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GABA/glycine sensitivity of MNTB neurons. (A) 1 mM of GABA or glycine was pressure ejected onto the soma of a P6 (left) or P14 (right) MNTB neuron. (B) average responses to GABA (gray bars) did not change with age, whereas those to glycine (white bars) increased significantly (P 0.001).
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Maturation of some brain stem and spinal inhibitory systems is characterized by a shift from GABAergic to glycinergic transmission. Little is known about how this transition is expressed in terms of individual axonal inputs and synaptic sites. We have explored this issue in the rat medial nucleus of the trapezoid body (MNTB). Synaptic responses at...
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... GABA and glycine receptor expression were exam- ined by testing the sensitivity of MNTB neurons to the respec- tive agonists. The conductance elicited by puffs of saturating concentrations of GABA (1 mM) was similar in young and old rats ( Fig. 3; P 0.05). Interestingly, GABA-evoked responses were 10 times larger than the synaptically evoked GABAer- gic responses described below. If we assume that maximal stimuli recruited a significant fraction of input fibers, these data would suggest that a large fraction of GABA A receptors may be nonsynaptic. In contrast, sensitivity to ...
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... the synaptically evoked GABAer- gic responses described below. If we assume that maximal stimuli recruited a significant fraction of input fibers, these data would suggest that a large fraction of GABA A receptors may be nonsynaptic. In contrast, sensitivity to glycine (1 mM) increased by two orders of magnitude between ages P5-P7 and P13-P15 ( Fig. 3; 0.001 vs. 0.20 S; P 0.001). This increase in glycine sensitivity is consistent with previous studies of Kungel and Friauf (1997) and corresponds well to the observed age-dependent increase in the contribution of glycine receptors to the ...
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... affected intracel- lular calcium and internal stores ( Lim et al. 2003) and thus probably do not reflect multivesicular release. Hence, an in- creased number of receptors at single synaptic sites may contribute to the larger glycinergic mIPSCs, consistent with the increased expression of glycine receptors observed in MNTB neurons over development (Fig. 3). Other factors such as receptor occupancy could also contribute to larger mIPSCs. However, it should be noted that the observed increase in the mIPSC is not sufficient to explain the much larger increase in the evoked IPSCs (Fig. ...
Citations
... To measure mixed miniature spontaneous PSCs, a post-synaptic target is typically whole-cell voltage clamped in the presence of tetrodotoxin to block sodium-based action potentials. Mixed miniature PSCs have been observed in neurons that receive synapses that co-release glycine and GABA (Jonas et al., 1998;Awatramani et al., 2005), glutamate and Ach (Li et al., 2004;Borodinsky and Spitzer, 2007), and glutamate and GABA (Shabel et al., 2014;Zimmermann et al., 2015). ...
Multi-transmitter neurons, i.e., those that release more than one type of neurotransmitter, have been found in many organisms and brain areas. Given the peculiar biology of these cells, as well as the potential for diverse effects of each of the transmitters released, new tools, and approaches are necessary to parse the mechanisms and functions of synaptic co-transmission. Recently, we and others have studied neurons that project to the lateral habenula and release both gamma-aminobutyric acid (GABA) and glutamate, in some cases by packaging both transmitters in the same synaptic vesicles. Here, we discuss the main challenges with current electrophysiological approaches to studying the mechanisms of glutamate/GABA co-release, a novel statistical analysis that can identify co-packaging of neurotransmitters versus release from separate vesicle, and the implications of glutamate/GABA co-release for synapse function and plasticity.
... Varied cytosolic accumulation and synaptic co-release of GABA and glycine, as occurs in the majority of hindbrain inhibitory neurons, constitutes the most studied case of variability in neurotransmitter content (Jonas et al., 1998;Chery and de Koninck, 1999;O'Brien and Berger, 1999;Dumoulin et al., 2001;Awatramani et al., 2005;Dugue et al., 2005;Giber et al., 2015;Moore and Trussell, 2017;Nerlich et al., 2017). GABAergic, glycinergic and mixed inhibitory neurons persist into adulthood, when they can contact the same postsynaptic neurons (Ottersen et al., 1988;Todd and Sullivan, 1990;Dumba et al., 1998;Riquelme et al., 2001;Lu et al., 2008;Batten et al., 2010;Dufour et al., 2010;Husson et al., 2014;Paik et al., 2019). ...
... GABAergic, glycinergic and mixed inhibitory neurons persist into adulthood, when they can contact the same postsynaptic neurons (Ottersen et al., 1988;Todd and Sullivan, 1990;Dumba et al., 1998;Riquelme et al., 2001;Lu et al., 2008;Batten et al., 2010;Dufour et al., 2010;Husson et al., 2014;Paik et al., 2019). However, to date, the diversity of IPSCs properties has always been attributed to the expression by the postsynaptic neurons of different types of GABA A and glycine receptors (Rossi and Hamann, 1998;Chery and de Koninck, 1999;Chery and De Koninck, 2000;Mitchell and Silver, 2000;Dumoulin et al., 2001;Gao et al., 2001;Keller et al., 2001;Ahmadi et al., 2003;Awatramani et al., 2005;Gonzalez-Forero and Alvarez, 2005;Lu et al., 2008;Rousseau et al., 2012;Giber et al., 2015;Moore and Trussell, 2017;Nerlich et al., 2017). While presynaptic and postsynaptic co-maturation has been reported (Nabekura et al., 2004), the role of presynaptic transmitter content in the properties and strength of mature inhibitory synapses has been overlooked. ...
Neurotransmitter content is deemed the most basic defining criterion for neuronal classes, contrasting with the intercellular heterogeneity of many other molecular and functional features. Here we show, in the adult mouse brain, that neurotransmitter content variegation within a neuronal class is a component of its functional heterogeneity. Golgi cells (GoCs), the well-defined class of cerebellar interneurons inhibiting granule cells (GrCs), contain cytosolic glycine, accumulated by the neuronal transporter GlyT2, and GABA in various proportions. By performing acute manipulations of cytosolic GABA and glycine supply, we find that competition of glycine with GABA reduces the charge of IPSC evoked in GrCs and, more specifically, the amplitude of a slow component of the IPSC decay. We then pair GrCs recordings with optogenetic stimulations of single GoCs, which preserve the intracellular transmitter mixed content. We show that the strength and decay kinetics of GrCs IPSCs, which are entirely mediated by GABA A receptors, are negatively correlated to the presynaptic expression of GlyT2 by GoCs. We isolate a slow spillover component of GrCs inhibition that is also affected by the expression of GlyT2, leading to a 56% decrease in relative charge. Our results support the hypothesis that presynaptic loading of glycine negatively impacts the GABAergic transmission in mixed interneurons, most likely through a competition for vesicular filling. We discuss how the heterogeneity of neurotransmitter supply within mixed interneurons like the GoC class may provide a presynaptic mechanism to tune the gain of microcircuits such as the granular layer, thereby expanding the realm of their possible dynamic behaviors.
... Microglial inhibitory synapse elimination can be modulated by the MERTK signaling pathway in the hippocampus 48 . Although the MNTB is largely regulated by highly glutamatergic calyces, inhibitory input from the ventral nucleus of the trapezoid body provides glycinergic input to the MNTB which matches the large conduction of the calyceal input and can suppress MNTB spiking when activated 49,50 . MNTB cells are glycinergic and rapidly provide input to several auditory nuclei including the LSO 51-54 . ...
Specialized sound localization circuit development requires synapse strengthening, refinement, and pruning. Many of these functions are carried out by microglia, immune cells that aid in regulating neurogenesis, synaptogenesis, apoptosis, and synaptic removal. We previously showed that postnatal treatment with BLZ945 (BLZ), an inhibitor of colony stimulating factor 1 receptor (CSF1R), eliminates microglia in the brainstem and disables calyceal pruning and maturation of astrocytes in the medial nucleus of the trapezoid body (MNTB). BLZ treatment results in elevated hearing thresholds and delayed signal propagation as measured by auditory brainstem responses (ABR). However, when microglia repopulate the brain following the cessation of BLZ, most of the deficits are repaired. It is unknown whether this recovery is achievable without the return of microglia. Here, we induced sustained microglial elimination with a two-drug approach using BLZ and PLX5622 (PLX). We found that BLZ/PLX treated mice had impaired calyceal pruning, diminished astrocytic GFAP in the lateral, low frequency, region of MNTB, and elevated glycine transporter 2 (GLYT2) levels. BLZ/PLX treated mice had elevated hearing thresholds, diminished peak amplitudes, and altered latencies and inter-peak latencies. These findings suggest that microglia are required to repopulate the brain in order to rectify deficits from their ablation.
... For VGAT, it is less clear whether its tonotopic distribution in the first postnatal week reflects structural development of incoming inhibitory axons or molecular maturation of a specific protein. Although inhibitory neurotransmission in the MNTB can be recorded as early as P5-7 (Awatramani et al., 2005), it is unknown how it is associated with tonotopic arrangement. Nevertheless, given their essential roles in neurotransmitter loading and releasing, the gradient of VGLUT1, VGAT, Syt1, and Syt2 distribution along the tonotopic axis could be indicative of a tonotopic capability of terminals in neurotransmitter cycling, and thus serves as a fundamental presynaptic mechanism for tonotopic maturation of synaptic transmission (Leao et al., 2006). ...
Tonotopic organization is a fundamental feature of the auditory system. In the developing auditory brainstem, the ontogeny and maturation of neurotransmission progress from high to low frequencies along the tonotopic axis. To explore the underlying mechanism of this tonotopic development, we aim to determine whether the presynaptic machinery responsible for neurotransmitter release is tonotopically differentiated during development. In the current study, we examined vesicular neurotransmitter transporters and calcium sensors, two central players responsible for loading neurotransmitter into synaptic vesicles and for triggering neurotransmitter release in a calcium‐dependent manner, respectively. Using immunocytochemistry, we characterized the distribution patterns of vesicular glutamate transporters (VGLUTs) 1 and 2, vesicular gamma‐aminobutyric acid transporter (VGAT), and calcium sensor synaptotagmin (Syt) 1 and 2 in the developing mouse medial nucleus of the trapezoid body (MNTB). We identified tonotopic gradients of VGLUT1, VGAT, Syt1, and Syt2 in the first postnatal week, with higher protein densities in the more medial (high‐frequency) portion of the MNTB. These gradients gradually flattened before the onset of hearing. In contrast, VGLUT2 was distributed relatively uniformly along the tonotopic axis during this prehearing period. In mice lacking Fragile X mental retardation protein, an mRNA‐binding protein that regulates synaptic development and plasticity, progress to achieve the mature‐like organization was altered for VGLUT1, Syt1, and Syt2, but not for VGAT. Together, our results identified novel organization patterns of selective presynaptic proteins in immature auditory synapses, providing a potential mechanism that may contribute to tonotopic differentiation of neurotransmission during normal and abnormal development.
... The developmental features of GABAergic and glycinergic input properties are dependent on neuronal groups, as has been described in the hypoglossal nucleus (Singer et al., 1998), dorsal motor nucleus of the vagus (McMenamin et al., 2016), pre-Bötzinger complex (Ritter and Zhang, 2000), and medial nucleus of the trapezoid body (Awatramani et al., 2005). We showed that the developmental time course of GABAergic and glycinergic current properties differ even between jawclosing and jaw-opening MNs located within the trigeminal motor nucleus. ...
... Our previous studies have demonstrated that GABAergic and glycinergic inputs from premotor neuron areas are excitatory in rat P1-5 jawclosing and jaw-opening MNs, and the switch from excitatory to inhibitory synaptic transmission occurs after P8 (Gemba-Nishimura et al., 2010;Nakamura et al., 2008). These excitatory effects of GABA and glycine have been reported in various neuronal groups (Awatramani et al., 2005;McMenamin et al., 2016;Ritter and Zhang, 2000;Singer et al., 1998). It has been proposed that GABAergic and glycinergic depolarization can induce neuronal maturation by Ca 2+ entry into postsynaptic neurons via voltage-dependent Ca 2+ channels (Flint et al., 1998;Goodman and Shatz, 1993;Lo et al., 1998). ...
Trigeminal motoneurons (MNs) innervating the jaw-closing and jaw-opening muscles receive numerous inhibitory synaptic inputs from GABAergic and glycinergic neurons, which are essential for oromotor functions, such as the orofacial reflex, suckling, and mastication. The properties of the GABAergic and glycinergic inputs of these MNs undergo developmental alterations during the period in which their feeding behavior proceeds from suckling to mastication; however, the detailed characteristics of the developmental patterns of GABAergic and glycinergic transmission in these neurons remain to be elucidated. This study was conducted to investigate developmental changes in miniature inhibitory postsynaptic currents (mIPSCs) in masseter (jaw-closing) and digastric (jaw-opening) MNs using brainstem slice preparations obtained from Wistar rats on postnatal day (P)2–5, P9–12, and P14–17. The frequency and amplitude of glycinergic mIPSCs substantially increased with age in both the masseter and digastric MNs. The rise time and decay time of glycinergic mIPSCs in both MNs decreased during development. In contrast, the frequency of GABAergic components in masseter MNs was higher at P2–5 than at P14–17, whereas that in the digastric MNs remained unchanged throughout the postnatal period. The proportion of currents mediated by GABA-glycine co-transmission was higher at P2–5, and then it decreased with age in both MNs. These results suggest that characteristics related to the development of inhibitory synaptic inputs differ between jaw-closing and jaw-opening MNs and between GABAergic and glycinergic currents. These distinct developmental characteristics may contribute to the development of feeding behaviors.
... postnatal development of auditory brainstem neurons to prepare the auditory pathways for the onset of hearing around P12-14. The medial nucleus of the trapezoid body (MNTB) and its specialized terminal from the globular bushy cells from the aVCN, the calyx of Held, has been extensively studied during the pre-hearing to post-hearing periods of development and has been the source of most of the knowledge about the maturation of the brainstem auditory neurons.Most of these studies about the postnatal development of the electrophysiological and synaptic properties of MNTB principal neurons and the calyx of Held showed that the most changes occur before and near hearing onset(Iwasaki & Takahashi, 1998;Taschenberger & Von Gersdorff, 2000;Taschenberger et al., 2002; Joshi & Wang, 2002;Leão & Von Gersdorff, 2002;Oleskevich & Walmsley, 2002;Awatramani et al., 2005; Youssoufian et al., 2005; Leão et al., 2005a;Nakamura & Takahashi, 2007; Leão & von Gersdorff, 2009;Nakamura & Cramer, 2011). On the other hand, some hearing-dependent changes are observed but, preventing these changes with sound deprivation do not significantly impact the firing and neurotransmission in the MNTB and calyx of Held(Leão et al., 2006; Grande et al., 2014). ...
The dorsal cochlear nucleus (DCN) in the auditory brainstem integrates auditory and somatosensory information. Mature fusiform neurons express two qualitative intrinsic states in equal proportions: quiet, with no spontaneous regular action potential firing, or active, with regular spontaneous action potential firing. However, how these firing states and other electrophysiological properties of fusiform neurons develop during early postnatal days to adulthood is not known. Thus, we recorded fusiform neurons from mice from P4 to P21 and analyzed their electrophysiological properties. In the pre-hearing phase (P4-P13), we found that fusiform neurons are mostly quiet, with the active state emerging after hearing onset at P14. Subthreshold properties present more variations before hearing onset, while action potential properties vary more after P14, developing bigger, shorter, and faster action potentials. Interestingly, the activity threshold is more depolarized in pre-hearing cells suggesting that persistent sodium current (INaP) increases its expression after hearing. In fact, INaP increases its expression after hearing, accordingly with the development of active neurons. Thus, we suggest that the post-hearing expression of INaP creates the active state of the fusiform neuron. At the same time, other changes refine the passive membrane properties and increase the speed of action potential firing of fusiform neurons.
... It may be due to the looser arrangement of VNTB cells than in the P. hastatus bat. The VNTB is one of the major sources of glycinergic inhibitory input to the ipsilateral MNTB and able to suppress MNTB spiking when activated (Awatramani et al., 2005) which will make the bats more sensitive to the interaural level disparities. The P. hastatus is omnivorous, and, although it eats fruit and insects, it prefers meat, preying on small vertebrates, including other bats. ...
The present study was taken to test the hypothesis that the medial nucleus of the trapezoid body (MNTB) of echolocating neotropical bats with different foraging behavior will exhibit morphological variations in relative size, degree of complexity and spatial distribution. The brains were collected from six male adult bats of each species: Noctilio leporinus (fish-eating), Phyllostomus hastatus (carnivorous/ omnivorous) and Carollia perspicillata (fruit-eating) and were double-embedded and transverse serial sections were cut and stained with cresyl fast violet. The results showed that the MNTB is well developed in all the bats in general and the mean length of the MNTB was 1160 ± 124 µm in N. leporinus, 400 ± 59 µm in P. hastatus and 320 ± 25µm in C. perspicillata. The body and brain weight do not reflect proportionately on the size of the MNTB in the present study. The hearing frequency spectrum did not covary with the size of the MNTB among the bats studied. The MNTB is clearly demarcated from the ventral nucleus of the trapezoid body (VNTB) only in P. hastatus. The MNTB comprised mainly three types of cells in all three bats: dense-staining multipolar cells (12.5 µm and 25.0 µm diameter); light-staining multipolar cells measuring (12.5 µm and 25.0 µm diameter) and light-staining round cells (5.0 µm diameter). The large sized MNTB was observed in N. leporinus, which suggests that it relies heavily on echolocation whereas P. hastatus and C. perspicillata use echolocation as well but also rely on hearing, smell and vision.
... MNTB neurons receive glutamatergic excitation from the VCN through a giant synapse called the calyx of Held, and glycinergic and GABAergic inhibition from collateral projections and VNTB. 49,50 The GABAergic component declines through adulthood resulting in mostly glycinergic inhibition in the adult [51][52][53] ). The glycinergic component of inhibition is fast and large, capable of following rapid stimulus trains (several 100 Hz) that match and suppress firing of MNTB neurons despite the extremely large calyceal excitatory input. ...
... The glycinergic component of inhibition is fast and large, capable of following rapid stimulus trains (several 100 Hz) that match and suppress firing of MNTB neurons despite the extremely large calyceal excitatory input. 53,54 Disruptions to glutamatergic, GABAergic or glycinergic presynaptic inputs to MNTB could have profound effects on ILD encoding. ...
Autism spectrum disorders (ASD) are strongly associated with auditory hypersensitivity or hyperacusis (difficulty tolerating sounds). Fragile X syndrome (FXS), the most common monogenetic cause of ASD, has emerged as a powerful gateway for exploring underlying mechanisms of hyperacusis and auditory dysfunction in ASD. This review discusses examples of disruption of the auditory pathways in FXS at molecular, synaptic, and circuit levels in animal models as well as in FXS individuals. These examples highlight the involvement of multiple mechanisms, from aberrant synaptic development and ion channel deregulation of auditory brainstem circuits, to impaired neuronal plasticity and network hyperexcitability in the auditory cortex. Though a relatively new area of research, recent discoveries have increased interest in auditory dysfunction and mechanisms underlying hyperacusis in this disorder. This rapidly growing body of data has yielded novel research directions addressing critical questions regarding the timing and possible outcomes of human therapies for auditory dysfunction in ASD.
... Further maturation is highly relevant to auditory experience and could result in temporally precise and strengthened excitatory and inhibitory driving forces, which are crucial for the analysis of binaural sounds (Tollin, 2003;Benjamin et al., 2009;Kreinest et al., 2009;Cai et al., 2010;Popescu and Polley, 2010;Walcher et al., 2011;Alamilla and Gillespie, 2013;Keating et al., 2013;Kotak and Sanes, 2014;Tillein et al., 2016). This development is related to changes in receptor expression and transitions in subunit composition, as well as other mechanisms (Sanes and Friauf, 2000;Awatramani et al., 2005;. Previous research has shown that the MNTB, which is the origin of the inhibitory projections in the LSO, exhibits altered neurotransmission and receptor expression after unilateral cochlear ablation (Dai et al., 2018). ...
Unilateral auditory deprivation results in lateralization changes in the central auditory system, interfering with the integration of binaural information and thereby leading to a decrease in binaural auditory functions such as sound localization. Principal neurons of the lateral superior olive (LSO) are responsible for computing the interaural intensity differences that are critical for sound localization in the horizontal plane. To investigate changes caused by unilateral auditory deprivation, electrophysiological activity was recorded from LSO principal neurons in control rats and rats with unilateral cochlear ablation. At one week after unilateral cochlear ablation, the excitability of LSO principal neurons on the side ipsilateral to the ablation (the ablated side) was greater than that on the side contralateral to the ablation (the intact side); however, the input resistance increased on both sides. Furthermore, by analysing the miniature inhibitory postsynaptic currents (mIPSCs) and miniature excitatory postsynaptic currents (mEPSCs), we found that unilateral auditory deprivation weakened the inhibitory driving force on the intact side, whereas it strengthened the excitatory driving force on the ablated side. In summary, asymmetric changes in the electrophysiological activity of LSO principal neurons were found on both sides at postnatal day 19, one week after unilateral cochlear ablation.
... In the present study all experiments were performed on slices obtained from relatively young animals of postnatal days 15-21 (P15-P21). Several studies have shown that synaptic properties can change during development 13,48,49 . A study investigating the properties of inhibitory synapses in the medial nucleus of the trapezoid body (MNTB) showed that the amplitude and kinetics of evoked IPSCs change dramatically between P5-7 and P25 48 . ...
... Several studies have shown that synaptic properties can change during development 13,48,49 . A study investigating the properties of inhibitory synapses in the medial nucleus of the trapezoid body (MNTB) showed that the amplitude and kinetics of evoked IPSCs change dramatically between P5-7 and P25 48 . Another study of excitatory synapses in the MNTB showed changes in short-term plasticity of these synapses during the same developmental period 49 . ...
Short-term depression is a low-pass filter of synaptic information, reducing synaptic information transfer at high presynaptic firing frequencies. Consequently, during elevated presynaptic firing, little information passes to the postsynaptic neuron. However, many neurons fire at relatively high frequencies all the time. Does depression silence their synapses? We tested this apparent contradiction in the indirect pathway of the basal ganglia. Using numerical modeling and whole-cell recordings from single entopeduncular nucleus (EP) neurons in rat brain slices, we investigated how different firing rates of globus pallidus (GP) neurons affect information transmission to the EP. Whole-cell recordings showed significant variability in steady-state depression, which decreased as stimulation frequency increased. Modeling predicted that this variability would translate into different postsynaptic noise levels during constitutive presynaptic activity. Our simulations further predicted that individual GP-EP synapses mediate gain control. However, when we consider the integration of multiple inputs, the broad range of GP firing rates would enable different modes of information transmission. Finally, we predict that changes in dopamine levels can shift the action of GP neurons from rate coding to gain modulation. Our results thus demonstrate how short-term depression shapes information transmission in the basal ganglia in particular and via GABAergic synapses in general.
