Heterogeneity of intrinsic biophysical properties among cochlear nucleus neurons improves the population coding of temporal information.

Reliable representation of the spectrotemporal features of an acoustic stimulus is critical for sound recognition. However, if all neurons respond with identical firing to the same stimulus, redundancy in the activity patterns would reduce the information capacity of the population. We thus investigated spike reliability and temporal fluctuation coding in an ensemble of neurons recorded in vitro from the avian auditory brain stem. Sequential patch-clamp recordings were made from neurons of the cochlear nucleus angularis while injecting identical filtered Gaussian white noise currents, simulating synaptic drive. The spiking activity in neurons receiving these identically fluctuating stimuli was highly correlated, measured pairwise across neurons and as a pseudo-population. Two distinct uncorrelated noise stimuli could be discriminated using the temporal patterning, but not firing rate, of the spike trains in the neural ensemble, with best discrimination using information at time scales of 5-20 ms. Despite high cross-correlation values, the spike patterns observed in individual neurons were idiosyncratic, with notable heterogeneity across neurons. To investigate how temporal information is being encoded, we used optimal linear reconstruction to produce an estimate of the original current stimulus from the spike trains. Ensembles of trains sampled across the neural population could be used to predict >50% of the stimulus variation using optimal linear decoding, compared with ∼20% using the same number of spike trains recorded from single neurons. We conclude that heterogeneity in the intrinsic biophysical properties of cochlear nucleus neurons reduces firing pattern redundancy while enhancing representation of temporal information.

Dynamic processes shape spatiotemporal properties of retinal waves.

In the developing mammalian retina, spontaneous waves of action potentials are present in the ganglion cell layer weeks before vision. These waves are known to be generated by a synaptically connected network of amacrine cells and retinal ganglion cells, and exhibit complex spatiotemporal patterns, characterized by shifting domains of coactivation. Here, we present a novel dynamical model consisting of two coupled populations of cells that quantitatively reproduces the experimentally observed domain sizes, interwave intervals, and wavefront velocity profiles. Model and experiment together show that the highly correlated activity generated by retinal waves can be explained by a combination of random spontaneous activation of cells and the past history of local retinal activity.

The information content of spontaneous retinal waves.

Spontaneous neural activity that is present in the mammalian retina before the onset of vision is required for the refinement of retinotopy in the lateral geniculate nucleus and superior colliculus. This paper explores the information content of this retinal activity, with the goal of determining constraints on the nature of the developmental mechanisms that use it. Through information-theoretic analysis of multielectrode and calcium-imaging experiments, we show that the spontaneous retinal activity present early in development provides information about the relative positions of retinal ganglion cells and can, in principle, be used at retinogeniculate and retinocollicular synapses to refine retinotopy. Remarkably, we find that most retinotopic information provided by retinal waves exists on relatively coarse time scales, suggesting that developmental mechanisms must be sensitive to timing differences from 100 msec up to 2 sec to make optimal use of it. In fact, a simple Hebbian-type learning rule with a correlation window on the order of seconds is able to extract the bulk of the available information. These findings are consistent with bursts of action potentials (rather than single spikes) being the unit of information used during development and suggest new experimental approaches for studying developmental plasticity of the retinogeniculate and retinocollicular synapses. More generally, these results demonstrate how the properties of neuronal systems can be inferred from the statistics of their input.

Local excision of carcinoma of the rectum for cure.

During the past 10 years, we have treated 63 patients with invasive adenocarcinoma of the rectum by full-thickness local excision. Rigid criteria were employed in patient selection. None of the tumors was pedunculated or in situ carcinoma. Of the 63 lesions, 53 were confined to the bowel wall and constitute the basis for this report. Thirty-five lesions penetrated only the submucosa and 18 invaded the muscularis propria. Twenty-four patients underwent full-dose postoperative radiotherapy with minimal complications. Follow-up ranged from 12 to 130 months, with a median of 44 months. Four tumors recurred locally (8%). Of these, two patients apparently have been salvaged by reexcision. One patient died 32 months after abdominoperineal resection of brain metastases (without local tumor). One patient who did not receive close follow-up died of local recurrence. Seven have died of unrelated causes. The 5-year corrected disease-free survival is 90%. Local excision combined with radiotherapy for selected rectal cancers yields a high rate of cure with minimal morbidity and is now our preferred mode of treatment for all patients whose tumors meet our rigid criteria.

Results of 1,000 single-layer continuous polypropylene intestinal anastomoses.

Between 1979 and 1988, we created intestinal anastomoses in 1,000 patients using a single-layer, continuous suturing technique and a polypropylene suture. The technique is easily learned, flexible in its application, and incurs less cost than most other techniques. The anastomoses involved all levels of the colon and the upper (intraperitoneal and extraperitoneal) rectum. All patients were followed for a minimum of 1 year. The clinically suspected anastomotic leak rate was 1%. Other morbidity included would complications (2%), obstruction of the small intestine (2%), anastomotic stricture (1%), and death (1%). No death was due to anastomotic complications. These rates of complications are comparable with, and in many instances lower than, those reported with other techniques of intestinal anastomosis.

Congenital absence of the radius: the occupational therapist and a new orthosis.

Congenital absence of the radius (radial club hand) is a relatively common and disabling limb deficiency characterized by dislocation of the hand and carpus from the single forearm bore, the ulna. An understanding of the clinical-pathologic anatomy and consequent disruption of hand mechanics enables the orthopedic surgeon and the occupational therapist to formulate a team approach to this birth defect that can result in maximum functional capability for the child. The role of the occupational therapist and a specific therapy program for early stimulation and achievement of hand function are described. Orthotic support of the arm is indispensable to successful management. The design and fabrication of a dynamic upper-extremity orthosis for radial club hand is presented.

Fluid and electrolyte disorders associated with diabetic ketoacidosis and hyperglycemic hyperosmolar nonketotic coma.

DKA and HHNK are emergency conditions requiring quick medical care and nursing intervention. DKA can develop at any age and is most likely to occur in the insulin-dependent patient. The hallmark signs of DKA are a relative or absolute lack of insulin along with acidosis, ketosis, and hyperglycemia. Insulin and fluid and electrolyte therapy are initiated to control the hyperglycemia and prevent shock and further complications. The patient in HHNK presents with a very high serum glucose level (higher than in DKA), a high serum osmolarity, and usually no ketosis or acidosis. The patient may also experience more severe and sudden neurologic changes than those in DKA. Most patients who experience HHNK are older and may also have some other underlying disease process present. The nursing process should be used to correct the fluid and electrolyte imbalances and to prevent further complications in both DKA and HHNK. The patient needs to understand the reasons for his or her hyperglycemic crisis and how to prevent it from occurring in the future. Assessment of the patient's knowledge about diabetes is essential so that proper education can be incorporated into his or her plan of care.

Retinal waves are governed by collective network properties.

Propagating neural activity in the developing mammalian retina is required for the normal patterning of retinothalamic connections. This activity exhibits a complex spatiotemporal pattern of initiation, propagation, and termination. Here, we discuss the behavior of a model of the developing retina using a combination of simulation and analytic calculation. Our model produces spatially and temporally restricted waves without requiring inhibition, consistent with the early depolarizing action of neurotransmitters in the retina. We find that highly correlated, temporally regular, and spatially restricted activity occurs over a range of network parameters; this ensures that such spatiotemporal patterns can be produced robustly by immature neural networks in which synaptic transmission by individual neurons may be unreliable. Wider variation of these parameters, however, results in several different regimes of wave behavior. We also present evidence that wave properties are locally determined by a single variable, the fraction of recruitable (i.e., nonrefractory) cells within the dendritic field of a retinal neuron. From this perspective, a given local area's ability to support waves with a wide range of propagation velocities-as observed in experiment-reflects the variability in the local state of excitability of that area. This prediction is supported by whole-cell voltage-clamp recordings, which measure significant wave-to-wave variability in the amount of synaptic input a cell receives when it participates in a wave. This approach to describing the developing retina provides unique insight into how the organization of a neural circuit can lead to the generation of complex correlated activity patterns.

Development of invasive adenocarcinoma in a long-standing Kock continent ileostomy: report of a case.

The first case of adenocarcinoma developing in a continent ileostomy is reported. A healthy, 39-year-old man with a continent ileostomy for 17 years developed subacute obstructive symptoms and was found on endoscopy to have a large adenocarcinoma involving the intussusception valve. At operation, he was found to have a large tumor originating in the valve, extending through the reservoir, and involving the afferent ileal limb. A number of metastatic lymph nodes were identified in the mesentery of the small bowel. He underwent excision of the pouch and formation of an end ileostomy. He is currently undergoing adjuvant chemotherapy. Biochemical and morphologic changes in the ileal pouch, both in the pelvis and the continent ileostomy, are discussed. The implications of this apparent de novo cancer arising in an ileal pouch are discussed.

Urea kinetics with dialyzer reuse--a prospective study.

UNLABELLED: We performed a prospective study to examine the impact of dialyzer reuse on KT/V under rigidly standardized conditions on 3 membrane types. Heparin dosage was standardized with ACT during an eight week run-in period and remained unchanged through the study. Post dialysis BUN and weight were obtained at five minutes after exactly 80 +/- 0.5 l of blood were processed through the dialyzer. Dialyzers were reused after automated glutaraldehyde processing and after ensuring >80% open fiber bundles. Each membrane type was utilized 3 times on a set of 3 patients; each individual dialyzer was reused 8 times. KT/V was done on the 1st, 2nd, 4th and 8th uses of each dialyzer (36 measurements) starting mid week; BUN measurements were grouped. The KT/V (mean +/- SD) for the 1st, 2nd, 4th, and 8th uses of the cellulose acetate dialyzer were 1.3 +/- 0.2, 1.3 +/- 0.3, 1.3 +/- 0.2, 1.3 +/- 0.2 respectively; the corresponding values of the cuprophane dialyzer were 1.4 +/- 0.3, 1.4 +/- 0.3, 1.3 +/- 0.4, 1.3 +/- 0.3 respectively; and those of the polysulfone dialyzer 1.7 +/- 0.3, 1.6 +/- 0.2, 1.6 +/- 0.2 respectively. By a 3 way ANOVA there were no significant differences between the 1st and subsequent uses of any of the dialyzers tested. CONCLUSIONS: Reuse of dialyzers up to 8 times does not result in a loss of urea clearance. We believe this model is useful for further studies on reuse and quality assurance.

Single-layer polypropylene colorectal anastomosis. Experience with 100 cases.

The technique of single-layer continuous polypropylene colorectal anastomosis is described. The authors' experience with their initial 100 cases is analyzed in detail. No clinical leaks or anastomotic strictures were noted in a two-year follow-up period. The technique is safe, easily learned, rapidly performed, and it does not add significantly to the cost of medical care. The authors' total experience with this anastomosis now exceeds 350 cases.

Ambulatory surgical hemorrhoidectomy--a solution to postoperative urinary retention?

PURPOSE: The most frequent complication of surgical hemorrhoidectomy is urinary retention. This study evaluates the incidence of urinary retention in a series of patients undergoing surgical hemorrhoidectomy in an ambulatory setting. METHODS: The records of all patients undergoing anorectal surgical operative procedures during the calendar year 1990 were reviewed, with particular emphasis on urinary retention and other postoperative complications. RESULTS: Of 201 patients undergoing full surgical hemorrhoidectomy by Colon and Rectal Clinic, 91 percent had operations performed on an ambulatory basis (discharge less than four hours following surgery). Of these 190 patients, only 1 (0.53 percent) required urinary catheterization during the postoperative period. CONCLUSIONS: The ambulatory setting, when combined with careful patient education and perioperative fluid restriction, allows surgical hemorrhoidectomy to be performed with a very low incidence of urinary retention to the benefit of both patient and surgeon.

Single-layer continuous colon and rectal anastomosis using monofilament absorbable suture (Maxon): study of 500 cases.

PURPOSE: The study purpose was to evaluate the results of continuous, single-layer colon and rectal anastomoses using a monofilament absorbable suture material (Maxon). METHODS: Four hundred ninety-two consecutive patients undergoing five hundred colon and rectal anastomoses with the above technique were evaluated for outcome, including anastomotic leakage, stricture, and other complications, by means of chart review. RESULTS: Three patients (0.6 percent) died after surgery and 7 (1.4 percent) developed clinical evidence of anastomotic leakage. Twenty-four percent developed some postoperative complications, most of which were minor. CONCLUSIONS: Continuous, single-layer colorectal anastomosis using monofilament absorbable suture can be performed safely, quickly, and with a favorable cost ratio. Handsewn anastomoses should still be part of the armamentarium of the well-trained surgeon.