J. Perrin

Solitary tract nucleus sensitivity to moderate changes in glucose level.

Many neurons in the caudal nucleus tractus solitarii (NTS) recorded in vivo respond to moderate glycemic fluctuations through the local action of glucose molecules. To investigate this sensitivity in vitro, the extracellular activity of 112 neurons was recorded in hindbrain slices: 57 changed in firing rate when the glucose level in the bathing medium was increased by 2 mM. Since the glucose-responding neurons were located in catecholaminergic regions and depressed by the alpha-2 adrenoceptor agonist clonidine, they were likely to be adrenergic or noradrenergic. A comparison of the responses to glucose and 2-deoxy-D-glucose suggested that the bioenergetic metabolism is involved in NTS sensitivity to glucose.

Effects of lactate on glucose-sensing neurons in the solitary tract nucleus.

For nervous tissue, lactate is a valuable energy substrate that can be extracted from glucose by astrocytes and released for neuronal use. Therefore, we hypothesized that the glucose-sensing neurons that signal the glycemic changes involved in the control of body energy homeostasis may be responsive to extracellular lactate as well. To test this hypothesis, neuronal activity was recorded extracellularly in the solitary tract nucleus of anesthetized rats in order to compare the effects of microelectrophoretic applications of glucose and lactate and of moderate hyperglycemia and to assess the possible effects of lactate on the response to glucose. About 90% of the investigated neurons behaved in a similar manner after local ejections of glucose and lactate. Among them, most neurons activated by glucose were also activated by lactate and all neurons depressed by glucose were also depressed by lactate. This result suggests that the response to these two compounds is mediated by a common mechanism related to their utilization as oxidizible substrates. In half of the tested neurons, the response to glucose was eliminated or significantly reduced after repeated lactate ejections. This inhibitory effect is a likely result of a modification in glucose metabolism induced by a high extracellular lactate level. Most glycemia-sensitive neurons responded similarly to moderate hyperglycemia and to local lactate ejection, suggesting that high brain lactate levels might interfere with the brain mechanisms that mediate glucoprivic eating.

Specular Reflector Noise: Effect and Correction for in Vivo Attenuation Estimation

After reviewing the usual models proposed for the echographic response of soft tissues, we discuss the interaction between the ultrasonic wave and large size obstacles. Structures of this size, specular reflectors, can be found in tissues. The influence of such reflectors on in vivo attenuation measurements is detailed. We point out the importance of the specular echo noise originating from two kinds of reflectors: plane-like and vessel-like reflectors. We present a complete study of their influence on two different algorithms for attenuation estimates: the spectral centroid shift and the narrow band methods. Results are presented on stimulated data, a tissue-mimicking phantom and in vivo muscle data. Different procedures for minimizing the specular echo noise are also discussed.

Local versus indirect action of glucose on the lateral hypothalamic neurons sensitive to glycemic level

The neuronal activity in the lateral hypothalamus may be affected by moderate changes in blood glucose. The present study aimed to specify the direct or indirect origin of this sensitivity to glycemia, by recording the unit responses in this area to both local glucose application (by means of microelectrophoresis) and hyperglycemia (induced by an IV glucose injection). The activity of approximately 25% of the recorded LHA neurons was modified by topically ejected glucose. However, a large majority of these neurons sensitive to local glucose failed to respond to hyperglycemia. Conversely, only 1/3 of the glycemia-sensitive cells responded in the same direction to systemic and local glucose administration. Therefore, the response to IV glucose of the other 2/3 glycemia-sensitive cells could not result from the direct action of glucose molecules on these neurons, but probably involved an indirect afferent pathway conveying the glycemic cues from some central or peripheral glucose sensors to the cell under investigation.

Optimal precision in ultrasound attenuation estimation and application to the detection of Duchenne Muscular Dystrophy carriers

This paper deals with the measurement of the attenuation of ultrasound in muscle and its application to the detection of Duchenne Muscular Dystrophy (DMD) carriers. The precision obtained when measuring the attenuation is an important parameter to be considered. A statistical approach is taken on simulated data and compared to in vivo results. The results allow discussion for the minimum tissue volume needed for the estimation. Variations in muscle attenuation between normals were obtained from studies on 27 volunteers. These attenuation values were compared to those obtained from 19 carriers of DMD. Attenuation appears to be a potential clinical indicator of DMD carriers.

Sensitivity of lateral hypothalamic neurons to glycemic level: Possible involvement of an indirect adrenergic mechanism

Most of the lateral hypothalamic neurons responding to moderate changes in blood glucose fail to be affected by direct glucose applications. Therefore their sensitivity to glycemic level must be mediated by an indirect mechanism. In order to test whether adrenergic afferents might be involved, the activity of lateral hypothalamic neurons was recorded during hyperglycemia and local glucose and epinephrine microiontophoresis. A majority of the recorded cells sensitive to local epinephrine responded to this substance with a decrease in activity. While no consistent correspondence was found between the responses of the same cells to local glucose and epinephrine ejections, almost all the neurons sensitive to glycemic alterations responded in the same direction to hyperglycemia and iontophorised epinephrine. These results support the view that the activity of lateral hypothalamic cells can be modulated in relation to changes in glycemic level through adrenergic signals released by some neurons which are sensitive to the blood glucose. The possible localization in the solitary tract area of such neurons projecting to the lateral hypothalamus is discussed.

Diffraction Correction for Focused Transducers in Attenuation Measurements in Vivo

Diffraction effects are a cause of error when estimating the frequency dependent attenuation of ultrasound in biological tissues in the reflection mode. Comparison of attenuation values estimated in vivo by different investigators using different types of transducers makes calibration and correction for diffraction necessary. In this paper, we present experimental results for in vivo calibration and correction for the diffraction effect for focused transducers. We also study numerically the diffraction filter in a time-frequency representation, and show that for a focused probe, there is a region in the time-frequency domain where the frequency slope of the diffraction filter does not vary with time. The main consequence for in vivo estimation is that for a given probe, it is possible to select both the distance between the region of interest and the probe, and the frequency limits, such that the attenuation thus estimated is unbiased by the diffraction effect. This result, obtained by numerical calculations, is confirmed by experimental calibration of a foam phantom and in vivo muscle.

Detection of duchenne muscular dystrophy carriers: quantitative echography and creatine kinasemia

SummaryData obtained from simultaneous determinations of serum creatine-kinase levels and estimation of ultrasound attenuation values in muscles greatly improved the detection of obligate carriers of Duchenne muscular dystrophy than when only one of these methods was employed alone. Eleven carriers out of 19 had a high creatine-kinasemia level and nine carriers out of 19 had a high (abnormal) attenuation value. Because of the limited overlapping between the two parameters studied, we were able to recognize 17 obligate carriers out of the 19. This indicates that the parameters studied concern different features of the disease, and the practical and theoretical considerations are discussed. The techniques are discussed together with molecular genetic investigations.

Displacements induced in piezoelectric structures

From the knowledge of piezoelectric material tensorial components and using the finite-element method, it is possible to calculate the electrical impedance vs. frequency and simulate the mechanical deformation of piezoelectric bars. To check the validity of the simulation, interferrometric measurements of the mechanical deformation amplitude were performed. It is shown that these measurements can reveal the homogeneity of the materials under study and that a small error in the tensorial parameter absolute values leads to an inconsistent picture of simulated mechanical deformation.<<ETX>>