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Animal models of postpartum depression revisited. Psychoneuroendocrinology 2022; 136:105590. [PMID: 34839082 DOI: 10.1016/j.psyneuen.2021.105590] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 11/02/2021] [Accepted: 11/04/2021] [Indexed: 11/21/2022]
Abstract
Postpartum depression (PPD) is a heterogeneous mood disorder and the most frequent psychiatric complication of the postnatal period. Given its potential long-lasting repercussions on the well-being of the mother and the infants, it should be a priority in public health. In spite of efforts devoted to clinical investigation and preclinical studies, the underlying neurobiological mechanisms of this disorder remain unknown in detail. Much of the progress in the area has been made from animal models, especially rodent models. The aim of this mini-review is to update the current rodent models in PPD research and their main contributions to the field. Animal models are critical tools to advance understanding of the pathophysiological basis of this disorder and to help the development of new therapeutic strategies. Here, we group PPD models into 2 main categories (Models based on hormone manipulations, Models based on stress exposure), each of which includes different paradigms that reflect risk factors or physiological conditions associated with this disease. Finally, we provide an overview of emerging models that provide new perspectives on the study of possible pathophysiological factors related to PPD, to contribute to tackling potential therapeutic targets.
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Yu P, Yang M, Zhao H, Cao R, Chen Z, Gong D. Characteristics of pup ultrasonic vocalizations and parental behavior responses in midday gerbils (Meriones meridianus). Physiol Behav 2020; 224:113075. [PMID: 32663552 DOI: 10.1016/j.physbeh.2020.113075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 06/18/2020] [Accepted: 07/10/2020] [Indexed: 10/23/2022]
Abstract
Ultrasonic vocalizations (USVs) play an important role in parent-infant interactions during the neonatal period of rodents because of the pups' need to be suckled and protected by their parents. However, studies on the effects of USVs on parental care are focused on maternal behavior, and little data on paternal care are available, with especially few investigations in midday gerbils. In this study, we examined the effects of early social deprivation (ED) on offspring due to USVs and parental behavior responses in midday gerbils (Meriones meridianus). The results indicated that the number of USVs in ED gerbils increased on postnatal day nine (40 calls/minute), whereas the number of gerbils in the parental care (PC) group remained high for up to 2 weeks (46.6 calls/minute), before decreasing. The number of USVs and duration of single syllables from postnatal day 3 to 21 in ED pups were significantly lower than those in PC pups. ED increased maternal licking, grooming behavior, and nest-building, but decreased huddling and exploring behavior. Similarly, ED increased paternal behavior, like nest-building, but reduced exploring and self-grooming. Overall, gerbil pups displayed high levels of USVs and various syllable types before weaning. ED significantly reduced the number of USVs and syllable types, but increased maternal licking, grooming, and paternal nest-building behavior.
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Affiliation(s)
- Peng Yu
- Institute of Behavioral and Physical Sciences, College of Life Sciences, Northwest Normal University, Lanzhou, 730070, Gansu, China
| | - Minna Yang
- Institute of Behavioral and Physical Sciences, College of Life Sciences, Northwest Normal University, Lanzhou, 730070, Gansu, China
| | - Haochi Zhao
- Institute of Behavioral and Physical Sciences, College of Life Sciences, Northwest Normal University, Lanzhou, 730070, Gansu, China
| | - Ruidong Cao
- Institute of Behavioral and Physical Sciences, College of Life Sciences, Northwest Normal University, Lanzhou, 730070, Gansu, China
| | - Zhuo Chen
- Institute of Behavioral and Physical Sciences, College of Life Sciences, Northwest Normal University, Lanzhou, 730070, Gansu, China
| | - Dajie Gong
- Institute of Behavioral and Physical Sciences, College of Life Sciences, Northwest Normal University, Lanzhou, 730070, Gansu, China.
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Lambert KG, Byrnes EM. Challenges to the parental brain: Neuroethological and translational considerations. Front Neuroendocrinol 2019; 53:100747. [PMID: 31004617 DOI: 10.1016/j.yfrne.2019.04.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2018] [Revised: 03/15/2019] [Accepted: 04/16/2019] [Indexed: 02/05/2023]
Abstract
Extending from research documenting adaptive parental responses in nonthreatening contexts, the influences of various neuroethological and physiological challenges on effective parenting responses are considered in the current review. In natural habitats, rodent family units are exposed to predators, compromised resources, and other environmental stressors that disrupt HPA axis functions. With the additional physiological demands associated with caring for offspring, alterations in stress-related neuroendocrine responsiveness contribute to adaptive responses in many challenging contexts. Some environmental contexts, however, such as restricted nesting resources, result in disrupted maternal responses that have a negative impact on offspring wellbeing. Additionally, parental dysregulation associated with exposure to environmental chemicals or pharmacological substances, also compromise maternal responses with effects that often extend to future generations. Continued preclinical and clinical research elucidating parental responses to various stressors and physiological disruptors is necessary to provide valuable translational information identifying threats to effective parenting outcomes.
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Affiliation(s)
- Kelly G Lambert
- Department of Psychology, University of Richmond, VA 23173, United States.
| | - Elizabeth M Byrnes
- Cummings School of Veterinary Medicine, Tufts University, N. Grafton, MA 01536, United States
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Zhang YF, Li QQ, Qu J, Sun CM, Wang Y. Alterations of motor cortical microcircuit in a depressive-like mouse model produced by light deprivation. Neuroscience 2017; 341:79-94. [DOI: 10.1016/j.neuroscience.2016.11.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 11/16/2016] [Accepted: 11/17/2016] [Indexed: 01/01/2023]
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Antoniazzi CT, Boufleur N, Dolci G, Roversi K, Kuhn F, Pase CS, Dias VT, Roversi K, Barcelos R, Benvegnú DM, Bürger ME. Influence of neonatal tactile stimulation on amphetamine preference in young rats: Parameters of addiction and oxidative stress. Pharmacol Biochem Behav 2014; 124:341-9. [DOI: 10.1016/j.pbb.2014.07.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 06/20/2014] [Accepted: 07/06/2014] [Indexed: 01/13/2023]
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6
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Early maternal separation: Neurobehavioral consequences in mother rats. Behav Brain Res 2013; 248:25-31. [DOI: 10.1016/j.bbr.2013.03.040] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2013] [Revised: 03/26/2013] [Accepted: 03/28/2013] [Indexed: 12/24/2022]
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7
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Silveira PP, Benetti CDS, Portella AK, Diehl LA, Molle RD, Lucion AB, Dalmaz C. Brief daily postpartum separations from the litter alter dam response to psychostimulants and to stress. BRAZILIAN JOURNAL OF MEDICAL AND BIOLOGICAL RESEARCH = REVISTA BRASILEIRA DE PESQUISAS MEDICAS E BIOLOGICAS 2013. [PMID: 23739746 DOI: 10.1590/1414-431×20132784] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Neonatal handling induces several behavioral and neurochemical alterations in pups, including decreased responses to stress and reduced fear in new environments. However, there are few reports in the literature concerning the behavioral effects of this neonatal intervention on the dams during the postpartum period. Therefore, the aim of the current study was to determine if brief postpartum separation from pups has a persistent impact on the dam's stress response and behavior. Litters were divided into two neonatal groups: 1) non-handled and 2) handled [10 min/day, from postnatal day (PND) 1 to 10]. Weaning occurred at PND 21 when behavioral tasks started to be applied to the dams, including sweet food ingestion (PND 21), forced swimming test (PND 28), and locomotor response to a psychostimulant (PND 28). On postpartum day 40, plasma was collected at baseline for leptin assays and after 1 h of restraint for corticosterone assay. Regarding sweet food consumption, behavior during the forced swimming test or plasma leptin levels did not differ between dams briefly separated and non-separated from their pups during the postpartum period. On the other hand, both increased locomotion in response to diethylpropion and increased corticosterone secretion in response to acute stress were detected in dams briefly separated from their pups during the first 10 postnatal days. Taken together, these findings suggest that brief, repeated separations from the pups during the neonatal period persistently impact the behavior and induce signs of dopaminergic sensitization in the dam.
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Affiliation(s)
- P P Silveira
- Universidade Federal do Rio Grande do Sul, Programa de Pós-Graduação em Neurociências, Instituto de Ciências Básicas da Saúde, Porto Alegre, RS, Brasil.
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8
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Silveira PP, Benetti CDS, Portella AK, Diehl LA, Molle RD, Lucion AB, Dalmaz C. Brief daily postpartum separations from the litter alter dam response to psychostimulants and to stress. Braz J Med Biol Res 2013; 46:426-32. [PMID: 23739746 PMCID: PMC3854400 DOI: 10.1590/1414-431x20132784] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Accepted: 03/14/2013] [Indexed: 12/14/2022] Open
Abstract
Neonatal handling induces several behavioral and neurochemical alterations in pups, including decreased responses to stress and reduced fear in new environments. However, there are few reports in the literature concerning the behavioral effects of this neonatal intervention on the dams during the postpartum period. Therefore, the aim of the current study was to determine if brief postpartum separation from pups has a persistent impact on the dam's stress response and behavior. Litters were divided into two neonatal groups: 1) non-handled and 2) handled [10 min/day, from postnatal day (PND) 1 to 10]. Weaning occurred at PND 21 when behavioral tasks started to be applied to the dams, including sweet food ingestion (PND 21), forced swimming test (PND 28), and locomotor response to a psychostimulant (PND 28). On postpartum day 40, plasma was collected at baseline for leptin assays and after 1 h of restraint for corticosterone assay. Regarding sweet food consumption, behavior during the forced swimming test or plasma leptin levels did not differ between dams briefly separated and non-separated from their pups during the postpartum period. On the other hand, both increased locomotion in response to diethylpropion and increased corticosterone secretion in response to acute stress were detected in dams briefly separated from their pups during the first 10 postnatal days. Taken together, these findings suggest that brief, repeated separations from the pups during the neonatal period persistently impact the behavior and induce signs of dopaminergic sensitization in the dam.
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Affiliation(s)
- P P Silveira
- Universidade Federal do Rio Grande do Sul, Programa de Pós-Graduação em Neurociências, Instituto de Ciências Básicas da Saúde, Porto Alegre, RS, Brasil.
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Farid WO, Lawrence AJ, Krstew EV, Tait RJ, Hulse GK, Dunlop SA. Maternally administered sustained-release naltrexone in rats affects offspring neurochemistry and behaviour in adulthood. PLoS One 2012; 7:e52812. [PMID: 23300784 PMCID: PMC3530485 DOI: 10.1371/journal.pone.0052812] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Accepted: 11/21/2012] [Indexed: 02/06/2023] Open
Abstract
Naltrexone is not recommended during pregnancy. However, sustained-release naltrexone implant use in humans has resulted in cases of inadvertent foetal exposure. Here, we used clinically relevant dosing to examine the effects of maternally administered sustained-release naltrexone on the rat brain by examining offspring at birth and in adulthood. Maternal treatment (naltrexone or placebo implant) started before conception and ceased during gestation, birth or weaning. Morphometry was assessed in offspring at birth and adulthood. Adult offspring were evaluated for differences in locomotor behaviour (basal and morphine-induced, 10 mg/kg, s.c.) and opioid neurochemistry, propensity to self-administer morphine and cue-induced drug-seeking after abstinence. Blood analysis confirmed offspring exposure to naltrexone during gestation, birth and weaning. Naltrexone exposure increased litter size and reduced offspring birth-weight but did not alter brain morphometry. Compared to placebo, basal motor activity of naltrexone-exposed adult offspring was lower, yet they showed enhanced development of psychomotor sensitization to morphine. Developmental naltrexone exposure was associated with resistance to morphine-induced down-regulation of striatal preproenkephalin mRNA expression in adulthood. Adult offspring also exhibited greater operant responding for morphine and, in addition, cue-induced drug-seeking was enhanced. Collectively, these data show pronounced effects of developmental naltrexone exposure, some of which persist into adulthood, highlighting the need for follow up of humans that were exposed to naltrexone in utero.
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Affiliation(s)
- Waleed O. Farid
- Experimental and Regenerative Neurosciences, School of Animal Biology, The University of Western Australia, Perth, Western Australia, Australia
- Unit for Research and Education in Drugs and Alcohol, School of Psychiatry and Clinical Neurosciences, The University of Western Australia, Perth, Western Australia, Australia
| | - Andrew J. Lawrence
- Florey Neuroscience Institutes, The University of Melbourne, Melbourne, Victoria, Australia
- Centre for Neuroscience, The University of Melbourne, Melbourne, Victoria, Australia
| | - Elena V. Krstew
- Florey Neuroscience Institutes, The University of Melbourne, Melbourne, Victoria, Australia
| | - Robert J. Tait
- Unit for Research and Education in Drugs and Alcohol, School of Psychiatry and Clinical Neurosciences, The University of Western Australia, Perth, Western Australia, Australia
- Centre for Mental Health Research, The Australian National University, Canberra, Australian Capital Territory, Australia
| | - Gary K. Hulse
- Unit for Research and Education in Drugs and Alcohol, School of Psychiatry and Clinical Neurosciences, The University of Western Australia, Perth, Western Australia, Australia
| | - Sarah A. Dunlop
- Experimental and Regenerative Neurosciences, School of Animal Biology, The University of Western Australia, Perth, Western Australia, Australia
- The Western Australian Institute for Medical Research, Perth, Western Australia, Australia
- * E-mail:
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Abstract
Illicit use of opiates is the fastest growing substance use problem in the United States, and the main reason for seeking addiction treatment services for illicit drug use throughout the world. It is associated with significant morbidity and mortality related to human immunodeficiency virus, hepatitis C, and overdose. Treatment for opiate addiction requires long-term management. Behavioral interventions alone have extremely poor outcomes, with more than 80% of patients returning to drug use. Similarly poor results are seen with medication-assisted detoxification. This article provides a topical review of the three medications approved by the Food and Drug Administration for long-term treatment of opiate dependence: the opioid-agonist methadone, the partial opioid-agonist buprenorphine, and the opioid-antagonist naltrexone. Basic mechanisms of action and treatment outcomes are described for each medication. Results indicate that maintenance medication provides the best opportunity for patients to achieve recovery from opiate addiction. Extensive literature and systematic reviews show that maintenance treatment with either methadone or buprenorphine is associated with retention in treatment, reduction in illicit opiate use, decreased craving, and improved social function. Oral naltrexone is ineffective in treating opiate addiction, but recent studies using extended-release naltrexone injections have shown promise. Although no direct comparisons between extended-release naltrexone injections and either methadone or buprenorphine exist, indirect comparison of retention shows inferior outcome compared with methadone and buprenorphine. Further work is needed to directly compare each medication and determine individual factors that can assist in medication selection. Until such time, selection of medication should be based on informed choice following a discussion of outcomes, risks, and benefits of each medication.
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Affiliation(s)
- Gavin Bart
- Division of Addiction Medicine, Hennepin County Medical Center, Minneapolis, Minnesota 55415, USA.
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Byrnes JJ, Babb JA, Scanlan VF, Byrnes EM. Adolescent opioid exposure in female rats: transgenerational effects on morphine analgesia and anxiety-like behavior in adult offspring. Behav Brain Res 2010; 218:200-5. [PMID: 21138744 DOI: 10.1016/j.bbr.2010.11.059] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Revised: 11/08/2010] [Accepted: 11/29/2010] [Indexed: 10/18/2022]
Abstract
The use of narcotics by adolescent females is a growing problem, yet very little is known about the long-term consequences for either the user or her future offspring. In the current study, we utilized an animal model to examine the transgenerational consequences of opiate exposure occurring during this sensitive period. Female rats were exposed to increasing doses of morphine or its saline vehicle twice daily during adolescent development (postnatal days 30-40), after which they remained drug free. At 60 days of age, all females were mated and their adult offspring were tested for anxiety-like behavior and sensitivity to morphine. Specifically, offspring of adolescent morphine (MOR-F1)- or saline (SAL-F1)-exposed mothers were tested for acute locomotor responses in an open field, followed by testing of acute or chronic morphine analgesia on the hot plate. Open field testing indicated alterations in anxiety-like behavior in MOR-F1 female offspring, with effects dependent upon the stage of the estrus cycle. Hot plate testing revealed sex differences in baseline pain threshold and morphine sensitivity in all offspring, regardless of maternal exposure. However, when compared to their SAL-F1 counterparts, MOR-F1 male offspring demonstrated significantly increased sensitivity to the analgesic effects of acute morphine, and developed analgesic tolerance more rapidly following chronic morphine treatment. The findings indicate that prior opiate exposure during early adolescence in females produces sex-specific alterations of both emotionality and morphine sensitivity in their progeny.
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Affiliation(s)
- John J Byrnes
- Department of Biomedical Sciences, Section of Reproduction and Neuroscience, Tufts University, Cummings School of Veterinary Medicine, 200 Westboro Rd., North Grafton, MA 01536, United States
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12
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Wang YC, Wang CC, Lee CC, Huang ACW. Effects of single and group housing conditions and alterations in social and physical contexts on amphetamine-induced behavioral sensitization in rats. Neurosci Lett 2010; 486:34-7. [DOI: 10.1016/j.neulet.2010.09.039] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Revised: 09/09/2010] [Accepted: 09/14/2010] [Indexed: 10/19/2022]
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Daoura L, Hjalmarsson M, Oreland S, Nylander I, Roman E. Postpartum Behavioral Profiles in Wistar Rats Following Maternal Separation - Altered Exploration and Risk-Assessment Behavior in MS15 Dams. Front Behav Neurosci 2010; 4:37. [PMID: 20617189 PMCID: PMC2896302 DOI: 10.3389/fnbeh.2010.00037] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Accepted: 06/01/2010] [Indexed: 12/02/2022] Open
Abstract
The rodent maternal separation (MS) model is frequently used to investigate the impact of early environmental factors on adult neurobiology and behavior. The majority of MS studies assess effects in the offspring and few address the consequences of repeated pup removal in the dam. Such studies are of interest since alterations detected in offspring subjected to MS may, at least in part, be mediated by variations in maternal behavior and the amount of maternal care provided by the dam. The aim of this study was to investigate how daily short (15 min; MS15) and prolonged (360 min; MS360) periods of MS affects the dam by examining postpartum behavioral profiles using the multivariate concentric square field (MCSF) test. The dams were tested on postpartum days 24-25, i.e., just after the end of the separation period and weaning. The results reveal a lower exploratory drive and lower risk-assessment behavior in MS15 dams relative to MS360 or animal facility reared dams. The present results contrast some of the previously reported findings and provide new information about early post-weaning behavioral characteristics in a multivariate setting. Plausible explanations for the results are provided including a discussion how the present results fit into the maternal mediation hypothesis.
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Affiliation(s)
- Loudin Daoura
- Department of Pharmaceutical Biosciences, Division of Pharmacology, Uppsala UniversityUppsala, Sweden
| | - My Hjalmarsson
- Department of Pharmaceutical Biosciences, Division of Pharmacology, Uppsala UniversityUppsala, Sweden
| | - Sadia Oreland
- Department of Pharmaceutical Biosciences, Division of Pharmacology, Uppsala UniversityUppsala, Sweden
| | - Ingrid Nylander
- Department of Pharmaceutical Biosciences, Division of Pharmacology, Uppsala UniversityUppsala, Sweden
| | - Erika Roman
- Department of Pharmaceutical Biosciences, Division of Pharmacology, Uppsala UniversityUppsala, Sweden
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Stevenson CW, Goodwin PE, Tunstall B, Spicer CH, Marsden CA, Mason R. Neonatal maternal separation alters reward-related ultrasonic vocalizations in rat dams. Behav Brain Res 2009; 200:232-6. [PMID: 19378466 DOI: 10.1016/j.bbr.2009.01.035] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We examined the effects of brief or long durations of repeated maternal separation (MS) on ultrasonic vocalizations (USVs) in rat dams. 50-kHz USVs putatively identified as maternal in origin were emitted only immediately after pups were returned following MS. Maternal USV emission also depended on separation duration and pup age. Given that 50-kHz USVs are emitted in response to rewarding stimuli, MS may induce duration-dependent effects on maternal positive affect.
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Affiliation(s)
- Carl W Stevenson
- School of Biomedical Sciences, University of Nottingham, Queen's Medical Centre, Nottingham NG72UH, UK.
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Eklund MB, Johansson LM, Uvnäs-Moberg K, Arborelius L. Differential effects of repeated long and brief maternal separation on behaviour and neuroendocrine parameters in Wistar dams. Behav Brain Res 2009; 203:69-75. [PMID: 19394366 DOI: 10.1016/j.bbr.2009.04.017] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2008] [Revised: 04/08/2009] [Accepted: 04/16/2009] [Indexed: 11/18/2022]
Abstract
Repeated, prolonged maternal separation has been suggested to model the development of a depression-like syndrome in rats. The long separations from the pups have been proposed to be stressful for the dams, which in turn could mediate the changes seen in adult offspring. In the present study we investigated whether prolonged maternal separation really is stressful for rat dams by studying parameters known to be affected by long-term stress such as spontaneous motor activity, anxiety-like behaviour, adrenal gland weight and plasma corticosterone levels. Dams were separated from their litter for either 4 h (MS240) or 15 min (MS15) on eight random days during postnatal day 1-14, or left undisturbed (animal facility reared, AFR). After weaning MS240 dams showed decreased peripheral activity and habituated slower in horizontal activity. On the contrary, MS15 dams showed more peripheral activity and less rearing activity compared to both AFR and MS240 dams when habituated to the testing apparatus, suggesting that MS15 dams are more anxious. The adrenal glands from MS15 dams weighed significantly less and plasma corticosterone levels were significantly higher compared to AFR and MS240 dams. These results suggest that repeated brief maternal separations from pups could be stressful for rat mothers, whereas prolonged separations are not. Since these results are in contrast to the current notion that the short separation procedure may be considered as a safe milieu, whereas the prolonged separations have been suggested to be stressful for both dams and pups, further studies in this field are warranted.
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Affiliation(s)
- Malin B Eklund
- Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden
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Farkas J, Reglodi D, Gaszner B, Szogyi D, Horvath G, Lubics A, Tamas A, Frank F, Besirevic D, Kiss P. Effects of maternal separation on the neurobehavioral development of newborn Wistar rats. Brain Res Bull 2009; 79:208-14. [PMID: 19150489 DOI: 10.1016/j.brainresbull.2008.12.011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Accepted: 12/18/2008] [Indexed: 10/21/2022]
Abstract
Animal models of neonatal stress, like maternal separation, may provide important correlation with human stress-related disorders. Early maternal deprivation has been shown to cause several short- and long-term neurochemical and behavioral deficits. Little is known about the early neurobehavioral development after postnatal stress. The aim of the present study was to investigate the development of reflexes and motor coordination in male and female pups subjected to maternal deprivation. Pups were removed from their mothers from postnatal day 1-14, for 3h daily. Somatic development (weight gain, eye opening, ear unfolding, incisor eruption) and reflex development was tested during the first 3 weeks. The appearance of the following reflexes was investigated: crossed extensor, grasping, placing, gait, righting and sensory reflexes, and negative geotaxis. Timely performance of negative geotaxis, righting and gait were also tested daily during the first 3 weeks. Motor coordination and open-field tests were performed on postnatal weeks 3-5 (rotarod, elevated grid-walk, footfault, rope suspension, inclined board and walk initiation tests). The results revealed that a 3-h-long daily maternal separation did not lead to a marked delay or enhancement in reflex development and motor coordination. A subtle enhancement was observed in the appearance of hindlimb grasp and gait reflexes, and a better performance in footfault test in male rats suffering from maternal deprivation. In contrast, female maternally deprived (MD) rats displayed a slight delay in forelimb grasp and air righting reflex appearance, and surface righting performance. Open-field activity was not changed in maternally deprived rats. In summary, our present observations indicate that maternal deprivation does not induce drastic changes in early neurodevelopment, therefore, further research is needed to determine the onset of behavioral alterations in subject with maternal deprivation history. Gender differences described in this study could help to understand how gender-specific differences in early life experience-induced stress-related disorders appear in adult life.
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Affiliation(s)
- Jozsef Farkas
- Department of Anatomy, Medical Faculty, University of Pecs, Szigeti u 12, 7624 Pecs, Hungary.
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Roma PG, Huntsberry ME, Riley AL. Separation stress, litter size, and the rewarding effects of low-dose morphine in the dams of maternally separated rats. Prog Neuropsychopharmacol Biol Psychiatry 2007; 31:429-33. [PMID: 17182163 DOI: 10.1016/j.pnpbp.2006.11.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2006] [Revised: 10/12/2006] [Accepted: 11/03/2006] [Indexed: 11/29/2022]
Abstract
Potential differences in sensitivity to the rewarding effects of morphine as a function of litter separation stress were assessed in post-weaning rat dams. During the first two weeks postnatal, Sprague-Dawley rat litters were subjected to daily 15- or 180-min sessions of dam-pup separation while control litters only experienced twice-weekly animal facility care. One week after weaning, the dams (n=7 per group) underwent a fully unbiased conditioned place preference (CPP) procedure to 1 mg/kg subcutaneous morphine. CPP responses after each conditioning cycle were recorded. Rates of acquisition and asymptotic levels of CPP were comparable in all groups; however, an inverse relationship between litter size and magnitude of morphine CPP was revealed. Although these initial data indicate no differential sensitivity to the rewarding effects of low-dose morphine produced by the stress of litter separation, this assessment of litter size and drug-induced place conditioning in post-weaning litter-separated dams is the first of its kind. Potential effects of other doses, drugs of abuse and post-partum manipulations remain to be evaluated within this emerging etiological model.
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Affiliation(s)
- Peter G Roma
- Psychopharmacology Laboratory, Department of Psychology, American University, 4400 Massachusetts Avenue, NW, Washington, DC 20016, USA.
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Michaels CC, Holtzman SG. Neonatal stress and litter composition alter sucrose intake in both rat dam and offspring. Physiol Behav 2006; 89:735-41. [PMID: 16996094 DOI: 10.1016/j.physbeh.2006.08.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2006] [Revised: 06/14/2006] [Accepted: 08/15/2006] [Indexed: 11/26/2022]
Abstract
The early postnatal environment can have long lasting effects on the physiology and behavior of both mother and offspring. A great deal of evidence indicates that stress during this time period is a risk factor for the future development of a multitude of disorders including substance abuse. The maternal separation paradigm is used to model such stress in rats. The current study evaluated the effects of maternal separation and litter composition on sucrose consumption, a non-drug measure of reward, in both male Long-Evans rat offspring and mother. On postnatal day 2, rats were cross-fostered, placed in single-sex or mixed-sex litters, and subsequently stressed by daily dam-pup separations during the first two postnatal weeks. The length of the separation (15 min, 1 h, or 3 h) was randomly assigned to each day. A two-bottle choice test was given to maternally separated and nonhandled offspring when they were adults, and to dams 2-4 weeks after weaning. Intake of a 10% sucrose solution or water was compared for 1 h daily across five consecutive days. Rearing condition had a profound effect on total fluid intake and sucrose solution intake by both offspring and dam, with the separated offspring and dams generally consuming a greater amount of total fluid and 10% sucrose solution than their nonhandled counterparts. Litter composition also affected consumption, with the offspring from maternally separated mixed-sex litters consuming more total fluid and 10% sucrose solution than offspring from maternally separated single-sex litters. These results indicate that early postnatal and postpartum stress can lead to changes in sucrose consumption, a non-drug measure of reward, indicating that such stress may alter the underlying brain reward mechanisms.
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Affiliation(s)
- Clifford C Michaels
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, USA.
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Moffett MC, Vicentic A, Kozel M, Plotsky P, Francis DD, Kuhar MJ. Maternal separation alters drug intake patterns in adulthood in rats. Biochem Pharmacol 2006; 73:321-30. [PMID: 16962564 PMCID: PMC2692348 DOI: 10.1016/j.bcp.2006.08.003] [Citation(s) in RCA: 153] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2006] [Revised: 08/04/2006] [Accepted: 08/07/2006] [Indexed: 02/06/2023]
Abstract
Maternal separation/handling (MS/H) is an animal model of early life stress that causes profound neurochemical and behavioral alterations in pups that persist into adulthood. Many recent studies have used the MS/H model to study changes in drug effects in adulthood that are linked to behavioral treatments and stressors in the perinatal period. The drug effects focused on in this review are the reinforcing properties of the abused drugs, cocaine and alcohol. A striking finding is that variations in maternal separation and handling cause changes in ethanol and cocaine self-administration. Further, these changes indicate that various manipulations in the perinatal period can have long lasting effects of interest to biochemical pharmacologists. This article will review recent studies on ethanol and cocaine self-administration using the MS/H model and the neurochemical alterations that may play a role in the effects of MS/H on ethanol and cocaine self-administration. Studying the MS/H model can provide important clues into the vulnerability to drug abuse and perhaps identify a crucial window of opportunity for therapeutic intervention.
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Affiliation(s)
- M C Moffett
- Yerkes National Primate Research Center of Emory University, Atlanta, GA 30329, USA
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Moffett MC, Harley J, Francis D, Sanghani SP, Davis WI, Kuhar MJ. Maternal Separation and Handling Affects Cocaine Self-Administration in Both the Treated Pups as Adults and the Dams. J Pharmacol Exp Ther 2006; 317:1210-8. [PMID: 16517692 DOI: 10.1124/jpet.106.101139] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Repeated maternal separation of pups from dams is often used as an early life stressor that causes profound neurochemical and behavioral changes in the pups that persist into adulthood. The effects of maternal separation on both the dams and the treated pups as adults on cocaine self-administration were examined using four separation conditions: 15- or 180-min separation (MS15 and MS180), brief handling without separation (MS0), and a nonhandled group (NH). The separations and handling occurred daily on postnatal days 2 to 15. The acquisition of cocaine self-administration (0.0625-1.0 mg/kg/infusion) was evaluated in the treated pups as adults. The MS180 group acquired cocaine self-administration at the lowest dose tested (0.0625 mg/kg/infusion), whereas the MS15s did not respond for cocaine at rates greater than that seen with saline administration. The NH group received the greatest number of infusions and intake at the highest doses. After self-administration, no differences were observed between groups in activity of two liver carboxylesterases involved in the inactivation of cocaine, ES10 and ES4. Maternal separation affected cocaine self-administration in the dams as well. Although there was an overall significant affect of treatment on cocaine self-administration, the length of separation (15 or 180 min) did not affect cocaine self-administration on the dams. The MS0 dams averaged a greater number of infusions per session than NH group during the 1st week of acquisition. These data suggest that in addition to the profound changes that occur in pups as result of maternal separation, the dams are also susceptible to alterations in behaviors.
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Affiliation(s)
- Mark C Moffett
- Division of Neuroscience, Yerkes National Primate Research Center, Emory University, 954 Gatewood Road NE, Atlanta, GA 30329, USA.
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Vicentic A, Francis D, Moffett M, Lakatos A, Rogge G, Hubert GW, Harley J, Kuhar MJ. Maternal separation alters serotonergic transporter densities and serotonergic 1A receptors in rat brain. Neuroscience 2006; 140:355-65. [PMID: 16530973 DOI: 10.1016/j.neuroscience.2006.02.008] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Revised: 02/03/2006] [Accepted: 02/04/2006] [Indexed: 11/22/2022]
Abstract
RATIONALE The basic mechanisms underlying the association between early life maternal separation and adulthood psychiatric disorders are largely unknown. One possible candidate is the central serotonergic system, which is also abnormal in psychiatric illnesses. Neuroadaptational changes in serotonergic transporter and serotonergic 1A receptors may underlie links between early life stress and adulthood psychiatric disorders. OBJECTIVE The aim of this study was to investigate the consequences of a rat model of maternal separation on serotonergic transporter and serotonergic 1A receptor densities and function in adult rat forebrain. METHODS Rat pups were separated from dams from postnatal day 2 to postnatal day 14, each day, for zero time, 15 min and 180 min to determine the time-course of effects. A non-handled group was added to control for the effects of handling by an experimenter compared with the animal facility-reared group. Quantitative [(125)I]3beta-(4-iodophenyl)tropan-2beta-carboxylic acid methyl ester and [(125)I]-mPPI autoradiography was used to determine serotonergic transporter and serotonergic 1A densities, respectively. Adult rats were challenged with saline or serotonergic 1A agonist (+) 8-hydroxy-2-(di-n-propylamino)tetralin, 0.4 mg/kg, s.c.) and plasma adrenocorticotropic hormone and corticosterone were determined. RESULTS serotonergic transporter and serotonergic 1A densities were significantly lower in the non-handled group in the paraventricular, arcuate, dorsomedial and ventromedial nuclei of the hypothalamus. The non-handled group also displayed lower serotonergic transporter and serotonergic 1A densities in the basolateral anterior, basolateral ventral and basomedial amygdaloid nuclei. Serotonergic transporter densities were also decreased in the CA3 area of the hippocampus in the non-handled group. In contrast, the maternal separation 15 min group displayed the highest serotonergic transporter and serotonergic 1A densities in the basomedial nucleus of amygdala, basolateral anterior nucleus of amygdala, basolateral ventral nucleus of amygdala and basomedial nucleus of amygdala amygdaloid nuclei. CONCLUSIONS Early life maternal separation and the extent of handling can alter adult brain serotonergic transporter and serotonergic 1A levels and function in the forebrain. Alterations in these serotonergic systems by early rearing conditions might increase vulnerability for behavioral disorders in adulthood.
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Affiliation(s)
- A Vicentic
- The Yerkes National Primate Research Center of Emory University, 954 North Gatewood Road, Atlanta, GA 30329, USA.
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Byrnes EM. Transgenerational consequences of adolescent morphine exposure in female rats: effects on anxiety-like behaviors and morphine sensitization in adult offspring. Psychopharmacology (Berl) 2005; 182:537-44. [PMID: 16163528 DOI: 10.1007/s00213-005-0122-4] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2005] [Accepted: 07/01/2005] [Indexed: 10/25/2022]
Abstract
RATIONALE AND OBJECTIVE Opiate abuse in adolescent girls has increased in the past decade; however, few animal studies have examined the potential consequences of opiate use occurring at this time. The purpose of the present study was to determine whether exposing female rats to morphine during the peripubertal period can alter the adult behavior of their offspring. METHODS Beginning at 30 days of age, female rats were injected subcutaneously (s.c.) twice daily with either morphine sulfate or saline. The initial morphine dose of 2.5 mg/kg was increased by 2.5 mg/kg daily for a total of 20 days. Ten days after the final drug treatment, all subjects were mated. Their subsequent offspring were then tested as adults on the elevated plus maze, in a novel environment or were examined in a morphine locomotor sensitization paradigm. RESULTS Adult female offspring of dams exposed to morphine during puberty spent less time in the open arms of the elevated plus maze and displayed decreased exploration in a novel environment. Female offspring also demonstrated a more rapid induction of morphine sensitization. Finally, male offspring demonstrated a significant enhancement in the expression of morphine sensitization. CONCLUSIONS Chronic morphine exposure during adolescence can have significant transgenerational effects on adult offspring. Future studies will be needed to determine how these changes are transferred to the offspring and whether these effects are specific to drug exposure that occurs during the peripubertal period.
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Affiliation(s)
- Elizabeth M Byrnes
- Department of Biomedical Sciences, Tufts University, Cummings School of Veterinary Medicine, North Grafton, MA 01536, USA.
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Jaworski JN, Francis DD, Brommer CL, Morgan ET, Kuhar MJ. Effects of early maternal separation on ethanol intake, GABA receptors and metabolizing enzymes in adult rats. Psychopharmacology (Berl) 2005; 181:8-15. [PMID: 15830234 DOI: 10.1007/s00213-005-2232-4] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2004] [Accepted: 02/07/2005] [Indexed: 10/25/2022]
Abstract
RATIONALE Maternal separation (MS) in neonatal rats affects ethanol self-administration (SA) in adulthood; however, the conditions and mechanisms need to be clarified. OBJECTIVES The goal of this study was to determine the effect of MS on ethanol SA in adulthood in different groups of rats, which control for time of separation, handling, and rearing conditions and, for mechanistic assessment, to examine GABA-A receptors in the central nucleus of the amygdala (CeA) and levels of liver metabolizing enzymes. METHODS Newborn, male Long-Evans rats were randomly assigned to different groups and treated over postnatal days 2-14. The rats were picked up by their tails and put back down with no separation (MS0), separated from their mother for 15 min/day (MS15), separated from their mother for 180 min/day (MS180), handled once for a bedding change (NH), or were animal facility reared (AFR). In adulthood, these rats were allowed 5-day continuous access to ethanol, and GABA-A receptors and liver enzymes were measured. RESULTS The MS15 group consumed and preferred significantly less ethanol (about one third) than the MS180 group; however, neither group was different from the MS0 or the AFR group. The NH group consumed and preferred significantly more ethanol than all other groups, at least twice that of the MS180s. GABA-A receptors were increased in the CeA in MS15s, which could help explain the effects. Alcohol dehydrogenase may have been altered in the AFRs. CONCLUSIONS Various treatments in neonates affect ethanol intake and GABA-A receptors, and possibly ethanol metabolism, in adulthood. These changes were not simply related to time of separation but were also due to the degree of handling.
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Affiliation(s)
- J N Jaworski
- Yerkes National Primate Research Center and the Department of Pharmacology, Emory University, Atlanta, GA 30329, USA
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Vazquez V, Penit-Soria J, Durand C, Besson MJ, Giros B, Daugé V. Maternal deprivation increases vulnerability to morphine dependence and disturbs the enkephalinergic system in adulthood. J Neurosci 2005; 25:4453-62. [PMID: 15872092 PMCID: PMC6725024 DOI: 10.1523/jneurosci.4807-04.2005] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2004] [Revised: 03/09/2005] [Accepted: 03/15/2005] [Indexed: 11/21/2022] Open
Abstract
Maternal deprivation can trigger long-lasting molecular and cellular modifications in brain functions and might facilitate the appearance of pathogenic behaviors. This study focuses on the vulnerability to develop morphine dependence in adult rats that were separated from their mother and littermates for 3 h per day for 14 d after birth and examines the adaptive changes in the enkephalinergic pathways. Place-preference conditioning was observed with 2 mg/kg morphine in deprived rats, whereas 5 mg/kg morphine was necessary to induce conditioning in nondeprived animals. A prolonged morphine conditioning was shown in deprived rats. A strong increase in oral morphine self-administration behavior and preference was observed in deprived rats. Only a very slight increase in preference for sucrose solution, a more ethological reinforcer known to interact with the opioid system, was shown in deprived rats. These results indicate that this postnatal environment change leads to a hypersensitivity to the reinforcing properties of morphine and to the development of morphine dependence. A significant decrease in preproenkephalin mRNA expression was observed in the nucleus accumbens and the caudate-putamen nucleus of deprived rats. The basal extracellular levels of the Met-enkephalin-like immunoreactivity in the nucleus accumbens were significantly lower in deprived rats when compared with nondeprived animals, whereas no change in mu-opioid receptor binding occurred. These results strongly support that maternal deprivation leads to a basal hypoactivity of the enkephalinergic system and hypersensitivity to morphine effects. Together, our results suggest that maternal deprivation in pups likely represents a risk factor for morphine dependence in adult rats.
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MESH Headings
- Analysis of Variance
- Animals
- Animals, Newborn
- Autoradiography/methods
- Behavior, Animal
- Brain/drug effects
- Brain/metabolism
- Choice Behavior/drug effects
- Conditioning, Psychological/drug effects
- Dialysis/methods
- Dose-Response Relationship, Drug
- Drinking Behavior/drug effects
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/pharmacokinetics
- Enkephalin, Methionine/metabolism
- Enkephalins/genetics
- Enkephalins/metabolism
- Female
- In Situ Hybridization/methods
- Maternal Deprivation
- Morphine/administration & dosage
- Morphine Dependence/metabolism
- Narcotics/administration & dosage
- Nucleus Accumbens/drug effects
- Nucleus Accumbens/metabolism
- Pregnancy
- Protein Precursors/genetics
- Protein Precursors/metabolism
- RNA, Messenger/metabolism
- Radioimmunoassay/methods
- Rats
- Rats, Long-Evans
- Receptors, Opioid, mu/metabolism
- Self Administration
- Sucrose/metabolism
- Time Factors
- Tritium/pharmacokinetics
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Affiliation(s)
- Vincent Vazquez
- Institut National de la Santé et de la Recherche Médicale, U513, Laboratoire de Neurobiologie et Psychiatrie, Université Paris XII, Faculté de Médecine, 94010 Créteil, France
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26
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Abstract
This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology, Doctoral Sub-Program, Queens College, City University of New York, 65-30 Kissena Blvd., Flushing, NY 11367, USA.
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Kalinichev M, White DA, Holtzman SG. Individual differences in locomotor reactivity to a novel environment and sensitivity to opioid drugs in the rat. I. Expression of morphine-induced locomotor sensitization. Psychopharmacology (Berl) 2004; 177:61-7. [PMID: 15316716 DOI: 10.1007/s00213-004-1990-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2003] [Accepted: 05/13/2004] [Indexed: 11/25/2022]
Abstract
RATIONALE Vulnerability for development of substance abuse is often associated with a "sensation-seeking" or "thrill-seeking" phenotype. In an animal model, rats more reactive in a novel environment (high responders, HR) are more sensitive to stimulant/reinforcing effects of amphetamine and are more likely to self-administer this drug, than are less reactive animals (low responders, LR). OBJECTIVE We tested whether HR and LR also differ in sensitivity to effects of morphine on locomotor activity. METHODS Male Sprague-Dawley rats were categorized as HR or LR based on motor responses to novelty (sorting day; S). After 1 day (B) of baseline activity measurements, subjects were tested daily after SC injections of either morphine (10 mg/kg) or saline for 7 days and again on day 10. Beginning 5 days later, four daily injections of saline and 1.0-10 mg/kg morphine were tested in all animals. RESULTS LR and HR were similar in the onset and overall magnitude of sensitization and tolerance following daily morphine administration. HR were more sensitive than LR to locomotor stimulant effects of acute morphine. However, LR had more robust and persistent context-specific increases in activity due to conditioning than did HR, and expression of sensitization was apparent in all behavioral variables. CONCLUSIONS These results provide further evidence that phenotypic differences between HR and LR may, in part, be associated with differences in the endogenous opioid systems. Differences in sensitivity to acute versus repeated morphine suggest that at least in relation to opioid drugs, these phenotypes may reflect different aspects of drug vulnerability rather than simply the presence or absence of it.
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Affiliation(s)
- Mikhail Kalinichev
- Department of Pharmacology, Rollins Research Center, Emory University School of Medicine, 1510 Clifton Road, Suite 5074, Atlanta, GA 30322, USA.
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