310
Brain Research. 96 (1975) 310 31(~ ~:~ Elsevier Scientific Publishing Company, Amsterdam - Printed in The NetherlaJlds
Cinguloseptal projections in the squirrel monkey ERVIN W. POWELL ANDPAUL F. ROBINSON Department of .4natomy, School of Medicine, University of .4rkansas, Little Rock, Ark. 72201 (U.S.A.)
(Accepted June 20th, 1975)
The septum has profuse connections to the hypothalamus and certain thalamic nuclei 13,16A7. It has been suggested that these connections carry impulses which modulate emotion and lower autonomic manifestations2,6,10,15. If the septum has a modulatory influence on the hypothalamus and thalamus, it would seem reasonable for it to receive connections from the cerebral cortex, perhaps from the overlying cingulate gyrus which is part of the limbic system. CajaP described cinguloseptal connections as coursing anteriorly over the rostrum of the corpus callosum into the midline fibers of the septum. Others 4,8,20 have reported seeing degenerating fibers entering the midline of the septum from the ventral surface of the corpus callosum following cortical lesions but have not reported seeing terminals in septal nuclei. Domesick 4, using silver impregnation methods in the rat, found degeneration in the dorsal fornix following lesions which involved the indusium griseum. She concluded that most so-called cinguloseptal projections probably originate in the indusium griseum. Powell et al. 14 also using silver impregnation methods traced degenerating fibers from the middle cingulate gyrus of cats, via the ventral surface of the corpus callosum, into the septal midline. However, few intraseptal terminals were observed. The present experiment was an attempt to detect cingulate projections to septal nuclei. Since techniques employed in the silver method destroy fibers o f passage and the subsequent argyrophilia is not limited to degeneration originating at the lesion focus, we elected to use the recently applied radioactive tracer techniques for labeling fast protein components o f axoplasmic flow 3. The fast components are reported to collect primarily in axon terminals a. Nine adult squirrel monkeys were injected in areas o f the cingulate gyrus with radioactive L-leucine to label target nuclei (Fig. l). Four animals (84, 78, 80, 79) were injected in the anterior and posterior regions of Brodmann's area 24. Three animals (100, 101, 102) were injected in Brodmann's area 23 (anterior part}. Two cases (85, 86) received injections in a region of the posterior cingulate gyrus which involved Brodmann's areas 29 and 30 and the posterior part of area 23. The same general surgical procedures were followed in all cases. The monkeys were anesthetized with ketamine hydrochtoride (dosage 25 mg/kg, intramuscular), augmented every 20-30 min. A local anesthetic (Xytocaine, 1 - 2 ~ , containing epinephrine) was
311
88
o°
Fig. I. Sites of injection of tritiated leucine. The numbers relate to specific cases. Abbreviations in this and following figures: Ac, anterior commissure; Cb, cerebellum; Cc, corpus callosum; Cd, caudate nucleus; Cg, cingulate gyms; De, dorsal external nucleus of septum; Di, dorsal internal nucleus of septum; Din, dorsal medial nucleus of septum; Fc, frontal cortex; Ig, indusium griseum; Ma, anterior medial nucleus of septum; Mp, posterior medial nucleus of septum; Pn, pons; Rd, hippocampal rudiment; V, ventricle. injected into the scalp prior to surgery. A 10 #1 Hamilton syringe with a 26-gauge needle was stereotaxically positioned in areas of the cingulate gyrus. Each monkey received a 1 ,ul injection of tritiated L-[4,5-3H]leucine dissolved in normal saline (New England Nuclear, concentrated to 10 #Ci//B; specific activity, 5 Ci/mmole). Each injection was administered over a 5-rain period in 0.2 #1 aliquots/min. After injection of the entire amount (the last 0.2 #l aliquot), the syringe was left in place for an additional 5 rain before withdrawal. Following a survival period of one day, the monkeys were deeply anesthetized with sodium pentobarbital and perfused through the left ventricle of the heart with 1 0 ~ formalin in 0 . 9 ~ saline. The brains were removed and blocked for paraffin embedding. Sections (8 # m in thickness) were selected every 150 #m from the genu to the splenium of the corpus callosum. These were then mounted on slides and dipped back to back in undiluted K o d a k NTB-2 emulsion. Following exposure periods of 2, 4, 6 and 12 weeks, the slides were developed and fixed. Our autoradiographic procedure was essentially that described by Cowan et al. 3. The slides were stained with cresyl violet using a method modified from those reported by Thurston and Joftes 19 and Hendrickson et a L L Grain counts were made at a magnification of × 1000 using an ocular grid (10 ram/0.5 mm subdivisions) which covered an area of 0.01 sq.mm at that magnification. The background density of silver grains was determined by averaging counts over clear emulsion and neutral areas of the experimental material, e.g., caudate nucleus and globus pallidus. The nomenclature used to refer to cytoarchitectural subdivisions of the septum is that of Stephan and Andy is. The primary concern was to detect grain pattern
312 TABLE I GRAIN
D E N S I T Y IN S E P T A L N U C I , E I
Equal numbers of grains were counted in nuclear and background areas to achieve a 0.05 coetticient of variation z. The grain counts were made using an ocular grid measuring 0.01 sq.mm at 1000. Mean counts obtained in nuclei and background Septal nuclei
SM-80
SM-84
SM-86
S M- 101
De
ipsilateral contralateral
266.5 ~- 11.6 380.0 :£ 31.1
171.0 ~i_ 13.0 92.5 ::!: 3.5
57.3 ± 8.0 52.3 .± 8.0
43.5 ~:: 5.7 44.5 5_ 4.1
Di
ipsilateral contralateral
60.3 _ 4.0 56.5 i~ 9.1
633.3 -Q 41.4 164.3 ~_ 29.3
49.7 - 5.5 50.0 ± 6.9
53.8 ~_ 9.9 40.5 ~ 4.4
Dm ipsilateral contralateral
49.2 ± 12.8 48.7 ~ 9.4
63.5 _L 2.1 86.6 _k: 29.5
42.0 -2z 3.4 52.7 ~ 9.9
56.3 _~ 10.0 41.8 ~ 5.0
Ma ipsilateral contralateral
46.3 :~ 14.4 43.8 ~ 5.6
61.8 ~ 6.5 39.2:j. 3.7
52.3 ± 1.5 51.7~ 4.7
39.5 ±~ 7.3 40.5 :~ 9.9
Background
49.5 ~ 12.5
38.4 ~ 8.4
42.6 ~- 11.3
47.3 ~- 11.8
topography representing terminals in septal nuclei. The results are summarized i n Table I. Animals 80, 84, 86 and 101 have been selected to illustrate the data observed in the 9 animals. C a s e S M - 8 4 . The results obtained in this animal are considered representative o f those obtained following injections (84, 78) into the anterior part o f B r o d m a n n ' s area 24. The injection focus in squirrel m o n k e y 84 was located dorsal to the genu o f the corpus callosum at the rostral end o f B r o d m a n n ' s area 24. The indusium griseum was significantly involved as a part o f the injection site. Only a small n u m b e r o f silver grains representing radioactive label in terminals were observed in the anterior medial septal nucleus (Ma) and hippocampal rudiment (Rd) (Fig. 2), More posteriorly, the greatest grain density was observed in the internal dorsal septal nucleus (Di, Figs. 2 and 3). Grains also were evident in the external dorsal septal nucleus (De). C a s e S M - 8 0 . This animal was selected as representative o f injections (80, 79) into the posterior part o f B r o d m a n n ' s area 24 (Fig. 1). The injection did not significantly involve the indusium griseum; however, a moderate a m o u n t of grains were present in that structure. Radiographic labeling was found principally in the external part o f the dorsal septal nucleus (De) bilaterally. The terminal labeling found in De was greater than that observed in the same nucleus in SM-84. The grain density in more ventral septal nuclei (Ma and Dm) was not above background level for SM-80, C a s e S M - I O I . This animal is representative o f animals (100, 101, 102) which received injections into the anterior part o f B r o d m a n n ' s area 23. The results contrast with those obtained when injections were placed in more rostral portions o f the cingulate gyrus. Labeling above background was not observed in any o f the septal nuclei in this monkey.
313
SM 84 "X
r
,I
i', . i.:L ,.o°° °
> Cg /
~ ..':'.
")
1
t
3
I ,
Cd
-)
y S M 80 "//
C _............_z
\
i/
i )
°,,l yj,, A
, L
c__-~
-----U'--
[mm
Fig. 2. Typical grain pattern observed in septal nuclei in case SM-84 (top) and SM-80 (bottom). Diagrams of coronal sections are from anterior to posterior levels A-D. Case SM-86. This case was selected to represent the cingulale gyrus, posterior and ventral to the splenium of the corpus callosum (Brodmann's areas 29 and 30 and the posterior part of area 23). No labeling above background levels was observed in any of the septal nuclei. The results show that some areas of the cingulate gyrus project topographically to dorsal septal nuclei. Generally the projections are preferentially ipsilateral except for the De nucleus in case 80. The pathways probably course from the cingulum medially across the corpus callosum to mid-line septal structures 4,14. Some workers have traced fiber degeneration from cortical lesions to the fornix 4,12. In other studies in the cat, fibers have been traced through the corpus callosum near the mid-line and followed to the mid-line of the septum and into the thalamus and hypothalamus via
314
Fig. 3. Grain density observed in septal nuclei in cases SM-84 and SM-80. The two bottom fFa~e'~
315 the fornix c o l u m n 14. It seems unlikely t h a t fibers coursing a l o n g the mid-line o f the s e p t u m w o u l d n o t b r a n c h collaterals to septal nuclei. P e r h a p s these terminals have been difficult to see because they are especially small or o f such a c o m p o s i t i o n t h a t silver m e t h o d s do n o t a d e q u a t e l y i m p r e g n a t e them. D a t a f r o m 4 animals indicate a c o r r e l a t i o n between the degree o f i n v o l v e m e n t o f the i n d u s i u m griseum as p a r t o f the a n t e r i o r injection site a n d the labeling observed in the Di septal nucleus. This implies t h a t the i n d u s i u m griseum contributes a considerable n u m b e r o f terminals to the Di nucleus. C o n t r i b u t i o n s from the cingulate gyrus a n d i n d u s i u m griseum a p p e a r n o t to originate in the p o s t e r i o r cingulate region since injections into t h a t area did n o t result in the labeling o f terminals in septal nuclei. K r i e g 9 has suggested t h a t the cingulate a r e a 24 has a highly specific a n d t o p o g r a p h i c relation to subcortical structures. This m a y a c c o u n t for v a r i a t i o n in findings a m o n g cases. The presence o f grains in the i n d u s i u m griseum in case SM-80 seems to indicate t h a t the i n d u s i u m griseum receives c o n n e c t i o n s f r o m the overlying cingulate gyrus, a n d previous d a t a indicate t h a t it projects to layer I o f the cingulate cortex 11. Such reciprocal connections p r o v i d e p a t h w a y s , in a d d i t i o n to the direct cinguloseptal c o n n e c t i o n s described above, over which impulses f r o m the a n t e r i o r p a r t o f the cingulate gyrus might affect the firing o f n e u r o n s in septal nuclei.
1 CAJAL, S. RAM6N V, Histologie du Systdme Nerveux de l'Homme et des Vertdbrds, Maloine,
Paris, 1911, pp. 762-823. 2 CLEMENTE,C. D., AND CHASE, M. H., Neurological substrates of aggressive behavior, Ann. Rev. Physiol., 35 (1973) 329-356. 3 COWAN,W. M., GOTTL1EB, D. I., HENDRICKSON, A. E., PRICE, J. L., AND WOOLSEY, T. A., The autoradiographic demonstration of axonal connections in the central nervous system, Brain Research, 37 (1972) 21-51. 4 DOMESICK,V. B., Projections from the cingulate cortex in the rat, Brain Research, 12 (1969) 296-320. 5 ENGLAND,J. M., AND MILLER, R. G., The statistical analysis of autoradiographs. 11. Theoretical aspects including methods for optimal allocation of measurement effort, J. Microsc., 92 (1970) 167-177. 6 UELDMAN, S., Neurophysiological mechanisms modifying afferent hypothalamohippocampal conduction, Exp. Neurol., 5 (1962) 269-291. 7 HENDRICKSON,A. E., MOE, L., AND NOBLE, B., Staining for autoradiography of the central nervous system, Stain Technol., 47 (1972) 283-290. 8 KNOOK,H. L., The Fibre Connections of the Forebrain, Davis, Philadelphia, Pa., 1966, pp. 81-92. 9 KRIEG, W. J. S., Connections of the Cerebral Cortex, Brain Books, Evanston, Ilk, 1963, pp. 219-245. 10 NIEMER, W. T., POWELL, E. W., AND GOODFELLOW, E. F., The subcortex and hypothalamic after-discharge in the cat, Electroenceph. clin. Neurophysiol., 12 (1960) 345-358. 11 POWELL, E. W., Septal efferents revealed by axonal degeneration in the rat, Exp. Neurol., 8 (1963) 406422. 12 POWELL, E. W., Corticolimbic interrelations revealed by evoked potential and degeneration techniques, Exp. Neurol., l0 (1964) 463474. 13 POWEEL,E. W., Limbic projections to the thalamus, Exp. Brain Res., 17 (1973) 394-401. 14 POWELL, E. W., AKAGI, K., AND HATTON, J. B., Subcortical projections of the cingulate gyrus in cat, J. Hirnforsch., 15 (1974) 269-278. 15 POWELL, E. W., AND HINES, G., The limbic system: an interface, Behav. Biol., 12(1974) 149-164. 16 SIMMONS, H. J., AND POWELL, E. W., A quantitative analysis of septothalamic projections in the squirrel monkey, Anat. Rec., 166 (1970) 378.
316 17 SIMMONS, H. J., AND POWELL, E. W., Septomammillary projections in the squirrel monkey.
Acta anat. (Basel), 82 (1972) 159 178. 18 STEPHAN, H., AND ANDY, O. J., Cytoarchitectonics of the septal nuclei in Old World monkeys (Cercopithecus and Colobus), J. Hh'nfbrsch., 7 (1964) 1-23. 19 THURSTON, J. M., AND JO~'TES, D. L., Stains compatible with dipping radioautography, Stai~ Technol., 38 (1963) 231-235. 20 YAKOVLEV, P. 1., AND LOCKE, S., Limbic nuclei of thalamus and connections of limbic cortex. III. Corticocortical connections of the anterior cingulate gyrus, the cingulum, and the subcallosal bundle in monkey, Arch. Neurol. (Chic.), 5 (1961) 364-400.
Brain Research. 96 (1975) 310 31(~ ~:~ Elsevier Scientific Publishing Company, Amsterdam - Printed in The NetherlaJlds
Cinguloseptal projections in the squirrel monkey ERVIN W. POWELL ANDPAUL F. ROBINSON Department of .4natomy, School of Medicine, University of .4rkansas, Little Rock, Ark. 72201 (U.S.A.)
(Accepted June 20th, 1975)
The septum has profuse connections to the hypothalamus and certain thalamic nuclei 13,16A7. It has been suggested that these connections carry impulses which modulate emotion and lower autonomic manifestations2,6,10,15. If the septum has a modulatory influence on the hypothalamus and thalamus, it would seem reasonable for it to receive connections from the cerebral cortex, perhaps from the overlying cingulate gyrus which is part of the limbic system. CajaP described cinguloseptal connections as coursing anteriorly over the rostrum of the corpus callosum into the midline fibers of the septum. Others 4,8,20 have reported seeing degenerating fibers entering the midline of the septum from the ventral surface of the corpus callosum following cortical lesions but have not reported seeing terminals in septal nuclei. Domesick 4, using silver impregnation methods in the rat, found degeneration in the dorsal fornix following lesions which involved the indusium griseum. She concluded that most so-called cinguloseptal projections probably originate in the indusium griseum. Powell et al. 14 also using silver impregnation methods traced degenerating fibers from the middle cingulate gyrus of cats, via the ventral surface of the corpus callosum, into the septal midline. However, few intraseptal terminals were observed. The present experiment was an attempt to detect cingulate projections to septal nuclei. Since techniques employed in the silver method destroy fibers o f passage and the subsequent argyrophilia is not limited to degeneration originating at the lesion focus, we elected to use the recently applied radioactive tracer techniques for labeling fast protein components o f axoplasmic flow 3. The fast components are reported to collect primarily in axon terminals a. Nine adult squirrel monkeys were injected in areas o f the cingulate gyrus with radioactive L-leucine to label target nuclei (Fig. l). Four animals (84, 78, 80, 79) were injected in the anterior and posterior regions of Brodmann's area 24. Three animals (100, 101, 102) were injected in Brodmann's area 23 (anterior part}. Two cases (85, 86) received injections in a region of the posterior cingulate gyrus which involved Brodmann's areas 29 and 30 and the posterior part of area 23. The same general surgical procedures were followed in all cases. The monkeys were anesthetized with ketamine hydrochtoride (dosage 25 mg/kg, intramuscular), augmented every 20-30 min. A local anesthetic (Xytocaine, 1 - 2 ~ , containing epinephrine) was
311
88
o°
Fig. I. Sites of injection of tritiated leucine. The numbers relate to specific cases. Abbreviations in this and following figures: Ac, anterior commissure; Cb, cerebellum; Cc, corpus callosum; Cd, caudate nucleus; Cg, cingulate gyms; De, dorsal external nucleus of septum; Di, dorsal internal nucleus of septum; Din, dorsal medial nucleus of septum; Fc, frontal cortex; Ig, indusium griseum; Ma, anterior medial nucleus of septum; Mp, posterior medial nucleus of septum; Pn, pons; Rd, hippocampal rudiment; V, ventricle. injected into the scalp prior to surgery. A 10 #1 Hamilton syringe with a 26-gauge needle was stereotaxically positioned in areas of the cingulate gyrus. Each monkey received a 1 ,ul injection of tritiated L-[4,5-3H]leucine dissolved in normal saline (New England Nuclear, concentrated to 10 #Ci//B; specific activity, 5 Ci/mmole). Each injection was administered over a 5-rain period in 0.2 #1 aliquots/min. After injection of the entire amount (the last 0.2 #l aliquot), the syringe was left in place for an additional 5 rain before withdrawal. Following a survival period of one day, the monkeys were deeply anesthetized with sodium pentobarbital and perfused through the left ventricle of the heart with 1 0 ~ formalin in 0 . 9 ~ saline. The brains were removed and blocked for paraffin embedding. Sections (8 # m in thickness) were selected every 150 #m from the genu to the splenium of the corpus callosum. These were then mounted on slides and dipped back to back in undiluted K o d a k NTB-2 emulsion. Following exposure periods of 2, 4, 6 and 12 weeks, the slides were developed and fixed. Our autoradiographic procedure was essentially that described by Cowan et al. 3. The slides were stained with cresyl violet using a method modified from those reported by Thurston and Joftes 19 and Hendrickson et a L L Grain counts were made at a magnification of × 1000 using an ocular grid (10 ram/0.5 mm subdivisions) which covered an area of 0.01 sq.mm at that magnification. The background density of silver grains was determined by averaging counts over clear emulsion and neutral areas of the experimental material, e.g., caudate nucleus and globus pallidus. The nomenclature used to refer to cytoarchitectural subdivisions of the septum is that of Stephan and Andy is. The primary concern was to detect grain pattern
312 TABLE I GRAIN
D E N S I T Y IN S E P T A L N U C I , E I
Equal numbers of grains were counted in nuclear and background areas to achieve a 0.05 coetticient of variation z. The grain counts were made using an ocular grid measuring 0.01 sq.mm at 1000. Mean counts obtained in nuclei and background Septal nuclei
SM-80
SM-84
SM-86
S M- 101
De
ipsilateral contralateral
266.5 ~- 11.6 380.0 :£ 31.1
171.0 ~i_ 13.0 92.5 ::!: 3.5
57.3 ± 8.0 52.3 .± 8.0
43.5 ~:: 5.7 44.5 5_ 4.1
Di
ipsilateral contralateral
60.3 _ 4.0 56.5 i~ 9.1
633.3 -Q 41.4 164.3 ~_ 29.3
49.7 - 5.5 50.0 ± 6.9
53.8 ~_ 9.9 40.5 ~ 4.4
Dm ipsilateral contralateral
49.2 ± 12.8 48.7 ~ 9.4
63.5 _L 2.1 86.6 _k: 29.5
42.0 -2z 3.4 52.7 ~ 9.9
56.3 _~ 10.0 41.8 ~ 5.0
Ma ipsilateral contralateral
46.3 :~ 14.4 43.8 ~ 5.6
61.8 ~ 6.5 39.2:j. 3.7
52.3 ± 1.5 51.7~ 4.7
39.5 ±~ 7.3 40.5 :~ 9.9
Background
49.5 ~ 12.5
38.4 ~ 8.4
42.6 ~- 11.3
47.3 ~- 11.8
topography representing terminals in septal nuclei. The results are summarized i n Table I. Animals 80, 84, 86 and 101 have been selected to illustrate the data observed in the 9 animals. C a s e S M - 8 4 . The results obtained in this animal are considered representative o f those obtained following injections (84, 78) into the anterior part o f B r o d m a n n ' s area 24. The injection focus in squirrel m o n k e y 84 was located dorsal to the genu o f the corpus callosum at the rostral end o f B r o d m a n n ' s area 24. The indusium griseum was significantly involved as a part o f the injection site. Only a small n u m b e r o f silver grains representing radioactive label in terminals were observed in the anterior medial septal nucleus (Ma) and hippocampal rudiment (Rd) (Fig. 2), More posteriorly, the greatest grain density was observed in the internal dorsal septal nucleus (Di, Figs. 2 and 3). Grains also were evident in the external dorsal septal nucleus (De). C a s e S M - 8 0 . This animal was selected as representative o f injections (80, 79) into the posterior part o f B r o d m a n n ' s area 24 (Fig. 1). The injection did not significantly involve the indusium griseum; however, a moderate a m o u n t of grains were present in that structure. Radiographic labeling was found principally in the external part o f the dorsal septal nucleus (De) bilaterally. The terminal labeling found in De was greater than that observed in the same nucleus in SM-84. The grain density in more ventral septal nuclei (Ma and Dm) was not above background level for SM-80, C a s e S M - I O I . This animal is representative o f animals (100, 101, 102) which received injections into the anterior part o f B r o d m a n n ' s area 23. The results contrast with those obtained when injections were placed in more rostral portions o f the cingulate gyrus. Labeling above background was not observed in any o f the septal nuclei in this monkey.
313
SM 84 "X
r
,I
i', . i.:L ,.o°° °
> Cg /
~ ..':'.
")
1
t
3
I ,
Cd
-)
y S M 80 "//
C _............_z
\
i/
i )
°,,l yj,, A
, L
c__-~
-----U'--
[mm
Fig. 2. Typical grain pattern observed in septal nuclei in case SM-84 (top) and SM-80 (bottom). Diagrams of coronal sections are from anterior to posterior levels A-D. Case SM-86. This case was selected to represent the cingulale gyrus, posterior and ventral to the splenium of the corpus callosum (Brodmann's areas 29 and 30 and the posterior part of area 23). No labeling above background levels was observed in any of the septal nuclei. The results show that some areas of the cingulate gyrus project topographically to dorsal septal nuclei. Generally the projections are preferentially ipsilateral except for the De nucleus in case 80. The pathways probably course from the cingulum medially across the corpus callosum to mid-line septal structures 4,14. Some workers have traced fiber degeneration from cortical lesions to the fornix 4,12. In other studies in the cat, fibers have been traced through the corpus callosum near the mid-line and followed to the mid-line of the septum and into the thalamus and hypothalamus via
314
Fig. 3. Grain density observed in septal nuclei in cases SM-84 and SM-80. The two bottom fFa~e'~
315 the fornix c o l u m n 14. It seems unlikely t h a t fibers coursing a l o n g the mid-line o f the s e p t u m w o u l d n o t b r a n c h collaterals to septal nuclei. P e r h a p s these terminals have been difficult to see because they are especially small or o f such a c o m p o s i t i o n t h a t silver m e t h o d s do n o t a d e q u a t e l y i m p r e g n a t e them. D a t a f r o m 4 animals indicate a c o r r e l a t i o n between the degree o f i n v o l v e m e n t o f the i n d u s i u m griseum as p a r t o f the a n t e r i o r injection site a n d the labeling observed in the Di septal nucleus. This implies t h a t the i n d u s i u m griseum contributes a considerable n u m b e r o f terminals to the Di nucleus. C o n t r i b u t i o n s from the cingulate gyrus a n d i n d u s i u m griseum a p p e a r n o t to originate in the p o s t e r i o r cingulate region since injections into t h a t area did n o t result in the labeling o f terminals in septal nuclei. K r i e g 9 has suggested t h a t the cingulate a r e a 24 has a highly specific a n d t o p o g r a p h i c relation to subcortical structures. This m a y a c c o u n t for v a r i a t i o n in findings a m o n g cases. The presence o f grains in the i n d u s i u m griseum in case SM-80 seems to indicate t h a t the i n d u s i u m griseum receives c o n n e c t i o n s f r o m the overlying cingulate gyrus, a n d previous d a t a indicate t h a t it projects to layer I o f the cingulate cortex 11. Such reciprocal connections p r o v i d e p a t h w a y s , in a d d i t i o n to the direct cinguloseptal c o n n e c t i o n s described above, over which impulses f r o m the a n t e r i o r p a r t o f the cingulate gyrus might affect the firing o f n e u r o n s in septal nuclei.
1 CAJAL, S. RAM6N V, Histologie du Systdme Nerveux de l'Homme et des Vertdbrds, Maloine,
Paris, 1911, pp. 762-823. 2 CLEMENTE,C. D., AND CHASE, M. H., Neurological substrates of aggressive behavior, Ann. Rev. Physiol., 35 (1973) 329-356. 3 COWAN,W. M., GOTTL1EB, D. I., HENDRICKSON, A. E., PRICE, J. L., AND WOOLSEY, T. A., The autoradiographic demonstration of axonal connections in the central nervous system, Brain Research, 37 (1972) 21-51. 4 DOMESICK,V. B., Projections from the cingulate cortex in the rat, Brain Research, 12 (1969) 296-320. 5 ENGLAND,J. M., AND MILLER, R. G., The statistical analysis of autoradiographs. 11. Theoretical aspects including methods for optimal allocation of measurement effort, J. Microsc., 92 (1970) 167-177. 6 UELDMAN, S., Neurophysiological mechanisms modifying afferent hypothalamohippocampal conduction, Exp. Neurol., 5 (1962) 269-291. 7 HENDRICKSON,A. E., MOE, L., AND NOBLE, B., Staining for autoradiography of the central nervous system, Stain Technol., 47 (1972) 283-290. 8 KNOOK,H. L., The Fibre Connections of the Forebrain, Davis, Philadelphia, Pa., 1966, pp. 81-92. 9 KRIEG, W. J. S., Connections of the Cerebral Cortex, Brain Books, Evanston, Ilk, 1963, pp. 219-245. 10 NIEMER, W. T., POWELL, E. W., AND GOODFELLOW, E. F., The subcortex and hypothalamic after-discharge in the cat, Electroenceph. clin. Neurophysiol., 12 (1960) 345-358. 11 POWELL, E. W., Septal efferents revealed by axonal degeneration in the rat, Exp. Neurol., 8 (1963) 406422. 12 POWELL, E. W., Corticolimbic interrelations revealed by evoked potential and degeneration techniques, Exp. Neurol., l0 (1964) 463474. 13 POWEEL,E. W., Limbic projections to the thalamus, Exp. Brain Res., 17 (1973) 394-401. 14 POWELL, E. W., AKAGI, K., AND HATTON, J. B., Subcortical projections of the cingulate gyrus in cat, J. Hirnforsch., 15 (1974) 269-278. 15 POWELL, E. W., AND HINES, G., The limbic system: an interface, Behav. Biol., 12(1974) 149-164. 16 SIMMONS, H. J., AND POWELL, E. W., A quantitative analysis of septothalamic projections in the squirrel monkey, Anat. Rec., 166 (1970) 378.
316 17 SIMMONS, H. J., AND POWELL, E. W., Septomammillary projections in the squirrel monkey.
Acta anat. (Basel), 82 (1972) 159 178. 18 STEPHAN, H., AND ANDY, O. J., Cytoarchitectonics of the septal nuclei in Old World monkeys (Cercopithecus and Colobus), J. Hh'nfbrsch., 7 (1964) 1-23. 19 THURSTON, J. M., AND JO~'TES, D. L., Stains compatible with dipping radioautography, Stai~ Technol., 38 (1963) 231-235. 20 YAKOVLEV, P. 1., AND LOCKE, S., Limbic nuclei of thalamus and connections of limbic cortex. III. Corticocortical connections of the anterior cingulate gyrus, the cingulum, and the subcallosal bundle in monkey, Arch. Neurol. (Chic.), 5 (1961) 364-400.
