Responses of the blue sensitive cone system from the visual cortex and the arterially perfused eye in cat and monkey

0042.6989/81jl1161 l-05SO2.00~0 Pergamon Press ttd

RESPONSES OF THE BLUE SENSITIVE CONE SYSTEM FROM THE VISUAL CORTEX AND THE ARTERIALLY PERFUSED EYE IN CAT AND MONKEY R. P. SCHUURMANS and E. ZRENNER Max-Planck-Institute

for Physiological and Clinical Research, W. G. Kerckhoff-Institute D-6350 Bad Nauheim, F.R.C.

lNTRODUCTlON

sensitive, or blue cone mechanism has some unique spectral, spatial and temporal features in cat and monkey (see Zrenner and Gouras, 1981). In the present paper, response characteristics of the blue cone mechanism and its interactions with longer wavelength sensitive cones will be described as they are revealed by recordings from three sites of the visual system. Furthermore, the data obtained by recordings from the arterially perfused eye indicate involvement of GABA in the control of the blue cone mechanism’s sensitivity. As shown in Fig. 1 (left) the electroretinogram (ERG) and the optic nerve response (ONR) were recorded from the cornea and trunk of the optic nerve in 49 enucbated and arterially perfused cat eyes as described by Gouras and Hoff (1970), Niemeyer (1975), Zrenner and Gouras (1979) as well as in 6 arterially perfused monkey eyes (Macaca mulatta). The ophthalmociliary artery of the macaque eye was cannula~~ in situ before enucleation after removing the lateral wail of the orbita according to Berke’s modification of Kriinlein’s procedure. The visually evoked cortical potentials (VECP) were recorded in the lateral wall of the orbita according to Berke’s modification of Kriinlein’s procedure. The visually evoked cortical potentials (VECP) were recorded in the intact animal from the left hemisphere with a silver-silver-chloride electrode. positioned underneath the dura at the area striata A (Doty. 1958). The short wavelength

RESULTS

When strong yellow adapting lights (Schott filter OG 515,400,OOOtd) are applied, the action spectra of the blue cone mechanism, peaking at 460nm (Fig. 1, right) can be obtained by constant response amplitude criteria at all three sites of the cat’s visual system: ERG (top), ONR (center) and VECP (bottom). *With strong purple adaptation. a third photopically active mechanism can be revealed, peaking near 5OOnm in cat (Ring0 ef 01.. 1977; Schuurmans and Zrenner. 1981). Both long wavelength sensitive mechanisms have similar response properties.

To a 448 nm test light and at intensities near threshold only the blue cone system responds, while 575 nm stimulates the long wavelength sensitive cone mechanism which has a sensitivity maximum at 560 nm. Using these two standard test lights, we shall describe the response characteristics of the blue and longer wavelength sensitive cone mechanisms. In comparison to the .%Onm-mechanism, the responses of the blue cone mechanism of the cat (Fig. 2a) can be characterized as follows: at all recording sites its responses have a longer latency; its optic nerve response is mainly tonic; in the ONR as well as in the VECP the fast, positive off-effect is lacking; the VECP amplitude vs log intensity (V-log I) functions of the blue cone mechanism have a flatter slope, saturating at much smaller amplitudes (Fig. 2b). However, with increasing test light intensities (510nm). a transition occurs from the 460 to the 56Onm mechanism (Fig. 2. open circles). The flatter slope of the short wavelength functions (Gouras, 1970) reflect the paucity of the blue cones (Zrenner and Gouras, 1979). In Fig. 3 (left), the blue cone ERG of the rhesus monkey shows, at low intensities (log E = 4.6), striking similarities with that of the cat considering its latency and the absence of a pronounced a-wave and positive off-effect. However, at high stimulus intensities (log E = 5.6), the saturated blue cone responses are obscured by those of the longer waveIength sensitive cones (Lizones*) which mediate ERG responses exhibiting predominantly positive off-effects in the macaque and negative off-effects in the cat. Apparently, the circuitry of the long wavelength sensitive cones’ off-system is different in cat and monkey at least up to the inner nuclear layer. Although the responses of the blue cone mechanism differ considerably from those of the long wavelength sensitive mechanism, they resemble in many respects those of rods. As shown in Fig. 3 (right), the rod responses also lack a pronounced a-wave and a positive off-effect, probably indicating a retinal circuitry similar for blue cones and rods (Zrenner and Gouras, 1979). The possibility that blue cones, like rods, mediate their responses through only one set of bipolar cells is indicated by the lack of a positive offeffect as well as by the observation that blue cones

1611

1612

R. P. SCHUURMANS

and E. ZRENNER

ERG

VECP

Fig. 1. Experimental set-up for ERG, ONR and VCEP recordings. Two beams served for Ganzfeld light stimulation The eye was arterially perfused with an oxygenated tissue culture medium which passed through a drop-counter. a heating-bath and a bubble trap chamber. The VECP was recorded under Nembutai anaesthesia. The action spectra for the ERG (top). ONR (center) and VECP (bottom) were fitted by two Dartnall (1953) nomograms (solid lines) having a peak sensitivity near 460 and 56Onm. E = irradiance (CIE. 1970). measured radiometrically. Xe = Xenon lamp.

feed only on-center channels. both in cat (Granit and Tansley. 1948; Cleland and Levick. 1974: Pearlman and Daw. 1970) and monkey (see Gouras and Zrenner. 1981 and Gouras and Zrenner. 1979). Moreover. in the cat’s VECP as well as ONR a

usually

paradoxical wavelength

transient

sensitivity

decrease

to

short

L-cone’s by strong yellow adaptation Zrenner. 1979). Although the does not stimulate the blue its extinction is accompanied

test lights was found during the

recovery from a bleach lights (Schuurmans and yellow adaptation light sensitive cones directly. by a decrease in sensitivity of the blue cone mechanism: this suggests that the hluc cone’s sensitivity modulated

by signals from longer wavelength

is

sensi-

tive cones (Mellon and Polden. 1977). As shown schematically in Fig. 4 (top), a yellow adaptation light was switched off every 19sec for 3 sec. At the left column the ONR responses to 448 nm-stimuli are shown underneath each other during (A). 400 msec after (B) and 14OOmsec after (C) extinction of the yellow adaptation light (hatched area). The response amplitudes show a transient decrease during the first second (B) of dark adaptation.

That this decrease in amplitude reflects a real change in sensitivity is evidenced by the V-log I functions in Fig. 5 (left). The increase in the L-cone’s sensitivity (575 nm) is accompanied by a decrease of the blue cone’s sensitivity (448 nm), as indicated by the shift of the V-log I functions (arrows). In order to find out whether this paradoxical sensitivity change of the blue cone mechanism is controlled by an inhibitory neurotransmitter. the GABA-antagonist bicuculline (Krnjevid. 1974) was added in 18 experiments to the perfusion medium in a concentration of 1 to 6pM. The initial fast component of the blue cone mechanism’s response slightly increased while the subsequent tonic component decreased in amplitude (center column in Fig. 4, row A). However, the transient amplitude decrease seen in the left column of Fig. 4 after switching off the yellow adaptation light is eliminated by adding bicuculline to the perfusion medium (row B in Fig 4). Thirty minutes after the stop of the injection, the responses recovered (right column in Fig. 4, row A) and the densensitization of the blue cone’s signal occurring after the off-set of the yellow adaptation light can be found again, When the corresponding V-log I func-

Cone system from the visual cortex of cat and monkey

1613

(4 ERG

Fig. 2(a) ERG. ONR and VECP responses recorded and averaged (n = 8 to 128) from the arterially perfused cat eye and visual cortex respectively during strong yellow light adaptation (OG 515. 400,000 td) as well as V-log I functions of the VECP. (b) To the 448 nm test light and at intensities of 1 to 2 log units above threshold. only the blue cone mechanism responds. while 575 nm test tights stimulate the long wavelength sensitive cone mechanism. The V-log I functions show the transition from responses mediated by the blue cone mechanism (below 20~V) to those of the longer wavelength sensitive cone mechanism at high stimulus intensities. best seen for the 510 nm-stimulus (open circles).

(bl .\ L0gE 399 53&F---427 448

(a)

Perfused macaque eye Yeltnw adaptation (1053tdl 1*44Snm

38 A._/.34-J+/---

464

32-&_/--

487

32 &.A----

510

32-f/_,--

527

33b

553

35JLf-

575

416

591

46-&/--

607

4gJ.i_.--

622

556

656

25-

b-wave.

DA

40

50

y

L

61 6 *ooybI

bs

300-

5.0 _.J& 200-

b - wave. DA a--o 427nm .-.. 118’ 0-a l .*

487 ” 510.

5: s 9: 3 ioos ! o-

m

4

20

30 Log

E (Quanta s+ pm-21

60

Fig. 3(a) Original cone ERG’s elicited by a 448 nm test light at 4 intensities during strong yellow light adaptation (400.000 td) in the arterially perfused monkey eye (averaged 16 times). (b) Original rod ERG’s and action spectrum obtained by a 90 /IV b-wave criterion from the V-log I functions (below) in the dark adapted (DA) macaque eye. The V; (CIE 1970) scotopic luminosity function is represented by the solid line.

1614

R.

P. SCHUURMANS

ancl E. ZRENNER

Fig. 4. A schematic drawing of the stimulus sequence is shown on top. In the left column (control), the transient sensitivity decrease for the optic nerve to a 448 nm-stimulus during (A) and after (B and C) extinction of the yellow adaptation light (hatched area) is shown. Bicuculline (center column) blocks this phenomenon reversibly (recovery, right column). tions (Fig. 5) before (left) and during the bicuculline injection (right) are compared, the L-cone’s sensitivity still increases 400 msec after the extinction of the yeilow adaption light (arrow, right, 575 nm). However, the sensitivity of the blue cone mechanism remains unchanged during the bicuculline injection (Fig. 5, right, 448nm) indicating that the paradoxical sensitivity decrease seen in the control measurements is blocked. It should be noted, that bicuculhne initially enhances the sensitivity of both cone mechanisms i.e. the irradiance E necessary to evoke a 5OpV amplitude decreases for both cone mechanisms. comparing the V-log I functions recorded before and during the injection (filled circles and triangles, in Fig. 5 for 448 and 575 nm respectively). However, the control mechanism of the blue cone’s sensitivity. mediated by the A

BC

longer wavelength sensitive cones, is blocked by bicuculline. This indicates that GABA is involved in a retinal circuitry which modulates the blue cone’s sensitivity through the L-cones. Autoradiographical studies (Ehinger, 1977) showed that amacrine cells may provide a gabanergic pathway. The blue cone meehanism’s control, however, might be well mediated also by other cells in the inner nuclear layer (see model of Zrenner and Couras, 1981), especially since the transient sensitivity decrease can be found already in the ERG b-wave in monkey.(Yaleton and van Norren, 1979). The action of GABA itself on the blue cone’s sensitivity could not be determined since systemic applications of GABA demand high ~n~trations A

BC

Control

P

Log E (Quatia's-"pm“)

Log E (Quanta.s-"pm-2)

Fig. 5. V-log I functions showing the sensitivity decrease for the 44tl nm test light and tbe increase for the 575 nm test light after extinction of the yellow adaptation light (arrows. kft). During the injection of bicuculline, the sensitivity of the L-cone mechanism increased (arrow at 575 nm right) whik that for the blue cone mechanism remains unchanged. Stimulus conditions as in Figs 2 and 4.

Cone system from the visual cortex of cat and monkey

(2~10

mM) in order to pass the blood-retina in vascular

resulting

caused

by

various

(Schuurmans not

seen

amino-acids

and Niemeyer.

in

barrier,

resistance changes as they are

systemic

such

as

glycine

1978). Such effects are

applications

of

bicuculline

(I 6PM).

St MMARY

Responses of the blue

cone

mechanism

can

be

recorded from the receptor layer on up to the neurons generating

the cat’s visually

evoked

tials. The striking similarities of in the arterially

cortical

poten-

its responses recorded

perfused eyes of the cat and monkey

with those of rods and the typical

differences

with

those of the longer wavelength sensitive cones are dis-

our data show that the sensi-

cussed. Furthermore,

tivity control of the blue cone mechanism is probably mediated

longer wavelength sensitive cones

through

using a gabanergic pathway.

Acknowledyements--Our thanks are due to Professor Dr E. Dodt for his support and stimulating discussions; Dr J. Tanabe for his participation in some of the experiments and to Miss M. Klein for excellent technical assistance.

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