Search PubMed⌕ Search

Biomedical subjects

G M Lambert

Publications and source records attributed to G M Lambert.

7 recordsLinked to original sources
PubMed1995

Flow cytometric analysis using digital signal processing.

Current commercial flow cytometers employ analog circuits to produce the feature values of the pulse waveforms that result from particle analysis. The use of analog pulse processing limits the features that can be measured to pulse integral, pulse height, and pulse width, and a large amount of potentially relevant information about the shape of the pulse waveform is lost. Direct digitizing of the waveform provides a means for the extraction of additional features, for example, pulse skewness and kurtosis, as well as the Fourier properties of the pulse. Here we describe a digital pulse waveform processing system that is compatible both with a commercial flow cytometer, and with a readily available computational platform. The performance of the digital and analog systems were compared through analysis of synthetic waveforms, and the waveforms produced by standard fluorescence microspheres and biological particles. The digital waveform processing system was found to be accurate and flexible, and the value of several of its unique attributes was demonstrated using biological cells. A protocol was designed in which digital pulse processing provided a means for the quantitative monitoring of the optical alignment of the flow cytometer. It was shown that digital pulse processing could be used to discriminate between particle classes which produce feature values indistinguishable through analog pulse processing, and to discriminate accurately single cells from doublets and larger aggregates.

Animals↗
PubMed1992

Sexual dimorphism in the effects of mating on the in vitro release of LHRH from the ferret mediobasal hypothalamus.

A sexually dimorphic pattern in the secretion of luteinizing hormone (LH) has previously been shown to occur in response to mating in an induced ovulating species, the ferret, with mating augmenting the secretion of LH in females but not in males. The aim of this study was to determine whether this dimorphic pattern in the postcoital secretion of LH reflects a dimorphic effect of mating on the neural release of luteinizing hormone releasing hormone (LHRH). The effect of mating on the in vitro release of LHRH from mediobasal hypothalami (MBH) collected from breeding male and female ferrets was studied. Luteinizing hormone releasing hormone release and content were significantly reduced in tissues from estrous females sacrificed 0.25 h after mating compared to unpaired estrous females and estrous females sacrificed 1 or 2.6 h after the mating stimulus. By contrast, the release of LHRH from MBH fragments and LHRH tissue content were equivalent in breeding males that were sacrificed 0.25 h after mating and in breeding males that were left unpaired. These data suggest that the postcoital surge of LH in the female ferret is preceded by a release of LHRH that initially depletes neuronal terminals within the MBH, whereas LHRH release, like pituitary LH secretion, is minimally affected by mating in males.

Animals↗
PubMed1992

Sex difference in the effect of mating on c-fos expression in luteinizing hormone-releasing hormone neurons of the ferret forebrain.

The pulsatile secretion of LH was previously found to rise in female ferrets after receipt of an intromission, whereas in males that achieved an intromission, both LH and testosterone secretion were either reduced or unchanged. We sought to determine whether this sexually dimorphic pattern of LH secretion reflects a sex difference in the effect of mating on the activity of forebrain neurons that secrete LHRH. Immunocytochemical methods were used to localize the nuclear protein product of the immediate early gene, c-fos, as an index of increased neuronal activity after mating. Nuclear FOS immunoreactivity (FOS-IR) was monitored in LHRH-IR neurons as well as other non-LHRH forebrain neurons. In confirmation of previous reports, LHRH-IR perikarya in ferrets of both sexes were located medially along the base of the brain at rostral, medial, and caudal levels of the preoptic-hypothalamic continuum. In each of these regions a significantly higher percentage of LHRH-IR neurons was colabeled with nuclear FOS-IR in mated than in unpaired females. By contrast, an equivalent low percentage of LHRH-IR neurons was colabeled with FOS-IR in mated and unpaired male ferrets. Significantly more FOS-IR neurons (not colabeled with LHRH) were detected in the bed nucleus of the stria terminalis, the medial preoptic area, the dorsal-medial hypothalamus, and the medial amygdala (MA) of mated vs. unpaired females. By contrast, mating significantly augmented FOS-IR only in the MA of male ferrets. The results suggest that the sexually dimorphic pattern of LH secretion that occurs in ferrets after mating reflects a selective activation of LHRH neurons in the female forebrain. This sex-specific increase in the responsiveness of LHRH neurons to mating may depend on input from a limbic circuit which includes the medial amygdala, bed nucleus of the stria terminalis, and medial preoptic area.

Animals↗
PubMed1991

Reciprocal relationships between pulsatile androgen secretion and the expression of mating behavior in adult male ferrets.

The pulsatile secretion of androgen was similar over a 12-hr period in breeding male ferrets implanted with jugular catheters which either achieved an intromission with an estrous female or received no socio-sexual contact. This negative result contrasts with the previous demonstration (Carroll, Erskine, and Baum, 1987, Endocrinology 121, 1349-1359) of a significant, delayed rise in mean plasma androgen concentrations in breeding male ferrets 5-12 hr after mating. Males used in that previous study had lower initial mean plasma levels of androgen and smaller testis diameters than the present males. We therefore asked whether differences in circulating androgen levels, characteristic of males in different phases of the seasonal breeding cycle, might affect the expression of mating behavior. Castrated males given 0, 0.2, 2.0, or 5.0 mg/kg of testosterone propionate (TP) showed dose-related increases in the expression of different components of sexual behavior, including neck gripping, mounting, and intromitting. Surprisingly, intromissive performance was significantly better in intact breeding males than in castrates given even the highest dosage of TP. These results suggest that ferrets' mating performance may vary with seasonal variations in androgen availability, and that the ability of males to exhibit a postcoital increase in the testicular secretion of androgen may be limited to the beginning or end of the breeding season, when circulating levels of androgen are relatively low. Mating-induced increments in androgen secretion at these times may enhance subsequent reproductive success by facilitating males' intromissive capacity, which is required for the induction of ovulation and optimal sperm transport in female partners.

Animals↗
PubMed1990

Endocrine correlates of mating-induced reductions in estrous behaviour in an induced ovulator, the ferret.

Experiments were conducted to assess the time course of behavioral and endocrine changes which occur in female ferrets as they switch from estrus to the pseudopregnant state. Significant reductions in females' acceptance of neck gripping by a stimulus male (receptivity) and in their latency to approach a stimulus male in an L-maze (proceptivity) were first observed 3 days after receipt of an intromission; no such changes occurred in other females which were only neck gripped by stimulus males during the initial test session. Corpora lutea were later found only in the ovaries of females which received intromissions, confirming that ovulation had occurred in these animals. Plasma concentrations of prostaglandin E1, prostaglandin F2 alpha, and the 13,14-dihydro 15-keto metabolite of prostaglandin F2 alpha (PGFM) were unchanged in female ferrets for 4-5 days after receipt of an intromission. By contrast, plasma concentrations of progesterone were significantly elevated beginning 5 days after, whereas plasma estradiol was significantly reduced beginning 4 days after receipt of an intromission. Daily sc administration of the progesterone receptor antagonist. RU 38486, significantly retarded the lengthening in females' approach latencies to a stimulus male, suggesting that postcoital elevations in circulating progesterone normally contribute to the expected decline in proceptive responsiveness. By contrast, postcoital reductions in acceptance quotients occurred at equivalent rates in females treated with RU 38486 versus vehicle, leading us to infer that postcoital reductions in estrogenic stimulation may cause this decline in ferrets' receptive responsiveness.

Animals↗
PubMed1990

Comparison of two different arterial tissues suggests possible 5-hydroxytryptamine2 receptor heterogeneity.

A comparison of activities and affinities of several known and novel compounds in the isolated rat thoracic aorta (RA) and the rabbit femoral artery (RFA) was undertaken to evaluate these two tissues for use in screening for functional 5-hydroxytryptamine2 (5-HT2) receptor activity. Affinities for 5-HT and for ketanserin against 5-HT-elicited contractions in both vascular tissues suggested the presence of homogeneous 5-HT2 receptors with values consistent with other reported 5-HT2 receptor preparations. However, further studies showed compounds which exhibited either partial agonism in the RFA and competitive antagonism of 5-HT in the RA, or antagonism of 5-HT in both arteries with different affinities. Affinity constants calculated from the isolated vascular tissue studies were compared with affinity constants calculated for inhibition of [3H]ketanserin binding in the frontal cortices of both the rat and the rabbit. There were no significant differences between the pKi values in the rat and the rabbit cortical membranes or between these pKi's in either species and the pA2 values in the RA. Several of the affinities for both the partial agonists and the antagonists in the RFA were significantly different from the binding pKi and the pA2 values in the RA. These findings suggest identity between the [3H]ketanserin binding site in the cortices of both species and the 5-HT2 receptor in the RA; however, the contractile 5-HT receptor in the RFA, although showing some characteristics of a 5-HT2 receptor, is significantly different. We suggest that there may be functional subtypes of the vascular 5-HT receptor.

Animals↗