Stimulation In Rhesus Monkeys Research Articles

Values encoded in orbitofrontal cortex are causally related to economic choices.

In the eighteenth century, Daniel Bernoulli, Adam Smith and Jeremy Bentham proposed that economic choices rely on the computation and comparison of subjective values1. This hypothesis continues to inform modern economic theory2 and research in behavioural economics3, but behavioural measures are ultimately not sufficient to verify the proposal4. Consistent with the hypothesis, when agents make choices, neurons in the orbitofrontal cortex (OFC) encode the subjective value of offered and chosen goods5. Value-encoding cells integrate multiple dimensions6-9, variability in the activity of each cell group correlates with variability in choices10,11 and the population dynamics suggests the formation of a decision12. However, it is unclear whether these neural processes are causally related to choices. More generally, the evidence linking economic choices to value signals in the brain13-15 remains correlational16. Here we show that neuronal activity in the OFC is causal to economic choices. We conducted two experiments using electrical stimulation in rhesus monkeys (Macaca mulatta). Low-current stimulation increased the subjective value of individual offers and thus predictably biased choices. Conversely, high-current stimulation disrupted both the computation and the comparison of subjective values, and thus increased choice variability. These results demonstrate a causal chain linking subjective values encoded in OFC to valuation and choice.

Ovarian reserve tests and their utility in predicting response to controlled ovarian stimulation in rhesus monkeys

Controlled ovarian stimulation (COS) is an alternative to natural breeding in nonhuman primates; however, these protocols are costly with no guarantee of success. Toward the objective of predicting COS outcome in rhesus monkeys, this study evaluated three clinically used ovarian reserve tests (ORTs): day 3 (d3) follicle-stimulating hormone (FSH) with d3 inhibin B (INHB), the clomiphene citrate challenge test (CCCT), and the exogenous FSH Ovarian Reserve Test. A COS was also performed and response was classified as either successful (COS+) or unsuccessful (COS-) and retrospectively compared with ORT predictions. FSH and INHB were assessed for best hormonal index in conjunction with the aforementioned tests. INHB was consistently more accurate than FSH in all the ORTs used. Overall, a modified version of the CCCT using INHB values yielded the best percentage of correct predictions. This is the first report of ORT evaluation in rhesus monkeys and may provide a useful diagnostic test before costly follicle stimulations, as well as predicting the onset of menopause.

Dynamic changes in ovarian follicles measured by ultrasonography during gonadotropin stimulation in rhesus monkeys

The objective was to study dynamic changes of ovaries in rhesus macaques stimulated by gonadotropins to identify an indicator for predicting ovarian response to stimulation. Twenty-one cycling monkeys were given 36 IU/d recombinant human follicle-stimulating hormone (rhFSH) for 8 d. Animals (n = 17) with ≥5 follicles (≥3 mm) in their ovaries on Day 9 of ovarian stimulation were deemed good responders, whereas those with a lesser response were poor responders (n = 4). For these two groups, the mean (±SD) numbers of oocytes retrieved were 44.3 ± 21.4 and 11.0 ± 4.6, respectively. In retrospect, the mean diameters of the ovaries and of the largest follicles, the total number of detectable follicles (diameter >0.5 mm), and serum estradiol concentrations gradually increased during the stimulation period in the good responders but did not increase in the poor responders. Comparing good and poor responders, the number of ovarian follicles >0.5 mm already exhibited a difference (12.9 ± 6.5 vs. 2.9 ± 1.3, respectively, P < 0.05) on Day 1 of stimulation. However, for other end points, differences were not significant until at least Day 5. Moreover, good responders yielded a fivefold higher blastocyst development rate than that of poor responders (P < 0.01). In conclusion, the number of ovarian follicles detected with ultrasonography could be useful to predict the response to FSH stimulation in non-human primates.

Effects of rhFSH dose on ovarian follicular response, oocyte recovery and embryo development in rhesus monkeys

The objective was to study the effects of dose of recombinant human follicular stimulating hormone (rhFSH) for ovarian stimulation in rhesus monkeys. Nineteen pubertal and 109 adult female rhesus monkeys were given 37.5, 18, or 9 IU of rhFSH twice-daily for 8 days (total of 600, 300, or 150 IU of rhFSH per cycle, respectively; designated Regimens 1, 2 and 3). Ovarian responses were assessed with ultrasonography, serum concentrations of E2 and FSH, and by in vitro developmental potential (following IVF) of retrieved oocytes. Regimen 1 had more monkeys with very large follicles (diameter > 8 mm) than Regimen 2 ( P < 0.05), which impaired development potential. However, there were no differences between Regimens 1 and 2 in oocyte recovery, whereas Regimen 3 did not elicit superovulation. The developmental potential of embryos obtained from Regimen 2 was higher than that of Regimen 1, as determined by culture to the blastocyst stage in vitro (proportion of blastocysts relative to collected MII oocytes was 55.8% versus 36.8% in pubertal and 63.8% versus 44.2% in adult monkeys; P < 0.05 for each), and the results of embryo transfer from Regimen 2 were acceptable. In conclusion, we inferred that the optimal rhFSH dose for ovarian stimulation in rhesus monkeys was a total of 300 IU; this dose should be efficacious for ovarian stimulation as the quality or recovered oocytes was higher and the risk of overstimulation was reduced.

Pharmacokinetics and pharmacodynamics of single-chain recombinant human follicle-stimulating hormone containing the human chorionic gonadotropin carboxyterminal peptide in the rhesus monkey

Objective: To compare the pharmacokinetics of a long-acting FSH analog containing the hCG-β carboxyterminal peptide (recombinant hFSH–CTP) with native recombinant hFSH and describe the pharmacodynamics of recombinant hFSH–CTP after SC injection in female rhesus monkeys. Design: Rhesus monkey study. Setting: Academic research environment. Animal(s): Ten female rhesus monkeys. Intervention(s): Recombinant hFSH and recombinant hFSH–CTP were administered via a single SC or IV dose to rhesus monkeys, and serial phlebotomy was performed (n = 2 and n = 4 for SC recombinant hFSH and recombinant hFSH–CTP, respectively; for IV dosing, n = 1 in each group). An additional two monkeys were pretreated with SC ganirelix and received SC recombinant hFSH–CTP after confirmation of pituitary suppression. Main Outcome Measure(s): Plasma disappearance rate of recombinant hFSH and recombinant hFSH–CTP and serum estradiol levels. Result(s): The elimination half-life of recombinant hFSH–CTP was twofold and fourfold longer than that for recombinant hFSH after SC and IV dosing, respectively. The absorption half-life was approximately threefold longer for recombinant hFSH–CTP than for recombinant hFSH after SC administration. Recombinant hFSH–CTP stimulates estradiol secretion for 5–7 days after an isolated SC dose. Conclusion(s): Addition of the hCG-β carboxyterminal peptide to hFSH-β results in an FSH analog with longer absorption and elimination half-lives compared with native hormone. This analog is capable of prolonged ovarian stimulation in rhesus monkeys after an isolated SC injection.

Initiation of periovulatory events in gonadotrophin-stimulated macaques with varying doses of recombinant human chorionic gonadotrophin.

During in-vitro fertilization (IVF) cycles, a large bolus of human chorionic gonadotrophin (HCG) is used to induce periovulatory events, but the efficacy of lower doses is undefined. Following follicular stimulation in rhesus monkeys, oocyte nuclear maturation, IVF, granulosa cell luteinization and corpus luteum function were compared after injection of 100, 300 or 1000 IU recombinant HCG or 1000 IU urinary HCG. Bioactive HCG rose to peak concentrations within 2 h that were proportional to the dose administered (100 < 300 < 1000 IU, recombinant HCG = urinary HCG). The duration of surge values (>100 ng/ml) was also dose-dependent (0 h, 100 IU; 24 h, 300 IU; >48 h, 1000 IU, recombinant and urinary HCG). While the proportions of oocytes resuming meiosis and undergoing IVF were similar among groups, fewer animals yielded fertilizable oocytes following 100 and 300 IU (five of nine) compared to 1000 IU recombinant and urinary HCG (nine of 10). Peak values of serum progesterone in the luteal phase were similar, but declined 2 days earlier after 100 and 300 IU relative to 1000 IU recombinant and urinary HCG. Thus, 3-10 fold lower doses of HCG elicit low amplitude surges of short duration that induce periovulatory events such as re-initiation of oocyte meiosis and granulosa cell luteinization. However, oocyte fertilization and luteal function may optimally require surges of higher amplitude and longer duration similar to those produced by standard doses of 1000 IU recombinant or urinary HCG.

Use of purified porcine follicle-stimulating hormone for ovarian stimulation of macaque monkeys

At present, in nonhuman primates, ovarian stimulation with heterologous gonadotropin preparations is the only reliable way to produce substantial numbers of competent ova for in vitro fertilization and embryo development studies. Preparations such as equine chorionic gonadotropin (eCG) and human menopausal gonadotropins (hMG or hFSH) have been used successfully, but eCG is crude and contains variable amounts of LH activity, while hMG/hFSH is very expensive and the supply is not stable. This study examined the use of a purified porcine FSH preparation (Folltropin V) for ovarian stimulation in rhesus monkeys. Twice-daily intramuscular injections of this preparation resulted in good follicular development, and was followed by a single intramuscular injection of hCG. Ova were collected laparoscopically 30 h post hCG, fertilized in vitro and then cultured until development ceased. Stimulation of 9 monkeys with Folltropin V yielded a mean of 20 ova per animal, of which 71% reached metaphase II and were inseminated; of these, 92% were fertilized in vitro and 48% developed into blastocysts in vitro. These results are similar to those reported by us and by others using eCG, hMG or an hFSH/hMG combination for ovarian stimulation of macaque monkeys. We conclude that Folltropin V is a suitable alternative preparation for ovarian stimulation in nonhuman primates and one that also has the advantages of being readily available and much less expensive than human gonadotropin preparations.

Maturity and fertility of rhesus monkey oocytes collected at different intervals after an ovulatory stimulus (human chorionic gonadotropin) in in vitro fertilization cycles.

In rhesus monkeys undergoing ovarian stimulation for in vitro fertilization (IVF), a midcycle injection of human chorionic gonadotropin (hCG) substitutes for the LH surge and induces preovulatory oocyte maturation. The time interval between injection and oocyte collection, ideally, allows for the completion of oocyte maturation without ovulation, which would reduce the number of oocytes available for harvest. To evaluate the influence of this time interval on oocyte parameters following hCG administration, we conducted a series of gonadotropin treatment protocols in 51 animals in which the interval from hCG administration to follicular aspiration was systematically varied from 27 to 36 hr. Follicle number and size, evaluated prior to hCG administration by sonography, did not vary significantly or consistently with preovulatory maturation time. Oocytes were harvested by laparotomy or laparoscopy, and scored for maturity before insemination. The percentage of mature, metaphase II (MII) oocytes at recovery increased significantly with increasing preovulatory time and was inversely proportional to that of metaphase I (MI) oocytes. However, oocyte yield tended toward a progressive decrease with increasing preovulatory maturation times from a high of 27 oocytes at 27 hr to a low of 17 oocytes/animal at the 36 hr time interval. Fertilization levels declined significantly from a high of 50% at 27 hr to a low of 30% at 36 hr. Thus, although higher percentages of mature oocytes were recovered at the longer time intervals, optimal oocytes/embryo harvests were realized after the shorter time intervals (27 and 32 hr) and are most compatible with the goal of achieving high yields of fertile oocytes and embryos following gonadotropin stimulation in rhesus monkeys.

Luteal function following ovarian stimulation in rhesus monkeys for in vitro fertilization: atypical response to human chorionic gonadotropin treatment simulating early pregnancy

This study determined if corpora lutea of hyperstimulated cycles in rhesus monkeys could be "rescued" by the pregnancy signal, chorionic gonadotropin (CG), given at the typical time of implantation. At menses, female monkeys received human follicle-stimulating hormone (hFSH, 60 IU, days 1 to 6) followed by human menopausal gonadotropin (hMG, 60 IU hFSH/60 IU luteinizing hormone [hLH], days 7 to 9). On day 10, human chorionic gonadotropin (hCG) was given to mimic the LH surge. Nine days later, a regimen of daily increasing doses of hCG (15 to 360 IU twice a day) was initiated to simulate rescue of the corpus luteum in early pregnancy. Serum levels of progesterone (P) increased through day 5 of the luteal phase but then declined. Circulating levels of bioactive LH were significantly less on days 7 to 9 of the luteal phase than at this stage in the natural cycle. The hCG regimen extended (P less than 0.05) the luteal phase in five of six animals. The hCG treatment elicited a persistent increase (P less than 0.05) in circulating P levels, rather than a transient rise typical of normal or simulated pregnancy in natural cycles. The authors conclude that (1) corpora lutea of hyperstimulated cycles can respond to CG, but (2) there are differences in luteal function during both the luteal phase and simulated early pregnancy that may be due to inadequate luteal development or the abnormal gonadotropin milieu existing after ovulation or both.

Ultradian barpressing for rewarding brain stimulation in rhesus monkeys

Rhesus monkeys were chronically implanted with stimulating electrodes at positive reinforcement sites in anterolateral hypothalamus and locus ceruleus. Monkeys were then allowed to roam free in a large cage for six days and deliver brain stimulation to themselves when they wished. No monkey sought stimulation at locus ceruleus after the first few minutes in the cage, but all repeatedly barpressed for anterolateral hypothalamic stimualtion. Barpressing rates in 3 of 4 monkeys were found to correlate significantly with a 40–45 min ultradian rhythm while the rate for the other monkey correlated best with an 85 minute rhythm.

Lymphocyte isolation, rosette formation, and mitogen stimulation in rhesus monkeys

Over 70%, of rhesus monkey peripheral mononuclear cells were isolated on sodium metrizoate-ficoll gradients with greater than 98% purity. Rhesus blood contained 47.8% active E, 58.2% total E, and 30.2% EAC rosette forming cells. Optimal conditions for mitogen studies were determined using phytohemagglutinin, concanavalin A, pokeweed mitogen, lipopolysaccharide and streptolysin 0.

Cortical potentials evoked by tooth pulp stimulation in rhesus monkeys

Tooth pulp was electrically stimulated in 21 rhesus monkeys and evoked electrical activity recorded on cerebral cortex. Gross surface potentials which were found on the postcentral gyrus at the tip of the intraparietal sulcus required electronic summation for identification. Pulp-activated potentials were distinguishable from those evoked by stimulation of periodontal structures on the basis of latency and amplitude. In addition, thirty-eight single pulp-driven units were isolated. They were concentrated in deep cellular layers at the base of the central sulcus. Units driven by oral mucosa were more superficially located.