Adaptation and responses to changes in illumination by second- and third-order neurones of locust ocelli

Simmons, Peter

doi:10.1007/bf00197771

Cited by 14 publications

(29 citation statements)

References 43 publications

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“…Illuminating an ocellus caused a sustained hyperpolarizing potential and a change in background noise, which increased relative to dark level for dim illumination but then decreased as light intensity increased (Simmons, 1993). The amplitudes of IPSPs (relative to current resting potential) decreased, largely because of the increase in L -neuron conductance arising from increased input from photoreceptors (Fig.…”

Section: Effects Of Illumination On Ipsps and On Background Noisementioning

confidence: 92%

“…The synapse from an L-neuron onto a third-order neuron has a gain of ϳ1 (Simmons, 1981(Simmons, , 1993. This is lower than the synapse from a photoreceptor to an L-neuron (Simmons, 1995), which is associated with the task the third-order neuron performs in integrating postsynaptic potentials from the ocellar pathway with those from wind-sensitive hairs (Simmons, 1980).…”

Section: Synaptic Performancementioning

confidence: 99%

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The Performance of Synapses That Convey Discrete Graded Potentials in an Insect Visual Pathway

Simmons

1999

J. Neurosci.

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Synapses from nonspiking neurons transmit small graded changes in potential, but variability in their postsynaptic potential amplitudes has not been extensively studied. At synapses where the presynaptic signal is an all-or-none spike, the probabilistic manner of neurotransmitter release causes variation in the amplitudes of postsynaptic potentials. I have measured the reliability of the operation of synapses that convey small graded potentials between pairs of identified large, second-order neurons in the locust ocellar system. IPSPs are mediated by small rebound spikes, which are graded in amplitude, in the presynaptic neuron. A transfer curve plotting amplitudes of spikes against amplitudes of IPSPs has a characteristic S shape with a linear central portion where IPSP amplitude is between Ϫ0.2 and Ϫ0.6 as large as spike amplitude but shows appreciable scatter. Approximately half of the scatter is attributable to background noise, most of which originates in photoreceptors and persists in darkness. The remaining noise is intrinsic to the synapse itself and is usually 0.3-0.7 mV in amplitude. It limits the resolution with which two spike amplitudes can be distinguished from one another to ϳ2 mV and, because the linear part of the transfer curve occupies ϳ10 mV in spike amplitudes, limits the number of discrete signal levels that can be conveyed across the synapse to approximately five. The amplitude of the noise is constant throughout the synaptic operating range, which means it is unlikely that presynaptic membrane potential controls transmitter release by setting a single probability level for quantal release.

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Section: Effects Of Illumination On Ipsps and On Background Noisementioning

confidence: 92%

Section: Synaptic Performancementioning

confidence: 99%

The Performance of Synapses That Convey Discrete Graded Potentials in an Insect Visual Pathway

Simmons

1999

J. Neurosci.

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“…We made intracellular recordings from the cell body of DNI or from L-neurons in the brain, or from the axon of the DNI in the nerve cord, as described previously (Simmons, 1980;Simmons, 1993). We identified DNI by the location of its cell body or axon, and by its responses to illumination from either the ipsilateral or median ocellus and to puffs of air.…”

Section: Methodsmentioning

confidence: 99%

“…The optical design of the ocelli (single-lens eyes that adult locusts have as well as compound eyes) ensures that they collect light from a wide area, and their second-order 'L-neurons' are extremely sensitive to changes in light, suggesting that they report alterations in the angle of the visual horizon by responding to fluctuations in the amount of light each ocellus receives (Wilson, 1978a). Graded potentials are transferred across synapses between photoreceptors and L-neurons (Simmons, 1995), and then from L-neurons to DNI and two other DN neurons on each side (Simmons, 1981;Simmons, 1993). The graded potential carried by L-neurons provides a faithful record of fluctuations in light up to at least 50Hz (Simmons, 1993), and then DNI converts the graded potential representation of the sensory stimulus into spikes that travel down the nerve cord.…”

Section: Introductionmentioning

confidence: 99%

“…Graded potentials are transferred across synapses between photoreceptors and L-neurons (Simmons, 1995), and then from L-neurons to DNI and two other DN neurons on each side (Simmons, 1981;Simmons, 1993). The graded potential carried by L-neurons provides a faithful record of fluctuations in light up to at least 50Hz (Simmons, 1993), and then DNI converts the graded potential representation of the sensory stimulus into spikes that travel down the nerve cord. Responses by DN neurons to moving horizons have been previously recorded over time-scales that would last several wing-beats (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Sparse but specific temporal coding by spikes in an insect sensory-motor ocellar pathway

Simmons

Steveninck

2010

Journal of Experimental Biology

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SUMMARYWe investigate coding in a locust brain neuron, DNI, which transforms graded synaptic input from ocellar L-neurons into axonal spikes that travel to excite particular thoracic flight neurons. Ocellar neurons are naturally stimulated by fluctuations in light collected from a wide field of view, for example when the visual horizon moves up and down. We used two types of stimuli: fluctuating light from a light-emitting diode (LED), and a visual horizon displayed on an electrostatic monitor. In response to randomly fluctuating light stimuli delivered from the LED, individual spikes in DNI occur sparsely but are timed to sub-millisecond precision, carrying substantial information: 4.5-7 bits per spike in our experiments. In response to these light stimuli, the graded potential signal in DNI carries considerably less information than in presynaptic L-neurons. DNI is excited in phase with either sinusoidal light from an LED or a visual horizon oscillating up and down at 20Hz, and changes in mean light level or mean horizon level alter the timing of excitation for each cycle. DNI is a multimodal interneuron, but its ability to time spikes precisely in response to ocellar stimulation is not degraded by additional excitation. We suggest that DNI is part of an optical proprioceptor system, responding to the optical signal induced in the ocelli by nodding movements of the locust head during each wing-beat.

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Differential expression of synapsin in visual neurons of the locust Schistocerca gregaria

Leitinger

Pabst

Rind

et al. 2004

J of Comparative Neurology

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In many taxa, photoreceptors and their second-order neurons operate with graded changes in membrane potential and can release neurotransmitter tonically. A common feature of such neurons in vertebrates is that they have not been found to contain synapsins, a family of proteins that indicate the presence of a reserve pool of synaptic vesicles at synaptic sites. Here, we provide a detailed analysis of synapsin-like immunoreactivity in the compound eye and ocellar photoreceptor cells of the locust Schistocerca gregaria and in some of the second-order neurons. By combining confocal laser scanning microscopy with electron microscopy, we found that photoreceptor cells of both the compound eye and the ocellus lacked synapsin-like immunostaining. In contrast, lamina monopolar cells and large ocellar L interneurons of the lateral ocellus were immunopositive to synapsin. We also identified the output synapses of the photoreceptors and of the L interneurons, and, whereas the photoreceptor synapses lacked immunolabeling, the outputs of the L interneurons were clearly labeled for synapsin. These findings suggest that the photoreceptors and the large second-order neurons of the locust differ in the chemical architecture of their synapses, and we propose that differences in the time course of neurotransmission are the reason for this.

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Adaptation and responses to changes in illumination by second- and third-order neurones of locust ocelli

Abstract: Abstract. Intracellular recordings have been made of responses to step, ramp and sinusoidal changes of light by second-order L-neurones and a third-order neurone, DNI, of locust (Locusta migratoria) ocelli.

Cited by 14 publications

References 43 publications

The Performance of Synapses That Convey Discrete Graded Potentials in an Insect Visual Pathway

The Performance of Synapses That Convey Discrete Graded Potentials in an Insect Visual Pathway

Sparse but specific temporal coding by spikes in an insect sensory-motor ocellar pathway

Differential expression of synapsin in visual neurons of the locust Schistocerca gregaria

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