efferent projections from the lateral hypothalamus in the guinea pig: an autoradiographic study

Brain Research Bulletin, Vol. 11, pp. 335-347, 1983. 0 Ankho International Inc. Printed in the U.S.A.

Efferent Projections from the Lateral Hypothalamus in the Guinea Pig:

An Autoradiographi~ Study

CHING LIANG SHEN

~n~tjt~te O~Neu~osc~ence, National Yang Ming Medical College Taipei, Taiwan, Re~~~li~ of China

Received 25 October 1982

SHEN, C. L. @f&rent projections from the lateral hypothalamus in rhe guinea pig: An autoradiugraph~c study. BRAIN RES BULL ll(3) 335-347, 1~3.-Auto~io~phy was employed to investigate the efferent projections from the lateral hy~th~~us in the guinea pig. Lateral hypothalamic axons were traced along the medial forebrain bundle in both ascending and descending directions. Anteriorly, the label was traced to the lateral preoptic area, diagonal band of Broca, and septal nuclei. Posterior projections included the ventral tegmental area of Tsai, central gray matter and the reticular formation throughout the brain stem. Laterally, the lateral hypothalamic efferents were found in the stria terminalis, amygdala and globus pallidus. Dorsally, the lateral hypothalamic axons projected to the midline nuclei of the thalamus and bilaterally to the lateral habenular nuclei. Projections to the medial hypothalamus included a labeled fiber bundle to the internal layer of the median eminence and to the posterior lobe of the pituitary gland. Labeled fibers and diffise labei were also found in some areas contralateral to the injection site.

Lateral hypothalamus Efferents Guinea pig Autoradiographic study

THE lateral h~th~~us is continuous rostrally with the lateral preoptic area and caudally with the mesencephalic tegmentum. It lies lateral to the medial hypothalamus. The border between the lateral and medial hypothalamus corre- sponds to the sag&al plane through which the fornix de- scends through the hypothalamus. A major part of the lateral hypothalamus is made up of the ascending and descending fibers of the medial forebrain bundle. Unlike the medial hy~th~~us, the lateral hy~th~amus is composed of medium sized to large sized cells which are diffusely ar- ranged.

It has been suggested that the mediation of autonomic control functions of the medial hypothalamus are relayed by neurons located in the lateral hypothalamus, paraventricular nucleus and retrochi~matic area 129, 38, 391. A number of behavioral mechanisms also are effected via the lateral hypothalamus [41. Recently, neural connections between the lateral hypothalamus and autonomic centers in the brain stem and spinal cord have been shown principally for the rat [29, 38, 391 by using the retrograde axonal transport technqiue.

The lateral hypothalamus contains the medial forebrain bundle. Therefore, the classical neuroanatomi~~ techniques using lesions are not able to reveal the efferents from the lateral hypothalamus in isolation. The fibers-of-passage in the lateral hypothalamus, however, are not a barrier for the autoradiographic study of the efferent projections from the lateral hypothalamus. Several investigators have employed this convenient technqiue and have revealed the axonal projections from the lateral hy~th~arni~ neurons in the rat 16,301 and cat [41]. In the present study, the lateral

hypothetic projections were studied in the guinea pig These results compared favorably with that found in the rat [WOI.

METHOD

Adult female guinea pigs weighing 400-600 g were used. Ten guinea pigs received an injection of tritiated proline lim- ited to the lateral hy~th~amus (Table I). The animals were anesthetized with sodium pentobarbital (32 mglkg) and placed in the stereotaxic instrument as described by Luparello ef al. [21]. A dental drill was positioned at the following range of coordinates (9.8 to 8.0 mm anterior to the interaural axis, I.5 mm lateral to the longitudinal cerebral fissure), and a hole was drilled through the skull. A 1 ~1 Hamilton syringe was used for injections at 9.0 to 11.0 mm below the brain surface. Fifteen minutes after positioning of the needle, 0.4-1.0 ~1 of tritiated proline (16 &!i/@) was slowly injected in lateral hypothalamus over approximately one hour using a microdrive. The needle was then left in place for fifteen minutes before slowly removing it. After a survival period of 65 to 120 hours, the animals were killed with an overdose of sodium ~ntob~it~ and perfused with 10% formalin. The brains were stereotaxically blocked and removed with the spinal cord from the skull and vertebral canal. The tissues were dehydrated in a series of ethanol of increasing grades, cleared in benzene and embedded in paraffin. Ten micron-thick serial sections were prepared in the coronal or sag&al planes. Every tifih section in the forebrain and every tenth section in the brain stem and spinal cord were retained. Before autoradiographic treatment, one

335

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anterior nucleus, thafamus anterior medial nucleus, thalamus medial nucleus, amygdala arcuate nucleus anterior nucleus, thaiamus central gray caudatoputamen diagonal band of Broca do& medial nucleus, hypothalamus anterior hypothalamic area lateral hypothaIamic area posterior hypothalamus lateral habenula lateral septum medial habenula lateral mammillary nucleus medial mammi~a~ nucleus medial septum nucleus of spinal tract of trigeminal tract parataenial nucleus periventricular nucleus, thaiamus lateral preoptic area medial preoptic area paraventricular nucleus, thalamus pontine tegmental nucleus paraventricular nucleus, hypoth~amus

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reticular nucleus, thalamus rhomboideal nucleus, thalamus reticular nucleus, thalamus reunien nucleus, thalamus substantia nigra supraoptic nucleus subth~amic nucleus supramammillary nucleus ventromedial nucleus ventral nucleus, thalamus ventral tegmental area of Tsai anterior commisure anterior pituitary corpus callosum cerebral peduncle decussation of superior cerebellar peduncle fomix fasciculus retroflexus globus pallidus inferior colliculus lateral ventricle median eminence medial lemniscus medial longitudinal fasciculus mammiIIothalamic tract optic chiasm optic tract pyramid posterior commissure posterior pituitary superior colliculus stria medullaris stria terminalis zona incerta third ventricle fourth ventricle

in every three sections were stained with Luxol Fast Blue for mvelinated fibers.

The autor~io~~~c techniques described by Hen- drickson and Edwards 1151 were followed. The slides were coated with Kodak NTB-2 and exposed for 4-8 weeks. The emulsion was then developed in D-19 and fixed in rapid fixer, stained with cresyl violet and mounted following general his- tological procedures.

The autoradiograms were systematically examined under the light microscope. Using an X-Y plotter, drawings were made from representative sections of each brain, and the labeled projections were plotted. The site of injection was defined as the area in which cell bodies were labeled more heavily than the surrounding neuropil. Background level of silver grams were assessed individually in each slide by ex- amining the cerebellum as well as the emulsion coat outside of the section. In representative sections, the number of silver grains per unit area on an eye-piece grid was deter- mined and noted directly on the drawing obtained with the X-Y plotter. This quantitative data helped to con&m the area and limits of diffuse, perhaps terminal, labelling.

RESULTS

There were ten brains which received the tritiated proline injection restricted to the lateral hypothalamus (Table 1).

TABLE 1 DATA FOR LATERAL HYPOTHALAMIC INJECTIONS

Animal No. Volume (~1) Survival time fhr)

H 20 0.6 88 H 26 0.8 96 H 27 1.0 93 H 30 1.0 91 H 37 1.0 71 H 106 0.6 91 H IO7 0.6 72 H 116 0.6 91 H 117 0.4 114 H 125 0.4 120

The injection sites were located either in the central, dorsal or ventral parts of the lateral hypothalamus (Figs. 1, 2, 3, 4, 5,6). In spite of small differences in the location of the injection sites in the lateral hypothalamus, the projection pattern of the lateral hy~th~amic neurons showed no significant difference. The efferents described for the lateral hypothal-

EFFERENTS OF LATERAL HYPOTHALAMUS 337

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FIG. 1. Drawings of representative coronal sections showing the distribution of labeled projections following injection of tritiated proline into the lateral hypothalamus. H 117. Large dots indicate labeled fibers, small dots indicate diffuse label.

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FIG. 2. The projections labeled following an injection confined to the lateral hy~thalamus. H30.


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FIG. 3. The projections labeled in the H 106 with an injection centered in the lateral hypothalamus in a parasagittal plane. E is contralateral to the injection site.

340 SHEN

FIG. 4. The injection sites and labeled projections in H 27 (A), H 1% (B), H 26 (C), and H 107 (D).

amus in this report will be detailed in the data from the brain of HI 1’7 (Fig. l), and support and variations will be contrib- uted from the other experiments.

From the injection site, efferent projections from the lateral hypothalamus projected in all directions. Anteriorly, the lateral hypothalamus projections followed the medial forebrain bundle. These fibers passed the lateral preoptic area. Some of these fibers terminated in the vertical and horizontal limbs of the nuclei of the diagonal band of Broca. Other fibers turned dorsally into the nucleus of the diagonal band of Broca (Fig. 7) and terminated in the medial and lateral septal nuclei (Fig. 8). Other fibers continued anteriorly to terminate in the nucleus accumbens. The prefrontal cortex was not kept for examination. The contralateral nucleus of the diagonal band of Broca, especially the genu, was also labeled by diffuse siiver grains. Diffuse grains, presumably terminals, also appeared to label the anterior hypotha~mic area, medial preoptic area, suprachiasmatic nucleus and magnocellular preoptic area.

Caudal projections along the medial forebrain bundle reached the ventral tegmental area of Tsai (Fig. 9). Here some fibers turned laterally and were distributed in the zona incerta and subthalamic region (Figs. 9, 21). From the zona incerta labeled fibers and terminals appeared in the capsule of the reticular nucleus of the thalamus (Fig. 21). In midbrain, light and diffuse fibers turned in a dorsomedial direc- tion from the medial forebrain bundle to reach and run within the central gray matter (Fig. 10) as far as the medulla oblon- gata at the level rostral to the hypoglossal nucleus. However, a sign~c~t portion of fibers went through the ventral tegmentum of the brain stem, and terminated in the reticular

formation. These caudal projections from the lateral hypothalamus could be traced as far as the lower medulla with diffuse terminal label in the area medial to the nucleus of the spinal tract of the trigeminal nerve. No spinal projection from the lateral hypothalamus was found.

Laterally, the lateral hypothalamic efferents reached several areas. Many short labeled fibers were seen traversing toward globus pallidus and distributed in this area. Labeled fibers from the lateral hypoth~amus projected into the stria terminalis (Figs. 11, l&21). In the dorsal traverse of the stria terminalis the label was heaviest on its ventral edge (Fig. 1 l), while it the ventral part of the stria terminalis where it ap- proaches the amygdala, the label was heaviest on its dorsal and medial aspects (Fig, 12). The third group of fibers was seen in the supraoptic decussation and terminated in the anterior and medial amygdala (Figs. 13,21). In the amygdala, the diffuse silver grains were heavier in the capsule of the nuclei than within the nuclei.

The lateral hypothalamus sent fibers dorsomedially to the septum via the preoptic area. These labeled fibers traversed the medial preoptic area to sweep around the anterior commissure (Fig. 14). Therefore, the septum received its lateral hy~thala~c afferents from two pathways, (1) directly from the lateral hypotha~mus via the medial preoptic area, and (2) via the medial forebrain bundle and the diagonal band of Broca. In the septal region, the dorsal lateral septum and the central part of the medial septum were the two areas labeled heaviest (Fig. 14). The septofimbrial nucleus was also labeled (Fig. 14). Contralateral lateral and medial septal nuclei were also labeled by fibers crossing the midline structure of the septum.

EFFERENTS OF LATERAL HY~THALAMUS 341

PLATE 1

FIG. 5. This photomicrograph of injection in the lateral hypothalamus autoradiogrm exposed 8 weeks. I-I 117. Scale bar 500 pm.

FIG. 6. This photomicrograph of injection site in the lateral hypothalamus in the parasagittal plane. I-I 107. Scale bar 500 ,um.

FIG. 7. The diagonal band of Broca is labeled in this darkfield photomicrograph. Scale bar 250 pm.

FIG. 8. The septal area is labeled in this picture. Central part of the medial septal area is labeled heavily. Scale bar 250 Frn.

FIG. 9. This darkfield micrograph shows the medial forebrain bundle at the level of the caudal most diencephalon and is labeled heavily. Zona incerta and subthalamic region (upper left in the picture) are labeled. Scale bar 250 pm.

FIG. IO. Ipsilateral central gray is labeled heavier than the contralateral one (darkfield). Scale bar 250 ,um.

342 SHEN

PLATE 2

1 I. St&t terminalis is labeled. Scale bar 250 iLm.

12. The stria terminalis which lies close to the amygdala is labeled on its medial and dorsal regions ~dark~e~d). Scale Lm.

FIG.

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13. This photomicrograph shows labeled fibers from the injection site in the lateral hypothalamus projected via ioptic decussation that terminate in the medial amygdala. Da&field. Scale bar 250 pm.

14. This darkfield photomicrograph shows the silver grams in the septai area. The central part of the medial septum orsolateral part of the lateral septum are two heavily labeled areas. Darkfield. Scale bar 250 pm.

15. Midline thalamic nuclei are labeled in this darkfield photomicrograph. The upper hatf is the side ipsifateral to d hypothalamic injection. Scale bar 250 pm.

FIG. Scale

16. Ipsilateral habenular complex and contralateral lateral habenular nucleus are labeled in this darkdeld microgr; bar 250 Wm.

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EFFERENTS OF LATERAL HYPOTHALAMUS

17. A labeled fiber bundle is distributed throughout the internal layer of the median eminence in this dark field graph. The ventromedial and arcuate nuclei are also labeled above the background level in this pciture. Scale bar 250

FIG. micra pm. FIG.

FIG. while

FIG.

18. This brightfield micrograph shows labeled fibers in the retrochiasmatic area. Scale bar 14 pm.

19. This photomicrograph shows the posterior lobe of the pituitary gland labeled by reduced silver grains (left the intermediate lobe is free from silver distribution (right half). Brightfield. Scale bar 14 pm.

20. This darktield micrograph shows the posterior lobe of the pituitary gland labeled heavily. Scale bar 250 pm.

PLATE 3

Fibers from the lateral hypothalamus traveling via the dorsal hypothalamus reached the midline thalamic nuclei, including the parataenial, paraventricular, reuniens, rhom- boid, and paraventricular nuclei (Fig. 15). These dorsomedial projections were located in the periventricular fiber system. This fiber system of the lateral hypothalamic compo- nent also projected bilaterally to the lateral habenular nuclei (Fig. 16). The ipsilateral medial habenular nucleus was labeled lightly (Fig. 16).

The proximity of the medial hypothalamus to the injection sites makes interpretation of the terminal labeling difftcult. In the medial hypothalamus, i.e., ventromedial, dorsomedial, and arcuate nuclei, there were no labeled fibers arising from the lateral hypothalamic injection, but silver grain den- sity in these medial hypothalamic nuclei was higher than the background level. However, a bundle of labeled fibers was seen projecting ventromedially from the injection sites (Figs. 17, 18) to reach the ventral surface of the hypothalamus and

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the retrochiasmatic area (Fig. 18). Many of these joined the median eminence. The internal layer of the median eminence was bilaterally labeled by the silver grains (Fig. 17). The stalk and the posterior pituitary gland was labeled moder- ately (Figs. 19,20). Other fibers crossed the midline through the retrochiasmatic area to reach the contralateral lateral hypothalamus. Some contralateral projections from the injection site were also seen via the supramammillary decussation to reach the lateral hypothalamus (Fig. 21). These contralateral labeled fibers passed anteriorly to the lateral septum by way of the diagonal band of Broca.

In brains H106 and H107 the tritiated proline injections were in the lateral hypothalamus and these were cut parasagittally (Figs. 3, 4D, 6). The labeled fibers were seen easily in the medial forebrain bundle. Anterior to the injection site, the labeled fibers were traced to the lateral preoptic area and medial septum. Dorsally, labeled fibers were in the stria terminalis and stria medullaris. From the stria ter-

SHEN

FIG. 21. A darkfield pbotomicrograph of transported label in the diencephalon. Scale bar 500 pm.

minalis, the labeled fibers were traced to the amygdala. The labeled fibers in the stria medullaris were followed to the lateral habenula. Caudal to the injection site, the labeled fibers in the medial forebrain bundle were seen in the ventral tegmentum of the midbrain. Then some fibers turned caudally and reached the central gray of the midbrain and pans. A few labeled fibers in the medial forebrain bundle continued to project caudaliy and distributed in the tegmentum of the rostra1 pons.

DISCUSSION

The lateral hypothalamus is a site of passage for the major pathways between the telencephalon and brainstem. There- fore, a lesion or horseradish peroxidase injection in the lateral hypothal~us is likely to interrupt or label pathways anatorhically and functionally unrelated to the cell group or groups being investigated by the lesion or horseradish peroxidase techniques. The tritiated proline injected directly into the lateral hypothalamus is taken up by neuronal somata, incorporated into protein and transported to the terminals. Axons, in contrast to somata, lack the necessary protein synthetic apparatus for the incorporation of radioactively labeled amino acid into transportable protein [15]. There- fore, autoradiography is the best technique to study the efferent projections from ‘the lateral hypothalamus.

In the present study, besides intrahypothalamic projections, lateral hypothalamic neurons of the guinea pig project to many areas including septal nuclei, midline thalamic nuclei, habenular nuclei. amygdaloid complex, central gray

matter and reticular formation of the brain stem, median eminence and posterior lobe of the pituitary gland.

Up to the present time, the rat and the cat are the only two species in which the lateral hypothalamic efferents have been studied autoradiographically. In the rat, Saper rt al. [30] reported that the lateral hypothalamic axons contribute ascending and descending fibers to the medial forebrain bundle and also project medially to the medial hypoth~amic nuclei. Rostrally, the lateral hypothalamic terminations ex- tend from the medial septal-diagonal band region through the lateral preoptic area to the mammillary complex and ventral tegmental area caudally. The parataenial and paraventricular nuclei of the thalamus, lateral habenular nucleus and central gray in the rat all receive these lateral hypothalamic projections. In the same species by using same technique, Berk and Finkelstein [6] reported a wider dist~bution of lateral hypothalamic axonal projections than that reported by Saper et al. [30]. Their findings suggest inclusion of the cingulum bundle, medial cortex and amygdala as a part of lateral hypothalamic projection in the rat. Besides cingulum and medial cortex, these projections from the lateral hypothalamic area of the rat are also found in the present study. However, in the guinea pig, there are some projections from the lateral hypothalamus to the median eminence, posterior lobe of the pituitary, and globus pallidus. In the cat, Troiano and Siegel [41] found lateral hypothalamic neurons project to most of the areas or nuclei as with the rat and guinea pig. But projections from the lateral hypothalamus in the cat to the midline thalamus have not been identified.

Lateral hypothalamic projections to the medial hypothal-

EFFERENTS OF LATERAL HYPOTHALAMUS

amus are found in this study. These medial projections of the lateral hypothalamus were also found in the rat [6,30]. How- ever, Troiano and Siegel [41] were unable to identify with any degree of confidence the presence of grains within the medial hypothalamic zone which could be interpreted as labeled axon terminals. Eager et at. 1121 reported success in demonstrating degeneration throughout the tuberal region of the hypothalamus following a lateral hypothalamic lesion. Using a chemical lesion in the lateral hypothalamus, Arees and Mayer [3] found degenerated nerve fibers in the ventromedial and arcuate nuclei of the -medial hypothalamus. Golgi ------- studies [24,40] revelaed (1) the long dendrites of me&&e- brain bundle neurons extended almost the entire width of the medial forebrain bundle from the ventral surface of the hypothalamus to the dorsal edge of the lateral hypothalamus, and medially reached the medial hypothalamus and medial preoptic area, (2) there was overlapping between the dendritic fields of the adjacent lateral hypothalamic cells and those of the medial hypothalamus, i.e., medial preoptic area, anterior hypoth~amic area, ventromedial nucleus, and (3) the axons of the neurons localized in the medial forebrain bundle proceeded into the medial forebrain bundle itself. Collaterals of these may also have reached the medial hypothalamus.

The lateral hypothalamus receives afferents from the medial hypothalamus, including the medial preoptic area [2, 9, 10, 3 1, 32,361. Efferent tibers of the medial hypothalamus terminate on the neurons of the lateral hypothal~us, which in turn project to other regions of the central nervous system. It has been suggested that the autonomic control functions of neurons in the medial hypothalamus may be relayed in part by the neurons of the lateral hypothalamus [29, 38, 391. Cells in the central gray and reticular formation of the midbrain and pons responded to stimulation of the lateral hy~thalamus [5,35]. This result is similar to the present study in that the central gray and reticular formation of the brain stem are labeled by reduced silver grains. In the rat, Saper et al. [29] injected horseradish peroxidase into the intermediolateral cell column in the spinal cord and found the horseradish peroxidase positive perikarya in the hypothalamus, including the lateral hypothalamus. In the autoradiographic study of rat lateral hypothalamic efferents, Saper et al. [30] developed sections after exposure period of 2 to 3 weeks. They could not find this spinal projection. In the present study, the survival and exposure times have been prolonged to 120 hours and 8 weeks respectively, but silver grains in the spinat cord still have not been obtained. This negative finding of the lateral hypothalamic projection to the spinal cord is also reported by studies in the rat and cat [6,18]. However, the radioactive material in the axonal transport has been identified only l-3 mm per day in mam- malian central nervous system [14]. Thus the bulk of radioisotope would not reach the spinal cord even at the longest survival times (120 hours) used in this study. This negative result obtained by the present autoradiographic study does not indicate the absence of direct neural connection to the spinal cord from the lateral hypothalamus. The positive connection remains to be established.

The silver grains are found in the globus pallidus in this autoradiographic study. Oomura et al. [25] also found that the lateral hypoth~amus and globus pallidus have a recip rocai relationship in their electrophysiological study.

The amygdala was labeled after the lateral hypothalamus received a tritiated proline injection in this study. Berk and Finelstein [6] found the amygdala was labeled after injecting of tritiated leucine into the lateral hypothalamus of the rat.

They pointed out the amygdala receives lateral hypothalamic fibers via the stria terminalis and from the ventral amyg- dalofugal pathways. Similar result was found in the guinea pig in the present study. Saper et al. 1301 reported the amygdaloid nuclei, especially the medial and central nuclei, were labeled after the tritiated amino acid injection into anterior lateral hypothalamus. But they explained these projections to the amygdala as an incidental involvement of the ventromedial nucleus of the hypothalamus. In the silver impreg- nation study in the rat. Wolf and Sutin 1431 found that all lateral hypothalamic lesions caused degeneration in the supraoptic commissure. Mehler [23] also observed horseradish peroxidase labeled celts in the lateral hy~thalamus after horseradish peroxidase injected into the amygdala in the monkey. In the present study, the amygdala is labeled very clearly via the supraoptic commissure and the injection site is quite far from the ventromedial nucleus.

The lateral habenular nucleus is labeled with reduced silver grains in the guinea pig. This finding confiis the autoradiographic results in rat and cat [30,41], and the horseradish peroxidase reports [16,20]. On the basis of this anatomical evidence, the lateral habenular nucleus could be an important efferent pathway from the lateral hypothalamus. Since the lateral habenular nucleus, in turn, sends its axons to the midbrain raphe nuclei and ventral tegmental region [ 17,271.

The internal lamina of the median eminence is labeled in the present study. In the rat, Saper et al. found the same result to occur after the tritiated amino acid injected into the tuberal lateral hypothalamus [301. However, they suggested that it was due to the spread of the label to the retrochiasmatic part of the supraoptic nucleus. This is not true in the present study because the injection site is far removed from the main and diffuse supraoptic nuciei (for location of these cell bodies see [33,34]).

It has been shown that most of the axons in the median eminence are of intrahypothalamic origin [22, 40, 421. How- ever, numerous data show that many extrahypothalamic brain regions also project directly to the median eminence [8, 13, 373. The present study found silver grains dist~buted in the internal layer of the median eminence. No evidence showed the neurons in the lateral hypothalamus to be pep- tidergic in nature. Most of the extrahypothalamic axons of the median eminence are of an aminergic character. Immunohistochemical techniques demonstrated that dopamine-containing fibers and serotonin-cont~ning fibers were located mainly in the external layer of the median eminence [8,13], and that most noradrenaline-cont~ning fibers terminated in the internal layer of the median eminence 1371. The existance of the lateral hypothalamic termination on the median eminence was also supported by the observa- tion that the transection of the lateral hypothalamic area re- sulted in degeneration axons in the median eminence [ 1,1 l]. However, the degenerated axons were located in the lateral part of the external layer.

In the present study, the lateral hypothalamic terminals are found on the posterior lobe of the pituitary gland. Horse- radish peroxidase injection into the cerebral and extracere- bra1 blood in rat [7] could not be found in neurons in the lateral hy~th~~us. Kelly and Swanson 1191 injected horseradish peroxidase into the posterior lobe of the pituitary gland of adult albino rat and found scattered retrogradely labeled neurons in many areas, including the perifomical nuclei. Strangely, in one of Swanson’s work [30], concerning the rat, labeling of the posterior lobe could not be found even

34fi

though the tritiated amino acid was injected into the anterior, tuberal and posterior lateral hypothalamus. The injection site in the present study involves the area lateral and dorsal to the fomix, thus including the perifornical nucleus. Using Gomori’s staining, Peterson [26] found the perifomical nucleus (he named anterior and posterior fornical nuclei) to be one of the magnoceflular neurosecretory centers in the rat hypothaIamus. Rhodes et al. 1281 used the immunohistochemical technqiue have also confirmed that the fomical nucleus contains oxytocin or vasopressin. This evidence allows the author to suggest that the neurons in the lateral

SHEN

hypothalamus, especially those located around the fornix. may have a neurosecretory function on the posterior lobe of the pituitary gland.

ACKNOWLEDGEMENTS

This study was supported by a grant from the National Science Council of the Repubtic of China (NS~70-~12-B010-~1~ and by the Tjing-Ling Medical Foundation in 1982-1983. The author wishes to thank Dr. C. H. Anderson. Department of Anatomy, University of Illinois at Chicago, for his critical comments on this manuscript.

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efferent projections from the lateral hypothalamus in the guinea pig: an autoradiographic study

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