Principal Olive Research Articles

Post Mortem Image Analysis of Astrocytes of the Human Principal Olivary Nucleus Using Geometrical and Fractal Parameters

Based on their morphology, the most abundant cells within the nervous tissue of the central nervous system, astrocytes, can be divided into two types, protoplasmic astrocytes and fibrous astrocytes. A further analysis of the brain tissue with the preserved astrocytes from the human principal olivary nucleus, based on their morphological differences with age, is successfully performed in this paper. Moreover, the images of 294 astrocytes, 148 fibrous and 146 protoplasmic, from the principal olivary nucleus were used. Applied for the first time in astrocytes image analysis, the principal component analysis was used to find the most informative parameters among geometrical and fractal in each of the four predefined groups, i.e., categories, of the morphological measurements of astrocytes in the images. The proposed subsets representing different morphological features can be used to distinguish astrocyte subtypes and predict their changes during normal aging. The values of the adequated parameters in different subsets were compared between the fibrous and protoplasmic astrocytes and correlated with age. Significant differences (p < 0.05) between the two subtypes were found in four Euclidean and four monofractal parameters. In addition, significant correlations were found between selected parameters and the age of subjects. In the upcoming iterations of this procedure, possible refinement and upgrades are expected.

Monofractal Dimension in Quantifying the Image of Neurons in the Plane: Analysis of Image Features of Multipolar Neurons from the Principal Olivary Nucleus in Humans with Age

The existing study examines four features of 2D images from the principal olivary nucleus of the adult human. The main goal of the research is to investigate the relationship between monofractal and computational parameters that quantify three features of neuronal images. An additional goal of the research is to examine the change in the four features of the image with age. The samples belonged to the histological collection from the Department of Anatomy of the University of Novi Sad. From the pool of binary images, a sample of medium-sized neurons was selected and further processed. A public computer program (Image J with FracLac plugin) with standard commands that calculate computational and monofractal parameters analyzed all images. The relationship between parameters or between parameters with age was performed by statistical evaluation of Pearson’s correlation coefficient. The monofractal dimension of corresponding images can qualitatively represent image properties and some features decrease with age, while some do not. This study confirms the previous conclusions according to which the monofractal dimension of neuronal image reliably quantifies three features of the image. On the other hand, the study shows the distribution of four features with age.

Price risk connectedness in the principal olive oil markets of the EU

This work investigates price risk connectedness in the leading olive oil markets of the EU. To this end, it relies on a flexible methodology that allows modelling price linkages across multiple markets in the physical and the product quality space and weekly prices from Spain, Italy, and Greece. The main empirical results suggest: First, price risk connectedness under extreme positive shocks is stronger than under extreme negative ones. Second, physical space is a much more important determinant of price risk spillovers relative to quality differentials. Third, the higher quality of olive oil (extra virgin) is more likely to transmit price risk to the lower quality of olive oil (virgin). Fourth, Spain (the largest supplier) plays a central role in the flow of information within the network of olive oil markets.

Input and output organization of the mesodiencephalic junction for cerebro‐cerebellar communication

Most studies investigating the impact of the cerebral cortex (CC) onto the cerebellum highlight the role of the pons, which provides the mossy fibers to the cerebellum. However, cerebro‐cerebellar communication may also be mediated by the nuclei of the mesodiencephalic junction (MDJ) that project to the inferior olive (IO), which in turn provides the climbing fibers to the molecular layer. Here, we uncover the precise topographic relations of the inputs and outputs of the MDJ using multiple, classical, and transneuronal tracing methods as well as analyses of mesoscale cortical injections from Allen Mouse Brain. We show that the caudal parts of the CC predominantly project to the principal olive via the rostral MDJ and that the rostral parts of the CC predominantly project to the rostral medial accessory olive via the caudal MDJ. Moreover, using triple viral tracing technology, we show that the cerebellar nuclei directly innervate the neurons in the MDJ that receive input from CC and project to the IO. By unraveling these topographic and prominent, mono‐ and disynaptic projections through the MDJ, this work establishes that cerebro‐cerebellar communication is not only mediated by the pontine mossy fiber system, but also by the climbing fiber system.

2D Images of Astrocytes in the Human Principal Olivary Nucleus: Monofractal Analysis of the Morphology

Introduction: Current knowledge postulated glia as active participants in various metabolic processes within nervous tissue. The most numerous glial cells were astrocytes, and qualitative analysis divided them into two types based on their anatomical locations: fibrous and protoplasmic. The main goal of this research was to examine the morphological difference between types, analyzing four features of the image. The secondary objective of this research was to explore their morphology through maturation and aging. Materials and Methods: The material originated from bilateral sections of the human principal olivary nucleus, without disorders in the central nervous system. The brains were taken from 30 human cadavers (35 - 90 years) and cut into samples corresponding to dimensions of the principal olivary nucleus. A light microscope digitized the histological preparations. The selection of 294 images was analyzed by monofractal parameters derived from the box-counting. These parameters quantified four image properties (size, shape, complexity and homogeneity) of the glial body or whole glial cell. Results: The first results showed that images of two types of astrocytes were significantly different (p < 0.05 and higher) in all properties of whole cells. The second results examined the differences between three age groups in both types of astrocytes. The differences between groups were more evident for protoplasmic than fibrous (nine vs. three parameters). Conclusions: The main limitation of this study lies in the fact that the quantification was performed only by fractal analysis techniques. Nevertheless, a detailed monofractal analysis of astrocytes was performed for the first time. Thus, although this study can be seen as an improvement of the previous qualitative results, future research will provide the complete procedure of the image analysis.

Classification by morphology of multipolar neurons of the human principal olivary nucleus

The principal olivary nucleus is the largest part of the inferior olivary complex and is involved in the spatial and temporal organization of movement and motor learning. Nearly all neurons in this nucleus is multipolar along with having a highly complex dendritic tree and significant asymmetry in shape. In this study, we updated the current classification scheme, examined morphological differences between the proposed groups, and investigated age-related morphological changes. Histological preparations were digitized by a light microscope and a sample of 259 images of neurons was analyzed by 17 computationally generated parameters of morphology. These were reduced to the four variables of principal component analysis and the sample was classified by k-means method of clustering into three clusters. The differences between clusters were documented and for medium-sized neurons the relationship between four morphological parameters and age were investigated. Finally, for two of the age groups the changes in the morphology were explored. This study includes a detailed and robust classification of the PON neurons and the findings improve upon past qualitative work.

Active integration of glutamatergic input to the inferior olive generates bidirectional postsynaptic potentials.

Key points We establish experimental preparations for optogenetic investigation of glutamatergic input to the inferior olive.Neurones in the principal olivary nucleus receive monosynaptic extra‐somatic glutamatergic input from the neocortex.Glutamatergic inputs to neurones in the inferior olive generate bidirectional postsynaptic potentials (PSPs), with a fast excitatory component followed by a slower inhibitory component.Small conductance calcium‐activated potassium (SK) channels are required for the slow inhibitory component of glutamatergic PSPs and oppose temporal summation of inputs at intervals ≤ 20 ms.Active integration of synaptic input within the inferior olive may play a central role in control of olivo‐cerebellar climbing fibre signals. The inferior olive plays a critical role in motor coordination and learning by integrating diverse afferent signals to generate climbing fibre inputs to the cerebellar cortex. While it is well established that climbing fibre signals are important for motor coordination, the mechanisms by which neurones in the inferior olive integrate synaptic inputs and the roles of particular ion channels are unclear. Here, we test the hypothesis that neurones in the inferior olive actively integrate glutamatergic synaptic inputs. We demonstrate that optogenetically activated long‐range synaptic inputs to the inferior olive, including projections from the motor cortex, generate rapid excitatory potentials followed by slower inhibitory potentials. Synaptic projections from the motor cortex preferentially target the principal olivary nucleus. We show that inhibitory and excitatory components of the bidirectional synaptic potentials are dependent upon AMPA (GluA) receptors, are GABAA independent, and originate from the same presynaptic axons. Consistent with models that predict active integration of synaptic inputs by inferior olive neurones, we find that the inhibitory component is reduced by blocking large conductance calcium‐activated potassium channels with iberiotoxin, and is abolished by blocking small conductance calcium‐activated potassium channels with apamin. Summation of excitatory components of synaptic responses to inputs at intervals ≤ 20 ms is increased by apamin, suggesting a role for the inhibitory component of glutamatergic responses in temporal integration. Our results indicate that neurones in the inferior olive implement novel rules for synaptic integration and suggest new principles for the contribution of inferior olive neurones to coordinated motor behaviours.

The molecular biology of the olive fly comes of age.

BackgroundOlive cultivation blends with the history of the Mediterranean countries since ancient times. Even today, activities around the olive tree constitute major engagements of several people in the countryside of both sides of the Mediterranean basin. The olive fly is, beyond doubt, the most destructive pest of cultivated olives. The female fly leaves its eggs in the olive fruit. Upon emergence, the larvae feed on the olive sap, thus destroying the fruit. If untreated, practically all olives get infected. The use of chemical insecticides constitutes the principal olive fly control approach. The Sterile Insect Technique (SIT), an environmentally friendly alternative control method, had been tried in pilot field applications in the 1970's, albeit with no practical success. This was mainly attributed to the low, non-antagonistic quality of the mixed-sex released insects. Many years of experience from successful SIT applications in related species, primarily the Mediterranean fruit fly, Ceratitis capitata, demonstrated that efficient SIT protocols require the availability of fundamental genetic and molecular information.ResultsAmong the primary systems whose understanding can contribute towards novel SIT approaches (or its recently developed alternative RIDL: Release of Insects carrying a Dominant Lethal) is the reproductive, since the ability to manipulate the reproductive system would directly affect the insect's fertility. In addition, the analysis of early embryonic promoters and apoptotic genes would provide tools that confer dominant early-embryonic lethality during mass-rearing. Here we report the identification of several genes involved in these systems through whole transcriptome analysis of female accessory glands (FAGs) and spermathecae, as well as male testes. Indeed, analysis of differentially expressed genes in these tissues revealed higher metabolic activity in testes than in FAGs/spermathecae. Furthermore, at least five olfactory-related genes were shown to be differentially expressed in the female and male reproductive systems analyzed. Finally, the expression profile of the embryonic serendipity-α locus and the pre-apoptotic head involution defective gene were analyzed during embryonic developmental stages.ConclusionsSeveral years of molecular studies on the olive fly can now be combined with new information from whole transcriptome analyses and lead to a deep understanding of the biology of this notorious insect pest. This is a prerequisite for the development of novel embryonic lethality female sexing strains for successful SIT efforts which, combined with improved mass-reared conditions, give new hope for efficient SIT applications for the olive fly.

Cerebellar Inhibitory Input to the Inferior Olive Decreases Electrical Coupling and Blocks Subthreshold Oscillations

GABAergic projection neurons in the cerebellar nuclei (CN) innervate the inferior olive (IO) that in turn is the source of climbing fibers targeting Purkinje neurons in the cerebellar cortex. Anatomical evidence suggests that CN synapses modulate electrical coupling between IO neurons. Invivo studies indicate that they are also involved in controlling synchrony and rhythmicity of IO neurons. Here, we demonstrate using virally targeted channelrhodopsin in the cerebellar nucleo-olivary neurons that synaptic input can indeed modulate both the strength and symmetry of electrical coupling between IO neurons and alter network activity. Similar synaptic modifications of electrical coupling are likely to occur in other brain regions, where rapid modification of the spatiotemporal features of the coupled networks is needed to adequately respond to behavioral demands.

Price dependence in the principal EU olive oil markets

The objective of this paper is to assess the degree and the structure of price dependence in the principal EU olive oil markets (Spain, Italy and Greece). To this end, it utilizes monthly olive oil price data and the statistical tool of copulas. The empirical results suggest that prices are likely to boom together but not to crash together; this is especially true for the prices of the two most important players, Italy (importer) and Spain (exporter). The finding of asymmetric price co-movements implies that the three principal spatial olive oil markets in the EU cannot be thought of as one great pool.

Factorial design optimisation of hydrocaffeic acid removal from an aqueous matrix by the use of a crude potato polyphenol oxidase

Hydrocaffeic acid (HCA) is a compound with high structural similarity to principal olive mill wastewater constituents, such as hydroxytyrosol and caffeic acid. This compound was chosen as a model substrate to investigate the enzyme-assisted removal from an aqueous medium, using a crude polyphenol oxidase (PPO) from potato waste peels. The process was optimised employing factorial design and response surface methodology, including treatment time, pH and polyethylene glycol (PEG) as crucial parameters that could affect removal. Data obtained from ANOVA indicated that neither time nor PEG concentration exerted a statistically significant effect on % HCA removal, but only the pH of the medium. Under optimal conditions, the theoretical % HCA removal was 99.2. High performance liquid chromatography (HPLC) analysis revealed that PPO-mediated oxidation of HCA resulted in the formation of three principal oxidation products. Liquid-chromatography–mass spectrometry (LC/MS) investigation suggested these products to be HCA dehydrodimers.

Sequence of Synaptogenesis in the Fetal and Neonatal Cerebellar System - Part 1: Guillain-Mollaret Triangle (Dentato-Rubro-Olivo-Cerebellar Circuit)

Precise temporal and spatial sequences of synaptogenesis occur in the cerebellar system, as in other synaptic circuits of the brain. In postmortem brain sections of 172 human fetuses and neonates, synaptophysin immunoreactivity was studied in nuclei of the Guillain-Mollaret triangle: dentato-olivo-rubro-cerebellar circuit. Synaptophysin demonstrates not only progressive increase in synaptic vesicles in each structure, but also shows the development of shape from amorphous globular neuronal aggregates to undulated nuclei. Intensity of synaptophysin reactivity is strong before the mature shape of these nuclei is achieved. Accessory olivary and deep cerebellar nuclei are intensely stained earlier than the principal olivary and dentate nuclei. The dorsal blades of both form earlier than the ventral, with reactivity initially peripheral. Initiation of synaptophysin reactivity is at 13 weeks in the inferior olive (r6, r7) and at 16 weeks in the dentate (r2). Initial synaptic vesicles are noted at 13 weeks in the red nucleus (r0); synapses form initially on the small neurons at 13 weeks but thereafter simultaneously on small and large neurons. Form and reactivity follow caudorostral, dorsoventral and mediolateral gradients in the axes of the rhombencephalon. This study provides control data to serve as a basis for interpreting aberrations in synaptogenesis in malformations of the cerebellar system, genetic disorders and acquired insults to the cerebellum and brainstem during fetal life, applicable to tissue sections and complementing biochemical and molecular techniques.

Progressive limb ataxia following inferior olive lesions

Cerebellar climbing fibres originate in the inferior olive (IO). Temporary IO inactivation produces movement deficits. Does permanent inactivation produce similar deficits and, if so, do they recover? The excitotoxin, kainic acid, was injected into the rostral IO of three cats. Behaviour was measured during reaching and locomotion. Two cats were injected during the reaching task. Within minutes, grasping became difficult and the trajectories of the reaches showed higher arcing than normally seen. During locomotion, both cats showed head and trunk deviation to the injected side, walking paths curved to the injected side, and the paws were lifted higher than normal. Limbs contralateral to the injections became rigid. Within 1 day, posture had normalized, locomotion was unsteady and high lifting of the paws had reversed to a tendency to drag the dorsum of the paws. Passive body movement produced vestibular signs. Over a few days, locomotion normalized and vestibular signs disappeared. Reach trajectories were normal but grasping deficits persisted. Over the first week, the amplitude of limb lift during reaching and locomotion began to increase. The increase continued over time and, after several months, limb movements became severely ataxic. The effects followed the somatotopy of the rostral IO: a loss of cells in medial rostral IO only affected the forelimb, whereas a loss of cells in medial and lateral IO affected both forelimb and hindlimb. Deficits produced by IO lesions involve multiple mechanisms; some recover rapidly, some appear stable, and some worsen over time. The nature of the progressive deficit suggests a gradual loss of Purkinje cell inhibition on cerebellar nuclear cells.

Spontaneous cluster activity in the inferior olivary nucleus in brainstem slices from postnatal mice

A distinctive property of the cerebellar system is olivocerebellar modules, where synchronized electrical activity in neurons in the inferior olivary nucleus (IO) evokes organized activity in the cerebellar cortex. However, the exact function of these modules, and how they are developed, is still largely unknown. Here we show that the IO in in vitro slices from postnatal mice spontaneously generates clusters of neurons with synchronous Ca(2+) transients. Neurons in the principal olive (PO), and the vestibular-related dorsomedial cell column (dmcc), showed an age-dependent increase in spontaneous calcium transients. The spatiotemporal activity pattern was occasionally organized in clusters of co-active neighbouring neurons,with regular (16 min-1) and irregular (2-3 min(-1)) repeating cluster activity in the dmcc and PO, respectively. IO clusters had a diameter of 100-170 μm, lasted~1 s, and increased in occurrence from postnatal day P5.5 to P12.5, followed by a sharp drop to near zero at P15.5. IO clusters were overlapping, and comprised nearly identical neurons at some time points, and a varied subset of neurons at others. Some neurons had hub-like properties, being co-active with many other neighbours, and some were co-active with separate clusters at different times. The coherence between calcium transients in IO neurons decreased with Euclidean distance between the cells reaching low values at 100-200 μm distances. Intracellular recordings from IO neurons during cluster formation revealed the presence of spikelet-like potentials, suggesting that electrical coupling between neighbouring IO neurons may serve as a synchronizing mechanism. In conclusion, the IO shows spontaneous cluster activity under in vitro conditions, coinciding with a critical postnatal period in olivocerebellar development. We propose that these clusters may be forerunners of the ensembles of IO neurons shown to be co-active in adult animals spontaneously and during motor acts.

Functional Relations of Cerebellar Modules of the Cat

The cerebellum consists of parasagittal zones that define fundamental modules of neural processing. Each zone receives input from a distinct subdivision of the inferior olive (IO)-activity in one olivary subdivision will affect activity in one cerebellar module. To define functions of the cerebellar modules, we inactivated specific olivary subdivisions in six male cats with a glutamate receptor blocker. Olivary inactivation eliminates Purkinje cell complex spikes, which results in a high rate of Purkinje cell simple spike discharge. The increased simple spike discharge inhibits output from connected regions of the cerebellar nuclei. After inactivation, behavior was evaluated during a reach-to-grasp task and during locomotion. Inactivation of each subdivision produced unique behavioral deficits. Performance of the reach-to-grasp task was affected by inactivation of the rostral dorsal accessory olive (rDAO) and the rostral medial accessory olive (rMAO) and, possibly, the principal olive. rDAO inactivation produced paw drag during locomotion and a deficit in grasping the handle during the reach-to-grasp task. rMAO inactivation caused the cats to reach under the handle and produced severe limb drag during locomotion. Inactivation of the dorsal medial cell column, cell group beta, or caudal medial accessory olive produced little deficit in the reach-to-grasp task, but each produced a different deficit during locomotion. In all cases, the cats appeared to have intact sensation, good spatial awareness, and no change of affect. Normal cerebellar function requires low rates of IO discharge, and each cerebellar module has a specific and unique function in sensory-motor integration.

Morphometric analysis of the neuronal numbers and densities of the inferior olivary complex in the donkey ( Equus asinus)

The morphometric interrelations between the compartments of the inferior olivary complex (IOC) in the donkey ( Equus asinus) were ascertained by examining serial sections throughout the entire length of the IOC for both sides. Nissl-stained celloidin sections of four brainstems of donkeys were used. The IOC consisted of three major nuclei and four small cell groups. The total neuronal count in both sides of the IOC was 202,040 ± 8480 cells. The medial accessory olivary nucleus (MAO) had the largest relative area (46%) and the highest number of neurons (90,800 ± 7600). The dorsal accessory olivary nucleus (DAO) had the second largest relative area (33%), while the principal olivary nucleus (PO) had the lowest relative area (21%). However, the total neuron count in the PO was larger (60,840 ± 1840) than DAO (50,360 ± 4040). The average neuronal density was 2700 ± 400 cells/mm 3. The numerical values of the current study of the IOC in the donkey were similar to those of other mammals.

In Vivo Structural and Functional Imaging of the Human Rubral and Inferior Olivary Nuclei: A Mini-review

Few imaging studies have been devoted to the structural and functional connectivity of the red and inferior olivary nuclei although these two nuclei represent two main targets of the cerebellum within the brainstem. However, the RN is anatomically and functionally related to a widespread sensorimotor, limbic, and executive brain network. It projects massively onto the principal olive with which it contributes to a cerebello-rubro-olivo-cerebellar loop modulated by cortical and subcortical afferents. Despite a minor role in planning and execution of rhythmic movements, the red nucleus in conjunction with the inferior olive, more specifically involved in the detection of "unexpected" events, contributes to sensorimotor, sensory and, likely, cognitive higher functions.

Difference of climbing fiber input sources between the primate oculomotor-related cerebellar vermis and hemisphere revealed by a retrograde tracing study

The cerebellar flocculus–paraflocculus complex, vermal lobule VII (V-7) and hemispheric lobule VII (H-7) are involved in learning-dependent smooth pursuit eye movement control. To locate the sources of climbing fiber inputs to the H-7 and V-7, we injected retrograde tracers and examined the locations of retrogradely labeled neurons in the inferior olive in 4 monkeys. After the injection of cholera toxin B (CTB) into the H-7, retrogradely labeled neurons were observed abundantly in cell group d, i.e., dorsal cap, of the caudal medial accessory olive (MAO) and ventral lamella of principal olive (PO). After injections of fast blue (FB) into the V-7, retrogradely labeled neurons were observed mainly in cell group b of MAO, but rarely in cell group d or PO. Cell group d is known to receive inputs from the nucleus optic tract (NOT) and project climbing fibers to the flocculus and ventral paraflocculus, and cell group b is known to receive inputs from the superior colliculus. These results suggest that the three oculomotor cerebellar areas may use different visual signals for the control of smooth pursuit: the flocculus–paraflocculus complex and H-7 receive visual climbing fiber inputs derived mainly from the NOT via cell group d, while the V-7 receive visual climbing fiber inputs derived mainly from the superior colliculus via cell group b.

5-HT 2A receptors are concentrated in regions of the human infant medulla involved in respiratory and autonomic control

The serotonergic (5-HT) system in the human medulla oblongata is well-recognized to play an important role in the regulation of respiratory and autonomic function. In this study, using both immunocytochemistry ( n = 5) and tissue section autoradiography with the radioligand 125I-1-(2,5-dimethoxy-4-iodo-phenyl)2-aminopropane ( n = 7), we examine the normative development and distribution of the 5-HT 2A receptor in the human medulla during the last part of gestation and first postnatal year when dramatic changes are known to occur in respiratory and autonomic control, in part mediated by the 5-HT 2A receptor. High 5-HT 2A receptor binding was observed in the dorsal motor nucleus of the vagus (preganglionic parasympathetic output) and hypoglossal nucleus (airway patency); intermediate binding was present in the nucleus of the solitary tract (visceral sensory input), gigantocellularis, intermediate reticular zone, and paragigantocellularis lateralis. Negligible binding was present in the raphé obscurus and arcuate nucleus. The pattern of 5-HT 2A immunoreactivity paralleled that of binding density. By 15 gestational weeks, the relative distribution of the 5-HT 2A receptor was similar to that in infancy. In all nuclei sampled, 5-HT 2A receptor binding increased with age, with significant increases in the hypoglossal nucleus ( p = 0.027), principal inferior olive ( p = 0.044), and medial accessory olive (0.038). Thus, 5-HT 2A receptors are concentrated in regions involved in autonomic and respiratory control in the human infant medulla, and their developmental profile changes over the first year of life in the hypoglossal nucleus critical to airway patency and the inferior olivary complex essential to cerebellar function.

Topography of olivocerebellar projections to the uvula and paramedian lobule in the rabbit: Comparison with other species

The organization of projections from the inferior olive (IO) to the uvula of the vermis and the paramedian lobule (PML) of the same hemisphere in the rabbit cerebellar cortex was studied using retrograde tracers: Diamidino Yellow (DY) and Fast Blue (FB) dyes were injected unilaterally into these two targets in the same animals. The distribution patterns of DY- and FB-labeled neurons consistently detected in spatially separate regions of the contralateral IO subnuclei show that the IO-uvular and IO-PML projections display a distinct topography. The absence of double labeling indicates that no neurons project divergently to both the uvula and PML. The lateral and medial regions of the medial accessory olive and of the ventral lamina of the caudal principal olive project to the uvula and PML, respectively. Several neuronal groups at more rostral levels of the principal olive send fibers solely to the PML. The medial and lateral regions of the beta nucleus and the dorsomedial cell column supply the uvula and PML, respectively. Neurons in the dorsal cap and the ventrolateral outgrowth also tend to display this type of localization. Moreover, the caudal part of the dorsal accessory olive and the dorsal lamina of the principal olive project exclusively to the PML. The most caudal and rostral aspects of the IO do not participate in projection. Topographical relationships in the IO-uvular and IO-PML projections have not been previously demonstrated in the rabbit, and they are discussed in the context of inter-animal differences and cerebellar zonal organization. The possible functional significance of the connections is also discussed.