Modification of postnatal development of neocortex in rat brain with experimental deprivation of locus coeruleus

Brai~; Research, 70 (1974) 515-520

515

~', Elsevier Scientific Publishing Company, Amsterdam

Printed in The Netherlands

Modification of postnatal development of neocortex in rat brain with experimental deprivatiort of locus coeruleus

TOSHIH1RO MAEDA, MASAYA TOHYAMA

AND N O B U O

SHIMIZU

l)epartn~elzt ~/' NeHroanatosny, Dzstitute o1' HigDer Nem'o//s Actirit.r, Osul
{Accepted January 18th, 1974)

The ascending noradrenaline (NA) axons originating from the locus coeruleus (LC) innervate the entire cerebral cortex< ll,14. This innervation to the cerebral cortex appears to be approximately established during prenatal ontogenesis a,l°, though true terminal systems of the NA fibers may be still undeveloped. This fact leads us to think that the NA-containing fibers innervating the premature cortex might play a role in subsequent maturation of the cerebral cortex, since the architectural transformation of the neocortical neurons has been demonstrated in the later course of ontogenesis of several mammalian species;, s. The present investigation was mainly concerned with a Golgi study on morphological modification of the pyramid-like neurons in the deep plexiform layer (layer VI) of the neocortex which was seen in rat brain with electrolytic destruction of LC just after birth. About 300 newborn albino rats were used less than 15 h after birth. Unilateral electrolytic lesions of LC were semistereotaxic~tlly performed under light ether anesthesia with the aid of a special fixation instrument. During the suckling period the animals were nurtured by their mothers. Of these, 98 rats survived and were killed 1.0-2.5 months following operation. The brains were removed and divided into sereval frontal slices, which were subjected to histological and monoamine oxidase 4 staining to examine sites of lesions, to histofluorescence analysis a to observe NA fibers in the cerebral cortex, and to Golgi preparation to elucidate the morphology of the neuronal elements of the cerebral cortex, respectively. For the silver impregnation, the Golgi rapid method was used and microscopic observation was restricted to the somatosensory area of the parietal cortex, mainly area 3, in this investigation. As a control, neurons of the same type were observed in the contralateral cortex. Lesions strictly confined to LC were successfully obtained in 4 rats. In two rats, cases A4-5 and A5-4, killed at 2.5 months of age and whose lesion involved exclusively LC (Fig. I), a complete disappearance of fluorescent fibers in the i psilateral cortex was observed (Fig. 2). This shows that sprouting of NA fibers from other neurons, such as those of the contralateral side or others, did not occur but the cerebral cortex developed at least in the absence of NA fibers. The most significant modification of

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I Fig. 1. Monoamme oxidase staining in frontal section of the pons of an experinaental rat brain (case 5-4L The locus coeruleus which shows a marked activity of the enzyme is completely destroyed on one side ~arrow'l 12.

n e u r o n a l structure o f ipsilateral neocortex was f o u n d in the pyramid-like n e u r o n s o f the deep plexiform layer (layer VI). T h e y were characterized by the apical dendrites which a p p e a r e d s o m e w h a t larger in d i a m e t e r and ascended in a rather direct m a n n e r as c o m p a r e d to those o f the contralateral cortex. T h e most p r o m i n e n t feature o f the dendrites was that they ran t h r o u g h the upper layers even to reach the m o l e c u l a r

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Fig. 2. Fluorescence photomicrograph showing the varicose terminals in the cerebral cortex of the same animal as Fig. 1. The fluorescent terminal completely disappeared in the cingutate area of the operated side (right side). 190.

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Fig. 3. Camera lucida drawings of the pyramid-like neurons in layer VI in the somatosensory area of the neocortex of the same animal as Fig. I. Apical dendrites of the neurons in the operated side (b) smoothly ascend a certain distance and some of them reach layer I, while those of the contralateral cortex (a) run upward in a winding fashion to terminate farthest in layer 111. layer (layer I) (Figs. 3b and 4b). In c o n t r a s t to the o p e r a t e d side, the dendrite o f this type o f neuron o f the c o n t r o l side ran u p w a r d in a delicate and winding fashion with several fine side branches and did n o t a p p e a r to ascend b e y o n d layer II1 (Figs. 3a and 4a). A c c o r d i n g l y , the dendrite was seen to be a p p a r e n t l y m o r e rich in dendritic a r b o r i zation in the c o n t r a l a t e r a l cortex. The dendritic spines a p p e a r e d , however, to cover the entire dendritic a r b o r i z a t i o n o f both sides in a similar fashion. N o n o t a b l e difference in m o r p h o l o g y o f the dendritic spines was observed between ipsilateral and c o n t r a lateral cortices. However, two other LC-deprived rats which were examined at 1 and 1.5 months o f age revealed less m a r k e d differences between both sides o f the cerebral cortex, since some dendrites o f the layer VI neurons often remained to ascend directly in the u p p e r layers even on the c o n t r a l a t e r a l side.

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Fig. 4. Photomicrographs of the somatosensory area in the Golgi preparation which ~tre draw~ in Fig. 3. a: control side. b: operated side. "/2.

It should be emphasized that no similar modification resulted from other types of lesion sparing LC, such as those involving the brachium conjunctivum or situated in the central grey and in several regions caudal or dorsorostral to L C . although a lesion involving the reticular formation rostral to LC was not successfully Obtained in the present study. It is of interest to note that scar formation was scarcely found anywhere in several rat brains, probably because of marked restoration capacity of the young rat brain tissue. Significant structural changes in the appendages of neurons in the course of ontogenesis have been demonstrated in several species of mammals 7. The pyramidlike neurons o f layer VI whose apical dendrites terminate in layer i during the early

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d e v e l o p m e n t a l p e r i o d lose their axonic and dendritic connections with layer 1 and undergo regressive changes in their dendritic a r b o r i z a t i o n s to result in the features o f p o l y m o r p h o u s neurons o f layer VI late in ontogenesis. It is postulated that this neuronal t r a n s f o r m a t i o n is a result o f a restructuring in the o r g a n i z a t i o n o f the m a m m a l i a n cortex which follows the arrival o f a new type o f corticil:etal fiber. Therefore, from the results o b t a i n e d in the present investigation it m a y be concluded that experimental LC d e p r i v a t i o n resulted in i m m a t u r i t y o f the neuronal element o f the neocortex. It is o f course not clear whether the modification o f develo p m e n t o f the neuronal element in the cortex is merely due to denervation o f corticipetal fibers such as those o f the coerulo-cortical neuron, or due to the absence o f release o f N A itself, or whether it is a secondary effect o f LC deprivation. In any case, it m a y be certain that this p h e n o m e n o n was caused by absence o f the N A - c o n t a i n i n g tibers in the course o f late cortical ontogenesis. It is likely that N A released from tibers o f the coerulo-cortical neuron may play a role in neuronal m a t u r a t i o n in a d d i tion to that as n e u r o t r a n s m i t t e r . The p y r a m i d - l i k e cells in layer V1 are the oldest in the course o f ontogenetic cell m i g r a t i o n in the m a m m a l i a n cerebral cortex ~,1' and also this type o f neuron, which has been described in the so-called general cortices o f a m p h i b i a n s and reptiles'-', seems to be phylogenetically very old. It is thus a likely possibility that the LC N A neuron has a relationship with d e v e l o p m e n t o f the neocortex in the course o f not only ontogenesis but also phylogenesis. Our recent c o m p a r a t i v e studies o f LC (ref. 13) have revealed the existence o f a p r i m o r d i a l N A neuron g r o u p h o m o l o g o u s to man> malian LC, in the avian and reptilian pontine region, which innervates both the general cortex and the h y p e r s t r i a t u m , the structures considered as forerunners o f the m a m m a lian neocortex in phylogenetic history 9.

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5 Maeoa, T., ET DRESSZ, A., Recherches sur le deve[oppement du locus coeruleus. 1. Etude des catecholamines au microscope de fluorescence, Acta neurol, belg., 69 (1969) 5 10. 6 MaeoA, T., ET SHIMIZU, N., Projections ascendantes du locus coeruleus et d'autres neurones aminergiques pontiques au niveau du prosenc6phale du rat, Brain Research, 36 (1972) 19-35. 7 MARIN-PADILLA, M., Prenatal ontogenetic history of the principal neurons of the neocortex of the cat (Felis domestica). A Golgi study. II. Developmental differences and their significances, Z. Anat. E , twiekl.-Gesch., 136 (1972) 125-142, 8 MoresT, D. K., A study of neurogenesis in the forebrain of opossum pouch young, Z. Auat. Entwiekl.-Gesch., 130 (1970) 265-305. 9 NAUTA, W. J. H., AND KARTEN, H.J., A general profile of the vertebrate brain, with sidelights on the ancestry of cerebral cortex. In F. O. SCHMITT(Ed.), The Neuroseienees, 2rid Stltd3' Program, The Rockefeller Univ. Press, New York, 1970, pp. 7-26. 10 OLSON, L., AND SEIGER, A., Early prenatal ontogeny of central monoamine neurons in the rat: Fluorescence histochemical observations, Z. Anat. Entwickl.-Geseh., 137 (1972) 301 316.

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11 SHIMIZU,N., OHNISHI,S., TOHYAMA,M., AND MAEDA,T., Demonstration of ascending projection from the locus coeruleus by degeneration silver method, Exp, Brain Res., in press. 12 SIDMAN, R.L., Cell proliferation, migration, and interaction in the developing mammalian central nervous system. In F. O. SCHMITT (Ed.), The Neurosciences, 2nd Study Program, The Rockefeller Univ. Press, New York, 1970, pp. 100-108. 13 TOHYAMA, M., MAEDA, T., HASHIMOTO,J., SHRESTI-IA,G. R., TAMURA, O., ANt) SH1MIZU, IN!., Comparative anatomy of the locus coeruleus. !. Organization and ascending projections of the pontine region of the bird, Melopsittacus undulatus, J. Hirnforsch., in press. 14 UNGERSTEDT,U., Stereotaxic mapping of the monoamine pathways in the rat brain, Acta physiol. stand., Suppl, 367 (1971) 1-48.