Labeled Latex Microspheres Research Articles

Do the same hypothalamic neurons project to both amygdala and cerebellum?

The possibility that individual hypothalamic cells project to the cerebellum (as hypothalamo-cerebellar fibers) and amygdala (hypothalamo-amygdaloid fibers) by means of collaterals, was studied by means of retrograde transport of Fast blue (FB) and Rhodamine (R)-labeled latex microspheres. Our findings show that R-labeled latex microspheres are well-suited for double labeling studies in combination with other retrograde fluorescent tracers. Neurons retrogradely labeled from cerebellum or from amygdala were found in the same hypothalamic nuclei, and they were often located adjacent to each other. Some additional animals were injected with a third tracer, Nuclear yellow (NY), in the spinal cord. The spinal projecting neurons were located in the same regions as cells retrogradely labeled with FB and R. All projections are bilateral with an ipsilateral preponderance. Some neurons were double-labeled, and all combinations of double-labeling (FB/R, NY/R, FB/NY) were found. This shows that some hypothalamic neurons may project to both cerebellum and amygdala, some to the spinal cord and amygdala, and others to cerebellum and the spinal cord. No triple labeled neurons were observed.

Divergent axon collaterals to cerebellum and amygdala from neurons in the parabrachial nucleus, the nucleus locus coeruleus and some adjacent nuclei. A fluorescent double labelling study using rhodamine labelled latex microspheres and fast blue as retrograde tracers.

After injections in the cat of Rhodamine labelled latex microspheres in the amygdala and of Fast Blue in the cerebellum neurons labelled with one of these tracers as well as some double labelled neurons were found in the parabrachial nucleus, the nucleus locus coeruleus and some adjacent nuclei (the nucleus subcoeruleus and the pontine tegmental reticular formation). All double labelled cells were located on the ipsilateral side. A few double labelled neurons were also found bilaterally in the dorsal raphe nucleus. It therefore appears that a certain number of cerebellar projecting neurons in these brain stem nuclei by means of divergent axon collaterals also project to the amygdala. The location of the double labelled cells found in this study suggests that at least some of the neurons are catecholaminergic. The findings are related to previous reports on the distribution of catecholaminergic neurons and on the amygdaloid and cerebellar projections from this part of the brain stem, and the possible involvement of these connections in cerebellar non-somatic responses are discussed. Some comments are made concerning the use of fluorescent latex microspheres for double labelling studies in combination with another fluorescent tracer.