Gestational chronic mild stress: Effects on acoustic startle in male offspring of rats

Reduction in hippocampal GABAergic transmission in a low birth weight rat model of depression

Prenatal stress is believed to increase the risk of developing neuropsychiatric disorders, including major depression. Adverse genetic and environmental impacts during early development, such as glucocorticoid hyper-exposure, can lead to changes in the foetal brain, linked to mental illnesses developed in later life. Dysfunction in the GABAergic inhibitory system is associated with depressive disorders. However, the pathophysiology of GABAergic signalling is poorly understood in mood disorders. Here, we investigated GABAergic neurotransmission in the low birth weight (LBW) rat model of depression. Pregnant rats, exposed to dexamethasone, a synthetic glucocorticoid, during the last week of gestation, yielded LBW offspring showing anxiety- and depressive-like behaviour in adulthood. Patch-clamp recordings from dentate gyrus granule cells in brain slices were used to examine phasic and tonic GABAA receptor-mediated currents. The transcriptional levels of selected genes associated with synaptic vesicle proteins and GABAergic neurotransmission were investigated. The frequency of spontaneous inhibitory postsynaptic currents (sIPSC) was similar in control and LBW rats. Using a paired-pulse protocol to stimulate GABAergic fibres impinging onto granule cells, we found indications of decreased probability of GABA release in LBW rats. However, tonic GABAergic currents and miniature IPSCs, reflecting quantal vesicle release, appeared normal. Additionally, we found elevated expression levels of two presynaptic proteins, Snap-25 and Scamp2, components of the vesicle release machinery. The results suggest that altered GABA release may be an essential feature in the depressive-like phenotype of LBW rats.

Life-Course Contribution of Prenatal Stress in Regulating the Neural Modulation Network Underlying the Prepulse Inhibition of the Acoustic Startle Reflex in Male Alzheimer's Disease Mice

The prepulse inhibition (PPI) of the acoustic startle reflex (ASR), as an index of sensorimotor gating, is one of the most extensively used paradigms in the field of neuropsychiatric disorders. Few studies have examined how prenatal stress (PS) regulates the sensorimotor gating during the lifespan and how PS modifies the development of amyloid-beta (Aβ) pathology in brain areas underlying the PPI formation. We followed alternations in corticosterone levels, learning and memory, and the PPI of the ASR measures in APPNL-G-F/NL-G-F offspring of dams exposed to gestational noise stress. In-depth quantifications of the Aβ plaque accumulation were also performed at 6 months. The results indicated an age-dependent deterioration of sensorimotor gating, long-lasting PS-induced abnormalities in PPI magnitudes, as well as deficits in spatial memory. The PS also resulted in a higher Aβ aggregation predominantly in brain areas associated with the PPI modulation network. The findings suggest the contribution of a PS-induced hypothalamic-pituitary-adrenal (HPA) axis hyperactivity in regulating the PPI modulation substrates leading to the abnormal development of the neural protection system in response to disruptive stimuli. The long-lasting HPA axis dysregulation appears to be the major underlying mechanism in precipitating the Aβ deposition, especially in brain areas contributed to the PPI modulation network.

A Preclinical Study of Casein Glycomacropeptide as a Dietary Intervention for Acute Mania

BACKGROUND

Casein glycomacropeptide is a peptide that lacks phenylalanine, tyrosine, and tryptophan. This profile may enable it to deplete phenylalanine, tyrosine, and tryptophan, and subsequently the synthesis of dopamine and serotonin in the brain. Dopamine- and serotonin-depleting amino acid mixtures have shown promise as acute antimanic treatments. In this study, we explore the depleting effects on amino acids, dopamine and serotonin as well as its actions on manic-like and other behavior in rats.

METHODS

Casein glycomacropeptide and a selection of amino acid mixtures were administered orally at 2, 4, or 8 h or for 1 week chronically. Amino acid and monoamine levels were measured in plasma and brain and behavior was assessed in the amphetamine-hyperlocomotion, forced swim, prepulse inhibition, and elevated plus maze tests.

RESULTS

Casein glycomacropeptide induced a time-dependent reduction in tyrosine, tryptophan, and phenylalanine in brain and plasma which was augmented by supplementing with leucine. Casein glycomacropeptide +leucine reduced dopamine in the frontal cortex and serotonin in the hippocampus, frontal cortex, and striatum after 2 and 4 h. Casein glycomacropeptide+leucine also had antimanic activity in the amphetamine-induced hyperlocomotion test at 2 h after a single acute treatment and after 1 week of chronic treatment.

CONCLUSIONS

Casein glycomacropeptide-based treatments and a branched-chain amino acid mixture affected total tissue levels of dopamine in the frontal cortex and striatum and serotonin in the frontal cortex, striatum, and hippocampus of rats in a time-dependent fashion and displayed antimanic efficacy in a behavioral assay of mania.

Olfactory Bulbectomy in Methamphetamine-Treated Rat Mothers Induces Impairment in Somatic and Functional Development of Their Offspring

Olfactory bulbectomy in rodents is considered a putative model of depression. Depression is often associated with drug addiction. Our previous studies demonstrated that methamphetamine (MA) administration to rat mothers affects both, mothers and their pups. The aim of the present study was to examine the effect of bulbectomy, as a model of depression, and MA administration on behavior of rat mothers and postnatal development of their pups. Adult female Wistar rats were randomly divided into two groups: bulbectomized (OBX) and sham-operated (SH). A period of 20 days was allowed for the development of the depressive-like phenotype. Animals were tested in the motor activity test and 2 % sucrose preference for anhedonia and hyperactive locomotor response to a novel environment, respectively. After then females were impregnated. Pregnant females were exposed to daily subcutaneous (s.c.) injection of MA (5 mg/kg) or saline (SA) during the entire gestation period. Postnatally, maternal behavior and pup development was examined. The effect of a challenge dose of MA (1 mg/kg, s.c.) on behavior was further examined in adult male offspring. Our results showed no differences in the maternal behavior as a matter of bulbectomy, only OBX rats slept more than all the SH controls. Pups from OBX mothers were born with lower birthweight and gained less weight during the postnatal development than pups from SH controls. Both, bulbectomy and MA administration, delayed the eyes opening. As a matter of functional development of the pups, maternal OBX procedure impaired the performance in the Bar-holding test, but only in saline group. OBX/SA group was the worst in the Bar-holding test relative to all the other groups. In addition, pups from OBX mothers dropped more boluses during the Bar-holding test, suggesting that they were more stressed. In adult male offspring, bulbectomy increased immobility only in the SA/SA group. Prenatal MA exposure increased locomotion, while decreasing immobility. In addition, challenge dose of MA in adulthood increased distance traveled, locomotion, rearing, and average and maximal velocity, while decreasing immobility and grooming. In conclusion, our results suggest that depressive-like phenotype of rat mothers induces impairment in somatic and functional development of their male offspring.

Chronic high-fat diet increases acute neuroendocrine stress response independently of prenatal dexamethasone treatment in male rats

OBJECTIVE

Intrauterine growth restriction (IUGR) has been associated with metabolic disorders later in life such as obesity and diabetes as well as psychiatric disorders such as depression and schizophrenia. Therefore, we wanted to investigate whether behavioural, metabolic or neuroendocrine abnormalities could be provoked or exacerbated by a high-fat diet (HFD) in an experimental model of IUGR.

METHODS

Pregnant dams were exposed to dexamethasone (DEX) in the third gestational week to induce IUGR. Late adolescent male offspring of DEX- and vehicle-treated dams were then fed a HFD or standard chow for 8 weeks and subjected to a variety of assessments.

RESULTS

Only diet affected the hypothalamus-pituitary-adrenal (HPA) axis stress response, as HFD doubled the observed corticosterone levels following acute restraint. HFD and prenatal DEX exposure concomitantly exacerbated depressive-like behaviour in the forced swim test, even though no interaction was seen. Prenatal DEX treatment tended to increase the basal acoustic startle response (ASR), while an interaction between HFD and DEX was present in the ASR pre-pulse inhibition suggestive of fundamental changes in neuronal gating mechanisms. Metabolic parameters were only affected by diet, as HFD increased fasting glucose and insulin levels.

CONCLUSION

We conclude that chronic HFD may be more important in programming of the HPA axis stress responsiveness than an adverse foetal environment and therefore potentially implies an increased risk for developing psychiatric and metabolic disease.