Purkinje Cells In Lobule Research Articles

Loss of CRMP1 and CRMP2 results in migration defects of Purkinje cells in the X lobule of the mouse cerebellum

The three-layered structure of the mammalian cerebellar cortex is generated through the coordinated migration of cerebellar neurons. Purkinje cells migrate and form a three- to four-cell-thick aggregate below the external granule cell layer during the embryonic stage, and align to form a monocellular arrangement in the Purkinje cell layer during the postnatal period. We previously reported the involvement of Cdk5-mediated CRMP2 phosphorylation in Purkinje cell migration and the synergistic roles of two other CRMPs, CRMP1 and CRMP4. In the present study, we investigated the loss of function of CRMP2 along with the synergistic function of CRMP1 in the migration and alignment of Purkinje cells. We found deficits in the migration and alignment of Purkinje cells in lobule X of the cerebella of CRMP1 and CRMP2 double knockout mice. Because lobule X, also called the flocculonodular lobe, is involved in the maintenance of balance equilibrium and muscle tone, we conducted balance beam and grip power tests in these mice and found impaired performance on the balance beam test and lower grip power in CRMP1 and CRMP2 double knockout mice, indicating the importance of these genes in proper cerebellar development.

Electrophysiological Excitability and Parallel Fiber Synaptic Properties of Zebrin-Positive and -Negative Purkinje Cells in Lobule VIII of the Mouse Cerebellar Slice.

Heterogeneous populations of cerebellar Purkinje cells (PCs) are arranged into separate longitudinal stripes, which have different topographic afferent and efferent axonal connections presumably involved in different functions, and also show different electrophysiological properties in firing pattern and synaptic plasticity. However, whether the differences in molecular expression that define heterogeneous PC populations affect their electrophysiological properties has not been much clarified. Since the expression pattern of many of such molecules, including glutamate transporter EAAT4, replicates that of aldolase C or zebrin II, we recorded from PCs of different “zebrin types” (zebrin-positive = aldolase C-positive = Z+; and Z−) in identified neighboring stripes in vermal lobule VIII, in which Z+ and Z− stripes occupy similar widths, in the Aldoc-Venus mouse cerebellar slice preparation. Regarding basic cellular electrophysiological properties, no significant differences were observed in input resistance or in occurrence probability of types of firing patterns between Z+ and Z− PCs. However, the firing frequency of the tonic firing type was higher in Z− PCs than in Z+ PCs. In the case of parallel fiber (PF)-PC synaptic transmission, no significant differences were observed between Z+ and Z− PCs in interval dependency of paired pulse facilitation or in time course of synaptic current measured without or with the blocker of glutamate receptor desensitization. These results indicate that different expression levels of the molecules that are associated with the zebrin type may affect the intrinsic firing property of PCs but not directly affect the basic electrophysiological properties of PF-PC synaptic transmission significantly in lobule VIII. The results suggest that the zebrin types of PCs in lobule VIII is linked with some intrinsic electrophysiological neuronal characteristics which affect the firing frequency of PCs. However, the results also suggest that the molecular expression differences linked with zebrin types of PCs does not much affect basic electrophysiological properties of PF-PC synaptic transmission in a physiological condition in lobule VIII.

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.

Regional differences in Purkinje cell morphology in the cerebellar vermis of male mice.

Regional differences in dendritic architecture can influence connectivity and dendritic signal integration, with possible consequences for neuronal computation. In the cerebellum, analyses of Purkinje cells (PCs), which are functionally critical as they provide the sole output of the cerebellar cortex, have suggested that the cerebellar cortex is not uniform in structure as traditionally assumed. However, the limitations of traditional staining methods and microscopy capabilities have presented difficulties in investigating possible local variations in PC morphology. To address this question, we used male mice expressing green fluorescent protein selectively in PCs. Using Neurolucida 360 with confocal image stacks, we reconstructed dendritic arbors of PCs residing in lobule V (anterior) and lobule IX (posterior) of the vermis. We then analyzed morphologies of individual arbors and the structure of the assembled "jungle," comparing these features across anatomical locations and age groups. Strikingly, we found that in lobule IX, half of the reconstructed PCs had two primary dendrites emanating from their soma, whereas fewer than a quarter showed this characteristic in lobule V. Furthermore, PCs in lobule V showed more efficient spatial occupancy compared to lobule IX, as well as greater packing density and increased arbor overlap in the adult. When analyzing complete ensembles of PC arbors, we also observed "hot spots" of increased dendritic density in lobule V, whereas lobule IX showed a more homogeneous spread of dendrites. These differences suggest that input patterns and/or physiology of PCs could likewise differ along the vermis, with possible implications for cerebellar function.

Reduced spike frequency adaptation in Purkinje cells of the vestibulocerebellum

Firing regularity has long been an issue of firing dynamics in the vestibular circuitry. Spike frequency adaption (SFA) is ubiquitous in neuronal activity and can modulate neural coding, which may disrupt the regularity or accuracy of firing. We previously observed different characteristics of intrinsic excitability in Purkinje cells (PCs) of lobule X (vestibulocerebellum) compared to lobules III–V (spinocerebellum). However, systematic comparison of the extent of SFA in PCs of different lobules has not yet been made. In this study we examined the degree of SFA and compared the firing regularity by measuring interspike interval (ISI). During the course of low-frequency spike trains, PCs in lobules III–V showed gradual lengthening of ISI due to SFA. In contrast, ISI showed little change during the propagation of spikes in lobule X PCs. In high-frequency firing, PCs in lobules III–V exhibited gradual SFA, whereas lobule X neurons showed dramatic increase in ISI during the first four spikes and then stayed unchanged. The coefficient of variation of ISI of lobule X PCs was significantly lower in lobules III–V PCs during low-frequency firing. The comparison of duration of action potential showed no significant difference between lobules III–V and lobule X PCs during SFA even in low-frequency firing. The lack of SFA in lobule X PCs, as a part of vestibulocerebellum, might be involved in a consistent and regular coordination of vestibular function by the cerebellar cortex in response to low vestibular stimulation. However, the difference of SFA between lobules may be explained by other mechanisms than those which have been reported to be responsible for the SFA formation.

Lobule‐specific membrane excitability of cerebellar Purkinje cells

Cerebellar Purkinje cells (PCs) are the sole output of the cerebellar cortex and function as key to a variety of learning-related behaviours by integrating multimodal afferent inputs. Intrinsic membrane excitability of neurons determines the input-output relationship, and therefore governs the functions of neural circuits. Cerebellar vermis consists of ten lobules (lobules I-X), and each lobule receives different sensory information. However, lobule-specific differences of electrophysiological properties of PC are incompletely understood. To address this question, we performed a systematic comparison of membrane properties of PCs from different lobules (lobules III-V vs. X). Two types of firing patterns (tonic firing and complex bursting) were identified in response to depolarizing current injections in lobule III-V PCs, whereas four distinct firing patterns (tonic firing, complex bursting, initial bursting and gap firing) were observed in lobule X. A-type K(+) current and early inactivation of fast Na(+) conductance with activation of 4-aminopyridine-sensitive conductances were shown to be responsible for the formation of gap firing and initial bursting patterns, respectively, which were observed only in lobule X. In response to current injection, PCs in lobule X spiked with wider dynamic range. These differences in firing pattern and membrane properties probably contribute to signal processing of afferent inputs in lobule-specific fashion, and particularly diversity of discharge patterns in lobule X, as a part of the vestibulocerebellum, might be involved in strict coordination of a precise temporal response to a wide range of head movements.

Identification and characterization of Cs+‐permeable K+ channel current in mouse cerebellar Purkinje cells in lobules 9 and 10 evoked by molecular layer stimulation

The mouse cerebellum consists of 10 lobules, which are distinguishable by their anatomical and functional properties. However, the differences in the slow postsynaptic currents (sPSCs) of Purkinje cells between lobules have not been well studied. We recorded the sPSCs of lobules 3, 9 and 10 evoked by tetanic stimulation of the molecular layer in cerebellar slices, and found a novel outward sPSC mediated by the GABA(B) receptor in loblues 9 and 10 but hardly at all in lobule 3. We showed that the lobule-specific difference is at least partly attributable to differences in the density of GABAergic neurons (higher in lobule 10 than in lobules 3 and 9), and the functional expression level of postsynaptic GABA(B) receptor currents (larger in lobules 9 and 10 than in lobule 3). The G-protein-coupled inward rectifying K(+) channel (GIRK) is known to be activated by GABA(B) receptors; however, the outward sPSC was not blocked by a GIRK blocker, was not sensitive to Cs(+) block, and was observed when Cs(+) was used as a charge carrier. These results suggest that a K(+) channel other than GIRK could be activated by GABA(B) receptors. KCNK13 is a Cs(+)-permeable K(+) channel that shows intense expression of mRNA in Purkinje cells. KCNK13 current was enhanced by co-expression of G(βγ) subunits and was observed when Cs(+) was used as a charge carrier in heterologous expression systems, and the amino acids critical for these features were identified by mutagenesis. Taken together, these results show that KCNK13 is a legitimate candidate for the Cs(+)-permeable K(+) channel activated by GABA(B) receptors, presumably via G(βγ) subunits in Purkinje cells.

Purkinje cell compartmentation of the cerebellum of microchiropteran bats

Transverse boundaries divide the mammalian cerebellar cortex into transverse zones, and within each zone the cortex is further subdivided into a symmetrical array of parasagittal stripes. This topography is highly conserved across the Mammalia. Bats have a remarkable cerebellum with presumed adaptations to flight and to echolocation, but nothing is known of its compartmentation. We have therefore used two Purkinje cell compartmentation antigens, zebrin II/aldolase C and phospholipase Cbeta4, to reveal the topography of the cerebellum in microchiropteran bats. Three species of bat were studied, Lasiurus cinereus, Lasionycteris noctivagans, and Eptesicus fuscus. A reproducible pattern of zones and stripes was revealed that is similar across the three species. The architecture of the bat cerebellum conforms to the ground plan of other mammals. However, two exceptions to the highly conserved mammalian architectural plan were revealed. First, many Purkinje cells in lobule I express zebrin II. A zebrin II-immunopositive lobule I has not been seen previously in mammals but is characteristic of the avian cerebellum. Second, lobules VI-VII comprise the large central zone. Within the central zone two subdomains are evident, a small anterior subdomain (lobule VI) in which Purkinje cells are predominantly zebrin II-immunopositive/PLCbeta4-immunonegative, as in other mammals, and a posterior subdomain (lobule VII), in which alternating zebrin II/phospholipase Cbeta4 stripes are prominent.

Alcohol exposure on postnatal day 5 induces Purkinje cell loss and evidence of Purkinje cell degradation in lobule I of rat cerebellum

The reduction in neuron number in specific brain regions is one of the most destructive aspects of alcohol-induced developmental brain injury, and its occurrence depends on the timing, pattern, and dose of maternal alcohol consumption during pregnancy. The purpose of this investigation was to quantify the dose–response aspect of Purkinje cell loss and rapid cellular degradation indicative of Purkinje cell loss following a single alcohol exposure on postnatal day 5 in lobule I, a lobule that has been shown to be vulnerable to alcohol-induced injury during cerebellar development. Fluoro-Jade B was used to identify Purkinje cell degeneration in 2-h intervals during the first 24 h following the single alcohol exposure. At the end of 24 h, stereology cell counting techniques were used to estimate the number of Purkinje cells in lobule I of the cerebellum. Significant Fluoro-Jade B labeling of lobule I Purkinje cells began at 12-h postexposure in the 6.0-g/kg group with continued significant expression of the marker at the 16- and 18-h time points. Notably, the magnitude of Fluoro-Jade B expression in the 6.0-g/kg group remained high during the period between 12 and 24 h even though the difference between the 6.0-g/kg group and other groups did not reach statistical significance at the 14-, 20-, and 24-h time points. On postnatal day 6, 24 h following the alcohol exposure, rats exposed to the highest alcohol dose (6.0 g/kg) had lost significantly more Purkinje cells than those in the nutritional or caloric control to the highest dose of alcohol group. These results are suggestive of a unique relationship among the quantity of alcohol, the onset and duration of cell degradation, and the degree of eventual cell loss. Given that cerebellar Purkinje cells (and many developing neurons) are vulnerable to alcohol-induced neuronal loss within hours of a single alcohol insult, women should be counseled to avoid drinking alcohol in a manner that significantly increases blood alcohol levels during pregnancy (e.g., binge drinking).

Doppel Induces Degeneration of Cerebellar Purkinje Cells Independently of Bax

Doppel (Dpl) is a prion protein paralog that causes neurodegeneration when expressed ectopically in the brain. To investigate the cellular mechanism underlying this effect, we analyzed Dpl-expressing transgenic mice in which the gene for the proapoptotic protein Bax had been deleted. We found that Bax deletion does not alter either clinical symptoms or Purkinje cell degeneration in Dpl transgenic mice. In addition, we observed that degenerating Purkinje cells in these animals do not display DNA fragmentation or caspase-3 activation. Our results suggest that non-Bax-dependent pathways mediate the toxic effects of Dpl in Purkinje cells, highlighting a possible role for nonapoptotic mechanisms in the death of these neurons.

Non‐uniform olivocerebellar conduction time in the vermis of the rat cerebellum

It has been proposed that the conduction velocities of cerebellar climbing fibre (olivocerebellar) axons are tuned according to length, in order to precisely fix the conduction time between the inferior olive and cerebellar cortex. Some data conflict with this view. We have re-evaluated this issue using the climbing fibre reflex. The white matter of the tip of one folium in lobule VI or VII was stimulated electrically 0.5-1 mm below the surface and recordings were made from Purkinje cells in lobules VIII and IX. Reflex evoked climbing fibre (CF) responses (33 units) were recorded at different depths from Purkinje cells found in a narrow sagittal zone of cortex as complex spikes. The responses had latencies ranging from 4.3 ms to 11.3 ms. A consistent trend was that Purkinje cell responses recorded at greater depth had shorter CF reflex latencies than those recorded more superficially, both in individual experiments and in grouped data. These data show that the CF reflex latency is not constant, but is directly proportional to the distance an action potential has to travel along a CF. These data are not consistent with tuning of CF conduction velocities to normalize olivocerebellar conduction time, but are consistent with a CF conduction velocity in the cortex of approximately 0.6 m s-1. This suggests that climbing fibres projecting to different parts of the cerebellar cortex may have differences in spike conduction time of a few milliseconds, and that submillisecond precision is not an important element of the climbing fibre signal.

Antioxidant Pretreatment Does Not Ameliorate Alcohol‐Induced Purkinje Cell Loss in the Developing Rat Cerebellum

Recent research has suggested that oxidative stress is a potential mechanism for alcohol-induced injury and that supplementation with antioxidants can ameliorate alcohol-induced damage. In this study, two known antioxidants, melatonin and U83836E, were assessed for their effectiveness in blocking the expected alcohol-induced cerebellar Purkinje cell loss in neonatal rat pups. Sprague-Dawley rat pups were artificially reared from postnatal days (PDs) 4-9 and were exposed to either alcohol or antioxidants (melatonin or U83836E) individually or in combination. A normal control group (raised by rat dams) was included in this study. On PD 9, the brain from each pup was removed and weighed, and the cerebellar vermis was processed for stereological cell counting. Alcohol exposure during the brain growth spurt produced microencephaly, in addition to significant decreases in the number and density of Purkinje cells in lobule I and the volume of lobule I. The antioxidants did not reduce any of the adverse effects observed from alcohol exposure, and they did not decrease the Purkinje cell number when administered alone. Furthermore, antioxidants did not change the only blood alcohol concentration measured on PD 6. The results confirmed alcohol-induced microencephaly and cerebellar Purkinje cell loss from neonatal alcohol exposure, and they showed that neither antioxidant could attenuate these adverse effects on the developing brain. The inability of antioxidants to reduce Purkinje cell loss from neonatal alcohol exposure suggests the existence of alternative mechanisms for developmental alcohol-induced Purkinje cell loss.

Connections of Purkinje cell axons of lobule X with vestibulocerebellar neurons projecting to lobule X or IX in the rat.

Connections of Purkinje cell axons of lobule X (nodulus) with vestibulocerebellar neurons projecting to lobule X or IX (uvula) were revealed in the rat. Purkinje cell axons were anterogradely labeled with biotinylated dextran (BD) injected into sublobule Xa while vestibular neurons were retrogradely labeled with cholera toxin subunit B (CTB) injected into sublobule Xa or IXc. Labeled terminals of Purkinje cell axons of lobule X were numerous in the superior vestibular nucleus (SV), medial parts of the parvocellular (MVpc) and the caudal part (MVc) of the medial vestibular nucleus (MV), and group y. These subdivisions of the vestibular nuclei contained many neurons projecting to lobule X or IX. Lobule-X-projecting and lobule-IX-projecting neurons were in contact with terminals of Purkinje cell axons of lobule X in the MVpc and MVc. They were distributed dorsally to medially in medial parts of the MVpc and MVc. The present study suggests that Purkinje cells in lobule X regulate the output of a population of lobule-X-projecting or lobule-IX-projecting neurons of the MVpc and MVc.

Overexpression of NGF ameliorates ethanol neurotoxicity in the developing cerebellum

Transgenic mice overexpressing NGF in the central nervous system under the control of the glial fibrillary acidic protein (GFAP) promoter were exposed to ethanol via vapor inhalation on postnatal days 4 and 5 (P4-5), the period of maximal cerebellar Purkinje cell sensitivity to ethanol. Wild-type controls were exposed in a similar manner. There were no differences in body weight or size following these procedures, but the transgenic brain weights at this age were significantly greater than wild-type controls. In the wild-type animals, a significant 33.3% ethanol-mediated loss of Purkinje cells in lobule I was detected via unbiased three-dimensional stereological counting on P5. In the GFAP-NGF transgenic animals, however, the 17.6% difference in Purkinje cell number in control and ethanol-exposed animals was not significant. There was a similar difference in Purkinje cell density in both groups, which did reach statistical significance (-32.7% in wild-type ethanol-treated animals, -17% in transgenic ethanol-exposed animals). These results suggest that endogenous overexpression of neurotrophic factors, which have previously been shown to protect against ethanol neurotoxicity in culture, can serve a similar protective function in the intact animal.

Abnormal expression of tyrosine hydroxylase immunoreactivity in Purkinje cells precedes the onset of ataxia in dilute– lethal mice

Expression of tyrosine hydroxylase (TH) immunostaining in the cerebellum was examined in dilute– lethal mice (DL) prior to and following the onset of ataxia. DL walked normally on postnatal days 7 and 8. Falling over when walking was exhibited by about 20% of DL on day 9 and by all DL by day 10. TH-positive Purkinje cells in lobules IX and X of the vermis of either ataxic or non-ataxic DL were clearly observed on day 9 when compared to control mice, and had drastically increased by day 10. These results revealed that abnormal TH expression occurred in some Purkinje cells of DL cerebella, preceding the onset of ataxia.

Galanin messenger rna during postnatal development of the rat brain: expression patterns in Purkinje cells differentiate anterior and posterior lobes of cerebellum

Following our initial mapping of preprogalanin messenger RNA in adult brain and its presence in a subpopulation of cerebellar Purkinje neurons, [Ryan M.C. and Gundlach A.C. (1996) Neuroscience 70, 709–728.] the present study examined the ontogenic expression of preprogalanin messenger RNA in the postnatal rat brain focussing on the Purkinje cells of the cerebellar cortex. Using in situ hybridization histochemistry, preprogalanin messenger RNA was detected in the developing forebrain and hindbrain from postnatal day 4 to day 60 (adult). On postnatal day 4 very light hybridization signal (labelling) was observed in cells of a number of nuclei including the central amygdaloid nucleus, the medial preoptic area, paraventricular nucleus and dorsomedial hypothalamic nucleus of the forebrain while lightly-labelled cells were detected in neurons of the nucleus of the solitary tract and locus coeruleus of the hindbrain. Hybridization signal was not apparent in other nuclei until later, with positively-labelled neurons first apparent in the dorsal cochlear nucleus at postnatal day 21. The abundance of preprogalanin messenger RNA-positive neurons and the intensity of the hybridization signal increased, in most regions, until postnatal day 28 when labelling resembled that of the mature rat. Preprogalanin messenger RNA was first detected in the cerebellum on postnatal day 10 only in Purkinje cells of lobule 10 of the posterior vermis and increased in distribution throughout Purkinje cell layers of the entire cerebellar cortex by postnatal day 13. The intensity of hybridization signal in Purkinje cells varied between lobules, with Purkinje cells in lobule 10 displaying a moderate to heavy degree of labelling, while lobules 6–9 and the more posterior lobules of the hemisphere including crus 2 of the ansiform lobule, the paramedian lobule and the copula pyramis, displayed only light labelling. The intensity of labelling in the anterior vermis and the remaining lobules of the hemisphere including crus 1 of the ansiform lobule, the simple lobule, the paraflocculus and the flocculus, was homogeneously weak. By postnatal day 21, Purkinje cell labelling reached maximum intensity in all lobules. Regional differences were still apparent, however, with labelling in the posterior vermis and hemisphere ranging from moderate to heavy, with only light to moderate labelling detected in the anterior vermis. The intensity of labelling in the posterior vermis and most lobules of the hemisphere was similar from postnatal day 21 to adulthood, while, in the anterior vermis, crus 1 of the ansiform lobule and the simple lobule, the intensity of hybridization decreased slightly by postnatal day 28 and was completely absent in Purkinje cells of the adult rat. Differential expression of preprogalanin messenger RNA in Purkinje cells of the developing rat cerebellum and transient expression in certain lobules suggests that galanin gene products may have a role in both the developing and mature rat brain and that galanin gene expression may represent a useful marker for differentiating the anterior and posterior cerebellar lobes.

Ibogaine neurotoxicity: a re-evaluation

Ibogaine is claimed to be an effective treatment for opiate and stimulant addiction. O'Hearn and Molliver, however, showed that ibogaine causes degeneration of cerebellar Purkinje cells in rats. The present study re-examined cerebellar responses to the high doses of ibogaine used by O'Hearn and Molliver (100 mg/kg or 3 × 100 mg/kg) and sought to determine whether a lower dose (40 mg/kg), one effective in reducing morphine and cocaine self-administration, produced similar responses. Purkinje cell degeneration was evaluated with a Fink-Heimer II stain, and enhanced glial cell activity with an antibody to glial fibrillary acidic protein. Every rat treated with the high dose of ibogaine displayed clear evidence of Purkinje cell degeneration. The degeneration consistently occurred in the intermediate and lateral cerebellum, as well as the vermis. Purkinje cells in lobules 5 and 6 were particularly susceptible. Given the response properties of cells in these lobules, this finding suggests any long-term motor deficits produced by ibogaine-induced degeneration should preferentially affect the head and upper extremity. In marked contrast, rats given the smaller dose of ibogaine displayed no degeneration above the level seen in saline-treated animals. When combined with information on other compounds, these data suggest that the degenerative and ‘anti-addictive’ properties of ibogaine reflect different actions of the drug.

Spatial and temporal pattern of Purkinje cell degeneration in shaker mutant rats with hereditary cerebellar ataxia.

Temporal-spatial patterns of surviving Purkinje cells were studied quantitatively in a rat mutant (shaker) with differential hereditary cerebellar ataxia and Purkinje cell degeneration. Shaker rat mutants are characterized behaviorally as mild if they are ataxic or as strong if they have ataxia and tremor. Purkinje cells degenerate in both mild and strong shaker mutants, but the temporal and spatial patterns of cell death are strikingly different. In mild shaker mutants, Purkinje cell death is temporally restricted, with 31-46% of the Purkinje cells in lobules I-IX dying by 3 months of age. Very few Purkinje cells degenerate after this age. Purkinje cell death is spatially random. In lobules I-IX, every second, third, or fourth Purkinje cell degenerates. Purkinje cells in lobule X do not degenerate. In strong shaker mutants, Purkinje cell degeneration is temporally protracted and spatially restricted. By 3 months of age, most Purkinje cells in lobules I-VIa, -b, and -d have degenerated. Numerous Purkinje cells in the paravermis of lobules VIIb-VIII have also degenerated. Surviving Purkinje cells in the vermis and lateral hemisphere of lobules VIIb-VIII are aligned in parasagittally oriented stripes or transversely oriented bands. Purkinje cells continue to degenerate in localized areas of the posterior lobe such that, by 18 months of age, surviving Purkinje cells are limited primarily to lobules VIc, VIIa, IXd, and X. Quantitative analysis indicates that none of the Purkinje cells in these lobules degenerate.

Novel developmental boundary in the cerebellum revealed by zebrin expression in the lurcher (Lc/+) mutant mouse.

The cerebellar cortex contains at least two classes of Purkinje cells, which are organized into alternating arrays of parasagittal bands. The clearest demonstration of this compartmentation is the pattern of expression of a family of polypeptide antigens, the zebrins, which are expressed selectively by Purkinje cell subsets. Furthermore, anterograde tracing experiments show that the zebrin compartments are closely correlated with both afferent and efferent projection maps. The further subdivision of long parasagittal bands into smaller modules may occur through several different mechanisms, including the intrinsic cerebellar lobulation and the selective distribution of afferent terminal fields. However, while the longitudinal subdivisions are straightforwardly shown, the mediolateral boundaries are more subtle. In this report we describe a novel mediolateral and anteroposterior compartmentation boundary in mice, running across lobule VIII, that is revealed by the consequences of the lurcher (Lc/+) allele for zebrin expression. In normal mice zebrin compartmentation develops in several discrete stages: until postnatal day 5 (PD5) there is no zebrin expression; from PD5-PD7 zebrin is found only in the posterior lobe vermis, with immunoreactive Purkinje cells in lobules X, IX, and VIII but not elsewhere; from PD7-PD12 most Purkinje cells in the vermis become zebrin+; from PD12-PD15 immunoreactivity also appears in the hemispheres so that almost all Purkinje cells now are zebrin+; and finally, from PD15-PD25 zebrin is gradually suppressed in those Purkinje cells that are zebrin- in the adult until the mature pattern of parasagittal compartments is revealed. In the Lc/+ mutant the normal developmental progression is interrupted at around PD7. As a result, the pattern of zebrin expression becomes frozen at that stage when immunoreactive Purkinje cells are confined exclusively to the posterior lobe vermis. A reproducible boundary between expressing and nonexpressing zones runs mediolaterally across the dorsal surface of lobule VIII. Apart from zebrin expression itself, there are no obvious structural correlates of this transition. This mediolateral boundary identifies a developmental unit in the posterior lobe vermis of the cerebellum, and provides further evidence that the cerebellum is a highly heterogeneous structure.

Afferents of the caudal fastigial nucleus in a New World monkey (Cebus apella)

The afferents of the fastigial nucleus (FN) were studied in two capuchin monkeys (Cebus apella) one of which had received a unilateral injection of horseradish peroxidase in the caudal FN, and a second monkey which received a control injection that involved the lateral caudal FN but extended into the cerebellar white matter between the FN and posterior interposed nucleus (PIN). All of the sources of FN afferents were found to be labeled bilaterally. In addition to the restricted distribution of labeled Purkinje cells in lobules VI and VII of the posterior lobe vermis ("oculomotor vermis"), retrogradely labeled cells were present in the dorsolateral pontine nucleus (DLPN), dorsomedial pontine nucleus (DMPN), nucleus reticularis tegmenti pontis (NRTP), pontine raphe (PR), paramedian nucleus reticularis pontis caudalis (NRPC), nucleus prepositus hypoglossi (NPH), subnucleus b of the medial accessory olivary nucleus (sbMAO), and vestibular complex (VC). The second (control) injection appeared to confirm a proposed (Langer et al. 1985b) projection from the flocculus to the basal interstitial nucleus. The results are discussed in terms of the functional relationships of the FN to the frontal eye field and oculomotor-related brainstem structures involved in the production of saccadic and smooth pursuit eye movements.