Introduction tal cell HC receptive field [13,14]. By analogy, this effect
Brain Research 887 2000 230–237 www.elsevier.com locate bres
Interactive report
Long-term light history modulates the light response kinetics of
1
luminosity L-type horizontal cells in the roach retina
A. Jenkins, M.W. Hankins
Imperial College School of Medicine , Division of Neuroscience and Psychological Medicine, Department of Integrative and Molecular Neuroscience,
Fulham Palace Road , London W6 8RF, UK
Accepted 17 October 2000
Abstract
We have examined the effects of prolonged periods of darkness on the responses of luminosity-type horizontal cells L-HCs in the freshwater cyprinid, Rutilus rutilus. Two groups of retinae were compared, those recorded after 10 min dark adaptation SA and those
recorded after 3 h dark adaptation LA. The results suggest that long-term light history does not modify the general responsiveness of the L-HCs in this species. However, there are apparent changes in the receptive field of the cells and modifications to the kinetics of the
light-evoked response. The kinetics changes involve both a delay in the onset of light response and a selective effect on the hyperpolarizing light-ON response. Thus the mean time constant
t for the SA cells was 32.462.39 ms n562, whilst that for the LA cells was 53.463.03 ms n561. These effects occur in the absence of changes in the relative spectral sensitivity or threshold sensitivity
of the HCs. The results suggest that in some vertebrate retinae, prolonged darkness light-history may regulate long-term plasticity in the kinetics of the cone–HC pathway.
2000 Elsevier Science B.V. All rights reserved.
Theme : Sensory systems
Topic : Retina and photoreceptors
Keywords : Retina; Horizontal cell; Adaptation; Plasticity
1. Introduction tal cell HC receptive field [13,14]. By analogy, this effect
was interpreted in relation to changes in the activity of the There is growing interest in the mechanisms that
dopaminergic interplexiform neurones, which have been subserve long-term plasticity of the retinal network.
shown to regulate HC coupling [3,20]. However, recent Numerous studies in the vertebrate retina suggest that
studies have established that dopamine release is not prolonged dark-adaptation has a profound effect on the
enhanced by periods of prolonged darkness in the daytime responsiveness of cone pathways. Following prolonged
[27]. dark adaptation, it was first shown that there are ana-
In a detailed study of the white perch retina Morone tomical changes in the cone pedicles, which were proposed
americana, a
similar phenomenon
was described
to be correlated with the loss of colour opponency and [21,29,30], although the extent of dark-suppression was
cone function at the ganglion cell level of the goldfish significantly more pronounced than in carp. This suggests
retina [16]. Subsequently it was demonstrated in the that the expression of dark-suppression may have a
goldfish that prolonged darkness was associated with species-dependent component. It has also been established
suppression of responsiveness of the L-type horizontal in the white perch that there are significant changes in the
cells [32]. Furthermore, it was shown that such dark- kinetics of the light response after prolonged darkness
suppression was associated with a reduction in the horizon- [12]. However, these changes were associated with
profound changes
in the
threshold sensitivity
and
1
chromatic sensitivity,
suggesting they
are mediated
Published on the World Wide Web on 7 November 2000.
through rod–cone interaction.
Corresponding author. Tel.: 144-208-846-7521. E-mail address
: m.hankinsic.ac.uk M.W. Hankins.
Preliminary experiments on the L-HCs in the roach
0006-8993 00 – see front matter
2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 6 - 8 9 9 3 0 0 0 3 0 7 3 - 0
A . Jenkins, M.W. Hankins Brain Research 887 2000 230 –237
231
retina Rutilus rutilus recorded through a 24-h diurnal tion. Cells were impaled with no photic stimuli and
cycle, reported no significant modulation of the HC light initially characterized using a single paired red and green
response amplitude, but noted significant changes in the flash of moderate intensity 650 nm, 531 nm, I
56.7
max 22
light response kinetics [9]. L-HCs in the roach, like most mW cm
, 450–500 ms. These responses provided the cyprinids receive a dominant LWS red cone input, with a
data for the principal amplitude and kinetic analysis with a weak MWS green cone input [2]. This raises the question
minimal light exposure SA, n569; LA, n579. The as to whether long-term light history or circadian diurnal
responses of the cells were then additionally characterized regulation might drive the changes in cone-driven L-HC
using a range of spectral or spatial stimuli. These responses kinetics. Interestingly, long-term light-history appears to
provided information confirming the relative spectral sen- affect the temporal response of the human photopic cone
sitivity, and allowed us to assess the extent of the HC electroretinogram [7]. Thus it was shown that the b-wave
receptive fields of individual cells. After the experiments, implicit time of the photopic cone ERG exhibits a pro-
detailed measurements of the individual light evoked nounced sinusoidal oscillation, the period of oscillation
responses S-potential were performed in accordance to being |24 h with peak temporal response in the middle of
those outlined in Fig. 1. This involved simple amplitude the day. This raises the possibility that the temporal
measurement of the principal components, together with a response of cone pathways is modulated according to
range of kinetic measurements on the rate of hyperpolari- long-term light-history.
zation and depolarization. An assessment of receptive field We have therefore examined the effect of long-term dark
size was made using two methods. Firstly, the amplitude of adaptation on the light responses of L-HCs cells in the
the annulus response for each cell was extrapolated to an roach retina. Some of this work has been reported in
equivalent amplitude response spot area Fig. 1c. Second- abstract form [5].
ly, the ratio of the amplitude of the annulus and spot annulus spot was calculated for each cell to give a
measure of the relative strength of surround response.