Cerebellar interposed nucleus lesions suppress lymphocyte function in rats

Connections of the Dentate Nucleus with the Amygdala: Experimental Rat and Human 3-Tesla Tractography Study

Background: The role of the cerebellum in motor function is well recognized. However, its role in higher nervous system activities such as cognition, emotion, endocrine, and autonomic activities is less known. The present study aims to show direct dento-amygdala projections using a biotinylated dextran amine (BDA) tracer in rats and 3-tesla (T) high-resolution diffusion tensor imaging (DTI)-based tractography in humans. Materials and Methods: The BDA tracer was pressure injected into the dentate nucleus of the cerebellum of Wistar albino rats. Labeled cells and axons were documented. High-resolution 3-T tractography data were obtained from the Human Connectome Project database. Dento-amygdala tracts were analyzed using diffusion spectrum imaging (DSI) Studio software. Results: The experimental study showed bilateral projections between the dentate nucleus and the central and basal nuclei and ipsilateral projections between lateral nuclei of the amygdala. The fibers from the dentate nucleus reached the amygdala through the superior cerebellar peduncle (SCP), and the contralateral fibers crossed in the decussation of SCP at the midbrain. The dento-amygdala results of the experimental study corresponded with the 3-T tractography findings on humans. Additionally, DTI findings showed that most of the dentate fibers passed through the hypothalamus before reaching the amygdala, and the amygdalae of the two sides are connected through the anterior commissure. Discussion: The 3-T DTI data of adult humans showed both direct dento-amygdala and indirect dento-hypothalamo-amygdala projections. Thus, this may indicate cerebellar contribution in modulation of emotional and autonomic functions. Furthermore, this can explain the emotional and cognitive deficits that occur in patients with cerebellar or SCP damage. Impact statement The present study showed direct dento-amygdala connections in the rat brain and human brain, which may provide evidence for cerebellar contribution in modulation of emotional and autonomic functions.

Fiber dissection and 3-tesla diffusion tensor tractography of the superior cerebellar peduncle in the human brain: emphasize on the cerebello-hypthalamic fibers

Experimental studies in various species using tract-tracing techniques showed clear evidence of the presence of cerebello-hypothalamic projections. However, these connections were not clearly described in humans. In the present study we aimed to describe the direct cerebello-hypothalamic connections within the superior cerebellar peduncle (SCP) using fiber dissection techniques on cadaveric brains and diffusion tensor tractography (DTI) in healthy adults. Fiber dissection was performed in a stepwise manner from lateral to medial on 6 cerebral hemispheres. The gray matter was decorticate and fiber tracts were revealed. The SCP was exposed and the fibers were traced distally using wooden spatulas. The MRI examinations were performed in seven cases using 3-tesla 3T unit. The direct cerebello-hyothalamic pathways were exposed using high-spatial-resolution DTI. The present study using both fiber dissection and DTI in adult human showed direct cerebello-hypothalamic fibers within the SCP. The SCP fibers course anterolateral to the cerebral aqueduct reaching the level of the red nucleus of the midbrain. The majority of the fibers crosses over and reached the contralateral diencephalic structures and some of these fibers terminated at the contralateral anterior hypothalamic area. Some of the uncrossed SCP fibers reached the ipsilateral diencephalic structures and terminated at the ipsilateral posterior hypothalamic area. We further reported the close relationship of the SCP with the MCP, lateral lemniscus, red nucleus and substantia nigra. In the DTI evaluations of the SCP we exposed unilateral left cerebello-hypothalamic fibers in five cases and bilateral cerebello-hypothalamic fibers in two cases. The present study demonstrates the direct cerebello-hypothalamic connections within the SCP for the first time using fiber dissection and DTI technique in the human brain. The detailed knowledge of the cerebello-hypothalamic fibers can outline the unexplained deficit that may occur during regional surgery.

Is the Cerebellum Involved in the Nervous Control of the Immune System Function?

BACKGROUND

According to the views of psychoneuroendocrinoimmunology, many interactions exist between nervous, endocrine and immune system the purpose of which is to achieve adaptive measures restoring an internal equilibrium (homeostasis) following stress conditions. The center where these interactions converge is the hypothalamus. This is a center of the autonomic nervous system that controls the visceral systems, including the immune system, through both the nervous and neuroendocrine mechanisms. The nervous mechanisms are based on nervous circuits that bidirectionally connect hypothalamic neurons and neurons of the sympathetic and parasympathetic system; the neuroendocrine mechanisms are based on the release by neurosecretory hypothalamic neurons of hormones that target the endocrine cells and on the feedback effects of the hormones secreted by these endocrine cells on the same hypothalamic neurons. Moreover, the hypothalamus is an important subcortical center of the limbic system that controls through nervous and neuroendocrine mechanisms the areas of the cerebral cortex where the psychic functions controlling mood, emotions, anxiety and instinctive behaviors take place. Accordingly, various studies conducted in the last decades have indicated that hypothalamic diseases may be associated with immune and/or psychic disorders.

OBJECTIVE

Various researches have reported that the hypothalamus is controlled by the cerebellum through a feedback nervous circuit, namely the hypothalamocerebellar circuit, which bi-directionally connects regions of the hypothalamus, including the immunoregulatory ones, and related regions of the cerebellum. An objective of the present review was to analyze the anatomical bases of the nervous and neuroendocrine mechanisms for the control of the immune system and, in particular, of the interaction between hypothalamus and cerebellum to achieve the immunoregulatory function.

CONCLUSION

Since the hypothalamus represents the link through which the immune functions may influence the psychic functions and vice versa, the cerebellum, controlling several regions of the hypothalamus, could be considered as a primary player in the regulation of the multiple functional interactions postulated by psychoneuroendocrinoimmunology.

The Cerebello-Hypothalamic and Hypothalamo-Cerebellar Pathways via Superior and Middle Cerebellar Peduncle in the Rat

The connections between the cerebellum and the hypothalamus have been well documented. However, the specific cerebellar peduncle through which the hypothalamo-cerebellar and cerebello-hypothalamic connections pass has not been demonstrated. The present study aims to define the specific cerebellar peduncle through which connects the cerebellum to specific hypothalamic nuclei. Seventeen male albino rats received 20-50-nl pressure injections of either Fluoro-Gold (FG) or biotinylated dextran amine (BDA) tracer into the superior (SCP), middle (MCP), and inferior (ICP) cerebellar peduncle. Following 7-10 days of survival period, the animals were processed according to the appropriate protocol for the two tracers used. Labeled cells and axons were documented using light or fluorescence microscopy. The present study showed connections between the hypothalamus and the cerebellum via both the SCP and the MCP but not the ICP. The hypothalamo-cerebellar connections via the SCP were from the lateral, dorsomedial, paraventricular, and posterior hypothalamic nuclei, and cerebello-hypothalamic connections were to the preoptic and lateral hypothalamic nuclei. The hypothalamo-cerebellar connections via the MCP were from the lateral, dorsomedial, ventromedial, and mammillary hypothalamic nuclei; and cerebello-hypothalamic connections were to the posterior, arcuate, and ventromedial hypothalamic nuclei. The hypothlamo-cerebellar connections were denser compared to the cerebello-hypothlamic connections via both the SCP and the MCP. The connection between the cerebellum and the hypothalamus was more prominent via the SCP than MCP. Both the hypothlamo-cerebellar and cerebello-hypothalamic connections were bilateral, with ipsilateral preponderance. Reciprocal connections were with the lateral hypothalamic nucleus via the SCP and the ventromedial nucleus via the MCP were observed. Cerebellum takes part in the higher order brain functions via its extensive connections. The knowledge of hypothalamo-cerebellar and cerebello-hypothalamic connections conveyed within the SCP and MCP can be important for the lesions involving the MCP and SCP. These connections can also change the conceptual architecture of the cerebellar circuitry and deepen current understanding.

GABAergic neurons in cerebellar interposed nucleus modulate cellular and humoral immunity via hypothalamic and sympathetic pathways

Our previous work has shown that cerebellar interposed nucleus (IN) modulates immune function. Herein, we reveal mechanism underlying the immunomodulation. Treatment of bilateral cerebellar IN of rats with 3-mercaptopropionic acid (3-MP), a glutamic acid decarboxylase antagonist that reduces γ-aminobutyric acid (GABA) synthesis, enhanced cellular and humoral immune responses to bovine serum albumin, whereas injection of vigabatrin, a GABA-transaminase inhibitor that inhibits GABA degradation, in bilateral cerebellar IN attenuated the immune responses. The 3-MP or vigabatrin administrations in the cerebellar IN decreased or increased hypothalamic GABA content and lymphoid tissues' norepinephrine content, respectively, but did not alter adrenocortical or thyroid hormone levels in serum. In addition, a direct GABAergic projection from cerebellar IN to hypothalamus was found. These findings suggest that GABAergic neurons in cerebellar IN regulate immune system via hypothalamic and sympathetic pathways.

Cerebellar fastigial nuclear glutamatergic neurons regulate immune function via hypothalamic and sympathetic pathways

We previously have shown that cerebellar fastigial nucleus (FN) modulates immune function, but pathways or mechanisms underlying this immunomodulation require clarification. Herein, an anterograde and retrograde tracing of nerve tracts between the cerebellar FN and hypothalamus/thalamus was performed in rats. After demonstrating a direct cerebellar FN-hypothalamic/thalamic glutamatergic projection, 6-diazo-5-oxo-L-norleucine (DON), an inhibitor of glutaminase that catalyzes glutamate synthesis, was injected bilaterally in the cerebellar FN and simultaneously, D,L-threo-β-hydroxyaspartic acid (THA), an inhibitor of glutamate transporters on cell membrane, was bilaterally injected in the lateral hypothalamic area (LHA) or the ventrolateral (VL) thalamic nucleus. DON treatment in the FN alone decreased number of glutamatergic neurons that projected axons to the LHA and also diminished glutamate content in both the hypothalamus and the thalamus. These effects of DON were reduced by combined treatment with THA in the LHA or in the VL. Importantly, DON treatment in the FN alone attenuated percentage and cytotoxicity of natural killer (NK) cells and also lowered percentage and cytokine production of T lymphocytes. These DON-caused immune effects were reduced or abolished by combined treatment with THA in the LHA, but not in the VL. Simultaneously, DON treatment elevated level of norepinephrine (NE) in the spleen and mesenteric lymphoid nodes, and THA treatment in the LHA, rather than in the VL, antagonized the DON-caused NE elevation. These findings suggest that glutamatergic neurons in the cerebellar FN regulate innate and adaptive immune functions and the immunomodulation is conveyed by FN-hypothalamic glutamatergic projections and sympathetic nerves that innervate lymphoid tissues.

Modulation of immune function by glutamatergic neurons in the cerebellar interposed nucleus via hypothalamic and sympathetic pathways

Our recent work has shown that the cerebellar interposed nucleus (IN) contains glutamatergic neurons that send axons directly to the hypothalamus. In the present study, we aimed to demonstrate modulation of cellular and humoral immunity by glutamatergic neurons in the cerebellar IN by means of gene interventions of glutaminase (GLS), an enzyme for glutamate synthesis, and to reveal pathways transmitting the immunomodulation. Injection of GLS-shRNA lentiviral vector into bilateral cerebellar IN downregulated GLS expression in the IN. The silencing of GLS gene in the cerebellar IN decreased interleukin (IL)-2 and interferon (IFN)-γ production, B-cell number, and IgM antibody level in response to antigen bovine serum albumin (BSA). On the contrary, injection of GLS lentiviral vector into bilateral cerebellar IN upregulated GLS expression in the IN. The GLS gene overexpression in the IN caused opposite immune effects to the GLS gene knockdown. Simultaneously, the GLS gene silencing in the cerebellar IN reduced and the GLS overexpression elevated glutamate content in the hypothalamus, but they both did not affect glycine and GABA contents in the hypothalamus. In addition, the immune changes caused by the GLS gene interventions in the IN were accompanied by alteration in norepinephrine content in the spleen and mesenteric lymph nodes but not by changes in adrenocortical and thyroid hormone levels in serum. These findings indicate that glutamatergic neurons in the cerebellar IN regulate cellular and humoral immune responses and suggest that such immunoregulation may be conveyed by cerebellar IN-hypothalamic glutamatergic projections and sympathetic nerves that innervate lymphoid tissues.

γ-Aminobutyric acid-mediated neurotransmission in cerebellar-hypothalamic circuit attenuates gastric mucosal injury induced by ischemia-reperfusion

BACKGROUND

Excessive greater splanchnic nerve (GSN) activation contributes to the progression of gastric ischemia-reperfusion (GI-R) injury. This study was designed to investigate the protective mechanism of cerebellar fastigial nucleus (FN) stimulation against GI-R injury.

METHODS

The GI-R injury model was induced in rats by clamping the celiac artery for 30 min, and then reperfusion for 30 min, 1, 3, 6, or 24 h, respectively.

KEY RESULTS

Microinjection of L-Glu (3, 6, 12 μg) into the FN dose-dependently attenuated GI-R injury and GSN activity. In addition, there was an enhancement of gastric mucosal blood flow in GI-R rats. Pretreatment with the glutamic acid decarboxylase antagonist into the FN, the GABAA receptor antagonist into the lateral hypothalamic area or lesion of superior cerebellar peduncle all reversed the protective effects of the FN stimulation. Furthermore, the FN stimulation reduced the TUNEL-positive gastric mucosal cell and Bax-positive gastric mucosal cell in GI-R rats.

CONCLUSIONS & INFERENCES

These results indicate that the protective effects of the FN stimulation against GI-R injury may be mediated by attenuation of the excessive GSN activation, gastric mucosal cell apoptosis, and Bax expression in GI-R rats.

Cerebellar fastigial nuclear GABAergic projections to the hypothalamus modulate immune function

Our previous work has shown that the cerebellar fastigial nucleus (FN) is involved in modulation of lymphocyte function. Herein, we investigated effect of FN γ-aminobutyric acid (GABA)-ergic projections to the hypothalamus on lymphocytes to understand pathways and mechanisms underlying cerebellar immunomodulation. By injection of Texas red dextran amine (TRDA), an anterograde tracer, into FN, we found that the TRDA-labeled fibers from the FN traveled through the superior cerebellar peduncle (SCP), crossed in decussation of SCP (XSCP), entered the hypothalamus, and primarily terminated in the lateral hypothalamic area (LHA). Further, by injecting Fluoro-Ruby (FR), a retrograde tracer, in LHA, we observed that the FR-stained fibers retrogradely passed through XSCP and reached FN. Among these FR-positive neurons in the FN, there were GABA-immunoreactive cells. We then microinjected vigabatrin, which is an inhibitor of GABA-transaminase (GABA-T) that degrades GABA, bilaterally into FN. The vigabatrin treatment increased both number of GABA-immunoreactive neurons in FN-LHA projections and GABA content in the hypothalamus. Simultaneously, vigabatrin significantly reduced concanavalin A (Con A)-induced lymphocyte proliferation, anti-sheep red blood cell (SRBC) IgM antibody level, and natural killer (NK) cell number and cytotoxicity. In support of these findings, we inhibited GABA synthesis by using 3-mercaptopropionic acid (3-MP), which antagonizes glutamic acid decarboxylase (GAD). We found that the inhibition of GABA synthesis caused changes that were opposite to those when GABA was increased with vigabatrin. These findings show that the cerebellar FN has a direct GABAergic projection to the hypothalamus and that this projection actively participates in modulation of lymphocytes.

Protective effect of chemical stimulation of cerebellar fastigial nucleus on stress gastric mucosal injury in rats

AIMS

We investigated the protective effects of chemical stimulation of cerebellar fastigial nucleus (FN) on stress gastric mucosal injury (SGMI) and its possible neuro-regulatory mechanisms in rats.

MAIN METHODS

Chemical stimulation, electrical stimulation, chemical ablation, electrolytic lesion, and microinjection were used to investigate the effects of FN simulation on SGMI. The model of SGMI was established by restraint and water (21±1°C)-immersion (RWI) for 3h in rats. The gastric mucosal injury index indicated the severity of gastric mucosal injuries.

KEY FINDINGS

We showed that microinjection of L-glutamic acid into the FN or electrical stimulation of the FN markedly attenuated SGMI. Either chemical lesion of the FN or electrical ablation of the decussation of superior cerebellar peduncle (DSCP) obviously aggravated SGMI. The protective effect of FN stimulation on SGMI was reversed after chemical ablation of the lateral hypothalamic area (LHA). The protective effect of FN was prevented by pretreatment with the glutamic acid decarboxylase antagonist, 3-MPA into the FN or GABA(A) receptor antagonist, bicuculline into the LHA. The protective effect of FN was abolished by pretreatment with sympathectomy. The discharge frequency of greater splanchnic nerve (GSN) was decreased and gastric mucosal blood flow (GMBF) was increased after chemical stimulation of FN. These results indicate that the FN participates in regulation of SGMI, and is a specific area in the CNS for exerting protective effects on the SGMI. The DSCP, LHA and peripheral sympathetic nerve may be involved in this process.

SIGNIFICANCE

Our findings might provide a new and improved understanding of the cerebellar function and an effective treatment strategy for stress gastric mucosal injury.

The cerebellum in feeding control: possible function and mechanism

Accumulating anatomical, functional, and behavioral studies reveal that the cerebellum is involved in the regulation of various visceral functions including feeding control. Cerebellar lesions may induce alterations in feeding behavior and decreases in body weight. Although the exact mechanisms underlying the cerebellar regulation of food intake is still unclear, a series of studies have demonstrated that there are neural pathways directly and/or indirectly connecting the cerebellum with several important centers for feeding control, such as the hypothalamus. Electrophysiological data suggest that via the direct cerebellohypothalamic projections, the cerebellar outputs may reach, converge, and be integrated with some critical feeding signals including gastric vagal afferents, CCK, leptin, and glycemia on single hypothalamic neurons. Furthermore, recent functional imaging studies provide substantial evidences that hunger, satiation, and thirst are accompanied with a cerebellar activation. Here we describe that the cerebellum may be much more than a movement coordinator and actively participate in feeding control, i.e., it may act as an essential node linking somatic and visceral systems and help to generate an integrated and coordinated somatic-visceral response in feeding behavior.