Plane-specific brainstem commissural inhibition in frog second-order semicircular canal neurons

2001 ◽  
Vol 137 (2) ◽  
pp. 190-196 ◽  
Author(s):  
Stefan Holler ◽  
Hans Straka
Keyword(s):  
Semicircular Canal ◽  
Second Order

scholarly journals Canal-Specific Excitation and Inhibition of Frog Second-Order Vestibular Neurons

1997 ◽  
Vol 78 (3) ◽  
pp. 1363-1372 ◽  
Author(s):  
H. Straka ◽  
S. Biesdorf ◽  
N. Dieringer
Keyword(s):  
Electrical Stimulation ◽  
Semicircular Canal ◽  
Second Order ◽  
Projection Neurons ◽  
Postsynaptic Potentials ◽  
Vestibular Neurons ◽  
Inhibitory Postsynaptic Potentials ◽  
Monosynaptic Epsp ◽  
Stimulation Of ◽  
Monosynaptic Excitation

Straka, H., S. Biesdorf, and N. Dieringer. Canal-specific excitation and inhibition of frog second-order vestibular neurons. J. Neurophysiol. 78: 1363–1372, 1997. Second-order vestibular neurons (2°VNs) were identified in the in vitro frog brain by their monosynaptic excitation following electrical stimulation of the ipsilateral VIIIth nerve. Ipsilateral disynaptic inhibitory postsynaptic potentials were revealed by bath application of the glycine antagonist strychnine or of the γ-aminobutyric acid-A (GABAA) antagonist bicuculline. Ipsilateral disynaptic excitatory postsynaptic potentials (EPSPs) were analyzed as well. The functional organization of convergent monosynaptic and disynaptic excitatory and inhibitory inputs onto 2°VNs was studied by separate electrical stimulation of individual semicircular canal nerves on the ipsilateral side. Most 2°VNs (88%) received a monosynaptic EPSP exclusively from one of the three semicircular canal nerves; fewer 2°VNs (10%) were monosynaptically excited from two semicircular canal nerves; and even fewer 2°VNs (2%) were monosynaptically excited from each of the three semicircular canal nerves. Disynaptic EPSPs were present in the majority of 2°VNs (68%) and originated from the same (homonymous) semicircular canal nerve that activated a monosynaptic EPSP in a given neuron (22%), from one or both of the other two (heteronymous) canal nerves (18%), or from all three canal nerves (28%). Homonymous activation of disynaptic EPSPs prevailed (74%) among those 2°VNs that exhibited disynaptic EPSPs. Disynaptic inhibitory postsynaptic potentials (IPSPs) were mediated in 90% of the tested 2°VNs by glycine, in 76% by GABA, and in 62% by GABA as well as by glycine. These IPSPs were activated almost exclusively from the same semicircular canal nerve that evoked the monosynaptic EPSP in a given 2°VN. Our results demonstrate a canal-specific, modular organization of vestibular nerve afferent fiber inputs onto 2°VNs that consists of a monosynaptic excitation from one semicircular canal nerve followed by disynaptic excitatory and inhibitory inputs originating from the homonymous canal nerve. Excitatory and inhibitory second-order (2°) vestibular interneurons are envisaged to form side loops that mediate spatially similar but dynamically different signals to 2° vestibular projection neurons. These feedforward side loops are suited to adjust the dynamic response properties of 2° vestibular projection neurons by facilitating or disfacilitating phasic and tonic input components.

Differential Inhibitory Control of Semicircular Canal Nerve Afferent-Evoked Inputs in Second-Order Vestibular Neurons by Glycinergic and GABAergic Circuits

2008 ◽  
Vol 99 (4) ◽  
pp. 1758-1769 ◽  
Author(s):  
Stefan Biesdorf ◽  
David Malinvaud ◽  
Ingrid Reichenberger ◽  
Sandra Pfanzelt ◽  
Hans Straka
Keyword(s):  
Inhibitory Control ◽  
Semicircular Canal ◽  
Vestibular Nucleus ◽  
Second Order ◽  
Membrane Properties ◽  
Synaptic Organization ◽  
Nerve Branch ◽  
Postsynaptic Potentials ◽  
Vestibular Neurons ◽  
Intrinsic Signal

Labyrinthine nerve-evoked monosynaptic excitatory postsynaptic potentials (EPSPs) in second-order vestibular neurons (2°VN) sum with disynaptic inhibitory postsynaptic potentials (IPSPs) that originate from the thickest afferent fibers of the same nerve branch and are mediated by neurons in the ipsilateral vestibular nucleus. Pharmacological properties of the inhibition and the interaction with the afferent excitation were studied by recording monosynaptic responses of phasic and tonic 2°VN in an isolated frog brain after electrical stimulation of individual semicircular canal nerves. Specific transmitter antagonists revealed glycine and GABAA receptor-mediated IPSPs with a disynaptic onset only in phasic but not in tonic 2°VN. Compared with GABAergic IPSPs, glycinergic responses in phasic 2°VN have larger amplitudes and a longer duration and reduce early and late components of the afferent nerve-evoked subthreshold activation and spike discharge. The difference in profile of the disynaptic glycinergic and GABAergic inhibition is compatible with the larger number of glycinergic as opposed to GABAergic terminal-like structures on 2°VN. The increase in monosynaptic excitation after a block of the disynaptic inhibition in phasic 2°VN is in part mediated by a N-methyl-d-aspartate receptor-activated component. Although inhibitory inputs were superimposed on monosynaptic EPSPs in tonic 2°VN as well, the much longer latency of these IPSPs excludes a control by short-latency inhibitory feed-forward side-loops as observed in phasic 2°VN. The differential synaptic organization of the inhibitory control of labyrinthine afferent signals in phasic and tonic 2°VN is consistent with the different intrinsic signal processing modes of the two neuronal types and suggests a co-adaptation of intrinsic membrane properties and emerging network properties.

Patterns of Canal and Otolith Afferent Input Convergence in Frog Second-Order Vestibular Neurons

2002 ◽  
Vol 88 (5) ◽  
pp. 2287-2301 ◽  
Author(s):  
H. Straka ◽  
S. Holler ◽  
F. Goto
Keyword(s):  
Semicircular Canal ◽  
Linear Acceleration ◽  
Afferent Input ◽  
Second Order ◽  
Head Movements ◽  
Otolith Organs ◽  
Otolith Organ ◽  
Horizontal Canal ◽  
Vestibular Neurons ◽  
Saccular Nerve

Second-order vestibular neurons (2°VN) were identified in the isolated frog brain by the presence of monosynaptic excitatory postsynaptic potentials (EPSPs) after separate electrical stimulation of individual vestibular nerve branches. Combinations of one macular and the three semicircular canal nerve branches or combinations of two macular nerve branches were stimulated separately in different sets of experiments. Monosynaptic EPSPs evoked from the utricle or from the lagena converged with monosynaptic EPSPs from one of the three semicircular canal organs in ∼30% of 2°VN. Utricular afferent signals converged predominantly with horizontal canal afferent signals (74%), and lagenar afferent signals converged with anterior vertical (63%) or posterior vertical (37%) but not with horizontal canal afferent signals. This convergence pattern correlates with the coactivation of particular combinations of canal and otolith organs during natural head movements. A convergence of afferent saccular and canal signals was restricted to very few 2°VN (3%). In contrast to the considerable number of 2°VN that received an afferent input from the utricle or the lagena as well as from one of the three canal nerves (∼30%), smaller numbers of 2°VN (14% of each type of 2°otolith or 2°canal neuron) received an afferent input from only one particular otolith organ or from only one particular semicircular canal organ. Even fewer 2°VN received an afferent input from more than one semicircular canal or from more than one otolith nerve (∼7% each). Among 2°VN with afferent inputs from more than one otolith nerve, an afferent saccular nerve input was particularly rare (4–5%). The restricted convergence of afferent saccular inputs with other afferent otolith or canal inputs as well as the termination pattern of saccular afferent fibers are compatible with a substrate vibration sensitivity of this otolith organ in frog. The ascending and/or descending projections of identified 2°VN were determined by the presence of antidromic spikes. 2°VN mediating afferent utricular and/or semicircular canal nerve signals had ascending and/or descending axons. 2°VN mediating afferent lagenar or saccular nerve signals had descending but no ascending axons. The latter result is consistent with the absence of short-latency macular signals on extraocular motoneurons during vertical linear acceleration. Comparison of data from frog and cat demonstrated the presence of a similar organization pattern of maculo- and canal-ocular reflexes in both species.

Disappearance Voltage Determinations Using a Convergent Beam

1971 ◽  
Vol 29 ◽  
pp. 184-185
Author(s):  
W. L. Bell
Keyword(s):  
Second Order ◽  
Objective Method ◽  
Uniform Thickness ◽  
Rocking Curve ◽  
Crystal Perfection ◽  
Kikuchi Line ◽  
Central Maximum ◽  
Diffraction Patterns ◽  
Convergent Beam ◽  
Beam Technique

Disappearance voltages for second order reflections can be determined experimentally in a variety of ways. The more subjective methods, such as Kikuchi line disappearance and bend contour imaging, involve comparing a series of diffraction patterns or micrographs taken at intervals throughout the disappearance range and selecting that voltage which gives the strongest disappearance effect. The estimated accuracies of these methods are both to within 10 kV, or about 2-4%, of the true disappearance voltage, which is quite sufficient for using these voltages in further calculations. However, it is the necessity of determining this information by comparisons of exposed plates rather than while operating the microscope that detracts from the immediate usefulness of these methods if there is reason to perform experiments at an unknown disappearance voltage.The convergent beam technique for determining the disappearance voltage has been found to be a highly objective method when it is applicable, i.e. when reasonable crystal perfection exists and an area of uniform thickness can be found. The criterion for determining this voltage is that the central maximum disappear from the rocking curve for the second order spot.

Sign in / Sign up

Export Citation Format

Share Document