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PubMed2002

Cell migration and evolutionary significance of GnRH subtypes.

Hypothetically it can be assumed that in advanced teleost fishes, GnRH-III and GnRH-IV neurons migrate along the 'telencephalonic' (anterior) and 'diencephalonic' (posterior) migratory route, which perhaps fuses in primitive teleost fishes and land vertebrates to form the 'ancient migratory route' (in all probability = nervus terminalis; see Von Bartheld et al., 1988) of GnRH-I neurons. The difference in distribution pattern of GnRH forms in the vertebrate brain is due to distinct embryonic origins: (1) Cells of olfactory origin, which give rise to GnRH-I (salmon, catfish, chicken I, mammalian GnRH) are distributed along the olfactory system and the basal forebrain in primitive fishes and in land vertebrates; GnRH-I might be pivotal for LH/FSH synthesis-release, olfaction and metamorphosis in lower vertebrates. In advanced teleost fishes, neurons synthesizing GnRH-III ('salmon' GnRH) originate from the olfactory system; they are distributed along the basal olfactory bulbs, with distinct ganglia (NOR) at the caudalmost part of the olfactory bulbs and few scattered cells in the basal telencephalon. The NOR might function as a neuromodulator, hypophysiotropic hormone and regulate visual associated reproductive behaviors. (2) Cells of mesencephalonic origin, which give rise to GnRH-II (chicken-II GnRH) are evolutionarily conserved; might function as a neuromodulator involved in motor-associated reproductive behaviors and acid-base balance. (3) Cells of diencephalonic origin, which give rise to GnRH-IV (seabream, medaka GnRH); they are localized in the anterior-basal OVLT-POA area and present only in advanced teleost fishes. GnRH-IV has been implicated in gonadal sex differentiation, gonadal maturation, LH/FSH secretion and territorial behavior. Advance teleost fishes for yet unknown functions might have acquired GnRH-IV. Although all GnRH subtypes participate in some aspect of reproduction; the precise function of each GnRH form still remains unclear.

Animals↗
PubMedDate not supplied

[The reproductive characteristics of adolescents and young adults in Mexico City].

This article presents the preliminary findings of the Survey on Teenagers and Youth Reproductive Behavior in the Metropolitan Area of Mexico City, which contains information on 1,010 teenagers and young adults from 10 to 25 years of age interviewed in 1987. The average age was 17 years; 51.7 per cent of those interviewed were male and 48.3 per cent were female. A total of 14.6 per cent were married, being the average age at marriage 19.2 years for males and 17.8 years for females. Menarche occurred at an average age of 12.4 years, and spermarche at 14. Of those interviewed, 32.7 per cent have had sexual intercourse at least once in their lives. The average age at which sexual activity had begun, in the case of males, was 16 years and for females, 17 years. Of this group, 33.8 per cent stated that they had used some form of contraception during the first sexual intercourse; the contraceptive methods used most often were rhythm and withdrawal. The main source of supply of other methods is the pharmacy, in 67 per cent. 18.4 per cent of women had been pregnant, and 20.4 per cent of men's partners had presented this same condition. The first pregnancy occurred at 17.8 years for women and 18.7 for men. Of those men and women with a pregnancy experience 66.1 per cent and 57.3 per cent, respectively, stated that their first pregnancy was an unplanned one. Also, first pregnancy was related to their first marriage in 48.1 per cent of women and 82.4 per cent of male. The data presented here will reinforce current knowledge and will enable us to obtain a profile of the reproductive behavior of teenagers and young adults in the metropolitan area of Mexico City.

Adolescent↗
PubMed2003

Postnatal maturational changes in rat pelvic autonomic ganglion cells: a mixture of steroid-dependent and -independent effects.

Androgens have potent effects on the maturation and maintenance of a number of neural pathways involved in reproductive behaviors in males. Most studies in this area have focused on central pathways, but androgen receptors are expressed by many peripheral neurons innervating reproductive organs, and previous studies have demonstrated structural and chemical changes in these neurons at puberty and after castration. We have performed the first electrophysiological comparison of pelvic autonomic ganglion neurons in male rats before and after puberty and following pre- or postpubertal castration. Studies were performed in vitro on intact ganglia with hypogastric and pelvic nerves attached to allow synaptic activation of sympathetic or parasympathetic neurons, respectively. Pelvic ganglion neurons underwent many changes in their passive and active membrane properties over the pubertal period, and some of these changes were dependent on exposure to circulating androgens. The most pronounced steroid-dependent effects were on membrane capacitance (soma size) in sympathetic neurons and duration of the action potential afterhyperpolarization in tonic neurons. Our study also showed that rat pelvic ganglion cells and their synaptic inputs were more diverse than previously reported. In conclusion, this study demonstrated that rat pelvic ganglion neurons undergo considerable postnatal changes in their electrophysiological properties. The steroid dependence of some of these changes indicates that circulating androgens may influence reproductive behaviors at many locations within the nervous system not just in the brain and spinal cord.

Age Factors↗
PubMedDate not supplied

Age-period-cohort analysis of breast cancer mortality.

The objective of this study is to develop a hypothesis about the carcinogenesis of breast cancer from a descriptive analysis. This study is an application of the age-period-cohort model (APC model) on the mortality rate of breast cancer in Taiwan over the period from 1964 to 1991. Age-specific and age-adjusted mortality rates are described and then age, period, and cohort effects are separately analysed. (Female) breast cancer mortality data in Taiwan from 1964 to 1991 were abstracted from the annual reports of the Taiwan Provincial Department of Health. The population data in Taiwan from 1964 to 1991 were abstracted from the demographic data in Taiwan compiled by the Ministry of Interior, R.O.C. The results show that both age-adjusted and age-specific mortality rates of breast cancer are increasing over the study period and with birth cohorts. The bimodal pattern becomes more apparent in later periods. The Clemmensen's hook is five years later both in the descriptive study and the APC analysis. The findings suggest a possible role of later life overnutrition as the major period effed (promoter) and a change in reproductive behavior as the cohort effect (initiator). The application of the APC model also denotes the possible role of later life overnutrition and a change in reproductive behavior after the birth cohort of 1929. These findings may help us develop hypotheses of carcinogenesis of breast cancer.

Adult↗
PubMed1986

Reproduction in the Mexican leaf frog, Pachymedusa dacnicolor. II. The male.

The Mexican leaf frog, Pachymedusa dacnicolor, an inhabitant of the semiarid, subtropical Mexican lowlands, displays a well-defined seasonal testicular cycle. Testis weight seems to be a reliable index of the reproductive status of the animal and plasma levels of androgens (testosterone, T; 5 alpha-dihydrotestosterone, DHT; androstenedione, A) correlate not only with testicular growth, but with callosity development, reproductive behavior, and breeding. During the fall and winter, testis weight reaches its minimum as do plasma concentrations of T, DHT, A, and estradiol-17 beta (E). Plasma levels of progesterone (P) are maintained at a very low level throughout the year. During the fall and winter, spermatogenesis is almost entirely absent and the callosities are white and smooth. No signs of reproductive behavior (calling and amplexus) are evident. Late spring marks the initiation of spermatogenesis, testis weight increase, darkening of callosities, and increase in plasma levels of androgens. The magnitude of callosity development and the onset of calling and amplectant behavior are correlated with a great rise in plasma androgen levels. Although plasma T concentrations were higher than plasma levels of DHT and A, this androgen failed to stimulate the development of callosities and calling behavior in successfully castrated males.

Androgens↗
PubMed1996

Responses of medullary reticular formation neurons to input from the male genitalia.

1. The medullary reticular formation (MRF) is known to be involved in the modulation of certain reproductive behaviors. Ejaculation in the male, disrupted after spinal transection, may depend on a spinal-bulbo-spinal connection. To determine whether single neurons in the MRF receive sensory input from the male genitalia, the present study was undertaken using electrophysiological techniques. 2. The MRF of 14 urethan-anesthetized mature male rats was searched for single neurons responsive to bilateral electrical stimulation of the dorsal nerve of the penis (DNP). In addition, each DNP-responsive neuron was tested for responsiveness to bilateral electrical stimulation of the pelvic nerve (PN) and to mechanical stimulation (gentle touch, pressure, pinch) of the external genitalia, anus, urethra, and skin over most regions of the body. 3. A total of 165 single neurons responsive to bilateral electrical stimulation of the DNP were isolated and characterized throughout the MRF. All neurons responded to both ipsilateral and contralateral DNP stimulation. The majority of responses were excitatory, and most neurons had no background activity. Some neurons required wind-up with bilateral electrical stimulation of the DNP to respond. 4. About half of the neurons were located in the nucleus reticularis gigantocellularis (Gi); the remainder were located in surrounding (dorsal, ventral, lateral) regions of the MRF. Variations in response properties were found among neurons located in different MRF regions. 5. Eighty-eight DNP-responsive neurons were additionally responsive to bilateral electrical stimulation of the PN. None of the responses to bilateral PN were stronger than those for bilateral DNP and many (48%) were weaker. 6. Of the 165 DNP-responsive neurons, all were responsive to pressure/pinching of the penis; 16% responded to gentle stroking of the glans. Most of these neurons were additionally responsive (bilaterally) to pinching more than one (often all) of the following areas: perineum, scrotum, anus, ears, and toes (forefoot and hindfoot). 7. In conclusion, neurons located in the MRF of male rats are involved in the processing of bilaterally convergent inputs from multiple cutaneous and visceral regions of the body, including the penis and male urogenital tract. These neurons likely exert their effects by directly and/or indirectly activating ascending pathways to rostral regions of the brain important for somatovisceral sensation and motor behavior, and descending pathways to the spinal cord for modulation of segmental sexual reflexes. Contributions are likely for a wide spectrum of sensations and reproductive behaviors.

Animals↗
PubMed1995

Pregnancy experience after delivery of a child with a major birth defect: a population study.

OBJECTIVE: Data from a large population-based, case-control study were analyzed to determine whether women giving birth to children with major birth defects have different subsequent pregnancy patterns than those giving birth to live-born babies without defects. Other studies examining this phenomenon have been smaller, have not been population-based, or have not addressed the different effects that a wide range of major defects might have on mothers' subsequent pregnancy rates. METHODS: Mothers of 4918 infants with major birth defects born from 1968 through 1980 in metropolitan Atlanta were compared with mothers of 3029 control infants, frequency-matched on birth year, birth hospital, and race. RESULTS: The pregnancy rate in the first 3 years after the index birth was higher among case mothers (36%) than among control mothers (30%, P < .0001). This excess was seen for mothers of stillborn case infants (64%) and mothers of case infants who survived the first year of life (31%). Pregnancy rates varied by birth defect type. Maternal and infant factors varied among case and control subjects and influenced subsequent pregnancy rates. CONCLUSION: The reproductive behavior observed in this study supports the theory that mothers of nonsurviving children with birth defects compensate by acting to "replace" the lost child. Reproductive behavior was also strongly associated with having completed a previous pregnancy and by the type of birth defect.

Case-Control Studies↗
PubMed1986

Cholinergic limbic projections and behavioral role of basal forebrain nuclei in the rat.

The purposes of the present study were to identify cholinergic non-neocortical projections of the basal forebrain and to determine the role of this region in the regulation of estrogen-dependent reproductive behaviors in the rat. Bilateral electrolytic lesions were placed in an area encompassing the horizontal limb of the diagonal band, as well as portions of the substantia innominata and magnocellular preoptic nucleus, and choline acetyltransferase (CAT) activity was assayed in microdissected brain areas seven days after lesion. Compared to sham surgery, lesions of this region significantly reduced CAT activity in the basal amygdala (34%), dorsal hippocampus (14%), cingulate cortex (25%), piriform cortex (36%), and entorhinal cortex (34%). Other limbic and midbrain structures do not appear to receive significant cholinergic innervation from this locus since no reductions in CAT were detected after bilateral lesions. These included the anterior hypothalamus, ventromedial hypothalamus, mammillary nucleus, habenula, subiculum, ventral hippocampus, insular cortex, central gray, and interpeduncular nucleus. Behaviorally, female rats with bilateral lesions of the basal forebrain displayed an unusually high incidence of rejection behavior in response to attempted mounts by stimulus male rats in sexual behavior tests. There was no effect of basal forebrain lesions on the incidence of lordosis exhibited by these females. The dissociation of rejection and lordosis suggests that distinct neural pathways mediate the occurrence of these reproductive behaviors and that rejection behavior may be regulated by basal forebrain pathways.

Animals↗
PubMed2002

Puberty and the maturation of the male brain and sexual behavior: recasting a behavioral potential.

The pubertal transition from the juvenile to adult state requires significant changes in behavior to meet the demands for success and survival in adulthood. These behavioral changes during puberty must be mediated by changes in the structure and/or function of the central nervous system. Despite the profound consequences of puberty on an animal's behavioral repertoire, the mechanisms underlying pubertal maturation of the nervous system remain largely unknown. In this review, we provide a synthesis of neural development during puberty as it relates to maturation of male reproductive behavior. We first outline neuroendocrine events associated with puberty and review work from our laboratory that identifies pubertal changes in the neural substrate controlling male reproduction by comparing the neural responses of prepubertal and adult males to steroids and female chemosensory cues. We then raise the question of whether puberty is a sensitive period in which gonadal hormones influence the structural and functional organization of neural circuits underlying male reproductive behavior. The central thesis of this review is that the development of the nervous system during puberty alters the way in which the male responds to social stimuli, involving the restructuring of neural circuits that integrate steroidal and sensory information and ultimately mediate steroid-dependent social behaviors in adulthood.

Androgens↗
PubMed1996

[Reproductive history of Chilean puerperal women hospitalized in a public hospital of the metropolitan region].

BACKGROUND: Maternal and infantile morbidity is closely related to the features of women's reproductive history. AIM: To study the reproductive behavior of women hospitalized due to labor or abortion in a public maternity of Metropolitan Santiago. SUBJECTS AND METHODS: One thousand women were interviewed about their reproductive behavior, 24 to 72 hours after pregnancy resolution. RESULTS: Ages of interviewed women ranged from 13 to 47 years old. Eighty seven percent had three children or less. The proportion of single women with a first pregnancy was 62% and decreased to 9.3% in those with a second pregnancy. At the first pregnancy, 1.3% of women were using contraceptives, notwithstanding that 27% did not want to become pregnant. Most women had a birth spacing of 24 to 59 months. There was a low number of stillbirths in this sample. CONCLUSIONS: This work shows that studied women have pregnancies at low risk ages and an adequate parity.

Adolescent↗
PubMed1995

Commentary on effects of anthropogenic and natural organic chemicals on development, swimming behavior, and reproduction of Daphnia, a key member of aquatic ecosystems.

Because of their trophodynamic role, small invertebrates are often critical components of ecosystems. An especially important group of freshwater invertebrates is the water fleas of the genus Daphnia. These animals are often the dominant herbivores in lakes and ponds. They play a key role in determining water clarity (by grazing on algae) and they are an important part of the diet of fish. Natural chemical signals (kairomones) produced by predators affect the development, life history strategy, and behavior of zooplankton. Laboratory studies of anthropogenic chemicals that have biological activity (xenobiotics), such as the insecticide carbaryl, have demonstrated effects of concentrations in the 1 to 5 ppb range on Daphnia development, growth rate, and swimming behavior in our laboratory experiments. Low concentrations of carbaryl inhibit growth and reproduction and delay maturation, whereas survivorship was not effected. These sublethal exposures to carbaryl reduced Daphnia population growth rate (productivity) by about 15% (at 5 ppb), enough to have significant ecological effects on the rest of the lake community. The insecticide carbaryl showed synergistic interactions with natural chemicals associated with predators (kairomones) that modify Daphnia development and life history characteristic. In addition, there were complex synergisms between carbaryl, the predator odors, and oxygen concentration (low oxygen concentration can be either a natural environmental stress or an anthropogenic stress). Daphnia produce males facultatively, usually in late fall; at other times, reproduction is asexual.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

A risk assessment for lead in birds.

Ecotoxicologists and ecologists have examined the effects of pollutants on individuals and populations largely in terms of one or only a few effects. Yet the recent trend toward a holistic approach to ecological risk assessment suggests that a rigorous paradigm should be applied to toxicants, from hazard identification to risk characterization. Recent discussions have recognized that an up-front problem formulation phase is more critical in ecological risk assessment than it is for human health risk assessment. In this article a modified environmental health risk assessment paradigm is used to examine the risk of lead to birds. This risk analysis is largely conceptual, based on laboratory and field data, and incorporates information currently available. The model expands the hazard identification phase to create a target identification phase that includes the identification of receptors, endpoints, relationships, spatial and temporal scales, and indicators. The target identification phase is unique to the particular hazard, species, population, or community being examined. Lead can cause mortality, or can indirectly affect populations through effects on the food base, avian behavior, reproductive success, and recruitment. Lead can (1) decrease the abundance and availability of prey, (2) bioaccumulate in prey causing increased lead toxicosis in predators, or (3) increase prey availability by interfering with its hiding or escape behavior. Moreover, lower abundance of prey can lead to starvation or nutrient deficiencies, which amplify the absorption and retention of lead. Lead also causes decreases in clutch and egg size, mortality of embryos and nestlings, depression of growth, and deficits in behavior that affect survival. Lead decreases migratory behavior, and increases vulnerability to cold stress, hunters, and other predators. Research needs for evaluating the risk of lead in birds include obtaining data on (1) metal dynamics within various tissues as a function of dose and time since initial exposure, (2) low-level effects on embryos, (3) effects on chicks following fledging and in the period prior to recruitment, (4) effects on adult foraging skills and reproductive behavior, and (5) the relationship between effects from exposure in the laboratory and those from exposure in the wild. This latter point is extremely important, particularly if wild birds have other means of ridding the body of lead not available or less apparent to laboratory birds.

Animals↗
PubMed2001

Co-expression of estrogen and thyroid hormone receptors in individual hypothalamic neurons.

Estrogen receptors (ER) and thyroid hormone receptors (TR) are members of the nuclear receptor family of transcription factors that induce or repress the expression of target genes. Previous behavioral studies in female rodents have demonstrated that thyroid hormones can antagonize the effects of estrogen in the central nervous system (CNS), particularly by attenuating estrogen's ability to facilitate reproductive behaviors. Additional molecular studies have suggested a mechanism for this antagonism by showing that ligand-activated ER alpha and TRs have the potential to interact in their transcriptional controls. Although the expression patterns of ER alpha and TRs in the rodent brain appear to overlap in behaviorally relevant areas, it remained to be determined whether these two classes of proteins coexist in vivo at the level of single neurons. To address this possibility, we employed a highly sensitive double-label in situ hybridization technique using digoxigenin and (35)S-labeled cRNA probes to analyze, in detail, the expression of ER alpha mRNA with TR alpha 1 and TR alpha 2 mRNAs in the same neurons of the ovariectomized (OVX) adult mouse brain. Our results demonstrate that a large majority of the ER alpha-positive neurons also expresses TR alpha 1 and TR alpha 2 mRNAs. Quantitative examination of the cellular expression in the ventromedial and arcuate nuclei of the hypothalamus (VMH and Arc) showed that 81.5% and 80.5% of the neurons endowed with ER alpha mRNA also contain TR alpha 1 and TR alpha 2 mRNAs, respectively. In the amygdala, more than 60.5% and 67% of ER alpha-positive cells also contain TR alpha 1 and TR alpha 2 mRNAs, respectively. These findings provide the first anatomical evidence that ER and TR can be found in the same neurons, including hypothalamic neurons. This coexpression of ER alpha and TR provides the cellular basis for a new level of neuronal integration in a brain region where estrogens control female reproductive behaviors.

Amygdala↗
PubMed1998

Ejaculatory abnormalities in mice with targeted disruption of the gene for heme oxygenase-2.

Nitric oxide (NO) is well established as a neurotransmitter in the central and peripheral nervous systems. More recently, another gas, carbon monoxide (CO) has also been implicated in neurotransmission. In the nervous system CO is formed by a subtype of heme oxygenase (HO) designated HO2. HO2 is localized to discrete neuronal populations in the brain resembling localizations of soluble guanylyl cyclase, which is activated by CO. CO may also function in the peripheral autonomic nervous system, in conjunction with NO. The majority of ganglia in the myenteric plexus possess both HO2 and neuronal NO synthase (NOS). Defects in myenteric plexus neurotransmission occur both in mice with targeted deletion of genes for HO2 and neuronal NOS. HO2 also occurs in other autonomic ganglia including the petrosal, superior cervical and nodose ganglia. Neuronal NOS is localized to neurons regulating male reproductive behavior, such as penile erection, and NOS inhibitors prevent erection. Because of the other parallels between NO and CO, we speculated that CO may play a role in male reproductive behavior. In the present study we describe HO2 localization in neuronal structures regulating copulatory reflexes. Reflex activity of the bulbospongiosus muscle, which mediates ejaculation and ejaculatory behavior, is markedly diminished in mice with targeted deletion of the gene for HO2 (HO2-).

Animals↗
PubMed2002

Effects of housing type and breeding system on the reproductive capacity of the red-legged partridge (Alectoris rufa).

Current methods of intensive breeding of the red-legged partridge (Alectoris rufa) are based on "industrial" laying practices, including removal and artificial incubation of eggs. These procedures can alter the reproductive behavior and physiology of the birds and, therefore, may not be suitable for use in breeding programs designed to increase wild populations. This study aimed to determine the effects of intensive housing and breeding methods on the laying capacity and reproductive behavior of the red-legged partridge. In Experiment 1, 70 pairs from a commercial game farm were randomly allocated into three treatment groups and placed in differing designs of breeding cages: 8 m2 cages with solid sides (n = 30), 4 m2 cages with solid sides (n = 30), and 4 m2 cages with mesh sides (n = 10). The number of eggs laid was recorded each week. In Experiment 2, 30 pairs, placed in 30 closed 8 m2 cages, were used. Fifteen pairs were birds reared under the intensive system used on game farms, and the other 15 pairs were birds adopted by pairs of foster parents when they were less than 48 h old. The total number of eggs laid during the reproductive period was recorded. In Experiment 1, egg production was greater in pairs housed in 8 m2 cages. There were no differences in egg production between birds housed in closed or open 4 m2 cages. In Experiment 2, the rearing method did not affect egg production. In both experiments, regardless of rearing history or cage type, the numbers of eggs laid were considerably higher than published figures for wild red-legged partridges. This fact, together with the absence of incubation by 100% of the females, indicates the considerable physiological and behavioral modifications that red-legged partridges have undergone due to domestication.

Animals↗
PubMed1990

Effects of the organophosphorus pesticide fenitrothion on behavior and reproduction in zebra finches.

Activity was significantly altered in zebra finch pairs orally dosed with fenitrothion insecticide at rates of 1.04 and 3.80 mg/kg. Both the level and the dirunal pattern of activity were affected. Recovery of normal activity required 1-2 days, depending on the dosage administered. Fenitrothion had only a slight effect on reproduction when parents were dosed at the egg-laying stage of the breeding cycle. The implications of these results for the interpretation of field monitoring studies are discussed.

Analysis of Variance↗