Sexual preferences of male hamsters (Mesocricetus auratus) for conspecifics in different endocrine conditions

The behavioral responses of sexually experienced male hamsters toward a pair of anesthetized conspecifics were investigated. Males spent significantly more time licking, sniffing, and mounting neonatally and adult castrated males than intact males. Adult castrated males receiving oil injections were preferred over castrates receiving exogenous testosterone propionate (TP). Ovariectomized females were preferred over intact males, adult castrated males, or spayed females receiving exogenous TP. It was concluded that the absence of an androgen-dependent factor(s) renders an animal more sexually attractive.     

Retention deficit for avoidance training in hypophysectomized rats: Time-dependent enhancement of retention performance with post-training ACTH injections

These experiments examined the effects of hypophysectomy on retention of avoidance training. In addition, the experiments examined the effects, on retention, of post-training ACTH injections administered to hypophysectomized rats. Rats were trained in a visual discriminated avoidance Y maze. Each rat received six training trials followed by six retraining trials the next day. Retention was measured by the number of correct choices during the retraining trials. When trained with a low-footshock intensity (0.8 mA), hypophysectomized rats showed retention performance which was significantly poorer than that of intact animals. There was no significant difference in performance when the animals were trained with a higher footshock intensity (1.4 mA), in part because of poorer retention performance of intact animals under these training conditions. Under both footshock conditions, a single post-training injection of ACTH enhanced later retention performance of hypophysectomized rats. This effect on memory was timedependent; injections delayed 2 or 6 hr after training did not significantly enhance retention. These findings are consistent with the view that hormonal responses to training may modulate later retention of the training experience.     

Lordosis: Inhibiting effects of progesterone in the female rat

Progesterone has two types of inhibitory effects on female sexual behavior that have been well-documented in the guinea pig. The first occurs when high levels of progesterone are present around the start of the estrogen-priming process (“concurrent inhibition”). The second occurs immediately after the display of an estrogen-progesterone-induced period of estrous behavior (“sequential inhibition”). In the present set of experiments, we show that the rat, like the guinea pig, is capable of exhibiting both of these inhibitory effects of progesterone. However, rats require higher doses of progesterone than guinea pigs, at least for concurrent inhibition to be evident. In addition, we show that the dose of progesterone required in a single injection to produce concurrent inhibition is higher than the dose required to produce sequential inhibition in rats. A theory of how progesterone may be accomplishing its inhibitory effects on female sexual behavior in rodents is presented.     

CULTURE AND HYBRIDIZATION STUDIES ON GIGARTINA PAPILLATA (RHODOPHYTA)1

The foliose red alga Gigartina papillata (C. Ag.) J. Ag. was studied in culture to determine its life history and possible relationship to the life history of Petrocelis middendorffii (Ruprecht) Kjellman. Carpospores cultured from individual female plants gave rise to either crustose Petrocelis-like plants that reproduced by tetraspores, or to another generation of foliose female (cystocarpic) plants that reproduced by carpospores. Apices cultured from blades of individual field-collected female plants produced either papillae with many procarps that developed cystocarps only when crossed with male plants, or papillae with few procarps that produced cystocarps in the absence of male plants. The results are interpreted to demonstrate that two types of life history occur in G. papillata: one, a sexual life history involving a crustose tetrasporophyte; the other, a possibly apomictic life history involving only cystocarpic plants. Hybridization experiments demonstrated, that G. papillata is interfertile with Gigartina-phase gametophytes cultured from tetraspores of P. middendorffii. Sexual plants of G. papillata are postulated to represent the naturally-occurring gametophyte of P. middendorffii in California. The possible relationships of the sexual and apomictic plants of G. papillata are discussed.     

Intramolecular determination of primary kinetic isotope effects in hydroxylations catalyzed by cytochrome P-450

Isotope effects for hydroxylation reactions catalyzed by cytochrome P-450 have usually been measured by comparing the overall reaction velocities of deuterated and nondeuterated substrates. Since the rate-limiting step is probably not the single reaction involving covalent bond cleavage, such an approach does not yield information about the primary isotope effect. We measured the primary kinetic isotope effect for benzylic hydroxylation by a method utilizing intramolecular competition, using the symmetrical substrate 1,3-diphenylpropane-1,1-d₂. These experiments yield a value of $\text{k}{}_{\mathrm{<mtext>H</mtext>}}\text{k}{}_{\mathrm{D}}\text{= 11}$, a larger effect than has previously been reported for benzylic hydroxylations.     

beta-Endorphin: structure-activity relationships in the guinea pig ileum and opiate receptor binding assays.

The opiate activities of some derivatives and enzymatic digests of camel and human β-endorphin were determined in the guinea pig ileum and rat brain opiate receptor binding assays. Derivatives of β-endorphins altered within the amino-terminal five residues showed pronounced losses in activity. Anisylation of the C-terminal glutamic acid residue of β_h-endorphin produced only small reductions in activity. Chymotryptic digestion greatly weakened the opiate activities of β_h-endorphin, whereas carboxypeptidase A, tryptic and leucine aminopeptidase digests showed only small losses in potency. The C-terminus of β-endorphin appears to contribute little directly to opiate activity. Amino acid analysis and assay of the leucine aminopeptidase digests suggest that the larger potency of β-endorphin relative to Met-enkephalin may be a consequence of its greater resistance to exopeptidase attack.     

The effect of cell density on the expression of cell adhesive properties in a cloned rat astrocytoma (C-6)

The cell-cell adhesion characteristic of C-6 astrocytoma cells changes as a function of cell density. Cell suspensions prepared from monolayers having a density lower than 1 × 10⁵ cells/cm² show maximal affinity for plasma membranes and cells obtained from monolayers at densities greater than 1 × 10⁶ cells/cm² shows minimal affinity for plasma membranes. The adhesive component retained on plasma membranes is present at essentially equal levels in membranes prepared from cells at different density. This modulation in cell surface affinity appears to be due to cell-cell contact and appears to represent a suitable model for the study of the modulation of cell-cell adhesion as a result of cell contact.     

Synthesis of leucine enkephalin derivatives: structure-function studies

Nucleoli isolated from livers of rats injected intraperitoneally with one dose of thioacetamide had a five-fold increase in the rate of RNA synthesis $\text{in vitro}$ when compared with livers of rats treated with saline or CCl₄. The stimulation was maximal 24 hours after treatment and decreased to control values 73 hours after treatment. The enhanced level of nucleolar activity was maintained at that level when thioacetamide was injected daily. Along with the increase in the endogenous activity there was a 7-fold increase in the “free” RNA polymerase I activity determined by blocking the bound enzyme with actinomycin D (7). The nucleoli of the thioacetamide-treated rats offer a useful model of modulation of ribosomal gene function.