ACTH4-9 analog (ORG 2766) facilitates acquisition of an inhibitory avoidance response in rats

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.

Learning and memory processes of an ACTH4-9 analog (ebiratide; Hoe 427) in mice and rats

These experiments investigated the effects of the new ACTH4-9 analog ebiratide (Hoe 427) [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-NH-(CH2)8-NH2 X 3 CH3COOH] on memory processes in mice and rats in five training tasks. With all five training and testing procedures (inhibitory avoidance test with ECS- or scopolamine-induced amnesia, up-hill avoidance, one-way shuttle box avoidance and eight-arm radial maze) ebiratide was most effective in a dose range of 1-10 micrograms/kg SC.

Acceleration of recovery from sciatic nerve damage by the ACTH (4-9) analog Org 2766: different routes of administration

Functional recovery following a sciatic nerve crush in rats was investigated by measuring the reflex withdrawal of the hindpaw to a hot air stream. The ACTH(4-9) analog Org 2766 accelerated recovery when administered subcutaneously (two-daily injections: 10 micrograms/animal; minipumps: 20-40 micrograms/animal per 24 hr: biodegradable microspheres: 40 micrograms/animal per 24 hr), but oral administration (1.5-20 mg/animal daily, in the drinking water; 1.5-15 mg/animal daily, by gavage) was not effective.

The effects of Org 2766 on the performance of sham, neocortical, and hippocampal-lesioned rats in a food search task

The behavioral effects of an ACTH4-9 variant, Org 2766, given for one week postoperatively at a dose of 1 microgram/rat daily, were evaluated in animals given hippocampal, neocortical, or "sham" lesions. After the week during which the injections were given, the animals were tested for 5 days in a food-search task in which food was hidden in two recessed holes in the floor. On the next day the ability of the rats to find food in these same two baited holes was tested in the presence of 14 additional holes that were not baited. On the following day, the animals were tested again, this time with all 16 holes baited. To assess the long-term effects of Org 2766 treatment, the animals were tested once again 2-3 months later in the same apparatus with 16 empty holes. In general, rats with lesions restricted to the neocortex were severely impaired in the task and were unaffected by prior treatment with Org 2766. Animals with hippocampal damage quickly learned the task and were hyperactive. During the test session with 16 baited holes they showed differential behavioral changes suggesting attentional deficits not seen in "sham" operated rats. These deficits were attenuated by prior Org 2766 treatment, whereas the lesion-induced hyperactivity was not. Treatment with Org 2766 impaired all aspects of performance of "sham" operated animals.

ACTH 4-9 analogue (Org 2766) in depressed elderly patients. II. Effect on memory and vigilance

In a double-blind interindividual comparison 80 mg of an ACTH 4-9 analogue (Org 2766) or placebo was administered daily to 49 elderly depressed in- and out-patients for 4 weeks. 20 patients then changed to the opposite treatment in a cross-over study for a further 2 weeks. All patients were tested for memory on days 0 and 29 with a battery consisting of the 30 World-Pair Test, the 30 Figure-Test and the 30 Personal-Facta Test. Three scores were obtained from each test, immediate memory score (IMS), delayed memory score (DMS) and their difference, forgetting score (FS). Cross-over patients were tested for vigilance on days 0, 29 and 43 in an apparatus testing ability to rapidly detect and react to specific minor changes at random intervals. Org 2766 had no better effect than placebo on learning, consolidation, or retrieval of memorized material in elderly depressed patients. Statistically significant fewer target misses in the test of vigilance suggest a higher degree of sustained attention after treatment with Org 2766.

Misleading concepts in the field of brain peptides

Peptide research, like all of science, requires a careful balance between building upon previously accumulated knowledge and exploring perspectives that are in conflict with prevailing views. Many of the concepts discussed here originally stimulated certain lines of research. The downfall of most of these concepts, and thus their misleading nature, lies in the limitation of possible modes by which peptides are perceived to affect the functioning of the central nervous system (CNS).

Arginine vasopressin enhances retention of morphine tolerance

The hot plate method was used to assess tolerance in rats following daily injections of morphine. Following analgesia assessment, or a time equated rest period, rats were injected with either saline or a pituitary peptide. Arginine vasopressin, but not ACTH 4-10, prolonged the retention of morphine tolerance when assessed five weeks after the last injection. Neither the rate nor the degree of tolerance development were influenced by either peptide. These hormones had no effect on retention of tolerance development were influenced by either peptide. These hormones had no effect on retention of tolerance in rats not assessed for analgesia during the period of tolerance development. The effects of pituitary peptides on morphine tolerance are analogous to the effects they have on learning and memory processes, suggesting that similar adaptational processes are occurring in both phenomena.

Dose-related facilitation and inhibition of passive avoidance behavior by the ACTH 4-9 analog (ORG 2766)

The effects of "low" and "high" doses of the ACTH 4-9 analog (ORG 2766) were studied on passive avoidance behavior of rats compared to ACTH 4-10 and [D-Phe7] ACTH 4-10. All peptides increased avoidance latency in a dose-dependent manner. However, "high" doses of ORG 2766 (500 and 1000 ng/rat) inhibited passive avoidance retention. "High" amounts of ACTH 4-10 and [D-Phe7] ACTH 4-10 still facilitated passive avoidance behavior. "High" doses of ORG 2766 like "low" amounts of this peptide delayed extinction of active avoidance behavior. "High" doses of [D-Phe7] ACTH 4-10 like "low" amounts of this peptide facilitated extinction of active avoidance behavior. The substituted analog apparently carries a dual effect on passive avoidance behavior.

Potency and duration of action of the ACTH 4-9 analog (ORG 2766) as compared to ACTH 4-10 and [D-Phe7] ACTH 4-10 on active and passive avoidance behavior of rats

Experiments were performed to examine the potency and duration of action of various ACTH analogs on active and passive avoidance behavior of rats. ACTH 4-10 and the ACTH 4-9 analog (ORG 2766) delayed extinction of pole-jumping avoidance behavior and facilitated passive avoidance responding. [D-Phe7] ACTH 4-10 facilitated extinction of pole-jumping avoidance behavior and facilitated passive avoidance responding. [D-Phe7] ACTH 4-10 facilitated extinction of pole-jumping avoidance behavior and facilitated passive avoidance responding. ORG 2766 was a thousand times more active than ACTH 4-10. The effect of ORG 2766 on extinction of pole-jumping avoidance behavior and on passive avoidance behavior was of longer duration than that of ACTH 4-10. As determined more precisely in the passive avoidance test it appeared that the action of ACTH 4-10 lasted 3 to 6 hours, while that of ORG 2766 amounted to at least 24 hours. Although [D-Phe7] ACTH 4-10 was a thousand times less active than ORG 2766 in the passive avoidance paradigm, its duration of action was of the same magnitude. In view of this, the marked increase in potency of the ACTH 4-9 analog cannot be explained only on the basis of its metabolic stability but also by an increased intrinsic activity.

Effects of beta-(Tyr9)melanotropin-(9-18) decapeptide on passive and active avoidance behavior and on open-field activity of rats

The effects of the administration of beta-(Tyr9)melanotropin-(9-18) into the lateral ventricle in a dose of 1.0 micrograms in 2 microliters were studied on passive avoidance behavior, extinction of active avoidance behavior, and open-field activity in rats. beta-(Tyr9) melanotropin-(9-18) given 30 min pretrial facilitated the acquisition of passive avoidance behavior; however, it was ineffective on retention when the material was given immediately posttrial or 30 min before retention testing. The extinction of active behavior was delayed. In open-field activity, the ambulation rate and rearing activity were increased 30 min following administration. The data suggest that beta-(Tyr9)melanotropin-(9-18) has distinct neurotropic properties, and is able to modify behavioral reactions.

Infundibular ACTH can be excluded as a critical mediator in social behaviours

Kainic acid lesions of the infundibulum resulted in a significant decrease in infundibular ACTH concentrations. However, the lesioned rats did not differ from the vehicle-injected controls in a social interaction test, in their latency to start drinking in a novel environment, or in their aggressive behaviour in home-cage intruder tests. It can therefore be concluded that endogenous infundibular ACTH does not play a significant role in these behaviours. This can be contrasted with the effects of exogenously administered ACTH which has previously been shown to reduce social interaction and increase aggression. Both the lesioned rats and the controls showed decreased social interaction after ACTH administration, and therefore the infundibulum can be excluded as a critical site of action of exogenous ACTH in mediating this behavioural change.