ABSTRACT
DNA methylation and histone modification are two major epigenetic mechanisms involved in the pathophysiology of major depressive disorder (MDD) and the action of antidepressants. We and others have recently shown that epigenetic regulation through histone acetylation within ventrolateral orbital cortex (VLO) contributes to the antidepressant-like effects of histone deacetylase inhibitors [HDACi, such as valproic acid (VPA) and MS-275] observed in rats. However, there is so far no investigation focused on the effect of DNA methylation in VLO on depressive-like behaviors. Here, we examined the effects of the DNA methyltransferases (DNMTs) inhibitor 5-aza-2-deoxycytidine (5-aza) on rat forced swimming test (FST) and locomotor activity when microinjected into VLO. We found that bilateral intra-VLO injections of 5-aza increased the duration of immobility in FST in a dose-dependent manner compared to vehicle-treated controls. The effects of 5-aza observed in the FST paradigms could not be attributed to non-specific decreases in activity since the inhibition of DNA methylation in VLO did not cause general impairment in locomotor activity. These results add to the evidence that DNA hypomethylation in VLO is involved in regulating depressive-like behaviors, and suggest that the effect of DNA methylation on depressive-like behaviors appear to be brain region-dependent.
Subject(s)
Azacitidine/analogs & derivatives , DNA Modification Methylases/antagonists & inhibitors , Depression/psychology , Prefrontal Cortex/drug effects , Animals , Azacitidine/pharmacology , DNA Methylation , Decitabine , Depression/metabolism , Depression/physiopathology , Male , Microinjections , Motor Activity/drug effects , Prefrontal Cortex/metabolism , Prefrontal Cortex/physiopathology , Rats, Sprague-DawleyABSTRACT
The present study examined the role of α2 adrenoceptor in mediating noradrenaline action in the ventrolateral orbital cortex (VLO) on allodynia induced by spared nerve injury (SNI) in the rat. The mechanical paw withdrawal threshold (PWT) was measured using von-Frey filaments. Microinjection of noradrenaline (1, 2, 4 µg in 0.5 µl) into the VLO, contralateral to the site of nerve injury, reduced allodynia; PWT increased in a dose-dependent manner. Similar to noradrenaline, microinjection of selective α2 adrenoceptor agonist clonidine into the same VLO site also reduced allodynia, and was blocked by selective α2 adrenoceptor antagonist yohimbine. Furthermore, administration of γ-aminobutyric acid A (GABAA) receptor antagonist bicuculline or picrotoxin to the VLO significantly enhanced clonidine-induced inhibition of allodynia, while GABAA receptor agonist muscimol or THIP (2,5,6,7-retrahydroisoxazolo(5,4-c)pyridine-3-ol hydrochloride) attenuated clonidine-induced inhibition. These results suggest that noradrenaline acting in the VLO can potentially reduce allodynia induced by SNI, and this effect is mediated by α2 adrenoceptor. Moreover, GABAergic disinhibition may participate in α2 receptor mediating effects in neuropathic pain in the central nervous system.
Subject(s)
Cerebral Cortex/metabolism , Hyperalgesia/metabolism , Norepinephrine/metabolism , Receptors, Adrenergic, alpha-2/metabolism , Sciatic Neuropathy/metabolism , Adrenergic alpha-2 Receptor Agonists/pharmacology , Adrenergic alpha-2 Receptor Antagonists/pharmacology , Animals , Bicuculline/pharmacology , Cerebral Cortex/drug effects , Cerebral Cortex/physiopathology , Clonidine/pharmacology , Dose-Response Relationship, Drug , GABA Antagonists/pharmacology , Hyperalgesia/physiopathology , Male , Pain Measurement , Pain Threshold/drug effects , Rats , Rats, Sprague-Dawley , Sciatic Nerve/drug effects , Sciatic Nerve/injuries , Sciatic Nerve/physiopathology , Sciatic Neuropathy/physiopathology , Yohimbine/pharmacologyABSTRACT
Glial cell line-derived neurotrophic factor (GDNF), after secreted from cells, plays a critical role in central and peripheral neuron survival and function. The secretion of GDNF can be either constitutive or regulated by physiological stimuli; however, the detailed mechanism driving GDNF secretion is still unknown. Here, we report that sorting protein-related receptor with A-type repeats (SorLA), a member of the mammal Vps10p domain receptor, interacts with GDNF and is localized to GDNF-containing vesicles. Overexpression of SorLA significantly increases, and knockdown of SorLA by siRNA decreases, the regulated secretion of GDNF in PC12 and MN9D cells but has no effect on GDNF constitutive secretion. In addition, overexpression of a truncated form of SorLA also impairs GDNF-regulated secretion. Finally, we found that the prodomain of GDNF mediates the interaction of GDNF with SorLA under acidic conditions. Moreover, overexpression of SorLA could enhance the regulated secretion of the GDNF prodomain-GFP fusion protein, suggesting that the prodomain of GDNF is responsible for its regulated secretion. Together, these findings will advance our understanding of the molecular mechanism underlying GDNF-regulated secretion.
