Neurotrophic peptide ACTH-(4-10) permits glucocorticoid-facilitated retention of acquired immobility response of hypophysectomized rats

Brain potentials and attention after acute and subchronic intranasal administration ofACTH 4-10 and desacetyl-alpha-MSH in humans

Neuropeptides related to adrenocorticotropin (ACTH) are potent regulators of neurobehavioral functions. In humans, ACTH and its behaviorally active fragment ACTH 4-10 have been consistently found to diminish event-related brain potential (ERP) signs of focussing attention. This study aimed at (1) evaluating effects of ACTH 4-10 on ERP indicators of attention in healthy controls after intranasal administration of the peptide. This route of administration has been proposed to provide a more direct access to the brain than the intravenous administration of the peptide, (2) comparing acute effects and effects of a subchronic treatment with ACTH 4-10, and (3) comparing effects of ACTH 4-10 with those of desacetyl-alpha-MSH (corresponding to ACTH 1-13 amide) which like ACTH 4-10 binds to subgroups of the melanocortin receptor family. Double-blind placebo-controlled experiments were completed in 54 healthy young subjects. ERPs were recorded while the subject performed an auditory selective attention task. Moreover, a modified Stroop interference test including motivational (food, sex) and nonmotivational words was performed. Acute intranasal administration of ACTH 4-10 (1 mg) reduced the processing negativity (PN) of the ERP over frontal and central cortical areas (p < 0.05) indicating diminished focussing of attention. Moreover, on this condition subjects were more prone to interference on the Stroop task especially with motivational words (p < 0.05). Subchronic administration of ACTH 4-10 (1 mg/day over 6 weeks) did not affect PN and Stroop performance. Acute intranasal administration of desacetyl-alpha-MSH at equimolar doses (1.68 mg) also remained ineffective. However, some measures of Stroop performance appeared to improve after subchronic desacetyl-alpha-MSH treatment. Results confirm an acute decrease in focussing of attention after ACTH 4-10. These effects of intranasal administration are likely to reflect a direct action of the peptide on respective brain functions. Moreover, they were specific to ACTH 4-10 and were not obtained after equimolar doses of desacetyl-alpha-MSH, thus excluding a mediation via the known melanocortin receptors.

Corticosterone influences forced swim-induced immobility

The effect of corticosterone (CS) synthesis inhibition with metyrapone-a blocker of the 11 beta-hydroxylase (150 mg/kg IP)-on immobility time during the forced swim test was recorded. Immobility time was measured during a 15-min forced swim (test). Twenty-four hours later rats were subjected to an additional 5 min forced swim (retest). In one experiment, metyrapone or vehicle was administered 3 h before the initial test, while CS (0, 5, 10, or 20 mg/kg SC) was administered 1 h prior to the initial test. Metyrapone significantly reduced immobility time during both test and retest. This effect was reverted in a dose-dependent fashion by CS. In a second experiment, animals exposed to the initial test 24 h before were injected with metyrapone or vehicle 3 h before the retest, while CS (0, 10, or 20 mg/kg SC) was administered 1 h prior the retest. Metyrapone, administered before the retest, reduced immobility time and CS partially reverted metyrapone effect. In another group of animals, serum CS concentrations were evaluated before and after test and retest. In vehicle groups, the high immobility time during test and retest was associated with high CS serum concentrations poststress. In animals receiving metyrapone prior to the initial test, the reduced immobility time was related to low levels of CS after the test and an attenuated secretion following the retest. Moreover, CS (20 mg/kg) and metyrapone+CS groups had high CS levels before the test, which remained high 2 h after the test, although after the retest, both groups showed a pattern of CS secretion similar to that observed in vehicle animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotrophic ACTH analogue promotes plasticity of type I corticosteroid receptor in brain of senescent male rats

Age-related changes were studied in the concentration of type-I and type-II corticosteroid receptors in the hippocampus of young adult (3 months) and aged (28.5 to 30.5 months) male rats. Using 3H-labelled ligands, in vitro binding of type-I and type-II corticosteroid receptors in the soluble cell fraction (cytosol) revealed an age-related decrease in concentration of both receptor types of 52% and 28%, respectively. Infusion of young and aged male rats for 2 weeks with the ACTH4-9 [adrenocorticotropin4-9] peptide analogue ORG 2766 (0.5 micrograms/0.5 microliter/hr) resulted in only a minor increase (+8%) in the number of type-I receptors in young rats. In the aged animals, however, the type-I receptor concentration was 68% higher than in the vehicle-treated aged animals. In contrast, no effect of the peptide treatment was noted on the concentration of type-II receptors in either young or aged rats. Furthermore, no effect was found for either age or treatment with peptide on the affinity of type-I and type-II receptors for their respective ligands. Binding of 3H-labelled ligands to brain sections of young and aged rats was performed using in vitro autoradiography. Quantitative image analysis of the film showed that in senescence there is a marked reduction in both type-I (62-75%) and type-II (29-56%) receptor concentrations in the hippocampal subregions (CA1, CA2, CA3 and dentate gyrus) as well as in the lateral septum. Treatment of aged rats with ORG 2766 selectively reversed the age-associated reduction in type-I receptors, while the peptide did not affect the type-II receptors.(ABSTRACT TRUNCATED AT 250 WORDS)