Jon R. Fee

Alcoholism and obesity: overlapping neuropeptide pathways?

Ethanol is a caloric compound, and ethanol drinking and food intake are both appetitive and consummatory behaviors. Furthermore, both ethanol and food have rewarding properties. It is therefore possible that overlapping central pathways are involved with uncontrolled eating and excessive ethanol consumption. A growing list of peptides has been shown to regulate food intake and/or energy homeostasis. Peptides such as the melanocortins, corticotropin releasing factor, and cholecystokinin promote reductions of food intake while others such as galanin and neuropeptide Y stimulate feeding. The present review highlights research aimed at determining if ingestive peptides also regulate voluntary ethanol intake, with an emphasis on the melanocortins and neuropeptide Y. It is suggested that research directed at ingestive peptides may expand our understanding of the neurobiological mechanisms that drive ethanol self-administration, and may reveal new therapeutic candidates for treating alcohol abuse and alcoholism.

A role for neuropeptide Y in neurobiological responses to ethanol and drugs of abuse

In recent years, evidence has emerged suggesting that neuropeptide Y (NPY) is involved with neurobiological responses to ethanol and other drugs of abuse. Here, we provide an overview of physiological, pharmacological, and genetic research showing that: (A) administration of ethanol, as well as ethanol withdrawal, alter central NPY expression, (B) NPY modulates ethanol consumption under certain conditions, and (C) NPY signaling modulates the sedative effects of several drugs, including ethanol, sodium pentobarbital, and ketamine. Evidence suggesting possible mechanism(s) by which NPY signaling modulates ethanol consumption are considered. It is suggested that NPY may influence ethanol consumption by regulating basal levels of anxiety, by modulating the sedative effects of ethanol, and/or by modulating ethanols rewarding properties.

Predictors of High Ethanol Consumption in RIIβ Knock-Out Mice: Assessment of Anxiety and Ethanol-Induced Sedation

BACKGROUND Genetic and pharmacological evidence suggests that the cyclic adenosine monophosphate-dependent protein kinase A pathway modulates neurobiological responses to ethanol. Mutant mice lacking the RIIbeta subunit of protein kinase A (RIIbeta(-/-)) are resistant to ethanol-induced sedation and drink significantly more ethanol than littermate wild-type mice (RIIbeta(+/+)). We determined whether high ethanol intake by the RIIbeta(-/-) mice on alternate genetic backgrounds is reliably predicted by high basal levels of anxiety or resistance to the sedative effects of ethanol. METHODS Two-bottle choice procedures and a battery of behavioral tests (elevated plus maze, open-field activity, and zero maze) were used to assess voluntary ethanol consumption and basal levels of anxiety in RIIbeta(-/-) and RIIbeta(+/+) mice on either a C57BL/6J or a 129/SvEv x C57BL/6J genetic background. Additionally, ethanol-induced sedation and blood ethanol levels were determined in RIIbeta(-/-) and RIIbeta(+/+) mice after intraperitoneal injection of ethanol (3.8 g/kg). RESULTS RIIbeta(-/-) mice on both genetic backgrounds consumed more ethanol and had a greater preference for ethanol relative to RIIbeta(+/+) mice. However, RIIbeta(-/-) mice showed reduced basal levels of anxiety when maintained on the C57BL/6J background but showed increased anxiety when maintained on the 129/SvEv x C57BL/6J background. Consistent with prior research, RIIbeta(-/-) mice were resistant to the sedative effects of ethanol, regardless of the genetic background. Finally, RIIbeta(-/-) and RIIbeta(+/+) mice showed similar blood ethanol levels. CONCLUSIONS These results indicate that high ethanol consumption is associated with resistance to the sedative effects of ethanol but that basal levels of anxiety, as well as ethanol metabolism, do not reliably predict high ethanol drinking by RIIbeta(-/-) mice.

Peripheral and central administration of a selective neuropeptide Y Y1 receptor antagonist suppresses ethanol intake by C57BL/6J mice.

BACKGROUND Neuropeptide Y (NPY) is a 36-amino acid neuromodulator that is expressed throughout the central nervous system. Recent genetic and pharmacological evidence suggests that the NPY Y1 receptor modulates ethanol intake. To further characterize the role of the Y1 receptor, we examined voluntary ethanol consumption by mice after administration of [(-)-2-[1-(3-chloro-5-isopropyloxycarbonylaminophenyl)ethylamino]-6-[2-(5-ethyl-4-methyl-1,3-tiazol-2-yl)ethyl]-4-morpholinopyridine] (compound A), a novel and selective Y1 receptor antagonist (Y1RA) that acts centrally on brain receptors when administered peripherally. METHODS C57BL/6J mice were habituated to drinking a 10% (v/v) ethanol solution by using a two-bottle-choice procedure and were then given an intraperitoneal (ip) injection (5 ml/kg) of the Y1RA (0, 25, 50, or 75 mg/kg). In a second study, mice were given intracerebroventricular infusion of the Y1RA (0, 30, or 100 microg). Finally, we determined whether the Y1RA alters open-field locomotor activity, ethanol-induced sedation (3.8 g/kg, ip), or blood ethanol levels. RESULTS Relative to control treatment, ip injection (50 and 75 mg/kg) and intracerebroventricular infusion (100 microg) of the Y1RA significantly reduced ethanol consumption and food intake without altering water drinking. However, the Y1RA did not alter open-field locomotor activity, ethanol-induced sedation, or blood ethanol levels. CONCLUSIONS These data indicate that acute blockade of the NPY Y1 receptor with a systemically bioavailable NPY Y1RA reduces voluntary ethanol consumption by C57BL/6J mice. These results are consistent with observations that hypothalamic infusion of NPY increases ethanol drinking by rats.

Corticotropin releasing factor-1 receptor antagonist, CP-154,526, blocks the expression of ethanol-induced behavioral sensitization in DBA/2J mice.

RATIONALE Manipulation of glucocorticoid receptor signaling has been shown to alter the acquisition and expression of ethanol-induced locomotor sensitization in mice. It is unknown if other components of the hypothalamic-pituitary-adrenal (HPA)-axis modulate locomotor sensitization resulting from repeated ethanol administration. In the present investigation, we determined if pretreatment with an i.p. injection of CP-154,526, a selective corticotropin releasing factor (CRF) type-1 receptor antagonist, would block the acquisition and/or expression of ethanol-induced locomotor sensitization in male DBA/2J mice. METHODS To assess the role of the CRF1 receptor in the acquisition of behavioral sensitization, mice were pretreated with an i.p. injection of CP-154,526 30 min before each of 10 sensitizing i.p. injections of ethanol. To determine the role of the CRF1 receptor in modulating the expression of ethanol-induced sensitization, mice that had previously been sensitized to the locomotor stimulant effects of ethanol were pretreated with CP-154,526 30 min before an i.p. injection of ethanol on the test day. In a third study, ethanol-naïve mice were pretreated with CP-154,526 30 min before an initial i.p. injection of ethanol to determine the combined effects of the CRF1 receptor antagonist and ethanol on locomotor activity. Blood ethanol concentrations were assessed at the termination of sensitization studies. RESULTS Pretreatment with CP-154,526 blocked the expression of ethanol-induced locomotor sensitization in DBA/2J mice but did not prevent the acquisition of sensitization. The ability of CP-154,526 to block the expression of ethanol-induced locomotor sensitization was not attributable to alterations in blood ethanol levels or possible sedative effects produced by the combined administration of CP-154,526 and ethanol. CONCLUSIONS These data provide novel evidence that CRF1 receptor signaling modulates the expression of ethanol-induced locomotor sensitization, and add to a growing literature suggesting a role for neurochemicals and hormones associated with the HPA-axis in behavioral sensitization resulting from repeated exposure to drugs of abuse.

The influence of dextromethorphan on morphine analgesia in Swiss Webster mice is sex-specific

NMDA (N-methyl-d-aspartate) antagonists are known to enhance the analgesic effects of opioids. However, virtually, all studies of this phenomenon have been done using male subjects. Here, the noncompetitive NMDA receptor antagonist dextromethorphan (DEX) was tested over a range of doses (10-200 microg intracerebroventricularly [i.c.v.]) in male and female Swiss Webster mice in combination with 5 mg/kg intraperitoneal (i.p.) morphine. Males exhibited enhanced morphine analgesia following either 100 or 200 microg DEX, but there was no evidence of DEX-mediated potentiation in females at any dose. Instead, DEX attenuated morphine analgesia in females. We also evaluated the effect of 100 microg i.c.v. DEX with different doses of morphine (1, 5 and 10 mg/kg). Again, DEX significantly enhanced morphine analgesia in male mice and attenuated it in females. Next, ovariectomized (OVX) female mice were compared to males following 5 mg/kg i.p. morphine and 100 microg i.c.v. DEX. Male and OVX females exhibited equivalent maximal levels of analgesia following administration of DEX. Morphine analgesia was not enhanced by DEX in sham-treated females and OVX mice with estradiol treatment (5 microg i.p. once daily for 7 days) also did not show DEX enhancement. These experiments demonstrate that the ability of NMDA receptor antagonists to potentiate morphine analgesia is modulated by an estrogen-sensitive mechanism and suggest that sex differences may play a critical role toward a more general understanding of the potentiation of opioid-induced analgesia through NMDA receptor antagonists.

Neuropeptide Y signaling modulates the expression of ethanol‐induced behavioral sensitization in mice

Neuropeptide Y (NPY) and protein kinase A (PKA) have been implicated in neurobiological responses to ethanol. We have previously reported that mutant mice lacking normal production of the RIIβ subunit of PKA (RIIβ−/− mice) show enhanced sensitivity to the locomotor stimulant effects of ethanol and increased behavioral sensitization relative to littermate wild‐type RIIβ+/+ mice. We now report that RIIβ−/− mice also show increased NPY immunoreactivity in the nucleus accumbens (NAc) core and the ventral striatum relative to RIIβ+/+ mice. These observations suggest that elevated NPY signaling in the NAc and/or striatum may contribute to the increased sensitivity to ethanol‐induced behavioral sensitization that is a characteristic of RIIβ−/− mice. Consistently, NPY−/− mice failed to display ethanol‐induced behavioral sensitization that was evident in littermate NPY+/+ mice. To examine more directly the role of NPY in the locomotor stimulant effects of ethanol, we infused a recombinant adeno‐associated virus (rAAV) into the region of the NAc core of DBA/2J mice. The rAAV‐fibronectin (FIB)‐NPY13–36 vector expresses and constitutively secretes the NPY fragment NPY13–36 (a selective Y2 receptor agonist) from infected cells in vivo. Mice treated with the rAAV‐FIB‐NPY13–36 vector exhibited reduced expression of ethanol‐induced behavioral sensitization compared with mice treated with a control vector. Taken together, the current data provide the first evidence that NPY signaling in the NAc core and the Y2 receptor modulate ethanol‐induced behavioral sensitization.

Involvement of protein kinase A in ethanol-induced locomotor activity and sensitization.

RATIONALE Mutant mice lacking the RIIbeta subunit of protein kinase A (regulatory subunit II beta(-/-)) show increased ethanol preference. Recent evidence suggests a relationship between heightened ethanol preference and susceptibility to ethanol-induced locomotor sensitization. It is currently unknown if protein kinase A signaling modulates the stimulant effects and/or behavioral sensitization caused by ethanol administration. To address this question, we examined the effects of repeated ethanol administration on locomotor activity RIIbeta(-/-) and littermate wild-type (RIIbeta(+/+)) mice on multiple genetic backgrounds. METHODS Over three consecutive days, mice were given single i.p. saline injections and immediately placed in a locomotor activity apparatus to establish a composite baseline for locomotor activity. Next, mice maintained on a hybrid 129/SvEvxC57BL/6J or pure C57BL/6J genetic background were given 10 i.p. ethanol injections before being placed in the activity apparatus. Each ethanol injection was separated by 3-4 days. To determine if changes in behavior were specific to ethanol injection, naïve mice were tested following repeated daily saline injections. The effects of ethanol injection on locomotor behavior were also assessed using an alternate paradigm in which mice were given repeated ethanol injections in their home cage environment. RESULTS Relative to RIIbeta(+/+) mice, RIIbeta(-/-) mice, regardless of genetic background, consistently showed significantly greater ethanol-induced locomotor activation. RIIbeta(-/-) mice also showed increased sensitivity to ethanol-induced locomotor sensitization resulting from repeated administration, an effect that was dependent on genetic background and testing paradigm. Increased locomotor activity by RIIbeta(-/-) mice was specific to ethanol injections, and was not related to altered blood ethanol levels. CONCLUSIONS These data provide novel evidence implicating an influence of protein kinase A signaling on ethanol-induced locomotor activity and behavioral sensitization. The observation that RIIbeta(-/-) mice are more sensitive to the effects of repeated ethanol administration suggests that normal protein kinase A signaling limits, or is protective against, the stimulant effects of ethanol and the plastic alterations that underlie behavioral sensitization.