Biomedical subjects

J Terkel

Publications and source records attributed to J Terkel.

At least 37 records · Page 2Linked to original sources

PubMed1990

Evidence for "memory" of cervical stimulation for the promotion of pregnancy in rats.

Successful pregnancy in the female rat depends upon two sets of physiological events: (1) transport of gametes (sperm and egg) through the reproductive tract so that fertilization can be effected and (2) establishment of an appropriate hormonal environment (progestational state) so that the fertilized egg can implant in the uterus and be maintained during subsequent gestation. This study highlights the independence of the mechanisms controlling the gametic and hormonal aspects of pregnancy by temporally separating the introduction of sperm into the female from the stimulation that triggers the progestational hormonal response. The progestational state was initiated by electrical stimulation of the cervix, and sperm was introduced directly into the uterus by artificial insemination. Although these two events were separated by up to 3 days, pregnancy could ensue. Cervical stimulation, normally a consequence of male intromission behavior, establishes a condition in the central nervous system, a "memory" that signals the probable induction of pregnancy. Without this "memory," animals with a short estrous cycle would continue to cycle after mating, thereby producing a hormonal environment incompatible with implantation. The "memory" is manifested by daily surges of prolactin irrespective of fertilization. This is the first physiological demonstration that a "memory" of cervical stimulation can be called upon to support a viable pregnancy.

Animals↗

PubMed1990

Hypothalamic neuronal activity associated with onset of pseudopregnancy in the rat.

The electrical activity of several hypothalamic sites, before and following cervical stimulation, was examined in an attempt to evaluate the central nervous system processes involved in the induction of pseudopregnancy in the rat. Cervical stimulation, resulting in pseudopregnancy, induced a sequence of neuronal changes at: 3.8, 4.4, 11.6, 20.1, 30.8, 44.5, 51.2, 51.7, 62.4, 85.1 and 111.5 min after stimulation in the preoptic area, lateral hypothalamus, ventromedial hypothalamus, preoptic area, suprachiasmatic nucleus, lateral hypothalamus, preoptic area, ventromedial hypothalamus, lateral hypothalamus and anterior hypothalamus, respectively. These results suggest that the preoptic region contains both the facilitatory neuronal mechanism and also an inhibitory system. The latter could tonically inhibit the expression of the nocturnal prolactin surge. We conclude that the sequence of neuronal events observed in various hypothalamic areas is in part responsible for the process which results in pseudopregnancy.

Animals↗

PubMed1989

Are seismic communication signals transmitted by bone conduction in the blind mole rat?

The anatomy of the middle ear of the blind mole rat, a subterranean rodent that uses seismic signals for long distance communication, is described qualitatively and quantitatively. The ossicular chain is of the parallel type with a lever arms ratio of 0.55 and an effective areal ratio of stapedial footplate to eardrum of 0.09. Assuming an ideal mechanical transform, the calculated fraction of acoustical energy theoretically transmitted to the cochlea, indicate low efficiency for airborne sounds. This is in accordance with the relatively high electrophysiological and behavioral threshold, shown previously. We suggest that a unique morphology of the middle ear and of the articulation between the lower jaw and the skull, as well as a peculiar 'jaw listening behavior' enable seismic vibrations to be transmitted to the inner ear mainly by bone conduction, thereby compensating for the limitation in receiving airborne signals.

Animals↗

PubMed1989

Abortifacient potential for the epigeal parts of Peganum harmala.

The effect of methanol and acetone extracts of the epigeal parts of Peganum harmala, a common medicinal plant among Bedouins in Israel, was studied on several parameters of reproduction in female rats. The methanol extract at a dose of 2.5 g/kg/day, offered in food or in drinking suspension for 30 days, significantly prolonged diestrus by 1.0 day. The methanol extracts at doses of 2.0, 2.5 and 3.5 g/kg/day appeared to produce a dose-dependent significant decrease in litter size. No change in the physical and nutritional status of the animals and no adverse toxicological effects were observed.

Abortifacient Agents↗

PubMed1988

Neuroendocrine processes in the establishment of pregnancy and pseudopregnancy in rats.

Rats, like mice, hamsters and other small rodents, have a short, incomplete estrous cycle. They lack a spontaneous luteal phase, and the corpora lutea (CL) of the estrous cycle are short-lived and nonfunctional. The activation of the luteal phase in these incompletely cycling females depends on the neuroendocrine reflex provided by the male at the time of mating. In this article we review our research on the cervix-brain-pituitary-ovary interaction at the endocrine, neuroendocrine, neurotransmitter and behavioural levels, dealing with the chain of events initiated by the male and necessary for the establishment of the progestational state.

Animals↗

PubMed1986

Nocturnal surges and reflexive release of prolactin in parentally behaving virgin female and male rats.

Maternally behaving virgin rats are capable of releasing prolactin reflexively in response to stimulation by pups, especially during the proestrous/estrous phase of the cycle. When such rats are chronically exposed to pups they usually undergo a state of pseudopregnancy during which prolactin is secreted in a pattern of nocturnal surges. The present series of experiments evaluated the initiation of nocturnal prolactin surges in maternally behaving virgins, the role of estrogen in the reflexive release of prolactin, and the influence of gender on these two modes of prolactin secretion. It was found that the nocturnal surges of prolactin are already present on Days 1 and 2 of pup-induced pseudopregnancy. At this stage, however, the surges are not yet autonomous, seeing that pseudopregnancy is interrupted shortly after removal of the pups on Day 2. Activation by vaginocervical stimulation of the "mnemonic" neurogenic system that controls the autonomous nocturnal prolactin surges did not interfere with the reflexive pup-induced release of prolactin in maternally behaving virgins. The capacity of reflexive prolactin release in the virgin rat was abolished by ovariectomy, restored by estrogen replacement, and persisted for only 24 hr following estrogen removal. Paternally behaving males subjected to chronic exposure to pups were incapable of secreting nocturnal surges of prolactin characteristic of the pseudopregnant female. Such males were also incapable of releasing prolactin reflexively in response to stimulation by pups, even when supplemented with exogenous estrogen. These results indicate that the two modes of prolactin secretion are sex dependent, and that the maternally behaving virgin, unlike the postpartum rat, requires concurrent estrogenic facilitation for releasing prolactin in response to stimulation by young.

Animals↗

PubMed1986

Lactational performance, consummatory behavior, and suppression of estrous cyclicity in rats suckling underfed pups.

The role of pups' appetite in the regulation of maternal consummatory behavior (food intake of nursing mothers), lactational performance and postpartum diestrus was studied over a period of 45 days postpartum in rats chronically exposed to either underfed or normally fed pups. Experimental rats (n = 10) daily received 5 pups, 4-10-days-old, that had been deprived of food for the preceding 24 h while under the care of nonlactating foster mothers. Control rats (n = 10) received normally fed pups obtained daily from lactating foster mothers. Throughout the experimental period, the daily milk yield (estimated by litter weight gain), the intake of food and water by the mother, as well as the ratio of litter weight gain to mother's intake of food and water were all markedly higher in rats nursing underfed pups than in rats nursing normally fed pups. After a peak in lactation around Day 15 postpartum, experimental rats produced the same amount of milk during extended lactation as they did in the beginning of lactation, while control rats produced only half the amount of milk during extended lactation as they did in early lactation. Regardless of the nutritional state of the suckling pups, maternal body weight increased progressively over the first four weeks of lactation and remained unchanged during the time of extended lactation. The postpartum diestrus and the subsequent diestrous phase in the time of extended lactation were considerably longer in duration in rats that nursed underfed pups. On Day 45 of lactation, prolactin levels were higher and the adrenal glands were larger in experimental rats than in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Neuroendocrinology of coitally and noncoitally induced pseudopregnancy.

In this paper, I have outlined our research perspective on coitally and noncoitally induced PSP. Coitally induced PSP requires a minimal threshold of vaginal stimulation to establish the repetitive nocturnal PRL surges which are essential for converting the corpora lutea from a nonfunctional to a functional state. The induction of PSP requires the activation of the adrenergic system and simultaneous inhibition of the cholinergic system. Reduction of neural activity in the medial preoptic area occurs at the time of coital stimulation, and is believed to be associated with the initiation of the nocturnal PRL surges. Apparently, cervical stimulation acts by inhibiting the nocturnal PRL surge inhibitory neurons at this brain site, thereby instituting PSP. It is proposed that the specific mating pattern of cervical stimulation activates a "mnemonic system" which retains information from vaginocervical stimulation permitting the expression of the repeated nightly PRL surges. In our view, each pregnancy originates as a direct continuation of the initial "hypothalamic PSP" triggered by the neural signal of mating. The mechanisms involved in the activation of the "mnemonic system" and the hypothalamically pseudopregnant state remain to be elucidated. Pseudopregnancy can be initiated by a number of socioenvironmental factors as well, such as cohabitation in all-female groups in mice or concaveation with foster pups in virgin rats. However, unlike coitally induced PSP which activates the "mnemonic system," noncoitally induced pseudopregnancies lack a "mnemonic system," and therefore require the continued presence of the initiating stimulus until progesterone levels become sufficiently elevated to provide positive feedback on PRL secretion.

Animals↗

PubMed1986

Female reproductive function and sexually dimorphic prolactin secretion in rats with lesions in the medial preoptic-anterior hypothalamic continuum.

The role played by the medial preoptic area-anterior hypothalamus (MPOA-AH) in the regulation of reproductive function of the female rat was examined in the first part of the present study. Extensive bilateral lesions placed in different locations of the MPOA-AH continuum resulted in three different patterns of vaginal smears. Lesions located most rostrally and dorsally, sparing the suprachiasmatic nuclei (SCN), resulted in series of successive pseudopregnancies. Lesions located more caudally and ventrally, still sparing the SCN, eventuated in regular oestrus cycles with only occasional pseudopregnancies. MPOA-AH lesions encroaching upon the SCN were associated with persistent vaginal cornification. MPOA-AH-lesioned females exhibiting repeated pseudopregnancies were capable of mating, conceiving, and giving birth. Parturition in these females was uniformly delayed by 1 day and was associated with a variable incidence of stillbirth, cannibalism of newborn, or incomplete placentophagy. As a rule, MPOA-lesioned mothers did not retrieve pups but they did show crouching behaviour and some of them even secreted milk. Thus, while the MPOA subserves in the regulation of oestrous cyclicity and maternal behaviour, it appears to play no essential role in mating behaviour or in ovarian function during pregnancy and lactation. The pattern of prolactin secretion in MPOA-AH-lesioned male and female rats was evaluated in the second part of this study. Both intact and orchidectomized males were incapable of generating nocturnal prolactin surges following extensive bilateral ablation of the MPOA-AH. On the other hand, 6 out of 9 ovariectomized MPOA-AH-lesioned females exhibited spontaneous nightly surges of prolactin. The absence of the surges in the remaining 3 females was associated with invasion of the lesion into the SCN and/or structures rostral to the MPOA. During the light period, prolactin levels remained within the basal range in all lesioned females, irrespective of the presence or the absence of the nocturnal surge. These lesioned ovariectomized females, in contrast to nonlesioned females, were incapable of producing a diurnal (afternoon) surge of prolactin in response to administration of oestrogen, though their basal prolactin levels were much higher than the levels seen in oestrogen-treated, nonlesioned castrated males. These results support the view that the MPOA is inhibitory to the nocturnal prolactin surge while stimulatory to the diurnal surge. The results also suggest that the male rat is functionally devoid of both a 'diurnal-surge centre' residing in the MPOA, and a 'nocturnal-surge centre' located outside the MPOA.

Animals↗

PubMed1986

Prolactin release and milk ejection in rats suckling underfed pups.

Mother rats chronically exposed to underfed pups (obtained daily from nonlactating mothers) show increased milk production which is associated with increased consumption of food and water. The purpose of the present study was 2-fold: to examine whether the magnitude of maternal PRL discharge is related to the nutritional state of the pups and to differentiate between the role of the mother and that of the pups themselves in the regulation of milk intake. PRL release in response to reunion with pups (preceded by 4-h separation from pups) was measured between days 12 and 14 postpartum; each mother was tested twice, once with hungry pups (deprived of food for 24 h) and once with satiated (normally fed) pups. The magnitude of PRL discharge elicited by hungry pups in lactating as well as in thelectomized rats was twice as large as the discharge elicited by satiated pups. For each type of stimulus pups, the magnitude of PRL release was smallest in thelectomized rats, largest in rats that had nursed normally fed pups before testing, and intermediate in rats that had nursed underfed pups. The frequency of milk ejection was considerably reduced in mothers that were chronically exposed to underfed pups compared with mothers that had nursed normally fed pups. Regardless of the mother's previous history, and independent of the milk ejection frequency or maternal food and water intake, hungry pups ingested more milk than did satiated pups over the same suckling period even when both types of pups were suckled simultaneously by the same female. Milk ingestion in satiated pups was not enhanced by the vigorous sucking exerted by hungry littermates. It is suggested that hungry pups are able to meet their increased nutritional demands both directly, by withdrawing a larger portion of the milk available in the mammary glands, and indirectly, by enhancing maternal PRL secretion which in turn may promote maternal consummatory behavior and milk production.

Animal Population Groups↗

PubMed1985

Home odor preferences in young hares (Lepus capensis syriacus): effects of age and role of maternal presence.

The odor preferences of mother-reared and hand-reared young hares between 1-30 days of age were studied. Subjects were exposed daily to three choice tests in which the following pairs of odors were presented: home cage odor (HCO)-neutral odor (NO); HCO-strange cage odor (SCO); SCO-NO. All young strongly preferred their HCO over SCO throughout the 30-day period. HCO was preferred over NO until the age of 20 days, while avoidance of SCO was shown during the first 10 or 20 days. The same experiment conducted on postweaned hares (31-50 days of age) revealed a strong preference for SCO over both HCO and NO. These findings may be interpreted with respect to the natural history of the hare and its unusual mother-young relationship, which, in the wild, is limited to a single daily meeting for nursing. It is suggested that the highly precocial hare recognizes and prefers its home odor independently of any maternal contribution to that odor, possibly relying on odor cues from its own body to return to its nursing site. Other possible advantages of these olfactory preferences, including predation avoidance and facilitation of social relationships, are discussed.

Animals↗

PubMed1985

Transition from pup killing to parental behavior in male and virgin female albino rats.

In the first part of this study, the effect of habituation to pups was examined in virgin female and male Sprague-Dawley rats that committed infanticide in a screening test. With repeated exposure to test pups (5-10 days old), the rats ceased to commit infanticide and came to behave parentally. Preexposure to inaccessible pups (confined inside wire-mesh baskets) did not accelerate the rate of disappearance of infanticide during subsequent contact with young, which suggests that pup killing is not a neophobic response to the novelty of young. In the second part of the study, three groups of infanticidal male Wistar rats were mated and tested for their responses towards unrelated pups after different intervals of cohabitation with their mates. The males continued to commit infanticide at the time that their mates were at midpregnancy or 24 hr before parturition, but males that cohabited with their mates till day 9 postpartum no longer attacked the young. Thus, the mother rat, presumably by means of postpartum aggression, renders her mate noninfanticidal, thereby reducing the likelihood of her offspring being harmed when she is away from the nest.

Aggression↗

PubMed1985

Role of nipple stimulation in the suppression of estrous cyclicity during extended lactation in the rat.

The role of nipple stimulation in the suppression of the estrous cycle during extended lactation was studied in rats subjected to either total, partial, or sham excision of the nipples. Each female cohabited with 4 pups, 4-14 days old, over a period of 70 days postpartum, during which vaginal smears were recorded daily. Initially, regardless of the presence of nipples, all rats exhibited a postpartum diestrus that lasted for 12-20 days. Intact females (bearing 6 pairs of nipples) continued to exhibit successive prolonged diestrous phases over 70 days of lactation. A comparable result was obtained with females bearing only the anterior pair of nipples, which, in a separate experiment, was found to be the most frequently suckled pair. However, females devoid of nipples resumed regular (4-day) estrous cycles between Days 12 and 27 postpartum, in spite of their continuous contact with pups. Thus, when lactation is prolonged beyond the normal time of weaning (Day 21 postpartum), stimulation of the nipples by sucking becomes indispensable for the continued arrest of the estrous cycle. The possible mechanisms underlying this phenomenon are discussed.

Animals↗

PubMed1985

Components of the rat conceptus that account for prolactin inhibition.

The secretions from developed concepti in the rat appear to inhibit both the rhythmic nocturnal secretion of prolactin (Prl) during the second half of pregnancy and the neurally mediated Prl release in response to suckling stimulation. In order to identify the parts of the concepti capable of inhibiting Prl secretion, the components of the concepti were systematically removed and their effect on plasma Prl levels was examined. In the first experiment, female rats which were simultaneously pregnant and lactating were tested for Prl secretion in response to suckling stimulation after one of the following treatments: 1) removal of the foetuses only, 2) removal of the foetuses and trophoblasts, 3) removal of the complete concepti. In the second experiment, pregnant rats were tested for the presence of nocturnal Prl surges after either removal of the foetuses and trophoblasts or removal of the entire concepti. The results indicate that after removal of the foetuses alone, the inhibition of Prl secretion remains. Following removal of both the foetus and the trophoblast, leaving the decidua in situ with a supplementary progesterone implant, the decidua still retain a partial capacity to inhibit Prl secretion in response to suckling stimulation, while their inhibitory effect on the nocturnal Prl surges was very minute. Degeneration of the decidua occurred following the removal of the trophoblast, when no exogenous progesterone was supplied. The deterioration of the decidua or total removal of the concepti eliminates the entire inhibition of Prl secretion, both on the nocturnal surges as well as in response to suckling stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Incidence of pup killing and parental behavior in virgin female and male rats (Rattus norvegicus): differences between Wistar and Sprague-Dawley stocks.

The responses toward young shown by males and nulliparous females differed substantially between two outbred stocks of laboratory rats. Sprague-Dawley females showed maternal behavior either spontaneously (35% of the naive rats) or through concaveation (92% of the initially neutral virgins). Of the Wistar females, however, only 10% showed maternal behavior spontaneously, and only 29% of the neutral virgins came to behave maternally during 15 days of concaveation. Prepubertal cohabitation with lactating rats did not facilitate maternal responsiveness in adulthood in the Wistar virgin females. Of the Sprague-Dawley males, 50% showed paternal behavior spontaneously, and only 4% killed the young. Among the Wistar males, however, only 4% showed paternal behavior spontaneously, and 76% killed pups. Such profound differences between outbred stocks of rats may be a source of discrepancies between the results of studies dealing with the induction of parental behavior in nonlactating rats.

Aggression↗

PubMed1985

Effect of postweaning social experience on response of Siberian hamsters (Phodopus sungorus sungorus) toward young.

Between 18 and 50 days of age, Siberian hamsters were housed either with same-sex littermates, opposite-sex littermates, opposite-sex littermates and parents, or opposite-sex littermates, parents, and a younger litter. When adults, these animals were presented with two 3-8-day-old pups for 8 hr, and their responses were recorded. Rearing conditions did not affect behavior of females. Males housed with female littermates in the absence of a younger litter showed fewer pup attacks and more nesting with pups than did males housed only with other males. Thus, housing with females in the early postweaning period may influence males' later (adult) responses toward pups. Only among hamsters housed with same-sex littermates did males and females differ in their response to pups, a result emphasizing that sex differences in behavior may depend on early social rearing.

Animals↗

PubMed1984

The effect of Aroclor 1254 (PCB) on the physiology of reproduction in the female rat--I.

Daily oral exposure of rats to 30 mg/kg of Aroclor 1254 for 1 month caused deleterious effects on the reproductive process, which were reflected in a decrease in the reproductive potential. The following disturbances were observed: prolongation of the estrous cycle; decrease in sexual receptivity; delay in timing of copulation; vaginal bleeding during gestation; decrease in litter size and delay in the time of parturition. The offspring, whether exposed to PCBs either prenatally and/or postnatally, showed a slower rate of body weight gain than controls. This was accompanied by high mortality until weaning of treated pups. Vaginal opening in the PCB-treated (as young) females occurred precociously, while other reproductive parameters were not affected at adulthood. Discontinuance of PCB treatment reversed the above symptoms.

Animals↗

PubMed1984

Response of male and female Siberian hamsters towards pups.

The influence of sex, reproductive maturity, and parental experience on the behavior of Siberian hamsters (Phodopus sungorus sungorus) toward strange pups was examined in this study. Immature, mature, or parentally experienced male and female Siberian hamsters were presented with 3- to 8-day-old pups. We recorded pup carrying during the initial 10 min, nesting with pups after 8 or 14 h, and attacking pups during the test period. Among inexperienced animals, more mature males attacked pups than did immature males or mature females. Parental experience significantly decreased pup attacks by males and increased nesting with pups by both males and females. Repeated testing did not modify the responses to pups. We conclude that in Siberian hamsters both caretaking and aggressive responses to pups may be shown by immature and mature animals of both sexes. Parental experience resulted in increased caretaking by males and females and decreased aggressive responses by males.

Aggression↗