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Columnar organization in the subiculum formed by axon branches originating from single CA1 pyramidal neurons in the rat hippocampus
Brain Research, 412 (1987) 156- 160 Elsevier
156 BRE 22277
Columnar organi origi
n inthe subioulum for from CA1 in the rat mp,Js
by axon bran
s
rl~u~ns
Nobuaki Tamamaki 1, Koutarou Abe 2 and Yoshiaki Nojyo ~ t Department of Anatomy, Fukui Medical School, Matsuoka, Fukui (Japan) and 2Toyolinks Corporation, Higashi Shinagawa, Shinagawa, Tokyo (Japan) (Accepted 17 February 1987)
Key words: Columnar organization; Hippocampus;CA1pyramidal neuron; Subiculum; Axonal arborization; Horseradish peroxidase (HRP); Computer analysis
An intraceUular horseradish peroxidase study combined with immunoperoxidase techniques was carried out on hippocampal CA1 pyramidal neurons in the rat. Most axon branches originating from a single CA1pyramidal neuron ran caudally and terminated in the subiculum. The individual axon branches of the single pyramidal neurons bifurcated repeatedly in the subiculumand finally formed a slab-like or columnar terminal arborization (250-300/~m wide, 500-550/,m high and 1.8-2.2 mm long). The present results suggest, in association with other data, that the CA~ pyramidal neurons receive afferent information through lameUar organized connections and they send efferent information to the subiculum through columnar organizedconnections. Accumulated anatomical 6's,9,11,15-17 and neurophysiological2'3'7 evidence showed the presence of the efferent system of hippocampal CA 1 field to the ipsilateral subiculum, entorhinal cortex and lateral septum. However, it was still not clear how a single pyramidal neuron in C A 1 participates in the efferent system and forms axonal arbors in each projecting region. We carried out an intracellular horseradish peroxidase (HRP) study combined with immunoperoxidase technique 18 on the CA 1 pyramidal neurons, and achieved to visualize the axonal arborization in the subiculum. In this study, the axonal arbors of single pyramidal neurons were analyzed with a computer system 19, and the relationship between the axonal arbors and the structure of hippocampal formation were reported. Fifty male albino Sprague-Dawley rats, weighing from 250 to 350 g, were used. They were anesthetized with pentobarbital (50 mg/kg, i.p.) and fixed in a stereotaxic apparatus. A hole was made in the skull over the left hemisphere at a point 3.5-4 mm posterior and 2.5 mm lateral to the bregrna. Through this
hole we advanced a glass micropipette with a tip of 0.5/~m diameter and filled with a solution of 10% HRP in 1 M KCI. The micropipette encountered the hippocampal pyramidal cell layer at around 2 mm below the cortical surface, and a neuron was penetrated. While the resting potential more than 40 mV was maintained, a droplet of H R P solution was injected into the soma under pressure. After two days' survival, the rat was deeply re-anesthetized and perfused transcardiaUy with saline and aldehydes. Parasagittal frozen sections (65 #m thick) were made from the brain immersed in sucrose. For the demonstration of HRP, we applied the immunoperoxidase technique to the sections. The sections were incubated with diluted anti-HRP rabbit serum, anti-rabbit IgG goat serum and peroxidase-anti-peroxidase complex, then reacted with DAB. In the following step, the sections were mounted on gelatin-coated slide glasses for the treatment of osmification and counterstaining. Details of these procedures were reported previously 18. All of the HRP-labeled neuronal structures, such
Correspondence: N. Tamamaki, Department of Anatomy, Fukui Medical School, Matsuoka, Fukui 910-11, Japan. 0006-8993/87/$03.50© 1987Elsevier Science Publishers B.V. (BiomedicalDivision)
157 as soma, dendrites and axons, plus the borders of the pyramidal cell layer were traced with a drawing tube, and these data were entered into a computer with the aid of newly developed software (Toyolinks, LIPS) 19. In this manner, the pyramidal neuron was reconstructed and rotated. In this study, 6 single neurons with satisfactory axonal labeling were recovered. The somata of the labeled neurons were located in the stratum (str.) pyramidale. The basal dendrites were markedly developed in a descending tuft that entered the str. oriens. The apical dendrites had many fine side branches in the str. radiatum (Fig. 1A). Spines were furthermore
SM SL
SR
SP
SQ
B
Fig. 1. A: labeled soma and dendrites of hippocampal CA 1pyramidal neuron. SM, stratum moleculare; SL, stratum lacnosum; SR, stratum radiatum; SP, stratum pyramidale; SO, stratum oriens; A, alveus; arrow, thick axon branch. B: a thick axon branch indicated by an arrow in A. Most of the axon branches had varicosities. C: axon terminal branches in the subiculum. The branches formed many small boutons on their course. Calibration bars are 100pm in A and 10/~m in B and C. In the computer drawings (Figs. 2 and 3), the structure such as B and C are presented with simple lines.
observed on the surface of dendrites. From these aspects of labeled neurons, they were identified as C A 1 superficial pyramidal neurons 13,~4. The dendrites of a pyramidal neuron formed in general a columnar dendritic field of 250-300 p m in diameter and 600 p m in height. Five in 6 pyramidal neurons had an axon arising from the basal side of the soma, while the pyramidal neuron shown in Fig. 1A had axons arising from a primary basal dendrite. The axon bifurcated repeatedly among the basal dendrites. Numerous varicosities, large on one occasion (Fig. 1B) and small on another occasion (Fig. 1C), were found on most of these axon branches. The axon running in the alveus showed irregular swelling. These structures labeled in Golgi-like image could be followed through serial sections. As mentioned above, the labeled structures of single pyramidal neurons observed in the hippocampal formation 17 and the septal nuclei were reconstructed by a computer system. A n example of the single neuron was shown in Fig. 2. The dorsal view of the neuron provides for the typical appearance of labeled pyramidal neurons in this study. In the aspect of efferent projections, one axon branch ran rostrally toward the lateral septal nucleus, and 2 or 3 thicker axon branches (Fig. 1B) toward the entorhinal area. The rest of the numerous axon branches ran toward the subicular area. The trajectory of the axon branches for subicular projection fanned out caudo-laterally to an extent of about 2 mm, at the border between the C A 1 field and the subiculum (dotted line in Fig. 2). The axon branches ran caudally through the str. oriens and the alveus, and gave off collaterals repeatedly, especially after passing the border between the C A 1 field and the subiculum. The collaterals then ran ventrally, entered into the gray matter of the subiculum and ramified forming a band-like terminal arborization which lay along the border between the C A 1 field and the subiculum. The extent of band-like terminal arborizations was mostly 1.8-2.2 m m long. Numerous small boutons were present on these collaterals (Fig. 1C). Fig. 3 shows morphological characteristics of the pyramidal neuron observed from the direction indicated by the arrow in Fig. 2. The view from this direction clarified that the terminal arborization had a slab-like form (250-300 p m wide, 550 ~tm high, 2.2 mm long), which would be a so-called 'column' in configuration. The subiculum itself is shaped in a
158 \
De
o
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'-,
/
$
Fig. 2. Dorsal view of the pyramidal neuron in Fig. 1 reconstructed with the aid of a computer system. The soma of the pyramidal neuron is presented by a filled circle. Dotted line indicates the border between the CA 1 field and the subiculum. The axon collaterals form a slab-like terminal arborization, which will be so called 'column', in the subiculum. The column is 250-300.um wide, 550/~m high and 2.2 mm long. Arrow indicates the long axis of the column. The long axis of the column is directed caudo-laterally 38 ° away from the medioqateral axis of the brain and declined 10° in the direction of the arrow. Arrowhead indicates axon branches proceeding caudolaterally. S, the lateral septum; C, caudal; De, dextral. Bar = 1 mm.
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/ ' / 'i ? !
.) /
i \
/
Fig. 3. Drawing of the pyramidal neuron in Figs. 1 and 2 observed from the direction indicated by the arrow in Fig. 2. The axon branches in the lateral septum are eliminated in this figure. The soma of the pyramidal neuron is presented b y a filled circle. Arrowheads indicate the axon branches in the str. radiatum. Bar = 500~m.
159 band-like form and laid in the caudal part of the CA a field. But the subiculum is about 800/~m in width, and wider than this labeled column. The columns of 6 pyramidal neurons all had a similar size in width and height. The width of the column seemed to fit in with the diameter of a columnar dendritic field (Fig. 3) and the height of the column to accord with the thickness of the subicular gray matter. The labeled terminal branches distributed from layer I to V of the gray matter ~3, although they were dense in layers II and III, and sparse in layer I. In general, such a column in the subiculum was arranged in parallel to the border between the CA x field and the subiculum with some distance. The column was curved slightly, and was convex dorsally. After giving off subicular collaterals, 2 or 3 thicker axon branches of the pyramidal neurons remained in the alveus and ran more caudo-laterally (arrowhead in Fig. 2). In one case, the thicker axon branches could be followed to the deeper part of gray matter in the entorhinal area. Five in 6 pyramidal neurons had, respectively, one axon branch rostrally running, and in two cases the axon branches were found to reach to the lateral septal nucleus (Fig. 2). The axon branches were found rarely in the str. radiatum. Even if there were seen labeled axon branches in the str. radiatum, they seemed to pass there only to reach the subiculure (arrowheads in Fig. 3). In the CA 1 field, 90% of pyramidal neurons were known at least to be similar from the aspect of efferent projections 16, and it became to be clear from the present study that the 3 efferent projections to the septum, entorhinal cortex and subiculum arise from one and the same pyramidal neuron. Although one pyramidal neuron in this study lacked septal projection, the other 5 labeled neurons would be regarded as belonging to a major group of pyramidal neurons which occupies 90% of pyramidal population. The 5 pyramidal neurons were similar, not only in the effer-
ent projections but also in the axonal arborization. In studies with degenerating silver method n and autoradiography 17, the efferent projection of the CA 1 field to the subiculum was reported to be fan-like in shape. This coincided well with the fan-like axonal trajectory of single pyramidal neurons in this study. Such a coincidence between the projection from the CA1 field and the projection from single pyramidal neurons may suggest that most of the pyramidal neurons give off axonal projections overlapping densely in the subiculum. The present study demonstrated in the rat that a single CA t pyramidal neuron forms a columnar organization in the subiculum with abundant axonal branching. As described above, the axonal arborization starting from a single pyramidal neuron finally made the columnar configuration (250-300 ktm wide, 500-550/~m high and 1.8-2.2 mm long) in the subiculum. In the monkey 1°, the axon terminals originating from the prefrontal cortex are reported to exhibit a columnar distribution in the presubiculum. These findings suggest an existence of the columnar organization in the allocortex as well as in the isocortex 1,5,12. On the other hand, in a physiological study e, the excitatory pathways of the hippocampal cortex is indicated to be organized nearly sagittally in a parallel lamellar fashion. In an anatomical study 4,a7, the similar lamellar arrangement is shown in the mossy fiber distribution of granule cells. Referring to these data, it may be said that the CA1 pyramidal neurons receive inputs through lamellar organized connections and they send outputs to the subiculum through columnar organized connections.
1 Akers, R.M. and Killackey, H.P., Organization of corticocortical connections in the parietal cortex of the rat, J. Comp. Neurol., 181 (1978) 513-538. 2 Andersen, P., Bliss, T.V.P. and Skrede, K.K., Lamellar organization of hippocampal excitatory pathways, Exp. Brain Res., 13 (1971) 222-238. 3 Andersen, P., Bland, B.H. and Dudar, J.D., Organization
of the hippocampal output, Exp. Brain Res., 17 (1973) 152-178. 4 Blackstad, T.W., Brink, K., Hem, J. and Jeune, B., Distribution of hippocampal mossy fibers in the rat. An experimental study with silver impregnation methods, J. Comp. Neurol., 138 (1970) 433-450. 5 Cipolloni, P.B. and Peters, A., The bilaminar and banded
The authors thank Miss Yayoi Yamada for her technical help. This work was supported by a Grantin-Aid for Research from the Japan Ministry of Education, Science and Culture. (Projects nos. 59770045 and 60770057.)
160
6 7
8
9
10
11 12
distribution of the callosal terminals in the posterior neocortex of the rat, Brain Research, 176 (1979) 33-47. Chronister, R.B. and DeFrance, J.F., Organization of projection neurons of the hippocampus, Exp. Neurol., 66 (1979) 509-523. Finch, D.M. and Babb, T.L., Neurophysiology of the caudally directed hippocampal efferent system in the rat: projections to the subicular complex, Brain Research, 197 (1980) 11-26. Finch, D.M. and Babb, T.L., Demonstration of caudally directed hippocampal efferents in the rat by intracellular injection of horseradish peroxidase, Brain Research, 214 (1981) 405-410. Finch, D.M., Nowlin, N.L. and Babb, T.L., Demonstration of axonal projections of neurons in the rat hippocampus and subiculum by intracellular injection of HRP, Brain Research, 271 (1983) 201-216. Goldman-Rakic, P.S., Selemon, L.D. and Schwartz, M.L., Dual pathways connecting the dorsolateral prefrontal cortex with the hippocampal formation and parahippocampat cortex in the rhesus monkey, Neuroscience, 12 (1984) 719-743. Hjorth-Simonsen, A., Some intrinsic connections of the hippocampus in the rat: an experimental analysis, J. Comp. Neurol., 147 (1973) 145-162. Isseroff, A., Schwartz, M,L., Dekker, J.J. and GoldmanRakic, P.S., Columnar organization of callosal and associational projections from rat frontal cortex, Brain Research,
293 (1984) 213-223. 13 Lorente de N6, R., Studies on the structure of the cerebral cortex. II. Continuation of the study of the ammonic system, J. Psychol. Neurol., 46 (1934) 113-177. 14 Ram6n y Cajal, S., Structure of the Ammon's Horn, (Translated by Elisabeth M. Kraft), Charles Thomas, Springfield IL, 1955. 15 Swanson, L.W. and Cowan, W.M.. An autoradiographic study of the organization of the efferent connections of the hippocampal formation in the rat, L Comp. Neurol., 172 (1977) 49-84. 16 Swanson, L.W., Sawchenko, P.E. and Cowan, W.M., Evidence for collateral projections by neurons in Ammon's horn, the dentate gyrus, and the subicutum: a multiple retrograde labeling study in the rat. J. Neurosci., 1 (1981) 548-559. 17 Swanson, L.W., Wyss, J.M. and Cowan, W.M., An autoradiographic study of the organization of intrahippocampat association pathways in the rat, J. Comp. Neurol., 181 (1978) 681-716. 18 Tamamaki, N., Watanabe, K. and Nojyo, Y., A whole image of the hippocampal pyramidal neuron revealed by intraceUular pressure-injection of horseradish peroxidase, Brain Research, 307 (1984) 336-340. 19 Tamamaki, N., Abe, K., Aoyama, H. and Nojyo, Y., Three dimensional analysis of pyramidal neurons in the rat hippocampus with computer graphics, Neurosci. Res., Suppl. 3 (1986) S-100.
156 BRE 22277
Columnar organi origi
n inthe subioulum for from CA1 in the rat mp,Js
by axon bran
s
rl~u~ns
Nobuaki Tamamaki 1, Koutarou Abe 2 and Yoshiaki Nojyo ~ t Department of Anatomy, Fukui Medical School, Matsuoka, Fukui (Japan) and 2Toyolinks Corporation, Higashi Shinagawa, Shinagawa, Tokyo (Japan) (Accepted 17 February 1987)
Key words: Columnar organization; Hippocampus;CA1pyramidal neuron; Subiculum; Axonal arborization; Horseradish peroxidase (HRP); Computer analysis
An intraceUular horseradish peroxidase study combined with immunoperoxidase techniques was carried out on hippocampal CA1 pyramidal neurons in the rat. Most axon branches originating from a single CA1pyramidal neuron ran caudally and terminated in the subiculum. The individual axon branches of the single pyramidal neurons bifurcated repeatedly in the subiculumand finally formed a slab-like or columnar terminal arborization (250-300/~m wide, 500-550/,m high and 1.8-2.2 mm long). The present results suggest, in association with other data, that the CA~ pyramidal neurons receive afferent information through lameUar organized connections and they send efferent information to the subiculum through columnar organizedconnections. Accumulated anatomical 6's,9,11,15-17 and neurophysiological2'3'7 evidence showed the presence of the efferent system of hippocampal CA 1 field to the ipsilateral subiculum, entorhinal cortex and lateral septum. However, it was still not clear how a single pyramidal neuron in C A 1 participates in the efferent system and forms axonal arbors in each projecting region. We carried out an intracellular horseradish peroxidase (HRP) study combined with immunoperoxidase technique 18 on the CA 1 pyramidal neurons, and achieved to visualize the axonal arborization in the subiculum. In this study, the axonal arbors of single pyramidal neurons were analyzed with a computer system 19, and the relationship between the axonal arbors and the structure of hippocampal formation were reported. Fifty male albino Sprague-Dawley rats, weighing from 250 to 350 g, were used. They were anesthetized with pentobarbital (50 mg/kg, i.p.) and fixed in a stereotaxic apparatus. A hole was made in the skull over the left hemisphere at a point 3.5-4 mm posterior and 2.5 mm lateral to the bregrna. Through this
hole we advanced a glass micropipette with a tip of 0.5/~m diameter and filled with a solution of 10% HRP in 1 M KCI. The micropipette encountered the hippocampal pyramidal cell layer at around 2 mm below the cortical surface, and a neuron was penetrated. While the resting potential more than 40 mV was maintained, a droplet of H R P solution was injected into the soma under pressure. After two days' survival, the rat was deeply re-anesthetized and perfused transcardiaUy with saline and aldehydes. Parasagittal frozen sections (65 #m thick) were made from the brain immersed in sucrose. For the demonstration of HRP, we applied the immunoperoxidase technique to the sections. The sections were incubated with diluted anti-HRP rabbit serum, anti-rabbit IgG goat serum and peroxidase-anti-peroxidase complex, then reacted with DAB. In the following step, the sections were mounted on gelatin-coated slide glasses for the treatment of osmification and counterstaining. Details of these procedures were reported previously 18. All of the HRP-labeled neuronal structures, such
Correspondence: N. Tamamaki, Department of Anatomy, Fukui Medical School, Matsuoka, Fukui 910-11, Japan. 0006-8993/87/$03.50© 1987Elsevier Science Publishers B.V. (BiomedicalDivision)
157 as soma, dendrites and axons, plus the borders of the pyramidal cell layer were traced with a drawing tube, and these data were entered into a computer with the aid of newly developed software (Toyolinks, LIPS) 19. In this manner, the pyramidal neuron was reconstructed and rotated. In this study, 6 single neurons with satisfactory axonal labeling were recovered. The somata of the labeled neurons were located in the stratum (str.) pyramidale. The basal dendrites were markedly developed in a descending tuft that entered the str. oriens. The apical dendrites had many fine side branches in the str. radiatum (Fig. 1A). Spines were furthermore
SM SL
SR
SP
SQ
B
Fig. 1. A: labeled soma and dendrites of hippocampal CA 1pyramidal neuron. SM, stratum moleculare; SL, stratum lacnosum; SR, stratum radiatum; SP, stratum pyramidale; SO, stratum oriens; A, alveus; arrow, thick axon branch. B: a thick axon branch indicated by an arrow in A. Most of the axon branches had varicosities. C: axon terminal branches in the subiculum. The branches formed many small boutons on their course. Calibration bars are 100pm in A and 10/~m in B and C. In the computer drawings (Figs. 2 and 3), the structure such as B and C are presented with simple lines.
observed on the surface of dendrites. From these aspects of labeled neurons, they were identified as C A 1 superficial pyramidal neurons 13,~4. The dendrites of a pyramidal neuron formed in general a columnar dendritic field of 250-300 p m in diameter and 600 p m in height. Five in 6 pyramidal neurons had an axon arising from the basal side of the soma, while the pyramidal neuron shown in Fig. 1A had axons arising from a primary basal dendrite. The axon bifurcated repeatedly among the basal dendrites. Numerous varicosities, large on one occasion (Fig. 1B) and small on another occasion (Fig. 1C), were found on most of these axon branches. The axon running in the alveus showed irregular swelling. These structures labeled in Golgi-like image could be followed through serial sections. As mentioned above, the labeled structures of single pyramidal neurons observed in the hippocampal formation 17 and the septal nuclei were reconstructed by a computer system. A n example of the single neuron was shown in Fig. 2. The dorsal view of the neuron provides for the typical appearance of labeled pyramidal neurons in this study. In the aspect of efferent projections, one axon branch ran rostrally toward the lateral septal nucleus, and 2 or 3 thicker axon branches (Fig. 1B) toward the entorhinal area. The rest of the numerous axon branches ran toward the subicular area. The trajectory of the axon branches for subicular projection fanned out caudo-laterally to an extent of about 2 mm, at the border between the C A 1 field and the subiculum (dotted line in Fig. 2). The axon branches ran caudally through the str. oriens and the alveus, and gave off collaterals repeatedly, especially after passing the border between the C A 1 field and the subiculum. The collaterals then ran ventrally, entered into the gray matter of the subiculum and ramified forming a band-like terminal arborization which lay along the border between the C A 1 field and the subiculum. The extent of band-like terminal arborizations was mostly 1.8-2.2 m m long. Numerous small boutons were present on these collaterals (Fig. 1C). Fig. 3 shows morphological characteristics of the pyramidal neuron observed from the direction indicated by the arrow in Fig. 2. The view from this direction clarified that the terminal arborization had a slab-like form (250-300 p m wide, 550 ~tm high, 2.2 mm long), which would be a so-called 'column' in configuration. The subiculum itself is shaped in a
158 \
De
o
/? __
'-,
/
$
Fig. 2. Dorsal view of the pyramidal neuron in Fig. 1 reconstructed with the aid of a computer system. The soma of the pyramidal neuron is presented by a filled circle. Dotted line indicates the border between the CA 1 field and the subiculum. The axon collaterals form a slab-like terminal arborization, which will be so called 'column', in the subiculum. The column is 250-300.um wide, 550/~m high and 2.2 mm long. Arrow indicates the long axis of the column. The long axis of the column is directed caudo-laterally 38 ° away from the medioqateral axis of the brain and declined 10° in the direction of the arrow. Arrowhead indicates axon branches proceeding caudolaterally. S, the lateral septum; C, caudal; De, dextral. Bar = 1 mm.
\ \,
/ ' / 'i ? !
.) /
i \
/
Fig. 3. Drawing of the pyramidal neuron in Figs. 1 and 2 observed from the direction indicated by the arrow in Fig. 2. The axon branches in the lateral septum are eliminated in this figure. The soma of the pyramidal neuron is presented b y a filled circle. Arrowheads indicate the axon branches in the str. radiatum. Bar = 500~m.
159 band-like form and laid in the caudal part of the CA a field. But the subiculum is about 800/~m in width, and wider than this labeled column. The columns of 6 pyramidal neurons all had a similar size in width and height. The width of the column seemed to fit in with the diameter of a columnar dendritic field (Fig. 3) and the height of the column to accord with the thickness of the subicular gray matter. The labeled terminal branches distributed from layer I to V of the gray matter ~3, although they were dense in layers II and III, and sparse in layer I. In general, such a column in the subiculum was arranged in parallel to the border between the CA x field and the subiculum with some distance. The column was curved slightly, and was convex dorsally. After giving off subicular collaterals, 2 or 3 thicker axon branches of the pyramidal neurons remained in the alveus and ran more caudo-laterally (arrowhead in Fig. 2). In one case, the thicker axon branches could be followed to the deeper part of gray matter in the entorhinal area. Five in 6 pyramidal neurons had, respectively, one axon branch rostrally running, and in two cases the axon branches were found to reach to the lateral septal nucleus (Fig. 2). The axon branches were found rarely in the str. radiatum. Even if there were seen labeled axon branches in the str. radiatum, they seemed to pass there only to reach the subiculure (arrowheads in Fig. 3). In the CA 1 field, 90% of pyramidal neurons were known at least to be similar from the aspect of efferent projections 16, and it became to be clear from the present study that the 3 efferent projections to the septum, entorhinal cortex and subiculum arise from one and the same pyramidal neuron. Although one pyramidal neuron in this study lacked septal projection, the other 5 labeled neurons would be regarded as belonging to a major group of pyramidal neurons which occupies 90% of pyramidal population. The 5 pyramidal neurons were similar, not only in the effer-
ent projections but also in the axonal arborization. In studies with degenerating silver method n and autoradiography 17, the efferent projection of the CA 1 field to the subiculum was reported to be fan-like in shape. This coincided well with the fan-like axonal trajectory of single pyramidal neurons in this study. Such a coincidence between the projection from the CA1 field and the projection from single pyramidal neurons may suggest that most of the pyramidal neurons give off axonal projections overlapping densely in the subiculum. The present study demonstrated in the rat that a single CA t pyramidal neuron forms a columnar organization in the subiculum with abundant axonal branching. As described above, the axonal arborization starting from a single pyramidal neuron finally made the columnar configuration (250-300 ktm wide, 500-550/~m high and 1.8-2.2 mm long) in the subiculum. In the monkey 1°, the axon terminals originating from the prefrontal cortex are reported to exhibit a columnar distribution in the presubiculum. These findings suggest an existence of the columnar organization in the allocortex as well as in the isocortex 1,5,12. On the other hand, in a physiological study e, the excitatory pathways of the hippocampal cortex is indicated to be organized nearly sagittally in a parallel lamellar fashion. In an anatomical study 4,a7, the similar lamellar arrangement is shown in the mossy fiber distribution of granule cells. Referring to these data, it may be said that the CA1 pyramidal neurons receive inputs through lamellar organized connections and they send outputs to the subiculum through columnar organized connections.
1 Akers, R.M. and Killackey, H.P., Organization of corticocortical connections in the parietal cortex of the rat, J. Comp. Neurol., 181 (1978) 513-538. 2 Andersen, P., Bliss, T.V.P. and Skrede, K.K., Lamellar organization of hippocampal excitatory pathways, Exp. Brain Res., 13 (1971) 222-238. 3 Andersen, P., Bland, B.H. and Dudar, J.D., Organization
of the hippocampal output, Exp. Brain Res., 17 (1973) 152-178. 4 Blackstad, T.W., Brink, K., Hem, J. and Jeune, B., Distribution of hippocampal mossy fibers in the rat. An experimental study with silver impregnation methods, J. Comp. Neurol., 138 (1970) 433-450. 5 Cipolloni, P.B. and Peters, A., The bilaminar and banded
The authors thank Miss Yayoi Yamada for her technical help. This work was supported by a Grantin-Aid for Research from the Japan Ministry of Education, Science and Culture. (Projects nos. 59770045 and 60770057.)
160
6 7
8
9
10
11 12
distribution of the callosal terminals in the posterior neocortex of the rat, Brain Research, 176 (1979) 33-47. Chronister, R.B. and DeFrance, J.F., Organization of projection neurons of the hippocampus, Exp. Neurol., 66 (1979) 509-523. Finch, D.M. and Babb, T.L., Neurophysiology of the caudally directed hippocampal efferent system in the rat: projections to the subicular complex, Brain Research, 197 (1980) 11-26. Finch, D.M. and Babb, T.L., Demonstration of caudally directed hippocampal efferents in the rat by intracellular injection of horseradish peroxidase, Brain Research, 214 (1981) 405-410. Finch, D.M., Nowlin, N.L. and Babb, T.L., Demonstration of axonal projections of neurons in the rat hippocampus and subiculum by intracellular injection of HRP, Brain Research, 271 (1983) 201-216. Goldman-Rakic, P.S., Selemon, L.D. and Schwartz, M.L., Dual pathways connecting the dorsolateral prefrontal cortex with the hippocampal formation and parahippocampat cortex in the rhesus monkey, Neuroscience, 12 (1984) 719-743. Hjorth-Simonsen, A., Some intrinsic connections of the hippocampus in the rat: an experimental analysis, J. Comp. Neurol., 147 (1973) 145-162. Isseroff, A., Schwartz, M,L., Dekker, J.J. and GoldmanRakic, P.S., Columnar organization of callosal and associational projections from rat frontal cortex, Brain Research,
293 (1984) 213-223. 13 Lorente de N6, R., Studies on the structure of the cerebral cortex. II. Continuation of the study of the ammonic system, J. Psychol. Neurol., 46 (1934) 113-177. 14 Ram6n y Cajal, S., Structure of the Ammon's Horn, (Translated by Elisabeth M. Kraft), Charles Thomas, Springfield IL, 1955. 15 Swanson, L.W. and Cowan, W.M.. An autoradiographic study of the organization of the efferent connections of the hippocampal formation in the rat, L Comp. Neurol., 172 (1977) 49-84. 16 Swanson, L.W., Sawchenko, P.E. and Cowan, W.M., Evidence for collateral projections by neurons in Ammon's horn, the dentate gyrus, and the subicutum: a multiple retrograde labeling study in the rat. J. Neurosci., 1 (1981) 548-559. 17 Swanson, L.W., Wyss, J.M. and Cowan, W.M., An autoradiographic study of the organization of intrahippocampat association pathways in the rat, J. Comp. Neurol., 181 (1978) 681-716. 18 Tamamaki, N., Watanabe, K. and Nojyo, Y., A whole image of the hippocampal pyramidal neuron revealed by intraceUular pressure-injection of horseradish peroxidase, Brain Research, 307 (1984) 336-340. 19 Tamamaki, N., Abe, K., Aoyama, H. and Nojyo, Y., Three dimensional analysis of pyramidal neurons in the rat hippocampus with computer graphics, Neurosci. Res., Suppl. 3 (1986) S-100.