APP/PS1 mice. NRG1 could enhance GABAergic transmission, rescue E/I imbalance in M/Ts, and alleviate olfactory dysfunction in young adult APP/PS1 mice. OB: olfactory bulb, E/I: excitation/inhibition, Pr: probability of release, PV: parvalbumin interneurons, Aß: ß-amyloid, GABA: gamma-aminobutyric acid.

Maternal fluoxetine impairs synaptic transmission and plasticity in the medial prefrontal cortex and alters the structure and function of dorsal raphe nucleus neurons in offspring mice.

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are commonly prescribed to women during pregnancy and breastfeeding despite posing a risk of adverse cognitive outcomes and affective disorders for the child. The consequences of SSRI-induced excess of 5-HT during development for the brain neuromodulatory 5-HT system remain largely unexplored. In this study, an SSRI - fluoxetine (FLX) - was administered to C57BL/6 J mouse dams during pregnancy and lactation to assess its effects on the offspring. We found that maternal FLX decreased field potentials, impaired long-term potentiation, facilitated long-term depression and tended to increase the density of 5-HTergic fibers in the medial prefrontal cortex (mPFC) of female but not male adolescent offspring. These effects were accompanied by deteriorated performance in the temporal order memory task and reduced sucrose preference with no change in marble burying behavior in FLX-exposed female offspring. We also found that maternal FLX reduced the axodendritic tree complexity of 5-HT dorsal raphe nucleus (DRN) neurons in female but not male offspring, with no changes in the excitability of DRN neurons of either sex. While no effects of maternal FLX on inhibitory postsynaptic currents (sIPSCs) in DRN neurons were found, we observed a significant influence of FLX exposure on kinetics of spontaneous excitatory postsynaptic currents (sEPSCs) in DRN neurons. Finally, we report that no changes in field potentials and synaptic plasticity were evident in the mPFC of the offspring after maternal exposure during pregnancy and lactation to a new antidepressant, vortioxetine. These findings show that in contrast to the mPFC, long-term consequences of maternal FLX exposure on the structure and function of DRN 5-HT neurons are mild and suggest a sex-dependent, distinct sensitivity of cortical and brainstem neurons to FLX exposure in early life. Vortioxetine appears to exert fewer side effects with regards to the mPFC when compared with FLX.