PubMed Health⌕ Search

Biomedical subjects

R Santarelli

Publications and source records attributed to R Santarelli.

33 records · Page 2Linked to original sources
PubMed1995

Possible modulation of auditory middle latency responses by nitric oxide in the inferior colliculus of anaesthetized rats.

Nitric oxide (NO) is a short-lived radical species endowed with intercellular signalling functions in the mammalian brain. In the present study we have investigated the effects of focal injection into one inferior colliculus of N omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, on the acoustic middle latency responses (MLRs) evoked by click stimuli and recorded from the auditory cortex in anaesthetized rats. Microinfusion of L-NAME (1.0 mM) did not alter the latency of MLRs nor did it affect the evoked brain stem responses (ABRs). By contrast, L-NAME reduced P1a-N1 amplitude of MLRs by 51.7 +/- 6.6% (mean +/- SEM; n = 5) and almost complete recovery to background amplitude was obtained 15-25 min after treatment. The less active isomer, D-NAME (1.0 mM; n = 5), failed to produce consistent effects on the evoked MLRs. A higher concentration of L-NAME (5.0 mM; n = 5) yielded a 69.0 +/- 13.3% inhibition whereas maximum inhibition produced by 0.5 mM (n = 3) L-NAME was approximately equal to 10% of control value. The inhibitory effect typically evoked by 1.0 mM L-NAME was prevented by treating rats with L-arginine (5.0 mM; n = 5), the endogenous precursor of NO synthesis. Reduction of MLR amplitude was also obtained in rats receiving intracollicular injection of dizocilpine (MK801; 1.0 microM) and LY274614 (1.0 mM), two selective N-methyl-D-aspartate (NMDA) receptor antagonists. In conclusion, the present data support a role for intracollicular NO in the processing and transmission of the acoustic input to the auditory cortex in the rat.

Acoustic Stimulation↗
PubMed1995

Generation of human auditory steady-state responses (SSRs). I: Stimulus rate effects.

Auditory evoked responses were recorded in 16 normally hearing subjects in order to investigate the mechanisms underlying the generation of the 40 Hz steady-state response (SSR). In the first part of our study, auditory potentials were evoked by 0.1 ms clicks presented at 105 dB p.e. SPL with repetition rates of 7.9 (to obtain middle latency response, MLR), 20, 30, 40, 50, 60 Hz. In each subject predictions of the responses recorded at stimulus repetition rates of 30, 40, 50, 60 Hz were synthesized by superimposing MLRs at suitable time intervals. The calculated mean amplitude/rate and phase/rate functions behaved similarly for the recorded and predicted curves, showing the highest amplitude at 40 Hz and a linear increase of phase values when increasing the stimulus rate. Nevertheless the synthetic curves closely predicted amplitude and phase values of the recorded responses only at 40 Hz. At frequencies below 40 Hz, the mean amplitude of the predicted curve was lower than that of the recorded one while at frequencies above 40 Hz the mean amplitude was higher. Predicted phase values were found lagging at 30 Hz, and leading at 50 Hz and 60 Hz in comparison to phase values calculated on the recorded responses. Our findings suggest that a model based on the linear addition of transient MLRs is not able to adequately predict steady-state responses at stimulus rates other than at 40 Hz. Other mechanisms related to the recovery cycle of the activated system come into play in the steady-state response generation causing a decrease in amplitude and an increase in phase lag when increasing the stimulus repetition rate.

Acoustic Stimulation↗
PubMed1995

Generation of human auditory steady-state responses (SSRs). II: Addition of responses to individual stimuli.

In order to investigate the generation of the 40 Hz steady-state response (SSR), auditory potentials evoked by clicks were recorded in 16 healthy subjects in two stimulating conditions. Firstly, repetition rates of 7.9 and 40 Hz were used to obtain individual middle latency responses (MLRs) and 40 Hz-SSRs, respectively. In the second condition, eight click trains were presented at a 40 Hz repetition rate and an inter-train interval of 126 ms. We extracted from the whole train response: (1) the response-segment taking place after the last click of the train (last click response, LCR), (2) a modified LCR (mLCR) obtained by clearing the LCR from the amplitude enhancement due to the overlapping of the responses to the clicks preceding the last within the stimulus train. In comparison to MLRs, the most relevant feature of the evoked activity following the last click of the train (LCRs, mLCRs) was the appearance in the 50-110 ms latency range of one (in 11 subjects) or two (in 2 subjects) additional positive-negative deflections having the same periodicity as that of MLR waves. The grand average (GA) of the 40 Hz-SSRs was compared with three predictions synthesized by superimposing: (1) the GA of MLRs, (2) the GA of LCRs, (3) the GA of mLCRs. Both the MLR and mLCR predictions reproduced the recorded signal in amplitude while the LCR prediction amplitude resulted almost twice that of the 40 Hz-SSR. With regard to the phase, the MLR, LCR and mLCR closely predicted the recorded signal. Our findings confirm the effectiveness of the linear addition mechanism in the generation of the 40 Hz-SSR. However the responses to individual stimuli within the 40 Hz-SSR differ from MLRs because of additional periodic activity. These results suggest that phenomena related to the resonant frequency of the activated system may play a role in the mechanisms which interact to generate the 40 Hz-SSR.

Acoustic Stimulation↗
PubMed1995

Extraocular muscle proprioception and eye position.

In the lamb, acute unilateral section of the ophthalmic branch induced in the ipsilateral eye occasional oscillations of the resting position and misalignment of the horizontal vestibulo-ocular reflex (HVOR) with respect to the stimulus. Additional electrolytic lesion of the cells innervating the proprioceptors of the medial rectus muscle, or of the lateral rectus muscle in the contralateral semilunar ganglion, provoked a 4 degrees-7 degrees consensual eye deviation towards and away from the lesioned side, respectively. The optokinetic beating field was similarly deviated. Under these experimental conditions, HVOR showed enhanced gain and marked misalignment in both eyes. Therefore, the selective suppression of muscular proprioceptive input deviated both eyes towards the direction opposite to the muscle whose gangliar proprioceptive representation has been destroyed.

Animals↗
PubMed1993

Gravity load related asymmetries in the sagittal vestibulo-collic reflex.

EMG recordings of the neck muscles (biventer cervicis, complexus, splenius, longus capitis) of decerebrate cats were obtained during pitch and roll stimulations (sinusoidal stimulation: 30 degrees p-p amplitude, 0.2 Hz frequency). Most of the EMG responses to pitch showed activation peaks leading the position stimuli by 56 degrees and inhibition peaks leading by 11 degrees. Conversely, in response to roll the activation peak led by 16 degrees and the inhibition peak by 10 degrees. The activation peaks of the pitch responses were, thus, more asymmetric and more leading than those of the roll responses. Consequently, the harmonic distortion coefficient was significantly higher in pitch than in roll. Moreover, when the vertical semicircular canals were activated in absence of otolithic modulation, the pitch and roll responses maintained the same difference in timing observed in the presence of otolithic coactivation. It appeared that the simultaneous stimulation of both anterior semicircular canals (pitch) induces a greater lead than that of combined anterior and posterior canals (roll). Thus the timing of neck muscle responses to vestibular stimulation depends on the pair of activated vertical semicircular canals.

Animals↗
PubMed1993

Botulinum A toxin effects on rat jaw muscle spindles.

Botulinum A toxin (Botox) is used for the treatment of many muscular dystonias. However, the relief of the sustained and abnormal postures induced by Botox administration is not fully explained. In this work the possibility was considered that Botox can produce a block not only at the alpha motor endings, but also at the gamma motor endings, consequently reducing the spindle inflow to the alpha motoneurons, which have a great role in maintaining the tonic myotatic reflex. Jaw muscle spindle discharge was recorded before and after Botox injection in the deep masseter muscle. The drug consistently reduced the spindle afferent discharge. Such an effect is suggested to be direct on gamma endings as: i) muscle tension was not modified by Botox during the recording time; ii) saline administration never changed the spindle discharge. The Botox effect on muscle spindles suggests that the relief from dystonias could be due not only to a partial motor paralysis, but also to a decrease of the reflex muscular tone.

Animals↗
PubMed1993

Surgical management of intraluminal carotid thrombi.

The most suitable treatment for intraluminal carotid thrombi remains still a much debated question. Some authors have reported a lower morbidity in patients treated with anticoagulant or antiplatelet therapy; on the other side, urgent or delayed surgery is burdened with a high risk of perioperative stroke. Over 11 years (october 1981-november 1992) 602 surgical revascularizations on epi-aortic vessels have been performed at Vascular Surgery Unit of Udine Regional Hospital. Only 2 cases of intraluminal carotid thrombi were observed: both fulfilled the angiographic requirements for endovasal filling defect, surrounded by contrast medium, adherent to posterior wall and extending to distal internal carotid artery. First patient suffered a TIA 20 days before surgery, the second one a previous major stroke contralateral to the thrombus. The former was given preoperatively a medical anticoagulant treatment (warfarin). At operation we discovered a nearly complete resolution of the thrombus: only its adherent base was still present. Therefore we performed a routine endarterectomy and a PTFE patch angioplasty. The latter case reported had no preliminary medical treatment; a thrombus extending from carotid bulbus to external and internal carotid was detected and then removed without any distal embolization. Arteriotomy was closed by Dacron Velour patch angioplasty. No perioperative stroke occurred in both cases: our second patient showed a partial resolution of his motility deficit. According to our limited experience, delayed surgical treatment of intraluminal carotid thrombi seems not to be affected with higher risk of perioperative stroke than prophylactic carotid endarterectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Asymmetries in ocular and cervical responses to sagittal vestibular stimulations.

In rabbits and cats vestibulo-ocular reflex (VOR) and vestibulo-ocular reflex (VCR) were tested in frontal and sagittal planes. The VOR evoked by pitching the animals in side down position showed asymmetric responses with peak eye velocity higher in upward direction than in downward one. This asymmetry was abolished when pitching the animal in upright position. This indicate that the otolithic coactivation, occurring in upright position, symmetrizes canal-induced vertical responses. Vestibulo-ocular reflex evoked by rolling the animals was also symmetric, no matter the animal position was. The electromyographic response of neck muscles to sagittal VCR showed an asymmetric behaviour as far as the timing of extensor and flexor activation was concerning. In fact, the increase of extensor muscle activity was steeper than the decrease and the activation peak was more leading than the inhibition peak. The flexor muscles showed an opposite behaviour. This flexion-extension asymmetry was present either with or without otolithic coactivation. On the contrary, the EMG responses to frontal VCR were much more symmetric. It can be suggested that the upward preponderance is present in the sagittal vestibular circuitry to enhance the upward VCR against a gravity load which opposes head stability during downward head displacements. On the contrary, at level of the eye, in which the gravity does not oppose the responses, the canal-induced vertical asymmetry is cancelled by the otolithic coactivation.

Animals↗
PubMed1991

Plasmid functions involved in the stable propagation of the pKD1 circular plasmid in Kluyveromyces lactis.

Plasmid factors involved in the stable propagation of pKD1-derived vectors in Kluyveromyces lactis transformants have been identified. Three genes (A, B and C) have been found to be present in pKD1: the interruption of the B and C genes led to high plasmid instability. Stability could be restored in trans when host cells contained pKD1 as the resident plasmid (pKD1+ strains). The A gene, which codes for a site-specific recombinase, did not affect plasmid partitioning. Vectors bearing only the pKD1 replication origin (or a chromosomal ARS), and no other pKD1 sequence, were very unstable both in the presence and absence of the resident plasmid in host cells. These vectors could be stabilized in pKD1+ strains, but not in pKD1 degree strains, by the insertion of a 200 bp-long pKD1 sequence. This sequence, called the cis-acting stability locus (CSL), together with the products of the B and C genes, ensured plasmid partitioning at cell division. Possible hairpin structures and direct repeats were regularly spaced within the CSL. This region, and the corresponding cis-acting stabilizing elements of other yeast plasmids, did not have sequence homology but shared some structural regularities.

Base Sequence↗
PubMed1983

S-100 protein in "follicular dendritic" cells or rat lymphoid organs. An immunochemical and immunocytochemical study.

The presence as well as the cellular and subcellular distribution of S-100 protein were investigated in lymphoid organs of the adult rat by quantitative microcomplement fixation assay and by the immunocytochemical PAP method at the ultrastructural level. The protein appeared to be confined to the "follicular dendritic" cells both in the lymph node and the spleen, which are known to be exclusively associated with B lymphocytes in secondary follicles. The present data show an additional location for S-100 outside the nervous system. The protein may also be a useful tool to provide information on the origin and function of "follicular dendritic" cells, which are still poorly understood.

Animals↗
PubMedDate not supplied

[Leiomyosarcoma of the great veins: a case involving the left iliac vein extending to the inferior vena cava].

Large veins LMS is a rare slow growing malignant tumor originating from smooth muscle cells of the media. The authors report a case of LMS of the left common iliac vein propagating to the Inferior Vena Cava that presented with a left femoral-iliac deep thrombophlebitis. CT scan showed an uneven solid mass approximately 5 cm large within the left side of the pelvis. The mass displaced the left iliac artery and compressed the left iliac vein without a significant cleavage surface between the mass itself and the vascular structures. Location was next to the spine, medially and anteriorily to the psoas muscle. A thrombosis could be noticed within the distal segment of the inferior Vena Cava and within the proximal segment of the left iliac vein. US scan with fine needle biopsy of the mass didn't yield significant information. At surgical exploration a neoplastic mass involving and blocking the left iliac vein was found. Veinotomy performed on the iliac vein and on the distal segment of the Inferior Vena Cava but without infiltration of the vein walls. Surgical treatment consisted of asportation of the neoplastic mass, resection of the left iliac vein and thrombectomy of the Inferior Vena Cava. Histologic examination of the operated specimen revealed a mixoid LMS with vascular origin without involvement of the surrounding lymph nodes. Absence of clinical and radiological signs of relapse eight months after surgery makes further surgical and complementary (drug- and radiotherapy) treatments currently unnecessary.

Aged↗