Olfactory input is processed in the glomerulus of the main olfactory bulb (OB) and relayed to higher centers in the brain by projection neurons. Conversely, centrifugal inputs from other brain ...regions project to the OB. We have previously analyzed centrifugal inputs into the OB from several brain regions using single‐neuron labeling. In this study, we analyzed the centrifugal noradrenergic (NA) fibers derived from the locus coeruleus (LC), because their projection pathways and synaptic connections in the OB have not been clarified in detail. We analyzed the NA centrifugal projections by single‐neuron labeling and immunoelectron microscopy. Individual NA neurons labeled by viral infection were three‐dimensionally traced using Neurolucida software to visualize the projection pathway from the LC to the OB. Also, centrifugal NA fibers were visualized using an antibody for noradrenaline transporter (NET). NET immunoreactive (‐ir) fibers contained many varicosities and synaptic vesicles. Furthermore, electron tomography demonstrated that NET‐ir fibers formed asymmetrical synapses of varied morphology. Although these synapses were present at varicosities, the density of synapses was relatively low throughout the OB. The maximal density of synapses was found in the external plexiform layer; about 17% of all observed varicosities contained synapses. These results strongly suggest that NA‐containing fibers in the OB release NA from both varicosities and synapses to influence the activities of OB neurons. The present study provides a morphological basis for olfactory modulation by centrifugal NA fibers derived from the LC.
We accomplished visualization and reconstruction of noradrenergic neurons projecting to the olfactory bulb (OB) by infection of adeno‐associated viruses into the locus coeruleus of dopamine beta hydroxylase‐Cre mice. An individual noradrenergic axon traveled while forming several branches and was distributed in multiple glomeruli that were located in different areas of the glomerular layer in the OB.
Layer V of the entorhinal cortex (EC) receives input from the hippocampus and originates main entorhinal outputs. The deep-sublayer Vb, immunopositive for the transcription factor Ctip2, is thought ...to be the main recipient of hippocampal projections, whereas the superficial-sublayer LVa, immunonegative for Ctip2, originates the main outputs of EC. This disrupts the proposed role of EC as mediating hippocampal-cortical interactions. With the use of specific (trans)synaptic tracing approaches, we report that, in medial entorhinal cortex, layer Vb neurons innervate neurons in layers Va, II, and III. A similar circuitry exists in the lateral entorhinal cortex. We conclude that EC-layer Vb neurons mediate two circuits in the hippocampus-memory system: (1) a hippocampal output circuit to telencephalic areas by projecting to layer Va and (2) a feedback projection, sending information back to the EC-hippocampal loop via neurons in layers II and III.
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•Layer V (LV) circuitry in lateral and medial entorhinal cortex is similar•LV comprises two sublayers, Va and Vb, with Vb neurons projecting locally•LVb neurons contact telencephalic projecting neurons in LVa•LVb neurons also contact hippocampus-projecting neurons in LII and LIII
Ohara et al. demonstrate the intrinsic connectivity of layer Vb neurons of both the medial and lateral entorhinal cortex. Layer Vb neurons are key elements of two circuits in the hippocampus-memory system: a hippocampal-output circuit and a feedback loop to the hippocampus.
The bidirectional controller of the thermoregulatory center in the preoptic area (POA) is unknown. Using rats, here, we identify prostaglandin EP3 receptor-expressing POA neurons (POA
neurons) as a ...pivotal bidirectional controller in the central thermoregulatory mechanism. POA
neurons are activated in response to elevated ambient temperature but inhibited by prostaglandin E
, a pyrogenic mediator. Chemogenetic stimulation of POA
neurons at room temperature reduces body temperature by enhancing heat dissipation, whereas inhibition of them elicits hyperthermia involving brown fat thermogenesis, mimicking fever. POA
neurons innervate sympathoexcitatory neurons in the dorsomedial hypothalamus (DMH) via tonic (ceaseless) inhibitory signaling. Although many POA
neuronal cell bodies express a glutamatergic messenger RNA marker, their axons in the DMH predominantly release γ-aminobutyric acid (GABA), and their GABAergic terminals are increased by chronic heat exposure. These findings demonstrate that tonic GABAergic inhibitory signaling from POA
neurons is a fundamental determinant of body temperature for thermal homeostasis and fever.
Summary
Mu opioid receptor (MOR) is involved in various brain functions, such as pain modulation, reward processing, and addictive behaviors, and mediates the main pharmacologic effects of morphine ...and other opioid compounds. To gain genetic access to MOR‐expressing cells, and to study physiological and pathological roles of MOR signaling, we generated a MOR‐CreER knock‐in mouse line, in which the stop codon of the Oprm1 gene was replaced by a DNA fragment encoding a T2A peptide and tamoxifen (Tm)‐inducible Cre recombinase. We show that the MOR‐CreER allele undergoes Tm‐dependent recombination in a discrete subtype of neurons that express MOR in the adult nervous system, including the olfactory bulb, cerebral cortex, striosome compartments in the striatum, hippocampus, amygdala, thalamus, hypothalamus, interpeduncular nucleus, superior and inferior colliculi, periaqueductal gray, parabrachial nuclei, cochlear nucleus, raphe nuclei, pontine and medullary reticular formation, ambiguus nucleus, solitary nucleus, spinal cord, and dorsal root ganglia. The MOR‐CreER mouse line combined with a Cre‐dependent adeno‐associated virus vector enables robust gene manipulation in the MOR‐enriched striosomes. Furthermore, Tm treatment during prenatal development effectively induces Cre‐mediated recombination. Thus, the MOR‐CreER mouse is a powerful tool to study MOR‐expressing cells with conditional gene manipulation in developing and mature neural tissues.
Abstract
Tyramide signal amplification (TSA) is a highly sensitive method for histochemical analysis. Previously, we reported a TSA system, biotinyl tyramine-glucose oxidase (BT-GO), for bright-filed ...imaging. Here, we develop fluorochromized tyramide-glucose oxidase (FT-GO) as a multiplex fluorescent TSA system. FT-GO involves peroxidase-catalyzed deposition of fluorochromized tyramide (FT) with hydrogen peroxide produced by enzymatic reaction between glucose and glucose oxidase. We showed that FT-GO enhanced immunofluorescence signals while maintaining low background signals. Compared with indirect immunofluorescence detections, FT-GO demonstrated a more widespread distribution of monoaminergic projection systems in mouse and marmoset brains. For multiplex labeling with FT-GO, we quenched antibody-conjugated peroxidase using sodium azide. We applied FT-GO to multiplex fluorescent in situ hybridization, and succeeded in labeling neocortical interneuron subtypes by coupling with immunofluorescence. FT-GO immunofluorescence further increased the detectability of an adeno-associated virus tracer. Given its simplicity and a staining with a high signal-to-noise ratio, FT-GO would provide a versatile platform for histochemical analysis.
The medial geniculate body (MGB) is the thalamic center of the auditory lemniscal pathway. The ventral division of MGB (MGV) receives excitatory and inhibitory inputs from the inferior colliculus ...(IC). MGV is involved in auditory attention by processing descending excitatory and inhibitory inputs from the auditory cortex (AC) and reticular thalamic nucleus (RTN), respectively. However, detailed mechanisms of the integration of different inputs in a single MGV neuron remain unclear. Kv4.2 is one of the isoforms of the Shal-related subfamily of potassium voltage-gated channels that are expressed in MGB. Since potassium channel is important for shaping synaptic current and spike waveforms, subcellular distribution of Kv4.2 is likely important for integration of various inputs. Here, we aimed to examine the detailed distribution of Kv4.2, in MGV neurons to understand its specific role in auditory attention. We found that
Kv4.2
mRNA was expressed in most MGV neurons. At the protein level, Kv4.2-immunopositive patches were sparsely distributed in both the dendrites and the soma of neurons. The postsynaptic distribution of Kv4.2 protein was confirmed using electron microscopy (EM). The frequency of contact with Kv4.2-immunopositive puncta was higher in vesicular glutamate transporter 2 (VGluT2)-positive excitatory axon terminals, which are supposed to be extending from the IC, than in VGluT1-immunopositive terminals, which are expected to be originating from the AC. VGluT2-immunopositive terminals were significantly larger than VGluT1-immunopositive terminals. Furthermore, EM showed that the terminals forming asymmetric synapses with Kv4.2-immunopositive MGV dendritic domains were significantly larger than those forming synapses with Kv4.2-negative MGV dendritic domains. In inhibitory axons either from the IC or from the RTN, the frequency of terminals that were in contact with Kv4.2-positive puncta was higher in IC than in RTN. In summary, our study demonstrated that the Kv4.2-immunopositive domains of the MGV dendrites received excitatory and inhibitory ascending auditory inputs preferentially from the IC, and not from the RTN or cortex. Our findings imply that time course of synaptic current and spike waveforms elicited by IC inputs is modified in the Kv4.2 domains.
Memory recall and guidance are essential for motor skill acquisition. Like humans learning to speak, male zebra finches learn to sing by first memorizing and then matching their vocalization to the ...tutor’s song (TS) during specific developmental periods. Yet, the neuroanatomical substrate supporting auditory-memory-guided sensorimotor learning has remained elusive. Here, using a whole-brain connectome analysis with activity-dependent viral expression, we identified a transient projection into the motor region, HVC, from neuronal ensembles responding to TS in the auditory forebrain, the caudomedial nidopallium (NCM), in juveniles. Virally induced cell death of the juvenile, but not adult, TS-responsive NCM neurons impaired song learning. Moreover, isolation, which delays closure of the sensory, but not the motor, learning period, did not affect the decrease of projections into the HVC from the NCM TS-responsive neurons after the song learning period. Taken together, our results suggest that dynamic axonal pruning may regulate timely auditory-memory-guided vocal learning during development.
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•Specific manipulation of song-responsive neurons with a cFos-TetON system is created•Ablating tutor’s song (TS)-responsive neurons prevents juveniles from song learning•TS-responsive neurons transiently project to song premotor area, HVC, in juveniles•Sensory isolation does not delay song crystallization or axon pruning in HVC
Auditory memory guidance for motor shaping is necessary for vocal learning. Here, Louder et al. show transient axonal projections to the song premotor area from the neurons responsive to the tutor’s song (TS) playback in the auditory forebrain. Ablating TS-responsive neurons disrupts song learning in juveniles but not in adults.
The claustrum coordinates the activities of individual cortical areas through abundant reciprocal connections with the cerebral cortex. Although these excitatory connections have been extensively ...investigated in three subregions of the claustrum—core region and dorsal and ventral shell regions—the contribution of GABAergic neurons to the circuitry in each subregion remains unclear. Here, we examined the distribution of GABAergic neurons and their dendritic and axonal arborizations in each subregion. Combining in situ hybridization with immunofluorescence histochemistry showed that approximately 10% of neuronal nuclei-positive cells expressed glutamic acid decarboxylase 67 mRNA across the claustral subregions. Approximately 20%, 30%, and 10% of GABAergic neurons were immunoreactive for parvalbumin (PV), somatostatin (SOM), and vasoactive intestinal polypeptide, respectively, in each subregion, and these neurochemical markers showed little overlap with each other. We then reconstructed PV and SOM neurons labeled with adeno-associated virus vectors. The dendrites and axons of PV and SOM neurons were preferentially localized to their respective subregions where their cell bodies were located. Furthermore, the axons were preferentially extended in a rostrocaudal direction, whereas the dendrites were relatively isotropic. The present findings suggest that claustral PV and SOM neurons might execute information processing separately within the core and shell regions.
•The distribution of GABAergic neurons is examined in claustral subregions.•Nearly 10% of claustral neurons are GABAergic in each claustral subregion.•PV-, SOM-, and VIP-positive neurons comprise 20%, 30%, and 10% of GABAergic neurons.•PV and SOM neurons preferentially extend the axons along a rostrocaudal axis.•PV and SOM neurons localize the neurites within either the core or shell subregion.
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