Blood pressure regulation in the three-toed sloth, Bradypus variegatus

The aim of this study was to elucidate the role of the baroreflex in blood pressure control in sloths, Bradypus variegatus, since these animals show labile levels in this parameter. Unanesthetized cannulated sloths were positioned in an experimental chair and the arterial catheter was coupled to a strain gauge pressure transducer. Blood pressure was monitored before, during and after the administration of phenylephrine (0.0625 to 4 microg/kg) and sodium nitroprusside (0.0625 to 2 microg/kg), bringing about changes in mean blood pressure from +/-30 mmHg in relation to control values. The relation between heart rate changes due to blood pressure variation was estimated by linear regression analysis. The slope was considered the reflex baroreceptor gain. The results (means+/-SD) showed that the reflex baroreceptor gain was -0.3+/-0.1 bpm/mmHg (r=0.88) to phenylephrine and -0.5+/-0.1 bpm/mmHg (r=0.92) to sodium nitroprusside, denoting a reduced reflex baroreceptor gain when compared with other mammals, suggesting that in sloths the baroreceptors are minimally involved in the buffering reflex response to these drugs. These findings suggest that the labile blood pressure could be influenced or be a result of this lowering in the reflex baroreceptor gain.

Fecal estradiol and progesterone metabolite levels in the three-toed sloth (Bradypus variegatus)

The present study was carried out to assess the possibility of measuring fecal steroid hormone metabolites as a noninvasive technique for monitoring reproductive function in the three-toed sloth, Bradypus variegatus. Levels of the estradiol (E2) and progesterone (P4) metabolites were measured by radioimmunoassay in fecal samples collected over 12 weeks from 4 captive female B. variegatus sloths. The validation of the radioimmunoassay for evaluation of fecal steroid metabolites was carried out by collecting 10 blood samples on the same day as defecation. There was a significant direct correlation between the plasma and fecal E2 and P4 levels (P < 0.05, Pearson's test), thereby validating this noninvasive technique for the study of the estrous cycle in these animals. Ovulation was detected in two sloths (SL03 and SL04) whose E2 levels reached 2237.43 and 6713.26 pg/g wet feces weight, respectively, for over four weeks, followed by an increase in P4 metabolites reaching 33.54 and 3242.68 ng/g wet feces weight, respectively. Interestingly, SL04, which presented higher levels of E2 and P4 metabolites, later gave birth to a healthy baby sloth. The results obtained indicate that this is a reliable technique for recording gonadal steroid secretion and thereby reproduction in sloths.

Cardiovascular responses to locomotor activity and feeding in unrestrained three-toed sloths, Bradypus variegatus

Heart rate (HR) and systolic (SBP), diastolic (DBP) and mean (MBP) blood pressure were recorded by biotelemetry in nine conscious unrestrained sloths for 1 min every 15 min over a 24-h period. The animals were allowed to freely move in an acoustically isolated and temperature-controlled (24 +/- 1 degree C) experimental room with light-dark cycle (12/12 h). Behavior was closely monitored through a unidirectional visor and classified as resting (sitting or suspended), feeding (chewing and swallowing embauba leaves, Cecropia adenops), or locomotor activity around the tree trunk or on the room floor. Locomotor activity caused statistically significant increases in SBP (+8%, from 121 +/- 22 to 131 +/- 18 mmHg), DBP (+7%, from 86 +/- 17 to 92 +/- 10 mmHg), MBP (+8%, from 97 +/- 19 to 105 +/- 12 mmHg), and HR (+14%, from 84 +/- 15 to 96 +/- 15 bpm) compared to resting values, indicating a possible major influence of the autonomic nervous system on the modulation of cardiac function during this behavior. During feeding, the increase in blood pressure was even higher (SBP +27%, from 119 +/- 21 to 151 +/- 21 mmHg; DBP +21%, from 85 +/- 16 to 103 +/- 15 mmHg; MBP +24%, from 96 +/- 17 to 119 +/- 17 mmHg), while HR remained at 14% (from 84 +/- 15 to 96 +/- 10 bpm) above resting values. The proportionally greater increase in blood pressure than in HR during feeding suggests an increase in peripheral vascular resistance as part of the overall response to this behavior.

Postnatal development of the reproductive system in the grey short-tailed opossum, Monodelphis domestica

Postnatal phenotypic sex differentiation has been investigated in a laboratory marsupial, Monodelphis domestica, as part of a larger study to resolve apparent discrepancies between eutherian and marsupial mammals. These include the formation of sex-specific structures in marsupials prior to gonadal differentiation and the retention in both sexes of structures which are sex-specific in eutherians. The time-course and nature of differentiation was investigated in 131 specimens ranging in age from the day of birth to 56 days. Patent wolffian ducts extend to the urogenital sinus in both sexes at birth, while müllerian ducts are identified on day 1 and grow in a cranio-caudal direction to reach the urogenital sinus on day 6. The male müllerian duct shows signs of regression at its cranial end on day 10 and throughout its length on day 12; its lumen has completely disappeared by day 15. By this time the epididymis and vas deferens have developed from the wolffian duct; their histological differentiation occurs between days 26 and 56. Prostatic buds are identifiable in tissue surrounding the male urethra on day 14. In the female, the wolffian duct is larger than the müllerian duct until day 14; thereafter the wolffian duct begins to regress at its cranial end, disappearing by day 17, whereas the müllerian duct begins to enlarge, converging with its fellow at the urogenital sinus by day 19. Lateral vaginae, vaginal culs-de-sac, uteri and oviducts have differentiated from the müllerian ducts by day 25. Gonads of both sexes are elongated in shape at birth, attached along the medial aspect of the large mesonephroi in the abdominal cavity. However, from day 3 onwards the testis becomes more rounded than the ovary. Degeneration of the male mesonephros begins about day 10 and is almost completed by day 19; the female mesonephros is still relatively large at day 14 though it too has almost disappeared by day 19. By postnatal day 13 the abdominal phase of testis descent is underway and the inguinal phase begins at day 15. Testes have reached the scrotal sac by day 24 and achieve their final position at the base of the scrotum by day 28. In summary, postnatal reproductive tract development and gonadal descent has been examined in this important biomedical model, where differentiation of the wolffian and müllerian ducts takes place after gonadal differentiation, according to the normal eutherian pattern.

The role of androgens in development of the scrotum of the grey short-tailed Brazilian opossum ( Monodelphis domestica)

In eutherian mammals, sex differentiation is initiated by expression of the testis-determining gene on the Y chromosome. Subsequent phenotypic development of the reproductive tract and genitalia depends on the production of hormones by the differentiated testis. In marsupials the mechanisms of phenotypic development may vary from this pattern, as differentiation of the scrotal primordia has been shown to occur before that of the gonad. Thus, the development of the scrotum in the marsupial has been regarded as an androgen-independent process. We have sought to clarify the ontogeny of scrotal development and the appearance of androgen receptor immunoreactivity by examining Monodelphis domesticaembryos/pups from 1 day prior to birth until 2 days after birth. We have also used immunocytochemistry to determine the expression of the key steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase as an indicator of when the developing gonad may be capable of synthesizing androgens. Expression of this enzyme was first detected in the gonads and adrenals of both sexes 1 day prior to birth and before the appearance of scrotal bulges. Androgen receptor immunoreactivity was detected in the scrotal anlagen of male opossum pups as early as 1 day following birth. This finding is significantly earlier than previous reports and coincides with the appearance 1 day after birth of distinct scrotal bulges. Androgen receptor immunoreactivity was also observed in the genital tubercles of male pups, but not female pups, 2 days after birth. These results suggest that androgens may play an important role in the development of the male genitalia at a much earlier stage than that indicated by previously published work and that scrotal development in this species may not be androgen-independent.

Circadian rhythms in blood pressure in free-ranging three-toed sloths (Bradypus variegatus)

Blood pressure (BP) profiles were monitored in nine free-ranging sloths (Bradypus variegatus) by coupling one common carotid artery to a BP telemetry transmitter. Animals moved freely in an isolated and temperature-controlled room (24 degrees C) with 12/12-h artificial light-dark cycles and behaviors were observed during resting, eating and moving. Systolic (SBP) and diastolic (DBP) blood pressures were sampled for 1 min every 15 min for 24 h. BP rhythm over 24 h was analyzed by the cosinor method and the mesor, amplitude, acrophase and percent rhythm were calculated. A total of 764 measurements were made in the light cycle and 721 in the dark cycle. Twenty-four-hour values (mean +/- SD) were obtained for SBP (121 +/- 22 mmHg), DBP (86 +/- 17 mmHg), mean BP (MBP, 98 +/- 18 mmHg) and heart rate (73 +/- 16 bpm). The SBP, DBP and MBP were significantly higher (unpaired Student t-test) during the light period (125 +/- 21, 88 +/- 15 and 100 +/- 17 mmHg, respectively) than during the dark period (120 +/- 21, 85 +/- 17 and 97 +/- 17 mmHg, respectively) and the acrophase occurred between 16:00 and 17:45 h. This circadian variation is similar to that observed in cats, dogs and marmosets. The BP decreased during "behavioral sleep" (MBP down from 110 +/- 19 to 90 +/- 19 mmHg at 21:00 to 8:00 h). Both feeding and moving induced an increase in MBP (96 +/- 17 to 119 +/- 17 mmHg at 17:00 h and 97 +/- 19 to 105 +/- 12 mmHg at 15:00 h, respectively). The results show that conscious sloths present biphasic circadian fluctuations in BP levels, which are higher during the light period and are mainly synchronized with feeding.

Pharmacological analysis of extracellular dopamine and metabolites in the striatum of conscious as/agu rats, mutants with locomotor disorder

The as/agu rat is a spontaneously occurring mutation which exhibits locomotor abnormalities, reduced tyrosine hydroxylase levels in the substantia nigra and lower extracellular levels of dopamine. The animal could represent a model of some human locomotor disorders. High-potassium medium evoked a 460% rise of dopamine levels in control rats but double this in mutants. Amphetamine increased extracellular dopamine by 710% in controls and 1480% in mutants. Clorgyline produced a small increase of dopamine levels in controls but an 1170% increase in mutants. The uptake inhibitor nomifensine increased dopamine levels by 910% in controls but only 270% in mutants. After treatment with benserazide plus L-DOPA, an acute injection of L-DOPA evoked a release of dopamine which was twice as large in the as/agu rats compared with controls. The results show reduced extracellular dopamine in as/agu rats when the locomotor disorder is apparent, but there has been little loss of tyrosine hydroxylase. The responses to drugs are qualitatively different from those obtained using 6-hydroxydopamine.Overall, the effects of compounds affecting aminergic neurons suggest that one possible mechanism for the neuronal abnormality in as/agu rats is a defective regulation of dopamine release from striatal terminals.

Sloth biology: an update on their physiological ecology, behavior and role as vectors of arthropods and arboviruses

This is a review of the research undertaken since 1971 on the behavior and physiological ecology of sloths. The animals exhibit numerous fascinating features. Sloth hair is extremely specialized for a wet tropical environment and contains symbiotic algae. Activity shows circadian and seasonal variation. Nutrients derived from the food, particularly in Bradypus, only barely match the requirements for energy expenditure. Sloths are hosts to a fascinating array of commensal and parasitic arthropods and are carriers of various arthropod-borne viruses. Sloths are known reservoirs of the flagellate protozoan which causes leishmaniasis in humans, and may also carry trypanosomes and the protozoan Pneumocystis carinii.

An update on the physiology of two- and three-toed sloths

Physiological and pharmacological research undertaken on sloths during the past 30 years is comprehensively reviewed. This includes the numerous studies carried out upon the respiratory and cardiovascular systems, anesthesia, blood chemistry, neuromuscular responses, the brain and spinal cord, vision, sleeping and waking, water balance and kidney function and reproduction. Similarities and differences between the physiology of sloths and that of other mammals are discussed in detail.

Effects of mu, kappa, and delta opioid receptor agonists and antagonists on rat hypothalamic noradrenergic neurotransmission

We have investigated the effects of specific mu-, kappa-and delta-opioid receptor agonists and antagonists on the hypothalamic noradrenergic neurotransmission and on luteinising hormone (LH) release in the ovariectomised and steroid-primed rat. The opioid agents were infused intracerebroventricularly under ketamine anaesthesia and blood samples collected at hourly intervals on the afternoon of the anticipated LH surge. At the end of the experiment, the rats were decapitated and the medial preoptic area, suprachiasmatic nucleus, median eminence and arcuate nucleus surgically isolated by micropunch. The concentrations of noradrenaline (NA) and its metabolite (3,4-dihydroxyphenylglycol; DHPG) in these samples was determined by high performance liquid chromatography with electrochemical detection. Plasma LH levels were measured by radioimmunassay. The three opioid agonists reduced concentrations of NA and DHPG in all four hypothalamic areas. These inhibitory effects of the opioid agonists were mostly prevented following coadministration with their respective antagonists. However, naloxone had no significant effect on DHPG levels in any of the hypothalamic regions examined. Plasma LH levels were found to be either low or undetectable in all groups. These results suggest that mu-, kappa- and delta-opioid receptors have inhibitory influence on the hypothalamic noradrenergic neurotransmission around the time of the LH surge. It is thought that the ketamine anaesthesia interfered with LH release.

Effects of DPDPE (a specific delta-opioid receptor agonist) and naloxone on hypothalamic monoamine concentrations during the pre-ovulatory LH surge in the rat

We have investigated the inter-relationship between the opioid and aminergic systems in the control of secretion of the pro-oestrous LH surge and the involvement of delta-opioid receptor subtypes in this process. Conscious female rats bearing a cannula in the femoral artery were injected i.p. with a selective delta-opioid receptor agonist (DPDPE) either alone or with the opioid antagonist (naloxone) at 1300 h on the day of pro-oestrus. Blood samples were collected hourly between 1500 h and 1900 h, and plasma LH levels were measured by RIA. At the end of this period (1900 h), the animals were autopsied and the concentrations of the amines (noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5HT)) and their metabolites (dihydroxyphenolglycol (DHPG) and 5-hydroxyindoleacetic acid (5HIAA), metabolites of NA and 5HT respectively) were determined by HPLC with electrochemical detection in the medial preoptic area, suprachiasmatic nucleus, median eminence and arcuate nucleus. DPDPE abolished the LH surge and concomitantly decreased hypothalamic NA and DHPG concentrations in all the areas examined. The levels of DA, 5HT and 5HIAA were also reduced in all hypothalamic regions studied, except DA and 5HIAA in the suprachiasmatic nucleus. Naloxone reversed these inhibitory effects of the delta-agonist. We conclude that activation of delta-opioid receptors may exert an inhibitory effect on LH release. The effect is probably an indirect one mediated by the monoaminergic systems, as they are suppressed by DPDPE in nearly all the hypothalamic regions studied.

Extracellular levels of dopamine and its metabolite 3,4-dihydroxy-phenylacetic acid measured by microdialysis in the corpus striatum of conscious AS/AGU mutant rats

The AS/AGU rat is a mutant derived from the Albino Swiss (AS) strain. It is characterized by an ungainly, staggering gait, hind limb rigidity, whole body tremor and, in older animals, difficulty in initiating movement. As and AS/AGU males aged three, six and nine months (n=6 per group) were used to estimate the levels of dopamine and its metabolites in the extracellular fluid of the caudate-putamen. The results indicate a profound loss of dopamine in the extracellular fluid at all age points examined, together with an increase in the concentration of the metabolite 3,4-dihydroxyphenylacetic acid. It is suggested that these changes reflect a defect of dopaminergic neuron function which may underlie the motor disorder seen in these animals.

Postnatal development of Leydig cells in the opossum (Monodelphis domestica): an immunocytochemical and endocrinological study

This study involved characterization of Leydig cells of the opossum Monodelphis domestica, functionally by immunocytochemical identification of the enzyme 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and by measurement of testosterone levels using RIA. Immunostaining for 3 beta-HSD was first detected in a few Leydig cells on Day 16, was increased by Day 24, reached a peak at 4 mo, and was present even in senescent (3 yr) animals. Plasma testosterone was first measurable (0.35 nM) at prepuberty (3.5 mo). Prior to that, plasma testosterone concentrations were uniformly below the level of detection (< 0.3 nM) in both sexes from Day 5 to 2.5 mo. By 4 mo (puberty), plasma testosterone levels in males had risen significantly to 1.53 +/- 0.35 nM, continuing to increase to 1.79 +/- 0.4 nM at 6 mo and peaking at 2.71 +/- 0.29 nM in the adult (1-2 yr). Ovarian testosterone concentrations were consistently lower than those in the testis, as were those of adrenals of both sexes. Thus the testis would appear to be the major source of androgen production throughout life in this species. Our immunocytochemical study suggests that in Monodelphis, puberty is reached at 4 mo, and this was further supported by a rise in circulating testosterone levels at this time.

Age changes in dopamine levels in the corpus striatum of Albino Swiss (AS) and AS/AGU mutant rats

The AS/AGU rat is characterised by an ungainly, staggering gait, hind-limb rigidity, whole body tremor and (in older animals) difficulty in initiating movement. Brains of AS and AS/AGU males aged between 3 and 12 months (n = 10 per group) were sectioned transversely on a cryostat (-20 degrees C) to produce two successive cut faces (corresponding approximately to Bregma +1.2 and -0.5 mm) and 1 mm diameter x 1 mm deep micropunches were taken from four areas of the caudate-putamen. Levels of dopamine in all four areas (measured by HPLC-ECD followed by protein estimation) peaked at around 6 months and then declined in AS and AS/AGU rats. In the dorsal and lateral caudate-putamen, dopamine levels were significantly reduced in AS/AGU rats compared to AS controls from 6 months onwards. This provides further evidence that the AS/AGU mutant has impairment of its striatal dopaminergic systems.

The effects of pre- and postnatal exposure to the nonsteroidal antiandrogen flutamide on testis descent and morphology in the Albino Swiss rat

Exposure of male Albino Swiss rats to the nonsteroidal antiandrogen flutamide during the period from gestational day (d) 10 to birth resulted in feminisation of the external genitalia and the suppression of growth of the male reproductive tract. In adulthood, testes were found to be located in diverse positions. True cryptorchidism occurred in 10% of cases, whereas 50% of testes descended to the scrotum and 40% were located in a suprainguinal ectopic region. Varying degrees of tubule abnormality were seen in the testes of flutamide-treated animals, ranging from completely normal tubules with full spermatogenesis (and the expected frequency of the stages of spermatogenesis) to severely abnormal tubules lined with Sertoli cells only. For each individual testis, the overall severity of tubule damage was strongly correlated with its adult location, with intra-abdominal testes worst affected and scrotally-located testes least; only the latter contained normal tubules. Similarly, intra-abdominal testes were the smallest in weight and contained the least testosterone. By contrast, postnatal treatment of male rats with flutamide from birth to postnatal d 14 did not impair development of the external genitalia, the process of testicular descent or adult spermatogenesis. These findings confirm that androgen blockade during embryonic development interferes with testicular descent but also demonstrate that (1) prenatal flutamide treatment per se has a detrimental effect on adult testis morphology but (2) the degree of abnormality of the testes is strongly influenced by location.

Testis development in the opossum Monodelphis domestica

Testis development in the grey short-tailed opossum, Monodelphis domestica, was investigated by light and electron microscopy in 180 animals. On the day of birth, half the karyotyped males were found to have histologically differentiated testes. By day (d) 1 testicular cords were clearly distinguished in all XY gonads and the tunica albuginea was fully developed. At this stage the large and pale primordial germ cells could be differentiated from dark pre-Sertoli cells. From d 3 the testis became progressively rounded and testicular cords were surrounded by peritubular cells. Leydig cells were then distinguishable by the expected ultrastructural features of steroidogenically active cells, showing abundant vesicles of SER, extensive mitochondria with tubular cristae and numerous lipid inclusions. Subsequently these cells formed clusters and were surrounded by envelope cells until wk 12. Testes were located in the abdomen, attached to the large mesonephroi, until d 24 after birth when they began their descent to the scrotal sac. From 7 wk the interstitial tissue became less cellular. At the prepubertal stage (12 wk), the seminiferous tubules lacked lumina. Leydig cell cytoplasm was electron-dense with increased amounts of SER forming parallel profiles. By 4 mo (pubertal stage), seminiferous tubules were patent and various spermatogenic stages, including spermatozoa, were seen for the first time. Leydig cells then greatly outnumbered other interstitial tissue cells and were closely-packed around blood vessels but no longer clustered by envelope cells; their SER was very highly organised into masses of parallel arrays and lipid inclusions were reduced. In the adult (1 y) Leydig cells reached their greatest size; their morphological features resembled those seen at 4 mo except that lipid inclusions were sparse. In ageing Leydig cells (2-3 y), large amounts of SER were present but disorganised.

Neostriatal dopamine depletion and locomotor abnormalities due to the Albino Swiss rat agu mutation

The sub-strain of Albino Swiss rat (AS/AGU) is a spontaneous mutation characterised by an ungainly, staggering gait, hindlimb rigidity, whole body tremor and (when symptoms are fully developed) difficulty in initiating movement; it exhibits a progressive decrease in dopaminergic cells within the substantia nigra. A breeding programme involving Albino Swiss (AS) and AS/AGU parent rats was used to produce the F1 offspring of AS x AS/AGU matings and, subsequently, F1 x AS/AGU back crosses. When adult, the movement of all animals was assessed blind by observers on three occasions, each animal being identifiable by a subcutaneous transponder implanted before weaning. All AS/AGU and half the F1 x AS/AGU back cross animals had abnormal gait, while all AS, F1 and the remaining F1 x AS/AGU backcross animals showed normal gait, implying that the mutation is recessive. Brains of males aged 12-15 months (n = 10 per group) were sectioned transversely on a cryostat (-20 degrees C) to produce a cut face just caudal to the anterior commissure (approximately Bregma -0.5 mm) and 1 mm diameter x 1 mm deep micropunches were taken from three areas of the caudate-putamen. Levels of dopamine were measured in all samples by high performance liquid chromatography with electrochemical detection (HPLC-ECD) followed by protein estimation. Levels of dopamine in the dorsal and middle caudate-putamen varied according to a simple inheritance pattern, being high in males from AS, F1 and F1 x AS/AGU back crosses without locomotor impairment, but lower in AS/AGU and F1 x AS/AGU back crosses with disordered gait. Dopamine levels in the ventral caudate-putamen did not show such a clear variation.

Effect of exposure to morphine throughout gestation on feminine and masculine adult sexual behaviour in golden hamsters

Adult female hamsters were treated with a long-acting form of morphine before mating and throughout pregnancy; the drug was gradually withdrawn during lactation. The offspring produced were gonadectomized as adults and tested for their ability to display feminine and masculine sexual behaviour after appropriate hormonal priming. Chronic exposure to morphine during development resulted in males that showed an increase in both feminine and masculine sexual behaviour when compared with controls.

Perinatal exposure to morphine affects adult sexual behavior of the male golden hamster

Duromorph, a long-acting form of morphine, was administered to pregnant golden hamsters and/or their pups over the last 4 days of pregnancy and/or the first 4 days after birth. As adults, offspring were gonadectomized, primed with estrogen and progesterone, and tested for their ability to display feminine sexual behavior when placed with a stud male. They were then given testosterone over a 4-week period and tested for their ability to display masculine sexual behavior in the presence of a receptive female. Perinatal morphine exposure had little effect on the females' ability to display either feminine or masculine sexual behavior. In contrast, feminine sexual behavior was significantly enhanced in males exposed to morphine over the perinatal period. This suggests that exposure to opiates during the critical period of sexual differentiation may prevent the defeminization process in this species.

Neonatal serotonin reduction alters the adult feminine sexual behaviour of golden hamsters

HPLC analysis of hamster hypothalamic 5HT indicated higher levels in females than in males on day 12 after birth. Levels of 5HT and 5HIAA could be reduced in both sexes by pCPA administration. Male and female hamster pups were treated on days 1-7 or 7-14 after birth with either pCPA, 5HTP or buffer, and tested for feminine and masculine sexual behaviour in adulthood. 5HTP had no effect on behaviour in either sex. pCPA had no effect on masculine sexual behaviour nor did it affect feminine sexual behaviour when given between days 1-7. When administered on days 7-14, pCPA significantly decreased the time that females spent displaying feminine sexual behaviour, while significantly increasing it in males. We, therefore, suggest that serotonin may be modulating a neural substrate already differentiated by androgens.

Effects of different opiates on hypothalamic monoamine turnover and on plasma LH levels in pro-oestrous rats

Opiate inhibition of luteinizing hormone (LH) appears to involve changes in hypothalamic monoaminergic activity. Agonists of mu-, kappa- and sigma-opioid receptors and an opiate antagonist were administered at the onset of the preovulatory LH surge and their effects on hypothalamic monoamine turnover, and on plasma LH levels, investigated. The opiate antagonist, naloxone, significantly increased both noradrenaline (NA) turnover and plasma LH levels. Morphine (mu-agonist), significantly decreased NA concentration and plasma LH levels, but significantly increased dopamine (DA) and serotonin (5-HT) activity. Levorphanol (another mu-agonist) significantly decreased both NA and 5-HT concentrations and had no effect on circulating LH. Cyclazocine, ketocyclazocine and tifluadom (kappa-agonists) increased NA turnover but only tifluadom increased 5-HT turnover, also reducing LH levels significantly. N-Allylnormetazocine (SKF 10,047; sigma-agonist) increased 5-HT activity but did not alter LH levels. This study has confirmed the existence of a heterogenous group of opioid receptors within the hypothalamus which modulate monoamine neurotransmitters controlling LH release.

Regional differences in the catecholamine content of the rat brain: effects of neonatal castration and androgenization

The long-term organizational influence of perinatal androgen manipulations upon the central noradrenergic and dopaminergic systems was investigated in the rat. Males were castrated or sham-operated upon within 24 h of birth. Newborn females received either five daily sc injections of 100 micrograms of testosterone in oil, or vehicle only. Groups of animals were then decapitated at ages ranging from 12 to 180 days. Levels of noradrenaline and dopamine were measured in six brain regions using high-performance liquid chromatography with electrochemical detection. The results confirm that the noradrenaline and dopamine content of the brain are affected by perinatal androgen exposure and show that brain catecholamine levels alter during the first six months of life, in some areas merely increasing, but in others rising and later falling. Sex differences in catecholamine levels may be apparent at particular ages, but the direction of the difference is frequently reversed as the animals grow older. In the hypothalamus and amygdala broadly similar patterns of time-related changes in catecholamine levels were observed. However, although in other regions (cerebral cortex, cerebellum, corpus striatum and corpora quadrigemina) sex differences in the noradrenaline and dopamine content were frequently detected, on most occasions they were not affected in any recognizable fashion by steroid manipulation in the newborn. Once adult patterns of gonadotropin secretion and behaviour became established in early adulthood, a functional relationship between brain catecholamine levels and the early effects of testosterone is no longer so apparent. Nevertheless, it would seem that testosterone, acting during the neonatal period, tends to accelerate the fall in brain amine levels that occurs as the animals grow older.

The role of the hypothalamic beta-adrenergic system in controlling the LH rise in short-term castrated rats

Intraventricular infusions of adrenaline and various pharmacological agents acting on beta-adrenergic receptor subtypes were carried out in rats orchidectomized 16 h previously. Infusions (10 microliter) of solutions containing the drugs were administered under anaesthesia induced with alphaxalone and alphadolone. Levels of LH were measured in plasma collected immediately before and at predetermined intervals after the infusion. The acute rise in LH levels after castration was increased still further by isoprenaline (a mixed beta 1- and beta 2-agonist), fenoterol (a beta 2-agonist) and atenolol (a beta 1-antagonist). In contrast, prenalterol (a beta 1-agonist) and (2RS,3RS)-3-isopropylamino-1-(7-methylindan-4-yloxy)++ +butan-2-ol (ICI 118,551) (a selective beta 2-antagonist) were inhibitory to LH release. Adrenaline itself, salbutamol (another selective beta 2-agonist), propranolol (a mixed beta-antagonist) and metoprolol (a beta 1-antagonist) did not significantly alter plasma LH concentrations at the doses administered. The stimulatory effect of isoprenaline on LH release was partially reduced when given together with ICI 118,551, but was not affected when administered simultaneously with atenolol. The inhibitory effect of ICI 118,551 was, however, prevented by concomitant administration with fenoterol, as was that of prenalterol when infused with atenolol. The results suggest that the hypothalamic mediation of the short-term changes in LH release in response to castration is exerted, at least in part, through the activation of a beta 2-stimulatory component and the suppression of a beta 1-inhibitory component.

Evidence for a stimulatory beta-adrenergic component in the release of the ovulatory LH surge in pro-oestrous rats

The effect on ovulation of intraventricular infusions of noradrenaline, adrenaline and various pharmacological agents acting on the adrenergic receptor subtypes were investigated in cyclic female rats on the day of pro-oestrus. The inhibitory effects on ovulation of the different infusions were monitored by administering the drugs before 11.00 h (several hours before the critical period for the ovulatory LH surge). In experiments designed to show how the drugs under investigation might stimulate ovulation, pentobarbitone sodium (35 mg/kg) was given at 14.30 h; this anaesthetic inhibits ovulation and its effects can be overcome by substances that advance the preovulatory LH surge. Noradrenaline (an alpha-agonist) stimulated ovulation when administered on the morning of pro-oestrus to rats injected with pentobarbitone early in the afternoon of the same day. Phenoxybenzamine and phentolamine (non-selective alpha-antagonists) and clonidine (a selective alpha 2-agonist) all inhibited ovulation when infused on the morning of pro-oestrus. Yohimbine (a moderately selective alpha 2-antagonist) neither stimulated nor inhibited ovulation. Both isoprenaline (a non-selective beta-agonist) and fenoterol (a selective beta 2-agonist) stimulated ovulation in pentobarbitone-treated rats when administered on the morning of pro-oestrus and fenoterol was also able to overcome the pentobarbitone block when infused later in the afternoon. Propranolol (a non-selective beta-antagonist) and metoprolol (a selective beta 1-antagonist) were stimulatory only when administered in the afternoon. Adrenaline (both an alpha- and beta-agonist), prenalterol (a selective beta 1-agonist), atenolol (a selective beta 1-antagonist) and ICI 118,551 (a selective beta 2-antagonist) neither stimulated nor inhibited ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Organ-body weight relationships in the Common Brushtail Possum Trichosurus vulpecula (Marsupialia: Phalangeridae)

Organ-body weight relationships were studied in the adult, juvenile and pouch young Common Brushtail Possum, Trichosurus vulpecula. It was found that the relative sizes of spleen, heart and kidney were larger in the pouch young than in the juvenile and adult. The liver increased in relative size during pouch life but then fell around the time the pouch was vacated. In the adult possum all four organs examined were significantly larger in the male but this sex difference was only apparent in the size of the heart in the pouch young and juvenile. Significant seasonal changes were observed in the relative weights of the kidneys and heart in both sexes. However, only in the male did the relative liver size show significant seasonal variation.

Biogenic amine levels in the mid-term human fetus

Spectrophotofluorometric assays were used to measure concentrations of DA, NA, 5-HT and 5-HIAA present in extracts of brain tissue and CSF taken from midterm gestational fetuses of both sexes. The presence of biogenic amines was demonstrated in fetuses as early as 10.5 weeks gestation. In the hypothalamus, the concentrations (expressed in ng/100 mg tissue) ranged from 10.2 to 62.2 for NA, 11.6 to 258.8 for DA, 7.6 to 38.6 for 5-HT and 56.6 to 114.1 for 5-HIAA. Concentrations of DA and 5-HT were found to be significantly (P less than 0.05) higher in the hypothalamus than in the cortex, but those of NA and 5-HIAA were similar in both areas. No sex difference was observed. The concentrations of biogenic amines in the CSF (expressed in ng/ml) were 63.1-286.7 for NA, 43.2-108.1 for DA, 30.9-87.5 for 5-HT and 8.0-42.8 for 5-HIAA.

Indoleamine and catecholamine concentrations in the mid-term human fetal brain

Because of the likelihood that androgen-induced sex specific brain differentiation is mediated by various neurotransmitters, their concentrations were measured in the mid-term human fetal hypothalamus, cortex and cerebrospinal fluid (CSF). Tissue was collected from 32 hysterotomy specimens aged from 10 to 23 weeks, immediately frozen in liquid nitrogen, and stored at -20 degrees C. 5-Hydroxytryptamine (5-HT), 5-hydroxy indole acetic acid (5-HIAA), norepinephrine (NE) and dopamine (DA) levels were measured by a fluorometric assay. Cord serum testosterone levels were measured by radioimmunoassay. In the male fetuses, hypothalamic concentrations of 5-HT, 5-HIAA and NE were all significantly increased in comparison to those in the cortex. Because the number of female fetuses was small, only the 5-HIAA levels were seen to be significantly higher in the hypothalamus than in the cortex. In the CSF from fetuses of both sexes, the DA levels were greatly raised. Concentrations of NE were significantly higher in male fetuses aged from 14-16 weeks, a time when plasma testosterone levels are also elevated. It is hypothesized that the raised plasma testosterone and hypothalamic NE concentrations are inter-related.

Effect of local application of sympathomimetic drugs to the epididymis on fertility in rats

Insertion of Silastic rods containing the directly acting sympathomimetic drug, methoxamine, adjacent to the epididymis of rats caused a temporary reduction in fertility with no loss of ability to mate. This effect lasted up to 3 weeks. At the time of the maximal antifertility action (3-7 days after insertion), the number of spermatozoa in the ejaculate fell to almost zero, and there was a reduction in the total number of spermatozoa in the epididymis resulting from a significant drop in the number present in the cauda. Methoxamine also caused immotility and decapitation of the remaining epididymal spermatozoa. The indirectly acting sympathomimetics, tyramine and norephedrine, did not affect fertility. It is postulated that methoxamine acts to induce infertility principally by bringing about a reduction of sperm numbers in the ejaculate. This could have been produced either by a failure of the vas and cauda to contract normally at copulation or because the sperm store in the cauda had fallen below a critical threshold level.

The effect of sympathomimetic drugs on contractility of the vas deferens in vitro and in vivo

The sympathomimetic drugs noradrenaline, methoxamine, tyramine and norephedrine caused rhythmic contractions in isolated human vasa deferentia. Provided the drug was not washed out, these contractions lasted for the entire duration of the experiment (4-6 h). These contractions were mediated via alpha-adrenoreceptors. Intravenous administration of methoxamine or oxymetazolene to rats or guinea-pigs produced contractions of the vas deferens in vivo in some experiments but was accompanied by severe cardiovascular side effects. A local method of application was developed, using mixtures of tyramine with Silastic prepared as collars specially designed to fit round the vas deferens. Acute and chronic insertion of these slow-releasing devices around the vas deferens of rats produced rhythmic contractions of the vas deferens without any serious side effects.

Antifertility effect of sympathomimetic drugs on male rats when applied locally to the vas deferens

Local application of collars containing 25% methoxamine, 50% or 75% tyramine or 50% norephedrine to both vasa deferentia of rats caused a reduction in fertility but not in their ability to mate. A gradual return to fertility was seen in those animals which received the lower dose of tyramine or norephedrine, while the other treatments caused a permanent reduction in fertility. The cause of sterility was production of azoospermic ejaculates resulting from either a block in sperm transport in the vas deferens or from a deficiency in the ejaculatory mechanism. Only methoxamine caused a mechanical obstruction of the vas deferens, but it is possible that the other drugs caused a sustained spasm. An emission defect could have been due to transmitter depletion, receptor-specific desensitization or presynaptic alpha-adrenoreceptor-mediated inhibition. Spermatozoa from the cauda epididymidis were immotile following the treatments.

Presence and activity of LH-RH in the mid-term human fetus

Immunoreactive LH-RH was present in all the hypothalamic and cortical extracts of mid-term human fetuses studied and in the cortical tissue removed from the two youngest fetuses. Gonadotrophin-releasing activity of hypothalamic and cortical extracts was demonstrated by the significant rises of circulating LH after infusion into oestrogen and progesterone-primed ovariectomized rats.

The effect of ovarian steroids on hypothalamic thresholds for ovulation in the female rat

Electrochemical stimulation of the basal and preoptic hypothalamus, under sodium pentobarbitone anaesthesia, was carried out on the day of pro-oestrus in normal cycling and in ovarian hormone-treated female rats. Control rats ovulated in response to 25, 50 and 100 μA for 60 s in the median eminence and to 10 μA for 60 s in the preoptic area. Oestradiol (1 μg) given 24 h before median eminence stimulation significantly increased the number of rats ovulating. An injection of progesterone (1 mg) 24 h before median eminence stimulation did not affect the number of animals ovulating or the number of ova shed. In contrast, there was a significant reduction in the number of animals ovulating after preoptic stimulation. Stimulation of the median eminence 2–4 h after progesterone administration increased the number of animals ovulating. The results suggest that both oestradiol and progesterone exert a positive feedback effect at or below the level of the median eminence and that the negative feedback effect of progesterone is exerted on the preoptic area.

The Rate of Passage of Food in the Brush-Tailed Possum, Trichosurus Vulpecula

Detailed nutritional studies carried out on the macropod marsupial, Setonix brachyurus, by Moir, Somers, and Waring (1956) and by Calaby (1958) indicate that its digestive efficiency is intermediate between ruminant and non-ruminant herbivores. Ruminant digestion is characterized by the food being retained in the digestive tract for several days and by the very efficient digestion of fibre. Honigmann (1941) showed that the brush-tailed possum, Trichosurus vulpecula, was able to absorb large amounts of fibre. Earlier Honigmann (1936) had discussed experiments conducted on a number of mammals to determine the rate of passage of food through the digestive tract. No details of the experiments undertaken were given, but Honigmann claimed that the minimum time for the passage of food through the digestive tract of T. vulpecula was 10 hr, and the maximum 96 hr.