Es. Fortune et Gj. Rose, PASSIVE AND ACTIVE MEMBRANE-PROPERTIES CONTRIBUTE TO THE TEMPORAL FILTERING PROPERTIES OF MIDBRAIN NEURONS IN-VIVO, The Journal of neuroscience, 17(10), 1997, pp. 3815-3825
This study examined the contributions of passive and active membrane p
roperties to the temporal selectivities of electrosensory neurons in v
ivo. The intracellular responses to time-varying (2-30 Hz) electrosens
ory stimulation and current injection of 27 neurons in the midbrain of
the weakly electric fish Eigenmannia were recorded. Each neuron was f
illed with biocytin to reveal its anatomy. Neurons were divided into t
wo biophysically distinct groups based on their frequency-dependent re
sponses to sinusoidal current injection over the range 2-30 Hz. Fourte
en neurons showed low-pass filtering, with a maximum decline in the am
plitude of voltage responses of >2.6 dB (X = 4.30 dB, s = 1.10 dB) to
sinusoidal current injection, These neurons also showed low-pass filte
ring of electrosensory information but with larger maximum declines in
postsynaptic potential amplitude (X = 9.53 dB, s = 3.34 dB; n = 10).
These neurons had broad dendritic arbors and relatively spiny dendrite
s. Five neurons showed all-pass filtering, having maximum decline in t
he amplitude of voltage responses of <2.0 dB (X = 1,16 dB, s = 0.61 dB
). For electrosensory stimuli, however, these neurons showed low-, ban
d-, or high-pass filtering. These neurons had small dendritic arbors a
nd few or no spines. Voltage-dependent ''active'' conductances were re
vealed in eight neurons by using several levels of current clamp. In f
our of these neurons, the duration of the voltage-dependent conductanc
es decreased in concert with the period of the electrosensory stimulus
, whereas in the other four neurons the duration of the voltage-depend
ent conductances was relatively short (<30 msec) and nearly constant a
cross sensory stimulation frequencies. These conductances enhanced the
temporal filtering properties of neurons.