Showing papers by "Laval University published in 1990"

Regional distribution of body fat, plasma lipoproteins, and cardiovascular disease.

Abstract: Several epidemiological studies have reported that the regional distribution of body fat is a significant and independent risk factor for cardiovascular disease (CVD) and related mortality. Although these associations are well established, the causal mechanisms are not fully understood. Numerous studies have, however, shown that specific topographic features of adipose tissue are associated with metabolic complications that are considered as risk factors for CVD such as insulin resistance, hyperinsulinemia, glucose intolerance and type II diabetes mellitus, hypertension, and changes in the concentration of plasma lipids and lipoproteins. The present article summarizes the evidence on the metabolic correlates of body fat distribution. Potential mechanisms for the association between body fat distribution, metabolic complications, and CVD are reviewed, with an emphasis on plasma lipoprotein levels and plasma lipid transport. From the evidence available, it seems likely that subjects with visceral obesity represent the subgroup of obese individuals with the highest risk for CVD. Although body fat distribution is now considered as a more significant risk factor for CVD and related death rate than obesity per se, further research is clearly needed to identify the determinants of body fat distribution and the causal mechanisms involved in the metabolic alterations. It appears certain, however, that an altered plasma lipid transport is a significant component of the relation between body fat distribution and CVD.

The Response to Long-Term Overfeeding in Identical Twins

Abstract: We undertook this study to determine whether there are differences in the responses of different persons to long-term overfeeding and to assess the possibility that genotypes are involved in such differences. After a two-week base-line period, 12 pairs of young adult male monozygotic twins were overfed by 4.2 MJ (1000 kcal) per day, 6 days a week, for a total of 84 days during a 100-day period. The total excess amount each man consumed was 353 MJ (84,000 kcal). During overfeeding, individual changes in body composition and topography of fat deposition varied considerably. The mean weight gain was 8.1 kg, but the range was 4.3 to 13.3 kg. The similarity within each pair in the response to overfeeding was significant (P less than 0.05) with respect to body weight, percentage of fat, fat mass, and estimated subcutaneous fat, with about three times more variance among pairs than within pairs (r approximately 0.5). After adjustment for the gains in fat mass, the within-pair similarity was particularly evident with respect to the changes in regional fat distribution and amount of abdominal visceral fat (P less than 0.01), with about six times as much variance among pairs as within pairs (r approximately 0.7). We conclude that the most likely explanation for the intrapair similarity in the adaptation to long-term overfeeding and for the variations in weight gain and fat distribution among the pairs of twins is that genetic factors are involved. These may govern the tendency to store energy as either fat or lean tissue and the various determinants of the resting expenditure of energy.

Neuronal activities in brain-stem cholinergic nuclei related to tonic activation processes in thalamocortical systems

Abstract: This study was performed to examine the hypothesis that thalamic-projecting neurons of mesopontine cholinergic nuclei display activity patterns that are compatible with their role in inducing and maintaining activation processes in thalamocortical systems during the states of waking (W) and rapid-eye-movement (REM) sleep associated with desynchronization of the electroencephalogram (EEG) A sample of 780 neurons located in the peribrachial (PB) area of the pedunculopontine tegmental nucleus and in the laterodorsal tegmental (LDT) nucleus were recorded extracellularly in unanesthetized, chronically implanted cats Of those neurons, 82 were antidromically invaded from medial, intralaminar, and lateral thalamic nuclei: 570 were orthodromically driven at short latencies from various thalamic sites: and 45 of the latter elements are also part of the 82 cell group, as they were activated both antidromically and synaptically from the thalamus There were no statistically significant differences between firing rates in the PB and LDT neuronal samples Rate analyses in 2 distinct groups of PB/LDT neurons, with fast (greater than 10 Hz) and slow (less than 2 Hz) discharge rates in W, indicated that (1) the fast-discharging cell group had higher firing rates in W and REM sleep compared to EEG-synchronized sleep (S), the differences between all states being significant (p less than 00005); (2) the slow-discharging cell group increased firing rates from W to S and further to REM sleep, with significant difference between W and S (p less than 001), as well as between W or S and REM sleep (p less than 00005) Interspike interval histograms of PB and LDT neurons showed that 75% of them have tonic firing patterns, with virtually no high-frequency spike bursts in any state of the wake-sleep cycle We found 22 PB cells that discharged rhythmic spike trains with recurring periods of 08-1 sec Autocorrelograms revealed that this oscillatory behavior disappeared when their firing rate increased during REM sleep Dynamic analyses of sequential firing rates throughout the waking-sleep cycle showed that none of the full-blown states of vigilance is associated with a uniform level of spontaneous firing rate Signs of decreased discharge frequencies of mesopontine neurons appeared toward the end of quiet W, preceding by about 10-20 sec the most precocious signs of EEG synchronization heralding the sleep onset During transition from S to W, rates of spontaneous discharges increased 20 sec before the onset of EEG desynchronization(ABSTRACT TRUNCATED AT 400 WORDS)

Zebrin II: a polypeptide antigen expressed selectively by Purkinje cells reveals compartments in rat and fish cerebellum.

Abstract: Monoclonal antibody mab-zebrin II was generated against a crude homogenate of cerebellum and electrosensory lateral line lobe from the weakly electric fish Apteronotus leptorhynchus. On Western blots of fish cerebellar proteins, mab-zebrin II recognizes a single polypeptide antigen of apparent molecular weight 36 kD. Immunocytochemistry of apteronotid brains reveals that zebrin II immunoreactivity is confined exclusively to Purkinje cells in the corpus cerebelli, lateral valvula cerebelli, and the eminentia granularis anterior. Other Purkinje cells, in the medial valvula cerebelli and eminentia granularis posterior, are not zebrin II immunoreactive. Immunoreactive Purkinje cells are stained completely, including dendrites, axons, and somata. The antigen seems to be absent only from the nucleus. A similar distribution is seen in catfish, goldfish, and a mormyrid fish. Zebrin II immunoreactivity is also found in the rat cerebellum. Western blotting of rat cerebellar proteins reveals a single immunoreactive polypeptide, with apparent, molecular weight 36 kD, as in the fish. Also as in the fish, staining in the adult rat cerebellum is confined to a subset of Purkinje cells. Peroxidase reaction product is deposited throughout the immunoreactive Purkinje cells with the exception of the nucleus. No other cells in the cerebellum express zebrin II. At higher antibody concentrations, a weak glial cross reactivity is seen in most other brain regions: we believe that this is probably nonspecific. Zebrin II+ Purkinje cells are clustered together to form roughly parasagittal bands interposed by similar non-immunoreactive clusters. In all there are 7 zebrin II+ and 7 zebrin II− compartments in each hemicerebellum. One immunoreactive band is adjacent to the midline; two others are disposed laterally to each side in the vermis; there is a paravermal band; and finally three more bands are identified in each hemisphere. Both in number and position, these compartments correspond precisely to the bands revealed by using another antibody, mabQ113 (anti-zebrin I). In both fish and rat the compartmentation revealed by zebrin II immunocytochemistry is related to the organization of cerebellar afferent and efferent projections and may provide clues as to the fundamental architecture of the vertebrate cerebellum.

Identification and isolation of a membrane protein necessary for leukotriene production

Abstract: Several inflammatory diseases, including asthma, arthritis and psoriasis are associated with the production of leukotrienes by neutrophils, mast cells and macrophages. The initial enzymatic step in the formation of leukotrienes is the oxidation of arachidonic acid by 5-lipoxygenase (5-LO) to leukotriene A4. Osteosarcoma cells transfected with 5-LO express active enzyme in broken cell preparations, but no leukotriene metabolites are produced by these cells when stimulated with the calcium ionophore A23187, indicating that an additional component is necessary for cellular 5-LO activity. A new class of indole leukotriene inhibitor has been described that inhibits the formation of cellular leukotrienes but has no direct inhibitory effect on soluble 5-LO activity. We have now used these potent agents to identify and isolate a novel membrane protein of relative molecular mass 18,000 which is necessary for cellular leukotriene synthesis.

Determination of the secondary structure content of proteins in aqueous solutions from their amide I and amide II infrared bands. Comparison between classical and partial least-squares methods.

Abstract: A method for estimating protein secondary structure from infrared spectra has been developed. The infrared spectra of H{sub 2}O solutions of 13 proteins of known crystal structure have been recorded and corrected for the spectral contribution of water in the amide I and II region by using the algorithm of Dousseau et al. This calibration set of proteins has been analyzed by using either a classical least-squares (CLS) method or the partial least-squares (PLS) method. The pure-structure spectra calculated by the classical least-squares method are in good agreement with spectra of poly(L-lysine) in the {alpha}-helix, {beta}-sheet, and undefined conformations. The results show that the best agreement between the secondary structure determined by X-ray crystal-lography and that predicted by infrared spectroscopy is obtained when both the amide I and II bands are used to generate the calibration set, when the PLS method is used, and when it is assumed that the secondary structure of proteins is composed of only four types of structure: ordered and disordered {alpha}-helices, {beta}-sheet, and undefined conformation. Attempts to include turns in the secondary structure estimation have led to a loss of accuracy. The spectra of the calibration proteins were also recorded in {sup 2}H{sub 2}O solution.more » After correction for the contribution of the combination band of {sup 2}H{sub 2}O in the amide I{prime} band region, the spectra were analyzed with PLS, but the results were not as good as for the spectra obtained in H{sub 2}O, especially for the {alpha}-helical conformation.« less

Decreased dopamine in the retinas of patients with Parkinson's disease.

Abstract: Dopamine and it metabolites dihydroxyphenylacetic acid and homovanillic acid were measured in the retinas of eight patients with Parkinson's disease who died. They were divided into two groups according to their last dose of levodopa therapy. One group of three patients had not received levodopa therapy for at least 5 days before death, and the other group of five patients had received therapy 2-15 hours before death. Each patient was matched with controls for delay between death and freezing. In the three patients without levodopa therapy, the retinal dopamine content was lower than normal. In the five patients who received levodopa therapy before death, the retinal dopamine content was similar to that in the controls. This study is the first direct evidence to the authors' knowledge that retinal dopamine concentration is decreased in Parkinson's disease, as it is in the nigrostriatal pathway.

Direct Coupling of Marine Invertebrate Spawning with Phytoplankton Blooms

Abstract: Spawning of green sea urchins and blue mussels may be triggered by a heat-stable metabolite released by various species of phytoplankton. Mussels require a higher phytoplankton density for a maximum response than urchins, perhaps because mussels are exposed to higher concentrations of phytoplankton as a result of their filtering activity. Phytoplankton as a spawning cue appears to integrate numerous physical and biotic factors indicating favorable conditions for larval growth and survival. Evolution of similar direct coupling of the larval phase with phytoplankton blooms may be common among marine invertebrates.

Efferent projections of the subthalamic nucleus in the squirrel monkey as studied by the PHA-L anterograde tracing method.

Abstract: The organization of the efferent connections of the subthalamic nucleus was studied in the squirrel monkey (Saimiri sciureus) by using the lectin Phaseolus vulgaris-leucoagglutinin (PHA-L) as an anterograde tracer. At the level of the basal forebrain, anterogradely labeled fibers and axon terminals were mostly found in the striatopallidal complex and the substantia innominata. In cases in which the PHA-L injection sites were placed in the central or the lateral third of the subthalamic nucleus, numerous anterogradely labeled fibers were seen to arise from the injection loci and innervate massively the globus pallidus. At pallidal levels the fibers formed bands lying parallel and adjacent to the medullary laminae. The number and the complexity of the topographical organization of these bands varied with the size and the location of the PHA-L injection site. When examined at a higher magnification, the bands of subthalamopallidal fibers appeared as rich plexuses of short axon collaterals with small bulbous enlargements that closely surrounded the cell bodies and primary dendrites of pallidal cells. In contrast, PHA-L injection involving the medial tip of the subthalamic nucleus did not produce bandlike fiber patterns in the globus pallidus. Instead, the labeled fibers formed a diffuse plexus occupying the ventral part of the rostral pole of the globus pallidus as well as the subcommissural pallidal region. The substantia innominata contained a moderate number of labeled fibers and axon terminals following injection of PHA-L in the medial tip of the subthalamic nucleus. A small to moderate number of anterogradely labeled fibers were seen in the putamen after all PHA-L injections. These subthalamostriatal fibers were long, linear, and branched infrequently. At midbrain level the substantia nigra contained a significant number of anterogradely labeled fibers and axon terminals following PHA-L injection in the subthalamic nucleus. The subthalamonigral fibers descended along the ventromedial part of the cerebral peduncle and swept laterally to reach their target. Most of these fibers formed small plexuses along the base of the pars reticulata, whereas a few others ascended along the cell columns of the pars compacta that impinged deeply within the pars reticulata. More caudally in the brainstem, a small number of fibers occurred in the area of the pedunculopontine nucleus and in the periaqueductal gray. These findings indicate that besides its well-known connection with the pallidum, the subthalamic nucleus gives rise to widespread projections to other components of the basal ganglia in primates.

Different cellular types in mesopontine cholinergic nuclei related to ponto-geniculo-occipital waves.

Abstract: The only mesopontine neurons previously described as involved in the transfer of ponto-geniculo-occipital (PGO) waves from the brain stem to the thalamus were termed PGO-on bursting cells. We have studied, in chronically implanted cats, neuronal activities in brain-stem peribrachial (PB) and laterodorsal tegmental (LDT) cholinergic nuclei in relation to PGO waves recorded from the lateral geniculate (LG) thalamic nucleus during rapid-eye-movement (REM) sleep. We constructed peri-PGO histograms of PB/LDT cells' discharges and analyzed the interspike interval distribution during the period of increased neuronal activity related to PGO waves. Six categories of PGO-related PB/LDT neurons with identified thalamic projections were found: 4 classes of PGO-on cells: PGO-off but REM-on cells: and post-PGO cells. The physiological characteristics of a given cell class were stable even during prolonged recordings. One of these cell classes (1) represents the previously described PGO-on bursting neurons, while the other five (2-6) are newly discovered neuronal types. (1) Some neurons (16% of PGO-related cells) discharged stereotyped low-frequency (120-180 Hz) spike bursts preceding the negative peak of the LG-PGO waves by 20-40 msec. These neurons had low firing rates (0.5-3.5 Hz) during all states. (2) A distinct cell class (22% of PGO-related neurons) fired high-frequency spike bursts (greater than 500 Hz) about 20-40 msec prior to the thalamic PGO wave. These bursts were preceded by a period (150-200 msec) of discharge acceleration on a background of tonically increased activity during REM sleep. (3) PGO-on tonic neurons (20% of PGO-related neurons) discharged trains of repetitive single spikes preceding the thalamic PGO waves by 100-150 msec, but never fired high-frequency spike bursts. (4) Other PGO-on neurons (10% of PGO-related neurons) discharged single spikes preceding thalamic PGO waves by 15-30 msec. On the basis of parallel intracellular recordings in acutely prepared, reserpine-treated animals, we concluded that the PGO-on single spikes arise from conventional excitatory postsynaptic potentials and do not reflect tiny postinhibitory rebounds. (5) A peculiar cellular class, termed PGO-off elements (8% of PGO-related neurons), consisted of neurons with tonic, high discharge rates (greater than 30 Hz) during REM sleep. These neurons stopped firing 100-200 msec before and during the thalamic PGO waves. (6) Finally, other neurons discharged spike bursts or tonic spike trains 100-300 msec after the initially negative peak of the thalamic PGO field potential (post-PGO elements, 23% of PGO-related neurons).(ABSTRACT TRUNCATED AT 400 WORDS)

A Unified View of the IPA, SF, and LR Gradient Estimation Techniques

Abstract: We study the links between the likelihood-ratio LR gradient-estimation technique sometimes called the score-function SF method, and infinitesimal perturbation analysis IPA. We show how IPA can be viewed as a degenerate special case of the LR and SF techniques by selecting an appropriate representation of the underlying sample space for a given simulation experiment. We also show how different definitions of the sample space yield different variants of the LR method, some of them mixing IPA with more straightforward LR. We illustrate this by many examples. We also give sufficient conditions under which the gradient estimators are unbiased.

Allopatric origin of sympatric populations of lake whitefish (coregonus clupeaformis) as revealed by mitochondrial-dna restriction analysis.

Abstract: In the paper, restriction-fragment length polymorphisms in mitochondrial DNA (mtDNA) were studied to test the hypothesis that sympatric populations of lake whitefish in the Allegash basin have recently diverged through sympatric speciation Thirteen restriction enzymes were used to analyze mtDNA of 156 specimens representing 13 populations from eastern Canada and northern Maine where normal and dwarf phenotypes of whitefish exist in sympatry and allopatry Two monophyletic assemblages of populations that exhibit different geographic distributions were identified One showed an eastern distribution that expands from Cape Breton to the Allegash basin and the other exhibits a more western distribution The Allegash basin was the only area of overlap The western assemblage exhibited the normal size phenotype in all cases, whereas the eastern assemblage exhibited the normal size phenotype in allopatric conditions and the dwarf size phenotype in sympatry The existence of sympatric pairs in the Allegash basin result from the secondary contact of two monophyletic groups of whitefish that evolved allopatrically in separate refugia during the last glaciation events The weak mtDNA difference of sympatric pairs suggests that speciation of lake whitefish in eastern North America was accompanied by only minor alterations of the ancestral gene pool

On-line prediction of fermentation variables using neural networks

Abstract: This article presents an introduction to the use of neural network computational algorithms for the dynamic modeling of bioprocesses. The dynamic neural model is used for the prediction of key fermentation variables. This relatively hew method is compared with a more traditional prediction technique to judge its performance for prediction. Illustrative simulation results of a continuous stirred tank fermentor are used for this comparison. It is shown that neural network models are accurate with a certain degree of noise immunity. They offer the distinctive ability over more traditional methods to learn very naturally complex relationships without requiring the knowledge of the model structure.

Are women owner-managers challenging our definitions of entrepreneurship? An in-depth survey

Abstract: In the Quebec city area, 400 women owner-managers of business in the three industrial sectors answered a detailed questionnaire, and 75 of these subsequently underwent in-depth interviews. The main dimensions explored were the characteristics of the entrepreneurs and their firms, the experience of starting a business, the success criteria used, and their vision for the future of their firms. The results suggest the importance, to these women, of a model of “small and stable business”. This is not a transitory phase for their firm: most choose and value such a scale of business, and they seek recognition for what they do. This model seems to represent an innovative adaptation to their professional, social, family and personal demands and challenges our definitions of entrepreneurship and of “serious business”.

Structural changes during high-energy ball milling of iron-based amorphous alloys: Is high-energy ball milling equivalent to a thermal process?

Abstract: We report the first study of the effect of high-energy mechanical deformation on amorphous iron-based metallic alloys. The structural changes happening in amorphous iron-based materials containing Co or Ni during mechanical deformation show that the structural stability of an amorphous alloy against a thermal and a mechanical process are not related. Therefore, the concept of a high local effective temperature during the milling process cannot be singled out as the only reason for the observed structural transformations.

Electrophysiology and Pharmacology of the Corticothalamic Input to Lateral Thalamic Nuclei: an Intracellular Study in the Cat

Abstract: Though most experimental evidence indicates that the corticothalamic (CT) pathway would exert a direct excitatory action on thalamic relay neurons, the electrophysiological features of this excitation have never been clearly described. A methodological problem in previous electrophysiological studies was that direct corticofugal effects on relay cells could not be separated from those mediated by collateral activation of reticular thalamic neurons. In the present study, the reticular complex was lesioned by kainic acid and the CT response of relay neurons of the ventral lateral nucleus was recorded intracellularly in cats under pentobarbital or urethane anaesthesia. Following reticular thalamic lesions, a prominent depolarization was triggered in thalamic relay cells by stimulation of the CT pathway. This depolarization strongly drove spike discharges, and its amplitude augmented when the stimulation rate exceeded 2 Hz. Tetanizing the CT input with short trains (100–200 Hz for 200–300 ms) produced a similar augmentation to test volleys for 15–30 s after the tetanos. The CT excitation and its frequency-dependent augmentation were depressed by ketamine injection or by local application of N-methyl-D-aspartate (NMDA) antagonists. The augmenting phenomenon appeared strictly homosynaptic. For instance, it did not appear during repetitive stimulation of the cerebellar input, nor did the CT input potentiate subthreshold synaptic potentials of cerebellar origin during a conditioning procedure. Conversely, the cerebellar excitation was depressed when it occurred during the CT depolarization. It is concluded that the direct synaptic responses induced by CT fibres in relay neurons are mediated at least partly by the activation of NMDA receptors. Moreover, the marked non-linear additivity of cerebellar and CT synaptic potentials raises questions concerning the presumed improvement of thalamic transmission of peripheral informations ensured by the CT input. Instead, both inputs could compete for control of the firing of thalamic neurons. The numerical importance of CT fibres and the strong augmenting mechanism operating at synaptic sites in the thalamus suggest that the role of the thalamus is not only to transfer peripheral informations toward the cortex, but also and mainly to feed back to the cortex a modified copy of its own neuronal constructs.

Structure of two in tandem human 17β-hydroxysteroid dehydrogenase genes

Abstract: Two human 17β-hydroxysteroid dehydrogenase (17β-HSD) genes (h17β-HSDI and h17β-HSDII) included in tandem within an approximately 13 kilobase pair fragment were isolated from a genomic λEMBL3 DNA library using cDNA encoding human 17β-HSD (hpE2DH216) as probe. We have determined the complete exon and intron sequences of the two genes as well as their 5′ and 3′-flanking regions. Human 17β-HSDII contains six exons and five short introns for a total length of 3250 base pairs. The exon sequence of h17β-HSDII is identical to the previously reported hpE2DH216 cDNA while the overlapping nucleotide sequences of the corresponding exons and introns of h17β-HSDI and h170-HSDII show 89% homology. In addition, we have used the hpE2DH216 cDNA to demonstrate the widespread expression of 17β-HSD mRNAs in steroidogenic and peripheral target tissues. These new findings provide the basis for a better understanding of the molecular mechanisms involved in 17β-HSD deficiency and peripheral sex steroid metabolism.

Parasagittal organization of the rat cerebellar cortex: direct comparison of Purkinje cell compartments and the organization of the spinocerebellar projection.

Abstract: Retrograde and anterograde transport of tracers, electrophysiological recording, somatotopic mapping, and histochemical and immunological techniques have all revealed a parasagittal parcellation of the cerebellar cortex, including its efferent and many of its afferent connections. In order to establish whether the different compartments share a common organizational plan, a systematic comparative analysis of the patterns of parasagittal zonation in the cerebellar cortex of the rat has been undertaken, by using the parasagittal compartmentation of zebrin I+ and zebrin I- Purkinje cells as revealed by monoclonal antibody Q113 as a reference frame. The distribution of mossy fiber terminals originating from the lower thoracic-higher lumbar spinal cord was compared to the distribution of zebrin I bands. Three-dimensional reconstructions from alternate frontal sections processed either for the anterograde transport of tracer or for zebrin I immunoreactivity reveal that the limits of the spinocerebellar terminal fields in the granular layer correlate well with the boundaries of some, but not all, zebrin I compartments in the molecular layer above. This leads to a subdivision of the zebrin I compartments into spinal receiving and spinal nonreceiving portions. In lobules II and VIII, the spinocerebellar terminal fields assume different positions relative to the zebrin I compartments in the ventral compared to the dorsal faces. Thus, each longitudinal compartment may be further divided transversely into subzones, each receiving a specific combination of mossy fiber afferents. The further subdivision of zebrin I compartments by mossy fiber terminal fields increases the resolution of the topography to such a point that anatomical compartment widths become compatible with the width of the microzones and the patches identified by electrophysiological methods.

Expression of compartmentation antigen zebrin I in cerebellar transplants.

Abstract: The mammalian cerebellum is divided into multiple parasagittal compartments as defined by the organization of afferent and efferent projections and by the pattern of expression of several biochemical markers. One such marker is the antigen zebrin I, a 120 kD polypeptide of unknown function that is expressed differentially by a subset of Purkinje cells. Zebrin I+ Purkinje cells are grouped into an array of 14 parasagittal bands interposed by zebrin I- compartments. This Purkinje cell compartmentation corresponds to compartments in the olivocerebellar projection. The afferent axon compartments are present prior to the expression of the mature zebrin I phenotype, thus raising the possibility that differential afferent input regulates the zebrin I phenotype of the target of that input. Lesion studies in the neonate preclude a role for afferent inputs in the regulation of zebrin I expression postnatally, but a prenatal role in commitment still remains open. To explore this possibility, cerebellar anlagen were dissected from embryos at embryonic days 12-15, that is, prior to any contact with afferents, and transplanted ectopically into adult hosts. In the first series of experiments, the grafts were placed into the anterior chamber of the eye, and in the second series, into cavities prepared in the neocortex. Grafts were allowed to mature and then were immunoperoxidase or immunofluorescence stained for zebrin I immunoreactivity. Zebrin I was expressed by grafted Purkinje cells in cortico and in oculo. Double-labelling experiments confirmed that both the zebrin I+ and the zebrin I- phenotypes were present. The zebrin I immunoreactivity revealed that the zebrin I+ Purkinje cells resemble those in situ with an extensive dendritic arborization that extends through the molecular layer perpendicular to the long axes of the folia. In conclusion, the present data suggest that afferent input does not play a role in the determination of the zebrin I phenotype of Purkinje cells.