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Effect of deprivation of light on axonal transport in retinal ganglion cells of the rabbit
BRAIN RESEARCH
315
E F F E C T OF D E P R I V A T I O N OF L I G H T ON A X O N A L T R A N S P O R T IN R E T I N A L G A N G L I O N CELLS OF T H E RABBIT
J.-O. KARLSSON AND J. SJOSTRAND
Institute of Neurobiology, University of GiJteborg, Gi~teborg (Sweden)
(Accepted December 23rd, 1970)
INTRODUCTION The retina receives its functional stimulation from an easily controllable source and is therefore a very suitable model for studying the effects of sensory deprivation on a neuronal system. Rearing an animal in complete darkness from birth has been reported to produce several morphological and/or biochemical changes in the retina 1,4,Is,Is,21, in the lateral geniculate body3,5,7,10,14-16,20,22 and in the visual cortex s,6,t°. As far as we know, no study has been made on axonal transport in a neurone that has been exclusively deprived of its normal sensory input. The aim of the present investigation was to study the axonal transport of protein in retinal ganglion ceils of rabbits that had been reared in darkness from birth. The axonal transport of protein in this neurone under normal conditions has already been described and characterized12,13,19. After being synthesized in the retinal ganglion cells, proteins are transported along the axons in the optic nerve and tract to the nerve terminals in the lateral geniculate body at 4 different velocities: 150, 40, 6-12 and 2 mm/day, respectively 13. The present study was concerned only with the effects of deprivation of light on the most rapidly and most slowly transported proteins in this neurone. MATERIALAND METHODS Animals
Two litters o f albino rabbits, comprising a total of 12 animals, were used. The pregnant rabbits were obtained about one week before parturition and were placed in separate cages where the litters were born and housed throughout the duration of the experiment. The cages were placed in a completely dark room. To feed the animals an operator entered the room through a passage with two separate doors, so that no light was introduced during the procedure. Two and a half months after birth, when they weighed 1.8-2.2 kg, the rabbits were individually transferred to a separate room. They were anaesthetized by an intravenous injection of sodium pentobarbital and Brain Research, 29 (1971) 315-321
316
J . - o . KARLSSON A N D J. SJOSTRAND
injected with 50 #Ci of [ZH]leucine (e-leucine, 4,5, T.spec.act. 20-23 Ci/mmole, conc. 1 mCi/ml, The Radiochemical Centre, Amersham, England) in sterile aqueous solution into the vitreous body of each eye. Details of this procedure have been described elsewhere 19. During the injections the animals were exposed to a very weak red light from a Kodak Wratten filter (Type 1 M) for about 10 min. After the injections the animals were returned to the dark room.
General procedures At various intervals after injection the animals were killed by an overdose of sodium pentobarbital, and the relevant parts of the optic system were immediately dissected out and placed in ice-cold 0.44 M sucrose. After homogenization, the samples were precipitated with ice-cold 5 ~o T C A containing 10 m M L-leucine. Protein and radioactivity in the samples were determined as previously described 19.
Preparation of subcellular fractions All operations were carried out at 0-4°C, and ice-cold solutions were used. The optic nerve and tract were homogenized twice in 1 ml of 0.44 M sucrose with 6 up-anddown strokes at 1,300 rev./min in a teflon-glass homogenizer with a clearance of 0.15 ram. The samples were diluted to 6 ml with 0.44 M sucrose, and 5 ml of this suspension was centrifuged at 13,000 x g for 30 min in the SW 39 rotor of a Spinco Model L preparative ultracentrifuge. The resulting pellet was termed fraction P. The supernatant was centrifuged at 71,000 x g for 4 h in the SW 39 rotor to yield a microsomal fraction (Mic) and a soluble protein fraction (Sol). All fractions were precipitated with 5 ~ TCA containing 10 m M L-leucine, and were handled as described above.
1000" .c_ 500-
"0
50-
6~
/o
2'o
~o ~
doys ofter injection
Fig. 1. The specific radioactivity of retinal proteins in light-deprived animals at various time intervals after intraocular injections of [3H]leucine into both eyes, plotted on a semilogarithmic diagram. Each point represents the average specific radioactivity of the two retinas.
Brain Research, 29 (1971) 315-321
AXONAL TRANSPORTIN LIGHT-DEPRIVEDRABBITS
317
~o8. l,c
4
....--*
oJ hours ofler injection
Fig. 2. Radioactivity of labelled proteins in the two lateral geniculate bodies at various time intervals after intraocular injections of [aH]leucine into both eyes. ©, Light-deprived animals. Each symbol represents one animal. • , Normal animals. Each symbol represents the average of 3 animals. These values are compiled from Karlsson and Sj0strandZL RESULTS After an intraocular injection of [aH]leucine the incorporation of the isotope into proteins of the retina occurs at a rapid rate and is completed within a few hours 13. After about 1.5 days the radioactivity of retinal proteins decayed with a half-life of 6.4 days. In the animals that had been light-deprived from birth the half-life of retinal proteins was approximately 6 days (Fig. 1). Thus the turnover rate for the majority of the retinal proteins was not markedly changed by light deprivation. Nor was any evidence obtained for a depression of total protein-synthesizing capacity of the retina in the light-deprived animals. The rapidly transported labelled proteins in the arons of the retinal ganglion cells, which move at an average rate of 150 mm/day, reach the lateral geniculate body about 4 h after an intraocular injection of [3H]leucine in a normal animal 13. A similar rapid transport of proteins also occurs in the axons of retinal ganglion cells of lightdeprived animals (Fig. 2). The amount of labelled protein which reaches the lateral geniculate body during this early time interval after injection seems to be of a similar magnitude in light-deprived and in normal animals. No marked changes were noticed either in the amount of rapidly transported labelled proteins or in the rate of transport in the optic nerve and tract. However, a tendency towards a slight increase in both the rate and the amount of rapidly transported proteins was observed in some experimental animals. In a previous investigation 19 we studied the subcellular distribution of radioactivity bound to rapidly transported proteins in the optic nerve and tract. The microsomal fraction had a relatively high specific radioactivity whereas the soluble proteins had a relatively low activity. In the light-deprived animals the microsomal fraction had the highest specific radioactivity of all the fractions, and the soluble proteins had a lower activity than that of the homogenate, both in the optic nerve and tract, 4.8 h after injection of [SH]leucine (Table I). The pattern of isotope distribution is thus similar in light-deprived and in normal animals. A more exact comparison is difficult Brain Research, 29 (1971) 315-321
318
J.-O. KARLSSONAND J. SJ STRAND
TABLE I SPECIFIC RADIOACTIVITY OF DIFFERENT SUBCELLULAR FRACTIONS OF THE OPTIC NERVE OR TRACT
Expressed as a percentage of that of the homogenate at different intervals after intraocular injections of [aH]leucine in light-deprived animals. P, 13,000 x g pellet; Mic, microsomal fraction; Sol, soluble protein fraction. Time after injection
4.8 h 4.8 h 4.8 h 13days 14 days
Optic nerve
Optic tract
P
Mic
Sol
P
Mic
Sol
50 85 64 88 103
331 201 290 101 76
57 46 72 271 103
35 54 67 65 59
142 159 187 54 65
20 29 38 120 181
/0,~\ / 1 /
]
~o 6 ~t
\ " • •
\\
/
¢
\•
"O 4
O-..... ~
X\\
lb
is
2'o
is
t>
days after injection
Fig. 3. Radioactivity of labelled proteins in the two lateral geniculate bodies at various time intervals after intraocular injections of [aH]leucine into both eyes. ©, Light-deprived animals. Each symbol represents one animal, o, Normal animals. Each symbol represents the average of 2 animals. These values axe compiled from Kaxlsson and Sj6strand la. to m a k e because the isolation p r o c e d u r e for the fractions was n o t identical with t h a t e m p l o y e d in o u r p r e v i o u s study. T h e quantitatively d o m i n a t i n g t r a n s p o r t phase in axons o f retinal ganglion cells o f n o r m a l animals is the m o s t slowly migrating phase. This phase, which moves at an average rate o f 2 m m / d a y , reaches a m a x i m a l level in the optic t r a c t a b o u t 13 days, a n d in t h e lateral geniculate b o d y a b o u t 16 days, after injection 13. In the l i g h t - d e p r i v e d animals a similar slow t r a n s p o r t seemed to r e a c h a m a x i m u m in the lateral geniculate b o d y at 16 days after injection (Fig. 3), a n d the a m o u n t o f r a d i o a c t i v i t y in this p h a s e was at a c o m p a r a b l e level to t h a t in n o r m a l animals. W h e n this slow p h a s e was present in t h e optic t r a c t at 13-14 days after injection the soluble p r o t e i n s h a d the relatively Brain Research, 29 (1971) 315-321
AXONAL TRANSPORT IN LIGHT-DEPRIVED RABBITS
319
highest specific radioactivity and the activity in the microsomal fraction was relatively low (Table I). This is in accord with our earlier study on the subcellular distribution of radioactivity of the slow phase in the optic nerve and tract of normal animals19. DISCUSSION
The present study indicates that no marked changes in protein metabolism occur in the retina of light-deprived animals compared with normal animals. Previous studies on the retina of light-deprived animals have shown a reduction of the pentose nucleoprotein fraction to zero as well as a decreased protein content in the retinal ganglion cells 1, a decreased activity of several enzymes16,is and an increase in certain enzymesis. However, protein synthesis in the retina does not seem to be affected15. Several morphological studies on the retina of light-deprived animals8,11,~1 have yielded conflicting results, which is perhaps due in part to species differences. Our results show that there was both a rapid and a slow axonal transport of proteins in retinal ganglion cells of light-deprived rabbits. The migration rate, the amount and the subcellular distribution of the transported proteins in light-deprived animals were similar to that in normal animals. Our findings are only semiquantitative owing to the relatively small number of experimental animals. It is our impression that there may well be a difference of the order of 25 ~o or less between light-deprived and normal animals in the parameters studied. However, the results indicate that both rapid and slow axonal transport are at least qualitatively independent of an adequate stimulation of the retinal ganglion cells. It has been suggested12 that the rapidly transported proteins in this system could be implicated in the transmitter function of the retinal ganglion cell. Were this so, one would expect a decrease of this rapid phase of axonal transport or a change in its subcellular distribution in light-deprived animals. However, impulse propagation has been described in the optic nerve of animals kept in darkness2,17. The quantitatively dominating, slowly migrating phase of axonal transport is also present in light-deprived animals. A part of the proteins of this phase does not reach the nerve terminals and seems to be metabolized locally in the axon la. This phase is probably necessary for the maintenance of the axon. Morphological studies have also shown no, or only moderate, changes in the number or diameter of fibers in the optic nerve after an animal has been reared in darknessS,11,21. It is well established that rearing an animal in darkness can produce an impairment of visual functionS, 21. The axons and terminals of retinal ganglion cells seem to be relatively unaffected in these light-deprived animals. Although Cragg a has found a slight but significant increase in the diameter of axon terminals in the retina and the lateral geniculate body after light deprivation, lack of adequate stimulation may exert its major effect on the receptor part of the neurone, i.e. the dendrites and the cell body. These suggestions are supported by morphological observations both in the lateral geniculate body and in the visual cortexS,9,~o.
Brain Research, 29 (1971) 315-321
320
J.-O. KARLSSON AND J. SJ(}STRAND
SUMMARY
Rabbits were totally deprived of light from birth, and the axonal transport of protein in their retinal ganglion cells was studied. There was both a rapid and a slow axonal transport of protein in these cells. The migration rate, amount and subcellular distribution of the transported proteins in light-deprived animals was similar to that in normal animals. ACKNOWLEDGEMENTS
This work was supported by H. Hiertas Fund and the Swedish Medical Research Council (No. B71 - 13X - 2226 - 05). We are indebted to Mrs. Marie-Louise Eskilson for skilful technical assistance.
REFERENCES I BRATTG~RD, S.-O., The importance of adequate stimulation for the chemical composition of
retinal ganglion cells during early post-natal development, A cta radiol. (Stockh.), Suppl. 96 (1952) 1-80. 2 BURKE, W., AND HAYHOW, W. R., Disuse in the lateral geniculate nucleus of the cat, J. Physiol. (Lond.), 194 (1968) 495-519. 3 CRAGG,B. G., The effects of vision and dark-rearing on the size and density of synapses in the lateral geniculate nucleus measured by electron microscopy, Brain Research, 13 (1969) 53-67. 4 CRAGG, B. G., Structural changes in naive retinal synapses detectable within minutes of first exposure to daylight, Brain Research, 15 (1969) 79-96. 5 FIFKOV,~,E., The influence of unilateral visual deprivation on optic centers, Brain Research, 6 (1967) 763-766. 6 FIFKOV.~,E., Changes in the visual cortex of rats after unilateral deprivation, Nature (Lond.), 220 (1968) 379-381. 7 FIFKOV3,,E., AND HASSLER, R., Quantitative morphological changes in the visual centers in rats after unilateral deprivation, J. comp. Neurol., 135 (1969) 167-178. 8 GOODMAN,L., Effect of total absence of function on the optic system of rabbits, Amer. J. Physiol., C (1932) 46453. 9 GLoaus, A., AND SCHEIBEL, A. B., The effect of visual deprivation on cortical neurons: A Golgi study, Exp. NeuroL, 19 (1967) 331-345. 10 GYLLENSTEN, L., MALMFORS, T., AND NORRLIN, M.-L., Effect of visual deprivation on the optic centers of growing and adult mice, J. comp. Neurol., 125 (1965) 149-160. I l GYLLENSTEN, L., MALMFORS, T., AND NORRLIN-GRE'I~VE, M. L., Developmental and functional alterations in the fiber composition of the optic nerve in visually deprived mice, J. comp. NeuroL, 128 (1966) 413-418. 12 KARLSSON, J.-O., AND SJ(}STRAND,J., Transport of labelled proteins in the optic nerve and tract of the rabbit, Brain Research, 11 (1968) 431-439. 13 KARLSSON, J.-O., AND SJOSTRAND, J., Synthesis, migration and turnover of protein in retinal ganglion cells, J. Neurochem., (1971) in press. 14 MALETTA,G. J., AND TIMIRAS, P. S., Acetylcholinesterase activity in optic structures after complete light deprivation from birth, Exp. Neurol., 19 (1967) 513-518. 15 MARAINI,G., CARTA,F., FRANGUELLI,R., AND SANTORI,M., Effect of monocular light-deprivation on leucine uptake in the retina and the optic centres of the newborn rat, Exp. Eye Res., 6 (1967) 299-302. 16 MARAINI, G., CARTA, F., ANO FRANGUELLI,R., Metabolic changes in the retina and the optic centres following monocular light deprivation in the new-born rat, Exp. Eye Res., 8 (1969) 55-89. 17 RODIECK, R. W., AND SMITH, P. S., Slow dark discharge rhythms of cat retinal ganglion cells, J. NeurophysioL, 29 (1966) 942-953.
Brain Research, 29 (1971) 315-321
AXONAL TRANSPORT IN LIGHT-DEPRIVEDRABBITS
321
18 SCHIMKE,R. T., Effects of prolonged light deprivation on the development of retinal enzymes in the rabbit, J. biol. Chem., 234 (1959) 700-703. 19 SJ6Sa'RAND,J., AND KARLSSON,J.-O., Axoplasmic transport in the optic nerve and tract of the rabbit: A biochemical and radioautographic study, J. Neurochem., 16 (1969) 833-844. 20 SZ~NT~,C,OTnAI, J., AND H.~ORI, J., Growth and differentiation of synaptic structures under circumstances of deprivation of function and of distant connections. In S. H. BARONDES(Ed.), Cellular Dynamics of the Neuron, Symposium of the International Society for Cell Biology, VoL 8, Academic Press, New York, 1969, pp. 301-320. 21 WEISKRANTZ,L., Sensory deprivation and the cat's optic nervous system, Nature (Lond.), 181 (1958) 1047-1050. 22 WlESEL,T. N., ANDHUaEL, D. H., Effects of visual deprivation on morphology and physiology of cells in the cat's lateral geniculate body, J. Neurophysiol., 26 (1963) 978-993.
Brain Research, 29 (1971) 315-321
315
E F F E C T OF D E P R I V A T I O N OF L I G H T ON A X O N A L T R A N S P O R T IN R E T I N A L G A N G L I O N CELLS OF T H E RABBIT
J.-O. KARLSSON AND J. SJOSTRAND
Institute of Neurobiology, University of GiJteborg, Gi~teborg (Sweden)
(Accepted December 23rd, 1970)
INTRODUCTION The retina receives its functional stimulation from an easily controllable source and is therefore a very suitable model for studying the effects of sensory deprivation on a neuronal system. Rearing an animal in complete darkness from birth has been reported to produce several morphological and/or biochemical changes in the retina 1,4,Is,Is,21, in the lateral geniculate body3,5,7,10,14-16,20,22 and in the visual cortex s,6,t°. As far as we know, no study has been made on axonal transport in a neurone that has been exclusively deprived of its normal sensory input. The aim of the present investigation was to study the axonal transport of protein in retinal ganglion ceils of rabbits that had been reared in darkness from birth. The axonal transport of protein in this neurone under normal conditions has already been described and characterized12,13,19. After being synthesized in the retinal ganglion cells, proteins are transported along the axons in the optic nerve and tract to the nerve terminals in the lateral geniculate body at 4 different velocities: 150, 40, 6-12 and 2 mm/day, respectively 13. The present study was concerned only with the effects of deprivation of light on the most rapidly and most slowly transported proteins in this neurone. MATERIALAND METHODS Animals
Two litters o f albino rabbits, comprising a total of 12 animals, were used. The pregnant rabbits were obtained about one week before parturition and were placed in separate cages where the litters were born and housed throughout the duration of the experiment. The cages were placed in a completely dark room. To feed the animals an operator entered the room through a passage with two separate doors, so that no light was introduced during the procedure. Two and a half months after birth, when they weighed 1.8-2.2 kg, the rabbits were individually transferred to a separate room. They were anaesthetized by an intravenous injection of sodium pentobarbital and Brain Research, 29 (1971) 315-321
316
J . - o . KARLSSON A N D J. SJOSTRAND
injected with 50 #Ci of [ZH]leucine (e-leucine, 4,5, T.spec.act. 20-23 Ci/mmole, conc. 1 mCi/ml, The Radiochemical Centre, Amersham, England) in sterile aqueous solution into the vitreous body of each eye. Details of this procedure have been described elsewhere 19. During the injections the animals were exposed to a very weak red light from a Kodak Wratten filter (Type 1 M) for about 10 min. After the injections the animals were returned to the dark room.
General procedures At various intervals after injection the animals were killed by an overdose of sodium pentobarbital, and the relevant parts of the optic system were immediately dissected out and placed in ice-cold 0.44 M sucrose. After homogenization, the samples were precipitated with ice-cold 5 ~o T C A containing 10 m M L-leucine. Protein and radioactivity in the samples were determined as previously described 19.
Preparation of subcellular fractions All operations were carried out at 0-4°C, and ice-cold solutions were used. The optic nerve and tract were homogenized twice in 1 ml of 0.44 M sucrose with 6 up-anddown strokes at 1,300 rev./min in a teflon-glass homogenizer with a clearance of 0.15 ram. The samples were diluted to 6 ml with 0.44 M sucrose, and 5 ml of this suspension was centrifuged at 13,000 x g for 30 min in the SW 39 rotor of a Spinco Model L preparative ultracentrifuge. The resulting pellet was termed fraction P. The supernatant was centrifuged at 71,000 x g for 4 h in the SW 39 rotor to yield a microsomal fraction (Mic) and a soluble protein fraction (Sol). All fractions were precipitated with 5 ~ TCA containing 10 m M L-leucine, and were handled as described above.
1000" .c_ 500-
"0
50-
6~
/o
2'o
~o ~
doys ofter injection
Fig. 1. The specific radioactivity of retinal proteins in light-deprived animals at various time intervals after intraocular injections of [3H]leucine into both eyes, plotted on a semilogarithmic diagram. Each point represents the average specific radioactivity of the two retinas.
Brain Research, 29 (1971) 315-321
AXONAL TRANSPORTIN LIGHT-DEPRIVEDRABBITS
317
~o8. l,c
4
....--*
oJ hours ofler injection
Fig. 2. Radioactivity of labelled proteins in the two lateral geniculate bodies at various time intervals after intraocular injections of [aH]leucine into both eyes. ©, Light-deprived animals. Each symbol represents one animal. • , Normal animals. Each symbol represents the average of 3 animals. These values are compiled from Karlsson and Sj0strandZL RESULTS After an intraocular injection of [aH]leucine the incorporation of the isotope into proteins of the retina occurs at a rapid rate and is completed within a few hours 13. After about 1.5 days the radioactivity of retinal proteins decayed with a half-life of 6.4 days. In the animals that had been light-deprived from birth the half-life of retinal proteins was approximately 6 days (Fig. 1). Thus the turnover rate for the majority of the retinal proteins was not markedly changed by light deprivation. Nor was any evidence obtained for a depression of total protein-synthesizing capacity of the retina in the light-deprived animals. The rapidly transported labelled proteins in the arons of the retinal ganglion cells, which move at an average rate of 150 mm/day, reach the lateral geniculate body about 4 h after an intraocular injection of [3H]leucine in a normal animal 13. A similar rapid transport of proteins also occurs in the axons of retinal ganglion cells of lightdeprived animals (Fig. 2). The amount of labelled protein which reaches the lateral geniculate body during this early time interval after injection seems to be of a similar magnitude in light-deprived and in normal animals. No marked changes were noticed either in the amount of rapidly transported labelled proteins or in the rate of transport in the optic nerve and tract. However, a tendency towards a slight increase in both the rate and the amount of rapidly transported proteins was observed in some experimental animals. In a previous investigation 19 we studied the subcellular distribution of radioactivity bound to rapidly transported proteins in the optic nerve and tract. The microsomal fraction had a relatively high specific radioactivity whereas the soluble proteins had a relatively low activity. In the light-deprived animals the microsomal fraction had the highest specific radioactivity of all the fractions, and the soluble proteins had a lower activity than that of the homogenate, both in the optic nerve and tract, 4.8 h after injection of [SH]leucine (Table I). The pattern of isotope distribution is thus similar in light-deprived and in normal animals. A more exact comparison is difficult Brain Research, 29 (1971) 315-321
318
J.-O. KARLSSONAND J. SJ STRAND
TABLE I SPECIFIC RADIOACTIVITY OF DIFFERENT SUBCELLULAR FRACTIONS OF THE OPTIC NERVE OR TRACT
Expressed as a percentage of that of the homogenate at different intervals after intraocular injections of [aH]leucine in light-deprived animals. P, 13,000 x g pellet; Mic, microsomal fraction; Sol, soluble protein fraction. Time after injection
4.8 h 4.8 h 4.8 h 13days 14 days
Optic nerve
Optic tract
P
Mic
Sol
P
Mic
Sol
50 85 64 88 103
331 201 290 101 76
57 46 72 271 103
35 54 67 65 59
142 159 187 54 65
20 29 38 120 181
/0,~\ / 1 /
]
~o 6 ~t
\ " • •
\\
/
¢
\•
"O 4
O-..... ~
X\\
lb
is
2'o
is
t>
days after injection
Fig. 3. Radioactivity of labelled proteins in the two lateral geniculate bodies at various time intervals after intraocular injections of [aH]leucine into both eyes. ©, Light-deprived animals. Each symbol represents one animal, o, Normal animals. Each symbol represents the average of 2 animals. These values axe compiled from Kaxlsson and Sj6strand la. to m a k e because the isolation p r o c e d u r e for the fractions was n o t identical with t h a t e m p l o y e d in o u r p r e v i o u s study. T h e quantitatively d o m i n a t i n g t r a n s p o r t phase in axons o f retinal ganglion cells o f n o r m a l animals is the m o s t slowly migrating phase. This phase, which moves at an average rate o f 2 m m / d a y , reaches a m a x i m a l level in the optic t r a c t a b o u t 13 days, a n d in t h e lateral geniculate b o d y a b o u t 16 days, after injection 13. In the l i g h t - d e p r i v e d animals a similar slow t r a n s p o r t seemed to r e a c h a m a x i m u m in the lateral geniculate b o d y at 16 days after injection (Fig. 3), a n d the a m o u n t o f r a d i o a c t i v i t y in this p h a s e was at a c o m p a r a b l e level to t h a t in n o r m a l animals. W h e n this slow p h a s e was present in t h e optic t r a c t at 13-14 days after injection the soluble p r o t e i n s h a d the relatively Brain Research, 29 (1971) 315-321
AXONAL TRANSPORT IN LIGHT-DEPRIVED RABBITS
319
highest specific radioactivity and the activity in the microsomal fraction was relatively low (Table I). This is in accord with our earlier study on the subcellular distribution of radioactivity of the slow phase in the optic nerve and tract of normal animals19. DISCUSSION
The present study indicates that no marked changes in protein metabolism occur in the retina of light-deprived animals compared with normal animals. Previous studies on the retina of light-deprived animals have shown a reduction of the pentose nucleoprotein fraction to zero as well as a decreased protein content in the retinal ganglion cells 1, a decreased activity of several enzymes16,is and an increase in certain enzymesis. However, protein synthesis in the retina does not seem to be affected15. Several morphological studies on the retina of light-deprived animals8,11,~1 have yielded conflicting results, which is perhaps due in part to species differences. Our results show that there was both a rapid and a slow axonal transport of proteins in retinal ganglion cells of light-deprived rabbits. The migration rate, the amount and the subcellular distribution of the transported proteins in light-deprived animals were similar to that in normal animals. Our findings are only semiquantitative owing to the relatively small number of experimental animals. It is our impression that there may well be a difference of the order of 25 ~o or less between light-deprived and normal animals in the parameters studied. However, the results indicate that both rapid and slow axonal transport are at least qualitatively independent of an adequate stimulation of the retinal ganglion cells. It has been suggested12 that the rapidly transported proteins in this system could be implicated in the transmitter function of the retinal ganglion cell. Were this so, one would expect a decrease of this rapid phase of axonal transport or a change in its subcellular distribution in light-deprived animals. However, impulse propagation has been described in the optic nerve of animals kept in darkness2,17. The quantitatively dominating, slowly migrating phase of axonal transport is also present in light-deprived animals. A part of the proteins of this phase does not reach the nerve terminals and seems to be metabolized locally in the axon la. This phase is probably necessary for the maintenance of the axon. Morphological studies have also shown no, or only moderate, changes in the number or diameter of fibers in the optic nerve after an animal has been reared in darknessS,11,21. It is well established that rearing an animal in darkness can produce an impairment of visual functionS, 21. The axons and terminals of retinal ganglion cells seem to be relatively unaffected in these light-deprived animals. Although Cragg a has found a slight but significant increase in the diameter of axon terminals in the retina and the lateral geniculate body after light deprivation, lack of adequate stimulation may exert its major effect on the receptor part of the neurone, i.e. the dendrites and the cell body. These suggestions are supported by morphological observations both in the lateral geniculate body and in the visual cortexS,9,~o.
Brain Research, 29 (1971) 315-321
320
J.-O. KARLSSON AND J. SJ(}STRAND
SUMMARY
Rabbits were totally deprived of light from birth, and the axonal transport of protein in their retinal ganglion cells was studied. There was both a rapid and a slow axonal transport of protein in these cells. The migration rate, amount and subcellular distribution of the transported proteins in light-deprived animals was similar to that in normal animals. ACKNOWLEDGEMENTS
This work was supported by H. Hiertas Fund and the Swedish Medical Research Council (No. B71 - 13X - 2226 - 05). We are indebted to Mrs. Marie-Louise Eskilson for skilful technical assistance.
REFERENCES I BRATTG~RD, S.-O., The importance of adequate stimulation for the chemical composition of
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