Computer-based neuroanatomy laboratory for medical students.

BACKGROUND: To present the laboratory portion of our first-semester Human Neuroanatomy course at Temple University Medical School more effectively and efficiently and to replace the glass slide/microscope-based laboratory component of the course, we developed a computer-based substitute. METHODS: For this computer-based neuroanatomy laboratory program, we photographed the (a) gross brain sliced and dissected specimens and (b) all the glass slides, from the sacral cord through the head of the caudate nucleus. We digitized the photographed images and, using Multimedia ToolBook (Asymetrix), created a computerized atlas, laboratory guide, and a clinical problem-solving section. To assess the effectiveness of the computerized laboratory, we compared student performances between those classes that previously had the traditional laboratory with two succeeding classes that used the computer-based laboratory. RESULTS: Test score results of the laboratory portion of the course suggested that performance on laboratory material was virtually unchanged by the substitution of the computer program. By a survey taken at the end of the course, the students were very satisfied with the computerized program as a teaching method. CONCLUSIONS: The students and faculty enthusiastically agreed that the computer program was an effective substitute method for the traditional glass-slide laboratory and that it was a beneficial self-educational tool that fostered independent learning. The program encouraged student interaction and group learning and fostered independence. It was a more efficient method for faculty and students without sacrificing performance.

Transdermal absorption of radioprotectors in the rat using permeation-enhancing vehicles.

Topical radioprotection of rat skin with WR-2721 has not been effective presumably because the drug does not cross the stratum corneum to reach the epidermis and dermis. Earlier, we showed in the mouse that WR-2721 and cysteine dissolved in permeation-enhancing vehicles passed through the skin more readily than when in water. However, the most effective vehicles in the mouse were not necessarily as effective in the rat. Here we report that the most effective transport vehicles in the rat were (1) water with WR-2721, (2) water and dimethylformamide (DMF) with cysteine, and (3) water and DMF with prostaglandin E2 (PGE2). Pretreatment of the skin with dimethylsulfoxide (DMSO) further improved the transfer of the radioprotectors across the skin in most cases. After pretreatment with DMSO, the most effective vehicles were (1) water for WR-2721, (2) water and methyl-2-pyrrolidone (M-2-P) for cysteine, and (3) DMF for PGE2.

Transdermal absorption of radioprotectors using permeation-enhancing vehicles.

Radioprotectors are not currently used clinically due to concerns regarding toxicity and uncertainties regarding tumor protection. Topical radioprotection of skin might find clinical applications with protectors such as WR-2721, but laboratory studies in which protectors have been applied in water have not been promising. We have studied the absorption of 14C-WR-2721 and [14C]cysteine dissolved in skin permeation-enhancing vehicles through the skin of hairless mice and compared the absorption to that in water. Skin concentration of WR-2721 was increased most by dimethylformamide (DMF), but only propylene glycol increased absorption as far as the dermis, as measured by plasma concentration. Skin concentration of cysteine was improved by DMF, 2-pyrrolidone (2-P), and methyl-2-pyrrolidone (M-2-P); only dimethylsulfoxide (DMSO) resulted in increased plasma levels of the protector. Pretreating skin with DMSO before application of WR-2721, irrespective of the vehicle, improved its concentration within the skin. Plasma levels were improved (10 and 12 times) only with 2-P and DMF. Therefore, by choosing the appropriate vehicle, it is possible to breach the barrier of the stratum corneum and enhance the presence of the protector in all layers of the skin.

WR-2721 entry into the brain across a modified blood-brain barrier.

Radioprotection of the CNS by WR-2721 has not been possible because of its inability to cross the blood-brain barrier (BBB) and so gain access to the neural tissue. Modification of the BBB using hypertonic arabinose (1.8 m), injected via the internal carotid artery (ica), permitted entry of ip-injected [14C]WR-2721 into the ipsilateral cerebral hemisphere. The BBB-modified hemisphere had a 5.34-fold increased uptake compared to nonmodified controls. Delivery as a bolus via the ica further enhanced uptake after BBB opening; WR-2721 was 3.73 times greater than by ip injection. A 20-fold increase of WR-2721 brain uptake has been calculated for ica administration with the BBB opened as compared to the ip route without BBB modification. Toxicity of ip-administered WR-2721 with the BBB open was only 1.4 times greater than non-modified controls and 1.96 times more toxic when delivered via the ica. These data demonstrate significant uptake of WR-2721 into the CNS, a previously unprotected organ, and provide a model for future radioprotective studies.

Transplacental uptake of WR 2721 by the rat embryo.

On day 14 post-conception, near the end of the period of major organogenesis, pregnant rats were injected intravenously or intraperitoneally with WR 2721 spiked with 14C-WR 2721. The radioprotectant was shown to cross the placenta rapidly when administered by either route, and the concentration of WR 2721 in the embryos, placentae, and maternal blood plasma was determined during the period 5 to 90 minutes following administration. The concentration of WR 2721 increased continuously in the embryos during this period and did so against a decreasing concentration in the maternal blood. Injection of WR 2721 at 100 mg/kg of maternal body weight resulted in the presence of 8-9-mg/kg embryo weight; this embryo level is about 1/2 the injected dose of WR 2721 currently being used in human radiotherapy trials, that is, 20 mg/kg (740 mg/m2) body weight. Previous toxicity studies of 9, 11, and 14 day rat embryos have shown that this 100 mg/kg dose is much below the level which produces embryotoxic effects.

Effect of WR-2721 on fetal development in the rat.

The radioprotector WR-2721 has been shown to radioprotect all tissues studied except the central nervous system. However, it has not yet been used to radioprotect the fetus. In this study we determined that [14C]WR-2721 injected into pregnant rats quickly passed the placenta and was concentrated by the fetus. In addition, we evaluated the toxicity of WR-2721 (2.5-600 mg/kg) to pregnant rats and their fetuses during the period of major organogenesis at Days 9, 11, and 14 postconception. Pregnant animals were only slightly more (10%) sensitive (LD50, 580 mg/kg) to WR-2721 than nonpregnant cohort animals (LD50, 640 mg/kg). At concentrations of 50 mg/kg or less there was a small but statistically significant increase in fetal deaths, while at doses greater than 300 mg/kg a larger degree of fetal mortality occurred. Maximal fetal weight loss, to about 84% of control, was found at 500 mg/kg. No changes in head dimensions or gross malformations of the surviving fetuses were detected at any time or concentration. Of all the parameters measured in this study none demonstrated a predilection for any specific period of major organogenesis. The results of this study indicate that while WR-2721 demonstrates a dose-related embryotoxicity it is not teratogenic.

Comparison of cAMP with other radioprotectors against chronic damage to the rat parotid gland.

Radiation damage to the parotid gland is protectable by cAMP during the first week after irradiation (acute phase), though appreciable recovery occurred later with or without such protection. Further damage developed later (chronic phase, 60-90 days), and cAMP was still protective against this damage with a dose modification factor of 1.86 for gland weight. A summary of the protective factors, acute and chronic, for WR-2721, isoproterenol, and cAMP is included. Chronic damage is about 1.5 times as great as acute, and protection against acute and chronic damage is about equal for all three compounds.

Radioprotection of the rat parotid gland by cAMP.

Most earlier studies showing a radioprotective effect by cAMP show only slight degrees of protection. The present study demonstrates a substantial protective effect (DMF, 1.63) of exogenously administered cAMP on the rat parotid gland and supports the mechanism suggested previously for protection afforded the parotid glands by the beta-adrenergic agonist isoproterenol, which is known to elevate endogenous intracellular cAMP.

Radioprotection of the rat parotid gland by WR-2721 and isoproterenol and its modification by propranolol.

The aminothiol WR-2721 and beta-adrenergic agonist isoproterenol both conferred considerable radioprotection to the rat parotid gland. Isoproterenol acts on the beta-receptor, and its specific antagonist, propranolol, eliminated isoproterenol's protective effect, implicating the beta-receptor and possibly cAMP in the mechanism of the protection. Since other sulfhydryl-containing protectants have been shown to elevate cAMP it was reasoned that WR-2721 might do so as well. However, the radioprotection conferred by WR-2721 was not reduced by propranolol, showing that the beta-receptor played no part in WR-2721's action. The possible role of cAMP in radioprotection by isoproterenol is discussed.

Cytoplasmic crystalloids in irradiated rat parotid glands.

Cytoplasmic crystalloids were found in parotid acinar cells of rats given a large (6400 R) single exposure of X-rays to the head and neck. The crystalloids were first observed 1 day after irradiation and became numerous at 3-4 days. They were associated with autophagic vacuoles, which were seen in acinar cells as early as 3-6 h. Crystalloids sometimes appeared to be forming within autophagic vacuoles, which also contained membranous residues and apparently degenerating secretory material. They were bounded by a single smooth membrane and had a substructure consisting of dense, parallel longitudinal striations. They crystalloids were also seen in macrophages associated with the basal surface of acinar cells. At 3-4 days macrophages were numerous and many contained crystalloids, degenerated secretory droplets, and other cellular debris, which they apparently had phagocytosed. By 6-8 days crystalloids and macrophages were seen infrequently. Regarding mode of formation, removal by macrophages, and ultrastructure, the crystalloids resembled those described by others after ethionine intoxication. Ethionine-induced crystalloids have cytochemical characteristics consistent with a lysosomal identity. The crystalloids in irradiated parotid glands probably reflect a variant type of lysosome, which is a nonspecific manifestation of severe cellular injury and can be elicited by a variety of injurious agents.

Isoproterenol in comparison to WR-2721 as a chemoradioprotector of the rat parotid gland.

A comparison was made of the radioprotective abilities of the chemoradioprotector WR-2721, an amino-thiol, and the beta-sympathomimetic secretogogue isoproterenol on the rat parotid gland. Using the dose-response curve of WR-2721 for gland weights as a basis for comparison, isoproterenol was found to offer significant and equal protection during both the acute (DMF, 2.5) and the chronic (DMF, 2.3) periods.