High Exploratory Phenotype Rats Exposed to Environmental Stressors Present Memory Deficits Accompanied by Immune-Inflammatory/Oxidative Alterations: Relevance to the Relationship Between Temperament and Mood Disorders

Low-exploratory (LE) and high-exploratory (HE) rodents mimic human depressive and hyperthymic temperaments, respectively. Mood disorders (MD) may be developed by the exposure of these temperaments to environmental stress (ES). Psychiatric symptoms severity in MD patients is related to the magnitude of memory impairment. Thus, we aimed at studying the consequences of the exposure of LE and HE male Wistar rats, during periadolescence, to a combination of ES, namely, paradoxical sleep deprivation (PSD) and unpredictable stress (US), on anxiety-related behavior in the plus maze test, working (WM) and declarative memory (DM) performance. We also evaluated hippocampal immune-inflammatory/oxidative, as consequences of ES, and prevention of ES-induced alterations by the mood-stabilizing drugs, lithium and valproate. Medium exploratory (ME) control rats were used for comparisons with HE- and LE-control rats. We observed that HE-controls presented increased anxiolytic behavior that was significantly increased by ES exposure, whereas LE-controls presented increased anxiety-like behavior relative to ME-controls. Lithium and valproate prevented anxiolytic alterations in HE+ES rats. HE+ES- and LE+ES-rats presented WM and DM deficits. Valproate and lithium prevented WM deficits in LE-PSD+US rats. Lithium prevented DM impairment in HE+ES-rats. Hippocampal levels of reduced glutathione (GSH) increased four-fold in HE+ES-rats, being prevented by valproate and lithium. All groups of LE+ES-rats presented increased levels of GSH in relation to controls. Increments in lipid peroxidation in LE+ES- and HE+ES-rats were prevented by valproate in HE+ES-rats and by both drugs in LE+ES-rats. Nitrite levels were increased in HE+ES- and LE+ES-rats (five-fold increase), which was prevented by both drugs in LE+ES-rats. HE+ES-rats presented a two-fold increase in the inducible nitric oxide synthase (iNOS) expression that was prevented by lithium. HE+ES-rats showed increased hippocampal and plasma levels of interleukin (IL)-1β and IL-4. Indoleamine 2, 3-dioxygenase 1 (IDO1) was increased in HE+ES- and LE+ES-rats, while tryptophan 2,3-dioxygenase (TDO2) was increased only in HE+ES-rats. Altogether, our results showed that LE- and HE-rats exposed to ES present distinct anxiety-related behavior and similar memory deficits. Furthermore, HE+ES-rats presented more brain and plasma inflammatory alterations that were partially prevented by the mood-stabilizing drugs. These alterations in HE+ES-rats may possibly be related to the development of mood symptoms.

Major depression model induced by repeated and intermittent lipopolysaccharide administration: Long-lasting behavioral, neuroimmune and neuroprogressive alterations

Major depressed patients show increased bacterial translocation with elevated plasma levels of lipopolysaccharide (LPS), which may trigger immune-inflammatory and neuro-oxidative responses. Recently, an animal model based on chronic LPS administration was developed which was associated with long-lasting depressive-like and neuro-oxidative alterations in female mice. The aim of the current study was to investigate behavioral, neuroimmune and neuroprogressive alterations in female mice 6 weeks after LPS chronic exposure. Female mice received increasing doses of LPS during 5 days at one-month intervals repeated for 4 consecutive months. Six weeks after the last LPS-exposure, we assessed behavioral despair and anhedonia, microglial activation, alterations in tryptophan, 5-HT, kynurenine, quinolinic acid (QUIN) levels and spermidine/spermine N1-acetyltransferase (SAT1) expression in the hippocampus, both with and without fluoxetine administration. Our results show that six weeks post-LPS, mice present behavioral despair and anhedonia in association with increased IBA1 expression (a microglia activation marker), NF-kB p65 and IL-1β levels, indoleamine 2,3-dioxygenase (IDO1) mRNA expression, kynurenine, QUIN levels and QUIN/tryptophan ratio, and lowered tryptophan, 5-HT levels and SAT1 mRNA expression. Fluoxetine reversed the behavioral and neuroimmune alterations but had no effect in the reversal of IDO1 increased expression, QUIN levels and QUIN/tryptophan ratio. In conclusion, our results support the validity of the chronic LPS model of major depression and additionally shows its translational relevance with respect to neuroimmune and neuroprogressive pathways.

Gender and estrous cycle influences on behavioral and neurochemical alterations in adult rats neonatally administered ketamine

Neonatal N-methyl-D-aspartate (NMDA) receptor blockade in rodents triggers schizophrenia (SCZ)-like alterations during adult life. SCZ is influenced by gender in age of onset, premorbid functioning, and course. Estrogen, the hormone potentially driving the gender differences in SCZ, is known to present neuroprotective effects such as regulate oxidative pathways and the expression of brain-derived neurotrophic factor (BDNF). Thus, the aim of this study was to verify if differences in gender and/or estrous cycle phase during adulthood would influence the development of behavioral and neurochemical alterations in animals neonatally administered ketamine. The results showed that ketamine-treated male (KT-male) and female-in-diestrus (KTF-diestrus, the low estrogen phase) presented significant deficits in prepulse inhibition of the startle reflex and spatial working memory, two behavioral SCZ endophenotypes. On the contrary, female ketamine-treated rats during proestrus (KTF-proestrus, the high estradiol phase) had no behavioral alterations. This correlated with an oxidative imbalance in the hippocampus (HC) of both male and KTF-diestrus female rats, that is, decreased levels of GSH and increased levels of lipid peroxidation and nitrite. Similarly, BDNF was decreased in the KTF-diestrus rats while no alterations were observed in KTF-proestrus and male animals. The changes in the HC were in contrast to those in the prefrontal cortex in which only increased levels of nitrite in all groups studied were observed. Thus, there is a gender difference in the adult rat HC in response to ketamine neonatal administration, which is based on the estrous cycle. This is discussed in relation to neuropsychiatric conditions and in particular SCZ.

Effects of lithium on oxidative stress and behavioral alterations induced by lisdexamfetamine dimesylate: relevance as an animal model of mania

Lisdexamfetamine dimesylate (LDX) is a prodrug that requires conversion to d-amphetamine (d-AMPH) for bioactivity. Treatment with d-AMPH induces hyperlocomotion and is regarded as a putative animal model of bipolar mania. Therefore, we sought to determine the behavioral and oxidative stress alterations induced by sub-chronic LDX administration as well as their reversal and prevention by lithium in rats. A significant increment in locomotor behavior was induced by LDX (10 and 30 mg/kg). To determine Li effects against LDX-induced alterations, in the reversal protocol rats received LDX (10 or 30 mg/kg) or saline for 14 days. Between days 8 and 14 animals received Li (47.5 mg/kg, i.p.) or saline. In the prevention paradigm, rats were pretreated with Li or saline prior to LDX administration. Glutathione (GSH) levels and lipid peroxidation was determined in the prefrontal cortex (PFC), hippocampus (HC) and striatum (ST) of rats. Lithium prevented LDX-induced hyperlocomotion at the doses of 10 and 30 mg/kg, but only reversed LDX-induced hyperlocomotion at dose of 10mg/kg. In addition, both doses of LDX decreased GSH content (in ST and PFC), while Li was able to reverse and prevent these alterations mainly in the PFC. LDX (10 and 30 mg/kg) increased lipid peroxidation which was reversed and prevented by Li. In conclusion, LDX-induced hyperlocomotion along with associated increments in oxidative stress show promise as an alternative animal model of mania.

Prevention of haloperidol-induced alterations in brain acetylcholinesterase activity by vitamins B co-administration in a rodent model of tardive dyskinesia

Tardive dyskinesia (TD) is an iatrogenic syndrome being a significant adverse outcome of typical and atypical antipsychotic therapy. Recently we demonstrated that vitamins B (B1, B6, B12 alone or in combination) were able to prevent haloperidol-induced orofacial dyskinesia (OD) possibly by their antioxidant activity in the striatum, using a well-established model of TD. Here, based on the fact that alterations in cholinergic neurotransmission are related to TD pathophysiology and that vitamins B seems to influence brain cholinergic neurotransmission, we decided to investigate the effects of vitamins B1, B6, B12 and their association, vitamin B cocktail in haloperidol-induced cholinergic alterations, evaluated by alterations in acetylcholinesterase (AChE) activity, in striatum, prefrontal cortex and hippocampus, as a way to determine the participation of cholinergic neurotransmission, in these vitamins antidyskinetic mechanism. Haloperidol 1 mg/kg i.p. daily administration during 21 days to Wistar rats caused OD while decreased AChE activity in all brain areas studied. Vitamins B administration (B1:B6:B12 at 60:60:0.6 mg/kg, s.c) alone and vitamin B cocktail co-administered with haloperidol prevented OD development and increased AChE activity in all brain areas studied, with the maximum activity increment observed in the hippocampus of the animals co-treated with vitamin B12 and vitamin B cocktail. The antidyskinetic drug, clozapine did not induce OD and increased AChE activity similarly to the groups coadministered with vitamin B and HAL. The present data suggest that vitamins B can prevent haloperidol-induced alterations in AChE activity what can be related to the mechanism underlying their antidyskinetic effect.

Effects of omega-3 dietary supplement in prevention of positive, negative and cognitive symptoms: a study in adolescent rats with ketamine-induced model of schizophrenia

Omega-3 has shown efficacy to prevent schizophrenia conversion in ultra-high risk population. We evaluated the efficacy of omega-3 in preventing ketamine-induced effects in an animal model of schizophrenia and its effect on brain-derived neurotrophic factor (BDNF). Omega-3 or vehicle was administered in Wistar male rats, both groups at the 30th day of life for 15days. Each group was split in two to receive along the following 7days ketamine or saline. Locomotor and exploratory activities, memory test and social interaction between pairs were evaluated at the 52nd day of life. Prefrontal-cortex, hippocampus and striatum tissues were extracted right after behavioral tasks for mRNA BDNF expression analysis. Bloods for serum BDNF were withdrawn 24h after the end of behavioral tasks. Locomotive was increased in ketamine-treated group compared to control, omega-3 and ketamine plus omega-3 groups. Ketamine group had fewer contacts and interaction compared to other groups. Working memory and short and long-term memories were significantly impaired in ketamine group compared to others. Serum BDNF levels were significantly higher in ketamine plus omega-3 group. There was no difference between groups in prefrontal-cortex, hippocampus and striatum for mRNA BDNF expression. Administration of omega-3 in adolescent rats prevents positive, negative and cognitive symptoms in a ketamine animal model of schizophrenia. Whether these findings are consequence of BDNF increase it is unclear. However, this study gives compelling evidence for larger clinical trials to confirm the use of omega-3 to prevent schizophrenia and for studies to reinforce the beneficial role of omega-3 in brain protection.