Long-Lasting Analgesia With Transdermal Fentanyl: A New Approach in Rat Neonatal Research.

Background: With advances in neonatal care, management of prolonged pain in newborns is a daily concern. In addition to ethical considerations, pain in early life would have long-term effects and consequences. However, its treatment remains inadequate. It was therefore important to develop an experimental model of long-lasting analgesia for neonatal research. Materials and Methods: Experiments were performed in six groups of rats with transdermal fentanyl 0, 3, 12, 50, 100, or 200 µg/kg/h from second postnatal day (P2) until weaning. Assessment of analgesia was carried out at P21, with behavioral scores (ranging from 0 to 3) using a 4% formalin test. Plasma levels of fentanyl were determined by UPLC/TQD at P22. Growth rate was investigated. Results: Fentanyl 100 and 200 µg/kg/h reduced scores of formalin-evoked behavioral pain. They increased time spent in pain score 0 (8 min 55 s and 6 min 34 s versus 23 s in controls) as in low pain scores 1 and 2, and decreased time in the most severe pain score 3 (19 min 56 s and 17 min 39 s versus 44 min 15 s). Fentanylemia increased in a dose-dependent manner from 50 µg/kg/h (2.36 ± 0.64 ng/ml) to 200 µg/kg/h (8.66 ± 1.80 ng/ml). Concerning growth, no difference was observed except weaker growth from P17 to P22 with 200 µg/kg/h. Clinically, we noticed no visible side effect from 3 to 100 µg/kg/h. Concomitantly, 200 µg/kg/h was responsible for ophthalmological side effects with appearance of corneal bilateral clouding in 90% pups. No difference was observed between male and female rats. Conclusion: Altogether, results indicate that transdermal fentanyl 100 µg/kg/h is an efficient therapeutic for long-lasting analgesia in lactating pups. This new model provides a useful tool for protection and welfare, and future opportunity for studying long-term health consequences of sustainable neonatal analgesia.

Maternal prenatal undernutrition programs adipose tissue gene expression in adult male rat offspring under high-fat diet.

Several studies have shown that maternal undernutrition leading to low birth weight predisposes offspring to the development of metabolic pathologies such as obesity. Using a model of prenatal maternal 70% food restriction diet (FR30) in rat, we evaluated whether postweaning high-fat (HF) diet would amplify the phenotype observed under standard diet. We investigated biological parameters as well as gene expression profile focusing on white adipose tissues (WAT) of adult offspring. FR30 procedure does not worsen the metabolic syndrome features induced by HF diet. However, FR30HF rats displayed catch-up growth to match the body weight of adult control HF animals, suggesting an increase of adiposity while showing hyperleptinemia and a blunted increase of corticosterone. Using quantitative RT-PCR array, we demonstrated that FR30HF rats exhibited leptin and Ob-Rb as well as many peptide precursor and receptor gene expression variations in WAT. We also showed that the expression of genes involved in adipogenesis was modified in FR30HF animals in a depot-specific manner. We observed an opposite variation of STAT3 phosphorylation levels, suggesting that leptin sensitivity is modified in WAT adult FR30 offspring. We demonstrated that 11ß-HSD1, 11ß-HSD2, GR, and MR genes are coexpressed in WAT and that FR30 procedure modifies gene expression levels, especially under HF diet. In particular, level variation of 11ß-HSD2, whose protein expression was detected by Western blotting, may represent a novel mechanism that may affect WAT glucocorticoid sensitivity. Data suggest that maternal undernutrition differently programs the adult offspring WAT gene expression profile that may predispose for altered fat deposition.

Maternal perinatal undernutrition programs a "brown-like" phenotype of gonadal white fat in male rat at weaning.

Several studies indicate that maternal undernutrition sensitizes the offspring to the development of metabolic disorders, such as obesity. Using a model of perinatal maternal 50% food-restricted diet (FR50), we recently reported that rat neonates from undernourished mothers exhibit decreased leptin plasma levels associated with alterations of hypothalamic proopiomelanocortin system. The present study aimed at examining the consequences of FR50 on the brain-adipose axis in male rat neonates. Using quantitative RT-PCR array containing 84 obesity-related genes, we demonstrated that most of the genes involved in energy metabolism regulation are expressed in rat gonadal white adipose tissue (WAT) and are sensitive to maternal perinatal undernutrition (MPU). In contrast, hypothalamic gene expression was not substantially affected by MPU. Gene expression of uncoupling protein 1 (UCP1), a marker of brown adipocytes, showed an almost 400-fold stimulation in postnatal day 21 (PND21) FR50 animals, suggesting that their gonadal WAT possesses a brown-like phenotype. This was confirmed by histological and immunoshistochemical procedures, which demonstrated that PND21 FR50 gonadal adipocytes are multilocular, resembling those present in interscapular brown adipose tissue, and exhibit an overexpression of UCP1 and neuropeptide Y (NPY) at the protein level. Control animals contained almost exclusively "classical" unilocular white adipocytes that did not show high UCP1 and NPY labeling. After weaning, FR50 animals exhibited a transient hyperphagia that was associated with the disappearance of brown-like fat pads in PND30 WAT. Our results demonstrate that MPU delays the maturation of gonadal WAT during critical developmental time windows, suggesting that it could have long-term consequences on body weight regulation in the offspring.

Maternal perinatal undernutrition drastically reduces postnatal leptin surge and affects the development of arcuate nucleus proopiomelanocortin neurons in neonatal male rat pups.

A growing body of evidence suggests that maternal undernutrition sensitizes the offspring to the development of energy balance metabolic disorders such as type 2 diabetes, dyslipidemia, and obesity. The present study aimed at examining the impact of maternal undernutrition on leptin plasma levels in newborn male rats and on the arcuate nucleus proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons that are major leptin targets. Using a model of perinatal maternal 50% food-restricted diet (FR50) in the rat, we evaluated leptin plasma levels and hypothalamic POMC and NPY gene expression from postnatal day (PND) 4 to PND30 in both control and FR50 offspring. In control rats, a postnatal peak of plasma leptin was observed between PND4 and PND14 that reached a maximal value at PND10 (5.17 +/- 0.53 ng/ml), whereas it was dramatically reduced in FR50 pups with the higher concentration at PND7 (0.93 +/- 0.23 ng/ml). In FR50 animals, using semiquantitative RT-PCR and in situ hybridization, we showed that the hypothalamic POMC mRNA level was decreased from PND14 until PND30, whereas NPY gene expression was not significantly modified. In PND21 FR50 animals, we observed strikingly reduced immunoreactive beta-endorphin nerve fibers projecting to the hypothalamic paraventricular nucleus without affecting NPY projections. Our data showed that maternal undernutrition drastically reduces the postnatal surge of plasma leptin, disturbing particularly the hypothalamic wiring as well as the gene expression of the anorexigenic POMC neurons in male rat pups. These alterations might contribute to the adult metabolic disorders resulting from perinatal growth retardation.

HPA axis programming by maternal undernutrition in the male rat offspring.

Epidemiological and experimental studies have demonstrated that perinatal alterations such as maternal undernutrition are frequently associated with the onset of several chronic adult diseases. Although the physiological mechanisms involved in this "fetal programming" remain largely unknown, it has been shown that early exposure to undernutrition programs hypothalamic-pituitary-adrenal (HPA) axis throughout lifespan. However, the wide spectrum of experimental paradigms used (species, sex, age of the animals, and duration and severity of undernutrition exposure) has given rise to variable results that are difficult to interpret. To circumvent this problem, we used the same experimental protocol of maternal food restriction to study the effects of a severe maternal undernutrition on the HPA axis activity in the male rat offspring throughout the life, namely from fetal stage to adulthood. Mothers exposed to food restriction received 50% (FR50) of the daily intake of pregnant dams during the last week of gestation and lactation. In FR50 fetuses, HPA axis function was reduced and associated with a decreased placental 11beta-HSD2 activity and a greater transplacental transfer of glucocorticoids. At weaning, maternal food restriction reduced HPA axis activity in response to an ether inhalation stress. In young adults (4-month-old), only fine HPA axis alterations were observed, whereas in older ones (8-month-old), maternal undernutrition was associated with chronic hyperactivity of this neuroendocrine axis. Interestingly, excessive glucocorticoids production is observed in a growing number of pathologies such as metabolic, cognitive, immune and inflammatory diseases, suggesting that they could, at least in part, result from fetal undernutrition and thus have a neurodevelopmental origin.

Neurochemical and behavioral alterations in glucocorticoid receptor-impaired transgenic mice after chronic mild stress.

Mice (GR-i) bearing a transgene encoding a glucocorticoid receptor (GR) antisense RNA under the control of a neuron-specific neurofilament promoter were used to investigate the effects of a 4 week chronic mild stress (CMS) on the hypothalamo-pituitary-adrenocortical (HPA) axis and the serotoninergic system in a transgenic model of vulnerability to affective disorders. GR-i mice showed a decrease in both GR-specific binding (hippocampus and cerebral cortex) and GR mRNA levels [hippocampus, cerebral cortex, and dorsal raphe nucleus (DRN)] as well as a deficit in HPA axis feedback control (dexamethasone test) compared with paired wild-type (WT) mice. In the latter animals, CMS exposure caused a significant decrease in both GR mRNA levels and the density of cytosolic GR binding sites in the hippocampus, whereas, in the DRN, GR mRNA levels tended to increase. In contrast, in stressed GR-i mice, both GR mRNA levels and the density of GR binding sites were significantly increased in the hippocampus, cerebral cortex, and DRN. Electrophysiological recordings in brainstem slices and [gamma-35S]GTP-S binding measurements to assess 5-HT1A receptor functioning showed that CMS exposure produced a desensitization of DRN 5-HT1A autoreceptors in WT, but not in GR-i, mice. In addition, CMS was found to facilitate choice behavior of WT, but not GR-i, mice in a decision-making task derived from an alternation paradigm. These results demonstrate that impaired GR functioning affects normal adaptive responses of the HPA axis and 5-HT system to CMS and alters stress-related consequences on decision-making behaviors.

Prenatal morphine exposure affects sympathoadrenal axis activity and serotonin metabolism in adult male rats both under basal conditions and after an ether inhalation stress.

We have previously shown that prenatal morphine exposure inhibited the hypothalamo-pituitary-adrenal (HPA) axis and altered the hypothalamic metabolism of serotonin during the early postnatal period in the rat and induced a chronic sympathoadrenal hyperactivity under resting conditions in adult male rats. In this study, we examined the effects of prenatal morphine exposure on the responsiveness to an acute ether inhalation stress of the sympathoadrenal and HPA axis and the hippocampal and hypothalamic concentrations of serotonin (5HT) and 5-hydroxylindoleacetic acid (5HIAA) in 3-month-old male rats. The plasma levels of adrenocorticopic hormone (ACTH) and corticosterone (B) did not differ between the two groups both under resting conditions and after ether exposure. Ether inhalation increased adrenal tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) mRNA expression as well as adrenal epinephrine (E) concentration in control rats but not in prenatally morphine-exposed (PM) animals. Under basal conditions, hypothalamic concentrations of 5HT and 5HIAA increased in PM animals. In contrast to control animals, PM rats showed, in response to stress, an increased level of 5HT and 5HIAA in both the hypothalamus and in the hippocampus. In conclusion, prenatal morphine exposure produces long-lasting alterations in brain serotonin transmission and in the sympathoadrenal responsiveness to an acute systemic stress.

Could maternal perinatal atypical antipsychotic treatments program later metabolic diseases in the offspring?

An association is established between schizophrenia and the development of metabolic alterations including cardiovascular diseases, type 2 diabetes and obesity. Perinatal insults, such as undernutrition, have been shown to increase the propensity to develop these pathologies, reinforcing the idea that schizophrenia may have a neurodevelopmental origin. Moreover, the use of second generation antipsychotics (SGAs) also known as "atypical" neuroleptics has also been demonstrated to exacerbate metabolic anomalies in patients with schizophrenia. SGAs are able to cross the placental barrier and have been detected in milk from women receiving atypical neuroleptics treatment during the perinatal period. To date, the consequences of such treatment have only been examined on the birth weight and the cognitive capacities of the child from women with schizophrenia, but no data is available concerning the putative long-term effects of SGAs on their body weight and metabolic parameters. We have recently reported that rat offspring from prenatally undernourished mothers exhibit a low birth weight associated with modified sensitivity to clozapine and aripiprazole in adulthood reinforcing the idea that some forms of schizophrenia may be acquired during early development. In view of these observations, the risks of perinatal exposure to SGAs must be weighed against the growing evidence that maternal psychiatric illness poses risks to the fetus/newborn as well as for long-term susceptibility to diseases. Thus, metabolic follow-up of children born from mothers treated by SGAs during the perinatal period will be clearly recommended, in particular if they exhibit alterations of their body weight during this early critical period.

Influence of prenatal undernutrition on the effects of clozapine and aripiprazole in the adult male rats: relevance to a neurodevelopmental origin of schizophrenia?

Epidemiological and experimental data indicate that maternal undernutrition may sensitize the offspring to the apparition of chronic diseases such as metabolic syndrome and schizophrenia, suggesting that these pathologies may have a developmental origin. To test this hypothesis, we have compared the effects of a 4 weeks treatment of clozapine (30 mg/kg once daily, p.o.) or aripiprazole (10 mg/kg once daily, p.o.) on metabolic and hormonal parameters in 4-month-old male animals from control or 70% prenatally food-restricted mothers (FR30 model). Both neuroleptics did not markedly modify body weight gain and food intake in both controls and FR30 rats. Clozapine decreased insulin secretion in both groups but significantly diminished leptin, corticosterone and glucose plasma levels only in FR30 animals. Aripiprazole decreased corticosterone plasma levels only in FR30 animals. Using quantitative RT-PCR array containing 84 obesity-related genes, we identified several genes involved in energy metabolism regulation whose expression was modified by clozapine or aripiprazole in adult male rat hypothalami. In addition, we demonstrated that expression of some of these genes was differentially affected by each neuroleptic in the hypothalamus of both FR30 and control animals. Although no marked metabolic alterations were observed in both control and FR30 animals after clozapine or aripiprazole treatment, our data indicate that offspring from undernourished mothers exhibit a modified sensitivity to atypical neuroleptics. Our results do not rule out a putative developmental origin of schizophrenia and may help to understand the way by which atypical neuroleptics, such as clozapine, sensitize schizophrenic patients to the development of metabolic disorders.

Maternal prenatal undernutrition alters the response of POMC neurons to energy status variation in adult male rat offspring.

Epidemiological studies suggest that maternal undernutrition predisposes the offspring to development of energy balance metabolic pathologies in adulthood. Using a model of a prenatal maternal 70% food-restricted diet (FR30) in rats, we evaluated peripheral parameters involved in nutritional regulation, as well as the hypothalamic appetite-regulatory system, in nonfasted and 48-h-fasted adult offspring. Despite comparable glycemia in both groups, mild glucose intolerance, with a defect in glucose-induced insulin secretion, was observed in FR30 animals. They also exhibited hyperleptinemia, despite similar visible fat deposits. Using semiquantitative RT-PCR, we observed no basal difference of hypothalamic proopiomelanocortin (POMC) and neuropeptide Y (NPY) gene expression, but a decrease of the OB-Rb and an increase of insulin receptor mRNA levels, in FR30 animals. These animals also exhibited basal hypercorticosteronemia and a blunted increase of corticosterone in fasted compared with control animals. After fasting, FR30 animals showed no marked reduction of POMC mRNA levels or intensity of beta-endorphin-immunoreactive fiber projections. By contrast, NPY gene expression and immunoreactive fiber intensity increased. FR30 rats also displayed subtle alterations of food intake: body weight-related food intake was higher and light-dark phase rhythm and refeeding time course were modified after fasting. At rest, in the morning, hyperinsulinemia and a striking increase in the number of c-Fos-containing cells in the arcuate nucleus were observed. About 30% of the c-Fos-expressing cells were POMC neurons. Our data suggest that maternal undernutrition differently programs the long-term appetite-regulatory system of offspring, especially the response of POMC neurons to energy status and food intake rhythm.

Perinatal maternal undernutrition programs the offspring hypothalamo-pituitary-adrenal (HPA) axis.

There is now compelling evidence, coming both from animal and human studies that an early exposure to undernutrition is frequently associated with low birth weight and programs HPA axis alterations throughout the lifespan. Although animal models have reported conflicting findings arising from differences in experimental paradigms and species, they have clearly demonstrated that such programming not only affects the brain but also the pituitary corticotrophs and the adrenal cortex. In fetuses, maternal undernutrition reduces HPA axis function and implicates a reduction of placental 11beta-HSD2 activity and a greater transplacental transfer of glucocorticoids (GRs). In young adults, usually only fine HPA axis alterations were observed, whereas in older ones, maternal undernutrition was frequently associated with chronic hyperactivity of this neuroendocrine axis. In humans, evidence of HPA axis dysregulation in people who were small at birth has recently emerged. Thus, we suggest that such alterations in adults may be implicated in the aetiology of several disorders related to the metabolic syndrome as well as to immune or inflammatory diseases. To reverse such programming, recent experimental reports have shown that postnatal environmental interventions, dietary modifications and the use of agents modulating the epigenomic state could partly restore physiological functions and thus open new therapeutic strategies.

Effects of perinatal maternal food restriction on pituitary-gonadal axis and plasma leptin level in rat pup at birth and weaning and on timing of puberty.

The effects of maternal 50% food restriction (FR) during the last week of gestation and/or lactation on pituitary-gonadal axis (at birth and weaning), on circulating levels of leptin (at weaning), and on the onset of puberty have been determined in rats at birth and at weaning. Maternal FR during pregnancy has no effect at term on the litter size, on the basal level of testosterone in male pups, and on the drastic surge of circulating testosterone that occurs 2 h after birth. At weaning, similar retardation of body growth is observed in male and female pups from mothers exposed to FR. This undernutrition induces the most drastic effects when it is performed during both gestation and lactation or during lactation alone. Drastic retardation of testicle growth with reduction of cross-sectional area and intratubular lumen of the seminiferous tubules is observed in male pups from mothers exposed to undernutrition during both gestation and lactation or during lactation alone. Maternal FR during the perinatal period reduces circulating levels of FSH in male pups without affecting LH and testosterone concentrations. Maternal FR does not affect circulating levels of LH, estradiol, and progesterone in female pups. Female pups from mothers exposed to FR during both gestation and lactation show a significant increase of plasma FSH as well as a drastic retardation of ovarian growth. The follicular population was also altered. The number of antral follicles of small size (vesicular follicles) was increased, although the number of antral follicles of large size (graafian follicles) was reduced. Maternal FR occurring during both late gestation and lactation (male and female pups), during lactation alone (male and female pups), or during late gestation (female pups) induces a drastic reduction of plasma leptin and fat mass in pups at weaning. The onset of puberty is delayed in pups of both sexes from mothers exposed to FR during lactation and during both gestation and lactation. In conclusion, these data demonstrate that a perinatal growth retardation induced by maternal FR has long-term consequences on both size and histology of the genitals, on plasma gonadotropins and leptin levels, on fat stores at weaning, and on the onset of puberty.