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The avian pineal gland as an independent magnetic sensor
Neuroscience Letters, 62 ( 1985) I 19-122
I 19
Elsevier Seientitic Publishers Ireland Ltd. NSL 03644
T H E AVIAN PINEAL G L A N D AS AN I N D E P E N D E N T M A G N E T I C S E N S O R
('. DEMAINE/* and P. SEMM: '('niversity a~ Lomb)n. Chelsea Colle,ge, Department q]" PhvsioloKv, Manresa Road, London S14~3 6LX J U. K. ) and :,1. W. Goelhe University ~?['Frank[hrt, Department af Zoology. Sie.~'mayerstr. 70, D-6000 Frankti~rt (F.R.G.~
(Received August 21st, 1985:Accepted August 28th, 1985). Key wor~Z~" pineal gland magnetic field ~ light- pineal denervation
pigeon
The electrical activity of pigeon pineal cells was modified by gradual inversion of the natural magnetic field. Effects were also found in blinded birds, and following surgical and chemical interference with the neural connections of the pineal, indicating that the gland possesses intrinsic magnetic sensitivity. The results are in line with the concept that magnetic field detection is associated with photoreceptor activity.
The receptor and the sensory process by which the earth's magnetic field (MF) is perceived still remain a mystery, although the suggestion that magnetic detection m a y be a photoreceptor-based mechanism has recently been gaining m o m e n t u m [3, 10, 14]. There is clear evidence that the pineal gland [6, 8] and pineal-dependent function [7] respond to earth-strength magnetic stimulation. In birds, however, these observations do not deny the involvement o f a photoreceptor-dependent system since the avian pineal not only receives a substantial neural input from the visual system [12] but m a y also possess functioning p h o t o r e c e p t o r elements [9]. We have recorded the effects o f alterations in the earth's M F on the electrical activity of pineal cells in anesthetized pigeons under three conditions: (1) in intact birds, (2) after bilateral section o f the optic nerves and (3) following section of the pineal stalk and the administration o f the fl-adrenergic antagonist propranolol. We used 23 adult homing pigeons ( C o l u m b a livia), anesthetized with urethane (1.1 g/'kg b o d y wt., given i.p. in a 25%~, solution). Each animal was m o u n t e d in a stereotaxic frame at the center o f a coil system, so that its head pointed to the magnetic north pole. Three pairs o f Helmholtz coils, each 1.0 m diameter, were used to produce alterations in the horizontal and vertical c o m p o n e n t s o f the natural MF. The coil system was controlled by a m i c r o c o m p u t e r such that the horizontal a n d / o r vertical c o m p o n e n t s o f the M F could be inverted in a gradual manner, with the same inclination and intensity as the natural field. Inversion of the horizontal c o m p o n e n t took the needle o f a c o m p a s s from magnetic north via east to south; inversion o f the vertical c o m p o n e n t m o v e d the needle o f a perpendicularly oriented inclinatorium from
*Author for correspondence. 0304-3940'85;$ 03.30 © 1985 Elsevier Scientific Publishers Ireland Ltd.
120 pointing to the center of the earth until it indicated the opposite direction. Thc natural MF (field strength in the experimental room = 0.42 Gauss) and the artificial changes were continuously monitored by a Gaussmeter. Extracellular single unit potentials were recorded from cells in the pineal gland using glass micropipettes filled with 4 M NaC1. Recorded signals were amplified, filtered and displayed on an oscilloscope. Responses to magnetic stimulation were determined by constructing peri-stimulus-time histograms of amplitude discriminated electrical activity. The Kolmogorov-Smirnov test was applied to the spike counts in the pre- and post-stimulus bins of the histograms to determine if a unit's activity during alteration of the M F was significantly different from its spontaneous discharge. Responses to M F stimulation were characterized by an elevation or reduction of the average firing rate, to an extent well outside the range of spontaneous fluctuations in basal activity (P<0.05), for the whole of the time for which the natural M F was altered (Fig. l a). The responses did not appear to reflect any of the obvious characteristics of the stimulus, e.g. the direction or extent of the field change or the rate of change. Following an initial period of recording and magnetic stimulation, the pigeon was blinded by surgically sectioning both optic nerves. Under these conditions, responses still occurred and were qualitatively similar, but the magnitude of the changes in firing rate induced by M F stimulation was reduced, suggesting that input from the visual system does normally make some contribution to the pineal magnetic detection system.
a
90°
°° 20~
I
.
.
......
.
.
.
I
180° III
I I
I
Spikes per bin
b 20 T
300
Spikes
300
TIME (sec)
Fig. 1. Peri-stimulus time histograms of the electrical activity of pigeon pineal cells, showing the effects of magnetic field stimulation (gradual inversion of the horizontal component of the natural magnetic field). The field-strength of the laboratory in Frankfurt was H =0.42 Oe. The magnetic stimulus is indicated by the dark bar. a: excitatory response of a pineal cell in a sighted pigeon in dim light, b: reduced response of a second pineal cell in the same animal following section of both optic nerves, deflection of the pineal stalk and intraperitoneal injection of propranolol hydrochloride.
121
In 9 of the birds the pineal stalk was cut and deflected onto the dorsal surface of the cerebellum, using the method described by Zimmermann and Menaker [15], and the birds were given single intraperitoneal injections of the/3-adrenergic antagonist, propranolol hydrochloride (500 #g/kg). In 3 of these birds electrical activity could not be recorded from the pineal cells. In the remaining 6 spontaneously active units were located, and almost half of them responded to MF stimulation. The effects closely resembled those obtained after optic nerve section (Fig. l b), indicating that further interference with the neural connections of the gland did not influence the intrinsic magnetic sensitivity. The proportion of units responding to MF stimulation under the three experimental conditions are summarized in Table I. The results presented in this study demonstrate that single pineal cells can respond to alterations in the MF. In the rat, application of artificial earth's strength MFs significantly reduces nocturnal melatonin synthesis in the pineal gland [6]. However, these effects were clearly shown to be dependent on the intact retina. By contrast, in the present study, the reduction in response magnitude following optic nerve section suggests that although input from the visual system may be implicated, some units have an intrinsic sensitivity. Our recent investigations of the visual system of the pigeon [10] have provided support for the hypothesis, originally put forward by Leask, that MF detection may be a property of retinal photoreceptors [3]. However, in birds, photoreceptors also occur in the pineal gland. The evidence for this assertion comes from 4 lines of investigation. (1) Morphological studies have demonstrated that photoreceptor-like structures occur, although they have a degenerate appearance [5]. (2) In cultured chicken pineal glands specific enzyme activity responds to environmental lighting, the action spectrum of the photosensitivity resembling the absorption spectrum of rhodopsin [l, 2]. (3) In several species, including the pigeon, pineal cells have been shown to contain opsin immunoreactive material resembling that of retinal receptors [11]. (4) The electrical activity of pigeon pineal cells changes in response to direct illumination in blinded birds [9]. The persistence of magnetic sensitivity in the pineal of blinded pigeons indicates that pineal photoreceptors are sufficiently organized to detect M F
TABL E I RESPONSES OF P I N E A L CELLS TO A G R A D U A L I N V E R S I O N OF TH E N A T U R A L M A G N E TIC F I E L D , E X P R E S S E D AS P E R C E N T A G E S OF T H E T O T A L N U M B E R OF CELLS (n) TES TED U N D E R THE T H R E E C O N D I T I O N S + . excitation; - , inhibition; 0, no response. +
0
Untreated ( n - 140)
24
15
58
Blinded (n - 57)
35
14
51
Blinded + pineal deafferentation (n - 27)
33
11
56
122 as well as light. Since there a r e as yet no r e p o r t s o f r e p o n s e s to e a r t h ' s s t r e n g t h M F s t i m u l a t i o n o r i g i n a t i n g in structures w h i c h d o n o t have a p h o t o r e c e p t i v e c a p a c i t y , o u r results suggest that, in k e e p i n g with the L e a s k hypothesis, pineal p h o t o r e c e p t o r s also act as M F detectors. Thus, at least in the p i g e o n , there a p p e a r to be two s e p a r a t e inputs for m a g n e t i c i n f o r m a t i o n , one via the retina a n d the o t h e r via the pineal. F o r the well e s t a b l i s h e d use o f the g e o m a g n e t i c field for o r i e n t a t i o n , the retina a n d its p r o j e c t i o n s to the v e s t i b u l a r system are clearly i m p l i c a t e d [10]. A l t h o u g h o t h e r a u t h o r s have tested the role o f the p i n e a l g l a n d in m a g n e t i c c o m p a s s n a v i g a t i o n [4], the pineal m a g n e t i c d e t e c t i o n system is m u c h m o r e likely to be involved in n e u r o e n d o c r i n e responses to g e o m a g n e t i c d i s t u r b a n c e s [7]. Since pineal m e l a t o n i n synthesis is influenced by c h a n g e s in the n a t u r a l m a g n e t i c field [6, 13], the h o r m o n a l o u t p u t o f the g l a n d m a y be subject to the d u a l i n p u t s o f light a n d m a g n e t i s m . W e gratefully a c k n o w l e d g e the financial s u p p o r t o f the Stiftung V o l k s w a g e n w e r k a n d the D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t ( S F B 45). 1 Deguchi, T., Circadian rhythm of serotonin N-acetyltransferase activity in organ culture of chicken pineal glands, Science, 203 (1979) 1245-1247. 2 Deguchi, T., Rhodopsin-like photosensitivity of isolated chicken pineal gland, Nature (London), 290 (1981) 706-707. 3 Leask, M.J.M., A physicochemical mechanism for magnetic field detection by migratory birds and homing pigeons, Nature (London), 267 (1977) 144-145. 4 Maffei, L., Meschini, E. and Papi, F., Pineal body and magnetic sensitivity: homing in pinealectomized pigeons under overcast skies, Z. Tierpsychol., 62 (1983) 151-156. 5 Oksche, A., Morita, Y. and Vaupel-v. Harnack, M., Zur Feinstruktur und Funktion des Pinealorgans der Taube (Columba livia), Z. Zellforsch., 102 (1969) 1-30. 6 Olcese, J., Reuss, S. and Vollrath, L., Evidence for the involvement of the visual system in mediating magnetic field effects on pineal melatonin synthesis in the rat, Brain Res., 333 (1985) 382-384. 7 Ossenkopp, K.-P., Kavaliers, M. and Hirst, M., Reduced nocturnal morphine analgesia in mice following geomagnetic disturbance, Neurosci. Lett., 40 (1983) 321-325. 8 Semm, P., Neurobiological investigations on the magnetic sensitivity of the pineal gland in rodents and pigeons, Comp. Biochem. Physiol., 76 (1983) 683-689. 9 Semm, P. and Demaine, C., Electrical responses to direct and indirect photic stimulation of the pineal gland in the pigeon, J. Neural Transm., 58 (1983) 281-289. 10 Semm, P., Nohr, D., Demaine, C. and Wiltschko, W., Neural basis of the magnetic compass: interactions of visual, magnetic and vestibular inputs in the pigeon's brain, J. Comp. Physiol., 155 (1984) 283-288. 11 Vigh, B. and Vigh-Teichmann, I., Light- and electron-microscopic demonstration of immunoreactive opsin in the pinealocytes of various vertebrates~ Cell Tiss. Res., 221 (1981) 451-463. 12 VoUrath, L., The pineal organ. In A. Oksche and L. Vollrath (Eds.), Handbuch der mikroskopischen Anatomie des Menschen, Vol. 4, Part 7, Springer, Berlin, 1981. 13 Welker, H.A., Semm, P., Willig, R.P., Commentz, J.C., Wiltschko, W. and Vollrath, L., Effects of an artificial magnetic field on serotonin N-acetyltransferase activity and melatonin content of the rat pineal gland, Exp. Brain Res., 50 (1983) 426432. 14 Wiltschko, W. and Wiltschko, R., Disorientation of unexperienced young pigeons after transportation in total darkness, Nature (London), 291 (1981) 433~134. 15 Zimmermann, N.H. and Menaker, M., Neural connections of sparrow pineal: role in circadian control of activity, Science, 190 (1975) 477~,79.
I 19
Elsevier Seientitic Publishers Ireland Ltd. NSL 03644
T H E AVIAN PINEAL G L A N D AS AN I N D E P E N D E N T M A G N E T I C S E N S O R
('. DEMAINE/* and P. SEMM: '('niversity a~ Lomb)n. Chelsea Colle,ge, Department q]" PhvsioloKv, Manresa Road, London S14~3 6LX J U. K. ) and :,1. W. Goelhe University ~?['Frank[hrt, Department af Zoology. Sie.~'mayerstr. 70, D-6000 Frankti~rt (F.R.G.~
(Received August 21st, 1985:Accepted August 28th, 1985). Key wor~Z~" pineal gland magnetic field ~ light- pineal denervation
pigeon
The electrical activity of pigeon pineal cells was modified by gradual inversion of the natural magnetic field. Effects were also found in blinded birds, and following surgical and chemical interference with the neural connections of the pineal, indicating that the gland possesses intrinsic magnetic sensitivity. The results are in line with the concept that magnetic field detection is associated with photoreceptor activity.
The receptor and the sensory process by which the earth's magnetic field (MF) is perceived still remain a mystery, although the suggestion that magnetic detection m a y be a photoreceptor-based mechanism has recently been gaining m o m e n t u m [3, 10, 14]. There is clear evidence that the pineal gland [6, 8] and pineal-dependent function [7] respond to earth-strength magnetic stimulation. In birds, however, these observations do not deny the involvement o f a photoreceptor-dependent system since the avian pineal not only receives a substantial neural input from the visual system [12] but m a y also possess functioning p h o t o r e c e p t o r elements [9]. We have recorded the effects o f alterations in the earth's M F on the electrical activity of pineal cells in anesthetized pigeons under three conditions: (1) in intact birds, (2) after bilateral section o f the optic nerves and (3) following section of the pineal stalk and the administration o f the fl-adrenergic antagonist propranolol. We used 23 adult homing pigeons ( C o l u m b a livia), anesthetized with urethane (1.1 g/'kg b o d y wt., given i.p. in a 25%~, solution). Each animal was m o u n t e d in a stereotaxic frame at the center o f a coil system, so that its head pointed to the magnetic north pole. Three pairs o f Helmholtz coils, each 1.0 m diameter, were used to produce alterations in the horizontal and vertical c o m p o n e n t s o f the natural MF. The coil system was controlled by a m i c r o c o m p u t e r such that the horizontal a n d / o r vertical c o m p o n e n t s o f the M F could be inverted in a gradual manner, with the same inclination and intensity as the natural field. Inversion of the horizontal c o m p o n e n t took the needle o f a c o m p a s s from magnetic north via east to south; inversion o f the vertical c o m p o n e n t m o v e d the needle o f a perpendicularly oriented inclinatorium from
*Author for correspondence. 0304-3940'85;$ 03.30 © 1985 Elsevier Scientific Publishers Ireland Ltd.
120 pointing to the center of the earth until it indicated the opposite direction. Thc natural MF (field strength in the experimental room = 0.42 Gauss) and the artificial changes were continuously monitored by a Gaussmeter. Extracellular single unit potentials were recorded from cells in the pineal gland using glass micropipettes filled with 4 M NaC1. Recorded signals were amplified, filtered and displayed on an oscilloscope. Responses to magnetic stimulation were determined by constructing peri-stimulus-time histograms of amplitude discriminated electrical activity. The Kolmogorov-Smirnov test was applied to the spike counts in the pre- and post-stimulus bins of the histograms to determine if a unit's activity during alteration of the M F was significantly different from its spontaneous discharge. Responses to M F stimulation were characterized by an elevation or reduction of the average firing rate, to an extent well outside the range of spontaneous fluctuations in basal activity (P<0.05), for the whole of the time for which the natural M F was altered (Fig. l a). The responses did not appear to reflect any of the obvious characteristics of the stimulus, e.g. the direction or extent of the field change or the rate of change. Following an initial period of recording and magnetic stimulation, the pigeon was blinded by surgically sectioning both optic nerves. Under these conditions, responses still occurred and were qualitatively similar, but the magnitude of the changes in firing rate induced by M F stimulation was reduced, suggesting that input from the visual system does normally make some contribution to the pineal magnetic detection system.
a
90°
°° 20~
I
.
.
......
.
.
.
I
180° III
I I
I
Spikes per bin
b 20 T
300
Spikes
300
TIME (sec)
Fig. 1. Peri-stimulus time histograms of the electrical activity of pigeon pineal cells, showing the effects of magnetic field stimulation (gradual inversion of the horizontal component of the natural magnetic field). The field-strength of the laboratory in Frankfurt was H =0.42 Oe. The magnetic stimulus is indicated by the dark bar. a: excitatory response of a pineal cell in a sighted pigeon in dim light, b: reduced response of a second pineal cell in the same animal following section of both optic nerves, deflection of the pineal stalk and intraperitoneal injection of propranolol hydrochloride.
121
In 9 of the birds the pineal stalk was cut and deflected onto the dorsal surface of the cerebellum, using the method described by Zimmermann and Menaker [15], and the birds were given single intraperitoneal injections of the/3-adrenergic antagonist, propranolol hydrochloride (500 #g/kg). In 3 of these birds electrical activity could not be recorded from the pineal cells. In the remaining 6 spontaneously active units were located, and almost half of them responded to MF stimulation. The effects closely resembled those obtained after optic nerve section (Fig. l b), indicating that further interference with the neural connections of the gland did not influence the intrinsic magnetic sensitivity. The proportion of units responding to MF stimulation under the three experimental conditions are summarized in Table I. The results presented in this study demonstrate that single pineal cells can respond to alterations in the MF. In the rat, application of artificial earth's strength MFs significantly reduces nocturnal melatonin synthesis in the pineal gland [6]. However, these effects were clearly shown to be dependent on the intact retina. By contrast, in the present study, the reduction in response magnitude following optic nerve section suggests that although input from the visual system may be implicated, some units have an intrinsic sensitivity. Our recent investigations of the visual system of the pigeon [10] have provided support for the hypothesis, originally put forward by Leask, that MF detection may be a property of retinal photoreceptors [3]. However, in birds, photoreceptors also occur in the pineal gland. The evidence for this assertion comes from 4 lines of investigation. (1) Morphological studies have demonstrated that photoreceptor-like structures occur, although they have a degenerate appearance [5]. (2) In cultured chicken pineal glands specific enzyme activity responds to environmental lighting, the action spectrum of the photosensitivity resembling the absorption spectrum of rhodopsin [l, 2]. (3) In several species, including the pigeon, pineal cells have been shown to contain opsin immunoreactive material resembling that of retinal receptors [11]. (4) The electrical activity of pigeon pineal cells changes in response to direct illumination in blinded birds [9]. The persistence of magnetic sensitivity in the pineal of blinded pigeons indicates that pineal photoreceptors are sufficiently organized to detect M F
TABL E I RESPONSES OF P I N E A L CELLS TO A G R A D U A L I N V E R S I O N OF TH E N A T U R A L M A G N E TIC F I E L D , E X P R E S S E D AS P E R C E N T A G E S OF T H E T O T A L N U M B E R OF CELLS (n) TES TED U N D E R THE T H R E E C O N D I T I O N S + . excitation; - , inhibition; 0, no response. +
0
Untreated ( n - 140)
24
15
58
Blinded (n - 57)
35
14
51
Blinded + pineal deafferentation (n - 27)
33
11
56
122 as well as light. Since there a r e as yet no r e p o r t s o f r e p o n s e s to e a r t h ' s s t r e n g t h M F s t i m u l a t i o n o r i g i n a t i n g in structures w h i c h d o n o t have a p h o t o r e c e p t i v e c a p a c i t y , o u r results suggest that, in k e e p i n g with the L e a s k hypothesis, pineal p h o t o r e c e p t o r s also act as M F detectors. Thus, at least in the p i g e o n , there a p p e a r to be two s e p a r a t e inputs for m a g n e t i c i n f o r m a t i o n , one via the retina a n d the o t h e r via the pineal. F o r the well e s t a b l i s h e d use o f the g e o m a g n e t i c field for o r i e n t a t i o n , the retina a n d its p r o j e c t i o n s to the v e s t i b u l a r system are clearly i m p l i c a t e d [10]. A l t h o u g h o t h e r a u t h o r s have tested the role o f the p i n e a l g l a n d in m a g n e t i c c o m p a s s n a v i g a t i o n [4], the pineal m a g n e t i c d e t e c t i o n system is m u c h m o r e likely to be involved in n e u r o e n d o c r i n e responses to g e o m a g n e t i c d i s t u r b a n c e s [7]. Since pineal m e l a t o n i n synthesis is influenced by c h a n g e s in the n a t u r a l m a g n e t i c field [6, 13], the h o r m o n a l o u t p u t o f the g l a n d m a y be subject to the d u a l i n p u t s o f light a n d m a g n e t i s m . W e gratefully a c k n o w l e d g e the financial s u p p o r t o f the Stiftung V o l k s w a g e n w e r k a n d the D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t ( S F B 45). 1 Deguchi, T., Circadian rhythm of serotonin N-acetyltransferase activity in organ culture of chicken pineal glands, Science, 203 (1979) 1245-1247. 2 Deguchi, T., Rhodopsin-like photosensitivity of isolated chicken pineal gland, Nature (London), 290 (1981) 706-707. 3 Leask, M.J.M., A physicochemical mechanism for magnetic field detection by migratory birds and homing pigeons, Nature (London), 267 (1977) 144-145. 4 Maffei, L., Meschini, E. and Papi, F., Pineal body and magnetic sensitivity: homing in pinealectomized pigeons under overcast skies, Z. Tierpsychol., 62 (1983) 151-156. 5 Oksche, A., Morita, Y. and Vaupel-v. Harnack, M., Zur Feinstruktur und Funktion des Pinealorgans der Taube (Columba livia), Z. Zellforsch., 102 (1969) 1-30. 6 Olcese, J., Reuss, S. and Vollrath, L., Evidence for the involvement of the visual system in mediating magnetic field effects on pineal melatonin synthesis in the rat, Brain Res., 333 (1985) 382-384. 7 Ossenkopp, K.-P., Kavaliers, M. and Hirst, M., Reduced nocturnal morphine analgesia in mice following geomagnetic disturbance, Neurosci. Lett., 40 (1983) 321-325. 8 Semm, P., Neurobiological investigations on the magnetic sensitivity of the pineal gland in rodents and pigeons, Comp. Biochem. Physiol., 76 (1983) 683-689. 9 Semm, P. and Demaine, C., Electrical responses to direct and indirect photic stimulation of the pineal gland in the pigeon, J. Neural Transm., 58 (1983) 281-289. 10 Semm, P., Nohr, D., Demaine, C. and Wiltschko, W., Neural basis of the magnetic compass: interactions of visual, magnetic and vestibular inputs in the pigeon's brain, J. Comp. Physiol., 155 (1984) 283-288. 11 Vigh, B. and Vigh-Teichmann, I., Light- and electron-microscopic demonstration of immunoreactive opsin in the pinealocytes of various vertebrates~ Cell Tiss. Res., 221 (1981) 451-463. 12 VoUrath, L., The pineal organ. In A. Oksche and L. Vollrath (Eds.), Handbuch der mikroskopischen Anatomie des Menschen, Vol. 4, Part 7, Springer, Berlin, 1981. 13 Welker, H.A., Semm, P., Willig, R.P., Commentz, J.C., Wiltschko, W. and Vollrath, L., Effects of an artificial magnetic field on serotonin N-acetyltransferase activity and melatonin content of the rat pineal gland, Exp. Brain Res., 50 (1983) 426432. 14 Wiltschko, W. and Wiltschko, R., Disorientation of unexperienced young pigeons after transportation in total darkness, Nature (London), 291 (1981) 433~134. 15 Zimmermann, N.H. and Menaker, M., Neural connections of sparrow pineal: role in circadian control of activity, Science, 190 (1975) 477~,79.