FSH and LH (6,7). Since mature spermatozoa have no protein synthetic ability, the adenylate cyclase in this cell type must be synthesized at a specific developmental stage in which this distinctive Mn2+-sensitive adenylate cyclase appears in the testis. The properties of the distinctive adenylate cyclase system have been studied during its development in testis and epididymal sperm. It has been found that the properties of the Mn2+-sensitive adenylate cyclase in testis and sperm homogenates are similar. However, upon centrifugation, the bulk of activity in testis is in the soluble fraction of cytoplasm whereas in sperm, the adenylate cyclase system is firmly associated with membranes. MATERIALS AND METHODSRats (Charles River CD®) of various age groups were used. Immature rats younger than 21 days were kept in groups of ten with their mothers. Purina chow diet and water ad lib were provided to nursing mothers, suckling and weaned (more than 21 days old) rats. They were maintained at a temperature of 22-23°and a 14-hr light and a 10-hr dark period each day.[a-32P]ATP was purchased from International Chemical and Nuclear Corp., creatine phosphate and creatine phosphokinase (skeletal muscle, rabbit) from Calbiochem.The rats were sacrificed by decapitation and the testes were removed, decapsulated, freed of visible blood vessels and placed in ice-cold 5 mM Tris HCl buffer (pH 7.2) containing 3 mM MgCl2 and 1 mM EDTA (5 mM Tris buffer). In experiments where seminiferous tubules and interstitial cells were separated, the testes, after being excised, were placed in icecold Krebs-Ringer phosphate buffer (pH 7.2) containing 10 mg of bovine serum albumin per ml (KRP-BSA), with half of the usual calcium ion content replaced by the equivalent amount of sodium.Seminiferous tubules were isolated from testes by microdissection using procedures previously described (9).Interstitial cells were isolated by collagenase (Worthington; 1 mg/ml per 100 mg of tissue) treatment of testes for 5 min in a metabolic shaker at 60 cycles/min; cells were separated from the undigested tubules by filtration through a double layer of nylon mesh, and washed four times with KRP-BSA buffer. The cell fraction thus obtained is enriched with interstitial cells and is usually composed of 65% interstitial, 15% tubular, and 20% erythrocytes. Spermatozoa were collected in 5 mM Tris buffer from the caput, corpus, and cauda of epididymis. The epididymis was ligated in situ into these portions and separated accordingly after excision.

This action research study compares the efficacies of problem-based learning (PBL), traditional lecture, and a combination of PBL and traditional lecture to promote understanding and retention of the principle content of an elective science course, biochemistry, taught at a school for talented students. The study utilizes a pre- and post-course self-evaluation of student understanding, a measure of depth of understanding, and a questionnaire designed to determine student satisfaction. Lecture tended to widen the content coverage, while understanding and retention was promoted by PBL. Curriculum must be designed to provide a balance between content coverage and depth of understanding. Due to previous training and perceived needs, students sometimes demand more content coverage than is necessary for a complete and adequate education.

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This article describes the design of a biochemistry course that uses problem-based learning. Examples of some of the problems incorporated into the course are described in detail. Principle concepts and engagers encountered in this course are identified. Pedagogical advantages derived from science course is discussed.

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