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Stria Terminalis and Related Structures SANDRO BURG1

AND

V E R E N A M. B U C H E R

The Neurobiological Collection (Prof. W. R. Hess) and the Institute of’ Physiology, University of Zurich, Zurich (Switzerland)

INTRODUCTION A N D MATERIAL

Although the study of the stria terminalis (stria cornea or tlenia semicircularis) has received a good deal of attention, from fish to man, many unanswered questions persist with regard to the various components of this fibre tract and the direction of conduction of the impulses conveyed. This preliminary report of our studies on the tract and a few related structures, although far from complete, may throw light on some points that are still obscure. Our observations were made on Marchi impregnated sections from the amygdala, forebrain and diencephalon of cats, out of material supplied by the Neurobiological Collection of Prof. Hess and the Department of Physiology of Zurich (experiments of Dr. R. Hunsperger). Using the Hess or modified Hess-Wyss technique, fine electrodes were introduced into the brain of the animal in order to study stimulation effects, after which a discrete lesion was placed in one of the territories stimulated. After a survival period of 9 to 21 days, the animals were sacrificed, and the brains were serially sectioned in sagittal, horizontal or frontal planes and stained with the Marchi method. RESULTS

( A ) Stria terminalis ( I ) Thejrst or commissural bundle of the stria terminalis-to use the terminology of Johnston (1922/23)-was interrupted at the level of the amygdala in a few experiments, but was never seen degenerating (although the fibres could be seen to arise from, or to run toward, the nucleus of the lateral olfactory tract). Local degeneration was observed, however, after damage at the level of the anterior commissure. Ban and Omukai (1959) in the rabbit, using Marchi stain, also saw a few fibres of this bundle crossing over the midline within the commissure, but disappearing soon afterwards, an observation also made by Nauta (1958), using silver stain. (2) The second, hypothalamic or preoptic bundle, after damage to the amygdala, could only be followed to the bed of the stria at the level of the anterior commissure in our material. The fibres are rather fine and appear to correspond to the olfactory projection tract of Cajal. References p . 1681169

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Fox (1943) in the cat and Ban and Omukai (1959) in the rabbit followed this bundle to the hypothalamus. Adey and Meyer (1952) in the monkey, using the Glees technique, also traced the fibres to the hypothalamus, in particular to the ventromedial nucleus of both sides. (3) The third or infracommissural component was never seen degenerating in our material and, as far as we know, has never been identified in experimental material. ( 4 ) The fourth or supracommissural bundle conveys medium-sized fibres. They were seen degenerating after damage to the amygdala, and accompany the fine elements of the second component. They could only be followed to the bed at the level of the anterior commissure, and damage at this level only produced local degeneration. Our observations appear to confirm those of Fox, Adey and Meyer, and Ban and Omukai. (5) Regarding the jifth component, the so-called stria medullaris bundle of the stria terminalis, two observations may possibly be brought into relation with this fibre tract: (a) A needlz track passing lateral to the fornix in the region behind the stria terminalis bed and rostral to the thalamus, produces the degeneration of rather thick fibres that swing dorsomedially over the anterodorsal thalamic nucleus, enter the stria medullaris, and run back maintaining a dorsolateral position (Fig. 1). The fibres run

Fig. 1 . (Exp. 3, section 574). Sagittal section through stria rnedullaris (sm) showing degenerating fibres of the crossed component on side damaged (Hb, habenula; hp, fasc. habenulo-peduncularis; Th, thalamus), x20.

over the lateral habenular nucleus, and then cross over the midline in the rostral portion of the habenular commissure, run forward in the opposite stria medullaris (Fig. 2), again maintaining a dorsolateral position, and finally proceed downwards,

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lateral to the fornix, remaining close to blood vessels visible in the region. Most of the fibres appear to distribute to the region of the anterior perforate space (Biirgi, 1954, Biirgi and Bucher, 1960: ‘commissural bundle’ of stria medullaris).

Fig. 2. (Exp. 3, section 490). Sagittal section through lateral habenular nucleus (Hb), showing degenerating fibres of crossed component (‘cornmissural bundle’, cb) of stria medullaris (srn) on .side opposite lesion (hp, fasc. habenulo-peduncularis; Th, thalamus), x 20.

The tract has been described by Wallenberg in the rabbit (1902) and fitchet (1926), a fact that has often escaped notice. The question remains open whether this fascicle belongs to the stria terminalis, or whether it is homologous with a bundle described by Gamble (1956), in the tortoise, as leaving the lateral olfactory tract, entering the stria medullaris and crossing in the habenular commissure. Finally, it might correspond to the commissura telencephali superior of primitive forms. Marburg (1944) in human material saw fibres of the stria terminalis joining the stria medullaris by way of the anterodorsal thalamus, but could not trace them beyond the habenula. (b) The damage producing degeneration of the crossed component of the stria medullaris, produced simultaneous degeneration of an amygdalopetal component of fhe striu terminalis, briefly mentioned in a former paper (Burgi and Bucher, 1955). The fibres, not numerous and medium-sized, run along the caudodorsal end of the stria terminalis bed, remaining close to the reticular nucleus of the thalamus. They remain applied to the thalamus until, finally, they swing down, behind the internal capsule, to the amygdala. The cells of origin of this tract remain obscure (Figs. 3 and 4). Nauta (1958) in the cat (silver stain) observed arnygdalopetal fibres in the stria terminalis after damage to the lateral preoptic area. Ban and Omukai in the rabbit References p. 1681169

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Fig. 3. (Exp. 45, section 102). Sagittal section through stria terminalis bed at level of thalamus (Th), showing degenerating amygdalopetal fibres (st (ap)) (Nc, caudate nucleus; Ret, reticular nucleus of thalamus), x 20.

(Marchi stain), after interruptioii of the stria below the lenticular nucleus, followed such fibres to the piriform region. ( B j Otherjibre tracts, elrerent with regard to the amygdala (6) After damage to the amygdala, fine fibres can be seen in the stria terminalis bed at this level, running medially, applied to the surface of the optic tract. They abruptly swing rostrally (Fig. 5), and distribute to the region medial to the nucleus of the lateral olfactory tract, i.e., the anterior perforate space, or, possibly, farther ahead. In this connection, we should mention that Johnston (1922/23) described one branch of his fifth bundle as arising in the region towwds which our niedially running fibres are directed. The thought naturally arises that our fibres may represent an ending of the amygdalopetal component. In no experiment, however, were we able to trace the amygdalopetal component beyond the amygdaloid complex. ( 7 j The longitudinal association bundle Ba of Fox is an efferent tract that runs medially after damage to the amygdala. The bundle is rather compact at first and filled with dust, but splits up gradually as it passes beneath the pallidurn, rostra1 to the nucleus entopeduncularis. At this level the Marchi impregnation ceases. Some fibres appear to be distributed to the region of the anterior perforate space, a region to which the crossed component of the stria medullaris also proceeds. (8) The capsular system of the amygdala appears to correspond to what Johnston called the longitudinal amygdalo-piriform association bundle, which corresponds only in part to the longitudinal association bundle Ba of Fox. After damage to the amyg-

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dala, the capsule of the lateral nucleus is filled with dust and fine degenerated fibres, that can be followed in a lateral and caudal direction toward the piriform region and, possibly, the hippocampus.

Fig. 4. (Exp. 3, section 820). Sagittal section through subiculum, showing degenerating amygdalopetal fibres of stria terminalis (st (ap)) descending to amygdala (ci, capsula interna; fi, fimbria; to, tractus opticus), x 20.

Ban and Omukai followed amygdalopetal fibres to the piriforin region, perhaps by way of the capsular system. (9) Finally, it should be mentioned that damage to the amygdala was often followed by the degeneration of jine mid scnttereii jibres that ran toward the region of the diagonal band of Broca, i.e., its lateral portion. CONCLUSIONS AND SUMMARY

The stria terminalis, besides conveying amygdalofugal fibres, conveys less well-known amygdalopetal fibres. The stria medullaris carries a crossed component that is possibly in some waj connected with the stria terminalis and may correspond to the conimissura References p . 1681169

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Fig. 5. (Exp. 55, section 151). Sagittal section through region medial to nucleus of lateral olfactory tract. Fine fibres that run medially (rned.f) rostra1 to optic tract (to), here seen swinging to the region of the anterior perforate space (Ent, nucleus entopeduncularis; Pal, pallidum), x 20.

telencephali superior of more primitive forms. In addition to the amygdalofugal components of the stria terminalis, there are at least three groups of fibres that convey efferent, medially running fibres with regard to the amygdala : (1) our medially running fibres traced to the region of the anterior perforate space; ( 2 ) the longitudinal association bundle Ba of Fox; and (3) the fine and scattered fibres followed to the region of the diagonal band of Broca. Efferent too with regard to the amygdaloid complex, but laterally and caudally running, are the elements seen degenerating in the capsular system of the amygdala. The origin of all these fibre tracts remains obscure and requires further investigation. REFERENCES

ADEY,W. R.,ANDMEYER, M., (1952); Hippocampal and hypothalamic connexions of the temporal lobe in the monkey. Brain, 75, 358-384. BAN,T., AND OMUKAI, F., (1959); Experimental studies on the fiber connections of the arnygdaloid nuclei in the rabbit. J. comp. Neurol., 113, 245-279. BURGI,S., (1954); Ueber zwei Anteile der Stria medullaris. Arch. Psychiat. Nervenkr., 192,301-310. BURGI,S., UND BUCHER, V. M., (1955); Ueber einige rhinencephale Verbindungen des Zwischen- und Mittelhirns. Dfsch. 2. Nervenheilk., 174, 89-106. BURGI,S. UND BUCHER, V. M., (1960); Markhaltige Faserverbindungen im Hirnstamrn der Katze. Monographien aus dem Gesamtgebiet der Neurologie und Psychiafrie, Heft 81. Berlin. Gottingen. Heidelberg, Springer-Verlag. Fox, C. A., (1943); The stria terminalis, longitudinal association bundle and precommissural fornix fibers in the cat. J. comp. Neurol., 79, 277-295. GAMBLE, H. J., (1956); An experimental study of the secondary olfactory connexions in Testudo graeca. J. Anaf. (Lond.), 90, 15-29.

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JOHNSTON, J. B., (1922/23); Further contributions to the study of the evolution of the forebrain. J . comp. Neurol., 35, 337481. MARBURG, O., (1944); The structure and fiber connections of the human habenula. J . comp. Neurol., 80, 211-233. NAUTA,W. J. C., (1958); Hippccampal projections and related neural pathways to the mid-brain in the cat. Brain, 81, 319-340. A., (1902); Das basale Riechbiindel des Kaninchens. Anat. Anz., 20, 175-187. WALLENBERG, A., (1926); Beitrage zur Kenntnis des Iltisgehirns. Z . Anat. Entwick1.-Ges., 79,352-365. WALLENBERG,