Anatomical and physiological relationships between the anterior cerebellar vermis and the pontine parabrachial nucleus in the rabbit

A Systematic Review of Direct Outputs from the Cerebellum to the Brainstem and Diencephalon in Mammals

The cerebellum is involved in many motor, autonomic and cognitive functions, and new tasks that have a cerebellar contribution are discovered on a regular basis. Simultaneously, our insight into the functional compartmentalization of the cerebellum has markedly improved. Additionally, studies on cerebellar output pathways have seen a renaissance due to the development of viral tracing techniques. To create an overview of the current state of our understanding of cerebellar efferents, we undertook a systematic review of all studies on monosynaptic projections from the cerebellum to the brainstem and the diencephalon in mammals. This revealed that important projections from the cerebellum, to the motor nuclei, cerebral cortex, and basal ganglia, are predominantly di- or polysynaptic, rather than monosynaptic. Strikingly, most target areas receive cerebellar input from all three cerebellar nuclei, showing a convergence of cerebellar information at the output level. Overall, there appeared to be a large level of agreement between studies on different species as well as on the use of different types of neural tracers, making the emerging picture of the cerebellar output areas a solid one. Finally, we discuss how this cerebellar output network is affected by a range of diseases and syndromes, with also non-cerebellar diseases having impact on cerebellar output areas.

Cerebellar Prediction and Feeding Behaviour

Given the importance of the cerebellum in controlling movements, it might be expected that its main role in eating would be the control of motor elements such as chewing and swallowing. Whilst such functions are clearly important, there is more to eating than these actions, and more to the cerebellum than motor control. This review will present evidence that the cerebellum contributes to homeostatic, motor, rewarding and affective aspects of food consumption.Prediction and feedback underlie many elements of eating, as food consumption is influenced by expectation. For example, circadian clocks cause hunger in anticipation of a meal, and food consumption causes feedback signals which induce satiety. Similarly, the sight and smell of food generate an expectation of what that food will taste like, and its actual taste will generate an internal reward value which will be compared to that expectation. Cerebellar learning is widely thought to involve feed-forward predictions to compare expected outcomes to sensory feedback. We therefore propose that the overarching role of the cerebellum in eating is to respond to prediction errors arising across the homeostatic, motor, cognitive, and affective domains.

Involvement of the cerebellum in migraine

Migraine is a disabling neurological disease characterized by moderate or severe headaches and accompanied by sensory abnormalities, e.g., photophobia, allodynia, and vertigo. It affects approximately 15% of people worldwide. Despite advancements in current migraine therapeutics, mechanisms underlying migraine remain elusive. Within the central nervous system, studies have hinted that the cerebellum may play an important sensory integrative role in migraine. More specifically, the cerebellum has been proposed to modulate pain processing, and imaging studies have revealed cerebellar alterations in migraine patients. This review aims to summarize the clinical and preclinical studies that link the cerebellum to migraine. We will first discuss cerebellar roles in pain modulation, including cerebellar neuronal connections with pain-related brain regions. Next, we will review cerebellar symptoms and cerebellar imaging data in migraine patients. Lastly, we will highlight the possible roles of the neuropeptide calcitonin gene-related peptide (CGRP) in migraine symptoms, including preclinical cerebellar studies in animal models of migraine.

Multi-Level Regulation of Opioid-Induced Respiratory Depression

Opioids depress minute ventilation primarily by reducing respiratory rate. This results from direct effects on the preBötzinger Complex as well as from depression of the Parabrachial/Kölliker-Fuse Complex, which provides excitatory drive to preBötzinger Complex neurons mediating respiratory phase-switch. Opioids also depress awake drive from the forebrain and chemodrive.

Cerebellum-Specific Deletion of the GABAA Receptor δ Subunit Leads to Sex-Specific Disruption of Behavior

Granule cells (GCs) of the cerebellar input layer express high-affinity δ GABA_A subunit-containing GABA_A receptors (δGABA_ARs) that respond to ambient GABA levels and context-dependent neuromodulators like steroids. We find that GC-specific deletion of δGABA_A (cerebellar [cb] δ knockout [KO]) decreases tonic inhibition, makes GCs hyperexcitable, and in turn, leads to differential activation of cb output regions as well as many cortical and subcortical brain areas involved in cognition, anxiety-like behaviors, and the stress response. Cb δ KO mice display deficits in many behaviors, but motor function is normal. Strikingly, δGABA_A deletion alters maternal behavior as well as spontaneous, stress-related, and social behaviors specifically in females. Our findings establish that δGABA_ARs enable the cerebellum to control diverse behaviors not previously associated with the cerebellum in a sex-dependent manner. These insights may contribute to a better understanding of the mechanisms that underlie behavioral abnormalities in psychiatric and neurodevelopmental disorders that display a gender bias.

Rudolph et al. show that deletion of the neuromodulator and hormone-sensitive δGABA_A receptor subunit from cerebellar granule cells results in anxiety-like behaviors and female-specific deficits in social behavior and maternal care. δGABA_A deletion is associated with hyperexcitability of the cerebellar input layer and altered activation of many stress-related brain regions.

Evidence of Impaired Cerebellar Connectivity at Rest and During Autonomic Maneuvers in Patients with Autonomic Failure

The objective of the current study was to investigate whether patients with neurogenic orthostatic hypotension (NOH) secondary to autonomic failure have impaired functional connectivity between the cerebellum and central autonomic structures during autonomic challenges. Fifteen healthy controls (61 ± 14 years) and 15 NOH patients (67 ± 6 years; p = 0.12) completed the following tasks during a functional brain MRI: (1) 5 min of rest, (2) 5 min of lower-body negative pressure (LBNP) performed at - 35 mmHg, and (3) Three, 15-s Valsalva maneuvers (VM) at 40 mmHg. Functional connectivity (Conn Toolbox V18) between central autonomic structures and discrete cerebellar regions involved in cardiovascular autonomic control, including the vermis and posterior cerebellum, was assessed using a regions-of-interest approach during rest, LBNP and VM. Functional connectivity was contrasted between controls and patients with autonomic failure. At rest, controls had significantly more intra-cerebellar connectivity and more connectivity between cerebellar lobule 9 and key central autonomic structures, including: bilateral anterior insula (T_R-value: 4.84; T_L-value: 4.51), anterior cingulate cortex (T-value: 3.41) and bilateral thalamus (T_R-value: 3.95; T_L-value: 4.51). During autonomic maneuvers, controls showed significantly more connectivity between cardiovascular cerebellar regions (lobule 9 and anterior vermis) and important autonomic regulatory sites, including the brainstem, hippocampus and cingulate: vermis-brainstem (T-value: 4.31), lobule 9-brainstem (T_R-value, 5.29; T_L-value, 4.53), vermis-hippocampus (T-value, 4.63), and vermis-cingulate (T-value, 4.18). Anatomical and functional studies in animals and humans substantiate a significant role for the cerebellum in cardiovascular autonomic control during postural adjustments. In the current study, patients with NOH related to autonomic failure showed evidence of reduced connectivity between cardiovascular cerebellar regions and several important central autonomic structures, including the brainstem. The cerebellum is an established structure in cardiovascular autonomic control; therefore, evidence of impaired cerebellar connectivity to other autonomic structures may further contribute to the inability to properly regulate blood pressure during postural changes in NOH patients.

Anatomical Evidence for a Direct Projection from Purkinje Cells in the Mouse Cerebellar Vermis to Medial Parabrachial Nucleus

Cerebellar malformations cause changes to the sleep-wake cycle, resulting in sleep disturbance. However, it is unclear how the cerebellum contributes to the sleep-wake cycle. To examine the neural connections between the cerebellum and the nuclei involved in the sleep-wake cycle, we investigated the axonal projections of Purkinje cells in the mouse posterior vermis by using an adeno-associated virus (AAV) vector (serotype rh10) as an anterograde tracer. When an AAV vector expressing humanized renilla green fluorescent protein was injected into the cerebellar lobule IX, hrGFP and synaptophysin double-positive axonal terminals were observed in the region of medial parabrachial nucleus (MPB). The MPB is involved in the phase transition from rapid eye movement (REM) sleep to Non-REM sleep and vice versa, and the cardiovascular and respiratory responses. The hrGFP-positive axons from lobule IX went through the ventral spinocerebellar tract and finally reached the MPB. By contrast, when the AAV vector was injected into cerebellar lobule VI, no hrGFP-positive axons were observed in the MPB. To examine neurons projecting to the MPB, we unilaterally injected Fast Blue and AAV vector (retrograde serotype, rAAV2-retro) as retrograde tracers into the MPB. The cerebellar Purkinje cells in lobules VIII–X on the ipsilateral side of the Fast Blue-injected MPB were retrogradely labeled by Fast Blue and AAV vector (retrograde serotype), but no retrograde-labeled Purkinje cells were observed in lobules VI–VII and the cerebellar hemispheres. These results indicated that Purkinje cells in lobules VIII–X directly project their axons to the ipsilateral MPB but not lobules VI–VII. The direct connection between lobules VIII–X and the MPB suggests that the cerebellum participates in the neural network controlling the sleep-wake cycle, and cardiovascular and respiratory responses, by modulating the physiological function of the MPB.

Changes in cerebral blood flow during steady-state cycling exercise: a study using oxygen-15-labeled water with PET

Cerebral blood flow (CBF) during dynamic exercise has never been examined quantitatively using positron emission tomography (PET). This study investigated changes in CBF that occur over the course of a moderate, steady-state cycling exercise. Global and regional CBF (gCBF and rCBF, respectively) were measured using oxygen-15-labeled water (H(2)(15)O) and PET in 10 healthy human subjects at rest (Rest), at the onset of exercise (Ex1) and at a later phase in the exercise (Ex2). At Ex1, gCBF was significantly (P<0.01) higher (27.9%) than at Rest, and rCBF was significantly higher than at Rest in the sensorimotor cortex for the bilateral legs (M1(Leg) and S1(Leg)), supplementary motor area (SMA), cerebellar vermis, cerebellar hemispheres, and left insular cortex, with relative increases ranging from 37.6% to 70.5%. At Ex2, gCBF did not differ from Rest, and rCBF was significantly higher (25.9% to 39.7%) than at Rest in only the M1(Leg), S1(Leg), and vermis. The areas showing increased rCBF at Ex1 were consistent with the central command network and the anatomic pathway for interoceptive stimuli. Our results suggest that CBF increases at Ex1 in parallel with cardiovascular responses then recovers to the resting level as the steady-state exercise continues.

Neural correlates of minor hallucinations in non-demented patients with Parkinson's disease

BACKGROUND

Hallucinations are a frequent and severe complication in Parkinson's disease (PD). Minor hallucinations are generally not disturbing, but likely progress to well-structured hallucinations with loss of insight and a great impact on quality of life. Knowledge on the neural bases of minor hallucinations may help to describe those systems associated with the early development of psychotic phenomena in PD. In this study, we aimed to identify the pattern of structural brain alterations associated with minor hallucinations in PD by using voxel-based morphometry (VBM).

METHODS

We prospectively collected a sample of 46 non-demented PD patients, with (N = 17) and without (n = 29) minor hallucinations (passage and/or presence hallucinations), and 15 healthy controls. Groups were matched for age, education and global cognitive function. Presence and type of minor psychotic phenomena was assessed by the new MDS-UPDRS. Three dimensional T1-weighted MRI images were acquired with a 1.5 T magnet, and analyzed using optimized VBM.

RESULTS

Compared to controls, PD with minor hallucinations (PD-mH) showed reduced gray matter volume bilaterally in different areas of the dorsal visual stream, and in functionally related midbrain and cerebellar structures. Additionally, bilateral gray matter volume increases were observed in the PD-mH group in limbic and paralimbic regions.

CONCLUSIONS

Our data support a major role of the dorsal visual stream in the genesis of minor hallucinations in PD, reinforcing the importance of posterior cortical regions for the development of cognitive and psychiatric complications in PD.

Orexin-neuromodulated cerebellar circuit controls redistribution of arterial blood flows for defense behavior in rabbits

We investigated a unique microzone of the cerebellum located in folium-p (fp) of rabbit flocculus. In fp, Purkinje cells were potently excited by stimulation of the hypothalamus or mesencephalic periaqueductal gray, which induced defense reactions. Using multiple neuroscience techniques, we determined that this excitation was mediated via beaded axons of orexinergic hypothalamic neurons passing collaterals through the mesencephalic periaqueductal gray. Axonal tracing studies using DiI and biotinylated dextran amine evidenced the projection of fp Purkinje cells to the ventrolateral corner of the ipsilateral parabrachial nucleus (PBN). Because, in defense reactions, arterial blood flow has been known to redistribute from visceral organs to active muscles, we hypothesized that, via PBN, fp adaptively controls arterial blood flow redistribution under orexin-mediated neuromodulation that could occur in defense behavior. This hypothesis was supported by our finding that climbing fiber signals to fp Purkinje cells were elicited by stimulation of the aortic nerve, a high arterial blood pressure, or a high potassium concentration in muscles, all implying errors in the control of arterial blood flow. We further examined the arterial blood flow redistribution elicited by electric foot shock stimuli in awake, behaving rabbits. We found that systemic administration of an orexin antagonist attenuated the redistribution and that lesioning of fp caused an imbalance in the redistribution between active muscles and visceral organs. Lesioning of fp also diminished foot shock-induced increases in the mean arterial blood pressure. These results collectively support the hypothesis that the fp microcomplex adaptively controls defense reactions under orexin-mediated neuromodulation.

Cerebellar vermis volume in major depressive disorder

The vermis is located in the midline of the cerebellum and is involved in the regulation of affect and cognitive processes. Although changes in vermis size have been reported in several psychiatric disorders such as schizophrenia and bipolar disorder, no volumetric studies have been conducted on samples of patients with major depressive disorder (MDD). One-hundred and five adult subjects were recruited: 35 patients who were presenting for first treatment (FT; 22 females), 35 patients with known previous treatment (PT; 22 females), and 35 healthy controls (NC; 22 females), matched for age and gender. We compared the volumes of the total vermis, the anterior lobe (V1), the superior-posterior lobe (V2), and the inferior-posterior lobe (V3), among these study groups. Anterior vermis (V1) was larger in patients with MDD with a long history of antidepressant treatment compared to healthy controls. This finding was evident only in men [F(2, 36) = 9.23, p = .001]. Patients in the FT group did not differ from healthy controls in any vermian region. We found no correlations between vermian subregional volumes and clinical variables such as illness duration or age at onset of illness. We speculate that the larger anterior vermis volumes might arise from abnormalities in connectivity or as compensatory responses to the prefrontal dysfunction noted in patients with MDD but confirmation of this hypothesis awaits further studies.

Cardiovascular modules in the cerebellum

Mapping with local lesions, electrical or chemical stimulation, or recording evoked field potentials or unit spikes revealed localized representations of cardiovascular functions in the cerebellum. In this review, which is based on literatures in the field (including our own publications), I propose that the cerebellum contains five distinct modules (cerebellar corticonuclear microcomplexes) dedicated to cardiovascular control. First, a discrete rostral portion of the fastigial nucleus and the overlying medial portion of the anterior vermis (lobules I, II and III) conjointly form a module that controls the baroreflex. Second, anterior vermis also forms a microcomplex with the parabrachial nucleus. Third, a discrete caudal portion of the fastigial nucleus and the overlying medial portion of the posterior vermis (lobules VII and VIII) form another module controlling the vestibulosympathetic reflex. Fourth, the medial portion of the uvula may form a module with the nucleus tractus solitarius and parabrachial nucleus. Fifth, the lateral edge of the nodulus and the uvula, together with the parabrachial nucleus and vestibular nuclei, forms a cardiovascular microcomplex that controls the magnitude and/or timing of sympathetic nerve responses and stability of the mean arterial blood pressure during changes of head position and body posture. The lateral nodulus-uvula appears to be an integrative cardiovascular control center involving both the baroreflex and the vestibulosympathetic reflex.

Compromised pontocerebellar and cerebellothalamocortical systems: speculations on their contributions to cognitive and motor impairment in nonamnesic alcoholism

BACKGROUND

Corticopontocerebellar and cerebellothalamocortical circuits underlie a wide range of neuropsychological processes compromised by alcoholism. The analyses herein tested whether abnormalities of volumes of brain structures forming nodes of these separate feed-forward and feedback systems are selectively related to each other and whether any of these noncortical regions can account for cognitive and motor deficits occurring as sequelae of chronic alcoholism.

METHODS

Regional brain measures originated from our prior neuroimaging studies, showing in alcoholics significant volume deficits in the principal structures of interest: cerebellar hemispheres, vermis, pons, and thalamus as well as prefrontal, frontal, and parietal cortex. Neuropsychological functions targeted for analysis-problem solving, visuospatial ability, and static postural stability-showed 0.6 to 1.6 SD deficits in these alcoholic men.

RESULTS

In alcoholics, the patterns of correlations were consistent with dissociation of thalamic and pontine circuitry. Pontine and thalamic volumes were not correlated with each other. Pontine volumes correlated with white matter volumes of anterior superior vermis and gray and white matter volumes of the cerebellar hemispheres but not with cortical regional volumes. Thalamic volumes correlated with gray matter volumes of the cerebellar hemispheres, parietal cortex, and inferior posterior vermian lobule, which itself correlated with parietal, prefrontal, and frontal cortical volumes. Controls did not show these correlational patterns. Brain structure-function relationships in alcoholics examined with multiple regression identified anterior vermian but not prefrontal or parietal volume as a unique predictor of balance scores; vermian and thalamic but not prefrontal cortical volumes as predictors of card sorting scores; and cerebellar hemispheric white matter but not parietal cortical volume as a predictor of visuospatial ability.

CONCLUSIONS

Each major node of frontocerebellar circuitry shows volume deficits in alcoholics but can be independently compromised. Disruption of these circuits may underlie alcoholism-related neuropsychological deficits, either by abnormalities present in individual nodes or by disconnection via interruption of selective circuitry.

Functional magnetic resonance signal changes in neural structures to baroreceptor reflex activation

The sequence of neural responses to exogenous arterial pressure manipulation remains unclear, especially for extramedullary sites. We used functional magnetic resonance imaging procedures to visualize neural responses during pressor (phenylephrine) and depressor (sodium nitroprusside) challenges in seven isoflurane-anesthetized adult cats. Depressor challenges produced signal-intensity declines in multiple cardiovascular-related sites in the medulla, including the nucleus tractus solitarius, and caudal and rostral ventrolateral medulla. Signal decreases also emerged in the cerebellar vermis, inferior olive, dorsolateral pons, and right insula. Rostral sites, such as the amygdala and hypothalamus, increased signal intensity as arterial pressure declined. In contrast, arterial pressure elevation elicited smaller signal increases in medullary regions, the dorsolateral pons, and the right insula and signal declines in regions of the hypothalamus, with no change in deep cerebellar areas. Responses to both pressor and depressor challenges were typically lateralized. In a subset of animals, barodenervation resulted in rises and falls of blood pressure that were comparable to these resulting from the pharmacological challenges but different regional neural responses, indicating that the regional signal intensity responses did not derive from global perfusion effects but from baroreceptor mediation of central mechanisms. The findings demonstrate widespread lateralized distribution of neural sites responsive to blood pressure manipulation. The distribution and time course of neural responses follow patterns associated with early and late compensatory reactions.

Cooling lesions of the lateral parabrachial nucleus during LiCl activation block acquisition of conditioned taste avoidance in male rats

Lesions of the lateral parabrachial nucleus (lPBN) disrupt acquisition of LiCl-induced conditioned taste avoidance. Animals with lesions in this area also fail to exhibit taste neophobia. This raises the possibility that an inability of rats to recognize the taste solution as novel contributes to the deficit in taste avoidance learning. If this is the case, then one would expect conditioned taste avoidance not to be disrupted if the lPBN is functional during taste processing but not during LiCl processing. The first three experiments demonstrated that cooling was a viable method by which to temporarily inactivate the lPBN. Measurement of neural temperature during cooling indicated that the lPBN was cooled to temperatures that have been shown to block synaptic transmission but not axonal transmission. Cooling the lPBN itself induced a conditioned avoidance to a sucrose solution but this avoidance was abolished by exposure to daily cooling for 1 week prior to acquisition. In experiment 4, all animals were preexposed to lPBN cooling for 1 week. Those rats that received cooling lesions during a period that started immediately after sucrose solution consumption and extended through the peak effectiveness of LiCl failed to acquire a taste avoidance. These results fail to support the hypothesis that the deficit in taste avoidance learning after permanent lesions of the lPBN is due to an inability of lesioned animals to recognize the taste as novel. They are consistent with the hypothesis that this neural area processes ascending information about LiCl.

Role of the cerebellar deep nuclei in respiratory modulation

The cerebellum contains three deep nuclei, i.e., the fastigial, interposed and lateral nucleus. Recent studies demonstrate that these nuclei play different roles in respiratory modulation. Activation of fastigial nuclear neurons predominantly increases ventilation via elevation of respiratory frequency and/or tidal volume. Ablation of the fastigial nucleus did not significantly alter eupneic breathing, but did markedly attenuate the respiratory response to medium and severe hypercapnia as well as hypoxia. The fastigial nucleus contains respiratory-modulated neurons and about 25% of these neurons do not show their respiratory-related phasic activity until exposed to hypercapnia. The fastigial nucleus also contains CO2/H+ chemosensitive sites that contributed to the respiratory response to hypercapnia. Therefore, it is concluded that fastigial nuclear facilitatory influence on chemoreflexes emerges during hypercapnia via recruiting intrinsic chemoreception and respiratory-modulated neurons. Full expression of the fastigial nucleus-mediated respiratory responses depends on the integrity of the medullary gigantocellular nucleus at least partially via monosynaptic projections. Additionally, the fastigial nucleus receives inhibitory inputs primarily from Purkinje cells located in the medial vermis and recent observations indicate that simulation of these Purkinje cells inhibits respiration. As compared to chemoreflexes, fastigial nuclear role in the respiratory mechanoreflexes is not significant. The studies related to the role of the interposed and lateral nucleus in eupneic breathing are limited and the results appear controversial. However, there is evidence to show that the interposed nucleus contains respiratory-modulated neurons and is involved in coughing motor control.

Neural responses to intravenous serotonin revealed by functional magnetic resonance imaging

We examined the sequence of neural responses to the hypotension, bradycardia, and apnea evoked by intravenous administration of 5-hydroxytryptamine (serotonin). Functional magnetic resonance imaging signal changes were assessed in nine isoflurane-anesthetized cats during baseline and after a bolus intravenous low dose (10 microg/kg) or high dose (20-30 microg/kg) of 5-hydroxytryptamine. In all cats, high-dose challenges elicited rapid-onset, transient signal declines in the intermediate portion of the solitary tract nucleus, caudal midline and caudal and rostral ventrolateral medulla, and fastigial nucleus of the cerebellum. Slightly delayed phasic declines appeared in the dentate and interpositus nuclei and dorsolateral pons. Late-developing responses also emerged in the solitary tract nucleus, parapyramidal region, periaqueductal gray, spinal trigeminal nucleus, inferior olivary nucleus, cerebellar vermis, and fastigial nucleus. Amygdala and hypothalamic sites showed delayed and prolonged signal increases. Intravenous serotonin infusion recruits cerebellar, amygdala, and hypothalamic sites in addition to classic brain stem cardiopulmonary areas and exhibits site-specific temporal patterns.

Direct projection from the cardiovascular control region of the cerebellar cortex, the lateral nodulus-uvula, to the brainstem in rabbits

In decerebrate unanesthetized rabbits, electrical stimulation of the lateral nodulus-uvula in the cerebellar vermal cortex evoked an increase in renal sympathetic nerve activity, an increase in blood pressure and a decrease in renal arterial blood flow, which were all in contrast to the effects reported previously in the anesthetized rabbits. In order to identify the pathway mediating these responses, we investigated the Purkinje cell projection from the lateral nodulus-uvula using both anterograde (biotinylated dextran amine, BDA) and retrograde (horseradish peroxidase, HRP) tracing methods in rabbits. When BDA was iontophoretically injected into the lateral nodulus-uvula, labeled Purkinje cell axons were found within and around the superior and inferior cerebellar peduncles (SCP and ICP, respectively). Furthermore, terminal-like fields were found in the dentate and vestibular nuclei as reported in previous studies. However, the terminal-like patterns that we observed in the parabrachial nucleus (PB) in the rabbit have not been reported yet. When HRP was microinjected into the lateral PB, retrogradely labeled Purkinje cells were found in the lateral nodulus-uvula. These results indicate that Purkinje cells in the lateral nodulus-uvula project into the vestibular nuclei via the ICP and to the lateral PB via the SCP. We suggest that these two pathways mediating cardiovascular responses have different sensitivities to anesthetics.

Role of the Bötzinger complex in fastigial nucleus-mediated respiratory responses

We have reported that the phrenic neurogram (PN) is modulated by stimulation of the fastigial nucleus (FN) of the cerebellum. The present study was undertaken to search for brainstem site(s) involved in the FN efferent pathway to modulate phrenic nerve activities. Experiments were performed on 35 anesthetized, paralyzed, and ventilated cats, using the PN as the index of the respiratory motor output. Results showed that bilateral electrolytic lesions of the red nucleus (RN), the paramedian reticular nucleus (PRN), or the pontine respiratory group (PRG) had little effect on the ability of FN stimulation to modulate the respiratory output. However, the modulation was abolished by bilateral electrolytic lesions of the Bötzinger complex (BötC). Further studies showed that bilateral chemical inactivation of BötC neurons produced by topical microinjection of kainic acid or cobalt chloride failed to abolish the modulation. We concluded that fibers of passage, not synapses or cell bodies in the BötC, were involved in the modulatory effect of FN stimulation on the PN. The RN, PRN, and PRG appear not to be important in the neural circuitry responsible for the FN modulation of the phrenic activity.

Supraspinal connections and termination patterns of the parabrachial complex determined by the biocytin anterograde tract-tracing technique in the rat

We have re-evaluated, using the anterograde tracer biocytin, supraspinal efferent projections from the parabrachial complex (PBN) to gain new information about the nature of its connections and nerve terminal patterns. We selectively injected biocytin into the 3 main regions of the nucleus (lateral PBN, medial PBN and Kölliker-Fuse nucleus). We observed distinct groups of ascending and descending fibres of different calibre from the PBN running throughout the brain and reaching many brain areas involved in the regulation of autonomic function. Here we detected labelled bouton-like terminals and fibres with en-passage varicosities. The ascending efferents from the lateral PBN mainly reached the reticular, raphe and thalamic nuclei, the zona incerta (ZI), central nucleus of the amygdala (CeA) and lateral area of the periaqueductal grey (PAG). Thin descending efferents reached the ventral region of the solitary tract nucleus (STN). The ascending efferents from the medial PBN were seen in the raphe nuclei, reticular nuclei, ventral and lateral areas of the PAG, thalamic nuclei, and in the medial and lateral nuclei of the amygdala. Descending efferents were seen in the STN and in some reticular nuclei. The ascending projections from the Kölliker-Fuse targeted the ventral area of PAG, CeA, ZI, lateral hypothalamic area, ventromedial thalamic nucleus and, with only a few terminals, the ipsi and contralateral reticular area. A large number of descending efferents reached STN, caudal and paragigantocellular reticular nuclei. The higher sensitivity of biocytin compared with other types of markers allowed us to determine more effectively the distribution, nature and extent of the supraspinal PBN connections. This suggested that in several nerve circuits the PBN probably plays a more important role than previously thought.

Differential development of the human cerebellar vermis: immunohistochemical and morphometrical evaluation

Differential development of regions of the human cerebellar vermis was evaluated immunohistochemically and morphometrically between 18 weeks of gestation and 10 years of age. The density of Purkinje cells in the cerebellar vermis decreased rapidly until 38 weeks of gestation and slowly thereafter. At all stages of development, the density was higher in the posterior (lobules VI-IX) than the anterior vermis (lobules I-V). The area of cut sections of the anterior and posterior vermis in the mid-sagittal section increased rapidly before 40 weeks of gestation and gradually after birth, whereas growth was slower in the nodules. These developmental characteristics may be related to the selective susceptibility of cerebellar regions to environmental insults.

Localized cerebellar hypometabolism in patients with complex partial seizures

PURPOSE

We sought to determine the cause of cerebellar dysfunction in epilepsy and whether this dysfunction was directly related to seizures.

METHODS

Cerebellar metabolism was evaluated in 48 patients with a well-defined region of seizure onset and with corresponding hypometabolism. Regions of interest (ROI) were drawn according to a standardized template. If the ROI/nonepileptogenic cortex count rate ratio was outside the 95% confidence interval (CI) of controls, the ROI was defined as abnormal. The ratios from cerebellar hemispheres (defined as ipsi- or contralateral to the seizure onset region), were compared among controls (n = 8); patients who had seizure onsets and corresponding hypometabolism mesially in a temporal lobe (patient group 1, n = 19); patients whose seizures had onset mesially in a temporal lobe but spread rapidly to the ipsilateral frontal lobe and who had hypometabolism both in the affected temporal lobe and frontal lobe (patient group 2, n = 23); and patients who had seizure onsets and corresponding hypometabolism in the frontal lobe (patient group 3, n = 6).

RESULTS

Significant hypometabolism was noted in the contralateral cerebellum of patients in group 2 and 3 [p = 0.007 and p = 0.008, respectively; two-way analysis of variance (ANOVA)]. In contrast, patients in group 1 tended to have lower values in the ipsilateral cerebellum (p = 0.057).

CONCLUSIONS

The observed cerebellar changes are consistent with animal data showing that cerebellar connections to frontal lobes are numerous and crossed, whereas the connections to mesial temporal lobes are less abundant, bilateral, with an ipsilateral predominance. The difference between the two groups of patients with mesial temporal seizures suggests that cerebellar dysfunction in partial epilepsy, at least to a certain extent, is related to mechanisms involved in seizure generation and spread.