MSH/ACTH4-10: a tool to differentiate between the role of vasopressin in memory consolidation or retrieval processes

MSH/ACTH4-10 induces a dose dependent increase of latency scores during retention of a passive avoidance response, when injected SC prior to retention but not when administered immediately after the learning trial. Intracerebroventricular administration of anti-vasopressin serum immediately after the learning trial or 1 hr prior to retention induces marked deficits in passive avoidance behavior as indicated by low latencies during retention. SC injection of MSH/ACTH4-10 increased latency scores in animals which received anti-vasopressin serum prior to retention, but did not alter latencies in animals, which received anti-vasopressin serum after the learning trial. These results suggest that MSH/ACTH4-10 is involved in retrieval processes and is able to differentiate between the effects of vasopressin on memory consolidation and on retrieval.     

Effects of two ACTH analogs on successive odor discrimination learning in rats

Olfactory discrimination learning has been shown to provide a powerful tool to investigate the mechanisms involved in the formation, storage and retrieval of information in rodent CNS. In the present study we tested the effects of two ACTH analogs, which were previously reported to influence the processes of learning and memory, on various olfactory learning tasks. The ACTH(4-9) analog HOE 427 produced an apparent increase in storage of olfactory information as shown by the difficulty experienced by the animals to rapidly reverse their behavioral responses to previously learned odors. Similarly, the ACTH (4-9) analog ORG 2766 appears to enhance the storage of olfactory information when administered either before or after the learning trials. These data are consistent with the notion that ACTH and related analogs facilitate performance in a variety of learning tasks. In addition, our results suggest possible mechanisms by which some neuroactive peptides might modulate learning and memory processes in the CNS.     

Pre- and postnatally administered ACTH, Organon 2766 and CRF facilitate or inhibit active avoidance task performance in young adult mice

This study investigated the effect of learning/memory-related neuropeptides on behavioral task performance in later life. A 1 mg/kg dosage of adrenocorticotropic hormone 4-9, Organon 2766, ACTH/MSH 4-10, ACTH 1-24, CRF, or diluent was subcutaneously injected into either pregnant females or into newborn pups during specific neural developmental windows. Each of the progeny was trained in an active-avoidance task and tested for acquisition on postpartum days 35-37. The mice were then tested for memory task performance and reacquisition on days 42-44 postpartum using the identical experimental paradigm as that used in the training sessions. Prenatal treatment with these memory-related neuropeptides resulted in significant facilitation of learning/memory task performance in male and female mice treated with Organon 2766 (p less than 0.001), and a significant inhibition of learning/memory task performance in males and females treated with ACTH 1-24 (p less than 0.01). Additional sex-specific performance facilitations and inhibitions resulted from the pre- or postnatal administration of the various neuropeptides used in this study. These results suggest that neuropeptides, when available in increased amounts during specific neural developmental windows, can significantly improve or suppress related behavioral performance capability in later life.     

Development in ontogeny of the effect of ACTH fragment 4-7 on rat learning

Studies have been made of the effect of ACTH fragment 4-7 on learning in rats in early postnatal ontogenesis, as well as of the possibility of preservation of early learning during administration of this peptide to adult animals. It was shown that conditioned reaction of active avoidance practically cannot be formed in normal 13-15-day animals; however, administration of ACTH 4-7 increases the number of animals exhibiting adequate reactions. Weak effect of ACTH 4-7 in 12-15-day animals, in older ones (20-24 days) is changed by a significant stimulating effect.     

Changes in pituitary responses to synthetic ovine corticotrophin releasing factor in fetal sheep

The rise in cortisol in fetal sheep during late pregnancy has been related to increased responsiveness of the adrenal to ACTH. Most reports have suggested that plasma ACTH concentrations rise coincident with or after the prepartum increase in cortisol. To reexamine the relationship of cortisol with basal immunoreactive ACTH (IR-ACTH) throughout the last 40 days of pregnancy and to determine changes in fetal pituitary responsiveness during this time, we measured basal and synthetic ovine corticotrophin-releasing factor (oCRF) (10 ng-10 micrograms) induced rises in ACTH and cortisol in fetal sheep at days 110-115, 125-130, and 135-140 of pregnancy. The fetuses were catheterized on day 105-120 and entered spontaneous labour at greater than 140 days. Basal IR-ACTH (picograms per millilitre +/- SEM) rose from 16.7 +/- 2.9 pg/mL at day 110-115 to 34.8 +/- 8.7 pg/mL at day 141-145. There was a significant effect of time on basal ACTH concentrations with a mean increase of approximately 5 pg ACTH per millilitre of plasma per 5-day sampling interval. Plasma cortisol changed gradually between day 110 and 125 of gestation and then more rapidly to term. At day 110-115 of gestation there was no significant change in plasma ACTH after 10 or 100 ng oCRF, but there was a significant increase in ACTH after 1 microgram of oCRF. Plasma cortisol did not change after any CRF injection. The change in IR-ACTH after oCRF at day 125-130 of gestation was significantly greater than that at day 110-115. Plasma cortisol concentrations were elevated following 1- and 10-micrograms injections of oCRF.(ABSTRACT TRUNCATED AT 250 WORDS)     

灵芝对小鼠空间分辨学习与记忆的影响

本文用Y-型迷宫法测试小鼠空间分辨行为。实验结果表明,每日ig灵芝2.58/kg共7d,有明显促进学习的作用。每日ig灵芝2.5g/kg共7d或ig灵芝5g/kg共7d都能显著地拮坑东莨菪碱所致学习障碍的作用。此外,学习训练后立即ig灵芝2.5g/kg或ig灵芝5g/kg也有明显地改善东莨菪碱损害记忆巩固的作用。     

Transaminase reactions and glutamate dehydrogenase in gastropod hepatopancreas

Summary In toads,Bufo bufo L., ACTH (1 I.U.) causes a retardation of extinction compared with Ringer administration irrespective of whether the animals have received the ACTH injection before or at the end of acquisition. Treatment with ACTH 20 min prior to acquisition lowers the starting activity. Therefore, habituation is completed earlier than in Ringer controls. The effect of ACTH treatment is stimulus-specific, as toads habituated to a wormlike stripe show normal turning activity to a triangle even under the influence of ACTH.The conformity of these results with the ACTH effect on complex learning behaviour especially in rats may indicate an underlying common principle. It is concluded that ACTH and, possibly, related peptides elicite neuronal events which favour learning and memory processes even in lower vertebrates.We thank Prof. Dr. W. Hanke, Karlsruhe, for fruitful discussions.     

The hormonal indices of the reactivity of the central links in the hypothalamo-hypophyseal-adrenocortical system of rats during postnatal ontogeny]

Radioimmunological assay has been made of the amount of ACTH in the adenohypophysis and blood plasma in adult male rats as well as in 1, 3, 5, 7, and 20 days old rat puppies 30 minutes after a surgical stress, i. e. cutting the skin at the back of the body. Reliable increase of ACTH level was originally observed in 7-day puppies, whereas in younger animals surgical stress resulted in the decrease of ACTH in the blood. Changes in vasopressin content of the blood and hypophysis exhibit significant variations, but on the whole mainly the decrease was observed in younger animals together with the increase from the 5-7th day of postnatal development of rats. Accumulation of vasopressin was noted in the median eminence after surgical stress in younger animals. The data obtained suggest that the early period of development of the hypothalamo-hypophyseal-adrenocortical system is characterized rather by paradoxal reaction than by non-reactivity, which may be associated with poor neurohormonal transport in the outer zone of the median eminence.     

Effect of ACTH (tetracosactide) on steroid hormone levels in the mare. Part B: effect in ovariectomized mares (including estrous behavior)

The mare is the only non-primate species known to display estrous signs after ovariectomy and adrenal hormones have been implicated as a possible cause. Moreover, in several species, estradiol seems to have a stimulatory effect on the hypothalamic-pituitary-adrenal axis. The aim of the present study was to compare the effect of ACTH (tetracosactide) on pertinent hormones [cortisol, progesterone, androstenedione, testosterone (intact and ovariectomized mares) and estradiol (ovariectomized mares only)] in intact mares in estrus with the same mares after ovariectomy (n=5). Blood samples were collected hourly from 12:00 until 14:00 h the following day (half-hourly between 14:00 and 17:00 h) on two occasions, with saline or ACTH treatment at 14:00 h (saline treatment day or ACTH treatment day). The mares, both when intact and after ovariectomy, showed a significant increase in all measured hormones, except estradiol (not measured in intact mares), after ACTH treatment, lasting at least 3h post-treatment (P<0.001). On the saline treatment day, cortisol levels in ovariectomized mares were lower than in intact mares in the evening (18:00-23:00 h), but higher at night (24:00-05:00 h). No differences in cortisol response between mares, when intact and after ovariectomy, were found after ACTH treatment (P=0.3). Androstenedione levels were lower (P<0.001) and increased less after ACTH treatment in ovariectomized mares, as compared to when intact (P<0.05). Progesterone concentrations were lower in the ovariectomized mares at night (24:00-05:00 h) on the saline treatment day and at all times on the ACTH treatment day (P<0.05). Testosterone concentrations were lower in ovariectomized mares on both treatment days, as compared to when intact (P<0.001). It was concluded that ovariectomy affected basal cortisol pattern. Ovarian androstenedione and testosterone contributed to the basal circulating levels and, in the case of androstenedione, was stimulated by ACTH. Endogenous estradiol did not act stimulatory on adrenal gland hormone production in the mare.     

Activation of adrenal function in fetal sheep by the infusion of adrenocorticotropin to the fetus in utero

We determined whether ACTH1-24, infused into fetal lambs at a rate that is known to cause premature labor, elicits changes in the responsiveness of the fetal adrenal glands, and alters the pattern of corticosteroid output. Plasma cortisol (F), corticosterone (B) and progesterone (P4) were measured during 72 h of infusion of saline or ACTH (10 micrograms/h) beginning on Day 127 of pregnancy. Adrenals were then dispersed into isolated cells, and the output of F, B and P4 after exogenous ACTH determined in vitro. Plasma concentrations of F and B were higher in ACTH-treated fetuses. The increment in F (5-to 7-fold) was greater than that in B (2-fold) such that the F:B ratio in plasma of ACTH-treated fetuses on Days 2 and 3 of infusion was 2.5 times higher than in controls. After 72 h of infusion, the adrenal weights in ACTH-treated fetuses (741 +/- 38 mg, +/- SEM; n = 4) were greater than in the control animals (349 +/- 11 mg). There was a significant effect of ACTH pretreatment in vivo on F output by isolated adrenal cells in vitro. Mean increments in F output after addition of ACTH1-24 (5000 pg/ml) in vitro rose from 368 +/- 235 pg/50,000 cells in controls, to 64,639 +/- 19,875 pg/50,000 cells after ACTH in vivo. There was no significant effect of ACTH in vivo on B output in vitro; the ratio of F:B output, either in the absence or presence of ACTH in vitro, was significantly higher in cells from ACTH-pretreated fetuses. There was a significant effect of in vivo ACTH on in vitro P4 output. After ACTH treatment in vivo there was an increase in the vitro output ratio of F:P4, but no change in the output ratio of B:P4. We conclude that ACTH treatment of the fetal lamb in vivo results in activation of fetal adrenal function, increased fetal adrenal responsiveness to ACTH, and directed corticosteroid biosynthesis towards cortisol. Our results are consistent with an increase in fetal adrenal 17 alpha-hydroxylase activity after ACTH treatment.     

Development of the hypothalamic-pituitary-axis in the ovine fetus: ontogeny of action of ovine corticotropin-releasing factor

In samples from twenty chronically cannulated ovine fetuses the plasma immunoreactive adrenocorticotrophin (ACTH) concentrations were 12.5 +/- 3.2(8), 15.2 +/- 4.1(9) and 21.2 +/- 5.6(8) pg/ml at periods, prior to parturition, of -30 to -35, -25 to -29 and -20 to -24 days respectively. Values are mean +/- SEM (number of samples). These values were not significantly different from each other but were significantly lower (P less than 0.02) than values in the next two age groups -36.0 +/- 4.9(7) pg/ml at -19 to -15 days, and 39.6 +/- 6.6(11) pg/ml at -14 to -9 days. A further significant increase (P less than 0.05) occurred in the -8 to -3 day period, ACTH being 53.9 +/- 5.4(12) pg/ml. On day of delivery two samples had values of 325 and 360 pg/ml. A single injection, intravenously of 1.0 microgram ovine corticotrophin-releasing factor (O-CRF), caused a significant increase in fetal plasma ACTH concentrations in fetuses of -6 to -23 days prior to delivery but not in fetuses -24 to -35 days prior to parturition. The maximum values of ACTH after O-CRF were significantly greater in fetuses -2 to 0 days prior to parturition than in younger fetuses (P less than 0.01). In 6 experiments in 4 fetuses (parturition -1 to -13 days) the effect of 1.0 microgram O-CRF persisted for at least 2.5 h. The results support the hypothesis that the pituitary release of ACTH changes sensitivity to hypothalamic O-CRF at least twice during the last fifth of gestation; an increasing sensitivity is seen as term approaches.     

The effect of hypocholesterolemic drug treatment on adrenocortical cell function

The role of exogenous lipoprotein cholesterol versus endogenous cholesteryl esters as substrates in adrenal steroidogenesis was studied in isolated rat adrenal cells. Hypocholesterolemic drugs were used in rats to depress the plasma cholesterol concentration and the adrenal cholesterol concentration. Adrenal cortical cells were prepared in the usual way. The steroidogenic response to ACTH in normal adrenal cells and in cells which have been cholesterol-depleted was studied. Normal adrenal cells responded specifically over a 6 h incubation period to low doses of ACTH (half-maximal response equivalent to 40 microunits ACTH). These normal cells exhibited no altered response over a 3 h period to ACTH in the presence of serum or serum lipoproteins. The hypocholesterolemic drugs, 4-aminopyrazolo-[3,4-d]-pyrimidine, hexestrol and 17 alpha-ethinyl estradiol were used to lower plasma cholesterol, and after 1 day of 4-aminopyrazolo-[3,4-d]-pyrimidine and 5 days of hexestrol or 17 alpha-ethinyl estradiol treatment the plasma total cholesterol concentrations were similar. After 3 days of 4-aminopyrazolo-[3,4-d]-pyrimidine treatment the adrenal total cholesterol content was lower than after 1 day of this treatment, or 5 days of hexestrol treatment or 5 days of 17 alpha-ethinyl extradiol treatment. Lipoproteins had no significant effect on ACTH-stimulated steroidogenesis in cells isolated from rats treated for 1 day with 4-aminopyrazolo-[3,4-d]-pyrimidine, or for 5 days with hexestrol or 17 alpha-ethinyl estradiol. However, lipoproteins did stimulate steroidogenesis in cells from rats treated for 3 days with 4-aminopyrazolo-[3,4-d]-pyrimidine. The results show that normal adrenal cells contain a reserve of intracellular cholesterol so that the supply of endogenous cholesterol for steroidogenesis does not limit the response to ACTH and exogenous lipoproteins have no effect on steroidogenesis. However, if the cells are severely depleted of cholesterol then exogenous lipoproteins must be added for maximal steroidogenesis to occur.     

Circadian variations and extraadrenal effect of ACTH on insulinemia in rabbit.

The present experiment was designed to study the action of ACTH1-24 on insulin secretion during the circadian cycle in normal rabbits and to provide evidence that ACTH1-24 has an extra-adrenal effect on this secretion. In normal rabbits intravenous administration of three doses of ACTH1-24 (1, 10, 100 micrograms/kg) at 10 a. m. increased plasma insulin levels. Hyperglycemia only occurred with doses of 10 and 100 micrograms/kg. A maximum insulin response was already obtained at 1 micrograms/kg. The same experiment performed at 12 p. m. also induced hyperinsulinemia which was only noted at 10 and 100 micrograms/kg; hyperglycemia was only observed after stimulation by the highest dose (100 micrograms/kg). ACTH was therefore more effective during the day; however, at 12 p. m. plasma insulin levels were the highest, but only with the maximum dose of ACTH (100 micrograms/kg). The effect of ACTH1-24 was evaluated throughout the day on normal and adrenalectomized rabbits. In normal animals injection of ACTH1-24 increased plasma glucose and insulin levels both together. In the contrary, in rabbits deprived of adrenal glands, ACTH1-24 induced high insulinemia along with hypoglycemia. We could, therefore, reasonably conclude that ACTH stimulates directly the pancreatic secretion of insulin.     

Perinatal Exposure to Bisphenol-A Impairs Spatial Memory through Upregulation of Neurexin1 and Neuroligin3 Expression in Male Mouse Brain

Bisphenol-A (BPA), a well known endocrine disruptor, impairs learning and memory in rodents. However, the underlying molecular mechanism of BPA induced impairment in learning and memory is not well known. As synaptic plasticity is the cellular basis of memory, the present study investigated the effect of perinatal exposure to BPA on the expression of synaptic proteins neurexin1 (Nrxn1) and neuroligin3 (Nlgn3), dendritic spine density and spatial memory in postnatal male mice. The pregnant mice were orally administered BPA (50 µg/kgbw/d) from gestation day (GD) 7 to postnatal day (PND) 21 and sesame oil was used as a vehicle control. In Morris water maze (MWM) test, BPA extended the escape latency time to locate the hidden platform in 8 weeks male mice. RT-PCR and Immunoblotting results showed significant upregulation of Nrxn1 and Nlgn3 expression in both cerebral cortex and hippocampus of 3 and 8 weeks male mice. This was further substantiated by in-situ hybridization and immunofluorescence techniques. BPA also significantly increased the density of dendritic spines in both regions, as analyzed by rapid Golgi staining. Thus our data suggest that perinatal exposure to BPA impairs spatial memory through upregulation of expression of synaptic proteins Nrxn1 and Nlgn3 and increased dendritic spine density in cerebral cortex and hippocampus of postnatal male mice.     

ACTH Enhancement of T-Lymphocyte Cytotoxic Responses

1. Corticotropin (ACTH) was one of the first neuropeptides shown to bind to receptors on leukocytes and modulate immune responses. Generally ACTH inhibits immune responses, but certain functions can be enhanced. The present study was performed to determine the effects of ACTH on cytotoxic T-lymphocyte responses, the components, and the major phenotypes of the participating cells.2. The action of ACTH on cytotoxicity was measured in vitro, in assays utilizing T-lymphocytes that had been previously sensitized in vivo. The cells were then cultured with ACTH and target cells bearing the appropriate stimulatory major histocompatiblity antigens.3. ACTH did not significantly affect a primary mixed lymphocyte reaction whereas it enhanced a secondary (memory) cytotoxic response up to 100% following 2 days of ACTH treatment. The effect was a shift in the kinetics of effector cell generation so that ACTH-treated cultures demonstrated an augmented cytotoxic activity on day 2, that was not as pronounced on day 3 as cytotoxic activity in control cultures became maximal. ACTH also inhibited Concanavalin A-stimulated T-lymphocyte mitogenesis. Immature thymocyte mitogenesis was inhibited more than that of mature thymocytes.4. The finding that IFN-γ was elevated in the cultures suggested that ACTH may enhance memory cytotoxic responses through a combination of mechanisms such as direct cell alterations or synergy with regulatory cytokines. While corticosteroids are probably the most recognized neuroendocrine, stress hormone to affect immune functions, our study illustrates that other neuroendocrine factors such as ACTH, also directly affect immune functions.     

Endogenous ACTH concentration-dependent drive of pulsatile cortisol secretion in the human

According to current regulatory concepts, pulsatile ACTH concentrations (CON) stimulate time-lagged cortisol secretion rates (SEC) via an implicit CON-SEC dose-response relationship. The present analyses reconstruct nonlinear properties of this in vivo agonist-response interface noninvasively in order to investigate pulse-by-pulse coupling consistency and to obviate the need to infuse isotopes or exogenous effectors, which may disrupt pathway interactions. This approach required an ensemble strategy of 1) measuring ACTH and cortisol CON in plasma sampled every 10 min for 24 h in 32 healthy adults, and 2) estimating simultaneously a) variable-waveform ACTH and cortisol SEC bursts superimposed upon fixed basal SEC; b) biexponential kinetics of ACTH and cortisol disappearance; c) nonequilibrium exchange of cortisol among free and cortisol-binding globulin (CBG)- and albumin-bound moieties; d) two SEC-burst shapes demarcated by a statistically defined day/night boundary; e) feedforward efficacy, potency, and sensitivity; and f) stochastic variability in feedforward measures over time. Thereby, we estimate 1) ACTH SEC (microg.l(-1).day(-1)) of 0.27 +/- 0.04 basal and 0.87 +/- 0.07 pulsatile (means +/- SE); 2) cortisol SEC (micromol.l(-1).day(-1)) of 0.10 +/- 0.01 basal and 3.5 +/- 0.20 pulsatile; 3) free cortisol half-lives (min) of 1.8 +/- 0.20 (diffusion/advection) and 4.1 +/- 0.30 (elimination) and a half-life of total cortisol of 49 +/- 2.4 and of ACTH of 20 +/- 1.3; 4) ACTH potency (EC(50), ng/l) of 26 +/- 2.4, efficacy (nmol.l(-1).min(-1)) 10 +/- 1.8, and sensitivity (slope units) 0.65 +/- 0.09; 5) night/day augmentation of ACTH and cortisol SEC-burst mass by 2.1- and 1.7-fold (median); 6) abbreviation of the modal time to maximal ACTH and cortisol SEC rates by 4.4- and 4.3-fold, respectively, after a change point clock time of 0205 (median); 7) in vivo percentage distribution of cortisol as 6% free, 14% albumin bound, and 80% CBG bound with an absolute free cortisol CON (nmol/l) 11.5 +/- 0.54; and 8) significant (mean CV) stochastic variability in feedforward efficacy (140%), potency (38%), and sensitivity (56%) within the succession of paired ACTH/cortisol pulses of any given subject. In conclusion, the present composite formulation illustrates a platform for dissecting mechanisms of in vivo regulation of effector-response properties noninvasively in the corticotropic axis of the uninfused individual.     

Adrenocorticotropin administration during early gestation on conceptus development in swine

The purpose of this study was to examine the effect of exogenous adrenocorticotropin (ACTH), administered to gilts during early stages of gestation, upon fetal survival and various maternal and conceptus parameters. Forty-eight gilts of approximately 6-7 months of age were bred by means of artificial insemination after detection of the second estrus and randomly allotted to one of 12 treatment-period groups. Treatment consisted of a daily intramuscular injection of 0, 40 or 80 U.S.P. units of a long acting ACTH preparation for a period of five days. The injection periods were 1-5, 6-10, 11-15 or 16-20 days of gestation with day one corresponding to 48 hours post-estrus detection. All gilts were slaughtered at approximately 37 days of gestation. Forty-two of the 48 inseminated gilts conceived. Conception rate was not different (P>.10) among the 12 treatment-period combinations. Percent fetal survival was greater (P<.09) in gilts receiving 80 U.S.P. units of ACTH (82 +/- 4.3%; X +/- SEM ) than in gilts receiving 40 U.S.P. units of ACTH (68.8 +/- 4.5%). The percent fetal survival in the control group (71.7 +/- 3.9%) was not different (P>.10) from either of the two ACTH treatment groups. A significant (P<.05) treatment by period interaction for percent fetal survival was observed. The lowest percent fetal survival (48.0 +/- 9.0%) was observed in gilts receiving 40 U.S.P. units of ACTH on day 11-15 of gestation. No significant (P>.10) differences were detected among the 12 treatment-period combinations for any of the maternal or conceptus parameters measured.     

Adrenal adenylate cyclase and steroidogenic activities of 63 day old ovine fetuses: in vitro effects of ACTH1-24 and forskolin

This study examines the activity of the adenylate cyclase system and that of some enzymes of the steroidogenic pathway of adrenal cells from 62-63 day old ovine fetuses. Synthetic corticotropin (ACTH1-24), cholera toxin and forskolin stimulated both cAMP and corticoid productions by freshly isolated adrenal cells. The cAMP response to ACTH1-24 was lower than that to forskolin. However, forskolin-induced steroidogenesis was significantly lower than the ACTH1-24-induced steroid output. Freshly isolated cells metabolized quickly [14C]-labeled pregnenolone mainly through the 17-deoxy pathway. The amounts of cortisol and of corticosterone formed, in the presence of exogenous pregnenolone, were roughly 15-fold higher than under maximal stimulation by ACTH1-24. When the cells were cultured for 6 days in the absence or presence of ACTH1-24 (10(-8) M) or forskolin (10(-5) M), a small development of the cAMP response to these factors was observed in the course of the experiment. However, the mechanism of this development appeared different, according to the conditions of culture. The amounts of corticosterone secreted on day 6 by ACTH1-24- or forskolin-treated cells were 2- to 4-fold higher than on day 1, whereas cortisol outputs were much lower on day 6 than on day 1. The response to ACTH1-24 of cells maintained in ACTH-free media decreased dramatically during the culture in terms of both cortisol and of corticosterone. On day 6 of the experiment, the metabolism of [14C]pregnenolone was lower than on day 1 under all 3 conditions of culture. Only the 3 beta-hydroxysteroid dehydrogenase/isomerase activity could be maintained by continuous treatment with forskolin. However, both ACTH1-24 and forskolin enhanced the production of pregnenolone from an endogenous substrate. In conclusion, these results present evidence that: 1) the adenylate cyclase system is not a bottleneck in the steroidogenic response to ACTH1-24 of freshly isolated adrenal cells from 62-63 day old ovine fetuses; 2) the main rate-limiting step for steroidogenesis by these cells is the availability of pregnenolone; 3) neither ACTH1-24 nor forskolin is able to maintain the activity of most enzymes involved in the metabolization of pregnenolone by cultured cells while increasing pregnenolone availability; 4) some inhibiting factors are involved in the loss of adrenal cells responsiveness to ACTH between days 50 and 100 of gestation, and they probably act mainly on the adenylate cyclase system.     

The effects of the neurotoxin DSP4 on spatial learning and memory in Wistar rats

The aim of the present study was to investigate the effect of DSP4-induced noradrenaline depletion on learning and memory in a spatial memory paradigm (holeboard). Since Harro et al. Brain Res 976:209-216 (2003) have demonstrated that short-term effects of DSP4 administration include both noradrenaline depletion and changes in dopamine and its metabolites-with the latter vanishing within 4 weeks after the neurotoxic lesion-the behavioural effects observed immediately after DSP4 administration cannot solely be related to noradrenaline. In the present study, spatial learning, reference memory and working memory were therefore assessed 5-10 weeks after DSP4 administration. Our results suggest that the administration of DSP4 did not lead to changes in spatial learning and memory when behavioural assessment was performed after a minimum of 5 weeks following DSP4. This lack of changes in spatial behaviour suggests that the role of noradrenaline regarding these functions may be limited. Future studies will therefore have to take into account the time-course of neurotransmitter alterations and behavioural changes following DSP4 administration.