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Female Sprague-Dawley rats were chronically implanted with nuclear magnetic resonance (NMR) surface coils tuned to both 31P and 1H NMR frequencies. Alternated 31P and 1H NMR spectra were recorded at 2.5 min intervals in waking rats or rats under pentobarbital or chloral hydrate anesthesia. After a reference period, the metabolic changes were observed following intraperitoneal injection of potassium cyanide (KCN, 5 mg/kg). Among previously observed changes typical of cellular anoxia, attention was specifically paid to the relationship between the intracellular pH values and the lactate levels. The results show a strong lactate-pH correlation in waking rats, a partial decoupling under nembutal anesthesia and a complete decoupling under chloral hydrate anesthesia.

The authors report the results of experiments (performed on the dog in vitro and in vivo) which were designed to verify hypotheses made concerning vascular elasticity and characteristics of CSF resorption, as well as to test the validity of a mathematical model that was described in a previous paper. The authors concluded that the equations of the model account for most of the phenomena satisfactorily, but fail to predict a rebound phenomena which occurs after sudden injections in the cisterna magna. The elasticity coefficient S appears to be constant over a range of 200 mm Hg. On the other hand, the filtration coefficient K depends upon pressure, probably due to morphological changes in the size and shape of the CSF valves. These discrepancies are taken into account in a more general model that is presented in the following paper.

Extracellular electrical recordings of single units in the anaesthetized rat demonstrate that about two thirds of the neurons in the lateral habenula respond to peripheral noxious stimuli in a way similar to that of the cells in the centrum-medianum complex which can be activated (with several peaks of various latencies) or inhibited. The firing pattern of these lateral habenula cells is either excitatory (75%) or inhibitory (24%) and is related to the intensity of the stimulus; their receptive field is large and bilateral. Most of these cells also respond to other kinds of noxious but not to non-noxious stimuli. The present study strongly suggests that the lateral habenula is a central target at the upper brainstem level for nociceptive inputs. This original finding is consistent with our previous observation of naloxone reversible analgesia induced by stimulation of the habenula and suggests an involvement of this structure in the processing of noxious inputs.

The authors reported previously an elementary mathematical model of intracranial pressure (ICP) as well as result from an experimental verification of the model. The experimental tests revealed that certain factors had been neglected in the theoretical formation, and the present article offers an expanded version of model which takes into account those factors: changes in the formation of the CSF as a function of ICP; cerebral vasomotricity; cortical and sinusal venous pressures, and variations of the filtration coefficient of the subarachnoidal spaces. A generalized mathematical model of ICP, in the form of four equations, is proposed. The major aspects of both normal and pathological ICP are studied in the light of this model, and are integrated into a generalized theory.

Chronic implantation of surface coils on the skull has been developed to record 31P NMR spectra of the brain in unanesthetized rats. Intraperitoneal sublethal potassium cyanide doses induce strong and reversible changes in high-energy phosphate compounds in the brain, similar in part to those induced by ischemia. These effects are dose-dependent as far as phosphocreatine, inorganic orthophosphates and pH are concerned; ATP does not seem to be altered by KCN doses ranging from 3 to 5 mg/kg but starts decreasing at a dose of 6 mg/kg. The fraction of Mg2+ complexed ATP which could be estimated as about 90% was not affected by KCN intoxication. For high doses (6 mg/kg) a new peak, appearing on the upfield side of the inorganic phosphate peak, may correspond to an acidic compartment, the significance of which is discussed.

Cervical myelopathy represents a good indication for study by Magnetic Resonance Imaging (MRI). The MRI examination may be performed without hospitalisation and without any pain or risk for the patient. It often gives sufficient information to decide whether to proceed with surgical intervention, after imaging on standard plain films and ever before cervical myelography. An efficient study of the cervical spinal cord requires special surface coils adapted to this region. We have developed a surface coil, working as a receiver, inductively coupled, tuned and matched all at once, and easy to use. The concave form of this coil has been studied so as to be comfortable for all patients. It can be directly connected to our Thomson CGR machines (Magniscan 5000). In continuous routine use for 6 months, without any problems, it has been found to be very reliable. We present here some results on different types of myelopathy and discuss methodological aspects concerning the choice of acquisition parameters in the examinations. The simplicity of its realisation and the low cost leads us to believe that it will be possible to construct other surface coils convenient on many other parts of the body.

During a previous study of the nucleus parafascicularis (Pf), cells were recorded in the lateral habenula (HbL) which exhibited response patterns to peripheral noxious stimuli similar to those recorded in the Pf. In order to study the possible role of the habenular complex (Hb) in pain processing, we investigated the effect of electrical stimulation of the Hb on the tail-flick latency. For each series of experiments, the Hb of 15 female rats was implanted unilaterally, with bipolar electrodes, on either the right or left side. A week later, the animals were submitted to measurements of tail-flick latency, every 10 min, for a period of 3 h. The amount of analgesia was estimated by the percentage increase in latency. Five intensities of current (50, 100, 200, 300 and 400 microA) were used for stimulation during 60 s, at 50 Hz and 0.5-ms pulse width. A group of animals were given naloxone i.p. (1 mg/kg) 40 min after Hb stimulation at 200 microA to study the reversibility of the analgesia. A second group had their Hb destroyed by coagulation and the effect on tail-flick latency was checked once a week for 4 weeks. The results of these experiments clearly demonstrate Hb stimulation-induced analgesia, the maximum of which occurs 60-80 min after stimulation and then decreases slowly. The maximal amount of analgesia increases with the intensity of current up to 200 microA, without any behavioral side effects. At 300 microA, the analgesia is not significantly different from the one induced at 200 microA. However at 400 microA, behavioral side effects (fear, escape) appear and the analgesia is weaker. Two-hundred microA appears to be the most efficient current intensity and induces an average of 80% increase in tail-flick latency. The group which was given naloxone exhibited a dramatic and complete reversal of analgesia. The group which had their Hb destroyed did not show any difference from the control group a week after surgery. During the following weeks, both lesioned animals and controls exhibited a habituation-like analgesia, without any significant difference (the index of analgesia was 45.73 +/- 23.65% for the lesioned rats and 51.82 +/- 29.18% for the controls), which was not naloxone reversible. A review of the literature does not provide an explantation for Hb-induced analgesia.(ABSTRACT TRUNCATED AT 400 WORDS)

The cytologic diagnosis of 312 stereotaxic samplings performed on 292 patients suspected of having a brain tumor over an eight-year period was reviewed. At different depths of the stereotaxic track, biopsy specimens were secured for cytologic and histologic observations. Smears for cytology were stained both by the May-Grünwald-Giemsa and the Papanicolaou methods since each of them disclosed information complementary to the other. Cytology and histology were in good agreement in 87.5% of the cases. Analysis of the data revealed a cytologic sensitivity of 88.8% and a specificity of 81.9%. The main difficulty encountered was differentiating between nonspecific glial hyperplasia and low-grade astrocytoma. To a lesser degree, differentiating metastases from glioblastoma sometimes was a problem. Stress is laid on the reliability of this type of cytology, its great help when sectioning of unfit specimens makes histologic evaluation hazardous, and its obvious importance when craniotomy is not desirable but a precise pathologic diagnosis is necessary for therapeutic decision. The stereotaxic procedure is briefly reviewed, and the main cytologic findings for the principal lesions encountered are illustrated and discussed.

These experiments investigated the role of a specific thalamic nucleus in the cellular response to noxious and non-noxious inputs. Single-unit extracellular responses to peripheral noxious stimuli were recorded with glass micropipettes in the nucleus parafascicularis (Pf) of the rat under chloral hydrate anesthesia. Bipolar stimulating/recording electrodes were inserted in the nucleus ventro-postero-lateralis (VPL) of the thalamus, in areas responsive to the peripheral noxious stimulation. Single-unit records in Pf and multi-unit records in VPL demonstrated that both these nuclei are differentially sensitive to noxious and non-noxious inputs: Pf was more sensitive to late (200-600 ms latency) high threshold noxious inputs, while VPL was more responsive to early (10-40 ms) low threshold non-noxious inputs. Late, high threshold inputs to VPL were selectively suppressed by systemic morphine and restored by naloxone. Trains of stimuli applied to VPL suppressed the response of 76% of Pf units, to peripheral noxious stimuli but did not inhibit the response of spinal cord dorsal horn units to the same stimuli. This inhibitory effect of VPL on Pf cells was not reversed by systemically administered naloxone. The neural pathways responsible for the VPL suppression of Pf nociception appear to be neither monosynaptic nor mediated through the spinal cord dorsal horn, nor through any single, naloxone-reversible, central opioid process. Nevertheless, this inhibitory effect of VPL stimulation on Pf nociception provides a physiological basis for the analgesic effects of thalamic stimulation on clinically observed deafferentation pain. It also supports the existence of a pain modulating system at the thalamic level comparable, at least in part, with the spinal Gate Control concept.

To perform in vivo localized proton spectroscopy with water suppression, spin-echo sequences, made of binomial pulses, are commonly used with surface coils. The frequency selective response to such a sequence is also-spatially dependent, that is dependent on the sample shape and on the pulse angle adjustment. It is consequently pointed out in this paper that quantitative analysis for relative peak intensities may be strongly affected by the contribution of the high-flux regions. In vivo proton spectroscopy of rat brain exemplifies this difficulty. It is shown that the use of selective prepulses to suppress high-flux signals may be of poor efficiency depending on chemical shift, while the use of hard nonselective prepulses works for any chemical shift.

Compression of sciatic nerve of rabbits with an inoxidizable clip increases free and combinated cyanides levels both in blood and urine in days following the operation. A treatment with hydroxocobalamin decreases them significantly.

Stereoimpedoencephalography (SIEG) is routinely used by the authors during stereotactic investigations of glial brain tumours prior to stereotactic implantation of isotopes or prior to conventional surgery: the brain tissue impedance is measured along a probe track according to the four electrodes impedance technique. The correlation between the tissue structures and the corresponding impedance values has been studied by comparison with the CATScan data reported on the stereotactic schedules; impedance values are influenced by changes in arterial pCO2 and also by other unknown factors; in order to avoid these uninterpretable changes of the impedance, the recorded values have been normalized with respect to the average impedance along a control track in the normal hemisphere. As a rule, the impedance profile exhibits a "hole" at the site of the pathological processes like tumours as well as surrounding oedema, and the delimitation of the pathological area is very similar to that obtained by the CATScan. There is a good linear correlation between the values of normalized impedance and the x-ray absorption as given by the computer listing of the CATScan. Lastly, statistical values of normalized impedances are determined for the main structures of the brain, showing that the tumour tissue has an impedance equal to half the impedance of the normal tissue.

Authors study the neurological evolution of 50 cases of traumatic coma and recognize 5 misfunction levels corresponding to five steps of rostrocaudal deterioration. The level 1 (cortico-sub-cortical) is defined by the persistence of the mimic and flexion response to painful stimulation. The level 2 (diencephalic) is characterized by stereotypic responses to pain and lack of mimic. At these two levels, the fronto-orbicular and vertical oculo-vestibular reflexes are persistent. These reflexes disappear when the status impair caudodal to the level 3 (meso-diencephalix junction). The photomotor reflex disappear at the level 4 (mesencephalic), where the motor response to pain may be very poor, or may be a bilateral extension. The horizontal oculo-vestibular reflex is always persistent, except for the level 5 corresponding to a pontine lesion. The meso-diencephalic level 3 appears to be a critical impairment point: as long as the level is not overpassed, the half of the patients do improve and 10% only die. More than 75% of those who improve from this level have an excellent recovery. The restructuration probability is diminished by the half when the level of mesencephalic misfunction is reached.

The authors present a four electrode rheographic technique for simiquantitative continuous measurement of CBV, by examining changes in cerebral tissue impedance induced by changes in blood content of the brain parenchyma. Correlation between the data obtained and ICP measurements permits conclusions regarding the behaviour of the cerebral blood bed. pCO2 regulates CBV, and the phenomenon is reversible according to a hystereris shaped time course in acute experiments. The rebound of ICP after sudden injections of CSF into the cisterna magna is of a vasogenic nature. Changes in CSF volume induce contrary changes in CBV. Pharmacological effects can be studied. The validity of the method is discussed.

31P NMR spin-lattice (T1) and spin-spin (T2) relaxation times of phosphocreatine, ATP, inorganic phosphate, and phosphomonoesters have been measured in vivo at 4.7 T in rat brain and rat brain tumors implanted on nude mice. The relaxation data were acquired using a phase-cycled saturation-recovery spin-echo sequence. The problems associated with the phase modulation of the ATP lines by the homonuclear coupling constants were overcome by using selective refocusing pulses for the T2 measurements. In all the metabolites, large differences (1 to 2 orders of magnitude) are observed between the two relaxation times. T1 values in rat brain tumors are 30 to 90% longer than their counterparts in normal rat brain. T2 values follow the same trend with smaller variations except for phosphocreatine values which seem much less sensitive to the metabolic state of the tissues.