An HRP study of hypothalamo‐cerebellar and cerebello‐hypothalamic connections in squirrel monkey (saimiri sciureus)

Abstract

This study describes the distribution of labeled hypothalamic neurons in squirrel monkey following pressure injections of horseradish peroxidase (HRP) into cerebellar cortex and the pattern of labeling in the cerebellar nuclei subsequent to iontophoretic injections localized in the hypothalamus. Two types of HRP (HRP and a wheat germ agglutinin conjugate, HRP-WGA) were used as tracers; tetramethylbenzidine was the chromogen. Retrogradely filled neurons were found in lateral (LHAr) and posterior (PHAr) hypothalamic areas, and in the lateral mammillary (LMNu) and supramammillary (SMNu) nuclei following injections into ansiform and paramedian lobules and into the paraflocculus. Labeled cells were occasionally seen in the medial mammillary nucleus (parafloccular cases) and among fascicles of the mammillothalamic tract (all posterior lobe cases) immediately above the medial nucleus. After injections into the anterior lobe, labelling was again found in the LHAr, PHAr, LMNu, and SMNu. In addition, retrogradely filled cells were present in ventromedial, dorsomedial, and dorsal hypothalamic nuclei and in the dorsal hypothalamic area. Labeled cells were occasionally found among fascicles of the fornix along its intrahypothalamic course. In general, labeling extends into slightly more rostral hypothalamic levels in anterior lobe cases when compared to posterior lobe experiments. We interpret these data as indicating that some hypothalamic neurons project directly to the cerebellar cortex (i.e., hypothalamo-cerebellar fibers); this projection is bilateral with an ipsilateral preponderance. In experiments with injections of HRP-WGA into the cerebellar nuclei, anterogradely filled axons were traced into the contralateral PHAr and LHAr; this was suggestive of a direct cerebello-hypothalamic projection. Following iontophoretic injections localized in the LHAr and the medial mammillary nucleus, labeling was seen in the medial (NM), posterior interposed (NIP), and lateral (NL) cerebellar nuclei; this is essentially a contralateral projection. Retrogradely labeled cells were found in the rostral and ventral NM, the ventral and dorsocaudal NL, and diffusely throughout the NIP. On the basis of the known distribution of cerebello-thalamic fibers and other criteria, these labeled cells are representative of a true cerebello-hypothalamic projection. It is suggested that the cerebellum, through these pathways, may have a relatively direct influence on visceral centers in the brainstem and spinal cord.

Functional grouping and cortical–subcortical interactions in emotion: A meta-analysis of neuroimaging studies

“…Conversely, CB damage often leads to emotion dysregulation, characterized by fluctuations between flattened affect and inappropriate social behaviors (Schmahmann and Sherman, 1998) reminiscent of social and emotional deficits with OFC damage. The CB is connected with specific prefrontal regions in topographically mapped reciprocal circuits Strick, 1994, 2000) and with "limbic" regions, including the Hy (Haines and Dietrichs, 1984), OFC, dmPFC, portions of IFG, and inferior frontal convexity (BA 46/12) (Middleton and Strick, 2001). Cerebellar efferents to these areas pass largely through DM in the thalamus, which we also find is consistently activated in human emotion.…”

The Role of the Cerebellum in Unconscious and Conscious Processing of Emotions: A Review

“…These mechanisms are controlled by complex neuronal networks in which the cerebellum functions, as reported in the previous sections [26,57,60,61,115].…”

“…Thus, in the emotional domain, measuring cerebellar function with regards to state estimation and its ability to process and predict sequential events allows one to compare different states, integrating internal and external events at the unconscious and conscious levels. This is allowed by the cerebellar integrated functioning in the complex neural networks that subserve the unconscious and conscious components of the emotional domain [56][57][58][59][60][61][62][63][64][65].…”

“…In particular, it receives afferent nerves from the medial mammillary bodies [57,58] and multi-modal deep layers of the superior colliculus in addition to being connected bi-directionally to the hypothalamus [59] and the brainstem areas (ventral tegmental area, periaqueductal gray, and locus ceruleus) that are related to the limbic and paralimbic regions [60]. The cerebellum receives information from the paralimbic cortices in the cingulate gyrus [61] via their projections to the pontine nuclei [62,63].…”

Schizophrenia and cognitive dysmetria: a positron-emission tomography study of dysfunctional prefrontal-thalamic-cerebellar circuitry.

“…The anterior temporal regions and mammillary bodies are known to be key components of memory networks, based on PET and lesion studies (8)(9)(10)(11)(12)(13)(14)(25)(26)(27)(28)(29)(30). Further, the mammillary bodies have a direct reciprocal connectivity with the cerebellum (31). The lenticular nuclei also have established anatomic connectivity with the cerebellum and are a crucial amplifier for its role in higher cognitive functions (32).…”