Lesions in the cerebellar fastigial nucleus have a small effect on the hyperpnea needed to meet the gas exchange requirements of submaximal exercise

The purpose of this study was to test the hypothesis that an intact cerebellar fastigial nucleus (CFN) is necessary for the hyperpnea to meet the gas exchange needs of submaximal exercise. Bilateral stainless steel microtubules were implanted in the cerebellum inside (n = 12) or outside (n = 2) the CFN for injection (0.5 to 10 microl) of the neurotoxin ibotenic acid. All goats had difficulty maintaining normal posture and walking for up to 1 mo after the implantation of the microtubules and again for hours or days after the neurotoxin was injected. Postmortem histology indicated there were 55% fewer living neurons (P < 0.001, n = 9, 3,720 +/- 553 vs. 1,670 +/- 192) in the CFN of the experimental goats compared with a control group of goats. As is typical for goats before implantation of the microtubules, the decrease in arterial Pco(2) from rest during mild and moderate treadmill exercise was 2.0 +/- 0.39 and 3.5 +/- 0.45 Torr, respectively. Implantation of the microtubules did not significantly change this exercise hyperventilation. However, neurotoxic lesioning with 10 mul ibotenic acid significantly (P < 0.05) attenuated the decrease in arterial Pco(2) by 1.3 and 2.8 Torr at the first and second workload, respectively. The modest attenuation of the exercise hypocapnia at both workloads in CFN-lesioned goats suggests that the CFN is part of the control system that enables the ventilatory response to meet the gas exchange requirements of submaximal exercise.

Histamine improves rat rota-rod and balance beam performances through H(2) receptors in the cerebellar interpositus nucleus

Previous studies have revealed a direct histaminergic projection from the tuberomamillary nucleus of hypothalamus to the cerebellum and a postsynaptic excitatory effect of histamine on the cerebellar interpositus nucleus neurons via histamine H(2) receptors in vitro, indicating that the histaminergic afferent inputs of cerebellar nuclei may be involved in the cerebellar function of motor control. To test this hypothesis, in this study histaminergic agents were bilaterally microinjected into the cerebellar interpositus nucleus of intact adult male rats, and their effects on motor balance and coordination of the animals performing accelerating rota-rod treadmill and balance beam tasks were observed. The results showed that microinjection of histamine into the cerebellar interpositus nucleus remarkably increased the time that animals balanced steadily on the rota-rod and markedly shortened the duration of passage through the balance beam, whereas GABA significantly depressed motor performances of animals on the rota-rod and beam, and normal saline influenced neither. In addition, administration of selective histamine H(2) receptor antagonist ranitidine considerably decreased the animals' endurance time on rota-rod and noticeably increased the passing time on beam, but selective histamine H(1) receptor antagonist triprolidine showed no effect. Furthermore, microinjection of histamine reversed the inhibitory effects of ranitidine on rota-rod and beam performance. These results demonstrate that histamine enhances rat motor balance and coordination through activation of histamine H(2) receptors in the cerebellar interpositus nucleus and suggest that the hypothalamocerebellar histaminergic projections may play a modulatory role on the cerebellar circuitry to ensure that movements are accurately executed.

A long-range, wide field-of-view infrared eyeblink detector

Classical conditioning of the eyeblink response in the rabbit is one of the most advanced models of learning and memory in the mammalian brain. Successful use of the eyeblink conditioning paradigm requires precise measurements of the eyeblink response. One common technique of eyelid movement detection utilizes measurements of infrared (IR) light reflected from the surface of the eye. The performance of current IR sensors, however, is limited by their sensitivity to ambient infrared noise, by their small field-of-view and by short working distances. To address these limitations, we developed an IR eyeblink detector consisting of a pulsing (62.5 kHz) IR light emitting diode (LED) paired with a silicon IR photodiode and circuit that synchronously demodulates the recorded signal and rejects background IR noise. The working distance of the sensor exceeds 20 mm, and the field-of-view is larger than the area of a rabbit's eye. Due to its superior characteristics, the new sensor is ideally suited for both standard eyeblink conditioning and for studies that utilize IR-containing visual stimuli and/or that are conducted in an environment contaminated with IR noise.

Eyeblink conditioning in rats using pontine stimulation as a conditioned stimulus

Previous studies using rabbits and ferrets found that electrical stimulation of the pontine nuclei or middle cerebellar peduncle could serve as a conditioned stimulus (CS) in eyeblink conditioning (Bao, Chen, & Thompson, 2000; Hesslow, Svensson, & Ivarsson, 1999; Steinmetz, 1990; Steinmetz, Lavond, & Thompson, 1985; 1989; Steinmetz et al., 1986; Tracy, Thompson, Krupa, & Thompson, 1998). The current study used electrical stimulation of the pontine nuclei as a CS to establish eyeblink conditioning in rats. The goals of this study were to develop a method for directly activating the CS pathway in rodents and to compare the neural circuitry underlying eyeblink conditioning in different mammalian species. Rats were given electrical stimulation through a bipolar electrode implanted in the pontine nuclei paired with a periorbital shock unconditioned stimulus (US). Paired training was followed by extinction training. A subset of rats was given a test session of paired training after receiving an infusion of muscimol into the anterior interpositus nucleus. Rats given paired presentations of the stimulation CS and US developed CRs rapidly and showed extinction. Muscimol infusion prior to the test session resulted in a reversible loss of the eyeblink CR. The results demonstrate that electrical stimulation of the pontine nuclei can be used as a CS in rodents and that the CS pathway is similar in rats, rabbits, and ferrets. In addition, the loss of CRs following muscimol inactivation shows that the conditioning produced with pontine stimulation depends on cerebellar mechanisms.

Decreased proliferation in the adult rat hippocampus after exposure to the Morris water maze and its reversal by fluoxetine

Granular cell proliferation in the adult hippocampus decreases during aging and after chronic stress, while it can be increased by physical activity or treatment with the antidepressant fluoxetine. We investigated whether the physical and cognitive stimulation accompanied by stress in the commonly used Morris water maze affects the rate of proliferation and whether the induced changes can be influenced by antidepressant treatment with fluoxetine. Proliferating cells in the dentate gyrus were labeled by three injections of BrdU during the 24h preceding sacrifice. Early differentiation to neuronal progeny was studied by immunohistochemical staining for doublecortin (DCX), a microtubule binding protein expressed in newborn neurons. Acquisition learning in the water maze for 15 days caused a significant decrease in granular cell proliferation in the granular cell layer of the hippocampus. The decrease in the number of BrdU- and DCX-positive cells was reversed to control levels by the use of fluoxetine during the water maze training. Fluoxetine treatment alone increased the number of BrdU-positive cells, but did not increase the number of DCX-positive cells. We conclude that the exposure of adult male rats to water maze acquisition trials is a stressful experience that significantly suppresses the production of new granular cells and that this stressful effect can be blocked by the concomitant administration of the antidepressant fluoxetine.

[Comparative analysis of spontaneous unit activity of the cerebellum fastigial nucleus' neurons in different periods of vibration influence]

In conditions of acute experiment on white rats anaesthetized with Nembutal (40 mg/kg, interperitonially) recording and analysis of spontaneous impulse activity of the fastigial nucleus' neurons in norm and after 5, 10 and 15 days of vibration influence on the organism were carried out. Distribution of the neurons was evaluated by the dynamics of neuronal current flow and the modality of the interspike interval hystograms, as well as the statistical parameters: the average discharge frequency and the coefficient of the interspike interval variation. It is shown that more significant changes in neuronal activity of fastigial nucleus cells are formed during the first 10 days of vibration influence. On the 15th day, there was a tendency towards return to control levels of the parameters under study.

Inactivation of the brachium conjunctivum prevents extinction of classically conditioned eyeblinks

It is well established that the intermediate cerebellum is involved in the acquisition of classically conditioned eyeblink responses (CRs). Recent studies that inactivated the interposed nuclei (IN) demonstrated that blocking the intermediate cerebellum also interrupts CR extinction. Is this extinction deficit related to interrupting the information flow to efferent targets of the IN? To address this question, we inactivated axons of IN neurons in the brachium conjunctivum (BC). This treatment blocked the output of the intermediate cerebellum without directly affecting neurons in the deep cerebellar nuclei. Rabbits were trained in a delay classical conditioning paradigm, using a tone as the conditioned stimulus (CS) and a corneal air puff as the unconditioned stimulus (US). Then, the BC was microinjected with a sodium channel blocker, tetrodotoxin, during 4 extinction sessions in which rabbits were presented only with the CS. Tests performed after the 4-day injection period revealed that CRs did not extinguish in BC inactivation sessions but extinguished at a normal rate in the absence of the drug. CRs were then re-acquired. These data show that the normal flow of information along axons of cerebellar nuclear cells is required for CR extinction.

Saccade Dysmetria in Head-Unrestrained Gaze Shifts After Muscimol Inactivation of the Caudal Fastigial Nucleus in the Monkey

Lesions in the caudal fastigial nucleus (cFN) severely impair the accuracy of visually guided saccades in the head-restrained monkey. Is the saccade dysmetria a central perturbation in issuing commands for orienting gaze (eye in space) or is it a more peripheral impairment in generating oculomotor commands? This question was investigated in two head-unrestrained monkeys by analyzing the effect of inactivating one cFN on horizontal gaze shifts generated from a straight ahead fixation light-emitting diode (LED) toward a 40° eccentric target LED. After muscimol injections, when viewing the fixation LED, the starting position of the head was changed (ipsilesional and upward deviations). Ipsilesional gaze shifts were associated with a 24% increase in the eye saccade amplitude and a 58% reduction in the amplitude of the head contribution. Contralesional gaze shifts were associated with a decrease in the amplitude of both eye and head components (40 and 37% reduction, respectively). No correlation between the changes in the eye amplitude and in head contribution was observed. The amplitude of the complete head movement was decreased for ipsilesional movements (57% reduction) and unaffected for contralesional movements. For both ipsilesional and contralesional gaze shifts, the changes in eye saccade amplitude were strongly correlated with the changes in gaze amplitude and largely accounted for the gaze dysmetria. These results indicate a major role of cFN in the generation of appropriate saccadic oculomotor commands during head-unrestrained gaze shifts.

Role of cerebellar interpositus nucleus in the genesis and control of reflex and conditioned eyelid responses

The role of cerebellar circuits in the acquisition of new motor abilities is still a matter of intensive debate. To establish the contribution of posterior interpositus nucleus (PIN) to the performance and/or acquisition of reflex and classically conditioned responses (CRs) of the eyelid, the effects of microstimulation and/or pharmacological inhibition by muscimol of the nucleus were investigated in conscious cats. Microstimulation of the PIN in naive animals evoked ramp-like eyelid responses with a wavy appearance, without producing any noticeable plastic functional change in the cerebellar and brainstem circuits involved. Muscimol microinjections decreased the amplitude of reflex eyeblinks evoked by air puffs, both when presented alone or when paired with a tone as conditioned stimulus (CS). In half-conditioned animals, muscimol injections also decreased the amplitude and damped the typical wavy profile of CRs, whereas microstimulation of the same sites increased both parameters. However, neither muscimol injections nor microstimulation modified the expected percentage of CRs, suggesting a major role of the PIN in the performance of eyelid responses rather than in the learning process. Moreover, the simultaneous presentation of CS and microstimulation in well trained animals evoked CRs similar in amplitude to the added value of those evoked by the two stimuli presented separately. In contrast, muscimol-injected animals developed CRs to paired CS and microstimulation presentations, larger than those evoked by the two stimuli when presented alone. It is concluded that the PIN contributes to the enhancement of both reflex and conditioned eyelid responses and to the damping of resonant properties of neuromuscular elements controlling eyelid kinematics.

Ultrastructural study of cerebellar dentate nucleus astrocytes in chronic experimental model with valproate

The current study focuses on the morphogenesis of changes in the cerebellum dentate nucleus in the course of experimental valproate encephalopathy. Valproate - a broad spectrum antiepileptic and antipsychotic drug - chronically used in rats, intragastrically, once daily at a dose of 200 mg/kg b. w. for 1, 3, 6, 9 and 12 months, induced pronounced ultrastructural changes in the population of glial cells and nerve cells of the dentate nucleus of the cerebellum in the last two phases of the experiment. Astrocytic and neuronal lesions coexisted with a considerable damage to the elements of the blood-brain barrier of the cerebellar structure examined. The changes affected mainly the population of protoplasmic astrocytes lying loosely in a neuropile as well as astrocytes adhering to damaged large multipolar neurons. Focal proliferation of astrocytes was observed. Abnormal astrocytes showed marked swelling expressed by significantly decreased electron density of the cytoplasm that contained almost empty vacuolar structures and by a considerably reduced number of intracellular organelles. It was accompanied by dilation of endoplasmic reticular channels, loss of fibrillopoietic capacity of the cell and features of autophagocytosis. It should be assumed that the essential cause of protoplasmic astroglial damage of the cerebellar dentate nucleus could be associated, apart from the direct effect of valproate and/or its metabolites on these cells, with changes in structural elements of the blood-brain barrier of this CNS region.

Depression of extra-cellular GABA and increase of NMDA-induced nitric oxide following acute intra-nuclear administration of alcohol in the cerebellar nuclei of the rat

Gamma-aminobutyric acid (GABA) and nitric oxide are two key-transmitters in cerebellar nuclei, the major output of cerebellar circuitry. The aims of this study were to investigate the effects of acute intra-cerebellar administration of ethanol (20 mM) on extra-cellular levels of GABA and on the NMDA-induced nitric oxide (NO) production using microdialysis in the rat. We also studied: (i) the effects of a pre-administration of DNQX, a specific antagonist of AMPA receptors, on NO production, (ii) the effects of a pre-administration of 7-NI (7-nitroindazole, an inhibitor of neuronal nitric oxide synthase NOS) and APV (D-2-amino-5-phosphonovaleric acid, a specific blocker of the NMDA type glutamate receptors) on the actions of alcohol/NMDA on glutamate receptors, and (iii) the in vivo interaction between DNQX, ethanol and NMDA receptor activation. We found that ethanol decreased the amount of extra-cellular GABA, and that this effect was counterbalanced by administration of tiagabine 1 mg/kg, a potent inhibitor of GAT-1 GABA transporter, given by the i.p. route. In loco administration of NMDA increased the levels of NO, as previously reported. A pre-administration of DNQX (500 microM) increased significantly the production of NO up to toxic levels, as well as ethanol administration. A pre-administration of 7-NI or APV reduced significantly the amounts of NO when NMDA and alcohol were infused simultaneously. The combination of ethanol with DNQX was associated with a marked enhancement of the concentrations of NO. The activity of GAT-1 in cerebellar nuclei and around this target, including in glial cells expressing GAT-1 activated by ambient GABA, seems to be spared by ethanol. Tiagabine could be considered as a candidate for future investigational treatments of acute ethanol-induced dysfunction of cerebellar nuclei. We found a potentiation of the production of NO when AMPA antagonists are given simultaneously to ethanol. The hypothesis of AMPA neurotoxicity, which has convincing arguments during chronic exposure, is challenged in this model of acute cerebellar nuclear toxicity of alcohol.

Deficits in saccades and fixation during muscimol inactivation of the caudal fastigial nucleus in the rhesus monkey

The caudal fastigial nucleus (cFN) is a major nucleus by which the cerebellum influences the accuracy of saccades. In head-restrained monkeys generating saccades from a fixation light-emitting diode (LED) toward a flashed target LED, we analyzed the effects of unilateral pharmacological inactivation of cFN on horizontal, vertical, and oblique saccades. When animals were viewing the fixation LED, usually after one or more correction saccades, the positions of the eyes were slightly offset in comparison with the positions maintained before the injection (average offset = 1.1 degrees). The offset was ipsilateral to the injected side and did not depend on the target location. The horizontal component of all ipsilesional saccades was hypermetric and associated with a 32-42% increase in the amplitude of the deceleration displacement without significant change in the amplitude of the acceleration displacement. The horizontal component of all contralesional saccades was hypometric and associated with a decrease in the peak velocity and in the acceleration amplitude (30-35% decrease) without significant change in the deceleration amplitude. The amplitude of vertical saccades was not systematically affected, but their trajectory was always deviated toward the injected side. They missed the target with an error that depended on saccade duration or amplitude. If any, the effects of muscimol injections on the vertical component of oblique saccades were very small. The changes in fixation and the dysmetria are both viewed as consequences of an impairment in the cFN bilateral influence on the burst neurons located in the left and right brain stem.

Interaction between repetitive stimulation of the sciatic nerve and functional ablation of cerebellar nucleus interpositus in the rat

It is established that cerebellar nuclei exert a significant effect on the excitability of spinal neurons. However, their output is heterogeneous. Conditioning trains of dentate nucleus stimuli are known to modify the post-synaptic potentials evoked in motoneurons by stimulation of group Ia and Ib afferents in appropriate peripheral nerves. The role of the interpositus nucleus in the modulation of the excitability of rat spinal cord remains unclear. We investigated the interactions between tetrodotoxin (TTX)-induced inactivation of the interpositus cerebellar nuclei and repetitive electrical stimulation of the ipsilateral sciatic nerve (proximal segment) in the anesthetized rat. TTX (10 microM) was administered in cerebellar nuclei by the technique of microdialysis (coordinates of the extremity of the guide related to bregma: AP: -11.6, L: +2.3, V: -4.6). Peripheral stimulation consisted of trains of electric stimuli at a rate of 10 Hz, which were repeated every second during 1 hour. Stimulus intensity was adjusted to produce constant somatosensory evoked potentials. H-reflex, F-wave and M responses of the plantaris muscles were analysed ipsilaterally. H-reflex recruitment curve, Hmax/Mmax ratios, F-wave persistence and mean F/mean M ratios were studied. Functional blockade of cerebellar interpositus nucleus reduced the slope of H-reflex recruitment curve without affecting the Hmax/Mmax ratio, and depressed both F-waves persistence and mean F/mean M ratios. Concomitant repetitive stimulation of the sciatic nerve counteracted the depression of the H-reflex recruitment curve, without interacting with F-waves depression. Our results (1) show that TTX-sensitive sodium channels in cerebellar nucleus interpositus modulate the H-reflex recruitment, and (2) reveal an interaction between TTX-sensitive sodium channels in cerebellar nuclei and afferent repetitive activity not described so far.

Effects of muscimol inactivation of the cerebellar nuclei on precision grip

A single monkey was trained to perform a grasp, lift, and hold task in which a stationary hand- held object was sometimes subjected to brief, predictable force-pulse perturbations. The displacement, grip, and lifting forces were measured as well the three-dimensional forces and torques to quantify specific motor deficits after reversible inactivation of the cerebellar nuclei. A prior single-cell recording study in the same monkey provided the stereotaxic coordinates used to guide intranuclear injections of muscimol. In total, 34 penetrations were performed at 28 different loci throughout the cerebellar nuclei. On each penetration, two 1.0-microl injections of 5 microg/microl muscimol, were made 1.0 mm apart either within the nuclei or in the white matter just lateral or posterior to the dentate nucleus. Injections in the region corresponding to the anterior interpositus nucleus produced pronounced dynamic tremor and dysmetric movements of the ipsilateral arm when the animal performed unrestrained reaching and grasping movements. In contrast, no relatively short-latency (15-20 min.) deficits were observed after injection in the dentate nucleus, although some effects were observed after several hours. When tested in a primate chair with the forearm supported and restrained at the wrist and elbow, the monkey performed the lift and hold task without tremor or dysmetria. However, with the restraint removed, the forces and torques applied to the manipulandum were poorly controlled and erratic. The monkey's arm was ataxic and a 5-Hz intention tremor was clearly visible. In addition, the animal was generally unable to compensate for the predictable perturbations and the anticipatory grip force increases were absent. However, overall the results suggest that reversible cerebellar nuclear inactivation with muscimol has little effect on isolated distal movements of the wrist and fingers.

Glycine receptors and glycinergic synaptic transmission in the deep cerebellar nuclei of the rat: a patch-clamp study

To clarify possible glycinergic transmission in the cerebellum, principal neurons in deep cerebellar nuclei (DCN) of sliced cerebella (200 microm in thickness) from rats (aged 2-14 days) were studied using whole cell patch-clamp techniques. When glycine (100 microM) was applied to the DCN neurons from a "Y tube," large outward currents were induced (average peak amplitude of about 600 pA at -40 mV). The currents were blocked by strychnine (1 microM) and showed a reversal potential of -62 mV, which was approximately the estimated Cl- equilibrium potential. The dose-response relation of the currents showed an apparent dissociation constant of 170 microM for glycine and Hill coefficient of 1.6. In the presence of 6-cyano-7-nitroquinoziline-2, 3-dione (CNQX), d-(-)-2-amino-5-phosphonovaleric acid (APV) and bicuculline, which antagonize amino-3-hydroxy-5-methyl-isoxazol-propionate (APMA), N-methyl-d-aspartate (NMDA), and GABAA receptors, respectively, postsynaptic currents sensitive to strychnine (1 microM) were induced in DCN neurons by external perfusion of 20 mM K+ saline. Electrical stimulation of surrounding tissues in DCN evoked definite inhibitory postsynaptic currents (IPSCs) in these neurons. The IPSCs had a reversal potential of -62 mV and showed sensitivities to strychnine and tetrodotoxin. Thus this study has revealed that strychnine-sensitive glycine receptors are expressed in neurons of the DCN of rats and that glycinergic transmission mediated by these receptors is functional in these neurons from stages immediately after birth. The glycinergic innervations are presumably supplied by small interneurons located in the DCN.

GABA neurotransmission in the cerebellar interposed nuclei: involvement in classically conditioned eyeblinks and neuronal activity

The cerebellar interposed nuclei (IN) are an essential part of circuits that control classically conditioned eyeblinks in the rabbit. The function of the IN is under the control of GABAergic projections from Purkinje cells of the cerebellar cortex. The exact involvement of cerebellar cortical input into the IN during eyeblink expression is not clear. While it is known that the application of gamma-aminobutyric acid-A (GABA(A)) agonists and antagonists affects the performance of classically conditioned eyeblinks, the effects of these drugs on IN neurons in vivo are not known. The purpose of the present study was to measure the effects of muscimol and picrotoxin on the expression of conditioned eyeblinks and the activity of IN cells simultaneously. Injections of muscimol abolished conditioned responses and either silenced or diminished the activity of IN cells. Two injections were administered in each picrotoxin experiment. The first injection of picrotoxin slightly modified the timing and amplitude of the eyeblink, produced mild tonic eyelid closure, increased tonic activity of IN cells, and reduced the amplitude of the neural responses. The second injection of picrotoxin abolished conditioned responses, further increased tonic eyelid closure, dramatically elevated the tonic activity of IN cells, and in most cases, abolished neuronal responses. These results demonstrate that both GABA(A)-mediated inactivation and tonic up-regulation of IN cells can interrupt the expression of conditioned eyeblinks and that this behavioral effect is accompanied by the suppression of the neuronal activity correlates of the conditioned stimulus and response.

MR imaging and diffusion-weighted imaging changes in metronidazole (Flagyl)-induced cerebellar toxicity

We describe a case demonstrating reversible MR imaging findings, including diffusion-weighted imaging changes in association with metronidazole (Flagyl) toxicity. The diagnosis of metronidazole toxicity was made clinically and supported by the MR imaging findings. Quantitative apparent diffusion coefficient (ADC) maps demonstrated edema with associated increased ADC values within the dentate nuclei of the cerebellum on initial imaging. Follow-up imaging performed 8 weeks after cessation of metronidazole therapy demonstrated resolution of imaging findings, including diffusion changes.

Noradrenaline and 5-hydroxytryptamine in cerebellar nuclei of the rat: functional effects on neuronal firing

The firing rate of single cerebellar nuclear neurons was studied during microiontophoretic application of noradrenaline (NA), 5-hydroxytryptamine (5-HT) and their agonists in deeply anesthetized rats. NA application depressed the neuronal firing rate more in the medial nucleus (MN) than in the interpositus (IN) and in the lateral nucleus (LN). These responses were mimicked by alpha(2) and, to a lesser extent, beta receptor agonists. 5-HT evoked inhibition in MN and various effects (inhibitory, excitatory, biphasic) in IN and LN. Excitatory responses were more numerous in the posterior than in the anterior zone of IN. Agonists at 5-HT(1A) and 5-HT(2) receptors mimicked inhibition only. In conclusion, NA and 5-HT exerted a similar action on MN neurons; in contrast, the effects of 5-HT on IN and LN were more differentiated than those exerted by NA.

Fos induction in the rat deep cerebellar and vestibular nuclei following central administration of colchicine: a qualitative and quantitative time-course study

The present study was conducted to demonstrate Fos expression at four levels (anterior, prefastigial, postfastigial, posterior) of the cerebellar-vestibular nuclear complex in rats exposed to 1, 6, 24, and 48h of colchicine treatment using a light microscopic avidin biotin peroxidase (ABC) immunohistochemistry. Intracerebroventricular administration of colchicine (60microg per 10microl saline) elicited a continuous increase in the number of Fos-positive cells in the main cerebellar (fastigial, interpositus, dentatus) and vestibular (superior, medial, lateral, spinal, Y) nuclei. One and six hours after colchicine treatment, intensive Fos labeling was observed only in the pyriform cortex and the hypothalamic paraventricular nucleus, respectively, and there was no Fos immunolabeling in any of the cerebellar or vestibular structures investigated. On the other hand, moderate number of Fos-positive cells was visible in each of the cerebellar and vestibular nuclei 24h after colchicine treatment. Exposure of the animals to 48h of colchicine treatment induced an additional, more than 50%, rise in the accumulation of Fos-positive profiles in almost all the cerebellar and vestibular nuclei. In addition, at this time-point, a characteristic pattern of Fos distribution appeared almost in all of the cerebellar and vestibular nuclei, however, the numerical incidence of Fos-positive profiles in paired structures along the neuroaxis was bilaterally symmetric. The present data demonstrate for the first time that the central administration of colchicine causes a persistent and, in comparison with other brain areas, time-delayed activation of certain population of neurons in both cerebellar and vestibular nuclei. We assume that the delayed Fos activation in these structures indicate that the cerebellar and vestibular nuclei are not the primary targets of the central effect of colchicine and their activation seems to be rather a result of a postponed functional consequences of the central action of colchicine probably related to the coordination of motor performance.

An experimental study of posterior interpositus involvement in the genesis and control of conditioned eyelid responses

The participation of the rostral-dorsal part of the posterior interpositus nucleus in the genesis of classically-conditioned eyelid responses in alert cats was studied. Cats were prepared for the recording of left eyelid movements with the search-coil-in-a-magnetic-field technique and of the electromyographic activity of the orbicularis oculi muscle. A stimulating electrode was implanted in the contralateral red nucleus and a guide cannula in the ipsilateral interpositus. The cannula allowed unitary recordings, electrical microstimulation, drug injection, and push-pull perfusion of the selected interpositus site. Perfusate was used for amino acid analysis with an HPLC-EC method. Animals were conditioned with a delay (CS: tone, US: air puff) paradigm. Antidromically identified interpositus neurons fired during eyelid conditioned responses (CRs) with a variable delay to CR start. Some neurons (type A) increased and other (type B) decreased their firing during CR performance. Electrical microstimulation of posterior interpositus was able to increase CR amplitude when applied during CS presentation. Muscimol decreased CR amplitude in well-trained animals. The analysis of push-pull perfusate showed a significant increase in glutamate, glycine, and taurine, but not GABA levels, during conditioning in comparison with habituation and extinction periods. Results indicate an involvement of the rostral-dorsal part of the posterior interpositus nucleus in the genesis of eyelid conditioned responses, playing an enhancing or controlling role in CR performance, rather than being its initiator.

Neonatal ethanol produces cerebellar deep nuclear cell loss and correlated disruption of eyeblink conditioning in adult rats

Binge-like neonatal exposure to ethanol (EtOH) in rats, during the period of brain development comparable to that of the human third trimester, produces significant, dose-dependent Purkinje cell loss in the cerebellum and deficits in eyeblink classical conditioning. There are currently no published reports of whether neuronal loss in the cerebellar deep nuclei also results from binge-like neonatal exposure to EtOH and what the functional consequences of any cell loss might be. Since eyeblink conditioning requires cerebellar deep nuclear cells for normal learning to occur, we examined the effects of binge-like neonatal EtOH exposure on the total number of deep nuclear cells and eyeblink conditioning in adult rats. Group Ethanol (n=11) received EtOH doses of 5.25 g/kg/day on postnatal days 4-9, producing average peak blood alcohol concentrations of 363 mg/dl. Group Sham Intubated (n=11) underwent acute intragastric intubation on postnatal days 4-9 but did not receive any EtOH infusions. Group Unintubated Control (n=10) did not receive any intubations. When rats were at least 3 months old, they received either paired eyeblink conditioning or unpaired training. Following training, estimates of the total number of cerebellar deep nuclear cells were obtained using the optical fractionator, an unbiased stereological counting procedure. Rats in Group Ethanol had approximately 50% fewer deep nuclear cells compared to rats in Groups Sham Intubated and Unintubated Control, which did not differ. For 21 rats that received paired eyeblink conditioning, a highly significant correlation (+0.80) was found between the number of deep nuclear cells and learning rate in eyeblink conditioning.

Central serotonergic and adrenergic/imidazoline inhibitory mechanisms on sodium and water intake

Recent studies have shown the existence of two important inhibitory mechanisms for the control of NACL and water intake: one mechanism involves serotonin in the lateral parabrachial nucleus (LPBN) and the other depends on alpha(2)-adrenergic/imidazoline receptors probably in the forebrain areas. In the present study we investigated if alpha(2)-adrenergic/imidazoline and serotonergic inhibitory mechanisms interact to control NaCl and water intake. Male Holtzman rats with cannulas implanted simultaneously into the lateral ventricle (LV) and bilaterally into the LPBN were used. The ingestion of 0.3 M NaCl and water was induced by treatment with the diuretic furosemide (10 mg/kg of body weight)+the angiotensin converting enzyme inhibitor captopril (5 mg/kg) injected subcutaneously 1 h before the access of rats to water and 0.3 M NaCl. Intracerebroventricular (i.c.v.) injection of the alpha(2)-adrenergic/imidazoline agonist clonidine (20 nmol/1 microl) almost abolished water (1.6+/-1.2, vs. vehicle: 7.5+/-2.2 ml/2 h) and 0.3 M NaCl intake (0.5+/-0.3, vs. vehicle: 2.2+/-0.8 ml/2 h). Similar effects were produced by bilateral injections of the 5HT(2a/2c) serotonergic agonist 2,5-dimetoxy-4-iodoamphetamine (DOI, 5 microg/0.2 microl each site) into the LPBN on water (3.6+/-0.9 ml/2 h) and 0.3 M NaCl intake (0.4+/-0.2 ml/2 h). Injection of the alpha(2)-adrenergic/imidazoline antagonist idazoxan (320 nmol) i.c.v. completely blocked the effects of clonidine on water (8.4+/-1.5 ml/2 h) and NaCl intake (4.0+/-1.2 ml/2 h), but did not change the effects of LPBN injections of DOI on water (4.2+/-1.0 ml/2 h) and NaCl intake (0.7+/-0.2 ml/2 h). Bilateral injections of methysergide (4 microg/0.2 microl each site) into the LPBN increased 0.3 M NaCl intake (6.4+/-1.9 ml/2 h), not water intake. The inhibitory effect of i.c.v. clonidine on water and 0.3 M NaCl was still present after injections of methysergide into the LPBN (1.5+/-0.8 and 1.7+/-1.4 ml/2 h, respectively). The results show that the inhibitory effects of the activation of alpha(2)-adrenergic/imidazoline receptors in the forebrain are still present after blockade of the LPBN serotonergic mechanisms and vice versa for the activation of serotonergic mechanisms of the LPBN. Therefore, each system may act independently to inhibit NaCl and water intake.

Excitatory effects of histamine on cerebellar interpositus nuclear cells of rats through H(2) receptors in vitro

Neuroanatomical studies have revealed a direct hypothalamocerebellar histaminergic pathway, and our previous studies have demonstrated an excitatory effect of histamine on granule and Purkinje cells of the cerebellar cortex. In this study, we further investigated the effect of histamine on the neuronal firing of cerebellar interpositus nucleus (IN) by using cerebellar slice preparations. Eighty-seven IN cells were recorded from 38 slices. The vast majority of the cells responded to histamine stimulation with an excitatory response (79/87, 90.8%), and the rest of them showed no reaction (8/87, 9.2%). The histamine-induced excitation was not blocked by application of low-Ca(2+)/high-Mg(2+) medium (n=8), supporting a direct postsynaptic action of histamine. The histamine H(2) receptor antagonist ranitidine effectively blocked the excitatory response of IN cells to histamine (n=23), but the histamine H(1) receptor antagonist triprolidine could not significantly block the histamine-induced excitation, or only very slightly decreased the excitatory effect of histamine on the cells (n=21). On the other hand, the highly selective histamine H(2) receptor agonist dimaprit mimicked the excitatory effect of histamine on IN cells and the dimaprit-induced excitation was also blocked by ranitidine (n=14). Successively perfusing slices with the medium containing ranitidine and triprolidine, respectively, we found that ranitidine exhibited the same blocking effect on the dimaprit-induced excitation, but triprolidine had no such effect (n=8). Moreover, the histamine H(1) receptor agonist 2-pyridylethylamine did not show any effect on the IN cells (n=9). These results demonstrate that histamine excites cerebellar IN cells via the histamine H(2) receptor mechanism. Together with our previous results, we suggest that the hypothalamocerebellar histaminergic fibers may modulate neuronal activities of the cerebellar cortex and deep nuclei in parallel. The significance of the excitatory effect of histamine on the cerebellar nuclear cells is discussed.

Eyeblink classical conditioning and interpositus nucleus activity are disrupted in adult rats exposed to ethanol as neonates

Neonatal exposure to ethanol in rats, during the period of brain development comparable to that of the human third trimester, produces significant, dose-dependent cell loss in the cerebellum and deficits in coordinated motor performance. These rats are also impaired in eyeblink conditioning as weanlings and as adults. The current study examined single-unit neural activity in the interpositus nucleus of the cerebellum in adults following neonatal binge ethanol exposure. Group Ethanol received alcohol doses of 5.25 g/kg/day on postnatal days 4-9. Group Sham Intubated underwent acute intragastric intubation on postnatal days 4-9 but did not receive any infusions. Group Unintubated Control (from separate litters) did not receive any intubations. When rats were 3-7 mo old, pairs of extracellular microelectrodes were implanted in the region of the interpositus nucleus. Beginning 1 wk later, the rats were given either 100 paired or 190 unpaired trials per day for 10 d followed by 4 d of 100 conditioned stimulus (CS)-alone trials per day. As in our previous study, conditioned response acquisition in Group Ethanol rats was impaired. In addition, by session 5 of paired acquisition, Group Sham Intubated and Group Unintubated Control showed significant increases in interpositus nucleus activity, relative to baseline, in the CS-unconditioned stimulus interval. In contrast, Group Ethanol failed to show significant changes in interpositus nucleus activity until later in training. These results indicate that the disruption in eyeblink conditioning after early exposure to ethanol is reflected in alterations in interpositus nucleus activity.