Properties of the epiphysis cerebri of the small-spotted dogfish shark, Scyliorhinus caniculus L.

Won RLI.Vol.11,pp.189-198. Pergamon prols1971.Printed inCirUBritain.

PROPERTIES OF THE EPIPHYSIS CEREBRI SPOTTED DOGFISH SHARK, SCYLIORHINUS D. I.

HAMASAKI~~

OF THE SMALLCANICULUS L.’

and PETERSTRECK~

Abteilung f& Experimentelle Ophthalmologie (11. Physiologische Abt.) des W. G. Kerckhoff Instituts der Max-Planck-Gesellschaft, Bad Nauheim, Deutschland (Received 21 May 1970; in revised form 23 July 1970)

INTRODUCTION THE epiphysis cerebri (pineal organ) and the parapineal

organ (parietal eye, stirnorgan) develop embryonically as evaginations of the diencephalon as do the lateral eyes. As first shown by VON FRISCH(191 I), the epiphysisplays an important role in the control of pigment cells in the skin of fishes. The alteration of neural activity by direct illumination of the pineal system has been established by electrophysiological recordings in several species of animals. The first recordings of spike activity were made from the stirnorgan and the intracranial epiphysis of frogs (DODT and HEERD, 1962; DODT and JACOBSON,1963). Subsequently, the epiphysisof several species of frogs (DODT and MORITA, 1964; MORITA, 1965), of trout (MORITA, 1966; HANYU, NIWA and TAMURA, 1969), and lizards (HAMA~AKI and DODT, 1969) have been shown to be light sensitive. In general, all wavelength stimuli inhibited the spontaneous activity of the epiphysis.Occasional units have been recorded in trouts and bullfrogs which are excited by some wavelengths and inhibited by others (MORITA, 1966, 1969). These chromatic units were not seen in lizards. Among the other animals with a well-developed epiphysis,the selachians appeared to be worthy of investigation (see RUDEBERG, 1969 for review of epiphyds). STUDNIEKA(1905) reported the presence of ganglion and supporting cells as well as cells which appeared to be sensory in the epiphysisof the lantern shark, Spinax niger (Etmopterusspinax L.). HOLMGREN (19 18) described the outer and inner segments of the sensory cells of the spiny dogfish shark, ZQualus acanthias and compared them to the photoreceptors of the lateral eyes. ALTNER (1965) also reported the presence of sensory cells in the epiphysisof several species of sharks. The recent electron microscopic examination of the epiphysis’of the dogfish shark (RODEBERG, 1969) showed that the outer segments of the receptors consisted of stacked discs and were morphologically similar to the cones of the lateral eyes. The photoreceptors line the inner wall of the epiphysis with outer segments protruding into the lumen. Surprisingly, ’ This paper was presented in part at the symposium “Physiologic des Sehens” held at Physiologisches Institute der Freien U&emit& Berlin, l-5 December 1969. ’ Supportedby a CareerDevelopment Award from the National Institutes of Health, No. 5 K3 NB14692, Nationa Eye Institute, Bethesda, Maryland, U.S.A. 3 On leave of absence from the Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, Florida, U.S.A. l Present address: Bascom Palmer Eye Institute, P.O. Box 875, Biscayne Annex, Miami, Florida 33152, U.S.A. ’ Present address: Zoologisches Institut der J. W. Goethe-UniversitBt, Frankfurt/Main. Bundesrepublik, Deutschland. 189

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only orae ganglion. cell was observed in this electron microscopic study although many nerve fibers were observed to run in the outer layer of the epiphysis. The purpose of this study was to determine whether the epiphysis of the dogfish shark was light sensitive aad to examine its properties. ~~~~~natio~ of the epj~hys~~elicited both slow potentials and inhibition of the spike activity. The inhibition was then used to study the properties of the epiphysis. ‘MATERIALS AND METHODS Animals. The data were collected from ten adult dog&h sharks, Scyfiorhinus caniculus. The experiments were conducted between IS March and 4 June 1969 in Bad Nauheim, Germany. The animals were given an initial intramuscular injection of 50 mg nembutal and additional amounts of 25 mg until the animals failed to struggle when picked up. Curare (3 mg&c) was given int~mu~u~~ly to stop the respiratory movements. The animals were placed in a trough containing sea water and the head was braced SOthat the eyes and head, but not the gills, were above the water level. The animals were kept alive by circulating sea water over the gills by a centrifugal pump (HAMASAKZ and BRZDGES, 1965). The circulating sea water was aerated and cooied to Wf2”C by passing the water through a bath of cold water maintained at appr~xi~tely f-Z%. Anatomy. A schematic diagram of a sagittal section through the midline of a shark head is Shown in Fig. 1. The long, tubular cpiphysisextends from the diencephalon to its end vesicle which is located beneath the skull slightly anterior to the interocular line. Preparation a/the animd. The skin overlying the epiphysi was excised, and a dental drill was used to enter the brain cavity. The cartitagenous skull was removed to expose a large portion of the ep&&. The epiphyseal stalk was cut as far centrally as possible (Fig. l), but the point of transection varied between animals because of the rich blood supply on the surface of the epiphysis.

Fro. 1. Diagram of a sagittal section through the brain of the dogfish, Scyliorhinus caniculus R~DEBERO, 1969). T c Teiencephaton, D = diencephaton, M = mesencephaton, E = epiphysis cerebri (pine& organ), S = roof of the skutf, L = light stimulation, D.E. = different electrode, I.E. = indifferent electrode.

L., showing the stimulus and recording conditions (modified after

Recording. The peripheral end of the epiphyseal stalk was placed on a cotton wick electrode which was connected by a Ag-AgCl electrode to one side of the preampWier. An eltctrode in the cut skin acted as the indifferent electrode, and the animal was grounded through the sea water bath. For the recording of the slow potentials, a Ttinnies amplifier was used with either direct-coupling or coupled with a 1-Oset time-constant. In other animals only spikes were recorded and a Tektronix 122 preamplifier set at a time constant of 0*002set was used. The responses were displayed on an oscilloscope and permanent records were made by filming the oscilloscope. The responses were atso stored on tape for fater at%3i3&3.

Properties of the Epiphysis Cerebri of the Small-spotted Doglish Shark

191

Stimulus. Tk stimulus was obtained from a 1OOOW xenon lamp. Two independent beams were available and interference and neutral &en v&e used to alter the stimuhis (D~DTand JISSEN,1961).The unattenuated stimulus had a huninance of 4-3 x lo* lnJma. The stimulus was brought to a focus on the surface of the head in the region of the end vesicle of the epiphyssls(Fig. 1). The amount of light lost by passing through the skin artd skulf of the animal was measured by plachq a dissected, upper half of the head (the skin and skull without the brain) in the light path and visually matching the transmitted light to that of the second beam. It was found that the skin and skull reduced the light focused on the head by approximately 2.0 log units.

RESULTS

Characteristicsofthe epiphyseallight response. The spontaneous activity of the epiphysis was recorded immediately after the cut end of the stalk was placed on the electrode and the

animal placed in the dark. The recording technique was such that several units were recorded but usually one or two units were larger than the others and these were the units studied. The spontaneous activity of the units had a rate of 2-4 spikes/set (Figs. 2A and 2B) which is comparable to that seen for the lizards but lower than that of frogs (IO/set) or trouts (20@~).

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Fro. 2. Response of the epiphysis cerebri of the dog&h Scyiiorhinus canicuius to repeatedlight stimulation. DC-recording; spikes and slow potentials on the upper trace, stimuli on the lower trace, polarity and calibration marks as indicated. Stimulus duration: 0.1 set in A, 1 set in B; 4.0 log units above threshold. Recording speed in B is half of that in A. Spikeform with high recording speed is shown in C. The stimufi are numbered for ease of reference.

Stimulation of the epiphysisby a white light stimulus approximately 4 log units above threshold (0.1 set duration) elicits a positive wave (downward) accompanied by inhibition of spike activity (Fig. 2A). The potential level remains positive for ~pro~~~ly 15 sea and then slowly drifts back towards the baseline. In most eases, the potential level does not stop at the prestimulus level but overshoots it for a short time before returning to the prestimuhts level. This same pattern of potential change is seen following the second stimulus. The pattern of the spike discharge is roughly correlated with the slow potential changes. Thus the positive wave is aczompanied by a prompt inhibition or marked depression of spike activity, and the slow recovery of the slow.potential is accompanied by a return of the spikes. The overshoot is accompanied by a high rate of discharge and will be referred to as the rebound discharge. The responses to the first two stimuh in Fig. 2B are similar to that described. Stimuli which are presented during the positive phase of the slow potential elicit only a small respones (stimuli 3, 7 and 8) but nevertheless have considerable influence on subsequent stimuli as can be noted, for example, by comparing the responses to stimuli 4 and 6. The intertlash

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interval between stimuli 2 and 4 is the same as that between S and 6, and yet the response to stimulus 6 is considerably larger than that to stimulus 4. Thus, although stimulus 3 elicits only a small response it was effective in placing the epiphysiis in a relative refractory state. This same pattern can be observed to stimuli 6 through 10. This condition of restive refraction will have bearing on whether the slow potentials arise from the photoreceptors or from the ganglion cells. The spikes are triphasic with the major peak positive (Fig. 2C). In all probability these spikes are recorded from the nerve fibers rather than the ganglion cells. Eficct of stilly intensity on the slow potential. A stimulus slightly above ~shold (Fig. 3A, I = -7-10) elicits a slow-rising positive wave which reaches maximum amplitude approximately 2 set after the beginning of the stimulus (recorded witha 1*Oset time-constant). With increasing intensities, the amplitude of the positive wave increases and the latency decreases. The intensity range over which there is an increase in the amplitude is approximately 3-4 log units. Thereafter increases in the intensity merely prolong the duration of the positivity. This can be seen in Fig. 3A although the real course of the slow potential is distorted by the AC recording (1-O set time-constant). The schematic diagram illustrates better the response pattern of the epiphyd (Fig. 3B). Efict of stimulus intensity on spike activity. At threshold (I = -7*90), there is a period of decreased activity which begins about 6 see after the stimulus (Fig. 4). At the next intensity, a slight decrease in activity beginning 1-S see after the stimulus is recorded. The i~bition is stronger at I = -6-20 with the duration of complete inhibition lasting for about 6 sec. Further increases in the intensity result in decreasing the latency of the onset of inhibition

FIG. 4. Response of the epiphysis to light stimulation over a range of 8 log units of relative illumination. Log 0 is equal to 4.3 x lo4 Im/ma. Stimulus duration: 1 set AC-recording with a time constant of 0.002 sec.

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FIG. 3A. Response of the epiphysis cerebra’to light stimuli of increasing illumination. The numbers indicate the relative illumination in log units. Log 0 is equal to 4-3 x lo* lm/m*. Stimulus duration: 1 set AC-recording with a time constant of 1 sec.

FIG. 3B. Scheme of the response of the ep&!tys& cerebri to light stimulation (slow and spike pbtentials).

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FIG. 5A and 5B. Poststimulus time histograms of two units from the dogfish epiphpis. The relative illumination designated by numbers in each block with log 0 = 4.3 x lo* lm/m2. The average firing rate prior to the stimulus shown to the left of time = 0. The stimulus of 1 set duration was presented at time = 0, and the number of spikes for each 2 see counted. Ordinate, frequency of firing in spikesfsec; abscissa, time in seconds after the stimulus. FIG. SC and SD. Example of recordings from which histograms were made. The unit shown in 5C contributed to SA while that of SD-% Stimulus duration = 1 sec.

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FIG. 7. Effect of steady illu~nation of 1 min duration on the firing rate of unit from the epiphysis. (A) The firing rate of two units are shown by the open symbols while the firing rates of several units are shown by the closed symbols. The firing rate in the dark shown at the left and the rates determined after 1 min exposure to the various levels of illumination shown thereafter. (B) After the exposure, the light was turned off and the latency to the return of activity determined (t). The average values shown by the open circle determined after 1 min exposure and those with the closed circles after 2 min of steady illumination. (C) Recording from one preparation demonstrating that the time of return of activity after long exposure is more or less independent of level of illumination.

193

Properties of the Epiphysis Cerebri of the Small-spotted Dogfish Shark

and prolonging the duration of complete inhibition. Note that a stimulus only 2 log units above threshold can evoke a period of complete inhibition lasting for 6 set, and with a stimulus 7-8 log units above threshold, the duration can exceed 2 min. A poststimulus time histogram shows better the effect of stimulus intensity on two units (Figs. 5A and 5B). Samples of recordings from which the histograms were made are shown at the bottom (Figs. 5C and 5D). The first unit (Figs. 5A and 5C) demonstrates the occasional type of unit which responded by a decrease in spike frequency but not complete inhibition. This type of unit also showed very little rebound discharge. The second unit (Figs. 5B and 5D) is more common and demonstrates the long duration of complete inhibition and rebound discharge described above. The recording also demonstrates that during this recovery period the activity returns in bursts, which may be a sign of oscillation between the inhibitory action of the stimulus and the recovery of spontaneous activity (see HAMASAKI,1969). E$ect of stimulus intensity on the latency. The complete inhibition of spike activity made it difficult to quantitate the effectiveness of a given stimulus. However, latency measurements were found to give a good indication and three different measurements of latencies were made: tl, the time between the onset of the stimulus and the onset of inhibition (i.e. last spike); t2, the time between the end of the stimulus and the first return of activity; and t3, the time between the end of the stimulus and the beginning of the rebound discharge (Fig. 6). l

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FIG. 6. Effect of illumination on the latency of response of the epiphysis. Three measures of latencies were made as indicated in the figure. In A and B: white light (0 l l 0) n = 11; 401 mm = (A A A A), n = 5; 630 nm = (0000). n = 6. Stimulusduration = 1-Osec. Ordinate, latency in set; abscissa, log relative illumination. Note the difference in the scale of the ordinate. A total of 11 measurements from 11 recordings were made for tl and the average values are shown in Fig. 6A (0 0 0 0). At threshold, inhibition is not evident until 1.5 set after the stimulus. With increasing intensities, there is a linear decrease in tl for about 3.5 log units. Thereafter, the decrease in the latency for increasing intensities is slower, and with the full V.R.11/?--B

194

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intensity stimulus the latency is reduced to 0*15 sec. The two segments of the curves intersect at an intensity approximately 3.5 log units above threshold and at a latency of O-4 sec. Measurements of f2 were made on 11 recordings and the averages are shown in Fig. 6B (0 0 0 0). At threshold, f2 is about 3 set and there is a slow increase in f2 with increasing intensities. Between Z = -440 and -3.50 there is an abrupt increase in t,, which continues up to 100 set at the full intensity stimulus. The values for tJ (0 @a@, Fig. 6B) parallel those of t2. Both ti, t, and f3 show a kink at an intensity 3.5 log units above threshold. To determine whether the two portions of the latency curves are related to different systems with different spectral sensitivities, the same experiments were conducted with monochromatic stimuli. A 401 nm stimulus was selected to favor a blue-sensitive system, and a 630 nm stimulus to favor a red-sensitive system. Measurements were made for or and tz and the results are also included in Fig. 6 (A n n n and q 0 0 0). Ascan be seen, there was very little difference in the measurements for the violet and red stimuli. For tz, both curves showed a kink which occurred approximately 3.5 log units above threshold. Thus the difference in the slopes does not appear to be based on systems with different spectral sensitivities. The shift of the two curves on the intensity axis is merely due to reduction in intensity by the interference filters. Efict of steady illumination on activity of the epiphysis. In the earlier studies on the epiphysis of frogs, trouts and lizards, there was a decrease in neural activity as the level of steady illumination increased. For the dogfish shark, the rate of firing was tist determined in the dark, and then the white light stimulus at threshold intensity was turned on. After one minute of steady illumination, a recording of 15-20 set was taken from which the rate of firing was determined. The light was turned off and t2 determined. The intensity was increased by either O-8 or O-9 log units and the same procedure followed (Fig. 7C). In Fig. 7A are shown the values determined from three preparations. The values shown by the open symbols represent the count of a single unit while those shown by the filled symbols represent a count of several units. It should be noted that the spontaneous discharge rate in the dogBsh shark, as in the lizard, is fairly low and thus the range of change is limited. In general, there is a decrease in the neural activity which could be seen better when several units were counted. One unit (0 0 IJ 0) was completely inhibited by illumination l-2 log units above threshold. On the right side are shown the average values of t, demonstrating that the latency of recovery is approximately the same (4-6 set) over this intensity range of 8 log units. This is very different from the results obtained with one set flashes where the latency tz could be as long as 120 sec. Spectral sensitivity ef the dark-adapted epiphysis and lateral eye. The spectral sensitivity of the epiphysis was measured by determining the amount of light at different wavelengths which would inhibit the spike activity for a fixed time, i.e. for equal values of t2. Corrections were made for an equal quanta spectrum and the average values for four animals are shown in Fig. 9A (0 0 0 0). The spectral sensitivity curve peaks at 500 nm but is too narrow to fit the rhodopsin curve either of the spiny dogfish, Squab acanthias (WALD, 1939b), or of the frog (HECHT, SCHLAERand PIRENNE, 1942). The spectral sensitivity of the lateral eye was measured by determining the amount of light causing a constant amplitude of b-wave of the ERG. The averages for six animals are shown by the triangles (Fig. 8A) and can be seen to fit the rhodopsin curve for the frog and spiny dogfish much better.

Properties of the EpiphyssisCerebri of the Small-spotted Dogfish Shark

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FIG. 8A. Relative spectral sensitivity of the epiphysis cerebri(0 0 0 O), n = 4, and the lateral eyes (A A n A), n = 6, of the dogfish Scyliorhinuscaniculuscompared with the photopigment log extinction curve of the spiny dogfish squcilus ucanthiaf (- - - -), WALD(1939) and the ), HECHTef ut. (1942). The criterion response for the epiphysiscerebri frog Ram sp. (was an equal duration of inhibition, and for the lateral eyes a b-wave of constant amplitude (ten responses are averaged by CAT computer). Left ordinate: log relative sensitivity; right ordinate: log relative extinction; abscissa: wavelengthin nm. FOG.8B. Log extinction (d = 1 cm) spectrum of hemoglobin() and o~hemoglobin t - - - -), DRABKIN (1950) compared with the sensitivity difference between the lateral eyes and the epiphysiscerebri (a ClCl 0). Curves are matched at 500 run. Left ordinate: log relative

sensitivitydifference;right ordinate: log extinction; abscissa:wavelengthin nm. The difference in the sensitivities of the lateral eye and the epiphysis is plotted in the lower half of the figure by squares. The solid and dotted curves represent the extinction curves for oxidized and reduced hemoglobin (DRABKIN,1950). There is fairly good agreement between these two sets of data, and thus the narrowness of the epiphysisspectral sensitivity curves is probably due to the littering by the blood on the outer surface of the epiphysis. DiSCUSSION The results have shown that the epiphyds is an extremely sensitive light receptor. Thus a 1 set flash of 4 x 10m4 lm/mZ is sufficient to alter the on-going neural activity. As the stimulus light had to pass through the skin and skull, the sensitivity of the epiphys~per se must be at Ieast 20 log units higher (see Materials and Methods). This level of illumination is certainly below the photopic level, and demonstrates that the epiphysiscould be functional during full moon light which would give a luminance of 0.2 lm/mZ (LEGRAND, 1957). It is difficult to state definitely whether the slow potentials originated from the photoreceptors (receptor potentials) or the ganglion cells (inhibitory postsynaptic potentials). The

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following observations argue against the photoreceptor cells as the source. First, a latency of 150 msec with the full intensity stimulus, is much too long for a photoreceptor response. Second, the intensity range over which there is an increase in the amplitude of the slow potential is not correlated with the range over which the stimulus is effective (Figs. 3A and 3B). Thus from ~eshold to 2-3 log units above threshold there is an increase in the amplitude of the slow potential and also the duration of spike inhibition. Further increases in the intensity elicit no larger slow potentials but prolong the duration of the inhibition. And third, the observation with two flashes showed that the recorded slow potential is not correlated with its effectiveness (Fig. 2B). If the interhash interval is short, the second flash elicits only a slight response but nevertheless places the epiphysis in a refractory state. Thus it seems more likely that the slow potentials arise from the ganglion cells and are the summated inhibitory postsynaptic potentials spread elec~oni~lly to the electrode. This is supported by evidence obtained form the stirnorgan of the frog where the slow potentials recorded under similar conditions have been shown to be, in all probability, the excitatory and inhibitory postsynaptic potentials of the ganglion cells (BAUMANN,1962; KAMASAKI, 1970). If the photoreceptors are only of one kind and stimulation of them leads to inhibition, then the question arises as to the origin of the spontaneous activity. For the ganglion cells of the cat retina, RODIECK(I 967) has presented evidence that the spontaneous activity is due to synaptic input from the bipolar cells. For the shark epiphysis, we suggest that the membrane potential of the ganglion cells is set close to the critical level so that it fires continuously at a low rate. Stimulation of the epiphysis then leads to hyperpolarization and a decrease in the firing. The hy~rpola~~tion is graded and increases with increasing intensities up to a fixed level. Further increases in the intensity, do not lead to further increases in the amplitude but do increase the duration (Fig. 3B). It is apparent that further studies with intracellular recordings will have to be made before this hypothesis can be accepted. The spectral sensitivity of the epiphysis and the lateral eyes is determined by rhodopsin with &,,,, at 500 nm. Attempts to alter the sensitivity by light adaptation gave conflicting results and further experiments will be necessary. It is interesting to note that the photoreceptors of the ep~~hys~shave the fine structure of cones (R~~DEBERG, 1969) and yet contained a rhodopsin-like photopigment and have the sensitivity of a rod system. However, the classification of photoreceptors into rods and cones by the fine structure of the inner and outer segments alone may not be valid from the physiological point of view (see PEDLER, 1965). The synaptic region between the receptors and ganglion cells has not been analysed in detail although some interesting observations have been presented (RUDEBERG,1969). Both conventional and ribbon type synaptic structures were found with the conventional type more frequent, In addition, conventional type synapses were found with synaptic vesicles on the opposite or postsynaptic side of the membrane as has been reported between receptors of guinea pig (SJUSTRA~, 1958). The relatively long periods of complete inhibition (and presumably refractoriness) induced by a stimulus not excessively strong is difficult to understand as far as the function of this organ is concerned. Changes in illumination of this magnitude and greater must certainly be encountered in the natural enviro~ent of the shark. Perhaps the observations made with the steady illimination offers a clue as to the explanation. There it was noted that although there was strong depression of firing immediately after the stimulus was turned on, adaptation occurred and there was some return of ting. And when this stimulus was turned off,

Properties of the Epiphysis Cerebri of the Small-spotted Dogtish Shark

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there was a prompt recovery which was indepefidetit of the intensity of the adapted light. Thus it appears that the one second flash may not give the “normal” response of this structure and that the change in activity to longer flashes must be examined. Ackaowledgcmen~s-We wish to thank Professor Dr. 0. Krm~ (Biologische Anstalt, Helgoland) who has suuolied us with the donfish sharks. We also thank Professor Dr. E. DODT, Professor Dr. Y. MOIUTA(both of thei(crckhoff Institut,&ul Nauheim). and Dr. C. RUDEBE& (Anatomisches Institut, Universitat Giessen) for their helpful discussions and criticisms.

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E. and MOR~TA,Y. (1964). Purkinje-Verschiebung, absolute Schwelle und adaptives Verhalten einxelner Elemente der intrakranialen Anuren-Epiphyse. Vision Res. 4.413-421. DRABKM,D. L. (1950). Photometry and spectrophotometry, in Medico1 Physics, Vol. 2 (edited by Orro Gwrnt), Year Book, Chicago. VON FRISCH, K. (19lla). Uber das Parietalorgan der Fische als funktionierendes Organ. S.-B. Ges Morph. Physiol. Munchen 27, l&18. VON FRENCH, K. (191lb). Beitrage xur Physiologie der Pigmentxellen in der Fischhaut. Pptigcs Arch. ges. Physiof. 138, 319-387. HAMA~AKI, D. I. and Brunom. C. D. B. (1965). Properties of the electroretinogram in three elasmobranch species. Virion Res. 5.4834%. HAIHASAKI, D. I. (1969). Pre-excitatory inhibition in the stimorgan of the bullfrog. Virion Res. 9,1305-1307. HAMASAKI, D. I. (1970). Interaction of excitation and inhibition in the stimorgan of the frog. Vision Res. 10, 317-332. HAMASAKI. D. I. and DODT, E. (1969). Light sensitivity of the lizard’s epiphysis cerebri. Pflugers Arch. ges. DODT,

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HANXJ, I., Ntw~, H. and TAMURA,R. (1969). A slow potential from the epiphysis cerebri of fishes. Vision Res. 9, 621-623.

HECHT,S., SCHLAER, S. and PIRENNE, M. H. (1942). Energy, quanta, and vision. J. gen. Physiol. 25,819840. HOLMGREN, N. (1918). Zum Bau der Epiphyse von Squalus acanthiar. Ark. Zool. l&23 l-28. LEGRAND.Y. (1957). Light. Colour and Vision, John Wiley. New York. MORITA,Y. (1965). Extra-und intraxellulare Ableitungen einxelner Elemente des lichtempfindlichen Zwischenhirns anurer Amphibien. Pfbigers Arch. ges. Physiol. 286,97-108. MORITA.Y. (1966). Entladungsmuster pinealer Neurone der Regenbogenforelle (S&to (rideus) bei Belichtung des Zwischenhirns. Pjhigers Arch. ges. Physiol. 289, 155-167. MORIIA, Y. (1969). Wellenlangen-Diskriminatoren im intrakranialen Pinealorgan von RMO cutesbiuna. Experientia 25,1277.

MoR~~A,Y. and DODT,E. (1965). Nervous activity of the frog’s epiphysis cerebri in relation to illumination. Experientia 21,221-222.

PEDLER,C. (1965). Duplicity theory and microstructure of the retina. Rods and cones-a fresh approach. In Cofour Vision, (edited bv A. V. S. REUCKand JULIEKNIGHT).Churchill. London. RODIECK,R. W. (1967). Maintained activity of cat retinal ganglion’&ls. J. Neurophysiol. 30, 1043-1071. RODEBERG, Cl. (1969). Light and electron microscopic studies on the pineal organ of the dog&h, Scyliorhinus canicula L.). Z. Zellforsch 96, 548-581. SJ~STRAND, F. S. (1958). Ultrastructure of retinal rody synapses of the guinea pig eye as revealed by threedimensional reconstructions from serial sections. 1: Ultrustruct. Res. 2, 122-170. STUDNI~KA, F. K. (1905). Die Parietalorgane. In Lehrbuch der vergleichendenmikroskopischen Anatomie der Wirbeftiere (Herausg. A. OPPEL),Teil V. Gustav Fischer, Jena. WALD.G. (1939). The porphyrops in visual system. J. gen. Physiol. 22,775-794.

198

D.I.Hah~s~xr

AND PETERSTRECK

Abstract-A light stimulus, focused on the head of the dog&h shark (Scyliorhinus cuniculus) over the end vesicle of the epiphysis cerebri (pineal organ), elicits a positive slow wave accompanied by inhibition of spike activity which was recorded from the cut end of the epiphyseal stalk. A stimulus of 4.3 x lo-* lm/m* was sufficient to alter the on-going neural activity. From threshold to approximately 3 log units above threshold, there was good correlation between the amplitude of the slow potential and the inhibition of spikes. Further increases in the intensity of the stimulus did not elicit larger positive waves but greatly prolonged the duration of the inhibition of spikes. The observations can be best interpreted if the slow potentials arise from the ganglion cells and represent the summated inhibitory postsynaptic potentials transmitted electronically to the recording electrode. The spectral sensitivity of the epiphysis and the lateral eyes peak at 500 nm. R&tune-En focalisant un stimulus lumineux sur la t&e de la petiteroussette (Scyflorhinus cuniculus), sur la vCicule terminale de f’epiphysis cerebi (glande pintale), on engendre une onde lente positive accompag& par une inhibition de l’activite de decharges enregistree a l’extremitt section& de la racine de l’epiphyse. Un stimulus de 4,3 x lo-* lm/m2 suffit a modifier l’activitt nerveuse en cours. Depuis le seuil jusqu’ a environ trois unit& logarithmiques au-dessus du seuil, il y a une bonne correlation entre I’amplitude du potentiel lent et l’inhibition des dtcharges. Des augmentations ulterieures de l’intensitt du stimulus ne produisent pas d’ondes positives plus grandes mais prolongent beaucoup la dur& d’inhibition des d&harges. On peut interpreter au mieux ces resultats si les potentiels lents proviennent des cellules ganglionnaires et repr&se.ntent la somme des potentiels postsynaptiques inhibiteurs, transmis tlectriquement a l’dlectrode d’enregistrement. La sensibilite spectrale de I’epiphyse et des yeux lateraux culmine ii 500 nm.

Zusammenfassnng-Wenn ein Lichtreiz auf dem Kopf des Hundehaifhches (Scyliorhinus cuniculus) tiber dem End&kchen der Gehirnsepiphyse (dem Stimorgan) zum Brennpunkt gebracht wird, so wird eine langsame, von der Hemmung der Entladungstatigkeit begleitete Welle hervorgerufen, welche vom abgeschnittenen Ende des Epiphysenstammes abregistriert wurde. Es gentigte ein Reiz von 4,3 x 10m4 lm/m-‘, urn die bestehende Nervenaktivitat zu veriindem. Die Amplitude der langsamen Potentiale und die Entladungshemmung waren einander awischen Schwelle und ungefihr drei logarithmischen Einheiten dartiber parallel. Weitere Reizstilrkenerhohungen verllngerten die Dauer der Entladungshemmung stark, ohne grossere positive Wellen hervorzurufen. Die Beobachtungen sind am besten so zu verstehen, wenn man die langsamen Potentiale den Gaglienzellen zuschreibt und sie als die summierten, hemmenden, postsynaptischen elektronisch zur Registrierungselektrode geleiteten Potentiale betrachtet. Die Spektralempfindlichkeit der Epiphyse und der Seitenaugen gipfelt bei 500 nm. Peprosfe-CaeroaoiI c~ahryn, ~0kycupyeMbriI ria ronoee aKynbI (Scyllorhinus rian xonevtibrM ny3bIpeM epiphysis cerebri. (mmnkoarinnbtB opraa) abt3bmaeT

caniculus)

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