Methylene blue facilitates the extinction of fear in an animal model of susceptibility to learned helplessness

Department of Psychology, University of Texas at Austin, Austin, Texas, United States
Neurobiology of Learning and Memory (Impact Factor: 3.65). 03/2007; 87(2):209-17. DOI: 10.1016/j.nlm.2006.08.009
Source: PubMed


The objectives were to (1) extend previous findings on fear extinction deficits in male congenitally helpless rats (a model for susceptibility to learned helplessness) to female congenitally helpless rats, and (2) attempt a therapeutic intervention with methylene blue, a metabolic enhancer that improves memory retention, to alleviate the predicted extinction deficits. In the first experiment, fear acquisition (four tone-shock pairings in operant chamber) was followed by extinction training (60 tones in open field). Congenitally helpless rats showed fear acquisition similar to controls but had dramatic extinction deficits, and did not display the gradual extinction curves observed in controls. Congenitally helpless rats demonstrated greater tone-evoked freezing as compared to controls in both the acquisition and extinction contexts one week after extinction training, and also in the extinction probe conducted one month later. In the second experiment (which began one month after the first experiment) congenitally helpless subjects were further exposed to tones for 5 days, each followed by 4 mg/kg methylene blue or saline IP, and had a fear renewal test in the acquisition context. Methylene blue administration improved retention of the extinction memory as demonstrated by significant decreases in fear renewal as compared to saline-administered congenitally helpless subjects. The impaired ability to extinguish fear to a traumatic memory in congenitally helpless rats supports the validity of this strain as an animal model for vulnerability to post-traumatic stress disorder, and this study further suggests that methylene blue may facilitate fear extinction as an adjunct to exposure therapy.

Download full-text


Available from: F. Gonzalez-Lima
  • Source
    • "Almost thirty five years ago, Martinez et al. [59] demonstrated for the first time that memory improvement can be achieved by methylene blue, a potent mitochondrial metabolic enhancer, during memory consolidation but not before acquisition . More recent experiments demonstrated that extinction memory is effectively improved by brain metabolic enhancement with methylene blue administered 15 min after tone exposure during extinction training [30] [60]. The similarities in the effects of LLLT and methylene blue on extinction become even more remarkable when their common mitochondrial mechanism of action is noted. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cerebral hypometabolism characterizes mild cognitive impairment and Alzheimer's disease. Low-level light therapy (LLLT) enhances the metabolic capacity of neurons in culture through photostimulation of cytochrome oxidase, the mitochondrial enzyme that catalyzes oxygen consumption in cellular respiration. Growing evidence supports that neuronal metabolic enhancement by LLLT positively impacts neuronal function in vitro and in vivo. Based on its effects on energy metabolism, it is proposed that LLLT will also affect the cerebral cortex in vivo and modulate higher-order cognitive functions such as memory. In vivo effects of LLLT on brain and behavior are poorly characterized. We tested the hypothesis that in vivo LLLT facilitates cortical oxygenation and metabolic energy capacity and thereby improves memory retention. Specifically, we tested this hypothesis in rats using fear extinction memory, a form of memory modulated by prefrontal cortex activation. Effects of LLLT on brain metabolism were determined through measurement of prefrontal cortex oxygen concentration with fluorescent quenching oximetry and by quantitative cytochrome oxidase histochemistry. Experiment 1 verified that LLLT increased the rate of oxygen consumption in the prefrontal cortex in vivo. Experiment 2 showed that LLLT-treated rats had an enhanced extinction memory as compared to controls. Experiment 3 showed that LLLT reduced fear renewal and prevented the reemergence of extinguished conditioned fear responses. Experiment 4 showed that LLLT induced hormetic dose-response effects on the metabolic capacity of the prefrontal cortex. These data suggest that LLLT can enhance cortical metabolic capacity and retention of extinction memories, and implicate LLLT as a novel intervention to improve memory.
    Full-text · Article · Jul 2012 · Journal of Alzheimer's disease: JAD
  • Source
    • "Pharmaceutical grade (USP) methylene blue is an FDA-grandfathered drug with powerful antioxidant activity approved for the treatment of methemoglobinemia (Bradberry, 2003). While chemical grade methylene blue is an industrial dye that may contain contaminants with potential toxicity (Auerbach et al., 2010), purified pharmaceutical grade MB used at low doses has no toxic effects in humans (Bradberry, 2003; Naylor et al., 1986; Naylor et al., 1987) and is welldocumented for enhancing memory at the 4 mg/kg dose used in the present study (Bruchey and Gonzalez-Lima, 2008; Gonzalez-Lima and Bruchey, 2004; Martinez Jr. et al., 1978; Riha et al., 2005; Wrubel et al., 2007a; 2007b). The specificity of the brain metabolic changes and memory-enhancing effects induced by MB can be explained by both its pharmacokinetic and pharmacodynamic properties. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Posterior cingulate/retrosplenial cortex (PCC) hypometabolism is a common feature in amnestic mild cognitive impairment and Alzheimer's disease. In rats, PCC hypometabolism induced by mitochondrial dysfunction induces oxidative damage, neurodegeneration and memory deficits. USP methylene blue (MB) is a diaminophenothiazine drug with antioxidant and metabolic-enhancing properties. In rats, MB facilitates memory and prevents neurodegeneration induced by mitochondrial dysfunction. This study tested the memory-enhancing properties of systemic MB in rats that received an infusion of sodium azide, a cytochrome oxidase inhibitor, directly into the PCC. Lesion volumes were estimated with unbiased stereology. MB's network-level mechanism of action was analyzed using graph theory and structural equation modeling based on cytochrome oxidase histochemistry-derived metabolic mapping data. Sodium azide infusions induced PCC hypometabolism and impaired visuospatial memory in a holeboard food-search task. Isolated PCC cytochrome oxidase inhibition disrupted the cingulo-thalamo-hippocampal effective connectivity, decreased the PCC functional networks and created functional redundancy within the thalamus. An intraperitoneal dose of 4 mg/kg MB prevented the memory impairment, reduced the PCC metabolic lesion volume and partially restored the cingulo-thalamo-hippocampal network effects. The effects of MB were dependent upon the local sub-network necessary for memory retrieval. The data support that MB's metabolic-enhancing effects are contingent upon the neural context, and that MB is able to boost coherent and orchestrated adaptations in response to physical alterations to the network involved in visuospatial memory. These results implicate MB as a candidate intervention to improve memory. Because of its neuroprotective properties, MB may have disease-modifying effects in amnestic conditions associated with hypometabolism.
    Full-text · Article · Nov 2010 · NeuroImage
  • Source
    • "Indeed, in these animal models, more persistent fear responses can be observed after exposure to different stressors (e.g. Izquierdo et al., 2006; Miracle et al., 2006; Mitra & Sapolsky, 2009; Yamamoto et al., 2008; Baran et al., 2009), in animals acutely selected according to their individual differences in extinction (Herry & Mons, 2004; Bush et al., 2007), after selective breeding (Ponder et al., 2007; Muigg et al., 2008; Lopez-Aumatell et al., 2009; see also Shumake et al., 2005; Wrubel et al., 2007) or in naturally occurring extinction-deficient mouse strains (Falls et al., 1997; Stiedl et al., 1999; McCaughran et al., 2000; Waddell et al., 2004; Hefner et al., 2008; Camp et al., 2009), and following different genetic manipulations (e.g. Marsicano et al., 2002; Wellman et al., 2007). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Fear extinction is a form of inhibitory learning that allows for the adaptive control of conditioned fear responses. Although fear extinction is an active learning process that eventually leads to the formation of a consolidated extinction memory, it is a fragile behavioural state. Fear responses can recover spontaneously or subsequent to environmental influences, such as context changes or stress. Understanding the neuronal substrates of fear extinction is of tremendous clinical relevance, as extinction is the cornerstone of psychological therapy of several anxiety disorders and because the relapse of maladaptative fear and anxiety is a major clinical problem. Recent research has begun to shed light on the molecular and cellular processes underlying fear extinction. In particular, the acquisition, consolidation and expression of extinction memories are thought to be mediated by highly specific neuronal circuits embedded in a large-scale brain network including the amygdala, prefrontal cortex, hippocampus and brain stem. Moreover, recent findings indicate that the neuronal circuitry of extinction is developmentally regulated. Here, we review emerging concepts of the neuronal circuitry of fear extinction, and highlight novel findings suggesting that the fragile phenomenon of extinction can be converted into a permanent erasure of fear memories. Finally, we discuss how research on genetic animal models of impaired extinction can further our understanding of the molecular and genetic bases of human anxiety disorders.
    Full-text · Article · Feb 2010 · European Journal of Neuroscience
Show more