Gabrielle L. McLemore

The Effect of Development on the Pattern of A1 and A2a-Adenosine Receptor Gene and Protein Expression in Rat Peripheral Arterial Chemoreceptors

1995; Montoro et al., 1996; Wyatt et al., 1995). Reduction of K+ conductance in response to hypoxia is the signal that triggers Type I cell depolarization, Ca entry, and secretion of neurotransmitters that bind to receptors on the first order sensory nerve endings of the carotid sinus nerve with cell bodies in the petrosal ganglion {(Gonzalez et al., 1994;Gonzalez et al., 1992). These first order sensory neurons (chemoafferents) project to second order neurons within the nucleus tractus solitarii (nTS), which send projections to the muscles of respiration. While the cascade of molecular and cellular events occurs in multiple CB preparations from multiple mammalian species, key aspects of the cascade are still unknown, particularly identification of the specific oxygen sensor within the Type I cell that initiates the cascade and the specific excitatory neurotransmitter systems that are involved in chemoexcitation. Furthermore, in multiple immature mammalian species, including human infants, hypoxic chemosensitivity matures during the first several weeks of postnatal life. Specific mechanisms mediating that maturation are unknown. Adenosine (ADO) is an ubiquitous molecule that is released from metabolically active cells by facilitated diffusion or is generated extracellularly by degradation of released ATP (Zimmermann & Braun, 1996). ADO levels increase in response to hypoxia. ADO modifies cellular function by binding to specific cell-surface receptors. All four identified ADO-Rs (A1-R, A2a-R, A2bR, and A3-R) are members of the superfamily of G protein-coupled receptors (GPCRs). A1and A3-Rs interact with pertussis toxin-sensitive G proteins (Gi and Go), inhibit adenylyl cyclase (AC), and hyperpolarize cells by G proteincoupled K channels, whereas A2aand A2b-Rs interact with G proteins and

Increased high-affinity nicotinic receptor-binding in rats exposed to lead during development

Receptor autoradiography and membrane radioligand-binding assays were used to determine the expression of nicotinic cholinergic receptors in the brains of weanling rats exposed to low-levels of lead (Pb) during development. Nicotinic receptors were identified with the frog toxin epibatidine (EB) that binds with high affinity to a variety of receptors containing alpha and beta subunits. Rat pups were exposed to Pb from their mothers given 750-ppm Pb in the diet beginning on gestational day 0 through postnatal day (PN) 21. Blood Pb levels ranged from 36.5 to 46.5 microg/dl in the PN21 pups, and this exposure did not alter their body weight when compared to control rats. Several brain regions identified by autoradiographic studies as having significant binding of EB were dissected from control and Pb-treated pups and used in saturation-binding experiments with membrane preparations to determine the affinity constant (K(d)) and maximal-binding capacity (B(max)) of [3H]EB. Results indicate that the B(max) of [3H]EB was increased in several brain regions in Pb-treated rat pups, without a significant effect on K(d) estimates. [3H]EB-binding to membranes from untreated rats was not affected by in vitro exposure to 20-microM Pb, indicating that the effect of Pb on [3H]EB-binding in vivo was not likely due to direct influence of free Pb remaining in the tissue at the time of assay. The data therefore suggest that expression of nicotinic receptors that bind [3H]EB were increased by developmental exposure to Pb. Several possible mechanisms for these effects and the potential toxicological significance are discussed.

Novel pharmacotherapeutic strategies for treatment of opioid-induced neonatal abstinence syndrome.

The non-medical use of prescription drugs, in general, and opioids, in particular, is a national epidemic, resulting in enormous addiction rates, healthcare expenditures, and overdose deaths. Prescription opioids are overly prescribed, illegally trafficked, and frequently abused, all of which have created a new opioid addiction pathway, adding to the number of opioid-dependent newborns requiring treatment for neonatal abstinence syndrome (NAS), and contributing to challenges in effective care in maternal and fetal/neonatal (M-F/N) medicine. The standard of care for illicit or prescription opioid dependence during pregnancy is opioid agonist (methadone or buprenorphine) substitution therapy, which are also frequently abused. The next generation of pharmacotherapies for the treatment of illicit or prescription opioid addiction in the M-F/N interactional dyad must take into consideration the interplay between genetic, epigenetic, and environmental factors. Addiction to illicit drugs during pregnancy presents unique challenges to effectively treat the mother, and the developing fetus and infant after delivery. New pharmacotherapies should be safe to the developing fetus, effective in treating the physical and psychological consequences of addiction in the mother, and reduce the incidence and severity of NAS in the infant after birth. More pharmacotherapeutic options should be available to the physician such that a more individualized rather than a one-drug/strategy-fits-all approach can be used. A myriad of new and exciting pharmacotherapeutic strategies for the treatment of opioid dependence and addiction are on the horizon. This review focuses on such three strategies: (i) pharmacotherapeutic targeting of the serotonergic system; (ii) mixed opioid immunotherapeutics (vaccines); (iii) pharmacogenomics as a therapeutic strategy to insure personalized care. We review and discuss how these strategies may offer additional treatment modalities for the treatment of M-F/N during pregnancy and the treatment of the infant after birth.

Ontogeny of retrograde labeled chemoafferent neurons in the newborn rat nodose-petrosal ganglion complex: an ex vivo preparation.

Hypoxic chemosensitivity of the peripheral arterial chemoreceptors in the carotid body is developmentally regulated. Essential neural elements of the chemotransducing unit in the carotid body consist of the Type I cell that depolarizes and releases neurotransmitters in response to hypoxemia and the chemoafferent fibers which form synapses with Type I cells, contain postsynaptic receptors and have cell bodies in the petrosal ganglion. While many properties of the Type I cells have been characterized during postnatal development, less is known about the effect of development on the number and properties of the chemoafferents since localization of the cell bodies of chemoafferents are intermingled with the cell bodies of other sensory neurons that innervate the upper airway. Here, we describe a novel ex vivo preparation that we have developed to retrogradely label cell bodies of chemoafferents in the petrosal ganglion with rhodamine dextran. With this technique, in newborn rats, we show that there is a three-fold increase in retrogradely labeled neurons in the nodose-petrosal ganglion complex from postnatal day (PND) 3-7 with a three-fold decrease by PND 14 (P < 0.001, ANOVA). Furthermore, greater than 85% of these retrogradely labeled neurons co-express TH mRNA in all age groups. This novel ex vivo technique circumvents many of the technical difficulties encountered with retrogradely labeling chemoafferents in small newborn animals in vivo, and provides a method to identify and characterize essential neural components of the chemotranductive unit of the peripheral arterial chemoreceptors.

Opioids and clonidine modulate cytokine production and opioid receptor expression in neonatal immune cells.

Objective:Opioids and clonidine, used in for sedation, analgesia and control of opioid withdrawal in neonates, directly or indirectly activate opioid receptors (OPRs) expressed in immune cells. Therefore, our objective is to study how clinically relevant concentrations of different opioids and clonidine change cytokine levels in cultured whole blood from preterm and full-term infants.Study Design:Using blood from preterm (⩽ 30 weeks gestational age (GA), n=7) and full-term (⩾37 weeks GA, n=19) infants, we investigated the changes in cytokine profile (IL-1β, IL-6, IL-8, IL-10, IL-12p70 and TNF-α), cyclic adenosine monophosphate (cAMP) levels and μ-, δ- and κ- opioid receptor (OPR) gene and protein expression, following in-vitro exposure to morphine, methadone, fentanyl or clonidine at increasing concentrations ranging from 0 to 1 mM.Result:Following lipopolysaccharide activation, IL-10 levels were 146-fold greater in cultured blood from full-term than from preterm infants. Morphine and methadone, but not fentanyl, at >10–5 M decreased all tested cytokines except IL-8. In contrast, clonidine at <10–9 M increased IL-6, while at >10–5 M increased IL-1β and decreased TNF-α levels. All cytokine changes followed the same patterns in preterm and full-term infant cultured blood and matched increases in cAMP levels. All three μ-, δ- and κ-OPR genes were expressed in mononuclear cells (MNC) from preterm and full-term infants. Morphine, methadone and clonidine, but not fentanyl, at >10–5M decreased the expression of μ-OPR, but not δ- or κ-OPRs.Conclusion:Generalized cytokine suppression along with downregulation of μ-OPR expression observed in neonatal MNC exposed to morphine and methadone at clinically relevant concentrations contrast with the modest effects observed with fentanyl and clonidine. Therefore, we speculate that fentanyl and clonidine may be safer therapeutic choices for sedation and control of opioid withdrawal and pain in neonates.

Animal Models of Drug Addiction in Support of Novel Therapeutic Strategies

A ddictions to a variety of substances both licit (e.g., alcohol, nicotine) and illicit (e.g., marijuana, cocaine) are a pervasive national and international social and economic challenge, accounting for as much as

Cognitive Function and Cholinergic Neurochemistry in Weanling Rats Exposed to Chlorpyrifos

600 billion annually in cumulative losses in the United States (cited in Nicholson and Ator 2011). The treatment of addictions and addictive behaviors is thus an important public health concern. Basic animal studies have greatly contributed to progress in this area and will surely continue to yield signifi cant insights into the neuroanatomical circuitry, neurophysiological function, neurochemical changes, and behavioral processes underlying addiction. Current clinical neurobiological methods such as brain imaging have expanded knowledge and provided novel insights into the most complex human brain-behavior interactions. The science of addiction is revealing that alterations of brain-behavioral processes can have a complex mixture of intrinsic and extrinsic causes. A better understanding of the etiology and brain mechanisms directly involved will provide more effective addiction prevention and treatment approaches. The topic is critically important and broad enough to warrant two issues, in which experts review efforts both to understand a variety of substance dependences and to develop therapeutic treatments for them. In this issue the authors address addictions to alcohol, nicotine, marijuana, opiates, cocaine, methamphetamine, and ketamine. Articles in the subsequent , companion issue will focus on the neurobiology of addiction-like behaviors, addressing addiction and psychiatric disorders, sex differences in addiction, and various aspects of food addiction. Each issue also includes an article on IACUC considerations relevant to addiction-related research. Overview Substance addiction is a chronic relapsing brain disorder that results in the addicted individuals inability to limit drug consumption despite detrimental consequences (Meyer 1996). Although initially an individuals substance use is voluntary, with repeated use the brains reward system is commandeered and neuroadaptive alterations render the individual unable to withstand the irresistible urges to use substances and therefore chronically susceptible to relapse. The slippery slope of drug addiction may start with experimentation or social use to experience the positive reinforcing (euphoric) effects, and then spirals downward in a pattern of abuse—from escalating compulsive drug seeking and taking in an attempt to alleviate the undesirable negative effects (e.g., dysphoria, anxiety, stress), to dependence, and then to withdrawal and abstinence, during both of which relapse to compulsive use is likely (Koob and Le Moal 1997). Understanding vulnerability to relapse as an integral part of addiction is crucial to the effective treatment of …