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PubMed2006

Depolarization-induced retrograde synaptic inhibition in the mouse cerebellar cortex is mediated by 2-arachidonoylglycerol.

Endocannabinoids acting on CB(1) cannabinoid receptors are involved in short- and long-term depression of synaptic transmission. The aim of the present study was to determine which endocannabinoid, anandamide or 2-arachidonoylglycerol (2-AG), is involved in depolarization-induced suppression of inhibition (DSI) in the cerebellar cortex, which is the most widely studied form of short-term depression. Depolarization of Purkinje cells in the mouse cerebellum led to an increase in intracellular calcium concentration and to suppression of the inhibitory input to these neurons (i.e. DSI occurred). Orlistat and RHC80267, two blockers of sn-1-diacylglycerol lipase, the enzyme catalysing 2-AG formation, abolished DSI by acting downstream of calcium influx. In contrast, DSI occurred also in the presence of a phospholipase C inhibitor. Intact operation of the calcium-dependent messengers calmodulin and Ca(2+)-calmodulin-dependent protein kinase II were necessary for DSI. DSI was potentiated by an inhibitor of the main 2-AG-degrading enzyme, monoacylglycerol lipase. Interference with the anandamide metabolizing enzyme, fatty acid amide hydrolase, did not modify DSI. Thus, three kinds of observations identified 2-AG as the endocannabinoid involved in DSI in the mouse cerebellum: DSI was abolished by diacylglycerol lipase inhibitors; DSI was potentiated by a monoglyceride lipase inhibitor; and DSI was not changed by an inhibitor of fatty acid amide hydrolase. Further experiments indicated that 2-AG is the endocannabinoid mediating short-term retrograde signalling also at other synapses: orlistat abolished DSI in the rat cerebellum, DSI in the mouse substantia nigra pars reticulata and depolarization-induced suppression of excitation in the mouse cerebellum.

Animals↗
PubMedDate not supplied

Localization of ataxin-2 within the cerebellar cortex of the rat.

Spinocerebellar ataxia type 2 is caused by a polyglutamine stretch in the protein ataxin-2 that is due to an expansion of a CAG repeat in the spinocerebellar ataxia-2 gene. The function of wild-type ataxin-2 has not been clarified. A widespread distribution of this protein throughout the brain has been reported. We examined the expression of ataxin-2 in cortical cerebellar cells of the adult rat. We performed a single label immunohistochemical study of ataxin-2 and a single label immunofluorescence study of ataxin-2 and zebrin on adjacent sections, to compare the distribution of the observed parasagittal band pattern. We also performed a double label immunofluorescence study of ataxin-2 and one of each parvalbumin, calbindin, and calretinin. Single label studies revealed that between 50% and 70% of the Purkinje cells express ataxin-2. The abundance of ataxin-2 was different between hemisphere and vermis, with a clear prevalence for the former. Furthermore, the distribution of ataxin-2-positive Purkinje cells showed a peculiar alternating parasagittal band pattern. Among the other cortical cerebellar cells only basket and granule cells showed ataxin-2 staining. Our dual label studies showed that about 50% of calbindin and more than 70% of parvalbumin-immunoreactive Purkinje cells were also labeled for ataxin-2. The uneven distribution of ataxin-2 expression in the Purkinje cell layer does not support the hypothesized link between ataxin-2 content and cell vulnerability. The differences in ataxin-2 expression among the cell types of cerebellar cortex, on the other hand, suggest a possible correlation between ataxin-2 content and cell function.

Animals↗
PubMed1999

Functional recruitment of red blood cells to rat brain microcirculation accompanying increased neuronal activity in cerebellar cortex.

Scanning laser-Doppler flowmetry (SLDF) combines laser-Doppler flowmetry and laser scanning to provide images of cerebral blood flow (CBF) with high spatial and temporal resolution. We investigated the contribution of single vascular elements to the local increase of CBF accompanying increased neuronal activity in halothane-anesthetized rats. CBF was examined in the cerebellar cortex under control conditions and in response to electrical stimulation of parallel and climbing fibers. At rest, arterioles contributed 9%, venules 11-13% and small vessels (< 20 microm) 8-14%, while the background constituted 64-72% of the total SLDF signal. During activation the background signal decreased to 55-60% while the signal from arterioles increased to 11-12%, from venules to 14-15% and from small vessels to 14-19%. The signal increase in small vessels that did not give any laser-Doppler signal at rest was due to functional recruitment of red blood cells to the capillary bed. We conclude that functional recruitment may be an integral part of the hemodynamic response accompanying neuronal activity.

Animals↗
PubMed1994

The effects of undernutrition on connectivity in the cerebellar cortex of adult rats.

The effects of a 30 d period of undernutrition, followed in some animals by nutritional rehabilitation, on neuronal connectivity in adult rat cerebellum were investigated using the disector method. There was no significant difference between well fed (719 +/- 74, mean +/- S.E.) and undernourished (709 +/- 53) synapse-to-neuron ratios in 134-d-old rat cerebellar cortex, nor was there a significant difference in synapse-to-neuron ratios between control animals (941 +/- 71) and previously undernourished rats (813 +/- 42) at 175 d of age. However, the age-related changes were significant (P < 0.05) in the controls, but not in the experimental group. It may be that the period of undernutrition caused subtle changes in the rehabilitating group which reduced the capacity for growth seen in well fed, matched control animals.

Animals↗
PubMed1986

Persistence of deafferentation-induced presynaptic dendrites in the cerebellar cortex of adult rats.

The paper provides morphological evidence for a long-lasting morphogenetic potential of the excitatory granule cells and the inhibitory small Golgi neurons to manufacture and to maintain presynaptic sites on their otherwise exclusively postsynaptic dendritic processes and somata. The development of new dendrodendritic and somato-dendritic synapses follows and is the direct consequence of the mossy fiber deafferentation of the cerebellar cortex. By GABA-immunocytochemistry it was demonstrated that not only Golgi axons but also the Golgi somata and presynaptic dendrites contain GABA, suggesting that this inhibitory transmitter is an operating factor in many of the newly formed synapses.

Afferent Pathways↗
PubMed2005

Activity-induced tissue oxygenation changes in rat cerebellar cortex: interplay of postsynaptic activation and blood flow.

Functional neuroimaging relies on the robust coupling between neuronal activity, metabolism and cerebral blood flow (CBF), but the physiological basis of the neuroimaging signals is still poorly understood. We examined the mechanisms of activity-dependent changes in tissue oxygenation in relation to variations in CBF responses and postsynaptic activity in rat cerebellar cortex. To increase synaptic activity we stimulated the monosynaptic, glutamatergic climbing fibres that excite Purkinje cells via AMPA receptors. We used local field potentials to indicate synaptic activity, and recorded tissue oxygen partial pressure (P(tiss,O2)) by polarographic microelectrodes, and CBF using laser-Doppler flowmetry. The disappearance rate of oxygen in the tissue increased linearly with synaptic activity. This indicated that, without a threshold, oxygen consumption increased as a linear function of synaptic activity. The reduction in P(tiss,O2) preceded the rise in CBF. The time integral (area) of the negative P(tiss,O2) response increased non-linearly showing saturation at high levels of synaptic activity, concomitant with a steep rise in CBF. This was accompanied by a positive change in P(tiss,O2). Neuronal nitric oxide synthase inhibition enhanced the initial negative P(tiss,O2) response ('dip'), while attenuating the evoked CBF increase and positive P(tiss,O2) response equally. This indicates that increases in CBF counteract activity-induced reductions in P(tiss,O2), and suggests the presence of a tissue oxygen reserve. The changes in P(tiss,O2) and CBF were strongly attenuated by AMPA receptor blockade. Our findings suggest an inverse relationship between negative P(tiss,O2) and CBF responses, and provide direct in vivo evidence for a tight coupling between activity in postsynaptic AMPA receptors and cerebellar oxygen consumption.

Action Potentials↗
PubMed2006

Effects of methamphetamine on the cerebellar cortex: a preliminary study.

Methamphetamine (METH) targets monoamine nerve terminals and produces motor effects, which are related to changes in catecholamine activity within the basal ganglia. Cerebellum plays an important role in motor control, nonetheless only a few studies investigated the effects of METH in this area. In this article, we report preliminary results on protein expression in the cerebellum following METH administration. In particular, we focused on the rate-limiting catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). By using immunoblotting, we found that METH administration produces a dose-dependent increase of TH within the cerebellar cortex of mice, which is opposite to the decrease of TH within the striatum. Further investigations are needed in order to determine the time course, the cerebellar regions, the cellular (and subcellular) compartments, and the functional role related to these effects.

Animals↗
PubMed1997

[The histological identification of Lugaro cells in the cat cerebellar cortex].

Apart from main classic neuron types there is a small group of neurons known in literature as intermediate Lugaro cells. Two Lugaro cells types are distinguished: fusiform and those with triangular cell body. Fusiform cells vary not only in vertical, horizontal or diagonal position of cell body, but also have certain morphological peculiarities. Axons of some fusiform cells project either to molecular layer or reach Purkinje cells layer or remain at the level of granular layer. Along with it, there are true intermediate cells, described by Lugaro. These cell processes project from layer to layer. Neurons with triangular cell body located at different granular layer levels relate to the second group of Lugaro cells. Due to great extension of their processes Lugaro cells possess projection area ranging from molecular layer to white substance. Lugaro cells are independent neurons, always present in cerebellar cortex.

Aging↗
PubMed1985

Long term alcohol consumption induces microtubular changes in the adult rat cerebellar cortex.

The effects of prolonged alcohol consumption on the microtubules of Purkinje cell dendrites and granule cell axons were studied in adult rats fed alcohol for 1, 3, 6, 12 and 18 months and compared with respective age-matched controls. A significant consequential decrease in the number of dendritic microtubules in alcohol-fed rats was found when compared with the respective controls. Conversely, an increase in the number of these organelles was found in both ascending and parallel portion of the axons in the experimental animals. The possibility of a relationship between microtubular changes and previously reported cerebellar cortex alcohol-induced structural alterations is advanced.

Alcoholism↗
PubMed2002

Local field potential oscillations in primate cerebellar cortex: modulation during active and passive expectancy.

Cerebellar local field potential (LFP) oscillations were recorded in the paramedian lobule of one hemisphere, while monkeys were in two behavioral conditions: actively performing an elbow flexion-extension or a lever-press task in response to an auditory or visual stimulus to get reward (active condition), or waiting quietly for the reward to come in the same time window after the appearance of the stimulus (passive condition). The oscillations in the paramedian lobule were first characterized in four monkeys, and they showed an idiosyncratic frequency for each monkey, between 13 and 25 Hz. The granule cell layer multi-unit activity was phase-locked with the negative phase of the LFP oscillations, while Purkinje cell simple spikes were also sometimes phase-locked with the LFP. Three monkeys were trained to perform the motor tasks: the LFP oscillations were modulated, in the active condition, in a systematic manner in relation to the lever-press or elbow flexion-extension tasks. During periods when the monkey was waiting to initiate movement, LFP oscillations appeared and then stopped with movement initiation. This modulation was valid for the task being executed with either hand. Surprisingly, the LFP oscillations were also systematically modulated during the passive condition; as the monkey was waiting for the usual time to get a reward passively, oscillations appeared stronger and were stopped by the end of the usual delay, whether the monkey was rewarded or not. This type of modulation was not affected by the length of the stimulus, as long as the reward window was known to the monkey. If the monkey had not been previously trained to the active condition, the modulation appeared in the passive condition. These results show that cerebellar LFP oscillations in the paramedian lobule are reliably present when the monkey is involved in a waiting period, whether this period ends with an active or passive event. This study provides electrophysiological evidence for a specific pattern of activity in the cerebellum for the expectancy of events that are known to be bound to happen, either externally, or from voluntary action.

Acoustic Stimulation↗
PubMed1996

Cerebral blood flow increases evoked by electrical stimulation of rat cerebellar cortex: relation to excitatory synaptic activity and nitric oxide synthesis.

The purpose of this study was to examine mechanisms involved in the coupling of neuronal activity to cerebral blood flow (CBF). CBF was measured in rat cerebellum using laser-Doppler flowmetry during stimulus-evoked neuronal activity and related to the distribution of the extracellular field potential. Local electrical stimulation of the cerebellar cortex activated a narrow beam of parallel fibers (PFs) 100 microns across and evoked increases of CBF along (On-B) and perpendicular (Off-B) to the beam. Increases of CBF and field potentials were recorded for a distance of up to 1500 microns along the activated beam, and perpendicular to the beam, in a zone approximately 1000 microns wide, i.e. about 10 times wider than the zone in which synaptic excitation took place. CBF increased as a function of stimulus frequency up to 75 Hz, the response being larger On-B than Off-B. TTX abolished both the field potentials and the CBF responses at all frequencies, suggesting that action potentials were mechanistically related to the evoked CBF increases. CBF changes were unchanged by picrotoxin, a blocker of GABA(A) receptors, consistent with the idea that inhibitory synaptic activity does not contribute to CBF increases. The latency to the CBF rise was much shorter On-B than Off-B for the same distance from the stimulating electrode. This may suggest that the CBF response Off-B is dependent on diffusion of vasoactive substances from neuronal structures activated by the parallel fibers On-B. Nitric oxide (NO) synthase inhibition with NG-nitro-L-Arginine increased the time latency to onset of CBF rise by 2-4 times and attenuated the evoked CBF increase by approximately 50%. Sodium nitroprusside, a NO donor, increased baseline CBF, but did not reverse the effects of L-NNA. Thus the initial part of the evoked CBF rise is probably mediated by NO, which also contributes to the later part of the response. This study provides insight into the distribution and mechanism of neurally evoked increases of CBF, of putative importance for the interpretation of activation studies in animals and humans.

Action Potentials↗