A 24-hour rhythm in passive-avoidance behaviour in rats

The 24 h variation in the passive avoidance response of rats was measured. Different groups of 18 animals were tested at 4 hourly intervals throughout 24 h. In all cases, retention was measured 48 h after the first trial. All animals were housed under controlled conditions for 14 days before testing. A significant 24-h rhythm in passive avoidance response was found, the maximum and minimum effects being in the middle of the light and dark phases respectively.     

Membrane permeability characteristics of perfused human senile cataractous lenses

Human cataractous lenses were removed by the cryoprobe technique and were maintained for up to 24 hr in a solution of similar ionic composition to human aqueous humour. The bimodal distribution of internal sodium concentrations was similar to that previously reported for unincubated human lenses. Lenses with lower total and free sodium contents had relatively higher membrane potentials and they lost 86Rb at a slower rate than lenses with high internal sodium. The 86Rb efflux in these lenses was stimulated four-fold by removing external calcium. The efflux was reduced by increasing external calcium, but was increased during a small (60 mosmol) hyperosmotic shock. A similar hyperosmotic shock also surprisingly increased 86Rb efflux. Lenses with increasing internal sodium (and calcium) levels showed an increasing rate of loss of 86Rb and the stimulation by calcium removal was progressively diminished. The efflux from lenses with disturbed ion levels was also relatively insensitive to changes in external osmolarity and to increasing external potassium. Lenses with raised sodium concentrations also had an increased inulin space. Frog, rat and rabbit lenses were also exposed to the same range of stimuli and only frog lenses responded to the low calcium solution with more than a four-fold increase in efflux rate. Although only a two- to four-fold increase in efflux rate was obtained from rabbit lenses exposed to Ca-free conditions, this was the only type of animal lens so far tested that, like the human lens, responded to both hyperosmotic and isosmotic shocks with an increase in efflux rate. All three species of mammalian lenses responded with an increase in efflux rate when exposed to a hyperosmotic test solution while in the frog, the efflux rate from the lens decreased. The glucose efflux from human cataractous lenses was inhibited by cytochalasin B in a similar manner to the efflux from rat and frog lenses. It was concluded, therefore, that the cryoprobed human lens can be kept for a limited period in a relative simple artificial aqueous humour solution. The potassium permeability characteristics of low sodium cataracts remained relatively intact and showed a unique response (relative to lenses from other animals) when exposed to various stimuli that are known to be potentially cataractogenic.     

High nevus counts confer a favorable prognosis in melanoma patients

A high number of nevi is the most significant phenotypic risk factor for melanoma and is in part genetically determined. The number of nevi decreases from middle age onward but this senescence can be delayed in patients with melanoma. We investigated the effects of nevus number count on sentinel node status and melanoma survival in a large cohort of melanoma cases. Out of 2,184 melanoma cases, 684 (31.3%) had a high nevus count (>50). High nevus counts were associated with favorable prognostic factors such as lower Breslow thickness, less ulceration and lower mitotic rate, despite adjustment for age. Nevus count was not predictive of sentinel node status. The crude 5‐ and 10‐year melanoma‐specific survival rate was higher in melanomas cases with a high nevus count compared to those with a low nevus count (91.2 vs. 86.4% and 87.2 vs. 79%, respectively). The difference in survival remained significant after adjusting for all known melanoma prognostic factors (hazard ratio [HR] = 0.43, confidence interval [CI] = 0.21–0.89). The favorable prognostic value of a high nevus count was also seen within the positive sentinel node subgroup of patients (HR = 0.22, CI = 0.08–0.60). High nevus count is associated with a better melanoma survival, even in the subgroup of patients with positive sentinel lymph node. This suggests a different biological behavior of melanoma tumors in patients with an excess of nevi.     

Environmental risks to Canadian children travelling overseas

Canadian children and youth travelling overseas face numerous environmental risks, including trauma, extreme temperatures, sun exposure, high altitudes, environmental pollution, and a variety of bites, stings and envenomations. Because skilled emergency response is limited or nonexistent in places where serious illness or injury is most likely to occur, avoiding or limiting these risks is imperative. Travel and paediatric health care providers must be able to identify environmental risks and to advise parents appropriately. Anticipating potential dangers and planning preventive strategies in advance can reduce both parental anxiety and the risk to children.     

Aortic dissection, patent ductus arteriosus, iris hypoplasia and brachytelephalangy in a male adolescent.

We describe a 14-year-old male with dissection of the descending aorta, bilateral iris hypoplasia, striae distensae and brachytelephalangy, the latter being most marked in the thumbs. Inguinal herniae and a patent ductus arteriosus were surgically repaired in infancy. The pattern of abnormalities may constitute a previously undescribed syndrome. The proband died suddenly at the age of 17 years.     

Ulnar nerve injuries of the hand producing intrinsic muscle denervation on magnetic resonance imaging

Muscle and nerve injuries in the hand may be difficult to detect and diagnose clinically. Two cases are reported in which magnetic resonance imaging showed ulnar nerve injury and intrinsic hand muscle denervation. The clinical, anatomical and radiological features of injury to the deep motor branch of the ulnar nerve and associated muscle denervation are discussed and illustrated.