Biomedical subjects

C H Summers

Publications and source records attributed to C H Summers.

At least 37 records · Page 2Linked to original sources

PubMed1997

Unilateral ovariectomy influences hypothalamic monoamine asymmetries in a lizard (Anolis) that exhibits alternation of ovulation.

The lizard Anolis carolinensis alternates ovulation, and the resultant ovarian asymmetry correlates with alternating asymmetry of hypothalamic catecholamines. Unilateral and bilateral ovariectomies of cycling females were performed to determine if ovarian manipulations influence hypothalamic catecholamine asymmetries. During the middle of the ovarian cycle, we removed the larger ovary, i.e., the next one to ovulate an egg (N = 9), the smaller ovary with its corpus luteum (N = 8), or both ovaries (N = 5). A sham-operated control group was included (N = 9). The diameter of the largest ovarian follicle in each ovary was measured at the beginning and end of the experiment. After 12 days, the hemihypothalami from the sides of the initial smaller ovary (SO) and larger ovary (LO) were dissected and frozen for determination of monoamines and their metabolites using HPLC and electrochemical detection. Monoamine and metabolite concentrations at the end of the experiment in the original SO and LO sides of each hypothalamus were compared with an asymmetry ratio, or AR, of (SO side - LO side)/(SO side + LO side). No female ovulated during the experiment. Unilateral ovariectomy caused compensatory growth of the largest follicle in the remaining ovary. Removal of the SO or LO caused the AR of DOPAC to favor the brain side ipsilateral to that of the ovarian removal. Removal of the LO switched the NE AR from the SO to the LO side. Removal of the LO or SO caused the MHPG AR to favor the LO side. Ovariectomy of any kind caused 5-HT, which in the sham-operated animals favored the SO side, to become symmetric, and removal of the LO caused the 5-HIAA AR to favor the LO side. We conclude that the ovaries influence hypothalamic catecholamine asymmetries in Anolis via direct neural (as well as hormonal) pathways and that sensory input from the ovaries to the hypothalamus could be involved in control of ovarian alternation via both neural and hormonal efferent mechanisms.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1996

Acute toxicity of firefighting chemical formulations to four life stages of fathead minnow.

Laboratory studies were conducted with four early life stages of fathead minnow, Pimephales promelas, to determine the acute toxicity of five firefighting chemical formulations in standardized soft and hard water. Egg, fry, 30-day posthatch, and 60-day posthatch life stages were tested with three fire retardants (Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D75-F) and two fire-suppressant foams (Phos-Chek WD-881 and Ansul Silv-Ex). Fry were generally the most sensitive life stage tested, whereas the eggs were the least sensitive life stage. Formulation toxicity was greater in hard water than in soft water for all life stages tested. Fire-suppressant foams were more toxic than the fire retardants. The 96-hr LC50s derived for fathead minnows were rank ordered from the most toxic to the least toxic formulation as follows: Phos-Chek WD-881 (13-32 mg/liter) > Silv-Ex (19-32 mg/liter) > Fire-Trol GTS-R (135-787 mg/liter) > Phos-Chek D75-F (168-2250 mg/liter) > Fire-Trol LCG-R (519-6705 mg/liter) (ranges are the lowest and highest 96-hr LC50 for each formulation).

Ammonia↗

PubMed1995

Activation of central biogenic amines following aggressive interaction in male lizards, Anolis carolinensis.

Many stimuli, including social aggression, activate endocrine stress mechanisms, presumably mediated or modulated by central neurotransmitters. To determine the effects of aggression on central neurochemistry, reproductively active male Anolis carolinensis were paired and allowed to establish social dominance relationships. While combatants cohabited, the fight losers invariably became socially subordinate and displayed darker color, selection of lower perch sites, and lower body posture than the winners. After one hour, one day, one week, or one month of cohabitation animals were sacrificed. Each member of a pair was killed at approximately the same time, along with animals kept isolated as controls. Diencephalon, non-optic lobe midbrain and hindbrain were analyzed for indoleamines, catecholamines and metabolites by coulochem electrode array HPLC. Early activation (by one hour) of the serotonergic system in subordinate male lizards was indicated by decreased serotonin (5-HT), increased 5-hydroxy-indoleacetic acid (5-HIAA) levels and 5-HIAA/5-HT ratio. Substrate 5-hydroxy-tryptophan (5-HTP) also increased in losing males, suggesting enhanced production as well as turnover. Significant 5-HTP and 5-HIAA/5-HT increases for subordinate males, compared with levels in control and dominant males, were greatest at one hour and diminished thereafter. This pattern of indoleamine system activation is consistent with stress-induced stimulation of the serotonergic system and prolonged activation of the stress response in subordinate animals, as well as serotonergic inhibition of aggression. In contrast with serotonin, subordinate males did not have increased catecholamine system activation following one hour of interaction. The ratio of DOPAC/dopamine was lower following one hour of interaction in subordinate males. Adrenergic system activation, indicated by metanephrine/epinephrine ratio, increased with time in losing males, except that after one month of cohabitation, turnover returned to levels that equaled those of control animals. Noradrenergic metabolite MHPG, as well as MHPG/NE ratio, were significantly reduced in dominant males at one hour and one week. Changes in adrenergic system activation, not seen in or registered by noradrenergic systems, indicate a possible role for central epinephrine in social stress accommodation.

Aggression↗

PubMed1995

Limiting exposure to liability: simple but crucial steps when hiring.

Home care agencies serve a frail and often elderly population that requires competent and trustworthy caregivers. Solid personnel policies that establish thorough and clear hiring and training practices can ensure top-notch employees and reduce an agency's risk of exposure to liability.

Aged↗

PubMed1994

Somatic correlates of adrenergic activity during aggression in the lizard, Anolis carolinensis.

Aggressive interactions in Anolis carolinensis result in increased circulating levels of epinephrine (Epi) and norepinephrine (NE) and conspicuous color changes. This activation of the adrenergic component of an acute stress response is externally represented by the darkening of the postorbital eyespot of A. carolinensis. In adult males, this site darkens in response to stressful physical stimulation (trauma, passive restraint) or psychological stimuli, most notably the sight of an aggressively intruding conspecific. Aggressive male A. carolinensis exhibit postorbital eyespot darkening; animals that have a longer latency to expression of this eyespot and those that never show this response were defeated in agonistic interactions. Also, during agonistic interactions, subjects that subsequently win are the first to display eyespot darkening. Plasma catecholamine levels are significantly elevated within 30 sec in both combatants. At 30 sec following the determination of the outcome, winning male lizards have plasma NE levels which are higher than those of losers. Castration, however, significantly increases the latency to eyespot darkening and extends its duration. Testosterone levels may therefore enhance the onset of Epi-mediated eyespot darkening as well as other aspects of the endocrine stress response. Elevated androgen levels and more rapid activation of acute catecholamine response increases the likelihood of becoming socially dominant.

Adrenergic Fibers↗

PubMed1992

Cranial ontogeny in the direct-developing frog, Eleutherodactylus coqui (Anura: Leptodactylidae), analyzed using whole-mount immunohistochemistry.

Direct development in amphibians is an evolutionarily derived life-history mode that involves the loss of the free-living, aquatic larval stage. We examined embryos of the direct-developing anuran Eleutherodactylus coqui (Leptodactylidae) to evaluate how the biphasic pattern of cranial ontogeny of metamorphosing species has been modified in the evolution of direct development in this lineage. We employed whole-mount immunohistochemistry using a monoclonal antibody against the extracellular matrix component Type II collagen, which allows visualization of the morphology of cartilages earlier and more effectively than traditional histological procedures; these latter procedures were also used where appropriate. This represents the first time that initial chondrogenic stages of cranial development of any vertebrate have been depicted in whole-mounts. Many cranial cartilages typical of larval anurans, e.g., suprarostrals, cornua trabeculae, never form in Eleutherodactylus coqui. Consequently, many regions of the skull assume an adult, or postmetamorphic, morphology from the inception of their development. Other components, e.g., the lower jaw, jaw suspensorium, and the hyobranchial skeleton, initially assume a mid-metamorphic configuration, which is subsequently remodeled before hatching. Thirteen of the adult complement of 17 bones form in the embryo, beginning with two bones of the jaw and jaw suspensorium, the angulosplenial and squamosal. Precocious ossification of these and other jaw elements is an evolutionarily derived feature not found in metamorphosing anurans, but shared with some direct-developing caecilians. Thus, in Eleutherodactylus cranial development involves both recapitulation and repatterning of the ancestral metamorphic ontogeny.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Activation of the serotonergic system in chick spinal cord during hatching.

The objectives of the present study were to determine the levels of serotonin (5-HT), its major catabolic metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and norepinephrine (NE) in chick spinal cord before, during, and after hatching and also to determine if changes in the levels of these chemicals are directly related to the hatching behavior. The levels of 5-HT, 5-HIAA, and NE were measured by high performance liquid chromatography with electrochemical detection in whole spinal cords of 20-day-old "pre-hatching" embryos, 21-day-old "normal hatching" embryos, 0-day-old "post-hatching" chicks, and 0-day-old "glass egg hatching" chicks. NE was measured but no significant differences were found in NE levels among experimental groups. The concentration of 5-HT was elevated in chick embryo spinal cords during normal hatching compared to pre-hatching embryos and post-hatching chicks. The concentration of 5-HIAA was elevated during and after normal hatching compared to pre-hatching embryos. However, neither 5-HT nor 5-HIAA levels were found to be elevated in chick spinal cords during glass egg hatching compared to pre-hatching embryos or post-hatching chicks. Therefore, there appears to be an activation of the serotonergic system in chick spinal cord related to the specific event of hatching but this activation is not directly related to the movements common to both hatching and glass egg hatching.

Animals↗

PubMed1989

Morphological integration in the cranium during anuran metamorphosis.

We examined the role of thyroid hormone in mediating morphological integration between cranial cartilage and bone during anuran metamorphosis. Exogenous T3 applied to premetamorphic tadpoles (Bombina orientalis) via intracranial implants of plastic micropellets precociously induced typical metamorphic changes in both tissues, but also dissociated the relative timing of developmental events between them. Morphological integration between the two primary cranial tissues is achieved in part by each tissue responding independently to endocrine factors and does not reflect a tight developmental coupling between them.

Animals↗

PubMed1988

Skull development during anuran metamorphosis: III. Role of thyroid hormone in chondrogenesis.

Metamorphosis of cranial cartilages in anuran amphibians constitutes one of the most dramatic and extensive ontogenetic transformations in vertebrates. We quantitatively examined the role of thyroid hormone (3,3',5-triiodo-L-thyronine; T3) in mediating gross aspects of this morphological repatterning in the skull of the Oriental fire-bellied toad, Bombina orientalis. T3 was administered via plastic (Elvax) micropellets in three treatment dosages (2.5, 0.25, and 0.025 microgram) and one control dosage (0 microgram) to tadpoles of three Gosner developmental stages--28/29, 30/31, and 32/33; tadpoles were recoved up to 8 d (treatment and control dosages) or 14 d (control dosage) later. Response of larval cartilages to exogenous T3 was dosage dependent but not implant-stage dependent; chondrogenic tissues that participate in metamorphic transformation are competent to respond to T3 well before they normally do. Metamorphic effects of T3 were visible within 2 d; in most treatment groups, the normal metamorphic sequence was two-thirds complete after 8 d. While T3 also induced precocious ossification, the normal temporal relation between bone formation and cartilage transformation was dissociated in experimental groups. Morphological integration between cartilage and bone during cranial metamorphosis is at least partly the result of each tissue responding independently to endocrine factors.

Animals↗

PubMed1988

Gonadotropin-induced ovulation in a reptile (Anolis carolinensis): histological observations.

Although much is known about morphological changes in the apex of the mammalian ovarian follicle prior to its rupture (ovulation), information about this process in nonmammalian vertebrates is limited to only a few species. We describe here the histological changes in the stigma of the lizard (Anolis carolinensis) ovarian follicle preceding FSH-induced ovulation. Females with a large vitellogenic follicle received two injections, separated by 7 hr, of either porcine FSH (25 micrograms) or saline, and then were sampled at 6, 9, 12, 15, 18, and 24 hr after the first injection. Thus, all but the 6-hr group received two injections. By 12 hr, about half of the FSH-treated females had ovulated, and most had ovulated by 15 hr. In contrast, only 1 of 40 control females ovulated. Large unovulated follicles were fixed and bisected through the circular stigma; one hemisphere was embedded in paraffin and stained with Mallory's trichrome, and the other was embedded in plastic and stained with toluidine blue. FSH treatment produced marked histological changes in the stigma region, as well as alterations in nonstigmal areas of the follicle. The membrana granulosa of control follicles consisted of a single layer of squamous, darkly staining granulosa cells. After FSH treatment, nonstigmal granulosa cells separated slightly, and their nuclei became more clear and assumed an oval shape; in the stigma, these cells became widely separated, with round, light-staining nuclei containing one or two prominent nucleoli. The nonstigmal theca of FSH-treated follicles was similar to that of control follicles except that collagen fibers were more dissociated. In the stigma, collagen fibers were widely dissociated, and the theca swelled, presumably due to accumulation of extracellular fluid. Abundant fluid accumulated in the stigma, especially between the granulosa cells and their basement membrane and between the tunica albuginea and the theca externa. These changes in the lizard stigma are similar to those reported in mammals except that no marked inflammatory response occurs in the lizard stigma. We hypothesize that the Anolis follicle undergoes preovulatory luteinization, and that the stigma exhibits ischemic necrosis before rupture.

Animals↗

PubMed1987

Seasonal changes in the effects of arginine vasotocin and stretch on Anolis uterine contractions in vitro.

We determined the effects of acute stretch on spontaneous and arginine vasotocin (AVT)-driven contractions of the Anolis carolinensis uterus in vitro. Whole uteri from reproductively inactive females (October) were placed in a bath of oxygenated 32 degrees C Anolis "Ringer's." Two initial tensions were utilized, 1.5 g or 15 g, the latter being an estimate of the tension on the wall of a uterine compartment. Uteri were then exposed to either saline or AVT (50 ng/ml), and spontaneous or AVT-driven contractions were recorded for 20 min with the use of a strain gauge and physiograph. A similar experiment was performed on uteri from reproductively active females in the summer (June). Our results indicate that the effects of acute stretch and AVT on uterine contractility were qualitatively similar in summer and fall. That is, AVT induced a tonic contraction; stretch decreased the duration of the tonic contraction; the saline-treated uteri exhibited spontaneous rhythmic contractions; AVT increased the amplitude of the rhythmic contractions, but only at the lower tension; there were no effects of AVT on the timing (contraction interval, duration, rest interval) of the rhythmic contractions; and stretch increased the frequency of the rhythmic contractions. Season greatly influenced the magnitude of these contractile phenomena. Uteri tested during the breeding season exhibited greater distensibility, an increase in the amplitude and duration of the AVT-driven tonic contraction, and an increase in the frequency of both spontaneous and AVT-driven rhythmic contractions because of a decrease in both contraction duration and rest interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Induction of oviposition in cycling Anolis carolinensis requires a beta-adrenoreceptor blocker and a high dosage of arginine vasotocin.

In a previous study, a high dosage (2.0 micrograms) of arginine vasotocin (AVT), following 10 micrograms of dichloroisoproterenol, induced oviposition in Anolis carolinensis at the end of the breeding season. The present study determined if a lower dosage of AVT (0.25 microgram), comparable to that effective in other lizard species, would induce oviposition in cycling A. carolinensis. Only a high dosage of AVT (2.0 micrograms), following 10 micrograms of dichloroisoproterenol 15 min beforehand, induced oviposition. These results suggest that uterine smooth muscle of A. carolinensis is relatively insensitive to AVT.

Adrenergic beta-Antagonists↗

PubMed1984

Compensatory follicular hypertrophy during the ovarian cycle of the house gecko, Hemidactylus frenatus.

The house gecko ( Hemidactylus frenatus ) exhibits an ovarian cycle that can be divided into early follicular, vitellogenic, and luteal phases. Serial sections through the right ovary of animals in the three phases allowed us to quantify follicular size, condition, and number, as well as germinal bed activity. There are six to eight healthy, growing follicles in each ovary, arranged in a stepwise size hierarchy. This number does not vary among the three phases, even though one follicle becomes atretic and one ovulates during each cycle. Therefore, compensatory follicular hypertrophy occurs, leading to replacement of lost follicles and maintenance of the follicular size hierarchy.

Animals↗

PubMed1984

Compensatory testicular hypertrophy in the lizard Anolis carolinensis.

In reproductively responsive, male Anolis carolinensis undergoing artificially induced testicular recrudescence, unilateral orchidectomy of the left testis produced compensatory hypertrophy of the remaining testis. Testosterone inhibited this compensatory testicular hypertrophy on a weight basis, but did not reduce the rate of spermatogenic development. These results suggest that there is a mechanism of testosterone feedback in Anolis carolinensis that controls gonadotropin secretion during the recrudescent phase. In reproductively thermorefractory lizards, unilateral orchidectomy had no effect on the remaining testis. Administration of exogenous follicle-stimulating hormone to refractory animals increased testicular weight and stage of spermatogenic development. Sensitivity to gonadotropin, as well as failure of unilateral orchidectomy to produce compensatory hypertrophy in refractory male anoles, suggests that the control of the refractory period in A. carolinensis results from physiological mechanisms in the pituitary gland or brain rather than in the testis.

Animals↗

PubMed1984

Spontaneous, rhythmic contractions of the ovarian follicular wall of a lizard (Anolis carolinensis).

Collapsed walls of vitellogenic follicles from the lizard Anolis carolinensis were placed in an in vitro system to measure contractility. Three initial tensions were utilized, 0.15, 1.5, and 10.0 g; the latter, after relaxation, produced follicles with a tension similar to that on the wall of an intact vitellogenic follicle. Follicles at each tension then were exposed to either saline or 50 ng/ml arginine vasotocin (AVT). Spontaneous, rhythmic follicular contractions occurred (approx one every 3 min), regardless of initial tension. The higher the initial tension, however, the greater the amplitude of the contractions. Treatment with AVT did not influence any parameter of rhythmic contraction. This report of rhythmic contractions of whole follicular walls of Anolis suggests that contractile activity of myofibroblasts in the wall plays a role in follicular growth and/or ovulation.

Animals↗

PubMed1983

Ovarian, oviductal, and adrenal vascular connections in female lizards (genus Anolis).

The urogenital blood vessels of Anolis equestris and A. carolinensis were studied using dissection, injection of silicone rubber, and histology. A new blood-vascular connection between small veins in the pampiniform plexus at the base of the ovary and an ostial extension of the secondary oviductal vein is described. Chemical messengers could thus be carried in the blood from the ovarian venous drainage to the oviduct. Furthermore, close apposition of the secondary oviductal vein and artery provides an anatomical basis for countercurrent exchange of these messengers. A circular venous arcade, involving the supracardinal vein and branches of the oviductal veins, also is described; this arcade could serve to deliver adrenal hormones to each oviduct.

Adrenal Cortex Hormones↗

PubMed1983

The relationship among ovarian condition, steroid hormones, and estrous behavior in Anolis carolinensis.

The lizard Anolis carolinensis ovulates a single egg alternately from each ovary every 14 days. The ovulated egg enters the ipsilateral oviduct, acquires a shell, and is oviposited 18 or 19 days later. Thus, there is only a single egg in one of the oviducts (one-egg condition) during most of the estrous cycle, but there is a 4-5 day period when a mature, shelled egg is in one oviduct while a recently ovulated egg is in the contralateral oviduct (two-egg condition). Analysis of ovarian follicular diameters indicates that the largest follicle in a single ovary exhibits a growth spurt about halfway through its 28-day vitellogenic growth phase. The corpus luteum, once formed from the ovulated follicle, exhibits a linear decrease in weight, becoming fully regressed just before oviposition of the egg in the ipsilateral oviduct. Plasma concentrations of estradiol-17 beta and progesterone are high in two-egg animals. After oviposition, plasma concentrations of progesterone are still high in one-egg animals whereas those of estradiol-17 beta are much lower. These ovarian and hormonal changes during the estrous cycle are discussed in relation to the probable sources of estradiol-17 beta and progesterone, the control of the alternating pattern of ovulation and oviposition, and the role of steroid hormones in female sexual receptivity in this species.

Animals↗

PubMed1983

Adrenergic inhibition of uterine contractions and oviposition in the lizard Anolis carolinensis.

Injection of arginine vasotocin (AVT), which induces oviposition in several lizard species, fails to do so in Anolis carolinensis. We tested the hypothesis that epinephrine-induced activation of beta-adrenoreceptors in the uterus inhibits AVT action on uterine smooth muscle. Pretreatment of gravid females with the beta-adrenoreceptor antagonist dichloroisoproterenol 15 min before an AVT injection resulted in uterine sensitivity to AVT and subsequent oviposition. Furthermore, in vitro tests indicated that epinephrine as well as a beta-adrenoreceptor agonist (isoproterenol) inhibit uterine tonic and rhythmic contractions that normally follow exposure to AVT. These results suggest that stress-induced secretion of epinephrine can act as a short-term inhibitor of oviposition in this species.

Animals↗