Brain Research, 146 (1978) 205-220 © Elsevier/North-Holland Biomedical Press

205

Research Reports

MESENCEPHALIC AND DIENCEPHALIC AFFERENTS TO THE SUPERIOR COLLICULUS AND PERIAQUEDUCTAL GRAY SUBSTANCE DEMONSTRATED BY R E T R O G R A D E AXONAL TRANSPORT OF HORSERADISH PEROXIDASE IN THE CAT

IRENA GROFOVA, OLE PETTER OTTERSEN and ERIC RINV1K Anatomical Institute, University of Oslo, Oslo 1 (Norway)

(Accepted August 31st, 1977)

SUMMARY The mesencephalic and diencephalic afferent connections to the superior colliculus and the central gray substance in the cat were examined by means of the retrograde transport of horseradish peroxidase (HRP). After deep collicular injections numerous labeled cells were consistently found in the parabigeminal nucleus, the mesencephalic reticular formation, substantia nigra pars reticulata, the nucleus of posterior commissure, the pretectal area, zona incerta, and the ventral nucleus of the lateral geniculate body. A smaller number of cells was found in the inferior colliculus, the nucleus of the lateral lemniscus, the central gray substance, nucleus reticularis thalami, the anterior hypothalamic area, and, in some cases, in the contralateral superior colliculus, Forel's field, and the ventromedial hypothalamic nucleus. Only the parabigeminal nucleus and the pretectal area showed labeled cells following injections in the superficial layers of the superior colliculus. In the cats submitted to injections in the central gray substance, labeled cells were consistently found in the contralateral superior colliculus, the mesencephalic reticular formation, substantia nigra pars reticulata, zona incerta and various hypothalamic areas, especially the ventromedial nucleus. In some cases, HRP-positive cells were seen in the nucleus of posterior commissure, the pretectal area, Forel's field, and nucleus reticularis thalami. A large injection in the mediodorsal part of the caudal mesencephalic reticular formation, which included the superior colliculus and the central gray substance, resulted in numerous labeled cells in nucleus reticularis thalami. The findings are discussed with respect to the suggested functional division of the superior colliculus into deep and superficial layers. Furthermore, the possible implications of labeled cells in zona incerta and the reticular thalamic nucleus are briefly discussed.

206 INTRODUCTION The optic tectum and superior colliculus have in recent years attracted renewed interest from investigators working on the various aspects of visually guided behaviour (for references, see ref. 24). In particular, these studies have suggested that the deep layers of the superior colliculus may be a zone of convergence of fiber systems primarily concerned with conveying non-visual impulses z2,63. The periaqueductal gray substance, on the other hand, has for many years been considered a central nervous relay for nociceptive stimuli (for references, see ref. 42). This possible role of the central gray substance has been recently emphasized by reports on the action of opiates in this region of the brain a5,39,51. In the course of an investigation on the nigrofugal projections 57, retrogradely labeled cells were observed in several mesencephalic and diencephalic nuclei following injections of horseradish peroxidase (HRP) involving the superior colliculus and the periaqueductal gray substance. Some of these labeled cells were located to cell groups which, to our knowledge, are not known as sources of afferents to the tectum or mesencephalic central gray substance. It was, therefore, deemed of interest to undertake a more detailed investigation on these possible connections by means of the H R P technique. MATERIALS AND METHODS In 13 cats weighing between 2.5 and 5 kg single or multiple injections of' H R P were made unilaterally and, in some cases, bilaterally in the superior colliculus and in the central gray substance and reticular formation of the mesencephalon. The injections were performed under Mebumal anaesthesia by means of a 1/~1 Hamilton syringe mounted on a stereotaxic holder, using either a vertical or an oblique approach. Serva peroxidase was diluted to a 25 or 50 ~o solution of which 0.05-0.2/~1 was injected during 5-20 min. In one animal only (12078) Sigma type VI peroxidase was used. The cannula was left in place for at least 5 min at the end of the injection. After 2-3 days survival the cats were deeply anesthetized and perfused through the heart by a mixture of 0 . 4 ~ paraformaldehyde and 1.25 ~ glutaraldehyde in a 0.1 M phosphate buffer solution at p H 7.4. The brains were removed and left in the fixative in a cold room overnight, and then transferred to a phosphate buffered 30 sucrose solution. Blocks comprising diencephalon, mesencephalon, lower brain stem, and, in some cases, the occipital lobe were cut serially in a transverse plane on the freezing microtome at 50-60/~m. From every group of 5 sections two were treated with 3,3-diaminobenzidine according to the method of G r a h a m and Karnovsky 16 and mounted on slides. One of the sections was stained with cresyl violet, the other was left unstained. The sections were examined both in a bright and dark field for the identification of H R P labeled neurons. The exact location and number of labeled cells were determined using a pantograph, and the borders of cell groups were superimposed on the plots by means of a camera lucida. The location of the cannula tip and the extent of the reaction product at the injection site were carefully mapped in each case.

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Mesencephalic and diencephalic afferents to the superior colliculus and periaqueductal gray substance demonstrated by retrograde axonal transport of horseradish peroxidase in the cat.

Brain Research, 146 (1978) 205-220 © Elsevier/North-Holland Biomedical Press 205 Research Reports MESENCEPHALIC AND DIENCEPHALIC AFFERENTS TO THE S...
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