TY  - JOUR
AB  - In this comparative in vivo study of dendritic calcium accumulation, we describe the time course and spatial integration properties of two classes of visual interneurons in the lobula plate of the blowfly. Calcium accumulation was measured during visual motion stimulation, ensuring synaptic activation of the neurons within their natural spatial and temporal operating range. The compared cell classes, centrifugal horizontal (CH) and horizontal system (HS) cells, are known to receive retinotopic input of similar direction selectivity, but to differ in morphology, biophysics, presence of dendrodendritic synapses, and computational task. 1) The time course of motion-induced calcium accumulation was highly invariant with respect to stimulus parameters such as pattern contrast and size. In HS cells, the rise of [Ca2+](i) can be described by a single exponential with a time constant of 5-6 s. The initial rise of [Ca2+](i) in CH cells was much faster (tau approximate to 1 s). The decay time constant in both cell classes was estimated to be at least 3.5 times longer than the corresponding rise time constant. 2) The voltage-[Ca2+](i) relationship was best described by an expansive nonlinearity in HS cells and an approximately linear relationship in CH cells. 3) Both cell classes displayed a size-dependent saturation nonlinearity of the calcium accumulation. Although in CH cells calcium saturation was indistinguishable from saturation of the membrane potential, saturation of the two response parameters differed in HS cells. 4) There was spatial overlap of the calcium signal in response to nonoverlapping visual stimuli. Both the area and the amplitude of the overlap profile was larger in CH cells than in HS cells. Thus calcium accumulation in CH cells is spatially blurred to a greater extent than in HS cells. 5) The described differences between the two cell classes may reflect the following computational tasks of these neurons: CH cells relay retinotopic information within the lobula plate via dendritic synapses with pronounced spatial low-pass filtering. HS cells are output neurons of the lobula plate, in which the slow, local calcium accumulation may be suitable for local modulatory functions.
DA  - 1999
DO  - 10.1152/jn.1999.82.6.3327
KW  - presynaptic
KW  - membrane
KW  - stimulation
KW  - membrane potential
KW  - neuron
KW  - direction
KW  - direction selectivity
KW  - Signal
KW  - Synapse
KW  - Time constant
KW  - STIMULI
KW  - stimulus
KW  - response
KW  - size
KW  - interneuron
KW  - Morphology
KW  - TIME
KW  - biophysics
KW  - temporal
KW  - CELL
KW  - SYNAPSES
KW  - interneurons
KW  - VISUAL-STIMULI
KW  - Filtering
KW  - TASKS
KW  - TASK
KW  - CELLS
KW  - neurons
KW  - Information
KW  - system
KW  - fura-2
KW  - input
KW  - Intracellular calcium
KW  - HS-Cells
KW  - Lobula plate
KW  - lobula
KW  - CH-Cells
KW  - Calliphora
KW  - fly
KW  - Visual Interneuron
KW  - dendrodendritic
KW  - dendritic integration
KW  - retinotopic
KW  - Dendrite
KW  - ACTIVATION
KW  - calcium
LA  - eng
IS  - 6
M2  - 3327
PY  - 1999
SN  - 0022-3077
SP  - 3327-3338
T2  - Journal of neurophysiology
TI  - In vivo calcium accumulation in presynaptic and postsynaptic dendrites of visual interneurons
UR  - https://nbn-resolving.org/urn:nbn:de:0070-pub-17848581
Y2  - 2024-11-22T09:40:24
ER  -