Robert L. Snyder

Genetic influences on electrical seizure threshold.

C57BL/6J (B6) and DBA/2J (D2) mice have been characterized previously as seizure-resistant and seizure-sensitive, respectively, a distinction based primarily upon a differential response to the convulsant effects of various drugs. In the present study, electroconvulsive shock (ECS) was used to assess maximal electroshock threshold (MET) in B6, D2 and hybrid mice. Results revealed that D2 mice have a significantly lower MET compared to B6 mice. There was also a significant gender effect for B6 and F2 mice with females exhibiting a lower MET compared to males. METs for F1 and F2 intercross mice were intermediate between the two parental strains. The difference in variance between F2 and F1 generation mice indicated that about three-quarters of the total variance is due to genetic influence. Taken together, results of this study suggest that the large difference in MET between B6 and D2 mice is a highly heritable trait which may yield to genetic dissection through use of quantitative trait locus mapping.

Acute Cocaine-Induced Seizures: Differential Sensitivity of Six Inbred Mouse Strains

Mature male and female mice from six inbred stains were tested for susceptibility to behavioral seizures induced by a single injection of cocaine. Cocaine was injected ip over a range of doses (50–100 mg/kg) and behavior was monitored for 20 minutes. Seizure end points included latency to forelimb or hindlimb clonus, latency to clonic running seizure and latency to jumping bouncing seizure. A range of strain specific sensitivities was documented with A/J and SJL mice being most sensitive and C57BL/6J most resistant. DBA/2J, BALB/cByJ and NZW/LacJ strains exhibited intermediate sensitivity. EEG recordings were made in SJL, A/J and C57BL/6J mice revealing a close correspondence between electrical activity and behavior. Additionally, levels of cocaine determined in hippocampus and cortex were not different between sensitive and resistant strains. Additional studies of these murine strains may be useful for investigating genetic influences on cocaine-induced seizures.

Somatic Chromosomes of a Black Rhinoceros (Diceros bicornis Gray 1821)

We have recently had an opportunity to examine the somatic chromosomes of a black African rhinoceros [Perissodactyla:Mammalia]; to our knowledge the chromosomes of none of the five species of rhinoceros usually recognized have been studied heretofore. This species is known to occur in the southern and eastern parts of Africa. This adult female specimen came from Kenya and was in the collection of the Philadelphia Zoological Society. Death was attributed to pulmonary abscess.

Chromosomes of five artiodactyl mammals.

Somatic chromosomes of six specimens belonging to the following five species of artiodactyls (Artiodactyla: Mammalia) are described: A female nilgai (Boselaphus tragocamelus), 2n=46; male baresingha (Rucervus duvauceli), two specimens, 2n=56; a female Himalayan tahr (Hemitragus jemlahicus), 2n=48; a female Kirks dik-dik (Rhynchotragus kirki), 2n=46; and a male sambar (Cervus unicolor), 2n=58. In the baresingha and the sambar, one or more acrocentric chromosomes carried satellites on their long arms. 3H-thymidine radioautographs of cultured cells of the Himalayan tahr showed a long acrocentric chromosome to be late-replicating, suggesting that it is an X chromosome.

Coronary Arterial Lesions in Chickens Origin and Rates of Development in Relation to Sex and Social Factors

Single-comb, Hy-line white leghorns were hatched in one lot, brooded in one flock through 7 weeks, then assigned randomly to cages in one large room with 15 hours of light per day. The birds were studied in the following situations: a) separately caged cocks and hens, b) paired cocks and hens, and c) 3 cock-3 hen groups and 6 cock-6 hen groups. Basic space allowance was 2 square ft per bird which was increased to 8 square ft for some of the larger groups. Commercial rations and water were supplied ad libitum. Stenosing lesions of the intramural coronary arteries began development in cocks and hens before age 7 weeks (10 to 12 weeks before sexual maturity) and progressed with age. Progress, as measured by heart scores, was not influenced by space allowance but was related to social situation. The rate for separately caged cocks was significantly higher than for other birds. Cocks of the larger groups and cocks of the pairs were next in order, while heart scores for cocks of the smaller groups were third but not significantly higher than for grouped hens. Heart scores of grouped hens sometimes exceeded heart scores for cocks of corresponding groups. High mean heart scores for grouped cocks correlated with high mean heart scores for hens of their groups, and low heart scores for grouped cocks with low scores for hens of their groups.