Biomedical subjects

J M Ramirez

Publications and source records attributed to J M Ramirez.

At least 37 records · Page 2Linked to original sources

PubMed1998

The hypoxic response of neurones within the in vitro mammalian respiratory network.

1. The transverse brainstem slice preparation containing the pre-Bötzinger complex (PBC) was used in mice to study developmental changes of the response of the in vitro respiratory network to hypoxia. This preparation generates at different postnatal stages (postnatal days (P) 0-22) spontaneous rhythmic activity in hypoglossal (XII) rootlets that occur in synchrony with periodic bursts of neurones in the PBC. 2. In slices from P0-4 mice, hypoxia did not significantly affect the amplitude of rhythmic synaptic drive potentials in four of five inspiratory neurones. Hypoxia reduced, but did not suppress, the amplitude of synaptic drive potentials in only one inspiratory neurone. Spike discharge and phasic 'inspiratory' hyperpolarizations of six expiratory neurones were suppressed during hypoxia revealing a phasic 'inspiratory' depolarization. 3. The coupling between rhythmic activity in PBC neurones and XII bursts occurred under control conditions in preparations from P0-4 mice in a 1:1 manner (n = 11) and from mice older than P5 in a 3:1 manner (n = 9). During hypoxia, PBC and XII activity were linked in a 1:1 manner in all slices. 4. In six of fourteen inspiratory PBC neurones, the amplitude of synaptic drive potentials of slices from mice older than P8 was increased during the period of augmentation, reduced during the period of depression and suppressed during a hypoxic response which we refer to as central apnoea. Augmentation led to a weak-to-moderate membrane depolarization which on average was 4.8 +/- 3.7 mV. This depolarization was followed by a hyperpolarization of 6.2 +/- 4.1 mV only in four inspiratory neurones. In the majority of neurones (n = 9), however, membrane depolarization remained stable and was not followed by hyperpolarization. In expiratory neurones (n = 12) from this age group hypoxia suppressed phasic hyperpolarizations that occurred in synchrony with XII bursts. As similarly seen in inspiratory neurones, membrane potentials were depolarized by 5.1 +/- 4.1 mV during the period of hypoxic augmentation. 5. The hypoxic response of respiratory neurones within the pre-Bötzinger complex resembles the response of neurones that were previously described under in vivo conditions. Thus we conclude that the 'transverse rhythmic slice' is a good model for studying the hypoxic response of the respiratory network under in vitro conditions.

Animals↗

PubMed1998

The Guttmann Institute of Barcelona.

The Guttmann Institute is a hospital specialised in the comprehensive rehabilitation and medical/surgical treatment of persons suffering from spinal cord injury or from other severe physical disabilities. It opened in Barcelona in 1965 and was the first hospital in Spain dedicated to the treatment of paraplegic and tetraplegic patients, and the one which introduced into Spain the comprehensive approach to spinal cord injury developed by Sir Ludwig Guttmann at the Stoke Mandeville Hospital in the UK. The Guttmann Institute Foundation is a non-profit-making foundation and its hospital, the Guttmann Institute, forms part of the Public Service Hospital Network. The Guttmann Institute has a wide-ranging, multi-disciplinary group of staff made up of specialised professionals; and it has the appropriate resources for the provision of thorough medical attention from a technical, scientific and human point of view.

Hospital Units↗

PubMed1998

Reconfiguration of the respiratory network at the onset of locust flight.

Reconfiguration of the respiratory network at the onset of locust flight. J. Neurophysiol. 80: 3137-3147, 1998. The respiratory interneurons 377, 378, 379 and 576 were identified within the suboesophageal ganglion (SOG) of the locust. Intracellular stimulation of these neurons excited the auxillary muscle 59 (M59), a muscle that is involved in the control of thoracic pumping in the locust. Like M59, these interneurons did not discharge during each respiratory cycle. However, the SOG interneurons were part of the respiratory rhythm generator because brief intracellular stimulation of these interneurons reset the respiratory rhythm and tonic stimulation increased the frequency of respiratory activity. At the onset of flight, the respiratory input into M59 and the SOG interneurons was suppressed, and these neurons discharged in phase with wing depression while abdominal pumping movements remained rhythmically active in phase with the slower respiratory rhythm (Fig. ). The suppression of the respiratory input during flight seems to be mediated by the SOG interneuron 388. This interneuron was tonically activated during flight, and intracellular current injection suppressed the respiratory rhythmic input into M59. We conclude that the respiratory rhythm generator is reconfigured at flight onset. As part of the rhythm-generating network, the interneurons in the SOG are uncoupled from the rest of the respiratory network and discharge in phase with the flight rhythm. Because these SOG interneurons have a strong influence on thoracic pumping, we propose that this neural reconfiguration leads to a behavioral reconfiguration. In the quiescent state, thoracic pumping is coupled to the abdominal pumping movements and has auxillary functions. During flight, thoracic pumping is coupled to the flight rhythm and provides the major ventilatory movements during this energy-demanding locomotor behavior.

Animals↗

PubMed1998

Creatine protects the central respiratory network of mammals under anoxic conditions.

The effect of creatine (Cr) on the response of the respiratory center to anoxia was analyzed at different postnatal stages in a brainstem slice preparation of mice. Spontaneous rhythmic activity was recorded from hypoglossal rootlets (XII) and from identified neurons within the preBötzinger complex using the whole cell patch clamp technique. The hypoxic response was evaluated in slices from animals (n = 46), which received normal nutrition (controls, n = 16), from litters of animals fed with Cr (2 g/kg/day; nutrition group, n = 8), or after incubating slices for 3 h in Cr (200 microM) (incubation group, n = 22). ATP was measured in slices from controls and Cr-incubated slices which underwent 30-min anoxia. In neonatal animals (P0-5), amplitudes of hypoglossal bursts increased initially during anoxia by 14% in controls and by 41% in Cr-supplemented animals when compared with preanoxic values. Hypoglossal burst duration increased by 3% in controls, but by 18% in the Cr-nutrition group. In brainstem slices, the initial increase of amplitudes changed from 14% (controls) to 59% (Cr incubation) and prolongation of bursts from 3% (controls) to 37% (Cr incubation) compared with preanoxic values. In juvenile controls (P6-13), burst amplitude and duration increased by 12 and 14% during early anoxia when referred to preanoxic values. In slices from Cr-pretreated animals, increases of 48% (amplitude) and 21% (burst duration) occurred. The ATP levels remained constant during a 30-min anoxic period in the Cr-pretreated group compared with a decrease of 44% in slices from controls. Our data suggest that Cr can ameliorate hypoxic energy failure. Further studies will examine the neuroprotective potential in humans.

Animals↗

PubMed1997

Respiratory rhythm generation in mammals: synaptic and membrane properties.

Respiratory rhythm generation depends on a complex interaction between synaptic and membrane properties of functionally defined neurons. To gain a better understanding of how inhibitory and excitatory synaptic inputs lead to the generation of the respiratory rhythm we analyzed the depolarization pattern of respiratory neurons that were recorded in the transverse slice preparation of mice (P8-22) and the in vivo adult cat. Using voltage-calmp recordings from respiratory neurons and specific antagonists for inhibitory synaptic transmission we demonstrate under in vitro conditions, that inspiratory (n = 7) and post-inspiratory neurons (n = 13) received concurrent glycinergic and glutamatergic synaptic input during inspiration. A similar conclusion was gained with chloride injections into in vivo respiratory neurons. The inhibitory input was essential not only for generating the characteristic depolarization pattern of respiratory neurons, but also for switching the respiratory rhythm between inspiration and post-inspiration. The generation of the depolarization pattern depends also on intrinsic membrane properties. Negative current injections reveal that excitatory synaptic input was amplified by intrinsic bursting properties in some inspiratory neurons (n = 4) recorded in vitro. Although such properties have not been described under in vivo conditions our findings suggest that with respect to inspiratory, post-inspiratory and late-inspiratory neurons, the principle network organization is similar under both in vitro and in vivo conditions.

Animals↗

PubMed1997

Developmental changes in the hypoxic response of the hypoglossus respiratory motor output in vitro.

The transverse brain stem slice of mice containing the pre-Bötzinger complex (PBC), a region essential for respiratory rhythm generation in vitro, was used to study developmental changes of the response of the in vitro respiratory network to severe hypoxia (anoxia). This preparation generates, at different postnatal stages [postnatal day (P)0-22], spontaneous rhythmic activity in hypoglossal (XII) rootlets that are known to occur in synchrony with periodic bursts of neurons in the PBC. It is assumed that this rhythmic activity reflects respiratory rhythmic activity. At all examined stages anoxia led to a biphasic response: the frequency of rhythmic XII activity initially increased ("primary augmentation") and then decreased ("secondary depression"). In neonates (P0-7), anoxia did not significantly affect the amplitude of integrated XII bursts. Secondary depression never led to a cessation of rhythmic activity. In mice older than P7, augmentation was accompanied by a significant increase in the amplitude of XII bursts. A significant decrease of the amplitude of XII bursts occurred during secondary depression. This depression led always to cessation of rhythmic activity in XII rootlets. The anoxia-induced response of the respiratory rhythmic XII motor output is biphasic and changes during development in a similar way to the in vivo respiratory network. Whether this biphasic response is due to a biphasic response of the respiratory rhythm generator and/or to a biphasic modulation of the XII motor nucleus remains unresolved and needs further cellular analysis. We propose that the transverse slice is a useful model system for examination of the mechanisms underlying the hypoxic response.

Animals↗

PubMed1996

Postnatal changes in the mammalian respiratory network as revealed by the transverse brainstem slice of mice.

1. Spontaneous rhythmic activity in hypoglossal (XII) rootlets is generated at all postnatal stages from postnatal day (P) 0 to P22 in the transverse brainstem slice of mice containing the pre-Bötzinger complex (PBC). The PBC is known to be a region essential for respiratory rhythm generation. It contains neurones generating periodic bursts that occur in synchrony with rhythmic XII activity. This synchrony indicates that the rhythmic PBC activity generated by the transverse slice is the central respiratory rhythm. 2. The strength of coupling between XII bursts and PBC bursts decreased during early postnatal development. In younger mice (P0-4) each burst in XII rootlets corresponded to one burst in the PBC. In older mice (P5-18) one burst in XII rootlets occurred only every third to fourth burst in PBC neurones. 3. Cycle length and burst duration of rhythmic XII activity did not change significantly during the first three postnatal weeks. However, the pattern of XII bursts changed from decrementing (P0-7) to bell shaped (P8-18) while the rate of rise of XII bursts decreased significantly. 4. The rate of rise of rhythmic depolarizations in neurones of the PBC discharging in phase with XII bursts ('inspiratory neurones') decreased with postnatal development. During interburst intervals, membrane potentials of neurones of older mice (P6-18) were characterized by waves of synaptic input that were not observed in neonatal animals (P0-5). 5. Blockade of glycine receptors by strychnine increased the frequency of rhythmic XII activity in neonatal and older mice (P0-22). Although in expiratory PBC neurones glycinergic transmission was blocked at 10 microM strychnine, in inspiratory PBC neurones and XII rootlets even higher concentrations of up to 50 microM strychnine failed to abolish rhythmic activity.

Animals↗

PubMed1996

Intraoperative ultrasonography in the diagnosis of hepatic metastases during surgery for colorectal cancer.

Approximately 20-25% of colorectal cancers have hepatic metastases at the time of operation and occult liver secondaries appear in 10-30% of curatively operated cases. Intraoperative liver ultrasonography has been reported to be the most accurate method for detecting colorectal metastases. A consecutive series of 119 colorectal cancer patients was studied by routine extracorporeal preoperative ultrasound (EUS), inspection and palpation of the liver at laparotomy and intraoperative liver ultrasound (IUS). 19 patients had liver metastases at the time of surgery. In eight, diagnosis was by EUS. Inspection and palpation yielded a further seven, and IUS alone a further four. Additional lesions were detected in 3 patients after preoperative ultrasound and in 6 patients following intraoperative palpation of the liver. In a further 4 cases IUS demonstrated additional metastases. Follow up for a median 38 months (12-59) was by clinical examination and six monthly liver ultrasound. During this time 8 patients, who were thought to have a clear liver, developed hepatic metastases. The mean time from surgery to the detection of occult hepatic metastases was 14.7 (8-26) months and 4 of these appeared in the second year. Intraoperative ultrasonography is a sensitive and useful method in detecting liver metastases, and may improve clinical staging and the selection of patients for further therapy. However some occult hepatic metastases will remain undetected.

Adult↗

PubMed1996

Colonic J-pouch rectal reconstruction--is it really a neorectum?

PURPOSE: The aim of this study was to determine whether a colonic J-pouch has similar properties to that of a normal rectum, including recovery of rectoanal coordination. METHODS: Ten patients with colonic J-pouch-anal anastomosis (anastomotic distance from anal verge, 3.5 (range, 2.0-4.5) cm for low rectal cancer (7 men; mean age, 64.7 (range, 44-76) years) were studied clinically and in the anorectal physiology laboratory at least one year after operation. Results were compared with a series of ten matched patients who underwent high anterior resection for upper rectal carcinoma (anastomotic height, 12.7 (range, 9.5-16) cm). RESULTS: Although results seemed to be slightly better in the group with the rectum preserved, no statistical differences could be found either in functional outcome or anorectal physiology. One-half of the patients with colonic J-pouch (neorectum) had a positive rectoanal inhibitory reflex. CONCLUSION: Addition of a colon pouch neorectum would appear to improve function to the level of those patients with a high anastomosis and "normal" rectum.

Adult↗

PubMed1996

The neuronal mechanisms of respiratory rhythm generation.

New, improved in vivo and in vitro approaches have led to a better understanding of the mechanisms that generate respiratory rhythm, which depends on a complex interaction between network and intrinsic membrane properties. The pre-Bötzinger complex in the ventrolateral medulla is particularly important for respiratory rhythm generation. This complex can be studied in isolation, and it contains all the known types of respiratory neurons that are now amenable to detailed cellular and molecular analyses.

Animals↗

PubMed1995

Colonic J pouch-anal anastomosis after rectal excision for carcinoma: functional outcome.

A consecutive series of 23 patients with colonic J pouch-anal anastomosis for low rectal cancer (17 men; mean age 64.4 (range 44-76) years) was studied prospectively. The mean distance from the pouch-anal anastomosis to the anal verge was 3.5 (range 2.0-4.5) cm. During follow-up one patient died from an unrelated cause and four developed metastases, two local and two hepatic. In 19 surviving patients a mean of 7 months after ileostomy closure mean bowel frequency was 2.1 (range 1-4) per day, five patients had urgency and four had mild faecal seepage up to three times per week, and seven patients had some degree of incomplete evacuation. In 13 patients there were no manometric differences before and after surgery with respect to maximum tolerated volume or maximum resting pressure, but maximum squeeze pressure was significantly lower after surgery (mean 189 versus 132 cmH2O before and after surgery respectively, P < 0.05). Colonic pouch reconstruction should be considered as an alternative to straight coloanal anastomosis in patients undergoing very low anterior resection.

Adult↗

PubMed1994

Mechanisms of respiratory rhythm generation change profoundly during early life in mice and rats.

To study the ontogenesis of central respiratory rhythm generation, a novel brainstem slice preparation was developed that generates respiratory rhythmic activity spontaneously in mice and rats at all post-natal ages. The slice was made by tilting the brainstem to include both the ventrolateral and dorsomedial medulla. This 'tilted-sagittal' slice contained the nucleus ambiguus, the hypoglossal motor nucleus (XII) and the nucleus of the solitary tract which were preserved intact throughout their rostro-caudal extent. Using this rhythmic preparation it has been possible for the first time to directly compare the significance of glycinergic mechanisms for respiratory rhythmogenesis between newborns and mature rodents in vitro. Our findings demonstrate that during the first two weeks of life there are profound changes in both the motor pattern of rhythmic XII neurons and sensitivity of the respiratory rhythm to strychnine blockade of glycine receptors. Thus, developmental changes in strychnine-sensitive receptors are vital for the maturation of the respiratory network and it is suggested that any disturbance in their development may be lethal.

Aging↗

PubMed1994

Practical score to aid decision making in doubtful cases of appendicitis.

During recent years different procedures have been used to assist in diagnosis of questionable cases of appendicitis. Among these methods, there are few scoring systems that have been shown to be effective. The aim of this study was to create a scoring system and to test its accuracy in the preoperative diagnosis of acute appendicitis. Clinical data from 360 patients who had undergone appendicectomy were collected to identify attributes that distinguished patients having a negative laparotomy from those with appendicitis. Seven independent criteria were identified. Using Bayesian methodology a weight was given to each criterion and an overall score calculated. A cut-off point was identified to separate patients for surgery and those for observation. The scoring system was applied prospectively to 166 consecutive patients; 134 had appendicitis and 32 a normal appendix (19.3 per cent error diagnosis). For the 166 patients the method suggested surgery in 113, 107 (94.7 per cent) of whom were found to have appendicitis. The system suggested observation in hospital in 38 cases. For the whole group the scoring system showed a sensitivity of 80 per cent and specificity of 81 per cent. Scoring systems from a local database could become the ideal complementary method in the diagnosis of suspected acute appendicitis.

Acute Disease↗

PubMed1994

Endoluminal ultrasonography in the follow-up of patients with rectal cancer.

One principal aim in follow-up after curative surgery for colorectal cancer is to identify recurrent disease at an early and possibly treatable stage. The major problem for patients with rectal carcinoma is local recurrence, which occurs in 3-30 per cent of cases and carries a 5-year survival rate of less than 5 per cent. Since 1989, in addition to digital and sigmoidoscopic examination, endorectal ultrasonography has routinely been used in the follow-up of patients with rectal cancer. Sixty-six patients (40 men) who had undergone attempted radical surgery for mid- and lower-third rectal cancer were included in the study. The mean age was 68 (range 43-87) years. A total of 190 scans were performed, with a mean of 3 (range 1-9) for each patient. Thirteen (20 per cent) of the 66 patients developed local recurrence; in all cases this was suggested by rectal ultrasonography. Digital examination and rigid sigmoidoscopy failed to detect recurrence in three patients. Four detected recurrences were treated radically; the remaining patients received radiotherapy, palliative transanal resection or laser management because of advanced age or refusal to undergo surgery. Six patients were alive a mean of 21 (range 4-50) months after recurrence. Of these six patients, four were free from disease (three had undergone salvage surgery and one radiotherapy). Postoperative rectal ultrasonography can detect some local recurrences at an early treatable stage. The method is more accurate than digital examination and sigmoidoscopy, and should be used as part of a regular follow-up programme.

Adult↗

PubMed1994

Functionally intact in vitro preparation generating respiratory activity in neonatal and mature mammals.

The present report describes a novel rhythmically active brainstem slice preparation that generates respiratory activity spontaneously in both mice and rats of varying maturational states. The brainstems of neonatal (0-4 days) and mature (3-8 weeks) mice and rats were isolated and a 600- to 750-microns thick slice cut to include the dorsomedial and the ventrolateral regions of the complete rostro-caudal extent of the medulla. This plane of section we have termed "tilted-sagittal". Rhythmically discharging neurones were recorded extracellularly from both the dorsal and ventral regions of the slice. The recording sites of these neurones were found in the hypoglossal motonucleus (XII) and in areas of the ventrolateral medulla that includes the ventral respiratory group (VRG) region. Histological examination revealed the preservation of neuronal structures important for cardiorespiratory regulation and reflex control including the nucleus of the solitary tract as well as the nucleus ambiguus. In addition, pontine structures including the A5 region were also preserved. Rhythmic activity was found only in slices where the ambiguual column was preserved in its entirety. The mean frequency of discharge of XII neurones was 20 and 10 bursts per minute in neonates and mature rodents respectively. In preparations of mature animals we demonstrate that this frequency increased significantly (P < 0.05) by either raising temperature from 29 degrees C to 38 degrees C (54%), elevating extracellular potassium concentration from 4 to 7.5 mM (52%), blocking potassium channels (20%) or decreasing pH from 7.4 to 7.0 (18%). The burst duration to frequency ratio of XII and VRG rhythmic neurones was similar and therefore indicative of a common brainstem oscillator. Consistent with this finding was that rhythmic activity in the VRG persisted despite removal of the dorsomedial region of the slice. In contrast, rhythmic XII neurones became tonic following mechanical disconnection of the VRG.

Aging↗

PubMed1994

Immunohistochemical study of human retinal astroglia.

Immunocytochemical localization of glial fibrillary acidic protein (GFAP) has been used to study astrocyte distribution and morphology in whole mounted human retinas and vertical sections. Two types of astrocytes can be distinguished: elongated astrocytes are located in the nerve fibre layer (NFL); and star-shaped astrocytes are found in the ganglion cell layer (GCL). Astroglial processes join to form bundles. The bundles formed by the elongated astrocytes lie along and separate the nerve fibre bundles. Processes from star-shaped astrocytes reach towards other star-shaped astrocytes and towards the vessels to form a morphologically honeycombed plexus. These astrocytes also send other processes towards the internal nuclear layer (INL), forming an irregular plexus which accompanies the GCL capillaries that extend into the INL. Often, the cell bodies of the star-shaped GCL astrocytes lie over vessels and form cell clusters. Finally, none of the retinas examined for this study evidenced the "perivascular astrocytes" described by Wolter in the human retina.

Adult↗

PubMed1993

A structural role of the carotenoid in the light-harvesting II protein of Rhodobacter capsulatus.

The membrane-linked light-harvesting II protein (LHII) of Rhodobacter capsulatus was partly depleted of carotenoids by selective extraction with light petroleum. Carotenoid removal was accompanied by bleaching of the Qy(S1<--S0) absorption band of bacteriochlorophyll (Bchl) a near 800 nm, by a bathochromic shift and a broadening of the other Bchl Qy band at 850 nm, and by the formation of a weak Qy band of dissociated Bchl near 770 nm. The changes in the 800 and 850 nm bands seemed to reflect alterations in only those Bchl molecules that had lost their associated carotenoids, firstly, because the extent of the changes was closely correlated to the degree of carotenoid extraction, and, secondly, because the residual fraction of carotenoid-containing LHII, which could be almost quantitatively recovered from the membrane after detergent solubilization and ion-exchange chromatography, showed an unmodified LHII absorption spectrum. The Bchl responsible for the shifted 850 nm band remained bound to protein, since its visible (Qx) transition seemed to retain the induced optical activity of the native bound pigment. Besides, the shifted Bchl could act as an efficient acceptor of singlet excitation energy from the pigments of the intact LHII fraction. The close similarity between the spectroscopic Bchl changes that accompany carotenoid extraction and the differential spectral features of carotenoidless LHII of Rhodobacter mutants, previously reported, strongly suggests that the direct cause of the spectral modifications is the absence of carotenoid and not any independent effect of the experimental manipulation of the membrane. Several interpretations of the structural changes that underlie the observed spectral changes are possible. The simplest one is to assume that carotenoid removal elicits an alteration in the angle between the Qy transition moments of two strongly interacting Bchl molecules.

Carotenoids↗

PubMed1993

Octopamine effects mimick state-dependent changes in a proprioceptive feedback system.

The modulatory actions of the biogenic amine octopamine on the femur tibia (FT) control loop in the stick insect Carausius morosus were examined. The response properties of the FT control loop were determined under open loop conditions. Mechanical stimulation of the femoral chordotonal organ (fCO) was the input and tibial movement and motoneuronal activity were measured as the output of the system. Following octopamine injection into the hemolymph of intact, inactive animals, two consecutive phases occurred at the behavioral level. Octopamine caused initially an activation of the animal. During this first phase (3.5-12 min duration) the response properties of the FT control loop were similar to those found in animals that were activated by tactile stimuli under normal conditions. Afterward, animals became inactive. During this second phase (15-20 min duration), the gain of the control loop was zero and no resistance reflex in the FT joint was generated in response to fCO stimulation. However, active movements of the tibia could still be elicited. As we could show in restrained animals, where DL-octopamine was applied topically onto the undesheated mesothoracic ganglion, the complete suppression of the resistance reflex on the motoneuronal level was dose dependent starting at concentrations of 5 x 10(-3) M octopamine. We could show that octopamine specifically suppressed the pathways involved in the resistance reflex, while feedback loop responses to fCO stimuli typical for active animals could still be elicited. Our results indicate that an increase in the octopamine concentration mimicks activation of the animal: Properties being characteristic for the control of the FT joint in the inactive animal are inhibited by octopamine, while properties of the FT control loop typical for the active animal appear to be facilitated following octopamine injection. The results clearly demonstrate that different pathways in the neuronal network underlying the FT control loop are involved in the responses of the control loop to fCO stimuli in the inactive and active behavioral states of the stick insect.

Animals↗