Fos and FRA protein expression in rat nucleus paragigantocellularis lateralis during different space flight conditions

The nucleus paragigantocellularis lateralis (LPGi) exerts a prominent excitatory influence over locus coeruleus (LC) neurons, which respond to gravity signals. We investigated whether adult albino rats exposed to different gravitational fields during the NASA Neurolab Mission (STS-90) showed changes in Fos and Fos-related antigen (FRA) protein expression in the LPGi and related cardiovascular, vasomotor, and respiratory areas. Fos and FRA proteins are induced rapidly by external stimuli and return to basal levels within hours (Fos) or days (FRA) after stimulation. Exposure to a light pulse (LP) 1 h prior to sacrifice led to increased Fos expression in subjects maintained for 2 weeks in constant gravity (either at approximately 0 or 1 G). Within 24 h of a gravitational change (launch or landing), the Fos response to LP was abolished. A significant Fos response was also induced by gravitational stimuli during landing, but not during launch. FRA responses to LP showed a mirror image pattern, with significant responses 24 h after launch and landing, but no responses after 2 weeks at approximately 0 or 1 G. There were no direct FRA responses to gravity changes. The juxtafacial and retrofacial parts of the LPGi, which integrate somatosensory/acoustic and autonomic signals, respectively, also showed gravity-related increases in LP-induced FRA expression 24 h after launch and landing. The neighboring nucleus ambiguus (Amb) showed completely different patterns of Fos and FRA expression, demonstrating the anatomical specificity of these results. Immediate early gene expression in the LPGi and related cardiovascular vasomotor and ventral respiratory areas may be directly regulated by excitatory afferents from vestibular gravity receptors. These structures could play an important role in shaping cardiovascular and respiratory function during adaptation to altered gravitational environments encountered during space flight and after return to earth.     

Brainstem Fos expression following acute unilateral labyrinthectomy in the rat.

Detection of Fos protein expression with a polyclonal antibody was used to identify brainstem neurons responding to acute (24 h) effects of a unilateral sodium arsanilate chemical labyrinthectomy in Long-Evans rats. Asymmetrical expression was apparent in the medial and inferior vestibular nuclei, the prepositus hypoglossi, the dorsolateral central gray, and the inferior olivary beta subnucleus. These data suggest different distributions of neural activation compared with previous electrophysiological and 2-deoxyglucose results. In addition, there was some Fos expression bilaterally in the olivary dorsomedial cell column, interstitial nucleus of Cajal and the Darkschewitsch nucleus. These results support the concept of multiple systems participating in vestibular compensation and further define some specific nuclei involved in the acute stage.     

Distribution of Fos labeling in the inferior olive following transient blockade of the VIIIth cranial nerve

The sodium channel blocker, tetrodotoxin (TTX), is an effective tool for blockade of action potentials in neurons. Unilateral transtympanic administration of 3 mM TTX produced behavioral symptoms paralleling those previously reported following unilateral vestibular ablation. Behavioral symptoms were evident as early as 15 min post-TTX. Fos immunocytochemistry revealed an initial bilateral distribution of Fos in the inferior olive (IO) followed by an almost exclusively unilateral distribution of Fos. By 1 h, Fos was predominantly localized in subdivisions of the IO contralateral to TTX treatment. Fos labeling in the IO was most pronounced at 2- and 6-h survival times and was localized in the contralateral IOA, IOB, IOC, IOBe, and IOK subdivisions and bilaterally in the IOM and IODM. Other regions of the brainstem including the vestibular nuclei, prepositus hypoglossi, dorsal paragigantocellular reticular nucleus, nucleus of the tractus solitarius and locus coeruleus also exhibited altered patterns of Fos labeling following TTX. The finding that Fos activity in the IO is initially bilateral and then rapidly becomes unilateral has not been reported for the traditional vestibular ablation models and may be unique to the TTX model. In addition, since altered Fos activity is readily detected in the IO at time-points prior to detectable changes in Fos in the central vestibular complex it is possible that the IO is particularly sensitive to events precipitated by unilateral vestibular disturbance.     

Expression of Trk receptors in otolith-related neurons in the vestibular nucleus of rats

The expression of the three Trk receptors (TrkA, TrkB, and TrkC) in otolith-related neurons within the vestibular nuclei of adult Sprague-Dawley rats was examined immunohistochemically. Conscious animals were subjected to sinusoidal linear acceleration along either the anterior-posterior (AP) or interaural (IA) axis on the horizontal plane. Neuronal activation was defined by Fos expression in cell nuclei. Control animals, viz labyrinthectomized rats subjected to stimulation and normal rats that remained stationary, showed only a few sporadically scattered Fos-labeled neurons. Among experimental rats, the number of Fos-labeled neurons and their distribution pattern in each vestibular subnucleus in animals stimulated along the antero-posterior axis were similar to those along the interaural axis. No apparent topography was observed among neurons activated along these two directions. Only about one-third of the Trk-immunoreactive neurons in the vestibular nucleus expressed Fos. Double-labeled Fos/TrkA, Fos/TrkB and Fos/TrkC neurons constituted 85-98% of the total number of Fos-labeled neurons in vestibular nuclear complex and its subgroups x and y. Our findings suggest that Trk receptors and their cognate neurotrophins in central otolith neurons may contribute to the modulation of gravity-related spatial information during horizontal head movements.     

Maturation of otolith-related brainstem neurons in the detection of vertical linear acceleration in rats

To investigate the critical maturation time of otolith-related neurons in processing vertical orientations, rats (postnatal day 4 to adults) were studied for functional activation of c-fos expression in brainstem neurons by immuno-/hybridization histochemistry. Conscious rats were subjected to sinusoidal linear acceleration along the vertical plane. Labyrinthectomized and/or stationary controls showed only sporadically scattered Fos-labeled neurons in the vestibular nuclei, confirming an otolithic origin of c-fos expression. Functionally activated Fos expression in neurons of the medial and spinal vestibular nuclei and group x were identifiable by P7 and those in group y by P9. A small number of Fos-labeled neurons characterized by small soma size were found in the ventral part of lateral vestibular nucleus by P9. Other vestibular-related areas such as prepostitus hypoglossal nucleus, gigantocellular reticular nucleus and locus coeruleus of normal experimental rats showed functionally activated c-fos expression at P7. Neurons in dorsal medial cell column and beta subnucleus of the inferior olive only showed functionally activated c-fos expression by the second postnatal week. These findings revealed a unique critical maturation time for each of the vestibular-related brainstem areas in the recognition of gravity-related vertical head orientations. By mapping the three-dimensional distribution of Fos-immunoreactive neurons, we found an even distribution of otolith-related neurons within the spinal vestibular nucleus in groups x and y but a clustered distribution in the middle-lateral-ventral part of the medial vestibular nucleus. Taken together, our findings reveal the developmental profile of neuronal subpopulations within the vertical otolith system, thereby providing an anatomical basis for postnatal coding of gravity-related vertical head movements.     

Tonic gravity changes alter gene expression in the efferent vestibular nucleus

To assess effects of tonic gravity changes on efferent vestibular neurons, immediate early gene (IEG) protein expression was compared in the efferent vestibular nucleus (EVe) of adult rats exposed to microgravity during the NASA Neurolab Mission (STS-90), and matching control animals on the ground. Rats sacrificed 1 day and 12 days after launch (experiencing approximately 0g) showed significantly fewer IEG protein-expressing cells than corresponding ground control animals (at 1 g). Normal IEG protein-expressing cell numbers reappeared within I day after flight animals returned to earth, and were maintained at 14 days after landing. EVe neurons appear to play a role in gravity-induced modifications of vestibular hair cell synapses; a contribution to gravity-induced plasticity of the vestibulo-ocular reflex (VOR) is also suggested.     

VOR and Fos response during acute vestibular compensation in the Mongolian gerbil in darkness and in light

We measured binocular horizontal eye movements in the gerbil following unilateral labyrinthectomy during the acute phase (1-24 h) of vestibular compensation. Regardless of whether the animals compensated in the light or the dark, VOR gain progressively reduced following the lesion, and normal oculomotor symmetry was disrupted. Initially, the VOR was comparable at 1 h post-lesion for both visual conditions. However, by 3 h post-lesion the VOR response for head turns away from the lesion continued to drop in animals compensating in the dark. By 24 h, both groups displayed reduced VOR gains, but animals compensating in the light had improved frequency response characteristics. Optokinetic responses became unstable but were generally elevated compared to pre-lesion levels. Animals with vision had reduced optokinetic gains by 24 h, while the OKR response for animals in the dark remained elevated. Brainstem Fos labeling generally increased from 1 to 3 h, then decreased by 24 h. However, at 1 h, Fos labeling in the inferior olivary dorsal cap and prepositus contralateral to the lesion was significantly increased in animals compensating in the light. In both visual conditions, flocculus and paraflocculus Purkinje cell labeling was also observed, and some of the Fos-labeled cells in the medial vestibular nucleus were commissural. Fos in the dorsal cap and prepositus could be attributed to the presence of visual input. While the visually related prepositus Fos labeling preceded improved VOR performance, the dorsal cap appeared to be involved in resolving visual and motor deficits from spontaneous nystagmus.     

Localization of olivo-cerebellar fibers in inferior cerebellar peduncle in man

The localization of the olivo-cerebellar fibers in the inferior cerebellar peduncle was examined in a patient who showed severe degeneration of the left olivary nucleus due to an old hemorrhagic infarct in the contralateral cerebellum. Other precerebellar nuclei which send their cerebellipetal axons to the inferior cerebellar peduncle, such as the external cuneate nucleus, the lateral reticular nucleus and the arcuate nucleus, were normally preserved. The dorsal spino-cerebellar tract and the vestibular nuclei, together with the juxtarestiform body were also intact. Degeneration of the inferior cerebellar peduncle was noted only in its ventromedial portion contralateral to the olivary lesion. As a result, it is concluded that the olivo-cerebellar fibers seem to be located in this portion of the inferior cerebellar peduncle.     

Transtympanic tetrodotoxin alters the VOR and Fos labeling in the vestibular complex

The sodium channel blocker tetrodotoxin (TTX) is an effective tool for blockade of action potentials. Unilateral transtympanic administration of 3 mM TTX produced behavioral symptoms similar to those following unilateral peripheral vestibular ablation. Complete resolution of visible symptoms occurred between 48 and 72 h post-TTX. Eye-coil recordings indicated a spontaneous nystagmus and a decrease in the VOR in TTX-treated animals. Neuronal activity in the central vestibular complex (VC), as monitored with Fos immunocytochemistry, revealed an asymmetric pattern of Fos labeling in the medial, inferior and superior vestibular nuclei and the prepositus hypoglossal nucleus. Although the spatio-temporal pattern of Fos labeling was consistent and reproducible at each time-point, changes were noted among time-points. Transient blockade with TTX may be useful for studying the central vestibular response to recurrent or episodic vestibular disruption in the intact system.     

Vestibulosympathetic reflex mediates the pressor response to hypergravity in conscious rats: contribution of the diencephalon

To investigate the mechanism of arterial pressure (AP) regulation during hypergravity, the AP response to gravitational force was examined in conscious rats and the AP was found to increase, depending on the degree of gravity load induced by centrifugation. At 20 s after application of 2, 3, or 5 G, the AP increased by 9+/-2, 20+/-3, or 24+/-3 mm Hg, respectively. The AP increase during first 60 s was suppressed by vestibular lesion or pretreatment with hexamethonium, suggesting that the vestibular system and sympathetic nerve system be involved, respectively, in the afferent and efferent pathways. To further examine the central pathway of this response, Fos expression in the brain was examined after exposure to 5 G for 90 min. Intense Fos expression was seen in the medial vestibular nucleus, paraventricular hypothalamic nucleus, autonomic nuclei in the brain stem in intact rats, but not in rats with vestibular lesion. To examine the involvement of the diencephalic nuclei in this pressor response, AP was measured under hypergravity in rats with midcollicular transection. In these rats, the AP change was minimal at 2, 3, and 5 G, indicating that nuclei rostral to the transection level were involved in the pressor response. These results indicate that output from the vestibular system project to the diencephalon, and activation of diencephalic nuclei is indispensable to the pressor response via the sympathetic nerve system.     

Expression of inorganic phosphate/vesicular glutamate transporters (BNPI/VGLUT1 and DNPI/VGLUT2) in the cerebellum and precerebellar nuclei of the rat

Expression of inorganic phosphate/vesicular glutamate transporters (BNPI/VGLUT1 and DNPI/VGLUT2) was studied in the cerebellum and precerebellar nuclei of rats using immunohistochemistry and in situ hybridization. DNPI/VGLUT2-stained mossy fibers were principally seen in the vermis (lobules I and VIII-X) and flocculus, whereas BNPI/VGLUT1-stained mossy fibers were localized throughout the cortex. Some vermal and floccular mossy fibers were stained for both transporters. High levels of DNPI/VGLUT2 mRNA hybridization signals were demonstrated in many neurons throughout the vestibular nuclear complex as well as the lateral reticular, external cuneate, inferior olivary and deep cerebellar nuclei. Significant BNPI/VGLUT1 mRNA signals were demonstrated in the lateral reticular nucleus and vestibular nuclear complex but not in the inferior olivary nucleus, indicating that climbing fibers have DNPI/VGLUT2 only. These results show that DNPI/VGLUT2 is expressed preferentially to vestibulo-, reticulo- and cuneocerebellar neurons, some of which also possess BNPI/VGLUT1, suggesting some differential and co-operative functions between DNPI/VGLUT2 and BNPI/VGLUT1 in the cerebellum.     

Inferior olivary-induced expression of Fos-like immunoreactivity in the cerebellar nuclei of wild-type and Lurcher mice

Earlier behavioural studies have shown that the expression of the immediate-early gene c-fos, as visualized by the immunohistochemical detection of Fos, in the inferior olive (IO) correlated closely with expression in related areas of the cerebellar nuclei. It has been speculated that the expression of c-fos within the cerebellar nuclei may be induced by enhanced spiking activity of the immunopositive neurons in the inferior olive. Two potential mechanisms may play a role in this process: a direct induction by way of the collaterals of the olivary climbing fibres to the cerebellar nuclei, or indirectly, by climbing fibre activity-induced depression of mossy fibre-parallel fibre-induced simple spike frequency of the Purkinje cells resulting in a subsequent disinhibition of the related parts of the cerebellar nuclei. In an attempt to distinguish between these possible mechanisms, we analysed Fos immunoreactivity in the olivocerebellar system of wild-type mice and in the mutant mouse Lurcher which lacks Purkinje cells. The tremorgenic agent harmaline, which is known to induce enhanced and rhythmic firing of olivary neurons was given intraperitoneally to anaesthetized mice of both genotypes. Harmaline application coincides with the induction of Fos-immunoreactive neurons in most areas of the IO in both wild-type and Lurcher mice. Both types of mice also showed enhanced expression in the larger neurons of the cerebellar nuclei. However, in the smaller, GABAergic nucleo-olivary neurons, increased c-fos expression was only observed in the wild-type mice. We conclude that: (i) increased olivary activity indeed may result in increased c-Fos expression in related areas of the cerebellar nuclei; (ii) because the indirect mode of induction is not operative in Lurcher mice, the olivary collateral innervation of the cerebellar nuclei is sufficient for c-fos induction in the larger nucleobulbar neurons in Lurcher and potentially also in wild-type mice; however (iii) for the nucleo-olivary cells an intact cerebellar cortical input is necessary to evoke increased expression of c-fos following harmaline application.     

Fos expression in the cat brainstem after unilateral vestibular neurectomy

Immediate early genes are generally expressed in response to sensory stimulation or deprivation and can be used for mapping brain functional activity and studying the molecular events underlying CNS plasticity. We immunohistochemically investigated Fos protein induction in the cat brainstem after unilateral vestibular neurectomy (UVN), with special reference to the vestibular nuclei (VN) and related structures. Fos-like immunoreactivity was analyzed at 2, 8, and 24 h, and 1 and 3 weeks after UVN. Data from these subgroups of cats were quantified in light microscopy and compared to those recorded in control and sham-operated animals submitted to anesthesia and anesthesia plus surgery, respectively. Results showed a very low level of Fos expression in the control and sham conditions. By contrast, Fos was consistently induced in the UVN cats. Asymmetrical labeling was found in the medial, inferior, and superior VN (ipsilateral predominance) and in the prepositus hypoglossi (PH) nuclei and the β subnuclei of the inferior olive (βIO) (contralateral predominance). Symmetrical staining was observed in the autonomic, tegmentum pontine, pontine gray, locus coeruleus and other reticular-related nuclei. As a rule, Fos expression peaked early (2 h) and declined progressively. However, some brainstem structures including the ipsilateral inferior VN and the bilateral pontine gray nuclei displayed a second peak of Fos expression (24 h–1 week). By comparing these data to the behavioral recovery process, we conclude that the early Fos expression likely reflects the activation of neural pathways in response to UVN whereas the delayed Fos expression might underlie long-term plastic changes involved in the recovery process.     

Spinocerebellar ataxias types 2 and 3: degeneration of the precerebellar nuclei isolates the three phylogenetically defined regions of the cerebellum

Summary. The precerebellar nuclei act as a gate for the entire neocortical, brainstem and spinal cord afferent input destined for the cerebellum. Since no pathoanatomical studies of these nuclei had yet been performed in spinocerebellar ataxia type 2 (SCA2) or type 3 (SCA3), we carried out a detailed postmortem study of the precerebellar nuclei in six SCA2 and seven SCA3 patients in order to further characterize the extent of brainstem degeneration in these ataxic disorders. By means of unconventionally thick serial sections through the brainstem stained for lipofuscin pigment and Nissl material, we could show that all of the precerebellar nuclei (red, pontine, arcuate, prepositus hypoglossal, superior vestibular, lateral vestibular, medial vestibular, interstitial vestibular, spinal vestibular, vermiform, lateral reticular, external cuneate, subventricular, paramedian reticular, intercalate, interfascicular hypoglossal, and conterminal nuclei, pontobulbar body, reticulotegmental nucleus of the pons, inferior olive, and nucleus of Roller) are among the targets of both of the degenerative processes underlying SCA2 and SCA3. These novel findings are in contrast to the current neuropathological literature, which assumes that only a subset of precerebellar nuclei in SCA2 and SCA3 may undergo neurodegeneration. Widespread damage to the precerebellar nuclei separates all three phylogenetically and functionally defined regions of the cerebellum, impairs their physiological functions and thus explains the occurrence of gait, stance, limb and truncal ataxia, dysarthria, truncal and postural instability with disequilibrium, impairments of the vestibulo-ocular reaction and optokinetic nystagmus, slowed and saccadic smooth pursuits, dysmetrical horizontal saccades, and gaze-evoked nystagmus during SCA2 and SCA3.     

Fos-defined activity in rat brainstem following centripetal acceleration.

To identify rat brainstem nuclei involved in the initial, short-term response to a change in gravito-inertial force, adult Long-Evans rats were rotated in the horizontal plane for 90 min in complete darkness after they were eccentrically positioned off the axis of rotation (off-axis) causing a centripetal acceleration of 2 g. Neural activation was defined by the brainstem distribution of the c-fos primary response gene protein, Fos, using immunohistochemistry. The Fos labeling in off-axis animals was compared with that of control animals who were rotated on the axis of rotation (on-axis) with no centripetal acceleration, or who were restrained but not rotated. In the off-axis animals there was a significant labeling of neurons: in the inferior, medial, and y-group subnuclei of the vestibular complex; in subnuclei of the inferior olive, especially the dorsomedial cell column; in midbrain nuclei, including the interstitial nucleus of Cajal, nucleus of Darkschewitsch, Edinger-Westphal nucleus, and dorsolateral periaqueductal gray; in autonomic centers including the solitary nucleus, area postrema, and locus coeruleus; and in reticular nuclei including the lateral reticular nucleus and the lateral parabrachial nucleus. Also, there was greater Fos expression in the dorsomedial cell column, the principal inferior olive subnuclei, inferior vestibular nucleus, the dorsolateral central gray, and the locus coeruleus in animals who had their heads restrained compared to animals whose heads were not restrained. As one control, the vestibular neuroepithelium was destroyed by injecting sodium arsanilate into the middle ear, bilaterally. This resulted in a complete lack of Fos labeling in the vestibular nuclei and the inferior olive, and a significant reduction in labeling in other nuclei in the off-axis condition, indicating that these nuclei have a significant labyrinth-sensitive component to their Fos labeling. The data indicate that several novel brainstem regions, including the dorsomedial cell column of the inferior olive and the periaqueductal gray, as well as more traditional brainstem nuclei including vestibular and oculomotor related nuclei, respond to otolith activation during a sustained centripetal acceleration.     

c-fos mRNA, Fos, and Fos-related antigen induction by hypertonic saline and stress

The induction of c-fos mRNA was assessed using Northern blots and in situ hybridization in adult rats administered hypertonic saline (HS) and isotonic saline (IS). HS induced c-fos mRNA in magnocellular paraventricular nucleus (PVNm), parvocellular paraventricular nucleus (PVNp), supraoptic nucleus (SON), and lamina terminalis (LMT). This occurred within 5 min, peaked at 30-60 min, and disappeared by 180 min. Fos protein, detected using a specific monoclonal antibody, was maximal at 1-2 hr and disappeared 4-8 hr after HS administration. This confirms observations showing that the c-fos gene response is transient even in the presence of a continuing stimulus. In contrast, Fos-like immunoreactivity (FLI), detected using two polyclonal antisera, was observed in PVNm, PVNp, SON, and LMT for 1-24 hr during continuous osmotic stimulation. Moreover, FLI was observable in these structures for 7 d in rats administered HS and allowed to drink water ad libitum beginning 24 hr later. At times greater than 8 hr, FLI presumably represents Fos-related antigens (FRA), proteins immunologically and functionally related to Fos, whose expression is much more prolonged than authentic Fos following the osmotic stimulus. In addition to induction of c-fos expression in regions specifically involved in osmotic regulation, HS injections also induced c-fos in many other forebrain regions. In order to assess the induction of c-fos mRNA due to the "stress" of the injections, rats injected with isotonic saline were compared to uninjected controls. Isotonic saline injections induced c-fos mRNA in the PVNp, anterior hypothalamus, suprachiasmatic nucleus, cingulate gyrus, neocortex, ventral lateral septal nucleus, piriform cortex, hippocampal pyramidal and dentate granule neurons, paraventricular and intralaminar thalamic nuclei, bed nuclei of stria terminalis, cortical and medial amygdaloid nuclei, and other structures. In accord with other work, we interpret this pattern of c-fos expression to result from the stress of handling and injections. Since Fos and FRA probably bind to the promoters of target genes and regulate their expression, they likely mediate biochemical changes in the cells activated by the osmotic and stressful stimuli. Whereas the Fos signal is transient, FRA may act on target genes for the duration of the stimulus or longer.     

Precerebellar Cell Groups in the Hindbrain of the Mouse Defined by Retrograde Tracing and Correlated with Cumulative Wnt1-Cre Genetic Labeling

The precerebellar nuclei are hindbrain and spinal cord centers that send fibers to the cerebellum. The neurons of the major hindbrain precerebellar nuclei are derived from the rhombic lip. Wnt1, a developmentally important gene involved in intercellular signaling, is expressed in the developing rhombic lip. We sought to investigate the relationship between the cell clusters expressing Wnt1 and the precerebellar nuclei in the hindbrain. We therefore defined the hindbrain precerebellar nuclei by retrograde tracing, following cerebellar injections of HRP, and compared these results with the cell clusters expressing Wnt1 in newborn mice. We found that 39 distinct hindbrain nuclei project to the cerebellum. Of these nuclei, all but three (namely the oral pontine reticular nucleus, the caudal pontine reticular nucleus, and the subcoeruleus nucleus) contain neurons expressing Wnt1. This shows a high degree of overlap between the precerebellar nuclei and the nuclei that express Wnt1. However, it should be noted that neurons expressing Wnt1 are also found in the superior olivary complex, which is a basal plate derivative lacking cerebellar projections.     

Fos expression in otolith-related brainstem neurons of postnatal rats following off-vertical axis rotation

To determine the critical time of responsiveness of developing otolith organ-related brainstem neurons and their distribution, Fos protein expression in response to off-vertical axis rotations (OVAR) was mapped in conscious Sprague Dawley rats from P5 to adulthood. OVAR was used to activate sequentially all utricular hair cells per 360 degrees revolution. We detected the coding of horizontal head positions in otolith organ-related neurons within the vestibular nucleus as early as P7. In the vestibular nuclear complex and its subgroups, the density of Fos-immunoreactive (Fos-ir) neurons increased steadily with age and reached the adult level by P21. In both labyrinthectomized rats subjected to OVAR and normal rats kept stationary, labeled neurons were found sporadically in the aforementioned brain regions in each age group, confirming that Fos labeling observed in neurons of normal experimental rats subjected to OVAR was due to otolith organ stimulation. Whereas OVAR-induced Fos-ir neurons were also first observed in vestibular-related brain areas, such as the prepositus hypoglossal nucleus, gigantocellular reticular nucleus, and locus coeruleus, of normal experimental rats at P7, those in the inferior olive were observed only from P14 onward. This indicates the unique maturation time of inferior olivary neurons in gravity-related spatial coding. In general, age-dependent increase in OVAR-induced Fos-ir neurons was observed in brain areas that received otolith inputs. The locus coeruleus was exceptional in that prominent OVAR-induced Fos-ir neuronal number did not change with maturation, and this was well above the low but significant number of Fos-ir neurons in control preparations. Taken together, our results suggest that neuronal subpopulations within the developing network of the horizontal otolith system provide an anatomical basis for the postnatal development of otolith organ-related sensorimotor functions. J. Comp. Neurol. 470:282-296, 2004.     

Spinocerebellar ataxia type 6: Systematic patho‐anatomical study reveals different phylogenetically defined regions of the cerebellum and neural pathways undergo different evolutions of the degenerative process

Spinocerebellar ataxia type 6 is a late onset autosomal dominantly inherited ataxic disorder, and previous patho‐anatomical studies have only reported neurodegeneration in SCA6 as being confined to the cerebellar cortex, dentate nucleus and inferior olive. However, the characteristics of cerebellar symptoms and many poorly understood “extracerebellar” symptoms reveal the three cerebellar regions and the corresponding precerebellar nuclei may undergo differing evolution of the degenerative process, and a more widespread brainstem degeneration in SCA6. We carried out a detailed immunohistochemical study in two SCA6 patients who had rather early onset and short disease duration with 25 CAG repeats, which is atypical for SCA‐6. We investigated the severity of neurodegeneration in each of the cerebellar regions and the corresponding precerebellar nuclei, and further characterize the extent of brain degeneration. This study confirmed that vestibulocerebellar, spinocerebellum and pontocerebellar are consistent targets of the pathological process of SCA6, but the severity of neurodegeneration in each of them was different. Vestibulocerebellum and the inferior cerebellar peduncle undergo the most severe neurodegeneration, while neurodegeneration in the pontocerebellar is less severe. Furthermore, we observed obvious neurodegeneration in layers II and III of the primary motor cortex, vestibular nuclei, inferior olivary nucleus, nucleus proprius and posterior spinocerebellar tract. Our detailed postmortem findings confirmed that SCA6 was not a simple “pure” cerebellar disease, but a complex neurodegenerative disease in which the three cerebellar regions underwent different evolutions of neurodegeneration process, and the corresponding precerebellar nuclei and the neural pathway were all involved.     

Increased neuronal cell death after intermittent hypercapnic hypoxia in the developing piglet brainstem

We examined the immunohistochemical expression of caspase-3 (CASP3), active caspase-3 and TUNEL in the normal piglet brainstem at 13-14 days of age and evaluated the effects of exposure to 2 vs. 4 days of intermittent hypercapnic hypoxia (IHH) on their expression. Eight nuclei from the level of the caudal medulla were studied. In control piglets, CASP3 was present in approximately 45% of neurons while active caspase-3 and TUNEL were present in approximately 5%, indicating that approximately half the neuronal population of the piglet medulla express caspase-3 in a latent state and that only approximately 5% undergo 'normal' programmed cell death. After 2 days of IHH, CASP3 increased in the nucleus of the solitary tract (NTS), gracile and cuneate nuclei (P<0.05 for all). Active caspase-3 increased in the dorsal motor nucleus of the vagus (DMNV) (P<0.05) but decreased in the lateral reticular nucleus (LRt) (P<0.05), while TUNEL increased in both the DMNV and LRt (P<0.05 for both). After 4 days of IHH, CASP3 remained elevated in the cuneate nucleus (P<0.01) but decreased in the hypoglossal and DMNV (P<0.05) when compared to controls. Active caspase-3 levels were not changed, whereas TUNEL was increased in the DMNV, LRt, and inferior olivary nucleus (P<0.05 for all). These results show that IHH induces neuronal cell death within certain nuclei in the piglet caudal medulla that are functionally important in cardiorespiratory, sleep and arousal control. This could have important implications for clinical conditions including obstructive apnea and prone sleeping as a risk for SIDS.