Use of recombinatory PCR to insert subtle genetic markers into Moloney murine leukemia virus-based retroviral vectors.

As tools to examine template switches and recombination events during the process of reverse transcription, two nearly identical Moloney murine leukemia virus-based (MoMLV) retroviral vectors were constructed using the technique of recombinatory polymerase chain reaction (PCR). The experimental vectors designed for this study were based on the well-characterized LN series vectors. The protein coding regions normally present in the retroviral genome have been replaced by the coding regions for two drug resistance markers, neomycin phosphotransferase (Neo) and hygromycin phosphotransferase (Hyg). With only one functional drug resistance gene in each vector, the individual vectors as well as recombination events between them can be followed by phenotypic selection. Utilization of recombinatory PCR allowed the insertion of very subtle nucleotide changes resulting in a series of restriction site polymorphisms in the two retroviral vectors. The ability to create these subtle mutations in specific locations of these retroviral vectors allowed the utilization of naturally occurring areas of variability in the vectors and avoid regions important for replication.

Potentials evoked by the sinusoidal modulation of the amplitude or frequency of a tone.

Steady state responses to the sinusoidal modulation of the amplitude or frequency of a tone were recorded from the human scalp. For both amplitude modulation (AM) and frequency modulation (FM), the responses were most consistent at modulation frequencies between 30 and 50 Hz. However, reliable responses could also be recorded at lower frequencies, particularly at 2-5 Hz for AM and at 3-7 Hz for FM. With increasing modulation depth at 40 Hz, both the AM and FM response increased in amplitude, but the AM response tended to saturate at large modulation depths. Neither response showed any significant change in phase with changes in modulation depth. Both responses increased in amplitude and decreased in phase delay with increasing intensity of the carrier tone, the FM response showing some saturation of amplitude at high intensities. Both responses could be recorded at modulation depths close to the subjective threshold for detecting the modulation and at intensities close to the subjective threshold for hearing the stimulus. The responses were variable but did not consistently adapt over periods of 10 min. The 40-Hz AM and FM responses appear to originate in the same generator, this generator being activated by separate auditory systems that detect changes in either amplitude or frequency.

Lower limb ischemia in young adults: prognostic implications.

Fifty patients (41 men and nine women) less than 36 years of age were evaluated for lower limb ischemia. Claudication was the presenting symptom in 30 patients (60%) and distal ulceration in 20 (40%). The mean age was 28.3 years. Premature atherosclerosis was present in 24 patients (48%) and thromboangiitis obliterans in 12 (24%). Other causes included a variety of unusual etiologies. Risk factors were analyzed. Twenty-two patients with claudication underwent arterial reconstruction; three had sympathectomy. Arterial reconstruction was possible in only three patients with ulceration; 17 had sympathectomy. No operative deaths or early amputations occurred. Follow-up averaged 13.5 years. Twenty-four patients with claudication were improved, three were unchanged, one developed ulceration, one required late amputation, and one was lost to follow-up. Four patients with ulceration were improved, one was unchanged, 14 required late amputation, and one was lost to follow-up. Ten patients, all with atherosclerosis obliterans, developed coronary artery disease; five died of myocardial infarction. No patient developed cerebrovascular disease. We conclude that reconstructive arterial surgery for claudication can be performed with low risk and a strong likelihood of long-term improvement. Most patients presenting with ulceration, however, will ultimately require amputation. Patients with atherosclerosis obliterans are at risk for coronary artery disease and death of myocardial infarction.