Receptor-Mediated AKT/PI3K Signalling and Behavioural Alterations in Zebrafish Larvae Reveal Association between Schizophrenia and Opioid Use Disorder

Abstract

The link between substance abuse and the development of schizophrenia remains elusive. In this study, we assessed the molecular and behavioural alterations associated with schizophrenia, opioid addiction, and opioid withdrawal using zebrafish as a biological model. Larvae of 2 days post fertilization (dpf) were exposed to domperidone (DMP), a dopamine-D2 dopamine D2 receptor antagonist, and morphine for 3 days and 10 days, respectively. MK801, an N-methyl-D-aspartate (NMDA) receptor antagonist, served as a positive control to mimic schizophrenia-like behaviour. The withdrawal syndrome was assessed 5 days after the termination of morphine treatment. The expressions of schizophrenia susceptibility genes, i.e., pi3k, akt1, slc6a4, creb1 and adamts2, in brains were quantified, and the levels of whole-body cyclic adenosine monophosphate (cAMP), serotonin and cortisol were measured. The aggressiveness of larvae was observed using the mirror biting test. After the short-term treatment with DMP and morphine, all studied genes were not differentially expressed. As for the long-term exposure, akt1 was downregulated by DMP and morphine. Downregulation of pi3k and slc6a4 was observed in the morphine-treated larvae, whereas creb1 and adamts2 were upregulated by DMP. The levels of cAMP and cortisol were elevated after 3 days, whereas significant increases were observed in all of the biochemical tests after 10 days. Compared to controls, increased aggression was observed in the DMP-, but not morphine-, treated group. These two groups showed reduction in aggressiveness when drug exposure was prolonged. Both the short- and long-term morphine withdrawal groups showed downregulation in all genes examined except creb1, suggesting dysregulated reward circuitry function. These results suggest that biochemical and behavioural alterations in schizophrenia-like symptoms and opioid dependence could be controlled by common mechanisms.

Integrative Roles of Dopamine Pathway and Calcium Channels Reveal a Link between Schizophrenia and Opioid Use Disorder

“…The up-regulation of these Ca v s will lead to a sustained activation of CREB in the NAc, which leads to anhedonia-like and pro-depression-like symptoms [ 101 , 102 ]. This could be further supported by our previous study, where creb1 was up-regulated after treatment with DMP and morphine [ 103 ]. The upregulation of these Ca v s will also allow excessive influx of calcium ions inside the cells.…”

“…The significance of mTOR in neuron development and its regulation of translational control and protein synthesis implicated that mTOR is involved in the pathology of schizophrenia [ 111 , 112 , 113 , 114 ]. Although the role of mTOR was not tested in the current study, upregulation of eif4ebp1 after drug exposure and morphine withdrawal could be explained by the downregulation of pi3k and akt1 in our previous study [ 103 ].…”

“…The optimization of maximum-tolerated concentration (MTC) of each drug and identification of its optimal condition in inducing schizophrenia were based on our previous study [ 103 ]. At 2 dpf, both strains of the zebrafish were dosed at MTC according to the short- (3 days) and long-term (10 days) treatment protocols.…”

Genome-wide association study reveals multiple loci for nociception and opioid consumption behaviors associated with heroin vulnerability in outbred rats

“…For example, Adamts2, an extracellular matrix proteinase [62] localized within the mesolimbic and mesocortical regions within the brain [63], is a biomarker for heavy tobacco smoking and is downregulated following long-term morphine exposure and withdrawal [64]. Though further investigation is required, Adamts2 may also serve as a biomarker for OUD consumption vulnerability.…”

“…Adamts2 is as an extracellular matrix proteinase [59] localized within the mesolimbic and mesocortical regions within the brain [60] , and is upregulated in the periphery in response to dopamine [60] . Overexpression of Adamts2 is associated with schizophrenia [60] , however, a downregulation of this gene as a consequence of inhibition of dopamine D2 receptors was observed following long-term morphine exposure and withdrawal [61] . Low levels of dopamine D2 receptors are found in human heroin addicts [62] , and are predictive of sensitivity to drugs of abuse [63] .…”