Metabotropic glutamate receptor 5 mediates the potentiation of N-methyl-D-aspartate responses in medium spiny striatal neurons

Medium spiny neurons were recorded from striatal slices obtained from mice lacking the group I metabotropic glutamate receptor (mGluR) subtype 1 or subtype 5. In wild-type animals, N-methyl-D-aspartate (NMDA)-induced membrane depolarization/inward currents were potentiated in the presence of both the group I mGluR agonist 3,5-dihydroxyphenylglycine (3,5-DHPG) and the mGluR5 selective agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG). Likewise, in mGluR1 knockout mice, both 3,5-DHPG and CHPG were able to potentiate NMDA responses. Conversely, in neurons recorded from mGluR5-deficient mice, the enhancement of NMDA responses by both 3,5-DHPG and CHPG was absent. Pharmacological analysis performed from rat slices confirmed the data obtained with mice. In the presence of the competitive mGluR1 antagonist LY367385, the NMDA responses were potentiated in the presence of CHPG, whereas the CHPG-induced enhancement was not observed in slices treated with the non-competitive mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine. As in wild-type mice, in neither of the mGluR1- and mGluR5-deficient mice did (2S,1'R,2'R,3'R)-2-(2,3-dicarboxylcyclopropyl)-glycine (1 microM), nor L-serine-O-phosphate (30 microM) (agonists for group II and III mGluRs, respectively) affect the NMDA-evoked responses. In striatal medium spiny neurons, NMDA responses are potentiated by endogenous acetylcholine via M1-like muscarinic receptors. Since the enhancement of NMDA responses by 3,5-DHPG and by M1-like muscarinic agonists was shown to share common post-receptor mechanisms, we verified whether the muscarinic potentiation of NMDA responses was affected in these group I mGluR-deficient mice. Both in mGluR1 and mGluR5 knockout animals, in the presence of either muscarine or the M1-like muscarinic receptor agonist McN-A-343, the positive modulation of the NMDA-induced membrane depolarization persisted.These results confirm the permissive role of group I mGluRs on NMDA responses in striatal neurons and reveal that this functional interplay occurs exclusively through the mGluR5 subtype. The NMDA-mGluR5 interaction might play an important modulatory role in the final excitatory drive from corticostriatal afferents and suggests that drugs acting at mGluR5 might prove useful for the treatment of movement disorders involving the striatum.

Presynaptic modulation by group III metabotropic glutamate receptors (mGluRs) of the excitatory postsynaptic potential mediated by mGluR1 in rat cerebellar Purkinje cells

Purkinje neurons were recorded from rat cerebellar slices. Parallel fibres stimulation elicited a fast excitatory postsynaptic potential (EPSP) mediated by ionotropic glutamate (iGluR) -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors followed by the inhibitory gamma-aminobutyric acidA (GABAA)-dependent postsynaptic potential. In the presence of antagonists for iGluRs and for GABAA receptors, brief tetanic activation evoked a slow metabotropic glutamate receptor (mGluR)-dependent EPSP (mGluR-EPSP). This mGluR-EPSP was blocked by the selective mGluR1 antagonists LY367385 and CPCCOEt, but not by the mGluR5 antagonist MPEP. Group II agonists affected neither iGluR-EPSP nor mGluR-EPSP. Conversely, L-AP4 and L-SOP, group III mGluR agonists, inhibited both iGluR- and mGluR-EPSPs. The depolarisations evoked by both AMPA and group I agonists were unaffected, indicating a presynaptic action of group III mGluRs. These data suggest that glutamate released by parallel fibres activates group III mGluR autoreceptors, depressing both iGluR- and mGluR1-mediated EPSPs.

Adenosine-mediated inhibition of striatal GABAergic synaptic transmission during in vitro ischaemia

Several reports have shown that energy deprivation, as a result of hypoxia, hypoglycaemia or ischaemia, depresses excitatory synaptic transmission in virtually all brain areas. How this pathological condition affects inhibitory synaptic transmission is still unclear. In the present in vitro study, we coupled whole-cell patch clamp recordings from striatal neurones with focal stimulation of GABAergic nerve terminals in order to characterize the electrophysiological effects of combined oxygen and glucose deprivation (in vitro ischaemia) on inhibitory postsynaptic currents (IPSCs) in this brain area. We found that brief periods (2-5 min) of in vitro ischaemia invariably caused a marked depression of IPSC amplitude. This inhibitory effect was fully reversible on removal of the ischaemic challenge. It was coupled with an increased paired-pulse facilitation, suggesting the involvement of presynaptic mechanisms. Accordingly, the ischaemic inhibition of striatal GABAergic IPSCs was not caused by a shift in the reversal potential of GABA(A)-receptor mediated synaptic currents, and was independ- ent of postsynaptic ATP concentrations. Endogenous adenosine, acting on A1 receptors, appeared responsible for this presynaptic action as the ischaemic depression of IPSCs was prevented by CPT [8-(4-chlorophenylthio) adenosine] and DPCPX, two adenosine A1 receptor antagonists, and mimicked by the application of adenosine in the bathing solution. Conversely, ATP-sensitive potassium channels were not involved in the inhibition of IPSCs by ischaemia, as demonstrated by the fact that tolbutamide and glipizide, two blockers of these channels, were ineffective in preventing this electrophysiological effect. The early depression of GABA-mediated synaptic transmission might play a role in the development of irreversible neuronal injury in the course of brain ischaemia.

Heart-targeted overexpression of caspase3 in mice increases infarct size and depresses cardiac function

Up-regulation of proapoptotic genes has been reported in heart failure and myocardial infarction. To determine whether caspase genes can affect cardiac function, a transgenic mouse was generated. Cardiac tissue-specific overexpression of the proapoptotic gene Caspase3 was induced by using the rat promoter of alpha-myosin heavy chain, a model that may represent a unique tool for investigating new molecules and antiapoptotic therapeutic strategies. Cardiac-specific Caspase3 expression induced transient depression of cardiac function and abnormal nuclear and myofibrillar ultrastructural damage. When subjected to myocardial ischemia-reperfusion injury, Caspase3 transgenic mice showed increased infarct size and a pronounced susceptibility to die. In this report, we document an unexpected property of the proapoptotic gene caspase3 on cardiac contractility. Despite inducing ultrastructural damage, Caspase3 does not trigger a full apoptotic response in the cardiomyocyte. We also implicate Caspase3 in determining myocardial infarct size after ischemia-reperfusion injury, because its cardiomyocyte-specific overexpression increases infarct size.

Selective involvement of mGlu1 receptors in corticostriatal LTD

Although metabotropic glutamate receptors (mGluRs) have been proposed to play a role in corticostriatal long-term depression (LTD), the specific receptor subtype required for this form of synaptic plasticity has not been characterized yet. Thus, we utilized a corticostriatal brain slice preparation and intracellular recordings from striatal spiny neurons to address this issue. We observed that both AIDA (100 microM) and LY 367385 (30 microM), two blockers of mGluR1s, were able to fully prevent the induction of this form of synaptic plasticity, whereas MPEP (30 microM), a selective antagonist of the mGluR5 subtype, did not significantly affect the amplitude and time-course of corticostriatal LTD. Both AIDA and LY 367385 were ineffective on LTD when applied after its induction. The critical role of mGluR1s in the formation of corticostriatal LTD was confirmed in experiments performed on mice lacking mGluR1s. In these mice, in fact, a significant reduction of the LTD amplitude was observed in comparison to the normal LTD measured in their wild-type counterparts. We found that neither acute pharmacological blockade of mGluR1s nor the genetic disruption of these receptors affected the presynaptic modulation of corticostriatal excitatory postsynapic potentials (EPSPs) exerted by DCG-IV and L-SOP, selective agonists of group II and III mGluRs, respectively. Our data show that the induction of corticostriatal LTD requires the activation of mGluR1 but not mGluR5. mGluR1-mediated control of this form of synaptic plasticity may play a role in the modulatory effect exerted by mGluRs in the basal ganglia-related motor activity.

Inhibition of mitochondrial complex II induces a long-term potentiation of NMDA-mediated synaptic excitation in the striatum requiring endogenous dopamine

Abnormal involuntary movements and cognitive impairment represent the classical clinical symptoms of Huntington's disease (HD). This genetic disorder involves degeneration of striatal spiny neurons, but not striatal large cholinergic interneurons, and corresponds to a marked decrease in the activity of mitochondrial complex II [succinate dehydrogenase (SD)] in the brains of HD patients. Here we have examined the possibility that SD inhibitors exert their toxic action by increasing glutamatergic transmission. We report that SD inhibitors such as 3-nitroproprionic acid (3-NP), but not an inhibitor of mitochondrial complex I, produce a long-term potentiation of the NMDA-mediated synaptic excitation (3-NP-LTP) in striatal spiny neurons. In contrast, these inhibitors had no effect on excitatory synaptic transmission in striatal cholinergic interneurons and pyramidal cortical neurons. 3-NP-LTP involves increased intracellular calcium and activation of the mitogen-activated protein kinase extracellular signal-regulated kinase and is critically dependent on endogenous dopamine acting via D2 receptors, whereas it is negatively regulated by D1 receptors. Thus 3-NP-LTP might play a key role in the regional and cell type-specific neuronal death observed in HD.

[Identification of patients with acute myocardial infarction that may be discharged early: prospective evaluation with simple clinical and instrumental indicators]

BACKGROUND

The hospital stay for "uncomplicated" acute myocardial infarction (AMI) is often too long. A reduction in the length of hospitalization, if proven to be safe, is advantageous in terms of costs and health organization. Accordingly the aims of the present, prospective study, were to evaluate: 1) the patients with AMI eligible for early discharge; 2) the incidence of adverse cardiovascular events within 2 weeks of myocardial infarction; 3) the incidence of cardiovascular mortality at 6-month follow-up.

METHODS

On the fifth day after AMI, 331 of 526 patients, consecutively admitted to our coronary care unit between March 1997 and August 1999, were assigned to "complicated" and "uncomplicated" AMI groups, according to clinical and non-invasive criteria. Uncomplicated myocardial infarction eligible for early discharge was defined in patients < 75 years, as the absence of a high risk personality, stroke, left bundle branch block, transient myocardial ischemia after the first 24 hours from AMI, clinical signs or echocardiographic evidence of left ventricular dysfunction (ejection fraction < 40%), ventricular fibrillation, sustained ventricular tachycardia, symptomatic bradyarrhythmias after the first 48 hours from AMI, cardioversion or defibrillation (after the first 48 hours) or the need for coronary angioplasty or coronary artery bypass grafting. Uncomplicated patients were discharged on the sixth day after AMI (hospital stay 6.5+/-0.72 days). A symptom-limited ergometric stress test was planned in the uncomplicated group 14 days after AMI. "Hard" (death, reinfarction) and "non-hard" (unstable angina, myocardial revascularization) adverse cardiovascular events were monitored at 2 weeks of follow-up, and cardiovascular mortality at 6-month follow-up.

RESULTS

Four (1.2%) hard (0.3% exitus and 0.9% reinfarction) and 7 (2.1%) non-hard adverse events occurred among patients with uncomplicated AMI at 2 weeks of follow-up. Patients with uncomplicated AMI who developed adverse events, presented during the primary coronary event creatine kinase (CK) and CK-MB serum levels which were significantly lower than those observed in patients who did not present adverse events. In the complicated group (hospital stay 9.9+/-1.79 days), from day 6 to 14 after AMI, 65 (33%) hard and non-hard events occurred. A significant reduction in mortality between the uncomplicated and complicated group (2.11 vs 27.17%, p < 0.0001) was observed at 6-month follow-up. Multivariate analysis showed a statistically significant difference for age and thrombolytic treatment.

CONCLUSIONS

This first Italian prospective study demonstrated the possibility of identifying, 5 days after AMI and on the basis of simple criteria and without a stress test, a low risk population of patients eligible for early discharge.

Coadministration of losartan and enalapril exerts additive antiproteinuric effect in IgA nephropathy

Angiotensin-converting enzyme (ACE) inhibitors and AT1-receptor antagonists (ARAs) are widely administered to reduce urinary protein loss and slow the progression of proteinuric nephropathy to end-stage renal failure. Our group recently observed that the combination of ACE inhibitors and ARAs may have an additive antiproteinuric effect, which may occur because ACE inhibitors do not completely reduce angiotensin II (Ang II) production. Ang II is also produced by chymase. Thus, combination therapy better antagonizes the effects of Ang II. The purpose of this study is to ascertain whether the additive antiproteinuric effect of ACE inhibitors plus ARAs is dose dependent and related to the drug-induced reduction in systemic blood pressure. Therefore, enalapril (E; 10 mg/d) and losartan (LOS; 50 mg/d) were randomly administered alone and then in association; initial dosages were doubled when drugs were administered alone and in association. To determine the influence of the drug-dependent effect on reducing blood pressure and the reduction in urinary proteinuria, both ambulatory and office blood pressures were recorded. E and LOS administered alone reduced proteinuria by the same extent; no further reduction was observed when E and LOS alone were administered at a doubled dose. When E and LOS were coadministered, proteinuria decreased by a greater extent compared with E and LOS alone; an additional reduction in proteinuria was observed when combined therapy doses were doubled. The reduction in proteinuria was not correlated with clinical through blood pressure; however, reductions in diastolic and mean ambulatory blood pressures significantly correlated with the decrease in proteinuria, as well as with creatinine clearance. In conclusion, this study shows that combination therapy with E and LOS has an additive dose-dependent antiproteinuric effect that is likely induced by the drug-related reduction in systemic blood pressure. In normotensive proteinuric patients, it is likely that even a small reduction in systemic blood pressure may affect intraglomerular hemodynamics by a great extent because efferent arteriole regulation is hampered more completely by the coadministration of ACE inhibitors and ARAs.

Selective blockade of type-1 metabotropic glutamate receptors induces neuroprotection by enhancing gabaergic transmission

Selective antagonists of mGlu1 (LY367385 and CPCCOEt) and mGlu5 (MPEP) metabotropic glutamate receptors were neuroprotective against NMDA toxicity when either applied to mixed cortical cultures or locally infused into the caudate nucleus. Neuroprotection produced by LY367385 or CPCCOEt was occluded by GABA and was abolished by a cocktail of GABA(A) and GABA(B) receptor antagonists. In contrast, GABAergic drugs did not influence the action of MPEP. In microdialysis studies, LY367385 and CPCCOEt substantially enhanced GABA release in the corpus striatum of freely moving animals, whereas MPEP had no effect on GABA but abolished the stimulation of glutamate release induced by NMDA. A role for mGlu1 receptors in modulating GABAergic transmission was supported by electrophysiological studies carried out in cortico-striatal slices. In this particular model, the mixed mGlu1/5 receptor agonist, DHPG, reduced bicuculline-sensitive inhibitory postsynaptic currents presumably via a presynaptic mechanism. The action of DHPG was antagonized by LY367385, but not by MPEP. Taken together, these results indicate that selective blockade of mGlu1 receptors produces neuroprotection by enhancing GABAergic transmission.

[ANMCO genetic area. Significance of family history in cardiology--Part III]

This is a proposal for collecting the family history throughout a guided form to be given to the patient when awaiting for ambulatory examination or hospital admission, before meeting the cardiologist. In this form, the patient is asked to make an effort in order to focus on his family history (diseases, signs, symptoms, medications, etc.) at least for parents, sibs, and off-springs. A nurse should be committed to give the form to the patient, making him sure that the incomplete filling does not limit the quality of the diagnostic and therapeutic work-up. Thanks to the guided form, the patient concentrates the attention on his family history, eventually consulting the relatives before being examined. The form opens stating that all data are potentially helpful, but none is essential for diagnosis and treatment. This new approach to the family history could support clinicians in having helpful news, only deepening information that seems to be more relevant for the diagnosis.

Colonoscopic removal of a polypoid arteriovenous malformation

A 53-year-old male presenting with a 3-month history of intermittent mild rectal bleeding was found, on double contrast barium enema, to have a large polyp on a long stalk in the sigmoid colon. Large bowel endoscopy confirmed the presence of a 2 cm pedunculated polyp which was removed using a diathermic snare, with slight bleeding following the procedure that did not require endoscopic haemostasis. Only after histologic examination was the polyp shown to be a colonic arteriovenous malformation. Endoscopically, arteriovenous malformations generally appear as flat or elevated bright red lesions. A pedunculated polypoid appearance is extremely uncommon. In this case, no gastrointestinal bleeding or polypoid recurrence was observed during the 12 months of clinical and endoscopic follow-up.

[The Genetic Area of the ANMCO. Family history in modern cardiology: cardiomyopathies -- Part II]

The family history plays an important role in the cardiomyopathy setting. Cardiomyopathies are defined as familial when at least two members of the family are proven as affected. Given that the definition of familial cardiomyopathy has to be evidence-based, the familial forms have to be identified and documented. Detailed family pedigrees are obtained by interviewing patients and relatives and examining all clinical and pathological reports. Then, the clinical non-invasive screening of relatives is proposed, and performed in all informed and consenting relatives. All patients diagnosed with cardiomyopathy are potentially affected by familial forms, until relatives are proven to be unaffected. A few exceptions could be for syndromic disorders for which the phenotypes provide certainty elements/signs analogous to those observed in the proband. Key points for family history interpretation are the phenotype at onset, the time of onset, the presence/absence of coronary risk factors (such as diabetes and hypertension) and concomitant diseases. Special attention has to be paid to neuromuscular disorders that represent a wide heterogeneous issue in which cardiac involvement (cardiomyopathy, arrhythmias and conduction defects) could be the first manifestation of the disease. Based on rigorous investigation, the information derived for each family will provide useful data for present and future management of the family members, and for future research in the field of cardiomyopathies.

Ionic mechanisms underlying differential vulnerability to ischemia in striatal neurons

Brain cells express extremely different sensitivity to ischemic insults. The reason for this differential vulnerability is still largely unknown. Here we discuss the ionic bases underlying the physiological responses to in vitro ischemia in two neostriatal neuronal subtypes exhibiting respectively high sensitivity and high resistance to energy deprivation. Vulnerable neostriatal neurons respond to ischemia with a membrane depolarization. This membrane depolarization mainly depends on the increased permeability to Na+ ions. In contrast, resistant neostriatal neurons respond to ischemia with a membrane hyperpolarization due to the opening of K+ channels. Interestingly, in both neuronal subtypes the ischemia-dependent membrane potential changes can be significantly enhanced or attenuated by a variety of pharmacological agents interfering with intracellular Ca2+ entry, ATP-dependent K+ channels opening, and Na+/Ca2+ exchanger functioning. The understanding of the ionic mechanisms underlying the differential membrane responses to ischemia represents the basis for the development of rational neuroprotective treatments during acute cerebrovascular insults.

[The genetic area of the Italian Association of Hospital Cardiologists. The family history in modern cardiology--part I]

The family history constitutes the first step in the cardiologist's clinical approach to the patient and is highly informative both for monogenic and multifactorial disorders. A detailed interview is a time-consuming activity: in their daily practice, cardiologists may have 10, 20 or more interviews to complete. The patient tends to concentrate his attention on his own clinical history, rather than on that of his family, and explaining the importance of the role of a well analyzed family history in the modern cardiology can be difficult and may further increase the loss of time. However, the information about a given phenotype revealed by a detailed and non-confounding family history is essential to define the inheritance of monogenic diseases, to calculate the penetrance, even when the disease genes are unknown, or to evaluate "clinically cryptic" risks in multifactorial diseases. The Genetic Area of the Italian Association of Hospital Cardiologists proposes a novel approach to the family history of the patients: a guide form to be filled in by the patient whilst awaiting for clinical evaluation or immediately after admission to the cardiology department. The proposal will be articulated in three parts: one dedicated to general considerations on the confounding or incomplete evaluation of potentially useful data from the family history, one specifically dedicated to cardiomyopathies, and one containing a model of the form to be eventually adopted by the cardiological scientific societies.

Functional coexpression of excitatory mGluR1 and mGluR5 on striatal cholinergic interneurons

The group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (3,5-DHPG) and the mGluR5 agonist 2-chloro-5-hydroxyphenylglycine both induced a membrane depolarisation of striatal cholinergic interneurons. The response to 3,5-DHPG was blocked only by the coadministration of mGluR1 and mGluR5 antagonists, suggesting that both mGluRs are involved in this excitatory effect in striatal cholinergic interneurons.

Oral tacrolimus long-term therapy in patients with Crohn's disease and steroid resistance

AIM

To report the results of a prospective, open-label, uncontrolled study in 13 patients affected by Crohn's disease with resistance to steroids.

METHODS

The patients were treated long-term with oral tacrolimus, aiming to both resolve acute attacks and maintain remission. Tacrolimus was administered at the dose of 0.1--0.2 mg.day/kg and adjusted in order to achieve levels of 5--10 ng/mL; only mesalazine was continued concomitantly. Steroids and total parenteral nutrition were tapered when appropriate.

RESULTS

Median treatment was 27.3 months. Only one patient dropped out due to adverse events. Crohn's disease activity index score significantly decreased after 6 months in 11 patients; for 1 year in nine of them, and 7 years in two of them. The inflammatory bowel disease life-quality questionnaire score significantly increased over the same periods. A marked drop in hospitalizations was recorded. In three out of six patients complete closure of fistulas occurred. Tacrolimus allowed total parenteral nutrition to be withdrawn in three out of five patients. Supplementation with low-dose steroids was required in five patients. Two patients underwent surgery.

CONCLUSIONS

Tacrolimus therapy appears to be associated with both short- and long-term benefits, and may represent a therapeutic option in Crohn's disease when conventional therapies fail. This study encourages its use in controlled trials.

Cell-type specificity of mGluR activation in striatal neuronal subtypes

The effects of metabotropic glutamate receptor (mGluR) activation were studied in medium spiny neurons and large aspiny (LA) interneurons by means of electrophysiological and optical recordings. DCG-IV and L-SOP, agonists for group II and III mGluRs, respectively, produced a presynaptic inhibitory effect on corticostriatal glutamatergic excitatory postsynaptic potentials (EPSPs) in both spiny and LA cells. Activation of group I mGluRs by the selective agonist 3,5-DHPG produced no effect on membrane properties and glutamatergic transmission in spiny neurons, whereas it did cause a membrane depolarization in LA interneurons coupled to increased input resistance. In combined optical and electrophysiological experiments, in spiny neurons 3,5-DHPG enhanced membrane depolarization and intracellular calcium (Ca2+) levels induced by NMDA applications, but not in LA interneurons. These data suggest the existence of a positive interaction between NMDA and group I mGlu receptors only in medium spiny cells which might, at least partially, account for the differential vulnerability to excitotoxic damage observed in striatal neuronal subtypes.

Stimulation of nitric oxide-cGMP pathway excites striatal cholinergic interneurons via protein kinase G activation

Conflicting data have been collected so far on the action of nitric oxide (NO) on cholinergic interneurons of the striatum. In the present in vitro electrophysiological study, we reported that intracellularly recorded striatal cholinergic interneurons are excited by both hydroxylamine and S-nitroso-N-acetylpenicillamine, two NO donors. This excitation persisted unchanged in the presence of glutamate, dopamine, and substance P receptor antagonists as well as after blockade of tetrodotoxin (TTX)- and calcium channel-sensitive transmitter release, suggesting that NO produces its effects by modulating directly resting ion conductances in the somatodendritic region of striatal cholinergic cells. The depolarizing effect of hydroxylamine was greatly reduced by lowering external concentrations of sodium ions (from 126 to 38 mm) and did not reverse polarity in the voltage range from -120 to -40 mV. The sodium transporter blockers bepridil and 3',4'-dichlorobenzamil were conversely ineffective in preventing NO-induced membrane depolarization. Intracellular cGMP elevation is required for the action of hydroxylamine on striatal cholinergic cells, as demonstrated by the findings that the membrane depolarization produced by this pharmacological agent was prevented by bath and intracellular application of two inhibitors of soluble guanylyl cyclase and was mimicked and occluded by zaprinast, a cGMP phosphodiesterase inhibitor. Finally, intracellular Rp-8-Br-cGMPS, a protein kinase G (PKG) inhibitor, blocked the hydroxylamine-induced membrane depolarization of cholinergic interneurons, whereas both okadaic acid and calyculin A, two protein phosphatase inhibitors, enhanced it, indicating that intracellular PKG and phosphatases oppositely regulate the sensitivity of striatal cholinergic interneurons to NO. The characterization of the cellular mechanisms involved in the regulation of striatal interneuron activity is a key step for the understanding of the role of these cells in striatal microcircuitry.

Role of tonically-active neurons in the control of striatal function: cellular mechanisms and behavioral correlates

1. The striatum is primarily involved in motor planning and motor learning. Human diseases involving its complex circuitry lead to movement disorders such as Parkinson's disease (PD) and Huntington's disease (HD). Moreover the striatum has been involved in processes linked to reward, cognition and drug addiction. 2. The high content of acetylcholine (ACh) found in the striatum is due to the presence of cholinergic interneurons. The intrinsic electrical and synaptic properties of these interneurons have been recently characterized. However, their functional significance is far from being fully elucidated. 3. In vivo electrophysiological experiments from behaving monkeys have identified these cholinergic interneurons as "Tonically Active Neurons" (TANs). They are activated by presentation of sensory stimuli of behavioral significance or linked to reward. 4. Experimental evidence showed that integrity of the nigrostriatal dopaminergic system is essential for TANs to express learned activity. 5. PD is known to be due to the loss of the nigrostriatal dopaminergic pathway and the ensuing imbalance between the content of dopamine and acetylcholine in the striatum. This evidence supports the hypothesis that cholinergic interneurons, or TANs, play a key role in the modulation of striatal function.

[Pituitary pathology in elderly patients admitted in a division of internal medicine. Description of 3 cases]

Pituitary diseases are often unrecognized in the elderly, although if they can be at the basis of several pathological conditions. We report three clinical cases. Patient n. 1: 87 years old woman, in poor general condition. Thyroid function evaluation showed secondary hypothyroidism. Subsequent pituitary function evaluation demonstrated hypopituitarism with empty sella. The diagnosis was "hypopituitarism with secondary hypothyroidism and adrenocortical insufficiency, in empty sella" starting substitutive treatment with glucocorticoids and L-thyroxine, with improvement in her clinical conditions. Patient n. 2: 74 years old woman, with severe congestive heart failure. Her clinical history revealed hypothyroidism. An endocrine evaluation (in absence of therapy) demonstrated panhypopituitarism with secondary hypothyroidism and adrenocortical insufficiency in presence of empty sella. The patients was started on substitutive treatment and her conditions improved. Patient n. 3: 74 years old man with several atrial fibrillation episodes and hyperthyroidism. Thyroid function evaluation suggested secondary hyperthyroidism confirmed by the presence of a pituitary macroadenoma. The patient underwent surgical adenomectomy by trans-sphenoidal route. The clinical conditions of the patient improved, but a slight secondary hyperthyroidism was still present caused by the persistence of residual pathological tissue in the right cavernous sinus region confirmed by octreoscan suggesting the presence of a lesion endowed with somatostatin receptors. The patient was started on long acting octreotide treatment, which is still in progress. In conclusion, pituitary diseases pass often unrecognized in the elderly. Their prompt recognition and treatment can resolve dangerous situations for the patients.

Ultrastructural study of the conjunctival epithelium in the Mongolian gerbil (Meriones unguiculatus)

The conjunctival epithelium of the Mongolian gerbil (Meriones unguiculatus) was studied using the transmission and scanning electron microscopy. The superficial cells of the conjunctival epithelium were isoprismatic in shape and were covered, on their luminal surface, with microplicae. They were connected with the adjacent cells by junctional complexes and desmosomes. Some of the superficial cells were partially or completely detached from the underlying intermediate cells: this morphological pattern was interpreted as an expression of cellular renewal of the conjunctival surface. Goblet cells were either isolated or gathered in clusters: in any case, they were firmly connected with the adjacent epithelial cells. The apical part of the goblet cells was covered with a great number of long microvilli: they showed a variety of morphological aspects, which were interpreted as occurring in a sequential pattern during the secretory process. The Mongolian gerbil can be considered among the laboratory animals used for ophthalmic research.

Anatomical and psychological mechanism of reduplicative misidentification syndromes

Reduplicative misidentifications syndromes (RMS) are rare memory disorders characterized by the subjective conviction that a place, person or event is duplicated. Even if RMS often follow a right frontal lesion, several studies have stressed the importance of bilateral hemispheric pathology. Moreover, from a psychological perspective, there is uncertainty if this symptom should be considered just as a kind of confabulation or if it should be associated with personal psychosocial and behavioral aspects. We report a patient who developed normal pressure hydrocephalus and RMS one year after a post-traumatic right frontal lesion. At the first neuropsychological evaluation, we found mild impairment of all functions, associated with the presence of reduplicative paramnesia. After the ventricle-peritoneal shunt intervention, we observed a progressive improvement of all functions but the frontal ones. The memory deficit became less specific and the RMS disappeared. We therefore postulate that a focal right frontal lesion is not sufficient to cause RMS per se. Our clinical report suggests that paramnesic events held on reasonable ground, not being just a kind of confabulation.

Synaptic transmission in the striatum: from plasticity to neurodegeneration

Striatal neurones receive myriad of synaptic inputs originating from different sources. Massive afferents from all areas of the cortex and the thalamus represent the most important source of excitatory amino acids, whereas the nigrostriatal pathway and intrinsic circuits provide the striatum with dopamine, acetylcholine, GABA, nitric oxide and adenosine. All these neurotransmitter systems interact each other and with voltage-dependent conductances to regulate the efficacy of the synaptic transmission within this nucleus. The integrative action exerted by striatal projection neurones on this converging information dictates the final output of the striatum to the other basal ganglia structures. Recent morphological, immunohistochemical and electrophysiological findings demonstrated that the striatum also contains different interneurones, whose role in physiological and pathological conditions represents an intriguing challenge in these years. The use of the in vitro brain slice preparation has allowed not only the detailed investigation of the direct pre- and postsynaptic electrophysiological actions of several neurotransmitters in striatal neurones, but also the understanding of their role in two different forms of corticostriatal synaptic plasticity, long-term depression and long-term potentiation. These long-lasting changes in the efficacy of excitatory transmission have been proposed to represent the cellular basis of some forms of motor learning and are altered in animal models of human basal ganglia disorders, such as Parkinson's disease. The striatum also expresses high sensitivity to hypoxic-aglycemic insults. During these pathological conditions, striatal synaptic transmission is altered depending on presynaptic inhibition of transmitter release and opposite membrane potential changes occur in projection neurones and in cholinergic interneurones. These ionic mechanisms might partially explain the selective neuronal vulnerability observed in the striatum during global ischemia and Huntington's disease.

A new rat model of small vessel stenting

OBJECTIVES

Restenosis is the major complication of coronary angioplasty and stenting. In addition, the small vessel diameter represents a major limitation to the wide use of the technology. The aim of this study was to assess the feasibility and the vascular response of stent deployment in rat small vessels.

METHODS

In 40 Wistar rats (500-550 g) a Nir stent crimped on a 1.5 mm Comet angioplasty balloon catheter was deployed at high pressure in the common carotid artery. Neointimal area, neointima/media ratio and the arterial dimension were assessed immediately and at 7, 14, 21, and 28 days after stenting.

RESULTS

After stent deployment, the neointimal area and the neointima/media ratio increased progressively and peaked at 14 days (p < 0.05 vs 0 and 7 days). Alpha-actin-positive cells were found circumferentially organized on the lumen surface. At 21 and 28 days after stenting, the neointima and the neointima/media ratio were not statistically different compared with the results obtained fourteen days after stent deployment. No significant differences in the area of external elastic lamina were observed during the study period. In contrast, the internal lumen area was reduced significantly at 14, 21, and 28 days after the stent deployment. Subacute thrombosis rate after stent implantation was 26.5 %.

CONCLUSIONS

The results of this study demonstrated that the balloon expandable stents can be safely placed into rat arteries and the reduction of the internal arterial lumen observed after stent deployment was only due to the neointima formation whereas remodeling did not occur.

Involvement of intracellular calcium stores during oxygen/glucose deprivation in striatal large aspiny interneurons

Striatal large aspiny interneurons were recorded from a slice preparation using a combined electrophysiologic and microfluorometric approach. The role of intracellular Ca2+ stores was analyzed during combined oxygen/glucose deprivation (OGD). Before addressing the role of the stores during energy deprivation, the authors investigated their function under physiologic conditions. Trains of depolarizing current pulses caused bursts of action potentials coupled to transient increases in intracellular calcium concentration ([Ca2+]i). In the presence of cyclopiazonic acid (30 micromol/L), a selective inhibitor of the sarcoendoplasmic reticulum Ca2+ pumps, or when ryanodine receptors were directly blocked with ryanodine (20 [micromol/L), the [Ca2+]i transients were progressively smaller in amplitude, suggesting that [Ca2+]i released from intracellular stores helps to maintain a critical level of [Ca2+]i during physiologic firing activity. As the authors have recently reported, brief exposure to combined OGD induced a membrane hyperpolarization coupled to an increase in [Ca2+]i. In the presence of cyclopiazonic acid or ryanodine, the hyperpolarization and the rise in [Ca2+]i induced by OGD were consistently reduced. These data support the hypothesis that Ca2+ release from ryanodine-sensitive Ca2+ pools is involved not only in the potentiation of the Ca2+ signals resulting from cell depolarization, but also in the amplification of the [Ca2+]i rise and of the concurrent membrane hyperpolarization observed in course of OGD in striatal large aspiny interneurons.

Activation of D2-like dopamine receptors reduces synaptic inputs to striatal cholinergic interneurons

Dopamine (DA) plays a crucial role in the modulation of striatal function. Striatal cholinergic interneurons represent an important synaptic target of dopaminergic fibers arising from the substantia nigra and cortical glutamatergic inputs. By means of an electrophysiological approach from corticostriatal slices, we isolated three distinct synaptic inputs to cholinergic interneurons: glutamate-mediated EPSPs, GABAA-mediated potentials, and Acetylcholine (ACh)-mediated IPSPs. We therefore explored whether DA controls the striatal cholinergic activity through the modulation of these synaptic potentials. We found that SKF38393, a D1-like receptor agonist, induced a membrane depolarization (also see Aosaki et al., 1998) but had no effects on glutamatergic, GABAergic, and cholinergic synaptic potentials. Conversely, D2-like DA receptor activation by quinpirole inhibited both GABAA and cholinergic synaptic potentials. These effects of quinpirole were mimicked by omega-conotoxin GVIA, blocker of N-type calcium channels. The lack of effect both on the intrinsic membrane properties and on exogenously applied GABA and ACh by quinpirole supports a presynaptic site of action for the D2-like receptor-mediated inhibition. Moreover, the quinpirole-induced decrease in amplitude was accompanied by an increase in paired pulse facilitation ratio (EPSP2/EPSP1), an index of a decrease in transmitter release. Our findings demonstrate that DA modulates the excitability of cholinergic interneurons through either an excitatory D1-like-mediated postsynaptic mechanism or a presynaptic inhibition of the GABAergic and cholinergic inhibitory synaptic potentials.

Acetylcholine-mediated modulation of striatal function

Striatal spiny neurones serve as a major anatomical locus for the relay of cortical information flow through the basal ganglia. these projection neurones also represent the main synaptic target of cholinergic interneurones, whose physiological role in striatal activity still remains largely enigmatic. The striatal cholinergic system has been implicated in the pathophysiology of movement disorders such as Parkinson's disease, but the cellular mechanisms underlying cholinergic-neurone function are still unknown. On the basis of in vitro electrophysiological evidence, obtained from a rat corticostriatal-slice preparation, we propose that endogenous ACh exerts a complex modulation of striatal synaptic transmission, which produces both short-term and long-term effects. ACh-mediated mechanisms might be of crucial importance in processing the cortical inputs to the striatum.

Oral tacrolimus (FK 506) in Crohn's disease complicated by fistulae of the perineum

We describe the cases of two patients with Crohn's disease affected by severe perineal fistulae resistant to conventional therapies, successfully treated with FK 506, a new immunomodulatory drug. It is well absorbed from diseased bowel and preliminary experiences have indicated its short-term use in complicated Crohn's disease. The first patient was a 24-year-old male with perineal fistula and severe skin ulceration (8 cm of external opening diameter). He had undergone colectomy and ileostomy because of severe pancolitis refractory to medical treatment and had been treated with azathioprine and metronidazole. Two months after starting FK 506, a dramatic improvement made further surgical operation unnecessary. Local and general benefit was observed during the following 26 months, until FK 506 was withdrawn. The second patient was a 28-year-old male with a diagnosis of ulcerative pancolitis changed to Crohn's disease two months after the onset of a perineal fistula, recurring despite drainage procedures, steroid therapy, and total parenteral nutrition. FK 506 was administered for two months with a complete healing of fistula. Successively, it was stopped and corticosteroids (associated to enteral nutrition) were given because of recurrent rectal bleeding. Our experience encourages the use of oral FK 506 in complicated Crohn's disease and suggests the possibility of a long-term primary therapy other than the use as a "bridge" to other treatments.

Effects of hydroxymethylglutaryl coenzyme A reductase inhibitor simvastatin on smooth muscle cell proliferation in vitro and neointimal formation in vivo after vascular injury

OBJECTIVES

We sought to evaluate the effects of hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors on vascular smooth muscle cell (VSMC) proliferation in vitro and neointimal formation in vivo after vascular injury.

BACKGROUND

Neointimal hyperplasia after vascular injury is responsible for restenosis after arterial stenting, whereas arterial remodeling and neointimal formation are the causes of restenosis after percutaneous transluminal coronary angioplasty.

METHODS

We assessed the effect of simvastatin on in vitro VSMC proliferation. To study the effects of simvastatin in vivo, balloon injury and stent deployment were performed in the common carotid artery of rats. Neointimal area was measured two weeks later in the balloon injury model and three weeks after stent deployment.

RESULTS

Simvastatin markedly inhibits VSMC proliferation in vitro. In vivo, simvastatin reduced, in a dose-dependent manner, the neointimal area and the neointima-media ratio after balloon injury from 0.266 +/- 0.015 mm2 to 0.080 +/- 0.026 mm2 and from 1.271 +/- 0.074 to 0.436 +/- 0.158 (p < 0.001 vs. control rats) at the highest dose. Simvastatin also significantly reduced the neointimal formation and the neointima-media ratio after stenting from 0.508 +/- 0.035 mm2 to 0.362 +/- 0.047 mm2 (p < 0.05 vs. control rats) and from 2.000 +/- 0.136 to 1.374 +/- 0.180 (p < 0.05 vs. control rats). The vessel thrombosis rate after stent deployment was 30% in the control group and 11.1% in the treated group (p = NS). Moreover, the systemic administration of simvastatin did not affect hepatic and renal functions, blood pressure or heart rate.

CONCLUSIONS

Simvastatin potently inhibits VSMC proliferation in vitro and reduces neointimal formation in a rat model of vascular injury.

Pharmacological inhibition of the Na(+)/Ca(2+) exchanger enhances depolarizations induced by oxygen/glucose deprivation but not responses to excitatory amino acids in rat striatal neurons

BACKGROUND AND PURPOSE

Neuronal Na(+)/Ca(2+) exchanger plays a relevant role in maintaining intracellular Ca(2+) and Na(+) levels under physiological and pathological conditions. However, the role of this exchanger in excitotoxicity and ischemia-induced neuronal injury is still controversial and has never been studied in the same neuronal subtypes.

METHODS

We investigated the effects of bepridil and 3',4'-dichlorobenzamil (DCB), 2 blockers of the Na(+)/Ca(2+) exchanger, in rat striatal spiny neurons by utilizing intracellular recordings in brain slice preparations to compare the action of these drugs on the membrane potential changes induced either by oxygen and glucose deprivation (OGD) or by excitatory amino acids (EAAs).

RESULTS

Bepridil (3 to 100 micromol/L) and DCB (3 to 100 micromol/L) caused a dose-dependent enhancement of the OGD-induced depolarization measured in striatal neurons. The EC(50) values for these effects were 31 micromol/L and 29 micromol/L, respectively. At these concentrations neither bepridil nor DCB altered the resting membrane properties of the recorded cells (membrane potential, input resistance, and current-voltage relationship). The effects of bepridil and DCB on the OGD-induced membrane depolarization persisted in the presence of D-2-amino-5-phosphonovalerate (50 micromol/L) plus 6-cyano-7-nitroquinoxaline-2,3-dione (20 micromol/L), which suggests that they were not mediated by an enhanced release of EAAs. Neither tetrodotoxin (1 micromol/L) nor nifedipine (10 micromol/L) affect the actions of these 2 blockers of the Na(+)/Ca(2+) exchanger, which indicates that voltage-dependent Na(+) channels and L-type Ca(2+) channels were not involved in the enhancement of the OGD-induced depolarization. Conversely, the OGD-induced membrane depolarization was not altered by 5-(N, N-hexamethylene) amiloride (1 to 3 micromol/L), an inhibitor of the Na(+)/H(+) exchanger, which suggests that this antiporter did not play a prominent role in the OGD-induced membrane depolarization recorded from striatal neurons. Bepridil (3 to 100 micromol/L) and DCB (3 to 100 micromol/L) did not modify the amplitude of the excitatory postsynaptic potentials evoked by cortical stimulation. Moreover, these blockers did not affect membrane depolarizations caused by brief applications of glutamate (0.3 to 1 mmol/L), AMPA (0. 3 to 1 micromol/L), and NMDA (10 to 30 micromol/L).

CONCLUSIONS

These results provide pharmacological evidence that the activation of the Na(+)/Ca(2+) exchanger exerts a protective role during the early phase of OGD in striatal neurons, although it does not shape the amplitude and the duration of the electrophysiological responses of these cells to EAA.

Morphological changes induced by prolonged darkness in the retinal pigment epithelium of the turtle (Pseudemys scripta elegans)

The retinal pigment epithelium of Vertebrates was shown to be sensitive to cyclic oscillations of light and darkness. The morphological changes induced by prolonged darkness on the retinal epithelial cells of the freshwater turtle were studied, with particular regard to their localization and to their reversibility if animals are recovered under cyclic light. The eyes were processed for light and electron microscopy and a morphological and morphometric analysis was performed on the specimens. After 7 days of prolonged darkness, the vitreal extremity of some epithelial cells was partially detached; on the basal zone the infoldings were missing and vesicles and tubules, often arranged in rows, were observed. After 30 days of prolonged darkness, partial or complete double layers of epithelial cells were present: the superficial layer was connected, by means of the apical fringes, to the photoreceptors, whilst the deepest layer showed vesicles and tubules on its basal zone. After 7 days of recovery to L:D = 12:12, no cyclic activity was demonstrated and only occasional double layers of cells were present; on the basal surface isolated basal infoldings were present where two adjacent cells were joined together. It could be concluded that the detachment of the apical part of some cells, rapidly covered by the lateral sliding of the adjacent cells, and the substitution of the basal infoldings with vesicles and tubules could represent the morphological response of the retinal epithelium to the functional changes induced by prolonged darkness.

Metabotropic glutamate receptors and cell-type-specific vulnerability in the striatum: implication for ischemia and Huntington's disease

Differential sensitivity to glutamate has been proposed to contribute to the cell-type-specific vulnerability observed in neurological disorders affecting the striatum such as Huntington's disease (HD) and global ischemia. Under these pathological conditions striatal spiny neurons are selectively lost while large aspiny (LA) cholinergic interneurons are spared. We studied the electrophysiological effects of metabotropic glutamate receptor (mGluR) activation in striatal spiny neurons and LA interneurons in order to define the role of these receptors in the pathophysiology of the striatum. DCG-IV and L-SOP, agonists for group II and III mGluRs respectively, produced a presynaptic inhibitory effect on corticostriatal glutamatergic excitatory synaptic potentials in both spiny neurons and LA interneurons. Activation of group I mGluRs by the selective agonist 3,5-DHPG produced no detectable effects on membrane properties and glutamatergic synaptic transmission in spiny neurons while it caused a slow membrane depolarization in LA interneurons coupled to increased input resistance. In combined electrophysiological and microfluorometric recordings, 3,5-DHPG strongly enhanced membrane depolarizations and intracellular Ca2+ accumulation induced by NMDA applications in spiny neurons but not in LA interneurons. Activation of protein kinase C (PKC) by phorbol 12,13-diacetate mimicked this latter action of 3,5-DHPG while the facilitatory effect of 3,5-DHPG was prevented by calphostin C, an inhibitor of PKC. These data indicate that a positive interaction between NMDA receptors and group I mGluRs, via PKC activation, is differently expressed in these two neuronal subtypes. Our data also suggest that differential effects of the activation of group I mGluRs, but not of group II and III mGluRs, might partially account for the selective vulnerability to excitotoxic damage observed within the striatum.

Weak effect of neuromodulators on climbing fiber-activated [Ca(2+)](i) increases in rat cerebellar Purkinje neurons

The effect of several neuromodulators (carbachol (CCh), serotonin (5-HT), noradrenaline (NE), and dopamine (DA)) on the climbing fiber (CF)-induced [Ca(2+)](i) increase in the dendrites of cerebellar Purkinje cells was examined in slices from the rat cerebellum. Purkinje cells were filled with the Ca(2+) indicator bis-fura-2 with patch electrodes on the soma. [Ca(2+)](i) changes were measured from regions of interest in the dendrites with a high speed camera. Changes evoked by one or three responses were measured in control conditions and with neuromodulators added to the bath. None of these four classic modulators caused a significant change in the CF-induced [Ca(2+)](i) amplitude. Buspirone, a partial 5-HT(1A) agonist and a weak DA receptor antagonist caused a small (10-15%) reduction in the response.

Additive antiproteinuric effect of converting enzyme inhibitor and losartan in normotensive patients with IgA nephropathy

We tested the hypothesis that the combination of converting enzyme inhibitor (CEI) with losartan (LOS) produces a more profound antiproteinuric effect than either drug alone in normotensive patients with immunoglobulin A (IgA) nephropathy. Eight normotensive (mean blood pressure, 88.9 +/- 2.1 mm Hg) patients with biopsy-proven IgA nephropathy, nonnephrotic proteinuria (protein, 1 to 3 g/d), and normal or slightly reduced creatinine clearance (range, 69 to 119 mL/min) were studied. Clinical evaluations and laboratory tests were performed (1) before CEI treatment (basal) and after (2) CEI alone (CEI, 12 weeks); (3) the combination of CEI and LOS, the latter at a dosage of 50 mg/d (CEI + LOS, 4 weeks); (4) LOS alone (LOS; 50 mg/d; 12 weeks); (5) the combination of LOS and CEI (LOS + CEI, 4 weeks, at the same dosage as CEI + LOS); and (6) a doubled dose of either CEI alone or LOS alone for 4 weeks. CEI and LOS as monotherapy significantly reduced proteinuria by 38% and 30%, respectively. No further reduction of proteinuria was achieved by doubling the dose of CEI or LOS. Both combinations induced a more remarkable reduction of proteinuria (73%; P < 0.05 v other periods) than either drug administered alone. The antiproteinuric effect of CEI or LOS and the more remarkable effect achieved with both combinations was not dependent on the reduction of blood pressure and/or creatinine clearance. In conclusion, this study provides first-time evidence that the combination of CEI and LOS in normotensive patients with IgA nephropathy produces a more profound decrease in proteinuria than either drug. This additive antiproteinuric effect is not dependent on changes in systemic blood pressure and creatinine clearance. Nevertheless, a larger controlled study is required to confirm this novel observation.

Electrophysiological recordings and calcium measurements in striatal large aspiny interneurons in response to combined O2/glucose deprivation

Electrophysiological recordings and calcium measurements in striatal large aspiny interneurons in response to combined O2/glucose deprivation. The effects of combined O2/glucose deprivation were investigated on large aspiny (LA) interneurons recorded from a striatal slice preparation by means of simultaneous electrophysiological and optical recordings. LA interneurons were visually identified and impaled with sharp microelectrodes loaded with the calcium (Ca2+)-sensitive dye bis-fura-2. These cells showed the morphological, electrophysiological, and pharmacological features of large striatal cholinergic interneurons. O2/glucose deprivation induced a membrane hyperpolarization coupled to a concomitant increase in intracellular Ca2+ concentration ([Ca2+]i). Interestingly, this [Ca2+]i elevation was more pronounced in dendritic branches rather than in the somatic region. The O2/glucose-deprivation-induced membrane hyperpolarization reversed its polarity at the potassium (K+) equilibrium potential. Both membrane hyperpolarization and [Ca2+]i rise were unaffected by TTX or by a combination of ionotropic glutamate receptors antagonists, D-2-amino-5-phosphonovaleric acid and 6cyano-7-nitroquinoxaline-2, 3-dione. Sulfonylurea glibenclamide, a blocker of ATP-sensitive K+ channels, markedly reduced the O2/glucose-deprivation-induced membrane hyperpolarization but failed to prevent the rise in [Ca2+]i. Likewise, charybdotoxin, a large K+-channel (BK) inhibitor, abolished the membrane hyperpolarization but did not produce detectable changes of [Ca2+]i elevation. A combination of high-voltage-activated Ca2+ channel blockers significantly reduced both the membrane hyperpolarization and the rise in [Ca2+]i. In a set of experiments performed without dye in the recording electrode, either intracellular bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid or external barium abolished the membrane hyperpolarization induced by O2/glucose deprivation. The hyperpolarizing effect on membrane potential was mimicked by oxotremorine, an M2-like muscarinic receptor agonist, and by baclofen, a GABAB receptor agonist. However, this membrane hyperpolarization was not coupled to an increase but rather to a decrease of the basal [Ca2+]i. Furthermore glibenclamide did not reduce the oxotremorine- and baclofen-induced membrane hyperpolarization. In conclusion, the present results suggest that in striatal LA cells, O2/glucose deprivation activates a membrane hyperpolarization that does not involve ligand-gated K+ conductances but is sensitive to barium, glibenclamide, and charybdotoxin. The increase in [Ca2+]i is partially due to influx through voltage-gated high-voltage-activated Ca2+ channels.

A critical role of the nitric oxide/cGMP pathway in corticostriatal long-term depression

High-frequency stimulation (HFS) of corticostriatal glutamatergic fibers induces long-term depression (LTD) of excitatory synaptic potentials recorded from striatal spiny neurons. This form of LTD can be mimicked by zaprinast, a selective inhibitor of cGMP phosphodiesterases (PDEs). Biochemical analysis shows that most of the striatal cGMP PDE activity is calmodulin-dependent and inhibited by zaprinast. The zaprinast-induced LTD occludes further depression by tetanic stimulation and vice versa. Both forms of synaptic plasticity are blocked by intracellular 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylyl cyclase, indicating that an increased cGMP production in the spiny neuron is a key step. Accordingly, intracellular cGMP, activating protein kinase G (PKG), also induces LTD. Nitric oxide synthase (NOS) inhibitors N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) and 7-nitroindazole monosodium salt (7-NINA) block LTD induced by either HFS or zaprinast, but not that induced by cGMP. LTD is also induced by the NO donors S-nitroso-N-acetylpenicillamine (SNAP) and hydroxylamine. SNAP-induced LTD occludes further depression by HFS or zaprinast, and it is blocked by intracellular ODQ but not by L-NAME. Intracellular application of PKG inhibitors blocks LTD induced by HFS, zaprinast, and SNAP. Electron microscopy immunocytochemistry shows the presence of NOS-positive terminals of striatal interneurons forming synaptic contacts with dendrites of spiny neurons. These findings represent the first demonstration that the NO/cGMP pathway exerts a feed-forward control on the corticostriatal synaptic plasticity.

[The endorectal repair of rectovaginal fistulae]

BACKGROUND

Twenty-one patients who had simple rectovaginal fistulas were treated at the Surgical Department of "Tor Vergata" University from 1992 to 1996 all of whom were at the first approach.

METHODS

The fistulas were treated with complete excision of the external tract and primary closure of the internal opening with advancement of a rectal mucosal flap, distal to the origin fistulas opening. The vaginal side is left open for drainage.

RESULTS

Eighteen of the twenty-one patients had good results; three patients required reoperation for recurrences; all of them had satisfactory results.

CONCLUSIONS

The advancement flap technique was very useful for simple rectovaginal fistulas with any sphincter damage, and it is very well tolerated by patients.

An in vitro electrophysiological study on the effects of phenytoin, lamotrigine and gabapentin on striatal neurons

We performed intracellular recordings from a rat corticostriatal slice preparation in order to compare the electrophysiological effects of the classical antiepileptic drug (AED) phenytoin (PHT) and the new AEDs lamotrigine (LTG) and gabapentin (GBP) on striatal neurons. PHT, LTG and GBP affected neither the resting membrane potential nor the input resistance/membrane conductance of the recorded cells. In contrast, these agents depressed in a dose-dependent and reversible manner the current-evoked repetitive firing discharge. These AEDs also reduced the amplitude of glutamatergic excitatory postsynaptic potentials (EPSPs) evoked by cortical stimulation. However, substantial pharmacological differences between these drugs were found. PHT was the most effective and potent agent in reducing sustained repetitive firing of action potentials, whereas LTG and GBP preferentially inhibited corticostriatal excitatory transmission. Concentrations of LTG and GBP effective in reducing EPSPs, in fact, produced only a slight inhibition of the firing activity of these cells. LTG, but not PHT and GBP, depressed cortically-evoked EPSPs increasing paired-pulse facilitation (PPF) of synaptic transmission, suggesting that a presynaptic site of action was implicated in the effect of this drug. Accordingly, PHT and GBP, but not LTG reduced the membrane depolarizations induced by exogenously-applied glutamate, suggesting that these drugs preferentially reduce postsynaptic sensitivity to glutamate released from corticostriatal terminals. These data indicate that in the striatum PHT, LTG and GBP decrease neuronal excitability by modulating multiple sites of action. The preferential modulation of excitatory synaptic transmission may represent the cellular substrate for the therapeutic effects of new AEDs whose use may be potentially extended to the therapy of neurodegenerative diseases involving the basal ganglia.

Sodium influx plays a major role in the membrane depolarization induced by oxygen and glucose deprivation in rat striatal spiny neurons

BACKGROUND AND PURPOSE

Striatal spiny neurons are selectively vulnerable to ischemia, but the ionic mechanisms underlying this selective vulnerability are unclear. Although a possible involvement of sodium and calcium ions has been postulated in the ischemia-induced damage of rat striatal neurons, the ischemia-induced ionic changes have never been analyzed in this neuronal subtype.

METHODS

We studied the effects of in vitro ischemia (oxygen and glucose deprivation) at the cellular level using intracellular recordings and microfluorometric measurements in a slice preparation. We also used various channel blockers and pharmacological compounds to characterize the ischemia-induced ionic conductances.

RESULTS

Spiny neurons responded to ischemia with a membrane depolarization/inward current that reversed at approximately -40 mV. This event was coupled with an increased membrane conductance. The simultaneous analysis of membrane potential changes and of variations in [Na+]i and [Ca2+]i levels showed that the ischemia-induced membrane depolarization was associated with an increase of [Na+]i and [Ca2+]i. The ischemia-induced membrane depolarization was not affected by tetrodotoxin or by glutamate receptor antagonists. Neither intracellular BAPTA, a Ca2+ chelator, nor incubation of the slices in low-Ca2+-containing solutions affected the ischemia-induced depolarization, whereas it was reduced by lowering the external Na+ concentration. High doses of blockers of ATP-dependent K+ channels increased the membrane depolarization observed in spiny neurons during ischemia.

CONCLUSIONS

Our findings show that, although the ischemia-induced membrane depolarization is coupled with a rise of [Na+]i and [Ca2+]i, only the Na+ influx plays a prominent role in this early electrophysiological event, whereas the increase of [Ca2+]i might be relevant for the delayed neuronal death. We also suggest that the activation of ATP-dependent K+ channels might counteract the ischemia-induced membrane depolarization.

Morphological and functional study of dwarf neurons in the rat striatum

Combination of morphological and electrophysiological techniques provided data, suggesting existence in the young rat striatum of a peculiar class of neurons, the neurogliaform or dwarf neurons. Striatal neurons (n = 92), intracellularly recorded from rat brain slices, were filled (one in each slice) with the intracellular marker biocytin, to compare physiological and morphological properties in the same cell. Moreover, some neurons (n = 7) were filled with biocytin plus the fluorescent calcium indicator fura-2, identifying cells during electrophysiological recording. Electrophysiological recording showed that striatal neurons had different firing patterns, suggestive in most cases (n = 80) of spiny neuron class and in others (n = 12) of interneuron class. Fura-2 injection clearly identified the body of six medium-sized cells and of one distinctive tiny cell. This small cell, however, showed a resting membrane potential and spontaneous and evoked firing pattern characteristic of striatal interneurons. Moreover, the fura-2 injected in such small neuron also completely filled the cell body of a near large neuron; the fura-2 fluorescence changed synchronously in the two paired neurons after electrical stimulation of the impaled small one. Accordingly, the biocytin staining identified the morphology of the small recorded neuron as a neurogliaform-like cell apposed to a dendrite of an aspiny neuron, suggesting that the dye injected in one neuron had diffused to the other of a different type. Furthermore, such heterologous dye coupling unexpectedly involved seven pairs of cells detected with biocytin staining (7.6% of the recorded neurons), invariably represented by a medium or large neuron on one side, and on the other side by a small (5.44 +/- 0.15 x 9.14 +/- 0.7 microns, mean +/- SD; n = 7) neurogliaform cell, roundish in shape with few slender and short processes, usually apposed to a dendrite of the companion neurons (six out of seven). In the other cases, the biocytin staining revealed in each slice either the morphology of single spiny or aspiny neurons (80.4% of recorded neurons), or of two-three medium-sized spiny neurons detected near to each other, suggesting that dye coupling had occurred typically between similar neurons (11.9% of the recorded neurons). These data suggest that some neurogliaform cells in the striatum of young rat can be identified as dwarf interneurons, that may be dye-coupled with neurons of different classes.

Early sodium elevations induced by combined oxygen and glucose deprivation in pyramidal cortical neurons

We investigated the effects of oxygen (O2)/glucose deprivation on intracellular sodium concentration ([Na+]i) of cortical pyramidal cells in a slice preparation of rat frontal cortex. Intracellular recordings were combined with microfluorometric measurements of [Na+]i using the Na+-sensitive dye sodium-binding benzofuran isophthalate (SBFI). Deprivation of O2/glucose caused an initial membrane hyperpolarization that was followed by a slowly developing large depolarization. Levels of [Na+]i started to increase significantly during the phase of membrane hyperpolarization. Neither tetrodotoxin, a combination of ionotropic and metabotropic glutamate receptor antagonists (D-amino-phosphonovalerate, 6-cyano-7-nitroquinoxaline-2,3-dione plus S-methyl-4-carboxyphenylglycine) nor bepridil, an inhibitor of the Na+/Ca2+-exchanger, affected these responses to O2/ glucose. The present results demonstrate that, in cortical neurons, O2/glucose deprivation induces an early rise in [Na+]i which cannot be ascribed to the activity of voltage gated Na+-channels, glutamate receptors or of the Na+/Ca2+-exchanger.

Endogenous ACh enhances striatal NMDA-responses via M1-like muscarinic receptors and PKC activation

Cortical glutamatergic fibres and cholinergic inputs arising from large aspiny interneurons converge on striatal spiny neurons and play a major role in the control of motor activity. We have investigated the interaction between excitatory amino acids and acetylcholine (ACh) on striatal spiny neurons by utilizing intracellular recordings, both in current- and in voltage-clamp mode in rat brain slices. Muscarine (0.3-10 microM) produced a reversible and dose-dependent increase in the membrane depolarizations/inward currents induced by brief applications of N-methyl-D-aspartate (NMDA), while it did not affect the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-induced responses. These concentrations of muscarine did not alter the membrane potential and the current-voltage relationship of the recorded cells. Neostigmine (0.3-10 microM), an ACh-esterase inhibitor, mimicked this facilitatory effect. The facilitatory effects of muscarine and neostigmine were antagonized either by scopolamine (3 microM) or by pirenzepine (10-100 nM), an antagonist of M1-like muscarinic receptors, but not by methoctramine (300 nM), an antagonist of M2-like muscarinic receptor. Accordingly, these facilitatory effects were mimicked by McN-A-343 (1-10 microM), an agonist of M1-like muscarinic receptors, but not by oxotremorine (300 nM), an agonist of M2-like receptors. Tetrodotoxin (TTX) did not block the facilitatory effect produced by the activation of muscarinic receptors suggesting that this effect is postsynaptically mediated. The action of neostigmine was prevented either by the intracellular calcium (Ca2+) chelator BAPTA (200 mM) or by preincubating the slices with inhibitors of protein kinase C (PKC) (staurosporine 100 nM or calphostin C 1 microM). McN-A-343 did not alter the excitatory post synaptic potentials (EPSPs) evoked by corticostriatal stimulation in the presence of physiological concentration of magnesium (Mg2+ 1.2 mM), while it enhanced the duration of these EPSPs recorded in the absence of external magnesium. Our data show that endogenous striatal ACh exerts a positive modulatory action on NMDA responses via M1-like muscarinic receptors and PKC activation.

Blockade of M2-like muscarinic receptors enhances long-term potentiation at corticostriatal synapses

Acetylcholine (ACh) exerts a crucial role in learning and memory. The striatum contains the highest concentration of this transmitter in the brain. This structure expresses two different forms of synaptic plasticity, long-term depression (LTD) and long-term potentiation (LTP), which might contribute to the storage of motor skills and some cognitive processes. We have investigated the role of M2-like muscarinic receptors in striatal LTP by utilizing intracellular recordings in vitro from a rat corticostriatal slice preparation. Methoctramine (250 nM), an antagonist of M2-like muscarinic receptors, enhanced striatal LTP induced in the absence of external magnesium (Mg2+) by high-frequency stimulation (HFS) of corticostriatal fibres. Methoctramine did not affect the amplitude of excitatory postsynaptic potentials (EPSPs) when bath applied either before or after the conditioning tetanus suggesting that a critical increase of ACh concentrations is produced only during HFS. Methoctramine per se failed to enhance the NMDA-mediated EPSPs recorded in the absence of external Mg2+ and in the presence of 10 microM CNQX. Methoctramine antagonized the presynaptic inhibitory action of neostigmine, an inhibitor of ACh-esterase, and oxotremorine, an agonist of M2-like muscarinic receptors. These data indicate that the activation of M2-like muscarinic receptors exerts a negative influence on striatal LTP, probably by reducing the release of glutamate from corticostriatal fibres and they suggest a complex modulatory effect of ACh in striatal synaptic plasticity.

Electrophysiology of the neuroprotective agent riluzole on striatal spiny neurons

Striatal spiny neurons are selectively vulnerable in Huntington's disease (HD). No effective treatment is available to limit neuronal death in this pathological condition. In an experimental model of HD, a beneficial effect has recently been reported by the neuroprotective agent riluzole. We performed intracellular recordings in order to characterize the electrophysiological effects of this compound on striatal spiny neurons. Riluzole (0.1-100 microM) affected neither the resting membrane potential nor the input resistance/membrane conductance of the recorded cells. Bath application of this pharmacological agent produced a dose-dependent reduction of the number of spikes evoked by long-lasting depolarizing pulses. The EC50 value for this effect was 0.5 microM. Low doses of riluzole selectively reduced the firing frequency in the last part of the depolarizing pulse suggesting a use-dependent action at low concentrations of this compound. Riluzole produced a dose-dependent reduction of the amplitude of the corticostriatal glutamatergic excitatory post-synaptic potentials (EPSPs) with an extrapolated EC50 value of 6 microM. This effect was reversible and maximal at a concentration of 100 microM. Paired-pulse facilitation (PPF) was not affected by riluzole suggesting that the reduction of excitatory transmission was not only caused by a decrease of presynaptic release. Accordingly, riluzole also reduced the amplitude of membrane depolarization induced by exogenous glutamate. The modulatory action of riluzole on the activity of striatal spiny neurons might support the use of this drug in experimental models of excitotoxicity and in the neurodegenerative disorders involving the striatum.

Hypoglycemia, hypoxia, and ischemia in a corticostriatal slice preparation: electrophysiologic changes and ascorbyl radical formation

Experimental and clinical data suggest that oxygen and/or glucose deprivation alters electrical transmission in the brain and generates free radicals, which may mediate neuronal death. We have analyzed the effects of oxygen and/or glucose deprivation on both excitatory transmission, by measuring field potential amplitude, and free radical production, by using electron spin resonance (ESR) spectroscopy, in a corticostriatal slice preparation. Combined oxygen and/or glucose deprivation (ischemia) lasting 10 to 20 minutes induced a long-term depression of field potential amplitude. The ascorbyl radical could only be detected in brain slices during the reperfusion-phase after 30 minutes of ischemia. It appeared in the early minutes after the washout of ischemic medium and remained stable throughout the reperfusion phase. This radical was never detected in the external medium. Ischemia induced only a slight, but progressive, release of lactate dehydrogenase (LDH) into the external medium during the reperfusion phase. In contrast, exposure of slices to hypoxia or hypoglycemia alone resulted in transient depression of field potential amplitude, and no generation of ascorbyl radicals was observed on reperfusion. We propose that the long-lasting loss of electrical signals is the early sign of neuronal damage during ischemia. On the other hand, ascorbyl radical formation may be considered an indicator of neuronal injury after prolonged energy deprivation.

Muscarinic IPSPs in rat striatal cholinergic interneurones

1. Intracellular recordings were made from neurones in slice of rat striatum in vitro. 2. The forty-nine neurones studied were immunoreactive for choline acetyltransferase and had the electrophysiological characteristics typical of large aspiny interneurones. 3. Focal stimulation of the slice elicited a hyperpolarizing inhibitory postsynaptic potential in thirty-five neurones. This IPSP lasted 0.5-1 s and reversed polarity at a membrane potential which was dependent on the logarithm of the extracellular potassium concentration. 4. The IPSP was reversibly blocked by scopolamine and methoctramine, which has some selectivity for M2 subtype of muscarinic receptor. It was unaffected by 6-cyano-7-nitroquinoxaline-2,3-dione (10 microM), DL-2-amino-phosphonovaleric acid (30 microM) and bicuculline (30 microM). 5. Exogenous acetylcholine and muscarine also hyperpolarized the neurones, and this was blocked by methoctramine by not by pirenzepine, which is an M1 receptor-selective antagonist. 6. The findings demonstrate that muscarinic IPSPs occur in the central nervous system. The IPSP may mediate an 'autoinhibition' of striatal cholinergic neurone activity.