Brain Research, 107 (1976) 433-436 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
433
Bilateral corticofugal projection to the red nucleus after neonatal lesions in the albino rat
S. H. NAH ANDS. K. LEONG Department of Anatomy, Faculty of Medicine, University of Malaya, Kuala Lumpur (Malaysia} (Accepted January 22nd, 1976)
A preliminary report by Leong and Lund 10 has shown that neonatal lesions in the sensorimotor and adjacent cortex (SMC) in the albino rat result in a bilateral projection to the spinal cord, pons and superior colliculus from the remaining contralateral cortex. The interpretation of the corticorubral projection was complicated by the abundance of nerve fibres coursing through the red nucleus, which, when not properly suppressed, might resemble degenerating fibres in the Fink-Heimer technique a. The present study was designed to reinvestigate the corticorubral projection in cases of neonatal SMC ablation in the albino rat, taking great care to suppress the normal fibres coursing through the red nucleus. Altogether 25 rats received SMC lesions either at birth or at 3 days, 5 days, l0 days or 15 days after birth. After a suitable period of time varying from 1.5-6 months after the initial lesion, some animals were sacrificed to test if the degeneration products resulting from the neonatal lesions had been cleared. A second lesion was then placed in a corresponding region in the remaining cortex, and 3-5 days later the animals were sacrificed by perfusion with 4 ~ paraformaldehyde adjusted to pH 7.27.4. After appropriate fixation, frozen sections of the brains were cut at 20 # m in a cryostat in the frontal, horizontal or sagittal plane. Every sixth section in the frontal and every third section in the horizontal or sagittal plane was stained with the Fink-Heimer method a for degenerating axons. In the staining procedure 0.1 ~ potassium permanganate was used for 7 min to ensure a proper suppression of the normal fibres coursing through the red nucleus. In addition to the experimental animals, 10 adult control animals were used to map the normal corticorubral projection from the SMC. In two of these control animals there was a near-complete removal of one cerebral cortex leaving only the piriform lobe and a small portion of the occipital cortex not ablated. Following ablation of the SMC in the control animals degenerating fibres could be traced to the ipsilateral red nucleus only. A very small contralateral projection could be detected only in the two cases of nearly total unilateral decortication. The corticorubral fibres were seen to reach the ipsilateral red nucleus from the cerebral
434
Fig. 1. A-E: degeneration produced in the ipsilateral (C and E) and the contralateral (A and D) red nucleus by a recent lesion of one sensorimotor cortical area in an animal from which the other sensorimotor cortex had been ablated at birth. Fink-Heimer stain. All magnifications same as that in A where the calibration bar represents 0.05 mm A: degeneration in a corresponding region of the contralateral red nucleus. B: anomalous fibres crossing the mid-line. C: degeneration in parvocellular portion of the ipsilateral red nucleus. D: degeneration in a corresponding region of the contralateral red nucleus. E: degeneration in the rostralmost region of the ipsilateral red nucleus, just caudal to the fasciculus retroflexus. All sections cut in the horizontal plane.
435 peduncle and the dorsal thalamus and to ramify in the rostral parvocellular part of the nucleus, i.e. the region containing small and medium-size neurones. The ramifications were densest in the most rostral part of the red nucleus, an area just caudal to the fasciculus retroflexus. No trace of fibre degeneration could be found in the caudal magnocellular part except for a small amount in its dorsolateral area at the junction between the rostral two-thirds and the caudal one-third of the red nucleus. The above observations of the normal corticorubral projection are in agreement with previous reports 1,6,9,14. In the experimental animals, following a recent SMC lesion in the intact contralateral cortex, aside from the ipsilateral corticorubral projection (Fig. 1C and E), a heavy anomalous projection was seen to cross the mid-line (Fig. 1B) and to ramify in the contralateral red nucleus (Fig. 1A and D). The terminal distribution of these anomalous fibres appeared to mirror the ipsilateral projection, being confined largely to the rostral parvocellular part and the dorsolateral portion of the magnocellular part of the red nucleus. The density of the anomalous projection did not differ much in animals that had received their initial lesion within the first 3 days after birth, was only slightly less in animals operated on day 5 after birth but was barely noticeable in animals operated on day 10 and thereafter. The present study demonstrates that following neonatal SMC lesions in the albino rat a contralateral corticorubral projection develops from a corresponding region in the intact hemisphere. Previous studiesS,9,1~ had already demonstrated the presence of a bilateral cortifugal projection to the spinal cord, pons and superior colliculus in animals receiving similar neonatal SMC lesions. It has been shown in these studies that in the spinal cord, the anomalous fibres deflect at the pyramidal decussation, whereas in the pons and superior colliculus and, as here shown, in the case of the red nucleus the anomalous fibres cross the mid-line to reach their respective target areas. In all these areas the anomalous projections mirror the normal projections, maintaining a topographic organization much the same as regenerating optic axons, arriving at the optic tectum of frogs by way of the oculomotor nerve4. Such ordered topographic arrangement of anomalous fibres stands in contrast with the results of previous studies7, ~5 which showed that the process of reinnervation in the central nervous system is unpredictable and could even be chaotic. As suggested in the previous report 11 the aberrant growth across the mid-line could be due to an attraction of intact nerve fibres to synaptic sites vacated as a result of the initial lesion. Similar competitive interactions between growing axons of two sources have also been suggested for the visual cortex13, the dentate gyrus5, and the cerebellorubral projectionlL In contrast with the substantial number of anomalous corticofugal fibers to the contralateral pons and superior colliculus in animals operated on day 10 after birth, hardly any anomalous projection to the contralateral red nucleus could be found in the same animals. Among other unknown factors the absence of commissural fibres T M connecting the red nuclei across the mid-line might account for the difference in the growth potential of anomalous fibres crossing over to the contralateral red nucleus on the one hand, and to the pons and superior colliculus on the other hand.
436 T h o u g h it has been demonstrated in some lower mammals as well as in primates 14 that the corticospinal and corticorubrospinal pathways have similar functions, i.e. the control o f flexor muscles and o f the distal musculature, Brown 2 showed that, in the rat at least, the terminal distribution o f the rubrospinal projection differs markedly f r o m that o f the corticospinal projection, a finding suggesting a functional difference between the corticospinal and rubrospinal systems in this species. Whereas the corticospinal projection is more concerned with the modulation o f sensory information, the rubrospinal tract is more concerned with the control o f m o t o r function. As no m o t o r deficit could be observed in the animals receiving neonatal lesionsS, 9, it would not seem unreasonable to believe that the anomalous corticorubral projection might be functionally useful and played some part in the functional compensation for the severe neonatal brain damage. Leong TMhas shown that following neonatal S M C lesions the anomalous fibres to the spinal cord, pons and superior colliculus establish synaptic relationships similar to those characterizing the normal projections, i.e. both form asymmetrical axodendritic synapses. It is therefore i m p o r t a n t to ask if the anomalous corticorubral fibres observed in this study do form synaptic relations with the contralateral red nucleus and if so whether the synapses formed are o f the axodendritic type I observed in the normal corticorubral projection. A preliminary electron microscopic study in this laboratory has indicated that the anomalous corticorubral fibres indeed establish axodendritic synaptic junctions in the contralateral red nucleus.
1 BROWN,L. T., Corticorubral projections in the rat, J. comp. Neurol., 154 (1974) 149-168. 2 BROWN, L. T., Rubrospinal projections in the rat, J. comp. NeuroL, 154 (1974) 169-188. 3 FINK, R. P., AND HEIMER, L., Two methods for selective silver impregnation of degenerating axons and their synaptic endings in the central nervous system, Brain Research, 4 (1967) 369-374. 4 GAZE,R. M., Regeneration of the optic nerve in Xenopus laevis, Quart. J. exp. Physiol., 44 (1959) 290-308. 5 GOTTLmB,D., ANDCOWAN,W. M., Evidence for a temporal factor in the occupation of available synaptic sites during development of the dentate gyrus, Brain Research, 41 (1972) 452-456. 6 GWYN, D. G., AND FLUr~RFELT, B. A., A comparison of distribution of cortical and cerebellar afferents in the red nucleus of the rat, Brain Research, 69 (1974) 130-135. 7 HICKS,S. P., BROWN,B. L., ANDD'AMATO,C. J., Regeneration and malformation in the nervous system, eye and mesenchyme of the mammalian embryo after radiation injury, Arner. J. Path., 33 (1957) 459-481. 8 HICKS,S. P., ANDD'AMATO,C. J., Motor sensory and visual behaviour after hemispherectomy in newborn and mature rats, Exp. Neurol., 29 (1970) 416-438. 9 HicKs, S. P., AND D'AMATO,C. J., Motor-sensory cortex - corticospinal system and developing locomotion and placing in rats, Amer. J. Anat., 143 (1975) 1-42. 10 LEONG, S. K., A qualitative electron microscopic investigation of the anomalous corticofugal projections following neonatal lesions in the albino rats, in print. 11 LEONG, S. K., AND LUND, R. D., Anomalous bilateral corticofugal pathways in albino rats after neonatal lesions, Brain Research, 62 (1973) 218-221. 12 LIM, K. H., AND LEONG, S. K., Aberrant bilateral projections from the dentate and interposed nuclei in albino rats after neonatal lesions, Brain Research, 96 (1975) 306-309. 13 LUND, R. D., Anatomic studies on the superior colliculus, Invest. Ophthal., II (1972)434 440. 14 MASSION,J., The mammalian red nucleus, PhysioL Rev., 47 (1967) 383-436. 15 SChNEIDeR,G. E., Early lesions of superior colliculus: factors affecting the formation of abnormal retinal projections, Brain Behav. Evol., 8 (1973) 73-109.
433
Bilateral corticofugal projection to the red nucleus after neonatal lesions in the albino rat
S. H. NAH ANDS. K. LEONG Department of Anatomy, Faculty of Medicine, University of Malaya, Kuala Lumpur (Malaysia} (Accepted January 22nd, 1976)
A preliminary report by Leong and Lund 10 has shown that neonatal lesions in the sensorimotor and adjacent cortex (SMC) in the albino rat result in a bilateral projection to the spinal cord, pons and superior colliculus from the remaining contralateral cortex. The interpretation of the corticorubral projection was complicated by the abundance of nerve fibres coursing through the red nucleus, which, when not properly suppressed, might resemble degenerating fibres in the Fink-Heimer technique a. The present study was designed to reinvestigate the corticorubral projection in cases of neonatal SMC ablation in the albino rat, taking great care to suppress the normal fibres coursing through the red nucleus. Altogether 25 rats received SMC lesions either at birth or at 3 days, 5 days, l0 days or 15 days after birth. After a suitable period of time varying from 1.5-6 months after the initial lesion, some animals were sacrificed to test if the degeneration products resulting from the neonatal lesions had been cleared. A second lesion was then placed in a corresponding region in the remaining cortex, and 3-5 days later the animals were sacrificed by perfusion with 4 ~ paraformaldehyde adjusted to pH 7.27.4. After appropriate fixation, frozen sections of the brains were cut at 20 # m in a cryostat in the frontal, horizontal or sagittal plane. Every sixth section in the frontal and every third section in the horizontal or sagittal plane was stained with the Fink-Heimer method a for degenerating axons. In the staining procedure 0.1 ~ potassium permanganate was used for 7 min to ensure a proper suppression of the normal fibres coursing through the red nucleus. In addition to the experimental animals, 10 adult control animals were used to map the normal corticorubral projection from the SMC. In two of these control animals there was a near-complete removal of one cerebral cortex leaving only the piriform lobe and a small portion of the occipital cortex not ablated. Following ablation of the SMC in the control animals degenerating fibres could be traced to the ipsilateral red nucleus only. A very small contralateral projection could be detected only in the two cases of nearly total unilateral decortication. The corticorubral fibres were seen to reach the ipsilateral red nucleus from the cerebral
434
Fig. 1. A-E: degeneration produced in the ipsilateral (C and E) and the contralateral (A and D) red nucleus by a recent lesion of one sensorimotor cortical area in an animal from which the other sensorimotor cortex had been ablated at birth. Fink-Heimer stain. All magnifications same as that in A where the calibration bar represents 0.05 mm A: degeneration in a corresponding region of the contralateral red nucleus. B: anomalous fibres crossing the mid-line. C: degeneration in parvocellular portion of the ipsilateral red nucleus. D: degeneration in a corresponding region of the contralateral red nucleus. E: degeneration in the rostralmost region of the ipsilateral red nucleus, just caudal to the fasciculus retroflexus. All sections cut in the horizontal plane.
435 peduncle and the dorsal thalamus and to ramify in the rostral parvocellular part of the nucleus, i.e. the region containing small and medium-size neurones. The ramifications were densest in the most rostral part of the red nucleus, an area just caudal to the fasciculus retroflexus. No trace of fibre degeneration could be found in the caudal magnocellular part except for a small amount in its dorsolateral area at the junction between the rostral two-thirds and the caudal one-third of the red nucleus. The above observations of the normal corticorubral projection are in agreement with previous reports 1,6,9,14. In the experimental animals, following a recent SMC lesion in the intact contralateral cortex, aside from the ipsilateral corticorubral projection (Fig. 1C and E), a heavy anomalous projection was seen to cross the mid-line (Fig. 1B) and to ramify in the contralateral red nucleus (Fig. 1A and D). The terminal distribution of these anomalous fibres appeared to mirror the ipsilateral projection, being confined largely to the rostral parvocellular part and the dorsolateral portion of the magnocellular part of the red nucleus. The density of the anomalous projection did not differ much in animals that had received their initial lesion within the first 3 days after birth, was only slightly less in animals operated on day 5 after birth but was barely noticeable in animals operated on day 10 and thereafter. The present study demonstrates that following neonatal SMC lesions in the albino rat a contralateral corticorubral projection develops from a corresponding region in the intact hemisphere. Previous studiesS,9,1~ had already demonstrated the presence of a bilateral cortifugal projection to the spinal cord, pons and superior colliculus in animals receiving similar neonatal SMC lesions. It has been shown in these studies that in the spinal cord, the anomalous fibres deflect at the pyramidal decussation, whereas in the pons and superior colliculus and, as here shown, in the case of the red nucleus the anomalous fibres cross the mid-line to reach their respective target areas. In all these areas the anomalous projections mirror the normal projections, maintaining a topographic organization much the same as regenerating optic axons, arriving at the optic tectum of frogs by way of the oculomotor nerve4. Such ordered topographic arrangement of anomalous fibres stands in contrast with the results of previous studies7, ~5 which showed that the process of reinnervation in the central nervous system is unpredictable and could even be chaotic. As suggested in the previous report 11 the aberrant growth across the mid-line could be due to an attraction of intact nerve fibres to synaptic sites vacated as a result of the initial lesion. Similar competitive interactions between growing axons of two sources have also been suggested for the visual cortex13, the dentate gyrus5, and the cerebellorubral projectionlL In contrast with the substantial number of anomalous corticofugal fibers to the contralateral pons and superior colliculus in animals operated on day 10 after birth, hardly any anomalous projection to the contralateral red nucleus could be found in the same animals. Among other unknown factors the absence of commissural fibres T M connecting the red nuclei across the mid-line might account for the difference in the growth potential of anomalous fibres crossing over to the contralateral red nucleus on the one hand, and to the pons and superior colliculus on the other hand.
436 T h o u g h it has been demonstrated in some lower mammals as well as in primates 14 that the corticospinal and corticorubrospinal pathways have similar functions, i.e. the control o f flexor muscles and o f the distal musculature, Brown 2 showed that, in the rat at least, the terminal distribution o f the rubrospinal projection differs markedly f r o m that o f the corticospinal projection, a finding suggesting a functional difference between the corticospinal and rubrospinal systems in this species. Whereas the corticospinal projection is more concerned with the modulation o f sensory information, the rubrospinal tract is more concerned with the control o f m o t o r function. As no m o t o r deficit could be observed in the animals receiving neonatal lesionsS, 9, it would not seem unreasonable to believe that the anomalous corticorubral projection might be functionally useful and played some part in the functional compensation for the severe neonatal brain damage. Leong TMhas shown that following neonatal S M C lesions the anomalous fibres to the spinal cord, pons and superior colliculus establish synaptic relationships similar to those characterizing the normal projections, i.e. both form asymmetrical axodendritic synapses. It is therefore i m p o r t a n t to ask if the anomalous corticorubral fibres observed in this study do form synaptic relations with the contralateral red nucleus and if so whether the synapses formed are o f the axodendritic type I observed in the normal corticorubral projection. A preliminary electron microscopic study in this laboratory has indicated that the anomalous corticorubral fibres indeed establish axodendritic synaptic junctions in the contralateral red nucleus.
1 BROWN,L. T., Corticorubral projections in the rat, J. comp. Neurol., 154 (1974) 149-168. 2 BROWN, L. T., Rubrospinal projections in the rat, J. comp. NeuroL, 154 (1974) 169-188. 3 FINK, R. P., AND HEIMER, L., Two methods for selective silver impregnation of degenerating axons and their synaptic endings in the central nervous system, Brain Research, 4 (1967) 369-374. 4 GAZE,R. M., Regeneration of the optic nerve in Xenopus laevis, Quart. J. exp. Physiol., 44 (1959) 290-308. 5 GOTTLmB,D., ANDCOWAN,W. M., Evidence for a temporal factor in the occupation of available synaptic sites during development of the dentate gyrus, Brain Research, 41 (1972) 452-456. 6 GWYN, D. G., AND FLUr~RFELT, B. A., A comparison of distribution of cortical and cerebellar afferents in the red nucleus of the rat, Brain Research, 69 (1974) 130-135. 7 HICKS,S. P., BROWN,B. L., ANDD'AMATO,C. J., Regeneration and malformation in the nervous system, eye and mesenchyme of the mammalian embryo after radiation injury, Arner. J. Path., 33 (1957) 459-481. 8 HICKS,S. P., ANDD'AMATO,C. J., Motor sensory and visual behaviour after hemispherectomy in newborn and mature rats, Exp. Neurol., 29 (1970) 416-438. 9 HicKs, S. P., AND D'AMATO,C. J., Motor-sensory cortex - corticospinal system and developing locomotion and placing in rats, Amer. J. Anat., 143 (1975) 1-42. 10 LEONG, S. K., A qualitative electron microscopic investigation of the anomalous corticofugal projections following neonatal lesions in the albino rats, in print. 11 LEONG, S. K., AND LUND, R. D., Anomalous bilateral corticofugal pathways in albino rats after neonatal lesions, Brain Research, 62 (1973) 218-221. 12 LIM, K. H., AND LEONG, S. K., Aberrant bilateral projections from the dentate and interposed nuclei in albino rats after neonatal lesions, Brain Research, 96 (1975) 306-309. 13 LUND, R. D., Anatomic studies on the superior colliculus, Invest. Ophthal., II (1972)434 440. 14 MASSION,J., The mammalian red nucleus, PhysioL Rev., 47 (1967) 383-436. 15 SChNEIDeR,G. E., Early lesions of superior colliculus: factors affecting the formation of abnormal retinal projections, Brain Behav. Evol., 8 (1973) 73-109.
