Chronic ACTH treatment increases striatal dopamine D-2 receptor binding in developing rat brain

ACTH and PMX53 recover synaptic transcriptome alterations in a rat model of infantile spasms

We profiled the gene expression in the hypothalamic arcuate nuclei (ARC) of 20 male and 20 female rats to determine the infantile spasms (IS) related transcriptomic alteration of neurotransmission and recovery following two treatments. Rats were prenatally exposed to betamethasone or saline followed by repeated postnatal subjection to NMDA-triggered IS. Rats with spasms were treated with ACTH, PMX53 or saline. Since ACTH, the first line treatment for IS, has inconsistent efficacy and potential harsh side effects, PMX53, a potent complement C5ar1 antagonist, was suggested as a therapeutic alternative given its effects in other epilepsy models. Novel measures that consider all genes and are not affected by arbitrary cut-offs were used, in addition to standard statistical tests, to quantify regulation and recovery of glutamatergic, GABAergic, cholinergic, dopaminergic and serotonergic pathways. Although IS alters expression of ~30% of the ARC genes in both sexes the transcriptomic effects are 3× more severe in males than their female counterparts, as indicated by the Weighted Pathway Regulation measure. Both treatments significantly restored the ARC neurotransmission transcriptome to the non-IS condition with PMX53 performing slightly better, as measured by the Pathway Restoration Efficiency, suggesting these treatments may reduce autistic traits often associated with IS.

Suppression of glucocorticoid secretion and antipsychotic drugs have similar effects on the mesolimbic dopaminergic transmission

Specific antagonists of central dopaminergic receptors constitute the major class of antipsychotic drugs (APD). Two principal effects of APD are used as criteria for the pre-clinical screening of their antipsychotic action: (i) inhibition of basal and depolarization-induced activity of mesolimbic dopaminergic neurons; (ii) antagonism of the locomotor effects of dopaminergic agonists. Given that glucocorticoid hormones in animals increase dopamine release and dopamine-mediated behaviors and that high levels of glucocorticoids can induce psychotic symptoms in humans, these experiments examined whether inhibition of endogenous glucocorticoids might have APD-like effects on mesolimbic dopaminergic transmission in rats. It is shown that suppression of glucocorticoid secretion by adrenalectomy profoundly decreased (by greater than 50%): (i) basal dopaminergic release and the release of dopamine induced by a depolarizing stimulus such as morphine (2 mg/kg, s.c.), as measured in the nucleus accumbens of freely moving animals by microdialysis; (ii) the locomotor activity induced by the direct dopaminergic agonist apomorphine. The effects of adrenalectomy were glucocorticoid specific given that they were reversed by the administration of glucocorticoids at doses within the physiological range. Despite its profound diminution of dopaminergic neurotransmission, adrenalectomy neither modified the number of mesencephalic dopaminergic neurons nor induced gliosis in the mesencephalon or in the nucleus accumbens, as shown by tyrosine hydroxylase and glial fibrillary acidic protein immunostaining. In conclusion, these findings suggest that blockade of central effects of glucocorticoids might open new therapeutic strategies of behavioral disturbances.

Specificity versus redundancy of melanocortins in nerve regeneration

The results of the present study demonstrate that administration of the ACTH-(4-9) analogue Org 2766 acutely enhances behavioral, morphological, and biochemical recovery after nigrostriatal destruction. Animals treated with Org 2766 (10 micrograms/kg every 24 hr) demonstrated an acceleration of denervation supersensitivity and a significantly decreased ipsilateral rotational response, as compared to their saline counterparts. Upon evaluation of the mesolimbic DA system using open field behavior, peptide-treated rats demonstrated a compensatory response in their rearing behavior. Furthermore, tyrosine hydroxylase immunocytochemical analysis indicated an enhanced staining in the Org 2766-treated groups. This evaluation was confirmed and quantified using specific high-affinity dopamine uptake. The brains of animals treated with Org 2766 maintained higher uptake levels, suggesting a greater fiber density than the saline-treated animals. Although recovery via reinnervation is very unlikely in this short period of time, improved recovery may be the result of a protective effect of Org 2766 after administration of 6-OHDA into the substantia nigra. Thus, it appears that Org 2766 provides the rapid effects in this system, by both accelerating some compensatory mechanisms necessary for functional recovery and promoting cell survival by providing neuronal protection. However, it does not appear that this protection is due to NMDA receptor manipulation. Org 2766 neither mimicked the NMDA antagonist MK-801 behaviorally nor biochemically in binding displacement studies. Interestingly, other studies have suggested that only the full ACTH molecule, and fragments larger than ACTH-(1-17), demonstrated binding activity at micromolar concentrations, whereas the shorter, noncorticotropic fragments were either less active or inactive (Table 2). As for ACTH-(4-10) immunoreactivity, it appears that this neurotrophic fragment of ACTH reappears in adults following injury to the nigrostriatal system. In addition, the systemically administered ACTH-(4-9) analogue, Org 2766, seems to be gaining access to the CNS, but is only effective in the injured system. Therefore, based on the immunocytochemical localization of the ACTH-(4-10) fragment in neonatal brains and in the injured adult rat CNS, the interesting possibility may be raised that endogenous ACTH peptides appear during both ontogeny and regeneration. These studies demonstrate once again that biological responses to the family of ACTH/MSH peptides depend on the specific peptide fragment administered, its dosage, and the timing of the administration. Consequently, since early intervention is of vital importance in CNS recovery processes, synergistic administration of ACTH fragments and other neurotrophic agents may offer a viable approach with which to combat degeneration in the CNS.

ACTH binds to [3H]MK-801-labelled rat hippocampal NMDA receptors

The molecular mechanism of the clinical antiepileptic/antimyoclonic action of adrenocorticotrophic hormone (ACTH) is unknown. To explore the possible role of excitatory amino acid receptors, we studied the influence of ACTH and ACTH fragments in vitro on the binding of [3H]MK-801 to rat hippocampus, a region relevant to epilepsy. ACTH-(1-39), ACTH-(1-24), and ACTH-(1-17) displayed micromolar affinities compared to the nanomolar affinity of MK-801, whereas ACTH-(4-10) and four clinically used anticonvulsants were inactive. These findings are not specific for NMDA receptors but conform to the rank order of potency of ACTH fragments at other receptor binding sites.