Behavioral and stereological analysis of the prefrontal cortex of rats submitted to chronic alcohol intake

Alcoholic neuropathy associated with chronic alcohol intake

Alcoholic neuropathy (AN), a debilitating condition that mainly affects chronic alcohol drinkers, is thought to cause lesions in the peripheral nervous system leading to sensory, autonomic, and motor dysfunctions. Despite many studies, the pathogenesis of these lesions is still not completely understood. We investigated few aspects on the development of alcohol-induced peripheral neuropathy, by assessing sensory, motor and autonomic functions, as well as stereological analysis of axonal fibers and myelin sheath of the sciatic nerve. Twelve male Wistar rats were divided into Control group and Alcohol group that was submitted to Two Bottle-Choice Paradigm of intermittent and voluntary alcohol solution intake (20%; v/v) during eight weeks. At the end of treatment, three different sensorium-motor tests were applied - Tactile Sensitivity, Thermal Sensitivity, and Functional Observational Battery (FOB). Quantitative morphometric analysis of sciatic nerve structures was performed by stereological method. Alcohol concentration in the blood was measured to analyze possible correlation between availability of alcohol in the blood and the magnitude of the peripheral nerve lesion. Our data showed a peripheral effect of chronic alcohol intake associated with hyperalgesia and a process of demyelination with a strong correlation with alcohol consumption. This process was associated with increased tactile sensitivity, with behavioral reflexes such as locomotor hyperactivity, changes in gait and balance, and autonomic reflexes such as piloerection.

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Alcoholic neuropathy and its consequences.

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Neuropathy and sensitive and motor alterations.

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Alcoholic neuropathy and thinner myelin sheath thickness.

Effects of moderate alcohol consumption on behavior and neural systems of Wistar rats

Chronic alcohol consumption affects various neurotransmitters, especially those implicated in the transitioning to alcohol use disorders (particularly dopaminergic and CRFergic systems). Few studies have investigated moderate alcohol consumption and its harmful consequences. The objective of this work was to analyze behavioral and neurochemical (dopaminergic and CRFergic systems) alterations during chronic moderate alcohol consumption. Twelve male Wistar rats were submitted to an intermittent alcohol ingestion protocol (alcohol group) for four weeks. The control group consisted of six rats. Open Field and Elevated Plus Maze tests were used for analysis of motor and anxiety-like behaviors. Immunohistochemistry analysis was performed in dopaminergic and CRFergic systems. Animals exposed to alcohol consumed moderate doses, chronic and intermittently. Behavioral tests detected fewer fecal boli in the alcohol exposed group, and immunohistochemical analysis indicated fewer dopamine-immunoreactive cells in the ventral tegmental area, and more CRF-immunoreactive cells in the anterior cingulate cortex and dorsolateral septum in this group. Thus we concluded that Wistar rats that consumed moderate doses of alcohol voluntarily and chronically showed a discreet anxiolytic effect in behavior, and a hypodopaminergic and hyperCRFergic neurochemical condition, which together are strong inducers of alcohol consumption predisposing to the development of alcohol use disorder (AUD).

Relationship between voluntary ethanol drinking and approach-avoidance biases in the face of motivational conflict: novel sex-dependent associations in rats

RATIONALE

Aberrant approach-avoidance conflict processing may contribute to compulsive seeking that characterizes addiction. Exploration of the relationship between drugs of abuse and approach-avoidance behavior remains limited, especially with ethanol.

OBJECTIVES

To investigate the effects of voluntary ethanol consumption on approach-avoidance conflict behavior and to examine the potential approach/avoidance bias to predict drinking in male and female rats.

METHODS

Long-Evans rats consumed ethanol for 5 weeks under the intermittent access two-bottle choice (IA2BC) paradigm. Approach-avoidance tendencies were assessed before and after IA2BC drinking using a previously established cued approach-avoidance conflict maze task and the elevated plus maze (EPM).

RESULTS

Female rats displayed higher consumption of and preference for ethanol than males. In the conflict task, males showed greater approach bias towards cues predicting conflict than females. In females only, a median split and regression analysis of cued-conflict preference scores revealed that the more conflict-avoidant group displayed higher intake and preference for ethanol in the first few weeks of drinking. In both sexes, ethanol drinking did not affect cued-conflict preference, but ethanol exposure led to increased time spent in the central hub in the males only. Finally, anxiety levels in EPM predicted subsequent onset of ethanol drinking in males only.

CONCLUSIONS

Our results highlight sex and individual differences in both drinking and approach-avoidance bias in the face of cued conflict and further suggest that cued-conflict preference should be examined as a potential predictor of ethanol drinking. Ethanol exposure may also affect the timing of decision-making in the face of conflict.

Ethanol-induced locomotor sensitization: Neuronal activation in the nucleus accumbens and medial prefrontal cortex

Ethanol consumption may promote neuroplasticity and alterations in synapses, resulting in modifications in neuronal activity. Here, we treated male Swiss mice with ethanol (2.2 g/kg) or saline once per day for 21 consecutive days. Nine days after the last ethanol administration, they received a challenge injection of ethanol or saline, and we assessed locomotor activity. After the behavioral analysis, we evaluated neuronal activation in the medial Prefrontal Cortex (Cingulate, Prelimbic, and Infralimbic) and the Nucleus Accumbens (Shell and Core) using Fos/DAB immunohistochemistry. In another group of animals, we performed the quantitative analysis of the ARC and PSD-95 protein levels by Western blotting in the medial prefrontal cortex and nucleus accumbens brain areas. Repeated ethanol administration produced locomotor sensitization, accompanied by an increase in the nucleus accumbens shell's activation but not core. Furthermore, the ethanol pretreatment reduced ARC expression in the nucleus accumbens and medial prefrontal cortex. Our results suggest the participation of the nucleus accumbens shell in ethanol behavioral sensitization and add new pieces of evidence that neuroplasticity in synapses may contribute to the mechanism underlying this behavior.

Environmental and Nutritional "Stressors" and Oligodendrocyte Dysfunction: Role of Mitochondrial and Endoplasmatic Reticulum Impairment

Oligodendrocytes are myelinating cells of the central nervous system which are generated by progenitor oligodendrocytes as a result of maturation processes. The main function of mature oligodendrocytes is to produce myelin, a lipid-rich multi-lamellar membrane that wraps tightly around neuronal axons, insulating them and facilitating nerve conduction through saltatory propagation. The myelination process requires the consumption a large amount of energy and a high metabolic turnover. Mitochondria are essential organelles which regulate many cellular functions, including energy production through oxidative phosphorylation. Any mitochondrial dysfunction impacts cellular metabolism and negatively affects the health of the organism. If the functioning of the mitochondria is unbalanced, the myelination process is impaired. When myelination has finished, oligodendrocyte will have synthesized about 40% of the total lipids present in the brain. Since lipid synthesis occurs in the cellular endoplasmic reticulum, the dysfunction of this organelle can lead to partial or deficient myelination, triggering numerous neurodegenerative diseases. In this review, the induced malfunction of oligodendrocytes by harmful exogenous stimuli has been outlined. In particular, the effects of alcohol consumption and heavy metal intake are discussed. Furthermore, the response of the oligodendrocyte to excessive mitochondrial oxidative stress and to the altered regulation of the functioning of the endoplasmic reticulum will be explored.

Alternative splicing of neurexins 1-3 is modulated by neuroinflammation in the prefrontal cortex of a murine model of multiple sclerosis

Mounting evidence points to immune-mediated synaptopathy and impaired plasticity as early pathogenic events underlying cognitive decline (CD) in Multiple sclerosis (MS) and in the experimental autoimmune encephalomyelitis (EAE) mouse model of the disease. However, knowledge of the neurobiology of synaptic dysfunction is still incomplete. Splicing regulation represents a flexible and powerful mechanism involved in dynamic remodeling of the synapse, which allows the expression of synaptic protein variants that dynamically control the specificity of contacts between neurons. The pre-synaptic adhesion molecules neurexins (NRXNs) 1-3 play a relevant role in cognition and are alternatively spliced to yield variants that differentially cluster specific ligands in the postsynaptic compartment and modulate functional properties of the synaptic contact. Notably, mutations in these genes or disruption of their splicing program are associated with neuropsychiatric disorders. Herein, we have investigated how inflammatory changes imposed by EAE impact on alternative splicing of the Nrxn 1-3 mouse genes in the acute phase of disease. Due to its relevance in cognition, we focused on the prefrontal cortex (PFC) of SJL/J mice, in which EAE-induced inflammatory lesions extend to the rostral forebrain. We found that inclusion of the Nrxn 1-3 AS4 exon is significantly increased in the PFC of EAE mice and that splicing changes are correlated with local Il1β-expression levels. This correlation is sustained by the concomitant downregulation of SLM2, the main splicing factor involved in skipping of the AS4 exon, in EAE mice displaying high levels of Il1β- expression. We also observed that Il1β-expression levels correlate with changes in parvalbumin (PV)-positive interneuron connectivity. Moreover, exposure to environmental enrichment (EE), a condition known to stimulate neuronal connectivity and to improve cognitive functions in mice and humans, modified PFC phenotypes of EAE mice with respect to Il1β-, Slm2-expression, Nrxn AS4 splicing and PV-expression, by limiting changes associated with high levels of inflammation. Our results reveal that local inflammation results in early splicing modulation of key synaptic proteins and in remodeling of GABAergic circuitry in the PFC of SJL/J mice. We also suggest EE as a tool to counteract these inflammation-associated events, thus highlighting potential therapeutic targets for limiting the progressive CD occurring in MS.

Effects of chronic alcohol consumption and withdrawal on the cholinergic neurons of the pedunculopontine and laterodorsal tegmental nuclei of the rat: An unbiased stereological study

The brain cholinergic system comprises two main recognized subdivisions, the basal forebrain and the brainstem cholinergic systems. The effects of chronic alcohol consumption on the basal forebrain cholinergic nuclei have been investigated extensively, but there is only one study that has examined those effects on the brainstem cholinergic nuclei. The last one comprises the pedunculopontine tegmental (PPT) and the laterodorsal tegmental (LDT) nuclei, which are known to give origin to the main cholinergic projection to the ventral tegmental area, a key brain region of the neural circuit, the mesocorticolimbic system, that mediates several behavioral and physiological processes, including reward. In the present study, we have examined, using stereological methods, the effects of chronic alcohol consumption (6 months) and subsequent withdrawal (2 months) on the total number and size of PPT and LDT choline acetyltransferase (ChAT)-immunoreactive neurons. The total number of PPT and LDT ChAT-immunoreactive neurons was unchanged in ethanol-treated and withdrawn rats. However, ChAT-immunoreactive neurons were significantly hypertrophied in ethanol-treated rats, an alteration that did not revert 2 months after ethanol withdrawal. These results show that prolonged exposure to ethanol leads to long-lasting, and potentially irreversible, cytoarchitectonic and neurochemical alterations in the brainstem cholinergic nuclei. These alterations suggest that the alcohol-induced changes in the brainstem cholinergic nuclei might play a role in the mechanisms underlying the development of addictive behavior to alcohol.

Developing neuroscience-based treatments for alcohol addiction: A matter of choice?

Excessive alcohol use is the cause of an ongoing public health crisis, and accounts for ~5% of global disease burden. A minority of people with recreational alcohol use develop alcohol addiction (hereafter equated with "alcohol dependence" or simply "alcoholism"), a condition characterized by a systematically biased choice preference for alcohol at the expense of healthy rewards, and continued use despite adverse consequences ("compulsivity"). Alcoholism is arguably the most pressing area of unmet medical needs in psychiatry, with only a small fraction of patients receiving effective, evidence-based treatments. Medications currently approved for the treatment of alcoholism have small effect sizes, and their clinical uptake is negligible. No mechanistically new medications have been approved since 2004, and promising preclinical results have failed to translate into novel treatments. This has contributed to a reemerging debate whether and to what extent alcohol addiction represents a medical condition, or reflects maladaptive choices without an underlying brain pathology. Here, we review this landscape, and discuss the challenges, lessons learned, and opportunities to retool drug development in this important therapeutic area.

Alcohol misuse and traumatic brain injury: a review of the potential roles of dopaminergic dysfunction and physiological underarousal post-injury

Although many researchers have demonstrated an increase in alcohol use following traumatic brain injury (TBI), there is also a body of research indicating that alcohol misuse predisposes one to injury and precedes TBI. Accordingly, various mechanisms have been proposed (e.g., self-medication, dampened levels of arousal, dopaminergic dysfunction, etc.) and variable results have emerged. This paper reviews the empirical evidence, for and against, TBI as a risk factor for alcohol misuse. In particular, this paper focuses on the brain-behavior relationships involved and examines the roles of physiological underarousal and dopaminergic dysfunction in the development of alcohol misuse after injury. Alcohol misuse impedes community reintegration among TBI survivors and creates additional rehabilitative challenges. Thus, in order to inform and improve treatment outcomes among this vulnerable population, a deeper understanding of the neural mechanisms implicated is needed.

Responsivity of lateral septum-mPFC connections in alloxan-induced hyperglycemia

The lateral septal nucleus (LSN) is related to the actions of antidepressants, and the prelimbic cortex (PL) and infralimbic cortex (IL) modulate responses to fear. However, unknown is whether experimental diabetes that is induced by alloxan alters the responsivity of these regions. We used a method in which one forebrain region (LSN) was electrically stimulated while single-unit extracellular recordings were performed in another mPFC region (PL and IL). Several experimental groups were tested: (a) animals that were subjected to long-term (42-day) alloxan-hyperglycemia and protected with insulin, (b) healthy animals that received a low dose of insulin that does not produce changes in glycemia, and (c) animals that received long-term treatment with fluoxetine. Additional healthy groups of animals received insulin or fluoxetine and underwent the forced swim test. Biological measurements indicated the induction of diabetes in alloxan-treated rats. In this group, a shift toward an inhibitory response to LSN stimulation was observed in the PL and IL compared with the control group. A low dose of insulin or fluoxetine produced similar changes in LSN-PL and LSN-IL responsivity. Long-term hyperglycemia increased inhibitory responsivity in the LSN-PL and LSN-IL, but this action was less pronounced than the action that was exerted by insulin and fluoxetine, which produced similar actions. Such similar actions were confirmed in the forced swim test, in which the antidepressant-like effects of insulin partially resembled the effects of fluoxetine. The changes that were observed in the alloxan group appeared to be related to neuronal damage, and a low dose of insulin exerted some antidepressant-like actions.