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Reorganization of the uncrossed visual pathways as revealed by Fos-like immunoreactivity in rats with neonatal monocular enucleation
Neuroscience Letters 304 (2001) 53±56
www.elsevier.com/locate/neulet
Reorganization of the uncrossed visual pathways as revealed by Fos-like immunoreactivity in rats with neonatal monocular enucleation Fumio Yagi a,*, Makoto Sakai b, Yukinobu Ikeda c, Fumino Okutani d,e, Seiichi Takahashi d,e, Jyunichi Fukata f a
Behavioral Neuroscience Laboratory, Kochi Medical School, Nankoku, Kochi 783±8505, Japan b Neuropsychology Laboratory, Saga Medical School, Saga 849±8501, Japan c Department of Psychology, Saga University, Saga 840±8502, Japan d Department of Physiology, Kochi Medical School, Nankoku, Kochi 783±8505, Japan e CREST, Japan Science & Technology Corporation, Saitama 332±0012, Japan f Department of Internal Medicine, Kochi Medical School, Nankoku, Kochi 783±8505, Japan Received 9 March 2001; accepted 19 March 2001
Abstract To elucidate the neuronal characteristics of the functional expansion in the uncrossed visual pathways (UXVPs), resulting from early monocular enucleation in rats, the feasibility of stimulus-dependent induction of the immediate early gene c-fos was examined immunohistochemically. In the UXVPs of rats with monocular enucleation at birth, patterned visual stimuli induced Fos-like immunoreactive (FLI) neurons much more densely in wide areas of the super®cial layer throughout the superior colliculus (SC), and in the striate and extrastriate areas of the visual cortex (VC). In the UXVPs of rats monocularly enucleated after maturity, however, only a few stimulus-dependent FLI neurons were scattered in the restricted portions of the SC and the VC. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Monocular enucleation; Uncrossed visual pathway; Superior colliculus; Visual cortex; c-Fos; Plasticity; Rat
Monocular enucleation has been a useful experimental manipulation for analyzing neuronal plasticity in the visual system (for review, see Ref. [15]). In rodents which were enucleated on one side at birth or in the early postnatal days, expansion of the uncrossed visual pathways (the expanded UXVPs) was induced to the visual cortex (VC) ipsilateral to the remaining eye, via both the dorsal lateral geniculate nucleus (LGNd) and the superior colliculus (SC)±lateroposterior thalamic nucleus (LP) [3,5,6,10±12,14,16,17,20]. Previous studies in several mammals have shown that the induction of the immediate early gene (IEG) c-fos in neurons by trans-synaptic activation, as revealed by immunocytochemical detection of the Fos protein (Fos-like immunoreactivity, FLI), enables its effective use as a single-cell resolution marker of neuronal responses to sensory stimulation in the central nervous system (for review, see Ref. [8]). As for the visual systems employed, * Corresponding author. Tel.: 181-88-8802271; fax: 181-888802272. E-mail address: [email protected] (F. Yagi).
light [1], global ¯ashes of light [2] and localized patterned visual stimulation [7] have been used to demonstrate the induction of c-fos in the subcortical and cortical visual centers. The present experiment by the FLI labeling technique was attempted to obtain morphological substrate for the functional expansion of the UXVPs in the rat, which was enucleated monocularly at birth. Twenty mature male albino rats of the KUD Wistar strain (Kyudou, Saga, Japan), weighing 420±465 g, were used for c-Fos immunohistochemistry. Half of the rats had the right eye, including the sclera, removed within 24 h after birth (OEBs), and as a control, the other group had the right eye enucleated at 3 months of age, at least a week before the experiment was started (OETs). The enucleation was performed under sodium pentobarbital anesthesia (50 mg/ kg intraperitoneally (i.p.)) for OETs and hypothermia for OEBs. At 3 months of age, all rats received a callosotomy under sodium pentobarbital anesthesia, in order to block the retinal inputs to the visual centers ipsilateral to the remaining eye via crossed optic and callosal ®bers. The method of this surgery was described previously [5]. After a 10-day
0304-3940/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 1) 01 76 2- 1
54
F. Yagi et al. / Neuroscience Letters 304 (2001) 53±56
recovery period from the callosotomy, the c-Fos immunohistochemistry was performed. After dark adaptation for about 20 h, the rats, which were anesthetized with urethane (0.8±1.0 g/kg i.p.) and injected with atropine sulfate (0.05 mg/kg subcutaneously), were ®xed on a stereotaxic apparatus. The remaining eye was immobilized with a ring made of Elgiloy wire (Rocky Mountain Morita, Tokyo, Japan) attached to the headholder; it was subsequently instilled with silicone ¯uid to prevent corneal desiccation. After these manipulations were carried out under low levels of illumination from a red safelight, the rats were left in darkness for about 1.5 h. Rectal temperature was maintained at 378C with a servo-controlled heating pad throughout the visual stimulation. Moving visual patterns, generated from a photostimulator with a movable slide holder, were projected on a translucent plexiglass which was centered on the remaining eye at 30 cm, a distance that has been found to be associated with the greatest acuity in the rat [18]. All rats were stimulated for 1 h with vertically-moving horizontal square wave-gratings and horizontally-moving vertical ones (bright: 202.1 cd/ m 2, dark: 6.2 cd/m 2); spatial frequency was 0.15 cycles/ degree, each for 15 min, alternately. The speed for these
moving patterns was 168/s. The rats were left in darkness for 90±120 min after the end of the stimulation to await optimum induction of the Fos protein. They were then perfused transcardially with 4% paraformaldehyde in 0.1 M phosphate buffer (PB, pH 7.4) after a brief ¯ush with phosphate-buffered saline. Immediately after perfusion, the brain was removed from the skull and was sectioned coronally with a razor blade into two blocks just in front of the optic chiasma. The tissue blocks were post®xed with the same ®xative solution at 48C overnight, and placed into 0.1 M PB containing 10, 15, and 20% sucrose with 0.1% NaN3 at 48C, each for an overnight period. Coronal 50 mm sections were prepared with a cryostat and the ¯oating sections were processed for FLI with a primary antiserum raised in sheep against a synthetic peptide derived from the N-terminal sequence of the c-Fos protein (Genosys Biotechnologies, Cambridge, UK). The sections were incubated with the primary antiserum diluted 1:2000 for 72 h at 48C, and then with biotinylated rabbit anti-sheep secondary antibody (Rockland, Gilbertsville, PA, USA), and ®nally with the avidin biotinylated horseradish peroxidase complex (Vector, Burlingame, CA, USA). The DAB reaction was intensi®ed with 0.01% nickel ammonium sulfate.
Fig. 1. Photomicrographs of coronal sections of the superior colliculus ipsilateral to the remaining eye of the OEB (A,B) and OET (C,D) rats, showing stimulus-induced FLI neurons. (B,D) are higher magni®cation views of the regions marked by squares in (A,C). Scale bars, 200mm.
F. Yagi et al. / Neuroscience Letters 304 (2001) 53±56
Fig. 2. Mean number and the standard deviation of stimulusinduced FLI neurons per 10 4 mm 2 in the superior colliculus (SC) and visual cortex (VC) ipsilateral to the remaining eye of the OEB and OET rats.
The patterned visual stimuli induced FLI neurons unequivocally in the SC and VC ipsilateral to the remaining eye, but not so much in the LGNd and LP, in which labeled cells
55
were relatively scarce. Therefore, the number and distribution pattern of FLI neurons were analyzed in the SC and VC. Throughout the following text, `ipsilateral' refers to the side ipsilateral to the remaining eye. In OETs, the patterned visual stimuli induced sparse labeling of FLI neurons, mainly in a restricted rostro-medial area of the super®cial layer (the stratum zonale, the stratum griseum super®ciale, and the stratum opticum) of the ipsilateral SC (Fig. 1). This restricted area of the SC roughly corresponded to the SC region innervated by uncrossed axons of the retinal ganglion cells in normal adult rats [6]. On the other hand, in OEBs, the patterned visual stimulation induced FLI neurons much more densely in a wide area of the super®cial layer of the ipsilateral SC, all along the rostro-caudal and latero-medial axes. The ipsilateral SC in the OEBs was approximately 70% smaller as compared to the normal size, whereas the SC in the OETs was normal in size. The mean number of FLI neurons per 10 4 mm 2 was measured for the overall area of the super®cial layer of the ipsilateral SC in both OEBs and OETs. The patterned visual stimulation induced signi®cantly more FLI neurons in the OEBs (4.6 ^ 2.5) than in the OETs (0.7 ^ 0.6) (t 9 4:55, P , 0:01) (Fig. 2). This SC area with FLI neurons in the OEBs appeared to correspond to the region where the crossed visual pathways projected in the rat with normal vision [13]. In the ipsilateral VC (including the striate and extrastriate
Fig. 3. Laminar distribution of stimulus-induced FLI neurons in coronal sections of the visual cortex ipsilateral to the remaining eye of the OEB (A,B) and OET (C,D) rats. (B,D) are higher magni®cation views of the regions marked by squares in (A,C). Roman numerals in dorsoventral axis: cortical layers; scales in medio-lateral axis above (A,C): distances (mm) from the midline; WH: the white matter. Scale bars, 500mm (A,C); 100mm (B,D).
56
F. Yagi et al. / Neuroscience Letters 304 (2001) 53±56
areas), the stimulus-induced FLI cells were seen in both the OEBs and OETs, with a predominant distribution in layers IV and VI (Fig. 3). The number of FLI neurons was counted for all layers within 1±5 mm from the midline and 1±6 mm from the tip of the occipital pole, where Fos-positive cells were distributed unequivocally. A signi®cant difference was observed in the mean number of FLI neurons per 10 4 mm 2 between OEBs (5.8 ^ 1.6) and OETs (1.6 ^ 0.9) (Fig. 2, t 9 6:86, P , 0:001). The stimulus-dependent FLI cells in layers IV and VI were observed more consistently and more densely in the OEBs than in the OETs. Moreover, the FLI cells were also seen in layer II and the deep part of layer III in OEBs. The projection ®bers from the LGNd to the VC terminate in layers IV and VI of area 17 [9], whereas the projection ®bers from the LP to the VC terminate in layers IV and VI of area 18 [4]. Therefore, although we did not attempt to differentiate areas 17 and 18 in the present study, the wide medio-lateral distributions of FLI cells suggest that the induction of the FLI cells in the VC was brought about through the activation of projection ®bers from the LGNd and LP. The present results clearly demonstrate that monocular enucleation at birth increases the number of neurons in the SC and VC, which receive input from the ipsilateral visual pathways. It has been well documented that the removal of one eye in the early postnatal period in the rodent results in an expansion of the retinal area from which uncrossed optic ®bers originate, and hence in an increase in the number of uncrossed optic ®bers projecting to the SC and LGNd [3]. In the SC, axon terminals of those uncrossed optic ®bers do not con®ne themselves in the rostral border, but rather spread to the caudal pole [6]. It has been reported that by monocular enucleation at birth, more cells of the SC were activated by those uncrossed optic ®bers, making the visual ®elds represented in the ipsilateral SC much larger than those by the normal uncrossed optic ®bers [14]. The present results are in good accordance with these previous reports. The functional reorganization of the VC after monocular enucleation was also examined morphologically [17,19] and electrophysiologically [12,16]. In our series of experiments, such functional changes in the VC in OEBs were re¯ected in the facilitation of visual discrimination learning [5,10,20] and an increase in the visual acuity [10,20], indicating that the ipsilateral VC was activated by increased visual input through both the retino±geniculo±VC pathway and the retino±SC±LP pathway. This assumption was con®rmed morphologically in the present study. The authors are grateful to Prof S. Ohnishi, Department of Internal Medicine, Kochi Medical School, for ®nancial assistance for this experiment. This research was supported in part by Grant-in-Aid for Scienti®c Research (C) (#08610089, #11891002) from The Ministry of Education, Culture, Sports, Science and Technology.
[1] Aronin, N., Sagar, S.M., Sharp, F.R. and Schwartz, W., Light regulates expression of a Fos-related protein in the rat SCN, Proc. Natl. Acad. Sci. USA, 87 (1990) 5959±5962. [2] Craner, S.L., Hoffman, G.E., Lund, J.S., Humphrey, A.L. and Lund, R.D., cFos labeling in rat superior colliculus: activation by normal retinal pathways and pathways from intracranial retinal transplants, Exp. Neurol., 117 (1992) 219±229. [3] Farid Ahmed, A.K.M., Dong, K. and Yamadori, T., A retrograde double-labeling study of uni- and bilaterally projecting retinal ganglion cells that project to the superior colliculi after unilateral eye removal at birth in the albino rat, Brain Res., 704 (1995) 307±312. [4] Hughes, H.C., Anatomical and neurobehavioral investigations concerning the thalamo-cortical organization of the rat's visual system, J. Comp. Neurol., 175 (1977) 311±336. [5] Ikeda, Y., Sakai, M. and Yagi, F., Long-term callosal lesions and learning of a black-white discrimination by one-eyed rats, Physiol. Behav., 52 (1992) 851±858. [6] Lund, R.D., Cunningham, T.J. and Lund, J.S., Modi®ed optic projections after unilateral eye removal in young rats, Brain Behav. Evol., 8 (1973) 51±72. [7] Montero, V.M. and Jian, S., Induction of c-fos protein by patterned visual stimulation in central visual pathways of the rat, Brain Res., 690 (1995) 189±199. [8] Morgan, J.I. and Curran, T., Stimulus-transcription coupling in the nervous system: involvement of the inducible proto-oncogenes fos and jun, Annu. Rev. Neurosci., 14 (1991) 421±451. [9] Peters, A. and Feldman, M.L., The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. I General description, J. Neurocytol., 5 (1976) 63±84. [10] Sakai, M., Ikeda, Y. and Yagi, F., Discrimination performance and resolution capacity of uncrossed visual pathways in one-eyed albino rats, Physiol. Behav., 59 (1996) 141±146. [11] Sakai, M. and Yagi, F., Evoked potential in the lateral geniculate body as modi®ed by enucleation of one eye in the albino rat, Brain Res., 210 (1981) 91±102. [12] Sakai, M., Yagi, F. and Ikeda, Y., Evoked potential in the visual cortex as modi®ed by enucleation of one eye in the albino rat, Physiol. Psychol., 11 (1983) 141±146. [13] Stein, B.E. and Gaither, N.S., Receptive-®eld properties in reptilian optic tectum: some comparisons with mammals, J. Neurophysiol., 50 (1983) 102±124. [14] Thompson, I.D., Changes in the uncrossed retinotectal projection after removal of the other eye at birth, Nature, 279 (1979) 63±69. [15] Toldi, J., FeheÂr, O. and Wolff, J.R., Neuronal plasticity induced by neonatal monocular (and binocular) enucleation, Prog. Neurobiol., 48 (1996) 191±218. [16] Toldi, J., JooÂ, F., FeheÂr, O. and Wolff, J.R., Modi®ed distribution patterns of responses in rat visual cortex induced by monocular enucleation, Neuroscience, 24 (1988) 59±66. [17] Valverde, F., Structural changes in the area striata of the mouse after enucleation, Exp. Brain Res., 5 (1968) 274±292. [18] Wiesenfeld, Z. and Branchek, T., Refractive state and visual acuity in the hooded rat, Vision Res., 16 (1976) 823±827. [19] Wree, A., Zilles, K. and Schleicher, A., Reproduction of plasticity in the primary visual cortex of the rat, In Flohr, H. (Ed.), Post-lesional Neural Plasticity, Springer, Berlin, 1988, pp. 173±186. [20] Yagi, F., Sakai, M. and Ikeda, Y., Effects of monocular enucleation at birth upon learning of a vertical-horizontal discrimination in hooded rats, Behav. Brain Res., 70 (1995) 181±190.
www.elsevier.com/locate/neulet
Reorganization of the uncrossed visual pathways as revealed by Fos-like immunoreactivity in rats with neonatal monocular enucleation Fumio Yagi a,*, Makoto Sakai b, Yukinobu Ikeda c, Fumino Okutani d,e, Seiichi Takahashi d,e, Jyunichi Fukata f a
Behavioral Neuroscience Laboratory, Kochi Medical School, Nankoku, Kochi 783±8505, Japan b Neuropsychology Laboratory, Saga Medical School, Saga 849±8501, Japan c Department of Psychology, Saga University, Saga 840±8502, Japan d Department of Physiology, Kochi Medical School, Nankoku, Kochi 783±8505, Japan e CREST, Japan Science & Technology Corporation, Saitama 332±0012, Japan f Department of Internal Medicine, Kochi Medical School, Nankoku, Kochi 783±8505, Japan Received 9 March 2001; accepted 19 March 2001
Abstract To elucidate the neuronal characteristics of the functional expansion in the uncrossed visual pathways (UXVPs), resulting from early monocular enucleation in rats, the feasibility of stimulus-dependent induction of the immediate early gene c-fos was examined immunohistochemically. In the UXVPs of rats with monocular enucleation at birth, patterned visual stimuli induced Fos-like immunoreactive (FLI) neurons much more densely in wide areas of the super®cial layer throughout the superior colliculus (SC), and in the striate and extrastriate areas of the visual cortex (VC). In the UXVPs of rats monocularly enucleated after maturity, however, only a few stimulus-dependent FLI neurons were scattered in the restricted portions of the SC and the VC. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Monocular enucleation; Uncrossed visual pathway; Superior colliculus; Visual cortex; c-Fos; Plasticity; Rat
Monocular enucleation has been a useful experimental manipulation for analyzing neuronal plasticity in the visual system (for review, see Ref. [15]). In rodents which were enucleated on one side at birth or in the early postnatal days, expansion of the uncrossed visual pathways (the expanded UXVPs) was induced to the visual cortex (VC) ipsilateral to the remaining eye, via both the dorsal lateral geniculate nucleus (LGNd) and the superior colliculus (SC)±lateroposterior thalamic nucleus (LP) [3,5,6,10±12,14,16,17,20]. Previous studies in several mammals have shown that the induction of the immediate early gene (IEG) c-fos in neurons by trans-synaptic activation, as revealed by immunocytochemical detection of the Fos protein (Fos-like immunoreactivity, FLI), enables its effective use as a single-cell resolution marker of neuronal responses to sensory stimulation in the central nervous system (for review, see Ref. [8]). As for the visual systems employed, * Corresponding author. Tel.: 181-88-8802271; fax: 181-888802272. E-mail address: [email protected] (F. Yagi).
light [1], global ¯ashes of light [2] and localized patterned visual stimulation [7] have been used to demonstrate the induction of c-fos in the subcortical and cortical visual centers. The present experiment by the FLI labeling technique was attempted to obtain morphological substrate for the functional expansion of the UXVPs in the rat, which was enucleated monocularly at birth. Twenty mature male albino rats of the KUD Wistar strain (Kyudou, Saga, Japan), weighing 420±465 g, were used for c-Fos immunohistochemistry. Half of the rats had the right eye, including the sclera, removed within 24 h after birth (OEBs), and as a control, the other group had the right eye enucleated at 3 months of age, at least a week before the experiment was started (OETs). The enucleation was performed under sodium pentobarbital anesthesia (50 mg/ kg intraperitoneally (i.p.)) for OETs and hypothermia for OEBs. At 3 months of age, all rats received a callosotomy under sodium pentobarbital anesthesia, in order to block the retinal inputs to the visual centers ipsilateral to the remaining eye via crossed optic and callosal ®bers. The method of this surgery was described previously [5]. After a 10-day
0304-3940/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 1) 01 76 2- 1
54
F. Yagi et al. / Neuroscience Letters 304 (2001) 53±56
recovery period from the callosotomy, the c-Fos immunohistochemistry was performed. After dark adaptation for about 20 h, the rats, which were anesthetized with urethane (0.8±1.0 g/kg i.p.) and injected with atropine sulfate (0.05 mg/kg subcutaneously), were ®xed on a stereotaxic apparatus. The remaining eye was immobilized with a ring made of Elgiloy wire (Rocky Mountain Morita, Tokyo, Japan) attached to the headholder; it was subsequently instilled with silicone ¯uid to prevent corneal desiccation. After these manipulations were carried out under low levels of illumination from a red safelight, the rats were left in darkness for about 1.5 h. Rectal temperature was maintained at 378C with a servo-controlled heating pad throughout the visual stimulation. Moving visual patterns, generated from a photostimulator with a movable slide holder, were projected on a translucent plexiglass which was centered on the remaining eye at 30 cm, a distance that has been found to be associated with the greatest acuity in the rat [18]. All rats were stimulated for 1 h with vertically-moving horizontal square wave-gratings and horizontally-moving vertical ones (bright: 202.1 cd/ m 2, dark: 6.2 cd/m 2); spatial frequency was 0.15 cycles/ degree, each for 15 min, alternately. The speed for these
moving patterns was 168/s. The rats were left in darkness for 90±120 min after the end of the stimulation to await optimum induction of the Fos protein. They were then perfused transcardially with 4% paraformaldehyde in 0.1 M phosphate buffer (PB, pH 7.4) after a brief ¯ush with phosphate-buffered saline. Immediately after perfusion, the brain was removed from the skull and was sectioned coronally with a razor blade into two blocks just in front of the optic chiasma. The tissue blocks were post®xed with the same ®xative solution at 48C overnight, and placed into 0.1 M PB containing 10, 15, and 20% sucrose with 0.1% NaN3 at 48C, each for an overnight period. Coronal 50 mm sections were prepared with a cryostat and the ¯oating sections were processed for FLI with a primary antiserum raised in sheep against a synthetic peptide derived from the N-terminal sequence of the c-Fos protein (Genosys Biotechnologies, Cambridge, UK). The sections were incubated with the primary antiserum diluted 1:2000 for 72 h at 48C, and then with biotinylated rabbit anti-sheep secondary antibody (Rockland, Gilbertsville, PA, USA), and ®nally with the avidin biotinylated horseradish peroxidase complex (Vector, Burlingame, CA, USA). The DAB reaction was intensi®ed with 0.01% nickel ammonium sulfate.
Fig. 1. Photomicrographs of coronal sections of the superior colliculus ipsilateral to the remaining eye of the OEB (A,B) and OET (C,D) rats, showing stimulus-induced FLI neurons. (B,D) are higher magni®cation views of the regions marked by squares in (A,C). Scale bars, 200mm.
F. Yagi et al. / Neuroscience Letters 304 (2001) 53±56
Fig. 2. Mean number and the standard deviation of stimulusinduced FLI neurons per 10 4 mm 2 in the superior colliculus (SC) and visual cortex (VC) ipsilateral to the remaining eye of the OEB and OET rats.
The patterned visual stimuli induced FLI neurons unequivocally in the SC and VC ipsilateral to the remaining eye, but not so much in the LGNd and LP, in which labeled cells
55
were relatively scarce. Therefore, the number and distribution pattern of FLI neurons were analyzed in the SC and VC. Throughout the following text, `ipsilateral' refers to the side ipsilateral to the remaining eye. In OETs, the patterned visual stimuli induced sparse labeling of FLI neurons, mainly in a restricted rostro-medial area of the super®cial layer (the stratum zonale, the stratum griseum super®ciale, and the stratum opticum) of the ipsilateral SC (Fig. 1). This restricted area of the SC roughly corresponded to the SC region innervated by uncrossed axons of the retinal ganglion cells in normal adult rats [6]. On the other hand, in OEBs, the patterned visual stimulation induced FLI neurons much more densely in a wide area of the super®cial layer of the ipsilateral SC, all along the rostro-caudal and latero-medial axes. The ipsilateral SC in the OEBs was approximately 70% smaller as compared to the normal size, whereas the SC in the OETs was normal in size. The mean number of FLI neurons per 10 4 mm 2 was measured for the overall area of the super®cial layer of the ipsilateral SC in both OEBs and OETs. The patterned visual stimulation induced signi®cantly more FLI neurons in the OEBs (4.6 ^ 2.5) than in the OETs (0.7 ^ 0.6) (t 9 4:55, P , 0:01) (Fig. 2). This SC area with FLI neurons in the OEBs appeared to correspond to the region where the crossed visual pathways projected in the rat with normal vision [13]. In the ipsilateral VC (including the striate and extrastriate
Fig. 3. Laminar distribution of stimulus-induced FLI neurons in coronal sections of the visual cortex ipsilateral to the remaining eye of the OEB (A,B) and OET (C,D) rats. (B,D) are higher magni®cation views of the regions marked by squares in (A,C). Roman numerals in dorsoventral axis: cortical layers; scales in medio-lateral axis above (A,C): distances (mm) from the midline; WH: the white matter. Scale bars, 500mm (A,C); 100mm (B,D).
56
F. Yagi et al. / Neuroscience Letters 304 (2001) 53±56
areas), the stimulus-induced FLI cells were seen in both the OEBs and OETs, with a predominant distribution in layers IV and VI (Fig. 3). The number of FLI neurons was counted for all layers within 1±5 mm from the midline and 1±6 mm from the tip of the occipital pole, where Fos-positive cells were distributed unequivocally. A signi®cant difference was observed in the mean number of FLI neurons per 10 4 mm 2 between OEBs (5.8 ^ 1.6) and OETs (1.6 ^ 0.9) (Fig. 2, t 9 6:86, P , 0:001). The stimulus-dependent FLI cells in layers IV and VI were observed more consistently and more densely in the OEBs than in the OETs. Moreover, the FLI cells were also seen in layer II and the deep part of layer III in OEBs. The projection ®bers from the LGNd to the VC terminate in layers IV and VI of area 17 [9], whereas the projection ®bers from the LP to the VC terminate in layers IV and VI of area 18 [4]. Therefore, although we did not attempt to differentiate areas 17 and 18 in the present study, the wide medio-lateral distributions of FLI cells suggest that the induction of the FLI cells in the VC was brought about through the activation of projection ®bers from the LGNd and LP. The present results clearly demonstrate that monocular enucleation at birth increases the number of neurons in the SC and VC, which receive input from the ipsilateral visual pathways. It has been well documented that the removal of one eye in the early postnatal period in the rodent results in an expansion of the retinal area from which uncrossed optic ®bers originate, and hence in an increase in the number of uncrossed optic ®bers projecting to the SC and LGNd [3]. In the SC, axon terminals of those uncrossed optic ®bers do not con®ne themselves in the rostral border, but rather spread to the caudal pole [6]. It has been reported that by monocular enucleation at birth, more cells of the SC were activated by those uncrossed optic ®bers, making the visual ®elds represented in the ipsilateral SC much larger than those by the normal uncrossed optic ®bers [14]. The present results are in good accordance with these previous reports. The functional reorganization of the VC after monocular enucleation was also examined morphologically [17,19] and electrophysiologically [12,16]. In our series of experiments, such functional changes in the VC in OEBs were re¯ected in the facilitation of visual discrimination learning [5,10,20] and an increase in the visual acuity [10,20], indicating that the ipsilateral VC was activated by increased visual input through both the retino±geniculo±VC pathway and the retino±SC±LP pathway. This assumption was con®rmed morphologically in the present study. The authors are grateful to Prof S. Ohnishi, Department of Internal Medicine, Kochi Medical School, for ®nancial assistance for this experiment. This research was supported in part by Grant-in-Aid for Scienti®c Research (C) (#08610089, #11891002) from The Ministry of Education, Culture, Sports, Science and Technology.
[1] Aronin, N., Sagar, S.M., Sharp, F.R. and Schwartz, W., Light regulates expression of a Fos-related protein in the rat SCN, Proc. Natl. Acad. Sci. USA, 87 (1990) 5959±5962. [2] Craner, S.L., Hoffman, G.E., Lund, J.S., Humphrey, A.L. and Lund, R.D., cFos labeling in rat superior colliculus: activation by normal retinal pathways and pathways from intracranial retinal transplants, Exp. Neurol., 117 (1992) 219±229. [3] Farid Ahmed, A.K.M., Dong, K. and Yamadori, T., A retrograde double-labeling study of uni- and bilaterally projecting retinal ganglion cells that project to the superior colliculi after unilateral eye removal at birth in the albino rat, Brain Res., 704 (1995) 307±312. [4] Hughes, H.C., Anatomical and neurobehavioral investigations concerning the thalamo-cortical organization of the rat's visual system, J. Comp. Neurol., 175 (1977) 311±336. [5] Ikeda, Y., Sakai, M. and Yagi, F., Long-term callosal lesions and learning of a black-white discrimination by one-eyed rats, Physiol. Behav., 52 (1992) 851±858. [6] Lund, R.D., Cunningham, T.J. and Lund, J.S., Modi®ed optic projections after unilateral eye removal in young rats, Brain Behav. Evol., 8 (1973) 51±72. [7] Montero, V.M. and Jian, S., Induction of c-fos protein by patterned visual stimulation in central visual pathways of the rat, Brain Res., 690 (1995) 189±199. [8] Morgan, J.I. and Curran, T., Stimulus-transcription coupling in the nervous system: involvement of the inducible proto-oncogenes fos and jun, Annu. Rev. Neurosci., 14 (1991) 421±451. [9] Peters, A. and Feldman, M.L., The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. I General description, J. Neurocytol., 5 (1976) 63±84. [10] Sakai, M., Ikeda, Y. and Yagi, F., Discrimination performance and resolution capacity of uncrossed visual pathways in one-eyed albino rats, Physiol. Behav., 59 (1996) 141±146. [11] Sakai, M. and Yagi, F., Evoked potential in the lateral geniculate body as modi®ed by enucleation of one eye in the albino rat, Brain Res., 210 (1981) 91±102. [12] Sakai, M., Yagi, F. and Ikeda, Y., Evoked potential in the visual cortex as modi®ed by enucleation of one eye in the albino rat, Physiol. Psychol., 11 (1983) 141±146. [13] Stein, B.E. and Gaither, N.S., Receptive-®eld properties in reptilian optic tectum: some comparisons with mammals, J. Neurophysiol., 50 (1983) 102±124. [14] Thompson, I.D., Changes in the uncrossed retinotectal projection after removal of the other eye at birth, Nature, 279 (1979) 63±69. [15] Toldi, J., FeheÂr, O. and Wolff, J.R., Neuronal plasticity induced by neonatal monocular (and binocular) enucleation, Prog. Neurobiol., 48 (1996) 191±218. [16] Toldi, J., JooÂ, F., FeheÂr, O. and Wolff, J.R., Modi®ed distribution patterns of responses in rat visual cortex induced by monocular enucleation, Neuroscience, 24 (1988) 59±66. [17] Valverde, F., Structural changes in the area striata of the mouse after enucleation, Exp. Brain Res., 5 (1968) 274±292. [18] Wiesenfeld, Z. and Branchek, T., Refractive state and visual acuity in the hooded rat, Vision Res., 16 (1976) 823±827. [19] Wree, A., Zilles, K. and Schleicher, A., Reproduction of plasticity in the primary visual cortex of the rat, In Flohr, H. (Ed.), Post-lesional Neural Plasticity, Springer, Berlin, 1988, pp. 173±186. [20] Yagi, F., Sakai, M. and Ikeda, Y., Effects of monocular enucleation at birth upon learning of a vertical-horizontal discrimination in hooded rats, Behav. Brain Res., 70 (1995) 181±190.