Changes in uterine expression of leukemia inhibitory factor receptor gene during pregnancy and its up-regulation by prolactin in the western spotted skunk.

The multifunctional cytokine leukemia inhibitory factor (LIF) is presumed to participate in preparing the uterus for blastocyst implantation. Increased production of LIF is positively correlated with termination of embryonic diapause and preparation for implantation in the spotted skunk. This study examined changes in the expression, localization, and hormonal regulation of LIF receptor (LIFRbeta) gene expression in the uterus of the skunk. Changes in the uterine concentration of LIFRbeta mRNA during pregnancy or in response to hormones after ovariectomy were determined by Northern hybridization analysis and reverse-transcriptase polymerase chain reaction. The skunk uterus produces two LIFRbeta transcripts, the levels of which increase in concentration when the blastocysts resume their development but then decline somewhat during the latter stage of blastocyst activation. Ovariectomy significantly reduced uterine LIFRbeta expression. Estradiol and/or progesterone failed to significantly elevate LIFRbeta mRNA levels in ovariectomized animals. Prolactin significantly increased uterine concentrations of LIFRbeta mRNA to greater than those of ovariectomized controls, but these levels were not comparable to those observed during preimplantation. The LIFRbeta mRNA was predominately localized to stromal cells surrounding the uterine glands and in yolk sac endoderm, syncytiotrophoblast, and cytotrophoblast of postimplantation embryos.

Spatiotemporal expression of cyclooxygenase 1 and cyclooxygenase 2 during delayed implantation and the periimplantation period in the Western spotted skunk.

Embryonic development in the western spotted skunk is arrested after blastocyst formation for about 200 days. This developmental arrest is believed to be due to insufficiency of uterine conditions to support continuous development. Implantation and decidualization are defective in cyclooxygenase 2 (Cox2)-, but not Cox1-, deficient mice. We therefore used Northern and in situ hybridization to investigate changes in uterine expression of Cox1 and Cox2 genes during various stages of pregnancy in the spotted skunk. Cox1 was constitutively expressed at all stages of pregnancy examined, but it did exhibit localized up-regulation in the trophoblast and necks of uterine glands at early implantation sites. Cox2 expression was highly regulated with little or no expression during delayed implantation. Cox2 expression was first detected in the uterus and trophoblast prior to blastocyst attachment and remained detectable for 5-6 days after blastocyst attachment. Cox2 expression was also localized in the luminal and glandular epithelia of uterine segments located between implantation chambers. Changes in Cox expression were not correlated with the abrupt increase in uterine weight that occurs simultaneously with renewed embryonic development but was correlated with an influx of serum proteins into the uterus observed in a previous study.

Changes in uterine expression of leukemia inhibitory factor during pregnancy in the Western spotted skunk.

Mutation of the leukemia inhibitory factor (LIF) gene results in reproductive failure in LIF -/- mice due to an inability to implant their blastocysts. This condition is reversed by infusion of LIF or by transferral of embryos to pseudopregnant, wild-type mice. This led us to hypothesize that embryonic diapause in the spotted skunk is due to insufficient uterine expression of LIF whereas resumption of development and implantation are associated with increased LIF expression. We also investigated the hormonal control of LIF expression. Uterine concentrations of LIF mRNA were determined by quantitative reverse transcription-polymerase chain reaction. Changes in cell-specific localization of LIF mRNA and protein were determined by in situ hybridization and immunocytochemistry. LIF mRNA was detected but was not abundant during embryonic diapause; it then increased when blastocysts resumed development and remained elevated prior to implantation. LIF mRNA and protein could not be localized in the uterus during embryonic diapause but were quite apparent in luminal and glandular epithelium during blastocyst activation. Prolactin, progesterone, and estradiol failed to increase uterine concentrations of LIF mRNA above those in ovariectomized controls. These data are consistent with the initial hypothesis and suggest that LIF may somehow be involved in preparing the uterus for implantation in the spotted skunk.

Progression of trophoblast into the endometrium during implantation in the western spotted skunk.

BACKGROUND: In mustelid carnivores, several blastocysts become implanted either approximately 12 days following fertilization or after a delay of implantation. In the western spotted skunk, implantation occurs following a long period of delayed implantation and a brief activation stage. Within each implantation chamber, a large number of trophoblastic plaques form, and the syncytial trophoblast of these plaques adheres to and penetrates into the uterine luminal epithelium. The presence of multiple attachment sites was used to analyse the way in which trophoblast adheres to, penetrates, and removes uterine epithelium and its subsequent association with the subepithelial vascular plexus. METHODS: Implantation chambers from 18 western spotted skunks were collected during the first week postimplantation and the tissue prepared for light microscopy and scanning and transmission electron microscopy. RESULTS: A series of trophoblastic plaques, which form a ring peripheral to the embryonic shield, attach to and penetrate the uterine epithelium. As new trophoblastic plaques are forming, the initial plaques enlarge and spread along the basal lamina of the luminal epithelium, and trophoblastic processes project through this basal lamina. Subsequently there is a stage of consolidation in which cytotrophoblast increases greatly in amount, attachment sites coalesce, and the luminal epithelium is eliminated. Syncytial trophoblast intrudes into endometrial gland lumina and surrounds subepithelial capillaries. CONCLUSIONS: It is suggested that the affinity of syncytial trophoblast for apical junctional complexes of uterine epithelial cells facilitates intrusion of syncytial trophoblast between cells, possibly guided by the marginal ridges of the uterine cells. The trophoblast shows no tendency to adhere to or invade maternal capillaries. This lack of adhesion to endothelial cells suggests either a change in adhesive properties of trophoblast following epithelial penetration or differences in adhesive properties between surface epithelial cells and endothelial cells. Although trophoblast differentiation appears to be chronologically regulated, it could be responding to maternally derived factors.

Changes in uterine estrogen and progesterone receptors during delayed implantation and early implantation in the spotted skunk.

Although the exact cause(s) of embryonic diapause in the western spotted skunk and other carnivores remains unknown, it has been hypothesized that it may be due to levels of ovarian hormone secretion that are insufficient to promote a uterine environment conducive to continuous embryonic development and implantation. Immunocytochemistry was used to determine whether changes in abundance or distribution of estrogen receptors (ER) and progesterone receptors (PR) may be associated with the cessation or renewal of embryonic development. Thirty pregnant skunks were killed during delayed implantation and periimplantation periods. ER and PR were detected in luminal and glandular epithelium, endometrial stroma, vasculature, and myometrium of the uterus during the period of delayed implantation. There was a significant reduction of both ER and PR receptors during the periimplantation period. The most pronounced change was the complete loss or reduction in staining intensity for PR and ER in the luminal epithelium during the first 2-3 days after implantation. These findings suggest that the failure of skunk blastocysts to undergo continuous development and implant without a prolonged period of diapause is not the result of an insufficient number of ER or PR in the uterus. The data also indicate that renewed embryonic development and implantation is not associated with an increase in these uterine steroid receptors.

Expression of epidermal growth factor receptor in the preimplantation uterus and blastocyst of the western spotted skunk.

The western spotted skunk is unique in that its blastocysts undergo a 180-220-day period of arrested development before implantation. We investigated the potential role of epidermal growth factor (EGF)-related growth factors in regulating uterine and embryonic development in this species by studying the status of EGF receptor (EGF-R) in these tissues during delayed implantation and resumption of embryonic development. The cell-specific distribution of EGF binding sites and the expression of EGF-R mRNA were assayed by autoradiography and Northern blot analysis, respectively. The size of EGF-R was determined by affinity cross-linking studies, and its bioactivity was examined by determining EGF-dependent subcellular protein tyrosine kinase (PTK) activity. EGF binding sites were localized in the uterine luminal and glandular epithelium, endometrial stroma, myometrium, and blood vessels during both stages of pregnancy. As examined by Northern blot hybridization, a cRNA probe specific to mouse EGF-R hybridized to poly(A)+ RNA of skunk uteri. Transcripts similar to those of mouse uterine EGF-R were identified. [125I]-EGF was cross-linked to a 170-kDa protein both in the uterus and in blastocysts collected during the delayed implantation and periimplantation periods. However, EGF-induced PTK activity was significantly elevated above background levels during the period of renewed embryonic development, but not during arrested embryonic development. The results suggest that EGF-related growth factors may play an important role in regulating embryonic development in this species and that a change in the number and/or functional status of the EGF-R may be a prerequisite for blastocyst activation and implantation in the spotted skunk.

Effect of melatonin on pituitary secretion of prolactin in vitro during delayed implantation and the periimplantation period in the spotted skunk.

The pars tuberalis of the western spotted skunk is the only region of the brain known to bind 2-[125I]iodomelatonin, thus suggesting that this region of the pituitary might be essential in mediating the effects of melatonin in this species. Female skunks were killed during short- and long-day photoperiods. Hemisections of the adenohypophysis, with and without the pars tuberalis were cultured in the presence and absence of 10 nM melatonin to determine whether the pars tuberalis mediates the previously observed suppressive effects of melatonin on the seasonal increase in plasma prolactin levels in this species. Pituitaries obtained during long-day photoperiods secreted significantly more prolactin than those obtained during the short-day photoperiod. Melatonin had no effect on pituitary response to gonadotropin releasing hormone and failed to inhibit prolactin secretion during the 48 h culture period. However, melatonin significantly reduced the inhibitory effects of dopamine on prolactin secretion. The latter response was observed in both photoperiods and in the presence and absence of the pars tuberalis. These results suggest that the pars tuberalis does not mediate the inhibitory effect of melatonin on prolactin secretion in the absence of the hypothalamus.

Embryonic diapause in vertebrates.

Embryonic diapause occurs in many species of vertebrates, but the physiological mechanisms which control this fascinating process are exceedingly different in the diverse groups which employ this reproductive strategy. In nonmammalian species and some bats, reduction in rate of embryonic development is temperature dependent, but this is not the case in most mammals. Development becomes arrested at the blastocyst stage of embryogenesis in mammals which exhibit delayed implantation, whereas postimplantation development is continuous but retarded in species exhibiting delayed development. The hormonal control of diapause is remarkably different in the various species. Pituitary secretion of prolactin prevents implantation in the tammar wallaby but hastens renewed development and implantation in the mink and spotted skunk. Ovariectomy results in the eventual death of blastocysts in mustelids but induces renewed development and implantation in the armadillo. Luteal function, as evidenced by elevated progesterone secretion, is essentially constant in the roe deer and armadillo, whereas the luteal cells fail to complete their differentiation and secrete low levels of progesterone in carnivores. Progesterone will induce implantation in the tammar wallaby, but estrogen is required to induce renewed development and implantation in rodents. Neither progesterone and/or estrogens appear to be capable of stimulating implantation in carnivores. The uterus plays an important role in maintaining the embryos in a viable state throughout the period of diapause. In many species the uterus undergoes histological changes and secretes increased amounts of protein, yet we still do not understand the role, if any, these proteins play in initiating renewed embryonic development. Thus the phenomenon of embryonic diapause still holds many mysteries for scientists to solve.

Influence of season on seminal characteristics, testis size and serum testosterone in the western spotted skunk (Spilogale gracilis).

The western spotted skunk is a seasonally breeding mammal: most copulations occur in late September and early October. This study was performed to characterize the seasonal changes in concentrations of testosterone and in ejaculate quality. Captive males (n = 22) were maintained on a natural photoperiod for 15 months. Semen samples were collected by electroejaculation; testis size was measured; and blood samples were collected. Of 110 electroejaculation attempts, 104 (95%) resulted in successful fluid collection and 101 (97%) samples contained spermatozoa. Significant increases (P < 0.05) in serum testosterone concentration, testis size and ejaculate volume were observed from August to November. Mean concentration of testosterone in serum ranged from 0.15 +/- 0.05 ng ml-1 in mid-January to 6.42 +/- 1.79 ng ml-1 in early October. Mean testis size ranged from 1.22 +/- 0.25 cm2 in February to 2.68 +/- 0.08 cm2 in October. Mean ejaculate volume ranged from 11 +/- 3 microliters in March to 129 +/- 22 microliters in October. Seasonal changes in the number of spermatozoa per ejaculate or motility of spermatozoa were not observed. Mean number of spermatozoa per ejaculate was 8.14 +/- 0.85 x 10(6) spermatozoa (n = 97); motility was 56 +/- 2.4% (n = 93); semen pH was 7.76 +/- 0.20 (n = 6); osmolarity was 394 +/- 13 mmol kg-1 (n = 10); and 70.3 +/- 1.5% of the spermatozoa were morphologically normal (n = 47).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of ovarian steroids in development of uterine binding sites for prolactin in the ferret.

The objectives of this study were to investigate 1) the presence of specific prolactin (PRL) binding sites in the ferret uterus, 2) the uterine location of 125I-labeled ovine PRL (oPRL) binding sites, 3) changes in uterine PRL binding sites during pseudo-pregnancy, and 4) regulation of PRL binding sites by ovarian steroids. Binding was determined through use of 125I-oPRL and 300-800 micrograms of protein from the 50,000 x g particulate fraction. Optimal binding occurred within 6 h at 25 degrees C. Scatchard analysis of saturation data revealed a single set of high-affinity (Kd = 4.99 x 10(-11) +/- 0.88 M), low-capacity (22.76 +/- 1.62 fmol/mg) binding sites. Analysis of hormonal specificity revealed that ovine growth hormone (oGH) cross-reacted with oPRL for the uterine binding sites, displacing 38% of the bound ligand. However, no inhibition of 125I-oPRL binding occurred in the presence of a 500-fold excess of bovine thyroid-stimulating hormone (bTSH), ovine LH (oLH), or ovine FSH (oFSH), suggesting hormonal specificity of the binding sites that are located in the luminal and glandular epithelium. Prolactin binding to ferret uterine membranes increased during the first half of pseudopregnancy, plateaued between Days 21 and 28, and then declined. The concentration of PRL binding sites in uteri of ferrets on Day 1 of pseudopregnancy was 4.91 +/- 0.42 fmol/mg of protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteal protein secretion during preimplantation in the ferret.

Ferret CL were collected on Days 5-11 of pregnancy or pseudopregnancy and incubated in McCoy's medium with radiolabeled amino acids to determine the ability of ferret CL to synthesize and secrete proteins during the preimplantation period. Products recovered from the medium were separated by one- and two-dimensional SDS-PAGE followed by fluorography and were quantified by densitometry. Selected secretory proteins were tentatively identified with specific antibodies on Western blots. Ferret CL synthesized and secreted a relatively large number of radiolabeled products. The predominant secretory proteins had molecular masses of 16, 22, 28, 32, 47, 68, and 185 kDa and were secreted at all stages of the preimplantation period. There were no qualitative changes in ferret luteal protein synthesis and secretion between Days 5-11 of pregnancy, and neither ovine prolactin (oPRL) nor dibutyryl cAMP (dcAMP) affected the pattern of protein secretion. However, oPRL (100 and 1000 ng/ml) increased incorporation of radiolabeled amino acids into luteal proteins during a 36-h incubation. The relative mobility of a 185-kDa radiolabeled product was identical to that of alpha 2-macroglobulin (alpha 2M) subunits. Antibody to human alpha 2M cross-reacted with a product (185 kDa) in ferret luteal extracts and culture medium, and the partially purified protein (185 kDa) inhibited trypsin activity. The major radiolabeled secretory protein (32 kDa) exhibited weak cross-reaction with antibody to a human tissue inhibitor of metalloproteinase (TIMP). This study demonstrates the wide range of proteinaceous secretory products of the ferret CL, two of which have been tentatively identified as protease inhibitors.

Autoradiographic localization of binding sites for 2-[125I]iodomelatonin in the pars tuberalis of the western spotted skunk (Spilogale putorius latifrons).

Pineal melatonin secretion mediates photoperiodic regulation of implantation of blastocysts in the female western spotted skunk. Autoradiography studies demonstrated that high affinity 2-[125I]iodomelatonin binding sites are present in the pars tuberalis but not in any other hypophyseal region or in the hypothalamus or thalamus of this species. This restricted localization of 2-[125I]iodomelatonin binding, which was characteristic of spotted skunks sacrificed at various times during their annual reproductive cycles, suggests that the pars tuberalis mediates photoperiodic responses in this species.

Prolactin levels in the western spotted skunk: changes during pre- and periimplantation and effects of melatonin and lesions to the anterior hypothalamus.

Prolactin (PRL) is the primary pituitary hormone responsible for initiating increased function of the corpus luteum and blastocyst implantation in the western spotted skunk. Therefore, we have designed experiments to validate a PRL RIA, characterize the preimplantation profile in PRL secretion, and determine the effects of exogenous melatonin and lesions to the anterior hypothalamic area (AHA) on PRL secretion in the skunk. These objectives were investigated with a heterologous RIA using canine PRL standards and antiserum. Displacement curves of skunk pituitary extract and serum were parallel to the canine PRL standard curve. Growth hormone-releasing hormone injection did not cause a significant change in plasma PRL levels as detected by the assay (p = 0.74). Injection of pimozide increased and bromocriptine decreased plasma PRL levels (p less than 0.05). A seasonal trend in plasma PRL levels was observed during the preimplantation period, with mean concentrations ranging from 5 ng/ml during the period of short day length in January to 17.1 ng/ml during the long day photoperiod in early May. The average date of blastocyst implantation in this study was 2 May (n = 16). Silastic capsules containing melatonin (n = 5) significantly delayed both the seasonal rise in plasma PRL levels and the time of implantation (p less than 0.05) compared to controls with empty capsules (n = 4). Lesions to the AHA (AHAx, n = 5) eliminated these effects of melatonin on both the rise in PRL and time of implantation. PRL levels were highly correlated with progesterone levels (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Photomanipulation of sexual maturation and breeding cycle of the steppe polecat (Mustela eversmanni) and other techniques for more rapid propagation of the species.

Twenty steppe polecats were divided into 2 groups, each consisting of 4 males and 6 females, and subjected to either a natural photoperiod (controls) or alternating periods of short (8 h light/16 hr dark for 8-9 weeks) and long days (16 h light/8 h dark for 16-20 weeks). The experimental photoperiod significantly accelerated sexual maturation in both sexes, with males developing maximal testis size within 57 days and females breeding after an average of 52 days exposure to 16L/8D. Males in the experimental group completed 2 1/2 testicular cycles and participated in mating during 3 successive breeding seasons during the 18 month period whereas males in the control group completed a single testicular cycle and only had an opportunity to mate during a single breeding season. Females in the experimental group produced 3 litters whereas females in the control group only gave birth to a single litter. Litter size averaged 6.9 +/- 2.0 (n = 23) and did not significantly differ with age, parity, or treatment. Pseudopregnant females returned to estrus within 12 days after the expected date of parturition, were bred, and gave birth to kits. Polecats which were subjected to the experimental photoperiods completed more molting cycles and underwent more photoperiod-induced changes in body weight than those in the control group. Death or removal of kits within 8 days after birth resulted in 12/12 females returning to estrus within 6-26 days. Eleven of these females were remated and gave birth to kits. Eight domestic ferrets readily accepted neonatal polecat kits and 5 successfully reared kits, although kit survival was quite poor.(ABSTRACT TRUNCATED AT 250 WORDS)

Testicular response to melatonin or suprachiasmatic nuclei ablation in the spotted skunk.

Testes of the Western spotted skunk enlarge and regress seasonally. The pineal hormone, melatonin, may be important in timing this seasonal reproductive activity. Likewise, the suprachiasmatic nuclei (SCN) have been implicated as possible neural regulators of pineal and reproductive events. These experiments were conducted to determine whether ablation of the SCN or constant administration of melatonin alters timing of the seasonal pattern of testicular regression and recrudescence. Male skunks (n = 24) were treated as follows: six received two empty Silastic capsules, six received two melatonin-filled Silastic capsules, six received sham lesions to the SCN, and six received lesions to the SCN (SCNx). All skunks were exposed to a natural photoperiod and had regressed testes at the onset of the experiment. Four of six males from the SCNx group had an average of 94 +/- 11.3% of these nuclei destroyed. Sham SCNx, animals with less than 40% of the SCN ablated, and males with empty capsules did not have fully enlarged testes until October. SCNx and melatonin-treated skunks exhibited a hastening of testicular recrudescence with maximal testis size being reached in June. Skunks with lesions to the SCN maintained enlarged testes for 5 months while all other groups exhibited rapid regression after attaining maximal testis size. Testicular regression occurred from July through October in animals receiving continuous melatonin, while controls exhibited recrudescence during this same period. Our data suggest that the SCN, melatonin, and thus the pineal gland, play a role in regulating the seasonal testicular cycle of the spotted skunk.

Vitamin C disposition in young and elderly men.

The pharmacokinetics of vitamin C after a 500-mg oral tablet dose were compared in 15 healthy young men aged 25.20 +/- 2.54 (means +/- SD) and in 15 healthy elderly men aged 69.31 +/- 2.52 y. The doses were characterized with the subjects in two states of vitamin C nutriture: a depleted state, which was achieved by 4-5 wk of compliance with a vitamin C-restricted diet of less than 10 mg/d and a supplemented state, in which the subjects were given 500 mg vitamin C/d for 3 wk. Plasma and urine samples were collected for 72 h after the dose of vitamin C from depleted subjects and for 24 h from supplemented subjects and analyzed for vitamin C. Several of the pharmacokinetic indices measured were different in depleted vs supplemented subjects but none exhibited any age-related differences. This indicates that vitamin C nutriture affects vitamin C pharmacokinetics but age does not.

Retention and metabolic fate of [3H]-melatonin in the spotted skunk.

Two experiments were designed to determine which tissues accumulate [3H]-melatonin and the metabolic fate of this hormone in the spotted skunk. Tritiated melatonin was injected into the jugular vein of 10 anesthetized skunks 1-3 h before the onset of darkness and allowed to circulate for 22 min before the vasculature was flushed with saline to clear radioactivity from the blood. Selected tissues were removed from five skunks and oxidized in a Packard Biological Oxidizer which yielded 95 +/- 5% recovery of radioactivity. Relatively high amounts of radioactivity were found in the pineal (367 +/- 304 dpm/mg tissue), ovary (69 +/- 38 dpm/mg), pituitary (89 +/- 56 dpm/mg), liver (107 +/- 29 dpm/mg), and kidney (63 +/- 15 dpm/mg). Relatively small amounts of [3H] were found in different brain regions (approximately 6-7 dpm/mg). The uterus, pancreas, and temporalis muscle also accumulated radioactivity (approximately 13 dpm/mg). The lung retained the least amount of radioactivity (4 +/- 1.3 dpm/mg). In the second experiment, hypothalami, pituitaries, and ovaries were removed from the remaining five females. Radioactivity from these tissues was extracted and subjected to thin-layer chromatography. Melatonin accounted for approximately 70% of the radioactivity recovered while 6-hydroxymelatonin and unidentified more polar compounds made up the majority of the melatonin metabolites. These data indicate that tissues other than the hypothalamus are able to accumulate [3H]-melatonin.

Reproductive cycle of the steppe polecat (Mustela eversmanni).

In laboratory conditions, in a natural photoperiod, testicular redevelopment began in late December. Maximal testis size was attained by the end of February. Testicular regression began in mid-May and was complete by the end of August. Oestrus was first observed in late March and continued throughout April. Females mated for the first time between 30 March and 8 April. Mating generally coincided with peak concentrations of urinary oestrone conjugates and when vaginal lavages contained greater than 90% cornified epithelial cells. Blastocyst implantation occurred by Day 13 and the post-implantation period was 29 days. Gestation ranged from 39 to 43 days and first parturition occurred in mid-May. Concentrations of urinary oestrone conjugates and free progesterone were elevated during the first half of pregnancy, reaching maximum values at mid-pregnancy, and then gradually declined as parturition neared. Litter size of primiparous females averaged 6.8 young/female. Females that were pseudopregnant or lost their litters shortly after birth, and several with weaned kits, exhibited a second oestrus.

Lesions to the anterior hypothalamus prevent the melatonin-induced lengthening of delayed implantation.

The anterior hypothalamic area (AHA) has been postulated as a site of action for melatonin. We tested the hypothesis that lesions to the AHA (AHAx) would counteract the inhibitory effect of exogenous melatonin on blastocyst implantation in the spotted skunk by removing a possible site of action. Forty-seven females were treated as follows during delayed implantation. In Exp 1, five received empty Silastic capsules, five received Silastic capsules containing melatonin, six received sham AHAx plus empty capsules, none received AHAx plus empty capsules, and eight received AHAx plus capsules containing melatonin. In Exp 2, four skunks each received two empty capsules, five skunks each received two capsules containing melatonin, and five skunks received AHAx plus capsules containing melatonin. All capsules were inserted sc in the interscapular region 14-35 days after surgery in Exp 1 and 2 weeks before surgery in Exp 2. Surgery was performed between January 22 and February 12, 1988, in Exp 1 and on March 2-3, 1989, in Exp 2. The skunks were subjected to a natural photoperiod, and the duration of preimplantation was measured. In Exp 1, AHAx plus empty capsules significantly (P less than 0.05) shortened the duration of preimplantation (163 +/- 14.7 days) compared to that in sham AHAx or intact controls (193 +/- 26.1 and 188 +/- 10.6 days, respectively). Melatonin significantly (P less than 0.05) prolonged the duration of preimplantation (289 +/- 2.9 days) in intact skunks, but failed to do so in skunks with AHAx, as the preimplantation period was significantly shortened (159 +/- 6.1 days). In Exp 2, AHAx reversed the inhibitory effect of melatonin on the duration of preimplantation (191 +/- 21.5 days), as intact melatonin-treated skunks had a significantly longer preimplantation period (260 +/- 2.5 days) than skunks receiving empty capsules (191 +/- 16.4 days). The inhibitory effect of melatonin was reversible in all intact skunks, as blastocysts implanted 23 days, on the average, after cessation of treatment with melatonin. These data are consistent with the hypothesis that a portion of the AHA and/or adjacent regions play an essential role in timing blastocyst implantation in the spotted skunk. The lesions may have given this result by ablating a neural pathway controlling PRL secretion and may or may not have involved a site of action for melatonin.

Psychological differentiation, arousal, and lipreading efficiency in hearing-impaired and normal children.

Psychological differentiation, psychophysiological arousal, hearing capacity, and ability to lipread unrelated sentences presented in a silent technicolor film were investigated in 62 children (mean age 10 years, 4 months), classified into three hearing categories (normal, mild to moderate hearing loss, severe hearing loss) based on their average hearing threshold in the range of speech frequencies for their best ear. All subjects were administered the Rod and Frame Test, Craig Lipreading Inventory, and skin conductance measures under two conditions (pre-task and task). The results showed that the ability to lipread sentences from a film was related significantly to psychological differentiation (cognitive style) and pre-task conductance level, but was not related to hearing capacity or task conductance level. The best predictors of lipreading ability were successful performance on the Rod and Frame Test and high increases in skin conductance from pre-task to task situation.