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R M Glantz

Publications and source records attributed to R M Glantz.

At least 37 records · Page 2Linked to original sources
PubMed1986

Integration and spike initiation in neuronal terminals.

Axoaxonal synapses impinge on the terminals of neurons and are thought to play a crucial role in the regulation of synaptic transmission. In the crayfish brain, the terminals of several identified interneurons exhibit both EPSPs and IPSPs in response to cephalic sensory stimulation. The terminal arbors extend into primary sensory neuropils near the terminals of primary afferent axons of the antennae and statocysts. The EPSPs arise monosynaptically from primary afferent stimulation and can elicit action potentials. Bidirectional conduction is routinely observed. Terminal IPSPs are transmitted via a polysynaptic pathway. Furthermore, two morphological classes of synaptic profiles impinge on the presynaptic terminals. These results indicate that the neuron terminal can function as a second, independent site of synaptic integration.

Action Potentials↗
PubMed1985

Dye coupling and gap junctions between crustacean neurosecretory cells.

Neurosecretory cells in the X organ-sinus gland system of the crayfish were impaled and Lucifer Yellow was intracellularly iontophoresed. In some neurons the injected dye was transferred to neighboring neurons. The interneuronal dye transfer was between adjacent somata. Coupling was also observed between neurons and smaller cells, possibly glia. Gap junctions were identified by freeze-fracture in neuron somata and glial cells in the X organ and also in neurosecretory axons in the sinus gland.

Astacoidea↗
PubMed1985

Synaptic mechanisms of a tonic EPSP in crustacean visual interneurons: analysis and simulation.

Light-evoked synaptic responses of identified visual interneurons, sustaining fibers (SFs), were quantitatively analyzed, and a neuronal cable model was used to calculate voltage attenuations and predict synaptic responses. The cable model is based on morphological measurements of SFs filled with Lucifer yellow and passive membrane properties assessed by current injection in the proximal portion of the dendritic arbor. The morphological and electrophysiological measurements were made in different preparations on homologues of the same identified interneurons. The excitatory postsynaptic potential (EPSP) elicited with high-intensity light consists of a transient phase (mean amplitude 33.1 mV) and a second phase (the plateau) that decays slowly relative to the membrane time constant (mean amplitude 24.4 mV). The mean extrapolated reversal potentials are -19.1 mV for the transient and -22.3 mV during the plateau. The change in input conductance associated with the plateau phase of the response showed a peak of 121% above the resting input conductance and decayed to approximately 50% above resting conductance over several seconds. Compartmental cable models (18, 19) were used to calculate voltage attenuations and local synaptic conductances within the SF dendritic tree. The dendrites are electrotonically compact, and voltage attenuations average 6% for current flowing distally from the recording site (injected) and 45% for current flowing proximally to the recording site. The steady-state EPSP is associated with a calculated 80% decrease in the net dendritic membrane resistivity. The synaptic response, calculated for an EPSP distributed throughout the dentritic tree (using this conductance change and the measured steady-state reversal potential) was 27.0 mV, compared with an observed mean value of 24.4 mV. The calculated relationship between steady-state EPSP amplitude and dendritic membrane resistivity (Rs) is a sigmoidal function that resembles the intensity/response function of the SF. We can therefore correctly predict the transformation from light intensity to compound EPSP amplitude by calculating the intervening synaptic membrane resistivity and voltage values. These functions are affected in a predictable manner by the passive membrane resistivity (Rm) and the EPSP reversal potentials. Tetrodotoxin (TTX) application abolished all SF spiking but left the EPSP essentially unchanged, suggesting that the neuronal pathway from photoreceptors to SFs is mainly or entirely comprised of nonspiking (i.e., TTX-insensitive) elements.

Animals↗
PubMed1984

Linear integration of convergent visual inputs in an oculomotor reflex pathway.

The functional connectivity between identified visual interneurons [sustaining fibers (SF)] and oculomotor neurons was assessed by simultaneous recording and cross-correlation analysis. A small group of SFs exhibit excitatory functional connections to an identified tonic oculomotor neuron. The excitatory interactions are found exclusively between SFs and oculomotor neurons with similar and/or overlapping excitatory receptive fields. A second group of SFs exhibit inhibitory connections to motor neurons. The excitatory receptive fields of these SFs correspond to the inhibitory receptive fields of the motor neurons. The collective action of the SFs is sufficient to produce all of the steady-state visual behavior of the motor neurons including the increment in firing rate elicited by illumination, unique features of the motor neuron receptive field, and differential sensitivity to blue light and polarized light. Pairs of SFs that converge on the same motor neuron sum their effects linearly. Thus the joint interaction of two SFs on a motor neuron is equal to the sum of the two postsynaptic effects taken separately. Coactivation of excitatory and inhibitory SF inputs to a motor neuron results in a partial cancellation of their postsynaptic effects on the motor neuron's firing rate. The antagonistic interactions protect the system from perturbations by stray light, visual adaptation, and variations in the central excited state. The ensemble information code, at the SF level of the optomotor pathway, is a set of differentially weighted mean firing rates. The weightings reflect differences in the strengths of the several SF-to- motor neuron interactions. One consequence of these differences is a selective weighting of the effects of illumination (in different regions of visual space) on the compensatory eye reflex.

Animals↗
PubMed1983

A quantitative correlation of contour sensitivity with dendritic density in an identified visual neuron.

Crayfish sustaining fibers are visual interneurons that are tonically excited by increases in illumination within their receptive fields. The receptive fields of sustaining fibers (SFs) are correlated with the two-dimensional position of their dendritic fields within the central neuropil. Dendritic branching patterns and contour sensitivity maps were obtained for SF 019 in several preparations. The contour sensitivity along the dorsal-ventral visual arc (which intersects 019's receptive field) is positively correlated with the variations in the spatial frequency of 019's dendritic arbor along the dorsal ventral midline of the neuropil. We conclude that an SF's receptive field is determined by the position and extent of its dendritic field and that sensitivity variations within the receptive field are principally determined by changes in its dendritic density.

Animals↗
PubMed1983

Light input to crustacean neurosecretory cells.

Electrical activity was recorded intracellularly from neurosecretory cells in the crayfish eyestalk identified by lucifer yellow injection. The activity is most commonly enhanced by illumination of retinal fields. Increments in spontaneous activity as well as bursts in otherwise silent cells were the most common type of response. Occasionally light-induced inhibitory responses were recorded. At neuropil level, light pulses result in EPSPs with amplitudes dependent on intensity of light and the previous adaptation to darkness.

Animals↗
PubMed1983

Retinal illumination produces synaptic inhibition of a neurosecretory organ in the crayfish, Pacifastacus leniusculus (Dana).

We have identified a cluster of neurosecretory cells in the crayfish eyestalk that possess dendrites in the second optic neuropil (Medulla) and project axons to the first optic neuropil (Lamina). Illumination of the ipsilateral retina produces a synaptic inhibition of these cells that is mimicked by iontophoresis of gamma-aminobutyric acid within the medullary neuropil. The neurosecretory nature of the cells, the efferent projection of their axons, and the strong inhibition of their spiking activity upon retinal illumination suggest that they may be involved in the feedback control of dark adaptation and/or circadian changes in visual sensitivity.

Animals↗
PubMed1983

Integrative properties of crayfish medial giant neuron: steady-state model.

A quantitative morphological description of the crayfish medial giant (MG) neuron was obtained on the basis of 14 individual cells filled with lucifer yellow. The cable parameters of seven MGs were measured in the axon with two or three microelectrodes. The length constant is 4.3 +/- 0.8 mm, the membrane time constant is 3.1 +/- 0.8 ms, the input resistance is 3.6 +/- 0.2 (X10(4) alpha, the mean axon diameter is 208 +/- 34 microns. The specific membrane resistance (Rm) is 2,000 +/- 204 alpha x cm2. The specific axoplasmic resistance (Ri) is 60 +/- 29 alpha x cm and the membrane capacitance is 1.6 +/- microF/cm2. The MG is electrotonically coupled to its symmetrical homolog. The coupling coefficient is 0.46 for both steady-state signals and spike transmission. A steady-state cable model of the MG was calculated on the basis of the axonal Rm and Ri values, the electrotonic coupling coefficient to the MG symmetrical homolog, and the mean dimensions of the 14 MG neurites. The model successfully predicts geometrically determined variations in input resistance and steady-state signal attenuation. A salient feature of the MG steady-state model is the extent to which dendritic input conductance and the attenuation of steady-state voltages is determined by the large input conductance of the axon. Because of the large diameter of the MG neurites, electrotonic distances between dendrite terminals and the integrating segment are short (0.3-0.74 lambda) and the principal basis of excitatory postsynaptic potential (EPSP) attenuation is variation is local input resistance. The time integral of the electrotonic coupling potential between the MGs is diminished by 9.5-21.4% during a monosynaptic sensory EPSP. The magnitude of the inferred synaptic conductance seen at the decussation is inversely related to the electrotonic distance between the decussation and the active dendritic branch. The modest change in input resistance near the electrotonic junction is consistent with the morphological and electrotonic separation of the electrotonic junction and the sites of synaptic action on the dendrites. When the reversal potentials of monosynaptic EPSPs are measured at the integrating segment, the measurements vary systematically with the input pathway selected and overestimate the dendritic reversal potentials by up to 60%.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

Interneurons of the crayfish brain: the relationship between dendrite location and afferent input.

This study was undertaken to examine the relationship between the structure and function of the descending interneurons of the crayfish brain. In particular, the dendritic fields were examined to ascertain if the location of an interneuronal dendrite in any of the six cerebral hemineuromeres (which subserve specific sensory modalities) is a necessary or sufficient condition to determine the functional and/or synaptic input to the interneuron. If a neuron projects a dendrite to a hemineuromere of the deutocerebrum or tritocerebrum, the neuron derives sensory input from the corresponding afferent root in 95% of our observations. Most of these inputs (86%) contain at the least a monosynaptic component. Conversely, if a cell derives monosynaptic input from any one of three of the four deutocerebral and tritocerebral roots tested, it has a corresponding dendrite (in 98% of our observations) in the appropriate hemineuromere. Input from the contralateral antennal nerve is an exception to this rule. The presence of a dendrite in the protocerebrum is not sufficient for predicting detectable visual input, but every instance of detectable visual input is associated with a protocerebral dendrite. Polysynaptic inputs are frequently (42%) not associated with corresponding dendrites. In neurons that were repeatedly dye filled in different animals, we observed significant variation only in the number and precise location of the smaller secondary and tertiary neurites. This variation rarely influenced the subset of sensory lobes innervated by the neuron.

Afferent Pathways↗
PubMed1980

Distributed processing by visual interneurons of crayfish brain. I. Response characteristics and synaptic interactions.

1. The visual responses and synaptic interactions of a small population of crayfish interneurons are described. 2. The discharge of optic nerve sustaining fibers (tonic on-cells) appears in the brain prior to the onset of the light-evoked discharge of any of the higher order, descending visual interneurons. Direct depolarization of impaled sustaining fibers elicits impulse responses in a large number of descending interneurons. These results indicate that the sustaining fibers provide the visual input to higher order interneurons. 3. Four classes of descending interneurons can be distinguished. All arise in the brain and have axons in the circumesophageal connectives. The response forms vary from tonic to phasic. Two classes of tonic cells are distinguished by response latency and two classes of phasic neurons are distinguished by the rate of response adaptation. The phasic neurons exhibit the most rapid habituation, the largest receptive fields, and the most potent nonvisual inputs. 4. Synaptic interactions are studied by cross-correlation of impulse trains and direct observation of synaptic potentials. About 84% of the cells examined reveal evidence of functional connections to other descending visual interneurons. 5. Cross-correlograms derived from impulses of parallel interneurons exhibit a mean time lage to peak of 6.6 +/- 2.8 ms (SD). The measured delay from EPSP onset to spike onset is 6.0 +/- 4.0 ms. Thus a substantial proportion of the correlogram's time lag to peak is associated with postsynaptic integration time. 6. Direct depolarization of impaled tonic on-cells elicits impulse activity at a fixed delay in other descending interneurons. 7. Synaptic potentials in descending visual interneurons are correlated 1:1 with axon spikes of other descending interneurons. 8. A third of the 80 interactions examined were reciprocal and many cells were implicated in multiple interactions. 9. The results suggest that the descending visual interneurons are organized in a complex network, which can cordinate the discharge of various subpopulations of the ensemble. It is proposed that the coordination of impulses in parallel interneurons may be a mechanism for coding and information transfer in the crayfish nervous system.

Animals↗
PubMed1980

Distributed processing by visual interneurons of crayfish brain. II. Network organization and stimulus modulation of synaptic efficacy.

1. Multiple interactions were examined between five or six visual neurons simultaneously monitored in the circumesophageal connective. 2. A single neuron can make divergent connections to at least five other visual interneurons. 3. Conversely, a single cell may receive convergent inputs from up to four visual interneurons. 4. The convergent interactions are sufficiently intense so that 80--90% of a postsynaptic cell's visual activity can be attributed to observed network interactions. 5. Connectivity diagrams suggest that the descending interneurons, which arise in the visual neuropil of the brain, are organized into three interconnected layers: a) neurons that receive input from the optic nerve and project to other visual interneurons, b) neurons that both receive input and project to other descending interneurons in the brain--these cells exhibit a preponderance of reciprocal interactions, c) neurons that receive input from both the first and second network layers and project exclusively to the more caudal ganglia of the ventral nerve cord. 6. The network is systematically organized with respect to visual and nonvisual responsiveness. The cells of the first layer exhibit the strongest visual responses. The cells of the third layer exhibit spontaneous activity and the strongest tactile and/or proprioceptive responses. 7. The intensity of the network interactions is under stimulus control. The synaptic efficacy of a presynaptic spike can vary by over 100-fold as a consequence of stimulus presentation and/or location. The expressed organization of the network thus exhibits a dynamic, stimulus-dependent, plasticity. 8. The results indicate that the descending visual interneurons of the brain rather than forming a parallel tract actually constitute a complex distributed network. Furthermore, the results indicate the feasibility of population neural coding based on stimulus-dependent inpulse coordination in an array of neurons.

Animals↗
PubMed1976

Sustained, synchronous oscillations in discharge of sustaining fibers of crayfish optic nerve.

1. The regularity of the sustaining fiber (SF) steady-state discharge increases with the intensity of a uniform field of illumination. 2. In a high levels of illumination SFs exhibit a highly periodic or rhythmically bursting steady-state discharge. 3. The period of the burst cycle is independent of the light intensity and the mean firing rate. 4. Multimodal interspike-interval histograms in which successive modes decline exponentially suggest that the discharge arises from a regular input. 5. In conditions of uniform illumination, the regular input must be common to all or several SFs since the period of the burst cycle of simultaneously monitored SFs are the same and cross-correlations indicate that the SFs burst in approximate synchrony. 6. It is proposed that the common, regular input is a network of presynaptic elements exhibiting recurrent lateral inhibition. Evidence supporting this hypothesis is that following a brief light pulse to the inhibitory surround, SFs exhibit cycles of silence and bursting, phase-locked to the stimulus but with a period equal to the steady-state burst-cycle period. 7. Furthermore, lateral inhibitory influences are common to several or all SFs as indicated by the close similarity in response time course of two SFs subjected to a common inhibitory stimulus. 8. The response of the lateral pathways to sinusoidally modulated illumination is highly selective to frequencies near the burst-repetition rate. The excitatory pathways exhibit frequency modulation or entrainment over a wide range of input frequencies. 9. The intersustaining burst cycle phase is under partial visual stimulus control (position and intensity) and the possibility of phase coding in the SF ensemble is discussed.

Action Potentials↗