Hormone Treatment Groups Research Articles

Behavioral Effects of Thyroxine in a Lizard (Ameiva undulata: Teiidae)

We investigated the effects of supplemental thyroxine (T₄) and thyroid deficiency on evoked and spontaneous behavioral responses in a lizard (Ameiva undulata). We quantified spontaneous behavior as distance walked without external stimulation and evoked behavior as organismal excitability during the first minute of forced activity on a treadmill, as running time to exhaustion during graded-intensity exercise, and as the outcome of staged competition for prey. Plasma T₄ was reduced to nondetectable levels by surgical thyroidectomy and was increased from 6.4 ± 0.59 to 22.0 ± 3.33 ng/mL (mean ± SE; P < 0.001) by intraperitoneal T₄-pellet implantation. Standard metabolic rate (SMR) was reduced by thyroid deficiency (P = 0.008) but was not stimulated by T₄ supplementation (P = 0.665). Excitability was increased by T₄ (P < 0.025) but was unaffected by thyroid deficiency. Spontaneous behavior was replicable between duplicate trials (r² = 0.47, P < 0.001) but did not differ among hormone treatment groups (P = 0.780) or among excitability categories (P = 0.881). Neither running endurance (P = 0.646) nor the outcome of staged competition for prey (0.05 < P < 0.10) were significantly affected by hormone treatment, and endurance was not correlated with spontaneous behavior (P = 0.148). However, running endurance was significantly lower in lizards of high than low excitability (P = 0.018), and winners in competition trials were usually more excitable than losers (P = 0.057). Physiologically realistic increments in plasma T₄ can increase evoked organismal excitability without being reflected in spontaneous behavior and without stimulating SMR. Excitability is reflected in rapid fatigue during activity and in success during competition for prey. Thyroxine can induce significant behavioral responses without an obligate energetic cost.

Medial nucleus of the amygdala in the adult Syrian hamster: A quantitative Golgi analysis of gonadal hormonal regulation of neuronal morphology

The medial nucleus of the amygdala (Me) processes both chemosensory and hormonal input. In the male Syrian hamster the integrity of this nucleus is essential for normal reproductive behavior. To determine if gonadal steroids modulate neuronal structure in this nucleus, the morphology of Golgi-stained neurons in the anterior and posterior regions of Me were compared in castrated and reproductively intact adult hamsters. In castrated males, neurons in the posterior, but not the anterior, region of Me undergo structural changes, as indicated by a decrease in the mean highest dendritic branch level and mean somal area compared to intact males. To further elucidate the importance of testosterone and its metabolites in maintenance of neuronal structure in the adult, seven groups of male Syrian hamsters were studied. Animals were castrated and received a blank silastic capsule or a capsule filled with either testosterone, dihydrotestosterone, or estradiol, or two capsules containing both metabolites, dihydrotestosterone and estradiol. Two groups of reproductively intact animals were included: brains from one group were processed simultaneously with the castrated and hormone-treated groups (control intact group), and the other group was processed at the beginning of the experiment. Animals were tested for mating behavior and flank glands were measured to test whether the capsules were effective in releasing the hormones into circulation. After a 12-week survival period, the brains were processed with Golgi stain and well-impregnated neurons from the posterior Me were quantitatively analyzed for somal area, highest dendritic branch, total dendritic length, and density of spines. All the measures analyzed revealed a consistent pattern of response to the different gonadal steroids. Castration resulted in a decrease in the mean somal area, the mean highest dendritic branch, and the percentage of neurons with tertiary branch segments. Dihydrotestosterone treatment also resulted in a significant decrease in somal area, mean highest dendritic branch, and percentage of neurons with tertiary dendritic branches. In addition, the total dendritic length and spine density on terminal dendrites were reduced in these brains. The remaining hormone treatment groups were not significantly different from the control group. These results suggest that in orchidectomized male Syrian hamsters, testosterone or its aromatized form, estradiol, but not dihydrotestosterone, is sufficient to maintain the normal morphology of the neurons in the posterior part of the medial nucleus of the amygdala.

Hormonal specificity and activation of social behavior in male red-winged blackbirds

Five groups of male red-winged blackbirds were observed 12 times over 14 days in an aviary setting. An estradiol-treated female was present during the last two observations of each group. Each group of males consisted of a castrated (CA) and an intact (IN) control and six castrated males given one of the following hormone treatments: the aromatizable androgens, testosterone (T) and androstenedione (AE); the nonaromatizable androgens, 5α-dihydrotestosterone (DHT), and androsterone (AN); the estrogen, estradiol (E); or a combination of E + DHT. Castration significantly reduced the frequency of singing and three common vocalizations, chucks, checks, and ips, below the levels shown by IN males. Only hormone treatments which provided both androgenic and estrogenic metabolites (A + E = T, AE, E + DHT) restored normal levels of these behaviors in castrated males. Endocrine status also modulated epaulet display. IN and A + E males were more likely than other males to keep their epaulets constantly exposed. The frequency of sidling and supplanting also varied significantly across hormone-treatment groups, with A + E males showing higher frequencies of these behaviors than other males. T was clearly the most effective hormone treatment in activating hormone-sensitive behaviors in this species. Hormone treatment was more important than size or plumage pattern in determining the outcome of aggressive interactions. In some groups, the dominant male clearly inhibited the performance of hormone-sensitive behaviors by other males. Among A + E males, the frequency of higher intensity song spread displays was highly correlated with the frequency of high-intensity aggressive behaviors and negatively correlated with the tendency to withdraw from other males. Patterns of correlations among behaviors suggest that some calls are more hormone dependent than others, and thus may serve different signal functions.

Effects of exogenous progesterone and estrone on conceptus development in swine.

Administration of progesterone (P4, .55 mg/kg) and estrone (E1, .275 micrograms/kg) during discrete periods in early gestation was found to have beneficial effects on conceptus development in gilts. Three trials were conducted, with each trial examining two hormone treatment groups and one control group. In all trials, P4-E1 supplementation for either one or both of the time periods examined resulted in larger (P less than .05) placentas at d 50 of gestation. Administration of exogenous P4-E1 from either d 20 to 30 (trial 1) or d 25 to 30 (trial 3) of gestation resulted in the greatest augmentation in placental development. In all three trials, exogenous P4-E1 elicited beneficial effects on areolae formation and development. In all nine groups examined (both P4-E1-treated and controls), a positive uterine artery minus uterine vein difference in progesterone concentration was found. This suggests that the conceptus is metabolizing progesterone to metabolites that may have a local effect within the pregnant uterus. It is suggested that augmentation of placental growth, as demonstrated in this study, may reduce secondary fetal death losses in latter gestation (i.e., post-d 70) due to placental insufficiency.

Androgenic involvement in conditioned taste aversion

The effects of castration and hormone substitution on conditioned taste aversion behavior were investigated in male rats. Conditioning involved the pairing of a novel solution (sucrose) with toxicity induced by LiCl. When given the choice between either water or sucrose 2 days later, all animals which has previously experienced the sucrose-plus LiCl condition showed an initial aversion to the sucrose solution while consumption of water was not affected. During the subsequent days of extinction differences in hormone-treatment groups did emerge. Within 15 days virtually all of the castrated control animals had a greater than 50% preference for sucrose while sham-operated animals still maintained their initial aversion to the solution. Treatment with testosterone or dihydrotestosterone was effective in maintaining a conditioned response to sucrose that was compatible with sham animals. 19-hydroxytestosterone, an estrogen precursor, was ineffective in altering the castration effect. The androgenic properties of this behavior were further clarified when cyproterone acetate was found to block the effects of testosterone on this behavior. The results implicate the involvement of androgens in the extinction of a conditioned taste aversion.

Protein and nucleic acid synthesis in rat mammary glands during early lactation.

A study of the effects of hypophysectomy and various hormone replacement therapies upon rates of DNA, RNA, casein and cytoplasmic protein synthesis and enzyme activities in rat mammary glands was undertaken in an attempt to gain information regarding the effects of prolactin and cortisol upon cell proliferation and development in early lactation. Two types of enzymatic responses were observed. One type of response, characteristic of most of the enzymes studied, appeared to be closely related to gland growth and cell proliferation in that activity per mg of DNA remained constant in all hormone treatment groups. A second type of response was observed in which the activity of glucose-6-P dehydrogenase per mg DNA was increased markedly by treatment with a combination of prolactin and cortisol, indicating that the 2 hormones acted together to cause a specific increase in the activity of this enzyme. A higher relative rate of DNA synthesis in hypophysectomized rats treated with prolactin than in those not treat...