Opiate agonist-induced re-distribution of Wntless, a mu-opioid receptor interacting protein, in rat striatal neurons

Abstract

Wntless (WLS), a mu-opioid receptor (MOR) interacting protein, mediates Wnt protein secretion that is critical for neuronal development. We investigated whether MOR agonists induce re-distribution of WLS within rat striatal neurons. Adult male rats received either saline, morphine or [D-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO) directly into the lateral ventricles. Following thirty minutes, brains were extracted and tissue sections were processed for immunogold silver detection of WLS. In saline-treated rats, WLS was distributed along the plasma membrane and within the cytoplasmic compartment of striatal dendrites as previously described. The ratio of cytoplasmic to total dendritic WLS labeling was 0.70±0.03 in saline-treated striatal tissue. Morphine treatment decreased this ratio to 0.48±0.03 indicating a shift of WLS from the intracellular compartment to the plasma membrane. However, following DAMGO treatment, the ratio was 0.85±0.05 indicating a greater distribution of WLS intracellularly. The difference in the re-distribution of the WLS following different agonist exposure may be related to DAMGO’s well known ability to induce internalization of MOR in contrast to morphine, which is less effective in producing receptor internalization. Furthermore, these data are consistent with our hypothesis that MOR agonists promote dimerization of WLS and MOR, thereby preventing WLS from mediating Wnt secretion. In summary, our findings indicate differential agonist-induced trafficking of WLS in striatal neurons following distinct agonist exposure. Adaptations in WLS trafficking may represent a novel pharmacological target in the treatment of opiate addiction and/or pain.

Ultrastructural evidence for synaptic contacts between cortical noradrenergic afferents and endocannabinoid-synthesizing post-synaptic neurons

“…For instance, prolonged stimulation using a cannabinoid agonist, HU-210 in cerebellar granule cells induces silencing of CB1r and mutes GABA-containing axon terminals (Ramirez-Franco et al, 2014). To unequivocally establish such a cellular interaction, a triple immunolabeling using immunoperoxidase and dual immunogold labeling approach (Reyes et al, 2011; Reyes et al, 2012b; Kravets et al, 2013) may be carried out in future studies.…”

“…Future studies are needed to define the frequency of co-localization of NET/DβH and glutamate in axon terminals and whether these terminals contact DGL-α in the FC. We have developed a triple immunoelectron microscopy approach that will help unveil this potential subcellular interaction in future studies (Reyes et al, 2011; Reyes et al, 2012b; Kravets et al, 2013). …”

Direct targeting of peptidergic amygdalar neurons by noradrenergic afferents: linking stress-integrative circuitry

“…The tissue sections were then immersed in 22 mg of 3-3′ diaminobenzidine (DAB, Sigma-Aldrich) with 10 μL of 30% hydrogen peroxide in 100 mL of 0.1 M TBS for 10 min. After visualization of NET, the tissue sections were processed for dual immunogold-silver labeling for CRF and DYN as previously described (Reyes et al 2012, Reyes et al 2011; Jin et al 2010). Sequential immunogold-silver labeling was conducted by incubating with one ultra-small gold conjugate, followed by silver enhancement, and then incubating with the second ultra-small gold conjugate, followed by a second silver enhancement (Yi et al 2001).…”

In Vivo Regulation of the μ Opioid Receptor: Role of the Endogenous Opioid Agents

“…For example, Met-ENK, Leu-ENK and MERF bind the δ opioid receptor and provide cardioprotection in an ischemia model (42). It was also shown that agonist-dependent μ activation modulates Wntless activity, a protein that mediates WNT function by regulating its secretion (43). Besides, Met-ENK-derived peptides can act as tonic inhibitory peptides on the opioid growth factor receptor, thus inhibiting proliferation either during normal growth and development or even in cancer models from neural and non-neural cell lines (11,44).…”