Prenatal treatment with a selective D1 receptor agonist (SKF 38393) alters adult [3H]paroxetine binding and dopamine and serotonin behavioral sensitivity

Prenatal stress and long-term consequences: implications of glucocorticoid hormones

We have shown that prenatal restraint stress (PNRS) induces higher levels of anxiety, greater vulnerability to drugs, a phase advance in the circadian rhythm of locomotor activity and an increase in the paradoxical sleep in adult rats. These behavioral effects result from permanent modifications to the functioning of the brain, particularly in the feedback mechanisms of the hypothalamic-pituitary-adrenal (HPA) axis: the secretion of corticosterone is prolonged after stress and the number of the central glucocorticoid receptors is reduced. These abnormalities are associated with modifications in the synthesis and/or release of certain neurotransmitters. Dysfunction of the HPA axis is due, in part, to stress-induced maternal increase of glucocorticoids, which influences fetal brain development. Some biological abnormalities in depression can be related to those found in PNRS rats reinforcing the idea of the usefulness of PNRS rats as an appropriate animal model to study new pharmacological approaches.

Developmental neurobiology: implications for pediatric psychopharmacology

Pediatric psychopharmacology can only be properly understood within the context of developmental neurobiology. Normal maturation of the brain is characterized by the complex anatomic, molecular, and organizational changes required for optimal adaptive functioning. In many areas of the developing nervous system, neurons, cell processes, neurotransmitters, and trophic nerve growth factors are produced in far greater numbers and in different areas than in the mature brain. Psychopathology and stressful environments can lead to enduring changes in brain structure and functioning. A few select psychopharmacological treatments are reviewed to assess their potential impact on CNS development. More clinical and basic science studies are needed to determine whether current treatments have neurotoxic or neuroprotective effects when administered over extended critical early periods of the lifespan.

Hormonal and behavioural abnormalities induced by stress in utero: an animal model for depression

Prenatal stress in rats can exert profound influence on the off spring's development, inducing abnormalities such as increased "anxiety", "emotionality" or "depression-like" behaviours.Prenatal stress has long-term effects on the development of the hypothalamo-pituitary-adrenal(HPA) axis and forebrain cholinergic systems. These long-term neuroendocrinological effects are mediated, at least in part, by stress-induced maternal corticosterone increase during pregnancy and stress-induced maternal anxiety during the postnatal period. We have shown a significant phase advance in the circadian rhythms of corticosterone secretion and locomotor activity in prenatally-stressed (PNS) rats. When subjected to an abrupt shift in the light-dark(LD) cycle, PNS rats resynchronized their activity rhythm more slowly than control rats. In view of the data suggesting abnormalities in the circadian timing system in these animals, we have investigated the effects of prenatal stress on the sleep-wake cycle in adult male rats. PNS rats exhibited various changes in sleep-wake parameters, including a dramatic increase in the amount of paradoxical sleep. Taken together, our results indicate that prenatal stress can induce increased responses to stress and abnormal circadian rhythms and sleep in adult rats.Various clinical observations in humans suggest a possible pathophysiological link between depression and disturbances in circadian rhythmicity. Circadian abnormalities in depression can be related to those found in PNS rats. Interestingly, we have recently shown that the increased immobility in the forced swimming test observed in PNS rats can be corrected by chronic treatment with the antidepressant tianeptine, or with melatonin or S23478, a melatonin agonist. Those results reinforce the idea of the usefulness of PNS rats as an appropriate animal model to study human depression and support a new antidepressant-like effect of melatonin and the melatonin agonist S23478.

Nicotine exposure during pregnancy is a factor which influences serotonin transporter density in the rat brain

We examined the effects of nicotine exposure during pregnancy on serotonin transporter (SERT) expression in the brain. Nicotine (6 mg/kg/day) was administered to pregnant rats via subcutaneous injections or infusion pumps. Irrespective of the route of administration, nicotine increased SERT density in the forebrain on postnatal day 22, but not in the other brain regions. Our results suggest that nicotine use by pregnant women might be an environmental factor influencing SERT expression in their children.

Prenatal dexamethasone exposure alters brain monoamine metabolism and adrenocortical response in rat offspring

In this study, it has been clearly demonstrated that prenatal dexamethasone treatment (Dex; 0.05 mg/kg on gestational days 17, 18, and 19) resulted in the significant reductions of 5-hydroxytryptamine (5-HT) turnover in four brain regions, including the neocortex, hippocampus, hypothalamus, and midbrain + pons-medulla (M + P-M) but not in the striatum in the offspring at 3 and 14 wk of life, as well as dopamine turnover in the hypothalamus. [3H]paroxetine binding densities were increased in the hypothalamus and M + P-M at 14 wk of life, which corresponded to increased 5-HT contents in both regions. On the other hand, significantly lower norepinephrine contents in the neocortex and hippocampus were observed in the Dex group compared with the control group at 14 wk of life. In addition, the exposure to new environmental condition elevated blood corticosterone levels and enhanced behavioral activities to a greater extent in the Dex group than in controls at 7 wk of life, suggesting that elevated glucocorticoid levels during the pregnancy mimicked prenatal mild stress, producing developmental alterations in brain monoamine metabolism, endocrine response, and behavior in adult offspring.

Pre/postnatal dopamine D1 receptor stimulation induces a differential reduction of serotonin levels in hippocampus and superior colliculus of puber rats

Previous data have shown that through dopamine D1 receptors serotonin and dopamine systems could be interdependent during development. In this study, we have analysed monoamine and metabolite levels in hippocampus, striatum and superior colliculus of puber male rats, which received 10 days of either prenatal or early postnatal D1 receptor stimulation with 0.03 mg/kg of the selective agonist SKF 38393. This substance induced a differential long-term and significant reduction in serotonin (5-HT) and/or 5-hydroxyindoleacetic acid (5-HIAA) levels, but it was dependent on the developing brain region. Norepinephrine (NE) levels were also reduced in superior colliculus, but only after early postnatal treatments. These results suggest that an abnormal stimulation of dopamine D1 receptors during sensitive stages of ontogeny may alter the development of 5-HT fibers innervating hippocampus and superior colliculus.

Heterotypic sprouting of serotonergic forebrain fibers in the brindled mottled mutant mouse

The brindled mottled mouse has a mutation on the X-chromosome which causes alterations in copper metabolism. One role for copper is as a cofactor for dopamine-beta-hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine (NE). This may explain the fact that the hemizygous males have low concentrations of NE, as well as high concentrations of 5-hydroxyindoleacetic acid (5-HIAA) in the brainstem and forebrain. The present study quantified serotonin (5-HT) immunoreactive fibers in the cerebral cortex and striatum of hemizygous males and control littermates on postnatal (P) days 7, 10, 12 and 14. The density of 5-HT immunoreactive fibers was measured using a digitized imaging system in conjunction with darkfield microscopy. Measurements of 5-HT innervation showed an age-dependent increase in density of 5-HT immunoreactive fibers in all layers of the cerebral cortex, with fiber density in brindled mice approximately 70% greater than controls by P14. High performance liquid chromatography confirmed the increased concentrations of 5-HT and 5-HIAA, and the low concentration of NE, in several regions. We believe that these results are an example of heterotypic sprouting of 5-HT neurons, similar to that observed in neonatal rats given 6-hydroxydopamine (6-OHDA). If so, these data provide the first description of 5-HT heterotypic sprouting in mice, and the first description of 5-HT heterotypic sprouting resulting from a natural disease state, rather than an experimentally induced lesion.

Ontogeny of endothelin and its receptors in rat brain

The ontogeny of endothelin (ET) system in rats was studied in preterm (18 days of gestation), term (21 days of gestation) and 1 week post term rats. Brains were dissected out and (1) processed for the estimation of endogenous ET-1 by RIA and (2) membranes were prepared for radioreceptor binding. Receptor characteristics, affinity (Kd) and density (Bmax) were determined using [125I] ET-1 and [125I] SRT 6b (which is structurally similar to ET) and cold ET-1 or SRT 6b as displacer. ET levels were found to be 25.66 +/- 3.18 pg/g protein in preterm, 47.37 +/- 5.31 pg/g protein in term and 48.30 +/- 1.90 pg/g protein in post term rats. ET levels were significantly lower in preterm as compared to term and post term rats. Preterm, term and post term rats showed single high affinity binding site for both [125I] ET-1 and [125I] SRT 6b. The Kd values for [125I] ET-1 and [125I] SRT 6b binding were similar in preterm, term and post term rats. The Bmax values of both [125I] ET-1 and [125I] SRT 6b binding were found to be similar in preterm and term rats while they were significantly higher in post term rats. In adult (4 month old) rats the Kd values were similar to neonatal rats while the Bmax values were significantly lower than the post term neonatal rats. It is concluded that ET and its receptors are developmentally regulated and there is a possibility that endogenous ET is involved in the regulation of ET receptor density.