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Biomedical subjects

D G Cyr

Publications and source records attributed to D G Cyr.

30 records · Page 2Linked to original sources
PubMed1991

Correlates of vestibular evaluation results during the first year of life.

Prenatal and perinatal correlates of abnormal auditory brainstem responses in neonates have been studied extensively. In contrast, vestibular function during the first year of life has received sparse attention. Using a specially modified vestibular test battery, 65 infants (17 low-risk, 48 high-risk) were initially evaluated during their first 6 months of life. Results revealed normal vestibular function in 46 infants (13 low-risk, 33 high-risk) and abnormal findings at either 3 or 6 months in 19 infants (4 low-risk, 15 high-risk). Correlations between vestibular results and variables such as auditory brainstem response results, birth history, and postnatal course in the neonatal intensive care unit were analyzed statistically. While some differences were mildly significant, none were highly significant. The lack of significant correlation between abnormal auditory brainstem response and vestibular results is of particular interest.

Data Interpretation, Statistical↗
PubMed1988

Seasonal patterns in serum levels of thyroid hormones and sex steroids in relation to photoperiod-induced changes in spawning time in rainbow trout, Salmo gairdneri.

Serum levels of thyroid hormones (T4 = L-thyroxine and T3 = 3,5,3'-triiodo-L-thyronine) were measured and correlated with previously published levels of 17 beta-estradiol, testosterone (T), and Ca2+ (index of vitellogenin) in four groups of female trout held for 1-3 years at 8.5-9.0 degrees on a ration of 0.5% of body weight day-1 under different constant photoperiod regimes. In group 1, trout under a regimen of 18L:6D became sexually mature (SM) in April/May and then SM again in September/October; in group 2, trout under a regimen of 6L:18D became SM in January/February; in group 3, trout under a regimen of 6L:18D became SM in March/April; in group 4 trout under a regimen of 18L:6D followed by 10L:14D became SM in September/October. In all groups, regardless of the photoperiod-induced changes in spawning time, serum T3 exceeded T4 and both serum T3 and T4 patterns showed a consistent relationship with the sequence of steroid hormone changes and spawning time. Thyroid hormone levels were high during previtellogenesis but fell as sex steroids and serum Ca2+ increased. T3 and T4 were lowest before spawning when sex steroids were at their peak and then increased sharply following spawning as sex steroid levels declined. Peak serum T coincided with ovulation and usually preceded the postreproductive surge in serum T3 and T4. The hypothesis is discussed that T3 enhances early ovarian development, but as energy-demanding vitellogenesis proceeds T3 formation is suppressed, thereby curtailing growth and favoring energy partition to the ova.

Animals↗
PubMed1988

The influence of short-term 17 beta-estradiol treatment on plasma T3 levels and in vitro hepatic T4 5'-monodeiodinase activity in immature rainbow trout, Salmo gairdneri.

To determine the effects of 17 beta-estradiol (E2) on aspects of thyroid function, immature rainbow trout were intraperitoneally injected with estradiol benzoate (0.5 mg/100 g) on Days 0 and 3 and sampled on Days 7 and 12. This protocol created plasma E2 concentrations during the first 7 days comparable to those during naturally induced vitellogenesis. Control trout received peanut oil alone. Plasma levels of 3,5,3'-triiodothyronine (T3) were significantly depressed on Day 7 but returned to levels by Day 12. Plasma thyroxine (T4) levels were not altered consistently by E2 treatment. Hepatic microsomal T4 5'-monodeiodinase (5'D) activity responsible for conversion of T4 to T3 was significantly depressed on Day 7 but returned to control levels by Day 12. Lineweaver-Burke plots showed that the lower hepatic 5'D resulted from a 10-fold decrease in Vmax, indicating a lower enzyme concentration. A slight reduction in Km was also observed. These results confirm that high E2 levels, comparable to those in vitellogenesis, depress plasma T3 levels in trout and show that, at least in part, this effect is the result of a decrease in the amount of functional hepatic 5'D.

Animals↗
PubMed1988

In vitro effects of thyroid hormones on gonadotropin-induced estradiol-17 beta secretion by ovarian follicles of rainbow trout, Salmo gairdneri.

Ovarian follicles isolated from rainbow trout during early exogenous vitellogenesis were used to study the in vitro effects of thyroid hormones on salmon gonadotropin (GtH)-induced estradiol-17 beta (E2) secretion. Triiodothyronine (T3) alone did not alter E2 secretion but T3 in the presence of GtH (0.5 micrograms/ml) modified E2 secretion according to a biphasic dose-response curve. Maximum E2 secretion occurred at 1.9 x 10(-8) M T3; a concentration of 3.0 x 10(-7) M was inhibitory. T3 was more potent in stimulating GtH-induced E2 secretion than thyroxine. The stimulatory and inhibitory effects of T3 were consistent over a range of GtH concentrations (0.1-1.0 micrograms/ml). Cycloheximide (0.1-10 microM) decreased E2 secretion by GtH-treated follicles in a dose-dependent manner, but failed to overcome all the stimulatory effects of T3. Time course studies with follicles incubated with GtH, GtH + T3, GtH + cycloheximide, or GtH + T3 + cycloheximide indicated that T3 stimulation of GtH-induced E2 secretion occurs within 6 hr. It is concluded that thyroid hormones amplify the effects of GtH on E2 secretion by isolated ovarian follicles; at least a part of this effect does not require de novo protein synthesis.

Animals↗
PubMed1986

The effects of sodium ipodate (ORAgrafin) on thyroid function in rainbow trout, Salmo gairdneri.

Immature rainbow trout held at 12 +/- 1 degree were injected intraperitoneally with a fine saline suspension of sodium ipodate (5 mg/100 g body wt) every 3 days. Plasma 3,5,3'-triiodo-L-thyronine (T3) fell to 40% of control levels by Day 1 and remained at about this level for the duration of the study (22 days). Plasma L-thyroxine (T4) level was not altered on Day 1 but was lowered to 50% of control values by Days 7 and 22. Immersion of trout in T4 (2 micrograms/100 ml water) elevated plasma T4 but did not alter the ipodate suppression of plasma T3. Injection of control or ipodate-treated trout with [125I]T4, [125I]T3, or Na131I indicated that in addition to blocking T45'-monodeiodination to T3, ipodate also decreased plasma clearance of T4 and T3 and their removal by the bile. Ipodate did not alter the hepatosomatic index but did depress the hematocrit by 22 days, possibly due to the hypothyroid state. In conclusion, ipodate at a dose of 5 mg/100 g, approximately one-tenth of a lethal dose, is an effective acute and chronic hypothyroid agent to administer to trout.

Animals↗
PubMed1985

Vestibular evaluation of infants and preschool children.

This article presents an updated summary of vestibular test modifications employed at the Boys Town National Institute for Communication Disorders in Children. In addition, we report the results of vestibular evaluations of 104 full-term and premature children (47 male and 57 female) ranging in age from 3 months to 6 years, including a group of postmeningitic patients. The evaluations utilized harmonic acceleration (HA). No age-related maturational differences in HA gain, phase, or symmetry for an 0.08 Hz screening frequency were found when full-term and premature infants were compared. Infrared video technology was adapted to provide continuous visual monitoring of head and eye position in the totally darkened test enclosure.

Caloric Tests↗
PubMedDate not supplied

Vestibular testing in children.

Vestibular evaluation in the pediatric population has in the past taken several forms. For the most part, the pediatric vestibular evaluation has been more subjective than objective. One of the primary reasons for this has been the obvious difficulties encountered in trying to conduct a standard, adult electronystagmography (ENG) procedure on a pediatric patient population not capable of performing in a manner conductive to a good ENG recording. The purpose of this paper is to suggest certain modifications of the standard adult ENG battery for use with young children and infants. Discussion consists of modifications in the areas of various ocular movement tests including sinusoidal pursuit, calibration, optokinetics and gaze testing. In addition, procedures relative to peripheral vestibular output from perrotational and caloric stimulation are discussed. Topics also include the use of a closed-loop caloric irrigator and simultaneous caloric irrigation as viable alternatives to standard, alternative water irrigation when testing the vestibular output of a young child or infant.

Calibration↗
PubMedDate not supplied

Vestibular findings in the deaf and hard of hearing.

One hundred sixty-six youngsters (3 to 19 years of age) with severe-to-profound hearing impairments underwent vestibular evaluations with electronystagmography as part of a comprehensive medical and psychoeducational test battery. Twenty-two percent of the children had unilateral or bilateral labyrinthine weakness in response to caloric stimulation, and 21% demonstrated spontaneous or positional nystagmus. The tandem Romberg test was most predictive of those patients with caloric labyrinthine weakness. The performance of mental alerting tasks (using sign language when appropriate) by the patients during testing proved essential in overcoming a marked tendency toward central suppression of nystagmus.

Adolescent↗
PubMedDate not supplied

Effects of short-term methylmercury exposure on metallothionein mRNA levels in the testis and epididymis of the rat.

Methylmercury (MeHg) is a widespread environmental contaminant that causes reproductive dysfunction in men. Metallothioneins (MTs) are low-molecular-weight proteins that can bind heavy metals and protect the cell from metal toxicity. MT levels are increased by exposure to metals and physiological stressors. Although MTs have been identified in the testis and epididymis, little is known about their distribution and regulation in the epididymis or the effects of MeHg on MT levels in male reproductive tissues. The objective of this study was to determine whether MT I, II, and III mRNA are present in the epididymis, if their relative levels differ between epididymal segments, and if MeHg alters cellular mRNA levels for MT I, II, and III in the testis and epididymal segments of the rat. Northern blot analysis was done on total cellular RNA isolated from each of the four epididymal segments (initial segment [IS], caput [CT], corpus [CS], and cauda [CA] epididymidis) using a cDNA probe for MT I and MT II. MT I transcripts were present in all epididymal segments. The lowest mRNA levels were observed in the IS; these levels were 4-fold less than in the CT and CS and 5.5-fold less than in the CA. MT II mRNA levels were similar in the IS and CT but were eightfold higher in the CS and CA. A cDNA probe for MT III was generated by reverse transcription-polymerase chain reaction using testicular RNA. MT III mRNA was detected only in the IS and CT and not in the CS and CA. To assess whether exposure to MeHg alters MT mRNA levels, rats were exposed for 14 days to one of five MeHg doses (0, 25, 50, 100, and 200 [microg/kg/day] via a subdermal osmotic pump. No changes were observed in either body weight or in the weights of the testis, epididymis, seminal vesicles, or ventral prostate between MeHg-treated and control rats. Serum testosterone levels were significantly decreased only at the highest MeHg dose. In the testis, MeHg treatment resulted in 2.5- to 7-fold increases in MT I mRNA levels. There were no changes in either MT II or MT III mRNA levels. In the initial segment of the epididymis, MT I mRNA levels were significantly increased only at the 50 microg/kg/ day dose, whereas there were no significant differences in MT II mRNA levels. In the caput epididymis, MT I mRNA levels were significantly lower at the 50 and 100 microg/kg/day dose. MT II mRNA levels were also lower, with the exception of the 50 microg/kg/day dose. Although MT III mRNA levels were lower at the two lower doses, levels were not different from controls in the two highest doses tested. In the corpus epididymidis, MeHg did not alter MT I mRNA levels, and MT II was higher only in the 50 microg/kg/day group. In the cauda epididymidis, MT I mRNA levels were decreased in a dose-dependent manner by up to 63%. MT II levels were unaltered. Together these data indicate that exposure of adult rats to MeHg can modulate MT mRNA levels in both the testis and epididymal segments. Furthermore, changes in MT mRNA levels following exposure to MeHg differ between epididymal segments, suggesting either differences in MeHg accumulation or differences in MT modulation.

Animals↗
PubMedDate not supplied

Expression and regulation of metallothioneins in the rat epididymis.

Metallothioneins (MTs) are cytosolic proteins involved in cellular stress responses. The objectives of this study were to determine which epididymal cells express MTs, how they are regulated, and whether mRNA levels for 3 MT isoforms (MT I, MT II, and MT III) are modulated by heavy metals. MT expression was noted mainly in basal cells of all epididymal regions but not in all basal cells of any given region. MT I mRNA levels were highest in the testis, followed by levels in the corpus, cauda epididymidis, liver (positive control), caput epididymidis, initial segment, seminal vesicles, and ventral prostate. MT II mRNA levels were also highest in testis, followed by levels in the cauda, corpus, liver, caput, and initial segment, but they were undetectable in the seminal vesicles and ventral prostate. MT III mRNA levels were highest in the caput followed by testis and initial segment. Orchidectomy and orchidectomy with testosterone replacement experiments showed that immunoreactive MT in all epididymal segments was androgen dependent. Epididymal MT I mRNA levels were dependent on androgens in all segments except the corpus. MT II mRNA levels were androgen dependent only in the initial segment and corpus. MT III mRNA levels in the initial segment were not altered by orchidectomy but increased significantly in testosterone-treated rats. In the caput, MT III mRNA levels decreased following orchidectomy, but control levels were maintained by testosterone. In cadmium-injected rats, MT I mRNA levels were significantly increased in the testis and initial segment, but there were no effects in the liver and other epididymal regions. MT II mRNA levels were increased by more than eightfold in the liver and by three- to fourfold in the initial segment and caput. In the corpus, MT II mRNA levels were decreased by cadmium treatment. MT III mRNA levels were unaltered by cadmium treatment. In conclusion, all 3 MT transcripts are present in high abundance in the epididymis. Furthermore, MT is expressed mainly in basal cells with regulation by testosterone. Heavy metal induction appears to affect the proximal regions of the epididymis.

Androgens↗