Tactile responses in the granule cell layer of cerebellar folium crus IIa of freely behaving rats.

We recorded activity from the granule cell layer (GCL) of cerebellar folium Crus IIa as freely moving rats engaged in a variety of natural behaviors, including grooming, eating, and free tactile exploration. Multiunit responses in the 1000-4500 Hz range were found to be strongly correlated with tactile stimulation of lip and whisker (perioral) regions. These responses occurred regardless of whether the stimulus was externally or self-generated and during both active and passive touch. In contrast, perioral movements that did not tactually stimulate this region of the face (e.g., chewing) produced no detectable increases in GCL activity. In addition, GCL responses were not correlated with movement extremes. When rats used their lips actively for palpation and exploration, the tactile responses in the GCL were not detectably modulated by ongoing jaw movements. However, active palpation and exploratory behaviors did result in the largest and most continuous bursts of GCL activity: responses were on average 10% larger and 50% longer during palpation and exploration than during grooming or passive stimulation. Although activity levels differed between behaviors, the position and spatial extent of the peripheral receptive field was similar over all behaviors that resulted in tactile input. Overall, our data suggest that the 1000-4500 Hz multiunit responses in the Crus IIa GCL of awake rats are correlated with tactile input rather than with movement or any movement parameter and that these responses are likely to be of particular importance during the acquisition of sensory information by perioral structures.

Composite dialysis access grafts.

Hemodialysis access devices constructed of expanded polytetrafluoroethylene (ePTFE) require a maturation period of seven to 14 days before cannulation. Percutaneously placed dual-lumen catheters can be used for temporary access during this interval but are associated with significant short and long term complications. Access devices constructed of Plasma-TFE (pl-TFE) (Atrium, Hollis) conduits have been reported to tolerate cannulation immediately after placement, but long term patency is inferior to that of conventional ePTFE. To combine the immediate access advantages of pl-TFE and the long term patency of ePTFE, composite grafts were constructed, which consisted of 10 to 12 centimeters of pl-TFE and the remainder of ePTFE. The pl-TFE segment was made available for immediate access and the ePTFE segment after an appropriate maturation period. Thirty percent of composite grafts were cannulated on the day of placement and 83.8 percent were cannulated within 72 hours. No complications of early access of the pl-TFE segment occurred. These grafts were compared with a cohort of conventional ePTFE grafts for the occurrence of thrombosis, infection and pseudoaneurysm. No significant differences were noted. Event-free patency of the two groups was equal (327.7 versus 346.3 days, p = 0.282). Patency after an initial thrombotic episode was slightly better in the composite group. We conclude that composite dialysis access grafts can be cannulated immediately after placement and demonstrate long term performance at least equal to that of conventional ePTFE grafts. Use of the composite graft concept should be considered when immediate dialysis is needed and to avoid the use of temporary access catheters.

Evaluation of a peritoneal dialysis solution containing polymer.

Glucose is used in peritoneal dialysate to produce the gradient for ultrafiltration. The peritoneal membrane's low reflection coefficient for glucose imposes a demand for high transmembrane concentrations, perhaps adding unwanted body burden of glucose. A polymer with a lower permeation rate used as an osmotic agent would circumvent this. We evaluated the mass transfer coefficient (mtc), T1/2 disappearance from the peritoneal cavity and ultrafiltration capabilities of a 900 dalton (Mn) starch derived polymer. We compared an 8% (455 mOsm/L) and a 10% (484 mOsm/L) polymer (Pol) solution to available dialysate solutions containing 2.5% (399 mOsm/L) and 4.25% (491 mOsm/L) X glucose (Glc). The dialysate compositions were otherwise similar. Using a randomized complete block design, 5 anephric dogs maintained on chronic peritoneal dialysis were studied. The mtc (ml/min) was greater for the glucose than the polymer solutions (p less than 0.05): 2.5%-13 and 4.25%-14 vs 8%-5 and 10%-6. The T1/2 disappearance (min) was also greater (p less than 0.05): 2.5% Glc-112 and 4.25% Glc-111 vs 8% Pol-281 and 10% Pol-252. Over a 180 min. period the 2.5% glucose solution generated the least volume of ultrafiltrate (ml, p less than 0.05): 2.5% Glc-113 and 4.25% Glc-589 vs 8% Pol-640; 10% Pol-912. We conclude that the lower permeation rate of the polymer yields ultrafiltration at a lower dialysate osmolality. A polymer solution may be a feasible alternative to glucose.

Substitution of a starch polymer for glucose in peritoneal dialysis.

We compared a starch-derived polymer (molecular weight = 900) as the osmotically active agent in peritoneal dialysate (3 and 6% solutions) to results obtained with commercially available glucose dialysate (1.5 and 4.25%). 12 dogs were dialyzed with glucose for 7 days, and 9 received the polymer for 5 days. For dialysate exchanges with an intraperitoneal residence of 240 min the 1.5 and 3% solutions generated similar volumes of ultrafiltrate as did the 4.25 and 6% solutions. However, for exchanges of 960 min the 1.5% dialysate was significantly reabsorbed when compared to the other dialysate concentrations. The serum polymer concentration increased with continued dialysis. The rate of transfer from dialysate to serum in man must still be determined. The lower diffusivity of the polymer will certainly be evidenced. For certain clinical applications where diminished ultrafiltration occurs, the polymer may be of benefit to man.