Low-dose in utero exposure to finasteride promotes developmental changes in both male and female gerbil prostates

The prostate is an accessory reproductive gland that is sensitive to the action of exogenous compounds known as endocrine disrupters that alter normal hormonal function. Finasteride is a widely used chemical that acts to inhibit the conversion of testosterone in its most active form, dihydrotestosterone. It is known that intrauterine exposure to finasteride causes changes in the male prostate even at low dosages; however, it is not known whether these dosages are capable of causing changes in the female prostate, which is present in a large number of mammalian species, including humans. In the present study, histochemistry, immunohistochemistry, immunofluorescence, serological dosages, and three-dimensional reconstruction techniques were employed to evaluate the effects of intrauterine exposure to a low dose of finasteride (100 μg.BW/d) on postnatal prostate development in male and female Mongolian gerbils. The results indicate that the gerbil female prostate also undergoes alterations following intrauterine exposure to finasteride, exhibiting a thickening of periductal smooth muscle and increased stromal proliferation. There are also intersex differences in the impact of exposure on the expression of the androgen receptor, which was increased in males, and of the estrogen-α receptor, which was decreased in the male prostate but unchanged in females. Altogether, this study indicates there are sex differences in the effects of finasteride exposure even at low dosages.

Immunohistochemical localization of nerve growth factor, glial fibrillary acidic protein and ciliary neurotrophic factor in mesencephalon, rhombencephalon, and spinal cord of developing mongolian gerbil

The distribution of the nerve growth factor (NGF), the glial fibrillary acidic protein (GFAP) and the ciliary neurotrohic factor (CNTF) was performed in coronal sections of the mesencephalon, rhombencephalon and spinal cord in the developing Mongolian gerbils. Generally, NGF specifically recognizes neurons with the NGF receptor, whereas GFAP does the glia, and CNTF does the motor neurons. The receptor expression was examined separately in gerbils between embryonic days 15 (E15) and postnatal weeks 3 (PNW 3). The NGF-IR was first observed in the spinal cord at E21, which might be related to the maturation. The GFAP reactivity was peaked at the postnatal days 2 (PND2), while the highest CNTF-reaction was expressed at PNW 2. The GFAP stains were observed in the aqueduct and the spinal cord, which appeared to project laterally at E19. The CNTF was observed only after the birth and found in both the neurons and neuroglia of the substantia nigra, mesencephalon, cerebellum and the spinal cord from PND1 to PNW3. These results suggest that NGF, GFAP and CNTF are important for the development of the neurons and the neuroglia in the central nervous system at the late prenatal and postnatal stages.

The normal development of Mongolian gerbil foetuses and, in particular, the timing and sequence of the appearance of ossification centres

To elucidate the normal development and growth of Mongolian gerbils, the timing and sequence of the appearance of ossification centres within foetuses were investigated. Average foetus body weight and tail length on the 15th day of pregnancy were found to be 0.042 g and 6.2 mm, respectively. For the 25th day of pregnancy, these measurements were 2.601 g and 29.4 mm, respectively. The body weight and tail length of foetuses increased significantly from the 20th day of pregnancy. Also, the first ossification centre of Mongolian gerbil foetuses appeared in the clavicle at the 17th day of pregnancy. The order in which ossification centres appeared in Mongolian gerbils resembles the pattern for rats and mice, except in some areas of the skull. Except for the clavicle, in which ossification centres appeared rather early, most ossification centres appeared in the last quarter of pregnancy. These results suggest that Mongolian gerbil foetal development is near completion by the last gestational stage. Also, ossification centres appear sooner in the skull and nasal bones than in other rodents.

NGF delays rather than prevents the cholinergic terminal damage and delayed neuronal death in the hippocampus after ischemia

Cerebral ischemia induces damage of cholinergic terminals in the hippocampus, which preceded the delayed neuronal death (DND) of the CA1 pyramidal cells. We investigated the effects of nerve growth factor (NGF) on the cholinergic terminal damage after ischemia. Continuous NGF infusion (0.5 microg/7 days) into the lateral ventricle before and after 5 min ischemia prevented a decrease in choline acetyltransferase (ChAT)-immunoreactivity and disturbance of acetylcholine (ACh) release on the 4th day after ischemia, but not on day 7, i.e., NGF infusion caused delay in the progress of the cholinergic terminal damage. These findings show that the cholinergic terminal damage may result from deficiency of endogenous NGF in an ischemic brain. In addition, we investigated whether NGF would prevent the DND after ischemia. NGF infusion also caused delay in the progress of the DND until day 14. Our results suggested that the neuroprotective effect of NGF on the DND may be secondarily yielded by maintenance of communication between cholinergic terminal and the target CA1 cell, and that prevention of cholinergic terminal damage may be useful for the treatment of cerebrovascular disease.

Evidence for modulation of dopamine-neuronal function by tachykinin NK3 receptor stimulation in gerbil mesencephalic cell cultures

Primary cultures of gerbil mesencephalon were used for studying the modulation exerted by tachykinin NK(3) receptor activation on the activity of dopamine (DA) neurons. Dopamine neurons were identified by their ability to take up [(3)H]DA in a nomifensine-dependent manner. Moreover, tyrosine hydroxylase immunohistochemistry revealed that these neurons accounted for 5-7% of the total cell population. The NK(3) receptor agonists, senktide (EC(50) = 0.58 nM) and [MePhe(7)]neurokinin B (EC(50) = 3 nM), increased spontaneous [(3)H]DA release in a concentration-dependent manner. In contrast, tested at a supramaximal concentration (IC(50) = 0.89 nM), neither septide nor substance P were found to affect [(3)H]DA release. The senktide-evoked [(3)H]DA release was not observed when extracellular Ca(2+) was chelated, but was unaffected by nomifensine. This indicates that this increase in [(3)H]DA outflow resulted more from an exocytotic process than from reversal of carrier-mediated DA uptake. Moreover, the senktide effect was unaffected by the Na+ channel blocker tetrodotoxin, a result suggesting a direct action of senktide on DA neurons. The non-peptide NK(3) receptor antagonist, SR 142801, shifted or blocked (IC(50) = 0.89 nM) the senktide-evoked [(3)H]DA release, while its (-)-antipode, SR 142806, was 80-fold less potent, in agreement with binding data. Selective antagonists for Nk1 (SR 140333) or Nk2 (SR 48968) receptors failed to reduce the senktide effect. Light scanning microscopic analysis of mesencephalic cells loaded with the Ca(2+) sensitive dye, fluo-3, showed that senktide induced a rise in cytosolic Ca(2+) in 8-10% of the cell population. The senktide-induced elevation in intracellular Ca(2+) was rapid in onset and transient (at 10-8 M) or more sustained with no further increase in fluorescence intensity (at 10(-7) M). The proportion of senktide-responsive cells was not significantly modified when extracellular Ca(2+) was chelated, but was reduced by 87% in the presence of SR 142801 and by 75% in cultures that were pre-treated with the DA neurotoxin 1-methyl-4-phenylpyridinium. The present study shows that enhancement of spontaneous [(3)H]DA release and intracellular Ca(2+) mobilization may be observed after NK(3) receptor stimulation and that both biochemical events are likely to occur in DA neurons.

Development of the hypothalamic vasopressin system and nephrons in Meriones shawi during ontogenesis

This study has evaluated the development of the hypothalamic vasopressin system and nephrons of the kidney in desert rodents, Meriones shawi, which effectively retain water by excretion of highly concentrated urine. The vasopressin system was studied immunocytochemically at the 18th fetal day, at the 2nd, 13th, 27th postnatal days and in adulthood. The kidneys were investigated at the 2nd, 13th postnatal days and in adulthood using microdissection technique. Occasional vasopressin-immunoreactive neurons were observed as early as the 18th fetal day, only in the paraventricular nucleus. From the 2nd postnatal day onwards, vasopressin neurons increased progressively in number, being mainly concentrated in the supraoptic and paraventricular nuclei, as well as in the ventral retrochiasmatic region. Transient neuronal populations were also observed at the 13th postnatal day in the lateral preoptic area and anterior hypothalamic nucleus. Apart from the neurons, the glandular cells of the tuberal lobe showed immunostaining from the 18th fetal day, the first age studied, until the 13th postnatal day. The fibers of differentiating vasopressin neurons grew towards the circumventricular/neurohemal organs, terminating in the organum vasculosum of the lamina terminalis and the lateral ventricles as early as the 18th fetal day, as well as the third ventricle, the posterior lobe and the external zone of the median eminence between the 2nd and 13th postnatal days. The kidney in 2-day-old Meriones comprised nephrons at different stages of development from an S-shaped body to well-differentiated nephrons. At the 13th postnatal day, as in adulthood, the nephrons were well differentiated and characterized by long, thin loops descending to different levels of papilla. Thus, according to our morphological data the hypothalamic vasopressin neurons and nephrons in the kidney of Meriones reach the definitive state by the end of the 2nd postnatal week.

Developmental changes in paramesonephric and mesonephric ducts and anogenital distance in fetal Mongolian gerbils during sexual differentiation

On day 13 of gestation in Mongolian gerbil fetuses, the mesonephric (Wolffian) duct was already visible. On day 14, the anlage of the paramesonephric (Müllerian) duct was first observed close to the mesonephric duct in both sexes at the cranial part of the mesonephros. Thereafter, the paramesonephric duct grew caudally in parallel with the mesonephric duct. On day 19, the duct reached the urogenital sinus. At this stage, the anogenital distance was significantly longer in male than in female. Also in male, the mesonephric duct was increased and the paramesonephric duct was decreased in diameter compared with those in female. These suggest that both testosterone and anti-Müllerian hormone are produced in fetal Mongolian gerbils at least before day 19 of gestation.

Immunohistochemical localization of fibronectin-like protein in the inner ear of the developing gerbil and rat

Immunohistochemistry was used to demonstrate the distribution of fibronectin-like protein within the developing inner ear of two species of altricial rodents: gerbils and rats. While there were temporal differences between the two species, the developmental sequence of immunostaining was virtually identical. Most notably, in rats from embryonic day 18 through day 1 postpartum, and in gerbils from birth through day 4 postpartum, intense, discrete fibronectin-like immunoreactivity was observed in the cochlea immediately beneath the inner and outer hair cells, sites of active auditory nerve fiber growth and nerve-hair cell synaptogenesis at these ages. The results suggest that fibronectin is appropriately positioned spatially and temporally to play a significant role in promoting, guiding and/or maintaining neural innervation within the developing organ of Corti. The temporo-spatial pattern of immunostaining in Schwann cells and auditory (VIIIth cranial) nerve neurons implies that fibronectin also plays a significant role in the early formation of myelin. In non-neural elements of the cochlea, fibronectin is a major structural component within the basilar membrane at all of the developmental stages investigated.

Sexual segregation in the left and right horns of the gerbil uterus: "the male embryo is usually on the right, the female on the left" (Hippocrates)

We examined reproductive tracts of 253 female Mongolian gerbils (Meriones unguiculatus) and recorded the uterine locations (relative to siblings of opposite sex) in which 812 male and 823 female fetuses were found. Within-litter comparisons revealed that sexes were not distributed randomly across uterine horns. The percentage of males in right horns (55.0%) was greater than the percentage of males in left horns (41.8%) and the percentage of females in right horns (45.0%) was significantly less than the percentage of females (58.2%) in left horns. We did not find differences in the total number of fetuses in left and right uterine horns or a sex bias in the total sample of 1635 fetuses. Results were discussed in terms of: (a) effects of sexual segregation of fetuses on expected probabilities of fetuses developing adjacent to 0, 1, or 2 fetuses of opposite sex and (b) consequent alterations in expected frequencies of behavioral phenotypes in populations of gerbils.

Duration of retinogenesis: its relationship to retinal organization in two cricetine rodents

The Mongolian gerbil (Meriones unguiculatus) has a prolonged period of development relative to other muroid rodents. We have explored the consequences of this relatively long period of maturation on retinal cell number and topography by comparing the duration and topography of neurogenesis in the gerbil retina with that of a closely related species which develops rapidly, the Syrian hamster (Mesocricetus auratus) (Sengelaub et al.: J. Comp. Neurol. 246:527-543, 1986). An analysis of thymidine-labeled retinas indicate that cells destined for the gerbil retinal ganglion cell layer are generated for at least 12 embryonic days, twice the duration in the hamster. The period of cell loss in the gerbil retinal ganglion cell layer extends for at least 14 postnatal days, more than twice as long as in the hamster. The gerbil retina is generated in a center-to-periphery gradient for both retinal ganglion cells and displaced amacrine cells, while no such gradients are evident in the hamster retina. We conclude that the longer developmental period of the gerbil is associated with 1) a longer period of neurogenesis resulting in greater retinal cell number, 2) the expression of spatial gradients in neurogenesis, and 3) a larger eye at maturity. The last two factors, in part, may be related to the development of a highly differentiated area centralis and visual streak in the retina of this rodent. Unrelated to duration of growth, early differences in retinal shape between these two species contributes to the development of retinal topography. The gerbil, but not the hamster retina, is initially asymmetric, longer in its nasotemporal than its dorsoventral dimension. The gerbil retina then grows asymmetrically, producing a spherical retina, and coincident in time, a nasotemporally extended visual streak.

Expression of virus-like particles in normal and transformed gerbil cells

Three types of virus-like particles (VLP) were observed in three of seven gerbil cell lines. One of these cultures was in a non-transformed state and contained R and C-type VLP, while the two others began to express R-type or intracisternal A-type VLP only after spontaneous transformation. These particles seem to be endogenous to the gerbil but do not appear to be directly involved in cell transformation.

"Hemogenic endothelium" of the embryonic aorta: Does it exist?

Aggregates of intravascular, presumably endothelial-derived, undifferentiated cell were found in the aorta of 14-15 day Mongolian gerbil embryos, in several 10 mm pig embryos, in one 10 day mouse embryo and in one 9.5 mm human embryo. As in other species in which they have been identified, these "aortic cell clusters" generally occurred in groups of 25-100 cells and were typically observed adherent to the ventral luminal wall of the abdominal aorta during a brief period in gestation. The present electron microscopic study shows that these cells possess many characteristics in common with undifferentiated primitive blood cells of the yolk sac blood island. Their in situ origin is supported by ultrastructural similarity to underlying endothelium as well as the presence of numerous intercellular junctions among themselves and with subjacent endothelium. It is suggested that they may be morphologically undifferentiated hemopoietic precursor cells. Hypotheses are proposed for the mechanism of their origin from aortic endothelium.

Succinic dehydrogenase activity during palate formation in the Mongolian gerbil

The palatal shelf epithelium of the Mongolian gerbil was examined for succinic dehydrogenase activity prior to, during and the after palatal fusion (days 18-20 post coitus). Enzyme activity was present during all stages examined, and was noted even in the epithelial pearls of fused palates. The presence of SDH activity in these epithelial pearls lends support to the theory 'epithelial stretching', and questions the theory of 'programmed cell death' in relation to the loss of the epithelium along the plane of fusion.

Embryonic and fetal hemopoiesis in the Mongolian gerbil (Meriones unguiculatus)

A study of the development of hemopoiesis in the Mongolian gerbil (Meriones unguiculatus) was conducted in order to determine the temporal sequence, the organs involved and the cytology of blood cell formation in this species. Hemopoiesis in the intrauterine life of the gerbil can be divided into four phases based on the site of blood cell formation: (1) the vitelline phase, (2) the hepatic phase, including thymic histogenesis, (3) the splenic phase and (4) the medullary phase, with the development of secondary lymphoid tissues. At the onset of each of these phases a blast-like cell was identifiable in each hemopoietic organ which, because of its morphology and its presumed multipotentiality was classified as a "lymphoid cell". In the yolk sac phase (gestational day 12) two generations of erythrocytes, a primitive and a definitive, are formed. The liver is by day 15 erythropoietic and megakaryopoietic, but later, a few granulocytes are also found in its extravascular compartment. The thymus is exclusively lymphopoietic from the appearance of its earliest cells on day 15. Splenic hemopoiesis is initiated with the presence of lymphoid cells (day 20) followed later by the appearance of morphologically identifiable blood cell lines. Early normoblastic and granulocytic activity begins in the marrow cavities on day 23, though the marrow is not considered to be a source of circulating blood cells during fetal life. Lymph node histogenesis occurs during the last four days of gestation, first in the cervical region and then in other parts of the body. The finding of undifferentiated lymphoid cells in all organs at the initiation of hemopoiesis and in the peripheral blood throughout gestation is discussed in light of the migratory theory of hemopoiesis.

Morphogenesis of the secondary palate in the Mongolian gerbil (Meriones unguiculatus)

This report describes the prenatal development and closure of the secondary palate in the Mongolian gerbil. Palatal shelves can be regularly observed on day 16, at which time they are directed vertically. On day 17, the shelves show an overall increase in size and length but remain vertically directed. During day 18, palatal shelves are usually in a state of transition from the vertical to the horizontal position. The process of palatal closure (fusion) occurs on the 19th day and is complete by day 20. The process of palatal formation and closure in the gerbil more closely resembles that of the rat and rabbit than that of the mouse.

Development of the squamosomandibular articulation in the Mongolian gerbil (Meriones unguiculatus)

The early development of the squamosomandibular articulation in the Mongolian gerbil was investigated from its inception through the 8th postnatal day. Pregnant gerbils were sacrified beginning on day 18 through day 23 of gestation by chlorofrom inhalation and the fetuses were extirpated and decapitated. Neonatal gerbils, 1-8 days of age, were also sacrificed. The severed heads were frozen in a cryostat and sectioned at 14mum in frontal and transverse planes and stained in 1% aqueous Safranin 0. The anlage of the mandibular joint along with membranous bony deposits lateral to Meckel's cartilage in the vicinity of the presumptive body and ramus first appeared on the 18th gestational day. Condylar chondrogenesis occurred on the 20th prenatal day, and by day 22 of gestation chondrocytic hypertrophy was noted preparatory to osteogenesis. The presumptive articular disc was observed on the 21st gestational day while an upper and lower synovial cavity was discernible on the 22nd prenatal day. The squamosa and zygoma were first noted on the 20th postcoital day. There appeared to be a developmental lag from onset through completion of the gerbil squamosomandibular joint formation in comparison with that reported for the mouse and rat.