Pax2-expressing neurons in the hindbrain and spinal cord predominantly differentiate as inhibitoryinterneurons (Maricich and Herrup, 1999; Gross et al., 2002; Cheng et al., 2004; Glasgow et al., 2005; Mizuguchi et al., 2006; Wildner et al., 2006). In the Pax2- mutant cord, there is a marked loss of GABAergic markers in the dorsal horn, demonstrating that Pax2 functions as an obligatory regulator of the inhibitory-neurotransmitter program in these cells (Cheng et al., 2004). These dorsal inhibitoryinterneurons, as well as the ventrally-derived V0 and V1 inhibitoryinterneurons, also express Lhx1 and Lhx5 (Burrill et al., 1997; Moran-Rivard et al., 2001; Gross et al., 2002; Muller et al., 2002) (this study). This has led to the suggestion that the co-expression of Pax2 and Lhx1 and/or Lhx5 may provide a transcription factor code for inhibitory neurons in the hindbrain and spinal cord. Although roles for Lhx1 and Lhx5 have been demonstrated in head, kidney and motor neuron development (Kobayashi et al., 2005; Kobayashi et al., 2004; Zhao et al., 1999; Kania et al., 2000), their overlapping expression in spinal interneurons (Sheng et al., 1997), coupled with the early embryonic lethal phenotype of the Lhx1 mutant (Shawlot and Behringer, 1995), has impeded analyzing their role(s) in spinal-interneuron development.
the protein ATXN1, which is involved in transcriptional regulation. Although symptoms appear relatively late in life, primarily from cerebellar dysfunction, pathogenesis begins early, with transcriptional changes detectable as early as a week after birth in SCA1-knockin mice. Given the importance of this postnatal period for cerebellar development, we asked whether this region might be developmentally altered by mutant ATXN1. We found that expanded ATXN1 stimulates the proliferation of postnatal cerebellar stem cells in SCA1 mice. These hyperproliferating stem cells tended to differentiate into GABAergic inhibitoryinterneurons rather than astrocytes; this significantly increased the GABAergic inhibitory interneuron synaptic connections, disrupting cerebellar Purkinje cell function in a non–cell autonomous manner. We confirmed the increased basket cell– Purkinje cell connectivity in human SCA1 patients. Mutant ATXN1 thus alters the neural circuitry of the developing cerebellum, setting the stage for the later vulnerability of Purkinje cells to SCA1. We propose that other late-onset degenerative diseases may also be rooted in subtle developmental derailments.
The auditory cortex is essential for encoding complex and behaviorally relevant sounds. Many questions remain concerning whether and how distinct cortical neuronal subtypes shape and encode both simple and complex sound properties. In chapter 2, we tested how neurons in the auditory cortex encode water-like sounds perceived as natural by human listeners, but that we could precisely parametrize. The stimuli exhibit scale-invariant statistics, specifically temporal modulation within spectral bands scaled with the center frequency of the band. We used chronically implanted tetrodes to record neuronal spiking in rat primary auditory cortex during exposure to our custom stimuli at different rates and cycle-decay constants. We found that, although neurons exhibited selectivity for subsets of stimuli with specific statistics, over the population responses were stable. These results contribute to our understanding of how auditory cortex processes natural sound statistics. In chapter 3, we review studies examining the role of different cortical inhibitoryinterneurons in shaping sound responses in auditory cortex. We identify the findings that support each other and the mechanisms that remain unexplored. In chapter 4, we tested how direct feedback from auditory cortex to the inferior colliculus modulated sound responses in the inferior colliculus. We optogenetically activated or suppressed cortico-collicular feedback while recording neuronal spiking in the mouse inferior colliculus in response to pure tones and dynamic random chords. We found that feedback modulated sound responses by reducing sound selectivity by decreasing responsiveness to preferred frequencies and increasing
Spatiotemporal patterns of neuronal activity, which underlie per- ceptual, cognitive, and behavioral outputs of nervous systems, depend on the connectivity of coupled systems of excitatory and inhibitory neurons (Buzsa´ki, 2010). One inhibitory motif rec- ognized as a ubiquitous building block of neural architecture mediates recurrent or feedback inhibition. Here, activity of an excitatory principal neuron stimulates not only downstream ex- citatory neurons but also inhibitoryinterneurons that feed back onto the same principal cell to limit the duration and/or magni- tude of its excitation (Isaacson and Scanziani, 2011). Most inhib- itory feedback is mediated by local circuit interneurons (LNs)
mutant mice develop a chronic scratching condition in associa- tion with a loss of a large population of GABAergic inhibitory in- terneurons, it is likely that their condition models neuropathic itch, namely itch associated with direct damage to the central nervous system. In this respect, the itch is comparable to the neuropathic pain that can be triggered by dysfunctional dorsal horn GABAergic circuits. By replenishing a pool of inhibitoryinterneurons, MGE transplantation can overcome the loss of inhibition, thus mitigating the presumptive underlying etiol- ogy of the neuropathic itch condition. Not only did we demon- strate that there was significantly reduced scratching in MGE cell–transplanted mice, but we also observed remarkable heal- ing of the previously affected region. Importantly, the area of skin that recovered corresponded to the spinal cord target of the transplant. In other words, the treatment does not result from a systemic response to mediators released from the transplant, but likely reflects local neuronal circuit reorganization. Indeed, when excessive scratching and lesions were present over mul- tiple body regions, only the region that corresponded to the transplant was influenced. Interestingly, even though the loss of GABAergic neurons in the Bhlhb5 mutant mice occurs through- out the spinal cord, bilaterally, most lesions only develop on one side of the body, indicating that loss of inhibition is not sufficient to trigger exacerbated scratching.
Cancer induced bone pain (CIBP) remains one of the most intractable clinical problems due to poor understanding of its underlying mechanisms. Recent studies demonstrate the decline of inhibitoryinterneurons, especially GABAergic interneurons in the spinal cord, can evoke generation of chronic pain. It has also been reported that neuronal MHC-I expression renders neurons vulnerable to cytotoxic CD8 + T cells and finally lead to neurons apoptosis in a variety neurological disorders. However, whether MHC-I could induce the apoptosis of GABAergic interneurons in spinal cord and contribute to the development of CIBP remains unknown. In this study, we investigated roles of MHC-I and underlying mechanisms in CIBP on a rat model. Our results showed that increased MHC-I expression on GABAergic interneurons could deplete GABAergic interneurons by inducing their apoptosis in the spinal dorsal horn of tumor-bearing rats. Pretreatment of MHC-I RNAi-Lentivirus could prevent the apoptosis of GABAergic interneurons and therefore alleviated mechanical allodynia induced by tumor cells intratibial injection. Additionally, we also found that CD8 + T cells were colocalized with MHC-I and GABAergic neurons and presented a significant and persistent increase in the spinal cord of tumor-bearing rats. Taken together, these findings indicated that MHC-I could evoke CIBP by promoting apoptosis of GABAergic interneurons in the dorsal horn, and this apoptosis was closely related to local CD8 + T cells.
The nonspiking interneurons analysed in this study do not represent the sampling of a particular population of nonspiking interneurons. The recordings were made from the neuropil and therefore different types of nonspiking interneurons were encountered largely at random. This is reflected in the fact that their cell bodies were in four different locations within the ganglion where cell bodies of nonspiking neurons are known to reside (Siegler and Burrows, 1979). On the basis of their morphology and physiological action, some of the interneurons encountered in the present study can be directly related to previous and more detailed descriptions (Siegler and Burrows, 1979; Watkins et al., 1985). For example, the interneuron in Fig. 3 is one in a group of three nonspiking interneurons described first in locusts (Siegler and Burrows, 1979; Wilson, 1981) and then in stick insects (Carausius morosus; Büschges, 1990). Two of the nonspiking interneurons with cell bodies in this position have the pattern of branches shown here, whereas the third has an additional ipsilateral field of branches. In stick insects, the two former interneurons were originally called E4 neurons (E for excitatory) but the name was subsequently revised so that one was called E4 and the other I4 (I for inhibitory) in both locusts and stick insects (Büschges and Wolf, 1995) to reflect the finding that there were two neurons with similar shapes (Wilson, 1981) but different actions on the same motor neurons (Wolf and Büschges, 1995). Interneurons with cell bodies in this position that we stained in five locusts always showed GABA immunoreactivity, suggesting that at cell body
Cockroaches escape from terrestrial predators by making an evasive turn and running away (Camhi, 1984). The air displacement produced by the predator’s strike is sensed by wind-sensitive receptors on the cerci, two posterior antenna-like organs. These receptors excite two distinct populations of giant interneurons, the ventral giant interneurons (vGIs) and the dorsal giant interneurons (dGIs), in the last abdominal ganglion of the nerve cord (Camhi, 1984). The vGIs are known to control the direction of the escape turn when the animal is on the ground (Camhi, 1988; Ritzmann, 1993; Comer and Dowd, 1993; Liebenthal et al. 1994), while the dGIs are known to initiate and maintain flight (Ritzmann et al. 1982; Libersat et al. 1989; Libersat, 1992). Since cockroaches are not equipped with an ultrasonic hearing sense (Yager and Scaffidi, 1993) and consequently do not respond to ultrasound with escape maneuvers, as many other insects do (Hoy et al. 1989; Libersat and Hoy, 1991), it is reasonable to envisage that, while flying, cockroaches may recruit their wind escape circuit to evade aerial predators such as bats. Indeed, recently Ganihar et al. (1994) have shown that flying cockroaches produce various flight maneuvers that should cause an evasive turn away from a wind stimulus. Such flight maneuvers are not produced after cercal ablation. The most likely candidates to mediate these evasive flying maneuvers are the dGIs, because the wind sensitivity of the vGIs is greatly reduced during flight (Libersat et al. 1989; Libersat, 1992). In contrast, the dGIs retain their wind sensitivity during flight (Libersat, 1992) and also they respond in a directionally sensitive manner to a wind puff delivered from the side (Ganihar et al. 1994). In this study, the possibility that the dGIs mediate evasive flying maneuvers was investigated by stimulating individual identified dGIs during flight and measuring the asymmetrical responses in a pair of left and right flight depressor muscles, the subalars of the metathoracic wings.
unclear (Schmitt and Ache, 1979; Koehl et al., 2002). There can be little doubt, however, that the act of flicking should itself generate hydrodynamic stimulation of the antennular sensilla. Previous electrophysiological studies of olfactory interneurons in the crayfish brain from my laboratory did not consider effects of hydrodynamic stimulation of the antennules during responses to odorants, since a continuous, regulated flow of freshwater bathed the immobilized antennular flagella during the course of an experiment (Mellon and Alones, 1995; Mellon, 1996). Similar electrophysiological studies of neurons in the olfactory midbrain of the spiny lobster Panulirus argus, using a different stimulus regimen, did provide evidence for transient effects of rapidly introducing seawater past the antennule but they were not followed up in any detail (Schmidt and Ache, 1996b).
Neuronal nitric oxide synthases require significant increases in intracellular calcium to become activated, possibly accompanied by activation of NMDA receptors (Garthwaite, 2008). Thus, the relatively sparse action potentials generated by LTS interneurons in brain slices may not be sufficient for significant nitric oxide production. In order to be able to photo-stimulate LTS interneurons selectively, we crossed transgenic mice expressing Cre-dependent channelrhodopsin constructs with mice expressing Cre recombinase exclusively in neurons expressing somatostatin. A similar transgenic strategy was recently used to stimulate striatal LTS interneurons by Rafalovich et al. (2015). As expected, in the striatum of the resulting offspring, photostimulation produced fast and large depolarizations in LTS interneurons but not in MSNs or cholinergic interneurons. However, prolonged light pulses evoked slowly developing, sustained depolarizations of cholinergic interneurons, often accompanied by robust action potential firing. These excitatory responses can be safely attributed to nitric oxide, as they were entirely blocked by L-NAME, a selective nitric oxide synthase inhibitor, while they were not affected by somatostatin or NPY receptor antagonists. GABA, the remaining transmitter released by LTS interneurons, can also be ruled out, as it would produce hyperpolarizing responses in cholinergic interneurons under our recording conditions.
published were based on measurements obtained exclusively in the laboratory using white noise stimuli (Plummer and Camhi, 1981; Levin and Miller, 1996; Clague et al., 1997). However, as shown recently in another electrophysiological study, the responses of the cercal interneurons to white-noise stimuli, which were used in many previous studies, are qualitatively and quantitatively different than responses elicited by air currents crafted to resemble those generated by natural predators (Mulder-Rosi et al., 2010). Hence, interpretation of those earlier studies on the effects of noise on interneuron responsiveness and on the response to predator attack may be problematic, and a neuroethologically relevant study of the perception of an approaching predator would require the use of realistic stimuli. Furthermore, experiments conducted in the field under more naturalistic noise conditions could shed light on the true operation of the cercal system.
Interneurons of the olfactory bulb survive rJ infection. As expected, given the cellular tropism of rJ, most surviving tdTomato-positive cells were neurons, as demon- strated morphologically and conﬁrmed by NeuroTrace (Thermo Fisher Scientiﬁc) stain- ing (Fig. 4). Some neurons within the olfactory bulb strongly expressed tdTomato throughout the cell. As demonstrated by morphology, neurons surviving rJ-Cre infec- tion were largely interneurons (Fig. 4B); no mitral cells were tdTomato positive, perhaps indicating that mitral cells did not survive rJ infection. Surviving interneurons were primarily located in the glomerular cell layer and granule cell layer of the olfactory bulb (Fig. 5A). These results indicate that interneurons comprised a large fraction of the cells that survived rJ infection, suggesting an increased ability to survive the viral infection. Interneurons of the olfactory bulb are classiﬁed based on their location and expres- sion of neurotransmitters and other cell markers. For example, periglomerular interneu-
A particularly unusual property of NMDAR channels is their high Ca2+ permeability, which endows NMDARs with profound physiological and pathological significance . Simultaneous pre- and post-synaptic activity stimulates Ca2+ influx through NMDARs, activating a variety of intracellular signaling pathways with diverse physiologic consequences. For instance, NMDAR activation on postsynaptic pyramidal neurons in the cerebral cortex leads to the release of glutamate and subsequent downstream neuronal activation. NMDAR activation on GABAergic interneurons, however, results in a release of GABA with subsequent downstream inhibitory effects. Therefore, activation of NMDARs on pyramidal neurons
Canonically, neurogenesis in the adult brain takes place in two niches: the subgranular zone of the hippocampus and the SVZ, which continuously supplies new interneurons to the olfactory bulb (OB). The latter niche is more suitable for discerning successive stages of the overall process in which VEGF might play a role, owing to the fact that neuronal birth, migration, differentiation and integration are spatially and temporally separated. Briefly, neuroblasts destined to become OB interneurons leave their respective sites of origin in the SVZ and migrate rostrally (tangential migration) along the rostral migratory stream (RMS). Upon reaching the OB, cells migrate radially and, upon reaching their destinations at the granule cell layer (GCL) or glomerular layer (GL), differentiate into granule cells (GCs) or periglomerular cells (PGNs), respectively, becoming fully functional interneurons (see Fig. 1C). Tangential migration in the mouse OB is completed within 2-7 days following cell division, radial migration within 5-7 days, and differentiation to GCs or PGNs within 2 or 4 weeks, respectively, from birth (Petreanu and Alvarez-Buylla, 2002). In the next period of 45 days, sensory inputs determine whether newly added interneurons will thrive or regress. Approximately 50% of newly integrated GCs survive beyond this critical period and function for ~100 additional days on average, prior to being replaced by new cells (Ninkovic et al., 2007; Petreanu and Alvarez-Buylla, 2002). Whereas adult-born GCs comprise a sustained fraction (10%) of all GCs, newly added PGNs have a better survival rate, resulting in a linear increase in their number, reaching 30% at the age of 9 months (Mizrahi et al., 2006; Ninkovic et al., 2007). Others have reported that the population of newborn GCs increases with time to reach ~60% at the age of 12 months (Imayoshi et al., 2008).
ABSTRACT The ventral midline of the embryonic neural tube, the ﬂoor plate, has a profound role in guiding axons during embryonic development. Floor plate-derived guidance cues attract or repel axons, depending on the neuronal subtype and developmental stage. Netrin-1 and its receptor, Deleted in Colon Carcinoma (DCC), are the key constituents of commissurral axons guidance cues toward the ﬂoor plate. Recent studies have implicated Down Syndrome Cell Adhesion Molecule (Dscam) as an additional Netrin-1 receptor. In this study, we examined the role of Dscam in guid- ing deﬁned spinal dorsal interneuron populations. In vivo knockdown and ectopic expression of Dscam were performed in the dorsal dI1, dI2 and dI3 interneurons of chick embryos, by separately increasing or decreasing Dscam expression in each of these three speciﬁc interneuronal popula- tions. Neuron-speciﬁc gain and loss of function of Dscam had no effect on the axonal trajectories of dI1-3 neurons. The commissural neurons, dI1c and dI2, crossed the midline, and the ipsilaterally projecting neurons, dI1i and dI3, projected ipsilaterally. However, the fasciculation of dI1 axons was diminished when Dscam expression was attenuated. Dscam is not required for either attraction to or repulsion from the ﬂoor plate. In contrast, Dscam is required for the fasciculation of axons, probably via homophilic interaction.
Usually, an activity switch in an HN(5) neuron occurred within one or one and a half heartbeat cycles (Figs 2, 3). Only in one HN(5) cell out of 21 different recordings did a switch from the active to the inactive state take several cycles. In 10 out of 20 recordings from different HN(5) cells, switches occurred during the volley of inhibitory potentials, resulting in the following cycle being fully expressed in the other activity state (Fig. 2). Switches occurred during the interval between the inhibitory potentials in 12 out of 20 different HN(5) cells (Fig. 3A,B). In Fig. 3A, a switch from the inactive to the active state is shown. The cell produces a small burst of action potentials which are terminated by the inhibitory inputs. By the next cycle, the neuron is in the fully active state. During a switch from the active state to the inactive state in the same cell (Fig. 3B), the membrane potential starts increasing, as in the active state, but only one action potential is produced before there is an abrupt decline in the potential.
The large majority of the SST + and PV + interneurons originates in the MGE (Gelman and Marin, 2010). Thus, compromised migration from the MGE into the developing neocortex might account for the observed deficits in polyST-deficient mice. In mouse, interneuron migration from the MGE starts at E12.5 and migrating precursors transiently express CB while entering the dorsal telencephalon and during their tangential migration through the marginal and intermediate zones (Anderson et al., 1997; Polleux et al., 2002). CB-immunoreactive cells with typical morphologies of migrating interneurons were detected in sections of control, St8sia4 −/− and St8sia2 −/− brains at E13.5 (Fig. 4A). Double labeling with polySia- specific antibody revealed that polySia is present on the migratory neurons as well as on structures in close contact with them (Fig. 4B). Densitometric analysis in the area of the intermediate zone indicated
of the network (Acton and Miles 2015; Witts et al. 2012). We have demonstrated that glial-derived adenosine reduces or, perhaps in a physiological context, limits the frequency of locomotor-related output during ongoing network activity. However, the cellular mechanisms that underlie this spinal adenosine-mediated modulatory system remain unknown. In the present study we therefore utilized whole cell patch-clamp recordings of spinal motoneurons and ventral horn interneu- rons to investigate the consequences of adenosine receptor activation on the cellular components of spinal motor circuitry. We show that adenosine reduces the probability of transmitter release from presynaptic terminals and also hyperpolarizes interneurons. In contrast, adenosine depolarizes motoneurons and has no effect on the probability of transmitter release from last-order premotor interneurons. Thus we propose that a general inhibitory effect of adenosine on higher-order ventral horn interneurons leads to a reduced frequency of locomotor network output, while the simultaneous depolarization of mo- toneurons may help to ensure the maintenance of motor output and therefore an appropriate intensity of muscle activation.