Some anatomical observations on the projections from the hypothalamus to brainstem and spinal cord: an HRP and autoradiographic tracing study in the cat.

The hypothalamus is closely involved in a wide variety of behavioral, autonomic, visceral, and endocrine functions. To find out which descending pathways are involved in these functions, we investigated them by horseradish peroxidase (HRP) and autoradiographic tracing techniques. HRP injections at various levels of the spinal cord resulted in a nearly uniform distribution of HRP-labeled neurons in most areas of the hypothalamus except for the anterior part. After HRP injections in the raphe magnus (NRM) and adjoining tegmentum the distribution of labeled neurons was again uniform, but many were found in the anterior hypothalamus as well. Injections of 3H-leucine in the hypothalamus demonstrated that: The anterior hypothalamic area sent many fibers through the medial forebrain bundle (MFB) to terminate in the ventral tegmental area of Tsai (VTA), the rostral raphe nuclei, the nucleus Edinger-Westphal, the dorsal part of the substantia nigra, the periaqueductal gray (PAG), and the interpeduncular nuclei. Further caudally a lateral fiber stream (mainly derived from the lateral parts of the anterior hypothalamic area) distributed fibers to the parabrachial nuclei, nucleus subcoeruleus, locus coeruleus, the micturition-coordinating region, the caudal brainstem lateral tegmentum, and the solitary and dorsal vagal nucleus. Furthermore, a medial fiber stream (mainly derived from the medial parts of the anterior hypothalamic area) distributed fibers to the superior central and dorsal raphe nucleus and to the NRM, nucleus raphe pallidus (NRP), and adjoining tegmentum. The medial and posterior hypothalamic area including the paraventricular hypothalamic nucleus (PVN) sent fibers to approximately the same mesencephalic structures as the anterior hypothalamic area. Further caudally two different fiber bundles were observed. A medial stream distributed labeled fibers to the NRM, rostral NRP, the upper thoracic intermediolateral cell group, and spinal lamina X. A second and well-defined fiber stream, probably derived from the PVN, distributed many fibers to specific parts of the lateral tegmental field, to the solitary and dorsal vagal nuclei, and, in the spinal cord, to lamina I and X, to the thoracolumbar and sacral intermediolateral cell column, and to the nucleus of Onuf. The lateral hypothalamic area sent many labeled fibers to the lateral part of the brainstem and many terminated in the caudal brainstem lateral tegmentum, including the parabrachial nuclei, locus coeruleus, nucleus subcoeruleus, and the solitary and dorsal vagal nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Topographic organization of projections from the amygdala to the hypothalamus of the rat.

Afferent fibers from the amygdala to subdivisions of lateral, ventromedial and dorsomedial hypothalamic nuclei were investigated in rat by retrograde transport of horseradish peroxidase. Small (intranuclear size) peroxidase deposits were placed in hypothalamic nuclei by iontophoresis of a tracer solution containing poly-L-alpha-ornithine which greatly limited diffusion. The medial, central and amygdalo-hippocampal nuclei of the amygdala were found to be the major donors of amygdaloid afferent fibers to the hypothalamus, but there was also substantial labeling of somata in cortical, basomedial, basolateral and lateral amygdaloid nuclei and the intra-amygdaloid bed nucleus of the stria terminalis. No fibers projected from the posterior cortical nucleus of the amygdala to the hypothalamus. Most amygdaloid projections to the lateral hypothalamic area originated in the anterior half of the amygdala, while projections to the ventromedial hypothalamic nucleus arose along the entire length of the amygdala except the posterior cortical nucleus. The amygdalo-hippocampal area projects to the medial hypothalamus. Other amygdaloid nuclei project to both the medial and lateral hypothalamic nuclei. These topographic organizations of amygdaloid afferent fibers to various subdivisions of the hypothalamic nuclei are discussed and compared with other anatomical studies on these connections.

[Description of a reciprocal connection between the zona incerta and the posterior nucleus of the hypothalamus. Anatomic study in rats]. / Description d'une connexion réciproque entre la zona incerta et le noyau postérieur du thalamus. Etude anatomique chez le rat.

This study describes a large reciprocal connection between zona incerta and posterior nucleus of the thalamus in the rat. The incerto-thalamic contingent of fibers arises essentially from pars caudalis of the ZI and is directed towards the caudal three quarters of the PT. The thalamo-incertal bundle originates from the central portion of the PT and is mainly directed to pars caudalis of the ZI.

Temporal pattern of HRP spread from an iontophoretic deposit site and description of a new HRP-gel implant method.

In the course of examining afferents to ventromedial hypothalamic (VMH) neurons using horseradish peroxidase (HRP), we needed to know how close to an iontophoretic deposit site neurons could be proved to be retrogradely labeled. In evaluating cells near but clearly outside HRP deposit sites visualized after a 24-hour survival period, for example, neurons which had been filled with HRP by somal or dendritic uptake could not be treated as retrogradely labeled and thus would not add to studies of intrahypothalamic connections. Rats were given standardized iontophoretic applications of HRP into VMH (continuous positive current 0.25 mu amp for 1 minute) and sacrificed after 5 or 15 minutes, 1, 4, 8, 12, or 24 hours in order to examine the pattern of HRP spread. The chromogen was tetramethylbenzidine. The volume of the application site visualized at 24 hours was less than 10% of maximum site size, which occurred at 1 hour. Since the cells located within the maximal spread boundary are candidates for nonretrograde labeling, HRP data on local connections obtained even from small iontophoretic deposits must be evaluated in the light of the demonstrated expansion and subsequent contraction of the application site. These results may also hold implications for the precision with which distant connections can be examined using the HRP retrograde method, as sites that appear discrete when visualized after 24-hour survival may have overlapped at shorter times post-iontophoresis. Incorporation of retrograde tracers into polyacrylamide gels provides an effective alternative to pressure injection or iontophoresis of aqueous tracer solutions. We describe a method for filling micropipettes with HRP-polyacrylamide gel. The pipettes are then implanted into brain sites to provide a confined pool of HRP. With postimplantation survival of 24 hour or longer, this method produces sites comparable in size to iontophoretic sites examined at 24 hours and results in improved retrograde labeling. Some results obtained with this method concerning the afferent connections of the dorsomedial hypothalamus are described.