The cerebellum monitors errors and entrains executive networks.

Frontal midline θ (Fmθ) activity occurs in medial prefrontal cortices (mPFC), when expected and actual outcomes conflict. Cerebellar forward models could inform the mPFC about this mismatch. To verify this hypothesis we correlated the mPFC activation during a visuomotor tracking task (VM) with performance accuracy, in control and cerebellum-lesioned participants. Additionally, purely visual (V), motor (M) and a motor plus visual tasks (V + M) were performed. An Independent Component, with a mid-frontal topography scalp map and equivalent dipole location in the dorsal anterior cingulate cortex accounted for Fmθ. In control participants Fmθ power increased during VM, when the error level crossed a threshold, but not during V + M, M and V. This increase scaled with tracking error. Fmθ power failed to increase during VM in cerebellar participants, even at highest tracking errors. Thus, in control participants, activation of mPFC is induced when a continuous monitoring effort for online error detection is required. The presence of a threshold error for enhancing Fmθ, suggests the switch from an automatic to an executive tracking control, which recruits the mPFC. Given that the cerebellum stores forward models, the absence of Fmθ increases during tracking errors in cerebellar participants indicates that cerebellum is necessary for supplying the mPFC with prediction error-related information. This occurs when automatic control falters, and a deliberate correction mechanism needs to be triggered. Further studies are needed to verify if this alerting function also occurs in the context of the other cognitive and non-cognitive functions in which the cerebellum is involved.

Modulation of Purkinje cell response to glutamate during the sleep-waking cycle.

The hypothesis that corticocerebellar responsiveness is modified by the behavioral state was tested in freely moving rats by evaluating the responses of extracellularly recorded Purkinje cells located in the cerebellar posterior vermis to microiontophoretically applied glutamate (8-80 nA for 3-5 s every 30-32 s) during the spontaneous sleep-waking cycle. Rats were chronically implanted for polygraphic recordings so that responses of Purkinje cells to glutamate could be related to the states of quiet waking, slow-wave sleep and paradoxical sleep. Analysis on a population of 33 neurons subjected to alternate periods of sleep and waking showed that the mean response to glutamate was significantly reduced to 75+/-18% during slow-wave sleep with respect to waking. This effect occurred independently on changes of basal firing rate which in sleep was slightly, although significantly, reduced to 94+/-12%. Independence of glutamate response modulation from changes of baseline firing was also observed in a different data set obtained from 19 Purkinje cells which were recorded during a continuous slow-wave sleep period that allowed several consecutive drug applications. In this condition responses to glutamate progressively decreased as sleep proceeded while spontaneous activity remained stable after a slight decrease at the transition from waking to sleep. Spectral analysis performed on the electroencephalogram signal, in particular on epochs centered around each glutamate pulse, revealed that for both data sets the reduction of neuronal responsiveness was related to the intensity of slow-wave sleep and more precisely to the delta and slow oscillation (0.6-4.2 Hz) content of the power spectrum of the electroencephalogram. Spontaneous and glutamate-evoked activity were also evaluated in 23 Purkinje cells during transition from slow-wave sleep to paradoxical sleep. In particular, during paradoxical sleep spontaneous activity became irregular so that for 44 out of 90 glutamate responses quantification was unreliable. The remaining 46 responses were characterized by high variability in amplitude even within the same episode of paradoxical sleep. With respect to the preceding slow-wave sleep values, 17/46 responses increased, 14/46 decreased and 15/46 remained within the 15% limit, giving a mean value of 132%. These data indicate that Purkinje cell response to glutamate is modulated during the spontaneous sleep-waking cycle. We speculate that this modulation depends upon the action of the neuromodulatory systems which diffusely project to the cerebellum, whose function would be to adapt the performance of the cerebellar circuits to changes of the animal state. On the other hand, the phasic changes in amplitude of Purkinje cell response during paradoxical sleep could be due to the interaction between the effects of glutamate application and those exerted by endogenous signals possibly related to the phasic events of this sleep stage.

Effects of unilateral labyrinthectomy on the norepinephrine content in forebrain and cerebellar structures of albino rats.

Albino (Wistar) rats were used to investigate whether unilateral labyrinthectomy (UL) modified the concentration of norepinephrine (NE) as well as of dopamine (DA) and the corresponding metabolite 3, 4-dihydroxyphenylacetic acid (DOPAC) in different areas of the cerebral and the cerebellar cortex and the striatum. The results obtained in 38 rats submitted to UL were compared to those of 18 rats submitted to sham-operation. The animals were operated under sodium pentobarbital anesthesia and sacrificed 1.5, 3 and 6 h after surgery. All rats submitted to UL showed phenomena of deficit (1.5-3 h after the lesion) followed by partial vestibular compensation (3-6 h after the lesion). Significant changes in the content of NE were neither found in different areas of the cerebral and the cerebellar cortex, nor in the striatum of rats sacrificed 1.5 h after UL. Three h after the lesion a bilateral increase in the NE content occurred in all the explored areas of the cerebral cortex (i.e., frontal, parieto-temporal and occipital) and the cerebellar cortex (i.e., the vermis and flocculus), as well as in the striatum. This increase, however, was more prominent in the parieto-temporal areas of the neocortex of the intact side, in all the explored areas of the cerebellar cortex of that side, as well as in the striatum of the lesioned side. This asymmetric increase in NE content could not be attributed, at least exclusively, to a generalized activation of the noradrenergic LC nuclei of both sides, due to waking and/or stress which may occur after UL, but did rather depend on asymmetric changes in unit discharge of the vestibular nuclei projecting to the LC of both sides, following UL. In particular, the increased discharge of the vestibular nuclei of the intact side would lead to activation of noradrenergic neurons projecting particularly to the parieto-temporal cortex and the cerebellar cortex of the intact side, as well as to the striatum of the lesioned side. A bilateral increase in NE content was still observed in different areas of the cerebral and cerebellar cortex of rats sacrificed 6 h after UL. This increase, however, was of smaller entity than that observed in the same areas 3 h after UL and quite symmetric. The content of DA and its metabolite DOPAC decreased bilaterally in the striatum of rats sacrificed 1.5 h after UL. This effect was attributed to a reduced synthesis and release of DA, which probably resulted from a reduced facilitatory influence that the deafferented vestibular nuclei exert on the dopaminergic, nigrostriatal system of both sides, although mainly on the intact side. The corresponding values, however, bilaterally recovered to slightly increase with respect to the control values in rats sacrificed 3 and 6 h after UL. In these experiments the content of both DA and DOPAC remained symmetric on both sides after UL, in contrast with the bilateral but asymmetric increase in NE concentration observed in the same structure 3 h the lesion. The present results integrate and extend those of previous experiments showing that: 1) albino rats sacrificed 6 h after UL displayed an increased synthesis of NE, which affected particularly the LC of the intact side as well as the medial vestibular nuclei of both sides (21); and 2) the structures which showed an increased content of NE at given time intervals after UL also displayed an increase in the expression of the immediate early gene c-fos (cf. 16 for ref.). These findings suggest that bilateral but asymmetric activation of the noradrenergic LC neurons following UL may lead to an asymmetric increase in c-fos expression in several target structures, thus contributing to the plastic changes responsible for vestibular compensation. In conclusion, it appears that UL induces in several brain structures of albino rats a short-term increase in synthesis and release of NE. (ABSTRACT TRUNCATED)

Fos-protein expression in noradrenergic locus coeruleus neurons after unilateral labyrinthectomy in the rat.

c-Fos mRNA and the related Fos-protein are rapidly induced by physiological stimuli and can be used as molecular markers of neural activation and plasticity. In a recent study (14), we found that rats submitted to unilateral labyrinthectomy (UL) displayed an asymmetric increase in the expression of both c-fos and Fos-protein not only in several vestibular, precerebellar and cerebellar structures and the caudate-putamen, but also in the locus coeruleus (LC)-complex, whose neurons integrate labyrinthine signals and are apparently involved in the plastic changes which are at the basis of vestibular compensation. In the present study we investigated the putative noradrenergic nature of the Fos-positive LC neurons observed after UL by combining Fos-protein immunocytochemistry with the immunocytochemical detection of tyrosine hydroxylase (TH), a synthetizing enzyme of noradrenaline. The experiments were performed in rats sacrificed 3, 6 and 24 h after surgical lesion of one labyrinth. The results obtained were in agreement with the previous findings, showing that already 3 h after UL an asymmetric increase of the c-fos and/or Fos-protein expression occurred in the vestibular nuclei, the inferior olive, the cerebellar cortex and the caudate-putamen. Most interestingly, the Fos-protein expression markedly increased in the LC-complex of both sides, although mainly ipsilaterally to the intact side. It appeared also that several Fos-positive LC-complex neurons were probably noradrenergic in nature, as they could be double-labeled with the Fos/TH technique. These findings were attenuated 6 h after UL and disappeared after 24 h, when partial compensation of the vestibular syndrome had occurred. Thus, UL results in asymmetric functional activation in the LC region of well identified noradrenergic neurons. This finding is attributed to the fact that asymmetric stimulation of labyrinth receptors gives rise to asymmetric changes in firing rate of LC neurons (45). Since these neurons send noradrenergic afferents to several target structures such as the vestibular nuclei, the inferior olive, the cerebellar cortex and the caudate-putamen, we postulated that the asymmetric labyrinthine activation of the noradrenergic LC system, occurring after UL, could increase the Fos-protein expression in the above mentioned brain structures. This possibility could then represent a key factor in determining the plastic changes, which are at the basis of vestibular compensation.

Microalbuminuria and renal haemodynamics in essential hypertension.

The present study was designed to evaluate the renal haemodynamic pattern of never-treated microalbuminuric and normoalbuminuric patients with essential hypertension. A total of 19 never-treated essential hypertensive patients with microalbuminuria were selected and, as control subjects, 24 never-treated essential hypertensive patients without microalbuminuria (determined on three 24-h urine collections) were recruited. In the two groups, we compared blood pressure values, standing plasma noradrenaline, plasma renin activity, plasma aldosterone, urinary aldosterone, lipid profile, serum glucose and uric acid, glomerular filtration rate and renal plasma flow. In comparison with normoalbuminuric patients, microalbuminuric patients showed significantly higher systolic blood pressure values (P < 0.05), higher renal vascular resistances (P < 0.05) and lower plasma renin activity values (P < 0.01). Urinary albumin excretion showed a significant positive correlation with systolic (r = 0.46, P < 0.005) and mean blood pressure (r = 0.38, P < 0.05), serum uric acid (r = 0.43, P < 0.005) and triglyceride values (r = 0.36, P < 0.005), and a significant negative correlation with plasma renin activity (r = -0.34, P < 0.05). The present data are consistent with the occurrence of renal vasoconstriction in microalbuminuric never-treated essential hypertensive patients.

c-fos Expression in the rat brain after unilateral labyrinthectomy and its relation to the uncompensated and compensated stages.

The expression of the immediate early gene c-fos has been studied in the entire brain of rats 3, 6 and 24 h after surgical unilateral labyrinthectomy. We combined in situ hybridization for c-fos messenger RNA with immunocytochemistry for Fos protein to document very early changes in c-fos expression and to identify with cellular resolution neuronal populations activated by unilateral labyrinthectomy. Three hours after unilateral labyrinthectomy a bilateral increase in both c-fos messenger RNA and protein levels was seen in the superior, medial and spinal vestibular nuclei, nucleus Y, and prepositus hypoglossal nucleus. These changes were asymmetric in the medial vestibular nucleus, being most prominent in the dorsal part of the contralateral nucleus (where second order vestibular neurons are located) and in the ventral part of the ipsilateral nucleus (where commissural neurons acting on the medial vestibular nucleus of the intact side are located). An increase in c-fos messenger RNA expression was seen bilaterally, but with an ipsilateral predominance, in the vermal and paravermal areas of the cerebellar cortex, flocculus and paraflocculus, as well as in the precerebellar lateral and paramedian reticular nuclei. c-fos messenger RNA and protein levels increased in a few regions of the contralateral inferior olive. A predominantly ipsilateral increase in c-fos expression also occurred in the caudate-putamen. A bilateral but not exactly symmetric increase in both c-fos messenger RNA and protein levels was present in several nuclei of the dorsal pontine tegmentum (parabrachial nucleus, locus coeruleus and laterodorsal tegmental nucleus), mesencephalic periaqueductal gray, and several hypothalamic, thalamic and cerebrocortical regions. No change was seen in the cerebellar nuclei, lateral vestibular nucleus and red nucleus. The increased expression of c-fos observed 3 h after unilateral labyrinthectomy, in conjunction with the sudden occurrence of postural and motor deficits, usually declined 6-24 h after the lesion, i.e. during the development of vestibular compensation. In the dorsal part of the medial vestibular nucleus, however, the pattern of c-fos expression observed 3 h after unilateral labyrinthectomy was reversed 6-24 h after the lesion: both c-fos messenger RNA and protein levels increased on the ipsilateral side, but greatly decreased on the contralateral side. In conclusion, asymmetric changes in c-fos expression occurred within 3 h after unilateral labyrinthectomy, but gradually declined or reversed 6 and 24 h after the lesion, thus being temporally related to the appearance and development of vestibular compensation.

Lack of correlation between microalbuminuria and endothelial function in essential hypertensive patients.

OBJECTIVE: To evaluate whether microalbuminuria, defined as urinary albumin excretion between 30 and 300 mg/24 h, is associated with endothelial dysfunction in essential hypertensive patients. DESIGN: We correlated urinary albumin excretion with vasodilatation in response to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) agonists in the forearm vascular bed in essential hypertensive patients with (n = 13) and without (n = 23) microalbuminuria and matched normotensive controls (n = 21). METHOD: We studied forearm vascular responses (strain-gauge plethysmography) to intrabrachial infusion of acetylcholine (0.15, 0.45, 1.5, 4.5 and 15 ng/100 ml forearm tissue/min) and of sodium nitroprusside (1, 2, 4ng/100 ml forearm tissue per min). Minimal forearm vascular resistances (the ratio between mean arterial pressure and maximal forearm vasodilation induced by 13 min of ischaemia + 1 min of exercise) were also evaluated. RESULTS: Responses to acetylcholine, but not to sodium nitroprusside, were significantly blunted and minimal forearm vascular resistances were increased in hypertensive patients compared with controls. However, no correlation was found between urinary albumin excretion and vasodilatation in response to acetylcholine or to sodium nitroprusside or between urinary albumin excretion and minimal forearm vascular resistances. CONCLUSIONS: In hypertensive patients, increased urinary albumin excretion is associated neither with functional nor with structural dysfunction in the forearm vasculature.

Sleep-waking changes after c-fos antisense injections in the medial preoptic area.

The preoptic hypothalamus has been consistently implicated in the homeostatic regulation of sleep and waking. Recently, it was shown that periods of either spontaneous or forced wakefulness result in the induction in this region of the immediate-early gene c-fos. In this study, antisense oligonucleotides complementary to c-fos mRNA were employed to interfere with the expression of Fos protein. Injections in the rat medial preoptic area of c-fos antisense, but not of sense, oligonucleotides blocked the expression of Fos protein detected immunocytochemically. Rats receiving bilateral antisense injections showed a higher percentage of wakefulness the day after the injection than controls receiving sense or sham injections or antisense injections outside the preoptic area. These results suggest that blocking the expression of Fos protein in the preoptic hypothalamus may interfere with the homeostatic regulation of sleep and wakefulness.

c-Fos expression during wakefulness and sleep.

We have recently demonstrated that c-fos expression is strongly induced by both spontaneous and forced wakefulness in many brain regions. c-Fos expression was considerably increased in regions involved in the regulation of arousal states, such as the locus coeruleus (noradrenergic neurons) and the medial preoptic area (non-GABAergic neurons). With c-fos antisense injection in the medial preoptic area, we demonstrated that c-fos expression in this region is causally involved in sleep regulation. c-Fos expression in other areas, such as the cerebral cortex and the hippocampus, may be related to the functional consequences of prolonged wakefulness and to the need of sleep. Further work should explore the mechanisms leading to changes in the expression of c-fos, and possibly of its target genes, during the sleep-wake cycle.

Trough:peak ratio of the blood pressure response to angiotensin converting enzyme inhibitors.

SHORT- VERSUS LONG-ACTING ANGIOTENSIN CONVERTING ENZYME (ACE) INHIBITORS: Although ACE inhibitors are widely used in the treatment of hypertension, there are few data on trough:peak ratios and the data are contradictory. Part of the explanation for this lies in differences in pharmacological properties. Depending on the kinetics of elimination, the trough:peak ratio of short- and long-acting ACE inhibitors has to be evaluated according to a dose regimen of twice or once a day, respectively, and must take account of the dose used, since long-acting ACE inhibitors appear to have a dose-dependent trough:peak effect. Further explanations for the contradictory trough:peak ratios reported for ACE inhibitors include measurement methods (clinic blood pressure versus ambulatory monitoring) and study design. TROUGH:PEAK RATIO: Data from randomly allocated, placebo-controlled studies indicate that both the short-acting ACE inhibitors captopril and quinapril given twice a day and the long-acting ACE inhibitors enalapril, lisinopril, benazepril and cilazapril given once a day have an acceptable trough:peak ratio (> 50%). The evidence suggests that when chemically different ACE inhibitors with similar kinetics of elimination are administered at equipotent doses, similar trough:peak ratios are obtained.

What effect does blood pressure control have on the progression toward renal failure?

Since hypertension is associated with nephrosclerosis and an increased progression toward end-stage renal failure, the therapeutic approach to the treatment of hypertension should aim to protect the kidney against damage or to halt the progression toward end-stage renal failure. It appears that compared with systolic and mean blood pressure, the level of diastolic blood pressure is particularly associated with renal damage. In the presence of kidney failure the choice of antihypertensive drug should be made according to pharmacokinetic and pharmacodynamic properties. From the pharmacokinetic point of view, drugs that are eliminated via the biliary route are preferable since no dosage adjustment is required, and those with a favorable trough to peak effect can achieve better blood pressure control by reducing blood pressure variability. Pharmacodynamic properties should include efficacy in lowering blood pressure, beneficial renal effects, and good tolerability. Hence, the dihydropyridine calcium antagonists, which are effective during volume repletion and which counteract vasoconstrictor mechanisms, seem to be particularly effective. There is some suggestion, but no definitive proof, that blood pressure should be lowered well below 140/90 mm Hg; to achieve this, combination therapy frequently must be used. The rationale for combining two or more antihypertensive drugs is based on the knowledge that this combination can exert an additive antihypertensive action while reducing side effects. The combination of an angiotensin converting enzyme inhibitor with a dihydropyridine calcium antagonist may well fulfill these criteria since this combination could enhance both antihypertensive and renal hemodynamic effects in comparison to single-drug treatment and could reduce the side effects of both drugs.

Dipyridamole decreases circulating renin-angiotensin system activity in hypertensive patients.

To study the effect of adenosine on renin release, n = 6 hypertensive patients, while on a constant 80 to 100 mEq/24 h Na+ diet, received oral 150 mg dipyridamole (an adenosine uptake inhibitor) three times daily for 3 days while upright plasma renin activity (PRA) and plasma aldosterone, urinary aldosterone, plasma and urinary Na+,K+, and creatinine clearance were monitored the day before (basal) the first and third day of the treatment and the day after the withdrawal (recovery). As compared to basal and to recovery, dipyridamole significantly decreased PRA, and plasma and urinary aldosterone without affecting plasma and urinary Na+ and K+, creatinine clearance, blood pressure, and heart rate. These data, showing that dipyridamole decreases PRA and aldosterone, confirm also in hypertensives that endogenous adenosine inhibits the circulating renin-angiotensin-aldosterone system.

The influence of dopamine-1 receptor blockade on the humoral and renal effects of low-dose atrial natriuretic factor in human hypertensives.

To test whether dopaminergic mechanisms can modulate the humoral and renal effects of atrial natriuretic factor (ANF), seven untreated, mildly hypertensive patients without complications were given a placebo (saline for 60 min) followed by a low dose of ANF (0.005 microgram/kg per min), or D-sulpiride (0.05 mg/kg per min), a specific dopamine-1 antagonist, or ANF + D-sulpiride at the same doses, for 60 min. The sequence of the three treatments was random, with a 72-h interval between treatments. The ANF infusion, which increased plasma ANF within the physiological range, significantly increased urinary sodium excretion, fractional sodium excretion and haematocrit; it reduced plasma aldosterone and tended to reduce plasma renin activity without changing blood pressure, the heart rate, renal plasma flow or the glomerular filtration rate. D-Sulpiride, when given alone, significantly increased mean blood pressure and reduced absolute and fractional sodium excretion without changing the heart rate, glomerular filtration rate, renal plasma flow, haematocrit, plasma renin activity or plasma aldosterone. When infused with D-sulpiride, ANF did not change absolute or fractional sodium excretion or haematocrit. This study provides evidence that dopaminergic mechanisms play a role in the natriuretic and plasma volume effects of a synthetic human ANF analogue infused at a low dose in patients with essential hypertension.