Two-way communication for programming and measurement in a miniature implantable stimulator.

Implantable stimulators are needed for chronic electrical stimulation of nerves and muscles in experimental studies. The device described exploits the versatility of current microcontrollers for stimulation and communication in a miniature implant. Their standard outputs can provide the required selectable constant-current sources. In this device, pre-programmed stimulation paradigms were selected by transcutaneous light pulses. The potential of a programmable integrated circuit (PIC) was thus exploited. Implantable devices must be biocompatible. A novel encapsulation method that require no specialised equipment and that used two classical encapsulants, silicone and Teflon was developed. It was tested for implantation periods of up to four weeks. A novel way to estimate electrode impedance in awake animals is also presented. It was thus possible to follow the evolution of the nerve-electrode interface and, if necessary, to adjust the stimulation parameters. In practice, the electrode voltage at the end of a known constant-current pulse was measured by the PIC. The binary coded value was then indicated to the user as a series of muscle twitches that represented the binary value of the impedance measurement. This neurostimulator has been successfully tested in vitro and in vivo. Thresholds and impedance values were chronically monitored following implantation of a self-sizing spiral cuff electrode. Impedance variations in the first weeks could reflect morphological changes usually observed after the implantation of such electrodes.

Biocompatibility of platinum-metallized silicone rubber: in vivo and in vitro evaluation.

Silicone rubber is commonly used for biomedical applications, including implanted cuff electrodes for both recording and stimulation of peripheral nerves. This study was undertaken to evaluate the consequences of a new platinum metallization method on the biocompatibility of silicone rubber cuff electrodes. This method was introduced in order to allow the manufacture of spiral nerve cuff electrodes with a large number of contacts. The metallization process, implying silicone coating with poly(methyl methacrylate) (PMMA), its activation by an excimer laser and subsequent electroless metal deposition, led to a new surface microtexture. The neutral red cytotoxicity assay procedure was first applied in vitro on BALB/c 3T3 fibroblasts in order to analyze the cellular response elicited by the studied material. An in vivo assay was then performed to investigate the tissue reaction after chronic subcutaneous implantation of the metallized material. Results demonstrate that silicone rubber biocompatibility is not altered by the new platinum metallization method.

Changes in tissue fatty acid composition during the first month of growth of the king penguin chick.

The switch from yolk to food (myctophid fishes) as the nutrient source for the newly hatched chick of the king penguin ( Aptenodytes patagonicus) results in a profound change in the pattern of fatty acid provision. This is characterized by major increases in the proportionate intake of n-3 polyunsaturates (20:5n-3 and 22:6n-3) and long chain (C(20-24)) monounsaturates, accompanied by relatively lower levels of n-6 polyunsaturates (18:2n-6 and 20:4n-6). The effects of this change on the fatty acid composition of tissue lipids during the first month of growth, a period of tissue maturation leading to thermal emancipation, were determined. The composition of adipose tissue triacylglycerol responded rapidly to the switch in nutrient source, the proportion of long chain monounsaturates (mainly 20:1n-9 and 22:1n-11) increasing five-fold between hatch and emancipation while the relative levels of 20:5n-3 and 22:6n-3 also increased significantly, by 3- and 1.2-fold, respectively. At emancipation, the fatty acid profile of adipose tissue triacylglycerol was essentially identical to that of the diet. At hatch, the main polyunsaturates of muscle phospholipid were 20:4n-6, 20:5n-3, and 22:6n-3, respectively, forming (w/w of fatty acids) 13.2%, 5.0%, and 12.0%. By emancipation, 20:4n-6 had decreased to 4.8%, 20:5n-3 increased to 10.9%, and 22:6n-3 at 11.4% showed little change. The main polyunsaturate in brain phospholipid at hatch was 22:6n-3 (19.3%): this remained almost constant until day 15 but then increased significantly to 23.6% by emancipation. Significant but minor changes in the proportions of 20:4n-6 (from 5.2% at hatch to 3.5% at emancipation) and 20:5n-3 (from 3.0% to 3.9%) were also observed in brain phospholipid. The data do not allow us to completely distinguish changes that are solely diet driven from those which are a consequence of tissue differentiation. Nevertheless, it is evident that, whereas the fatty acid composition of adipose tissue responds faithfully to the change in nutrient source, the phospholipids of muscle and, especially, of brain are much more refractory to the effects of diet during this period of tissue maturation.

Refeeding signal in fasting-incubating king penguins: changes in behavior and egg temperature.

This study is directed toward understanding the process of feeding stimulation ("refeeding signal") that has been suggested to operate below a body mass threshold or critical metabolic status in spontaneously fasting birds. Behavior and egg temperature (T(egg)) were continuously monitored by video monitoring and biotelemetry, respectively, in fasting-incubating king penguins kept in a pen to prevent relief by the partner until spontaneous egg abandonment. Penned birds fasted 10 days more and lost 1.2 kg more than birds relieved normally by their partner, abandoning the egg about 1 wk after reaching a critical body mass. Definitive egg abandonment was preceded by transitory abandonments of progressively increasing duration during which time the birds went further and further away from their egg. There were marked interindividual differences but on average transitory abandonments began 36 +/- 5 h before the definitive abandonment and were paralleled by resumption of display songs signaling the readiness of the bird to depart for feeding. T(egg) was maintained at around 35.7 degrees C during normal incubation but significantly decreased the last 2 days before egg abandonment. These changes are interpreted as reflecting a stimulation to refeed at a threshold body mass corresponding to a critical fat store depletion. Thus the fasting-incubating king penguin appears to be an interesting animal model for understanding the long-term metabolic control of feeding behavior in relation to energy status.