Physiological and morphological heterogeneity of dentate gyrus-hilus interneurons in the gerbil hippocampus in vivo

A variety of morphological types of dentate gyrus/hilus interneurons have been described, but little is known about their corresponding physiological characteristics. To address this issue, intracellular responses to current injection and perforant path stimulation were obtained from putative dentate interneurons in anaesthetized adult gerbils. Our sample of interneurons showed heterogeneity in their intrinsic physiological characteristics and spike thresholds to perforant path stimulation, suggesting the existence of distinct physiologically-defined classes. 'Fast-spiking' interneurons had a low threshold to perforant path stimulation, whereas 'slow-spiking' interneurons responded with predominantly inhibitory potentials. In several cases, cells were intracellularly labelled with biocytin for visualization. Interneurons with different physiological traits had distinct morphological features. These results confirm that, as in hippocampus proper, morphologically identifiable interneurons in the dentate hilus show electrophysiological features that are likely to reflect functionally specific roles in informational processing.     

The Changing Face of International Cryptography Policy: Part 16 — Export Control Regulation in the United States

In my September and November contributions, I deviated slightly from my usual theme and examined several of the technical and procedural matters associated with Digital Signature technology. Of course, Digital Signature represents one of the less politically sensitive applications of cryptographic technology, although it is undoubtedly destined to become one of the most pervasive.     

Effect of radiographic positioning on interpretation of cubital joint congruity in dogs

OBJECTIVE: To ascertain effects of x-ray beam centering and limb position on apparent congruity of a normal cubital joint (elbow). ANIMALS: 6 skeletally mature male Treeing Walker Coonhounds without physical, radiographic, or gross evidence of elbow abnormalities. PROCEDURE: Relative movement among humerus, radius, and ulna and measured joint space width on mediolateral and craniocaudal radiographic views was compared, using various x-ray beam centering and limb positions. RESULTS: Highest agreement and greatest certainty on subjective determination of congruity was for the flexed 90 degrees mediolateral radiographic view with the x-ray beam centered on the elbow. Distortion artifact of the proximal ulnar measurements was significant when the x-ray beam was centered on the midpoint of the radius. On the mediolateral view, the humeroradial joint space became significantly wide when the elbow was flexed. On the craniocaudal view, maximal humeroradial joint space width was obtained when the x-ray beam bisected the angle of the joint or was angled +30 degrees toward the humerus. CONCLUSIONS: Artifact distortion of joint width affected objective and subjective assessment of elbow congruity when the limb was placed in extreme flexion or extension or when the x-ray beam was not centered over the area of interest. Optimal visualization of the humeroradial joint space on the craniocaudal view was achieved when the x-ray beam bisected the angle of the elbow or was slightly angled toward the humerus. CLINICAL RELEVANCE: Elbow congruity was best assessed on the flexed 90 degrees lateral radiographic view with the x-ray beam centered on the joint.     

Fatal gastrointestinal haemorrhage due to coexisting primary aorto-enteric and aorto-colic fistulae. Complicating untreated atheromatous abdominal aortic aneurysm

We report a case of aorto-enteric and aorto-colonic fistulae in a 73 year old man with no previous abdominal surgery which resulted in massive gastrointestinal haemorrhage and death and was undiagnosed despite several hospital admissions and endoscopic examinations. This case serves to highlight an extremely rare but fatal condition, which is potentially treatable, if an early diagnosis is made.     

Methionine transport by pig colonic mucosa measured during early post-natal development

New-born pig proximal colon, incubated in vitro, transports methionine with a Km of 0-33 mM and a Vmax of 0-62 mumole cm-2h-1. There is still a net transport of methionine on day 4, but the Km now increases to 10 mM and the Vmax falls to 0-15 mumole cm-2h-1. There is no net transport of methionine across proximal colons taken from 10-day-old pigs. 2. The mean intramucosal concentration of methionine, following incubation in medium containing 1 mM methionine, is 7-18+/-0-8 mM for the new-born, 0-55+/-0-05 mM for the 4-day-old and 0-31+/-0-06 mM for the 10-day-old pig. 3. Both methionine and glucose cause an immediate increase in the short-circuit current of new-born and 1-day-old pig colons. The kinetics for this interaction with methionine gives a Km for methionine of 0-24 mM and a maximum effect of 27 muA cm-2. This effect is not seen in 4- or 10-day-old pigs. 4. Net Na+ transport across the new-born pig proximal colon, measured in the absence of methionine, is about three times that calculated from the measured short-circuit current. Methionine increases the mucosal to serosal flux of Na+ by an amount roughly equal to that predicted from the increase in short-circuit current. The ability of glucose and methionine to affect short-circuit current is lost by day 4. 5. Short-circuit current, measured in the absence of methionine or glucose, increases between day 1 and 2 of post-natal life. This increased electrogenicity is maintained for up to at least 10 days after birth. 6. The pig proximal colon has many of the properties of a small intestine at birth. It actively transports methionine and the presence of methionine stimulates the absorption of Na+. These effects could be physiologically important in the pig, where the normal absorptive function of the intestine is temporarily inhibited at birth by the intestinal transmission of immune globulins.