Biology subjects

Egger, V.

Publications and source records attributed to Egger, V..

8 recordsLinked to original sources

bioRxiv2025

Local olfactory nerve stimulation triggers patchy activation of columns across rat olfactory bulb

Columnar organization is a hallmark of neocortical sensory areas, most prominently in primary somatosensory and visual cortex. In the olfactory bulb, the existence of a vertical columnar organization of circuits associated with glomerular input channels has been implicated by various approaches. Here, based on activity-dependent labelling and tissue clearing, we provide direct evidence for functional bulbar columns formed by mitral cells and granule cells that display a uniform morphology.

neuroscience↗

bioRxiv2025

Synergistic olfactory nerve input and cholinergic neuromodulation can activate ERK in rat olfactory bulb vasopressin cells

Social discrimination in rats relies on vasopressin cells (VPCs) intrinsic to the olfactory bulb (OB). We had observed that VPCs responded to electrical stimulation of the olfactory nerve in acute OB slices with inhibitory postsynaptic potentials, and that the neuromodulator acetylcholine could revert these responses to excitation, resulting in action potentials (AP). Moreover, in behaving rats that were exposed to conspecifics, more VPCs were immunopositive to the neural activity marker pERK (pERK+ VPC) than in control rats. However, it is unclear whether these two observations, the increased ERK activation in vivo, and the generation of APs in the presence of ACh in vitro, can be actually mapped onto each other. Here we investigated ERK activation in acute OB slices from transgenic VP-eGFP rats upon either chemical stimulation or tetanic olfactory nerve stimulation. Both KCl and NMDA stimulation resulted in substantial pERK induction across bulbar layers and caused VPC spiking in whole-cell recordings, but only NMDA slightly increased pERK+ VPC percentage. Tetanic olfactory nerve stimulation yielded localized, column-like ERK activation of neurons across bulbar layers. The presence of ACh during tetanic stimulation substantially and specifically increased percentages of pERK+ VPCs within columns, indicating that columnar pERK+ VPCs were preferentially activated by coincident cholinergic neuromodulation and synaptic input. Our results validate pERK induction as a tool to monitor synaptic VPC excitation in the OB, and imply that depolarization of VPCs alone is insufficient to activate ERK. We propose that synaptically evoked APs are a prerequisite for pERK induction in VPCs.

neuroscience↗

bioRxiv2023

Blood pressure pulsations modulate olfactory bulb neuronal activity via mechanosensitive ion channels

AbstractThe transmission of heartbeat through the cerebral vascular system is known to cause intracranial pressure pulsations. Here we describe that arterial pressure pulsations within the brain can directly modulate central neuronal activity. In a semi-intact rat brain preparation, pressure pulsations elicit correlated local field oscillations in the olfactory bulb (OB) that are sensitive to hypoxia and block of mechanosensitive channels. We find that mitral cell spiking activity is in part synchronized to these oscillations. Indeed, in awake animals the firing of a subset of OB neurons is entrained to heartbeat within [~] 20 ms. Several lines of evidence indicate the expression of a mechanosensitive ion channel within the mitral cell membranes, most likely Piezo2, implementing a pressure pulsation transduction pathway and thus baroreception within the OB. We propose that this intrinsic interoceptive mechanism modulates OB neuronal activity e.g. during arousal and also could influence brain activity on a wider scale.

neuroscience↗

bioRxiv2020

Top-down acetylcholine enables social discrimination via unlocking action potential generation in olfactory bulb vasopressin cells

Social discrimination in rats requires activation of the intrinsic bulbar vasopressin system, but it is unclear how this system comes into operation, as olfactory nerve stimulation primarily inhibits bulbar vasopressin cells (VPCs). Here we show that stimulation with a conspecific can activate bulbar VPCs, indicating that VPC activation depends on more than olfactory cues during social interaction. A series of in-vitro electrophysiology, pharmacology and immunohistochemistry experiments implies that acetylcholine probably originating from centrifugal projections can enable olfactory nerve-evoked action potentials in VPCs. Finally, cholinergic activation of the vasopressin system contributes to vasopressin-dependent social discrimination, since recognition of a known rat was blocked by bulbar infusion of the muscarinic acetylcholine receptor antagonist atropine and rescued by additional bulbar application of vasopressin. Thus, we demonstrated that top-down cholinergic modulation of bulbar VPC activity is involved in social discrimination in rats.

neuroscience↗

bioRxiv2020

Local postsynaptic signalling on slow time scales in reciprocal olfactory bulb granule cell spines matches asynchronous release

In the vertebrate olfactory bulb (OB), axonless granule cells (GC) mediate self- and lateral inhibitory interactions between mitral/tufted cells via reciprocal dendrodendritic synapses. Locally triggered release of GABA from the large reciprocal GC spines occurs on both fast and slow time scales, possibly enabling parallel processing during olfactory perception. Here we investigate local mechanisms for asynchronous spine output. To reveal the temporal and spatial characteristics of postsynaptic ion transients, we imaged spine and adjacent dendrite Ca2+- and Na+-signals with minimal exogenous buffering by the respective fluorescent indicator dyes upon two-photon uncaging of DNI-glutamate in OB slices from juvenile rats. Both postsynaptic fluorescence signals decayed slowly, with average half durations in the spine head of t1/2_{Delta}[Ca2+]i ~500 ms and t1/2_{Delta}[Na+]i ~1000 ms. We also analysed the kinetics of already existing data of postsynaptic spine Ca2+-signals in response to glomerular stimulation in OB slices from adult mice, either WT or animals with partial GC glutamate receptor deletions (NMDAR: GluN1 subunit; AMPAR: GluA2 subunit). In a large subset of spines the fluorescence signal had a protracted rise time (average time to peak ~400 ms, range 20 ms - >1000 ms). This slow rise was independent of Ca2+ entry via NMDARs, since similarly slow signals occurred in {Delta}GluN1 GCs. Additional Ca2+ entry in {Delta}GluA2 GCs (with AMPARs rendered Ca2+-permeable), however, resulted in larger {Delta}F/Fs that rose yet more slowly. Thus GC spines appear to dispose of several local mechanisms to promote asynchronous GABA release, which are reflected in the time course of mitral/tufted cell recurrent inhibition.

neuroscience↗

bioRxiv2020

Concerted but segregated actions of oxytocin and vasopressin within the ventral and dorsal lateral septum determine female aggression

In contrast to males, aggression in females has been rarely studied. Here, we established a rat model of enhanced female aggression using a combination of social isolation and aggression-training to specifically investigate the involvement of the oxytocin (OXT) and vasopressin (AVP) systems within the lateral septum (LS). Using neuropharmacological, optogenetic, chemogenetic as well as microdialyses approaches, we revealed that enhanced OXT release within the ventral LS (vLS), combined with reduced AVP release within the dorsal LS (dLS), are required for female aggression. Accordingly, increased excitability of OXT-responsive neurons in the vLS and decreased excitability of AVP-responsive neurons in the dLS were essential to evoke female aggression. Finally, in vitro activation of OXT receptors in the vLS increased tonic GABAergic inhibition of dLS neurons. Overall, our data demonstrate that septal release of OXT and AVP affects female aggression by differential regulation of the excitatory-inhibitory balance within subnetworks of the LS.

neuroscience↗

bioRxiv2020

Dendritic integration in olfactory bulb granule cells: Thresholds for lateral inhibition and role of active conductances upon simultaneous activation.

The inhibitory axonless olfactory bulb granule cells (GCs) form reciprocal dendrodendritic synapses with mitral and tufted cells via large spines, mediating recurrent and lateral inhibition. Rat GC dendrites are excitable by local Na+ spine spikes and global Ca2+- and Na+-spikes. To investigate the transition from local to global signaling without Na+ channel inactivation we performed simultaneous holographic two-photon uncaging in acute brain slices, along with whole-cell recording and dendritic Ca2+ imaging. Less than 10 coactive reciprocal spines were sufficient to generate diverse regional and global signals that also included local dendritic Ca2+- and Na+-spikes (D-spikes). Individual spines could sense the respective signal transitions as increments in Ca2+ entry. Dendritic integration was mostly linear until a few spines below global Na+-spike threshold, where often D-spikes set in. NMDARs strongly contributed to active integration, whereas morphological parameters barely mattered. In summary, thresholds for GC-mediated bulbar lateral inhibition are low.

neuroscience↗

bioRxiv2018

Local reciprocal release of GABA from dendritic spines of olfactory bulb granule cells requires local sodium channel activation and occurs on both fast and slow timescales

In the rodent olfactory bulb the smooth dendrites of the principal glutamatergic mitral cells (MCs) form reciprocal dendrodendritic synapses with large spines on GABAergic granule cells (GC), where unitary release of glutamate can trigger postsynaptic local activation of voltage-gated Na+-channels (Navs), i.e. a spine spike. Can such single MC input evoke reciprocal release? We find that unitary-like activation via two-photon uncaging of glutamate causes GC spines to release GABA both synchronously and asynchronously onto MC dendrites. This release indeed requires activation of Navs and high-voltage-activated Ca2+-channels (HVACCs), but also of NMDA receptors (NMDAR). Simulations show temporally overlapping HVACC- and NMDAR-mediated Ca2+-currents during the spine spike, and ultrastructural data prove NMDAR presence within the GABAergic presynapse. This cooperative action of presynaptic NMDARs allows to implement synapse-specific, activity-dependent lateral inhibition and thus could provide an efficient solution to combinatorial percept synthesis in a sensory system with many receptor channels.

neuroscience↗