Direct projections from the medial vestibular nucleus to the posterior hypothalamic area in the monkey (Macaca fuscata)

ELSEVIER

Neuroscience Letters 219 (1996) 199-202

NEUROSCI$C[ I[IT[RS

Direct projections from the medial vestibular nucleus to the posterior hypothalamic area in the monkey (Macaca fuscata) Toshimichi Matsuyama a'*, Tetsuro Kayahara a, Junichi Nomura b, Katsuma Nakano a ~Department of Anatomy, Faculty of Medicine, Mie University Tsu, Mie 514, Japan bDepartment of Psychiatry, Faculty of Medicine, Mie University Tsu, Mie 514, Japan Received 7 October 1996; revised version received 25 October 1996; accepted 26 October 1996

Abstract

Direct projections from the medial vestibular nucleus to the posterior hypothalamic area was found in the macaque monkey by the anterograde and the retrograde tract-tracing methods. After injection of biotinylated dextran amine (BDA) into the ventrolateral part of the medial vestibular nucleus, anterogradely labeled axon terminals were seen bilaterally in the posterior hypothalamic area. After injection of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the posterior hypothalamic area, retrogradely labeled neuronal cell bodies were observed bilaterally in the ventral part of the medial vestibular nucleus with a contralateral predominance. Keywords: Hypothalamus; Vestibular nuclei; Motion sickness; Monkey; Biotinylated dextran amine; Wheat germ agglutinin-conjugated horseradish peroxidase

Disorders of the vestibular functions, such as motion sickness, are often accompanied by autonomic and emotional symptoms [3,4]. In fact, the vestibular nuclei are connected with the limbic regions including the hypothalamus through the nucleus of the solitary tract [2,11] and the parabrachial nuclei [1]. Direct projections from the vestibular nuclei to the limbic regions, however, have not been reported. In the present study, direct projections from the medial vestibular nucleus (MVN) to the posterior hypothalamic area (PHA) were found in the macaque monkey by the anterograde and retrograde tract-tracing methods. Eight Japanese monkeys (Macaca fuscata) were used for the present study. The animals were housed and cared for recording to the regulations of the Committee for Animal Research of Mie University. For surgical procedures, the monkeys were anesthetized by an intramuscular injection of 7 - 8 mg/kg o f ketamine hydrochloride, followed by intraperitoneal injection of 25 mg/kg of sodium pentobarbital. After occipital craniotomy, a part of the cerebellar vermis was removed by suction in five * Corresponding author. Tel.: +81 592 315002; fax: +81 592 315219.

monkeys. A total of 1.0-1.5 /xl of 5% B D A solution in 0.9% saline was pressure injected into 2 - 3 points in a distinct vestibular nucleus with a Picospritzer (PV800, W o r l d Precision Instruments); into the M V N in two monkeys, into the inferior vestibular nucleus (IVN) in two monkeys, and into the superior vestibular nuclei (SVN) in one monkey. Following a survival time of 1 0 - 1 4 days, the monkeys were deeply re-anesthetized and perfused transcardially with 1000 ml of 0.9% saline, with 3 0 0 0 - 7 0 0 0 ml of 0.1 M phosphate buffer (PB; pH 7.4) containing 8% formalin and 0.15% glutaraldehyde, and then with 500 ml of the PB containing 10% sucrose. The brains were removed, placed into a cold solution of 30% sucrose in the PB at 4°C for 2 days, and then cut serially 50 /xm thick into frontal sections on a freezing microtome. The sections were processed to visualize B D A for brightand dark-field microscopy [7]. The other three monkeys were pressure injected with a volume of 0.1 /zl of a 2% wheat germ agglutinin-conjugated horseradish peroxidase ( W G A - H R P ) solution in 0.05 M Tris buffer stereotaxically into the posterior hypothalamic area. After 2 days, the monkeys were perfused with 1000 ml of 0.9% saline, 3 0 0 0 - 7 0 0 0 ml of 8% formalin in the PB, and then with

0304-3940/96/$12.00 © 1996 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(96) 13206-7

200

T. Matsuyama el al. / Neurosciem'e Letters 219 (1996) 199 202

Fig. 1. Photomicrograph of a coronal section through a BDA rejection site in the ventral part of the medial vestibular nucleus. The section is counterstained with Cresyl violet. 4V, Fourth ventricle: IVN, inferior vestibular nucleus; MVN, medial vestibular nucleus; NTS, nucleus of the solitary tract; XII, hypoglossal nucleus. Scale bar, 500 ,am. 500 ml of the PB containing 10% sucrose. The brain sections were prepared as described above, and then processed for visualization of W G A - H R P with tetram e t h y l b e n z i d i n e [6]. R e t r o g r a d e l y labeled neuronal cell bodies w e r e plotted by c a m e r a lucida. In one o f the two m o n k e y s injected with B D A into the M V N , the injection site was c e n t e r e d on the ventral part of the M V N with a little i n v o l v e m e n t of the lateralmost part

o f the I V N (Fig. 1). The adjacent structures, such as the nucleus o f the solitary tract and the dorsal nucleus of the vagus nerve, were not i n v o l v e d within the injection site. S o m e labeled fibers arising from the injection site ran rostrally and laterally to terminate in the parabrachial nuclear c o m p l e x . Other fibers which ascended bilaterally through the medial longitudinal fascicles sent axon terminals to the abducens nucleus, the o c u l o m o t o r nuclear c o m p l e x and the interstitial nucleus of Cajal, bilaterally with a slight ipsilateral d o m i n a n c e . S o m e of these fibers further ascended through the region ventrolateral to the rostral interstitial nucleus to terminate bilaterally in the zona incerta (ZI). A few o f the labeled fibers were traced m o r e rostrally to the level of the m a m m i l l o t h a l a m i c tract; they were observed to terminate bilaterally in the posterior h y p o t h a l a m i c area ( P H A ) (Fig. 2). No labeled fibers were found in the brain regions rostral to the P H A . In the m o n key injected with B D A into the S V N , a few labeled fibers were traced to the ZI, but no labeled axon terminals were found in the P H A . In the m o n k e y s injected with B D A into the IVN, no labeled fibers were found in the brain regions rostral to the rostral interstitial nucleus o f Cajal. In one of the three m o n k e y s injected with W G A - H R P , the injection site was successfully centered on the P H A ; the injection site i n v o l v e d the P H A region w h e r e labeled axon terminals were o b s e r v e d in the m o n k e y injected with B D A into the M V N ( c o m p a r e Fig. 3A with Fig. 2A). M a n y

Fig. 2. (A) Photomicrograph of a Nissl-stained section through the PHA. The rectangles indicate the areas where the photomicrographs in (B) and (C) have been taken in the adjacent section. (B,C) BDA-labeled fibers and axon terminals in the PHA. Arrowheads in (B) indicate terminal boutons. Triangles in (C) point to varicosities of an axon of passage. 3V, Third ventricle; IC, internal capsule; trot, mammillothalamic tract; VApc, nucleus ventralis anterior pars parvocellularis; ZI, zona incerta. Scale bar, (A) 1 mm; (B,C) 50 ,am.

T. Matsuyama et al. / Neuroscience Letters 219 (1996) 199-202

201

NTS

A ~

A Co mX

MVN

B

G

Fig. 3. (A) A diagram of a WGA-HRP injection site (blackened area) in the PHA. (B-H) Camera lucida chartings showing anterogradely labeled axon terminals (small dots) and retrogradely labeled neuronal cell bodies (large dots) in the lower brainstem. Each large dot represents one neuron. 3V, Third ventricle; CG, central gray; Co, cochlear nucleus; Cue, external cuneate nucleus; f, forni x; g, genu of the facial nerve; LC, locus coeruleus; LVN, lateral vestibular nucleus; mX, dorsal motor nucleus of the vagus nerve; PB1, lateral parabrachial nucleus; PBm, medial parabrachial nucleus; Ph, nucleus prepositus hypoglossi; R, thalamic reticular nucleus; scp, superior cerebellar peduncle; SVN, superior vestibular nucleus; VA, nucleus ventralis anterior; y, group y of the vestibular nuclear complex. Other abbreviations are as in Figs. 1 and 2. anterogradely labeled axon terminals and retrogradely labeled neuronal cell bodies were observed in the periaqueductal gray, the dorsal raphe nucleus, the locus coeruleus, the parabrachial nuclear complex, and the nucleus of the solitary tract, bilaterally with an ipsilateral predominance (Fig. 3 B - H . ) . A small number of retrogradely labeled neuronal cell bodies were found in the MVN, bilaterally with a contralateral predominance (Fig. 3 C - H ) . These labeled vestibular neurons were seen throughout the rostrocaudal extent of the MVN, mainly in the ventral portion of the MVN. No labeled neurons, however, were observed in the other vestibular nuclei. In one monkey injected with W G A - H R P in the region medial to the PHA, few labeled cell bodies were seen in the MVN. In the remaining one monkey, the site of W G A - H R P injection involved a large hypothalamic area rostral to the PHA. In this monkey no retrogradely labeled neurons were observed in the vestibular nuclei. The present results indicate that some neurons in the ventral part of the M V N send projection fibers bilaterally

to the restricted region of the PHA. This particular region of the P H A contains large, densely stained, heterogeneous cells, and is cytoarchitectonically different from the ZI which is composed of small, less densely stained cells; this P H A region appears to correspond to the dorsal part of the P H A described by Veazey et al. [9]. Direct projections from the vestibular nuclei to the nucleus of the solitary tract [2,11] and the parabrachial nucleus [1] have been reported, and the existence of the disynaptic vestibulo-parabrachial-hypothalamic pathway has been suggested [1,5,8]. The present study further indicates the existence of direct vestibulo-hypothalamic pathway to the PHA. The P H A is connected with the basal forebrain regions, such as the hypothalamic areas, the amygdala and the septal regions, as well as with the limbic cortical regions including the perirhinal, the insular, the prelimbic and the infralimbic cortices [10]. Thus, the direct projections from the M V N to the P H A may constitute a pathway through which the vestibular inputs exert influences upon autonomic and limbic functions.

202

T. Matsuyama et al. / Neuroscience Letters 219 (1996) 199-202

T h i s w o r k h a s b e e n s u p p o r t e d in p a r t b y G r a n t s - i n - A i d for Scientific Research (C) 03670022

and 08680814

from

the Ministry of Education, Science, Sports and Culture of

[6]

Japan. [1] Balaban, C.D., Vestibular nucleus projections to the parabrachial nucleus in rabbits: implications for vestibular influences on the autonomic nervous system, Exp. Brain. Res., 108 (1996) 36738I. [2] Balaban, C.D. and Beryozkin, G., Vestibular nucleus projections to nucleus tractus solitarius and the dorsal motor nucleus of the vagus nerve: potential substrates for vestibulo-autonomic interactions, Exp. Brain Res., 98 (1994) 200 212. I31 Brandt, T., Physiological and psychophysiological vertigo. In R.W. Baloh and G.M. Halmagyi (Eds.), Disorders of the Vestibular System, Oxford University Press, New York. 1996, pp. 496 5(/8. [4] Jacob, R.G., Furman, J.M. and Balaban, C.D., Psychiatric aspects of vestibular disorders. In R.W. Baloh and G.M. Halmagyi (Eds.), Disorders of the Vestibular System, Oxford University Press, New York, 1996, pp. 509-528. 15] Fulwiler, C.E. and Saper, C.B., Subnuclear organization of the

[7]

[81 [9]

[10]

[ I 1]

efferent connections of the parabrachial nucleus in the rat, Brain Res., 319 (1984) 229 259. Mesulam, M.-M., Tetramethyl benzidine for horseradish peroxidase neurohistochemistry: a non-carcinogenic blue reaction product with superior sensitivity fur visualizing neural affcrents and efferents, J. Histochem. Cytochem., 26 (1978) 106 117. Reiner, A., Veenman, C.L. and Honig, M.G., Anterograde tracing using biotinylated dextran amine, Neurosci. Protocols, 93-050-14 (1993) 1-14. Saper, C.B. and Loewy, A.D., Efferent connections of the parabrachial nucleus in the rat, Brain Res., 197 (1980) 291-317. Veazey, R.B., Amaral, D.G. and Cowan, W.M., The morphology and connections of the posterior hypothalamus in the cynomolgus monkey (Macaca fascicularis), I. Cytoarchitectonic organization, J. Comp. Neurol., 207 (1982) 114-134. Vertes, R.P., Crane, A.M., Colom, L.V. and Bland, B.H., Ascending projections of the posterior nucleus of the hypothalamus: PHAL analysis in the rat, J. Comp. Neurol., 359 (1995) 90 116. Yates, B.J., Grelot, L., Kerman, I.A., Balaban. C.D., Jakus, J. and Miller, A.D., Organization of vestibular inputs to nucleus tractus solitarius and adjacent structures in cat brain stem, Am. J. Physiol., 267 (1994) R974-983.