Enhancement of neuronal excitability in the medial prefrontal cortex following prenatal morphine exposure.

The clinical use and abuse of opioids during human pregnancy have been widely reported. Several studies have demonstrated that opioids cross the placenta in rats during late gestation, and prenatal morphine exposure has been shown to have negative outcomes in cognitive function. The medial prefrontal cortex (mPFC) is believed to play a crucial role in cognitive processes, motivation, and emotion, integrating neural information from several brain areas and sending converted information to other structures. Dysfunctions in this area have been observed in numerous psychiatric and neurological disorders, including addiction. This current study aimed to compare the electrophysiological properties of mPFC neurons in rat offspring prenatally exposed to morphine. Pregnant rats were injected with morphine or saline twice a day from gestational days 11-18. Whole-cell patch-clamp recordings were performed in male offspring on postnatal days 14-18. All recordings were obtained in current-clamp configuration from mPFC pyramidal neurons to assess their electrophysiological properties. The results revealed that prenatal exposure to morphine shifted the resting membrane potential (RMP) to less negative voltages and increased input resistance and duration of action potentials. However, the amplitude, rise slope, and afterhyperpolarization (AHP) amplitude of the first elicited action potentials were significantly decreased in rats prenatally exposed to morphine. Moreover, the sag voltage ratio was significantly decreased in the prenatal morphine group. Our results suggest that the changes observed in the electrophysiological properties of mPFC neurons indicate an elevation in neuronal excitability following prenatal exposure to morphine.

Acute morphine injection persistently affects the electrophysiological characteristics of rat locus coeruleus neurons.

Administration of morphine is associated with critical complications in clinic which primarily includes the development of dependence and tolerance even following a single dose (acute) exposure. Behavioral and electrophysiological studies support the significant role of locus coeruleus (LC) neurons in tolerance and dependence following chronic morphine exposure. The current study was designed to explore the electrophysiological properties of the LC neurons following acute morphine exposure. In-vitro whole-cell patch-clamp recordings were performed in LC neurons 24 h after intraperitoneal morphine injection. Acute morphine injection significantly decreased the spontaneous firing rate of LC neurons, the rising and decay slopes of action potentials, and consequently increased the action potential duration. In addition, morphine treatment did not alter the rheobase current and first spike latency while affected the inhibitory postsynaptic currents elicited in response to orexin-A. In fact, single morphine exposure could inhibit the disinhibitory effect of orexin-A on LC neurons.

Sex-specific transgenerational effects of adolescent morphine exposure on short-term memory and anxiety behavior: Male linage.

Current estimates indicate that opioid use and misuse are a rising epidemic, which presents a substantial socioeconomic burden around the world. Chronic opioid consumption, specifically during the critical period of adolescence, can lead to enduring effects not only in individuals but also in future generations. Utilizing rodent model, we have previously reported the impacts of paternal exposure to chronic morphine during adolescence on neurobehavioral features in progenies. Currently, the potential transgenerational effects of paternal morphine exposure during adolescence on anxiety-like behavior and short-term memory remains unknown. Male Wistar rats were exposed to increasing doses of morphine for ten days in adolescence (PND 30-39). Thereafter, following a 30-days drug-free period, the treated male rats mated with naïve females. The anxiety-like behavior and short-term memory performance were assessed in adult male and female offspring (PND 60) using open field and Y-maze tests. Both male and female progenies of morphine-treated sires revealed a significant reduction in the movement velocity compared to progenies of saline-treated sires as measured by open field test. Morphine-sired male but not female offspring also showed a non-significant large decreasing effect on time spent in the center and frequency of entries to the center of open field box. Moreover, a significant reduction in the number of entries and percent of time spent in the novel arm was observed in male and female morphine-sired offspring, as measured using Y-maze test. Growth outcomes also did not demonstrate any difference in the number of dam's fertility, pups birth, and death between morphine-sired and saline-sired groups in both sexes. Collectively, paternal exposure to morphine during adolescence induces sex-specific and selective disturbances in short-term memory while anxiety-like behavior was slightly disturbed.

Adolescent drug exposure: A review of evidence for the development of persistent changes in brain function.

Over the past decade, many studies have indicated that adolescence is a critical period of brain development and maturation. The refinement and maturation of the central nervous system over this prolonged period, however, makes the adolescent brain highly susceptible to perturbations from acute and chronic drug exposure. Here we review the preclinical literature addressing the long-term consequences of adolescent exposure to common recreational drugs and drugs-of-abuse. These studies on adolescent exposure to alcohol, nicotine, opioids, cannabinoids and psychostimulant drugs, such as cocaine and amphetamine, reveal a variety of long-lasting behavioral and neurobiological consequences. These agents can affect development of the prefrontal cortex and mesolimbic dopamine pathways and modify the reward systems, socio-emotional processing and cognition. Other consequences include disruption in working memory, anxiety disorders and an increased risk of subsequent drug abuse in adult life. Although preventive and control policies are a valuable approach to reduce the detrimental effects of drugs-of-abuse on the adolescent brain, a more profound understanding of their neurobiological impact can lead to improved strategies for the treatment and attenuation of the detrimental neuropsychiatric sequelae.

Adolescent Morphine Exposure in Male Rats Alters the Electrophysiological Properties of Locus Coeruleus Neurons of the Male Offspring.

Opioid prescription and illegal use have been soaring, and it has become a global concern. Adolescence, as a critical developmental period, is radically influenced by drug exposure. In the recent decade, transgenerational effects of paternal environmental exposure have been given greater consideration. There is compelling evidence for the effect of paternal drug abuse such as alcohol, cocaine, and nicotine on the offspring; however, a limited number of studies have focused on the paternal effect of opioids during adolescence on progeny. Locus coeruleus (LC) is a noradrenergic nucleus involved in different brain functions and cognitive processes. The present study aimed to investigate the transgenerational effect of adolescent morphine exposure on electrophysiological properties of LC neurons of the offspring. For this purpose, adolescent male rats received morphine or saline for 10 days between postnatal days 31 and 40, and then after 20 days of washout period, they were mated with naïve female rats. Whole cell patch clamp recordings were performed in current clamp configuration from LC neurons of 14-21-day-old male offspring. The results demonstrated that the decay slope of the action potentials and the amplitude of afterhyperpolarization potential increased in morphine sired animals. Moreover, the duration of action potentials decreased in morphine sired animals. Besides, the coefficient of variation of interspike intervals increased in morphine sired animals compared to the saline sired ones. Overall, the altered electrophysiological properties observed in this study may suggest a functional enhancement of Ca2+ activated K+ channels in LC neurons of morphine sired animals.

Adolescent morphine exposure increases nociceptive behaviors in rat model of formalin test.

The number of adolescents who use illicit drugs has increased dramatically. Adolescence is a critical period for brain development and maturation. The importance of the study of pain perception and the possible mechanisms involved is crystal clear. Up until now, there has been no evidence regarding the long-term effect of adolescence morphine administration on pain perception. The objective of the present study was to investigate long-lasting effect of adolescent morphine exposure on pain perception as well as analgesic response to a single dose of morphine injection. Adolescent and adult rats received morphine or saline, and then after 30 days of washout period, formalin test was performed. To evaluate morphine analgesia, in a separate group of animals, formalin test was performed after injection of a single dose of morphine during adulthood. The results demonstrated that the adolescent rats treated by morphine exhibited higher pain-related behaviors compared to the control group, while the same results were not observed in adult rats that had been treated by morphine. Moreover, there was no significant difference in analgesic response to a single dose of morphine between two experimental groups. This study demonstrates enduring effect of morphine exposure during adolescence on pain perception.

Exposure to opiates in male adolescent rats alters pain perception in the male offspring.

During the past decades, the use/misuse of opioids has increased dramatically among adolescent population. It is now well acknowledged that various morphological and physiological changes occur in the brain during adolescence. During this critical period, brain development and maturation could be affected by several factors including stress, drug abuse, nutritional status, etc. Although studies on transgenerational effects of substances such as alcohol, nicotine, and cocaine have focused on both paternal and maternal drug exposure, most reports on transgenerational effects of morphine are restricted to maternal exposure. Thus, in this study, we aimed to investigate the transgenerational effect of paternal morphine exposure during adolescence on pain perception and antinociceptive effect of morphine in rat offspring. Male rats received escalating doses of morphine for 10 days during postnatal days 31-40. Twenty days after the last morphine injection, male rats were mated with intact female rats, and then behavioral tests were conducted on the male offspring on postnatal day 60. Pain perception and morphine antinociception were evaluated using the formalin test. Our results demonstrated that morphine-sired and saline-sired animals differed in the interphase and phase 2 of the formalin test. These findings indicate a significant transgenerational effect of paternal morphine exposure on pain-related behaviors in rat offspring.

Chronic adolescent morphine exposure alters the responses of lateral paragigantocellular neurons to acute morphine administration in adulthood.

Accumulating evidence support the growing non-medical use of morphine during adolescence. Despite this concern which has recently been addressed in some studies, cellular mechanisms underlying the long-term neurobiological and behavioral effects of opiate exposure during this critical period have still remained largely unexplored. Several reports have proposed that subtle long-lasting neurobiological alterations might be triggered by exposure to opiate derivatives or drugs of abuse particularly when this occurs during a critical phase of brain maturation such as adolescence. The present study was designed to investigate how chronic adolescent morphine exposure could affect the responsiveness of lateral paragigantocellular (LPGi) neurons to acute morphine administration in adult rats. Male Wistar rats received chronic escalating morphine or saline during adolescence (30-39d) for 10 days. During adulthood (65d), the extracellular unit activities of LPGi neurons were recorded in urethane-anesthetized animals. Results indicated that adolescent morphine treatment enhances the baseline activity of LPGi neurons. In addition, morphine-induced inhibition of spontaneous discharge rate was potentiated in adult rats received morphine during adolescence. However, this pretreatment did not affect the extent of morphine excitatory effect, onset or peak of cellular response and regularity of unit discharge in LPGi neurons. Our study supports the hypothesis that adolescent morphine exposure induces long-lasting neurophysiological alterations in brain regions known to play a role in mediating opiate effects. This finding sheds light on the possible effect of opiate pre-exposure on addiction susceptibility in future.

Inhibition of glycogen synthase kinase 3 increased subventricular zone stem cells proliferation.

The effects of Wnt signaling modifiers on cell proliferation, seem to be cell specific. Enhancing the proliferation of subventricular zone (SVZ) progenitors has been in the focus of research in recent years. Here we investigate the effect of CHIR99021, a Glycogen Synthase Kinase 3 (GSk-3) inhibitor, on SVZ progenitor's proliferation both in vivo and in vitro. Neural stem cells were extracted from the adult C57bl/6 by mincing and trypsin treatment followed by culturing in specific medium. Sphere cells formed within about 7-10days and were characterized by immunostaining. Number of spheres and their size was assessed following exposure to different concentration of CHIR99021 or vehicle. For in vivo studies, animals received intracerebroventricular (i.c.v.) injection of CHIR99021 or vehicle for four days. A subgroup of animals, after 4days treatment with CHIR99021 received intranasal kainic acid to induce local neurodegeneration in CA3 area of hippocampus. Inhibition of GSk-3 by CHIR99021 increased neural progenitor proliferation and the effect of CHIR99021 was long lasting so that the treated cells showed higher proliferation even after CHIR99021 removal. In vivo administration of CHIR99021 increased the number of neural progenitors at the rims of lateral ventricles especially when the treatment was followed by kainic acid administration which induces neural insult. Results showed that direct administration of CHIR99021 into the culture medium or animal brain increased the number of SVZ progenitors, especially when a neural insult was induced in the hippocampus.

Enhancement of µ-opioid receptor desensitization by orexin-A in rat locus coeruleus neurons.

Opioids have always been used in clinical practice for pain management. However, development of tolerance to their effects following long term administration, seriously restricts further clinical use of these drugs. In this regard, µ-opioid receptor (MOR) desensitization, as an initial step in development of opioid tolerance, is of particular significance. Previous studies support the involvement of orexinergic system in development of opioid tolerance. Locus coeruleus (LC) nucleus has been shown to modulate pain and development of tolerance. Opioid receptors (particularly µ) are densely expressed within the LC. Moreover, it receives widespread orexinergic inputs and orexin type 1 receptors (OX1Rs) are also highly expressed in this brain region. In the present study, the effect of orexin-A (OXA) on met-enkephalin (ME)-induced MOR desensitization was investigated in locus coeruleus neurons of male Wistar rats (2-3weeks of age). ME (30µM), as a potent MOR agonist, was applied for 10min and the outward K+ current was recorded using whole cell patch clamp recording. The percentage of decrease in ME-induced K+ current was considered as the degree of MOR desensitization. Results indicated that OXA (100nM) enhances ME-induced MOR desensitization via affecting OX1Rs in rat locus coeruleus neurons and this effect is mediated by a protein kinase C dependent mechanism within the LC. The activity of orexinergic system might potentiate the signaling pathways underlying opioid-induced receptor desensitization.