Canonical transient receptor potential channels and hypothalamic control of homeostatic functions

Recent molecular biological and electrophysiological studies have identified multiple transient receptor potential (TRP) channels in hypothalamic neurons as critical modulators of homeostatic functions. In particular, the canonical transient receptor potential channels (TRPCs) are expressed in hypothalamic neurons that are vital for the control of fertility and energy homeostasis. Classical neurotransmitters such as serotonin and glutamate and peptide neurotransmitters such as kisspeptin, neurokinin B and pituitary adenylyl cyclase-activating polypeptide signal through their cognate G protein-coupled receptors to activate TPRC 4, 5 channels, which are essentially ligand-gated calcium channels. In addition to neurotransmitters, circulating hormones like insulin and leptin signal through insulin receptor (InsR) and leptin receptor (LRb), respectively, to activate TRPC 5 channels in hypothalamic arcuate nucleus pro-opiomelanocortin (POMC) and kisspeptin (arcuate Kiss1 [Kiss1ARH]) neurons to have profound physiological (excitatory) effects. Besides its overt depolarizing effects, TRPC channels conduct calcium ions into the cytoplasm, which has a plethora of downstream effects. Moreover, not only the expression of Trpc5 mRNA but also the coupling of receptors to TRPC 5 channel opening are regulated in different physiological states. In particular, the mRNA expression of Trpc5 is highly regulated in kisspeptin neurons by circulating estrogens, which ultimately dictates the firing pattern of kisspeptin neurons. In obesity states, InsRs are "uncoupled" from opening TRPC 5 channels in POMC neurons, rendering them less excitable. Therefore, in this review, we will focus on the critical role of TRPC 5 channels in regulating the excitability of Kiss1ARH and POMC neurons in different physiological and pathological states.

Dynamic, sex- and diet-specific pleiotropism in the PAC1 receptor-mediated regulation of arcuate proopiomelanocortin and Neuropeptide Y/Agouti related peptide neuronal excitability by anorexigenic ventromedial nucleus PACAP neurons

This study furthers the investigation of how pituitary adenylate cyclase activating polypeptide (PACAP) and the PAC1 receptor (PAC1R) regulate the homeostatic energy balance circuitry. We hypothesized that apoptotic ablation of PACAP neurones in the hypothalamic ventromedial nucleus (VMN) would affect both energy intake and energy expenditure. We also hypothesized that selective PAC1R knockdown would impair the PACAP-induced excitation in anorexigenic proopiomelanocortin (POMC) neurones and inhibition of orexigenic neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurones in the hypothalamic arcuate nucleus (ARC). The results show CASPASE-3-induced ablation of VMN PACAP neurones leads to increased energy intake and meal frequency as well as decreased energy expenditure in lean animals. The effects were more robust in obese males, whereas we saw the opposite effects in obese females. We then utilized visualized whole-cell patch clamp recordings in hypothalamic slices. PAC1R knockdown in POMC neurones diminishes the PACAP-induced depolarization, increase in firing, decreases in energy intake and meal size, as well as increases in CO2 production and O2 consumption. Similarly, the lack of expression of the PAC1R in NPY/AgRP neurones greatly attenuates the PACAP-induced hyperpolarization, suppression of firing, decreases in energy intake and meal frequency, as well as increases in energy expenditure. The PACAP response in NPY/AgRP neurones switched from predominantly inhibitory to excitatory in fasted animals. Finally, the anorexigenic effect of PACAP was potentiated when oestradiol was injected into the ARC in ovariectomized females. This study demonstrates the critical role of anorexigenic VMN PACAP neurones and the PAC1R in exciting POMC and inhibiting NPY/AgRP neurons to control homeostatic feeding.

Current Review of the Function and Regulation of Tuberoinfundibular Dopamine Neurons

Tuberoinfundibular dopamine (TIDA) neurons have cell bodies located in the arcuate nucleus of the mediobasal hypothalamus. They project to the external zone of the median eminence, and the dopamine (DA) released there is carried by the hypophysial portal vasculature to the anterior pituitary. The DA then activates D2 receptors to inhibit prolactin (PRL) secretion from lactotrophs. The TIDA neuronal population is the principal regulatory factor controlling PRL secretion. The neuroendocrine role subserved by TIDA neurons sets them apart from other dopaminergic populations like the nigrostriatal and mesolimbic DA neurons. TIDA neurons exhibit intrinsic oscillatory fluctuations in their membrane potential that give rise to phasic firing and bursting activity. TIDA neuronal activity is sexually differentiated and modulated by gonadal hormones and PRL, as well as an array of small molecule and peptide neurotransmitters. This review covers these characteristics.

The vital role of arcuate nociceptin/orphanin FQ neurones in mounting an oestradiol-dependent adaptive response to negative energy balance via inhibition of nearby proopiomelanocortin neurones

We tested the hypothesis that N/OFQ neurones in the arcuate nucleus (N/OFQ^ARC ) inhibit proopiomelanocortin (POMC^ARC ) neurones in a diet- and hormone-dependent manner to promote a more extensive rebound hyperphagia upon re-feeding following an 18 h fast. We utilized intact male or ovariectomized (OVX) female mice subjected to ad libitum-feeding or fasting conditions. N/OFQ^ARC neurones under negative energy balance conditions displayed heightened sensitivity as evidenced by a decreased rheobase threshold, increased firing frequency, and increased burst duration and frequency compared to ad libitum-feeding conditions. Stimulation of N/OFQ^ARC neurones more robustly inhibited POMC^ARC neurones under fasting conditions compared to ad libitum-feeding conditions. N/OFQ^ARC inhibition of POMC^ARC neurones is hormone dependent as chemostimulation of N/OFQ^ARC neurones from fasted males and OVX females produced a sizable outward current in POMC^ARC neurones. Oestradiol (E₂ ) markedly attenuated the N/OFQ-induced POMC^ARC outward current. Additionally, N/OFQ tonically inhibits POMC^ARC neurones to a greater degree under fasting conditions than in ad libitum-feeding conditions as evidenced by the abrogation of N/OFQ-nociceptin opioid peptide (NOP) receptor signalling and inhibition of N/OFQ release via chemoinhibition of N/OFQ^ARC neurones. Intra-arcuate nucleus application of N/OFQ further elevated the hyperphagic response and increased meal size during the 6 h re-feed period, and these effects were mimicked by chemostimulation of N/OFQ^ARC neurones in vivo. E₂ attenuated the robust N/OFQ-induced rebound hyperphagia seen in vehicle-treated OVX females. These data demonstrate that N/OFQ^ARC neurones play a vital role in mitigating the impact of negative energy balance by inhibiting the excitability of anorexigenic neural substrates, an effect that is diminished by E₂ in females. KEY POINTS: Nociceptin/orphanin FQ (N/OFQ) promotes increased energy intake and decreased energy expenditure under conditions of positive energy balance in a sex- and hormone-dependent manner. Here it is shown that under conditions of negative energy balance, i.e. fasting, N/OFQ inhibits anorexigenic proopiomelanocortin (POMC) neurones to a greater degree compared to homeostatic conditions due to fasting-induced hyperexcitability of N/OFQ neurones. Additionally, N/OFQ promotes a sustained increase in rebound hyperphagia and increase in meal size during the re-feed period following a fast. These results promote greater understanding of how energy balance influences the anorexigenic circuitry of the hypothalamus, and aid in understanding the neurophysiological pathways implicated in eating disorders promoting cachexia.

The PACAP Paradox: Dynamic and Surprisingly Pleiotropic Actions in the Central Regulation of Energy Homeostasis

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP), a pleiotropic neuropeptide, is widely distributed throughout the body. The abundance of PACAP expression in the central and peripheral nervous systems, and years of accompanying experimental evidence, indicates that PACAP plays crucial roles in diverse biological processes ranging from autonomic regulation to neuroprotection. In addition, PACAP is also abundantly expressed in the hypothalamic areas like the ventromedial and arcuate nuclei (VMN and ARC, respectively), as well as other brain regions such as the nucleus accumbens (NAc), bed nucleus of stria terminalis (BNST), and ventral tegmental area (VTA) - suggesting that PACAP is capable of regulating energy homeostasis via both the homeostatic and hedonic energy balance circuitries. The evidence gathered over the years has increased our appreciation for its function in controlling energy balance. Therefore, this review aims to further probe how the pleiotropic actions of PACAP in regulating energy homeostasis is influenced by sex and dynamic changes in energy status. We start with a general overview of energy homeostasis, and then introduce the integral components of the homeostatic and hedonic energy balance circuitries. Next, we discuss sex differences inherent to the regulation of energy homeostasis via these two circuitries, as well as the activational effects of sex steroid hormones that bring about these intrinsic disparities between males and females. Finally, we explore the multifaceted role of PACAP in regulating homeostatic and hedonic feeding through its actions in regions like the NAc, BNST, and in particular the ARC, VMN and VTA that occur in sex- and energy status-dependent ways.

Pituitary Adenylate Cyclase Activating Polypeptide Inhibits A10 Dopamine Neurons and Suppresses the Binge-like Consumption of Palatable Food

Pituitary adenylate cyclase-activating polypeptide (PACAP) binds to PACAP-specific (PAC1) receptors in multiple hypothalamic areas, especially those regulating energy balance. PACAP neurons in the ventromedial nucleus (VMN) exert anorexigenic effects within the homeostatic energy balance circuitry. Since PACAP can also reduce the consumption of palatable food, we tested the hypothesis that VMN PACAP neurons project to the ventral tegmental area (VTA) to inhibit A₁₀ dopamine neurons via PAC1 receptors and K_ATP channels, and thereby suppress binge-like consumption. We performed electrophysiological recordings in mesencephalic slices from male PACAP-Cre and tyrosine hydroxylase (TH)-Cre mice. Initially, we injected PACAP (30 pmol) into the VTA, where it suppressed binge intake in wildtype male but not female mice. Subsequent tract tracing studies uncovered projections of VMN PACAP neurons to the VTA. Optogenetic stimulation of VMN PACAP neurons in voltage clamp induced an outward current and increase in conductance in VTA neurons, and a hyperpolarization and decrease in firing in current clamp. These effects were markedly attenuated by the K_ATP channel blocker tolbutamide (100 μM) and PAC1 receptor antagonist PACAP_6-38 (200 nM). In recordings from A₁₀ dopamine neurons in TH-Cre mice, we replicated the outward current by perfusing PACAP_1-38 (100 nM). This response was again completely blocked by tolbutamide and PACAP_6-38, and associated with a hyperpolarization and decrease in firing. These findings demonstrate that PACAP activates PAC1 receptors and K_ATP channels to inhibit A₁₀ dopamine neurons and sex-dependently suppress binge-like consumption. Accordingly, they advance our understanding of how PACAP regulates energy homeostasis via the hedonic energy balance circuitry.

Adaptive Changes in the Central Control of Energy Homeostasis Occur in Response to Variations in Energy Status

Energy homeostasis is regulated in coordinate fashion by the brain-gut axis, the homeostatic energy balance circuitry in the hypothalamus and the hedonic energy balance circuitry comprising the mesolimbcortical A10 dopamine pathway. Collectively, these systems convey and integrate information regarding nutrient status and the rewarding properties of ingested food, and formulate it into a behavioral response that attempts to balance fluctuations in consumption and food-seeking behavior. In this review we start with a functional overview of the homeostatic and hedonic energy balance circuitries; identifying the salient neural, hormonal and humoral components involved. We then delve into how the function of these circuits differs in males and females. Finally, we turn our attention to the ever-emerging roles of nociceptin/orphanin FQ (N/OFQ) and pituitary adenylate cyclase-activating polypeptide (PACAP)-two neuropeptides that have garnered increased recognition for their regulatory impact in energy homeostasis-to further probe how the imposed regulation of energy balance circuitry by these peptides is affected by sex and altered under positive (e.g., obesity) and negative (e.g., fasting) energy balance states. It is hoped that this work will impart a newfound appreciation for the intricate regulatory processes that govern energy homeostasis, as well as how recent insights into the N/OFQ and PACAP systems can be leveraged in the treatment of conditions ranging from obesity to anorexia.

Nociceptin/orphanin FQ neurons in the Arcuate Nucleus and Ventral Tegmental Area Act via Nociceptin Opioid Peptide Receptor Signaling to Inhibit Proopiomelanocortin and A10 Dopamine Neurons and Thereby Modulate Ingestion of Palatable Food

The neuropeptide nociceptin/orphanin FQ (N/OFQ) inhibits neuronal activity via its cognate nociceptin opioid peptide (NOP) receptor throughout the peripheral and central nervous systems, including those areas involved in the homeostatic and hedonic regulation of energy homeostasis. We thus tested the hypothesis that N/OFQ neurons in the hypothalamic arcuate nucleus (ARC) and ventral tegmental area (VTA) act via NOP receptor signaling to inhibit nearby anorexigenic proopiomelanocortin (POMC) and A10 dopamine neuronal excitability, respectively, and thereby modulate ingestion of palatable food. Electrophysiologic recordings were performed in slices prepared from transgenic male and ovariectomized (OVX) female N/OFQ-cre/enhanced green fluorescent protein-POMC, N/OFQ-cre and tyrosine hydroxylase-cre animals to see if optogenetically-stimulated peptide release from N/OFQ neurons could directly inhibit these neuronal populations. Binge-feeding behavioral experiments were also conducted where animals were exposed to a high-fat-diet (HFD) for one hour each day for five days and monitored for energy intake. Photostimulation of ARC and VTA N/OFQ neurons produces an outward current in POMC and A10 dopamine neurons receiving input from these cells. This is associated with a hyperpolarization and decreased firing. These features are also sex hormone- and diet-dependent; with estradiol-treated slices from OVX females being less sensitive, and obese males being more sensitive, to N/OFQ. Limited access to HFD causes a dramatic escalation in consumption, such that animals eat 25-45% of their daily intake during that one-hour exposure. Moreover, the NOP receptor-mediated regulation of these energy balance circuits are engaged, as N/OFQ injected directly into the VTA or ARC respectively diminishes or potentiates this binge-like increase in a manner heightened by diet-induced obesity or dampened by estradiol in females. Collectively, these findings provide key support for the idea that N/OFQ regulates appetitive behavior in sex-, site- and diet-specific ways, along with important insights into aberrant patterns of feeding behavior pertinent to the pathogenesis of food addiction.

Pituitary Adenylate Cyclase-Activating Polypeptide Excites Proopiomelanocortin Neurons: Implications for the Regulation of Energy Homeostasis

OBJECTIVE

We examined whether pituitary adenylate cyclase-activating polypeptide (PACAP) excites proopiomelanocortin (POMC) neurons via PAC1 receptor mediation and transient receptor potential cation (TRPC) channel activation.

METHODS

Electrophysiological recordings were done in slices from both intact male and ovariectomized (OVX) female PACAP-Cre mice and eGFP-POMC mice.

RESULTS

In recordings from POMC neurons in eGFP-POMC mice, PACAP induced a robust inward current and increase in conductance in voltage clamp, and a depolarization and increase in firing in current clamp. These postsynaptic actions were abolished by inhibitors of the PAC1 receptor, TRPC channels, phospholipase C, phosphatidylinositol-3-kinase, and protein kinase C. Estradiol augmented the PACAP-induced inward current, depolarization, and increased firing, which was abrogated by estrogen receptor (ER) antagonists. In optogenetic recordings from POMC neurons in PACAP-Cre mice, high-frequency photostimulation induced inward currents, depolarizations, and increased firing that were significantly enhanced by Gq-coupled membrane ER signaling in an ER antagonist-sensitive manner. Importantly, the PACAP-induced excitation of POMC neurons was notably reduced in obese, high-fat (HFD)-fed males. In vivo experiments revealed that intra-arcuate nucleus (ARC) PACAP as well as chemogenetic and optogenetic stimulation of ventromedial nucleus (VMN) PACAP neurons produced a significant decrease in energy intake accompanied by an increase in energy expenditure, effects blunted by HFD in males and partially potentiated by estradiol in OVX females.

CONCLUSIONS

These findings reveal that the PACAP-induced activation of PAC1 receptor and TRPC5 channels at VMN PACAP/ARC POMC synapses is potentiated by estradiol and attenuated under conditions of diet-induced obesity/insulin resistance. As such, they advance our understanding of how PACAP regulates the homeostatic energy balance circuitry under normal and pathophysiological circumstances.

Nociceptin/orphanin FQ modulates energy homeostasis through inhibition of neurotransmission at VMN SF-1/ARC POMC synapses in a sex- and diet-dependent manner

BACKGROUND

Orphanin FQ (aka nociceptin; N/OFQ) binds to its nociceptin opioid peptide (NOP) receptor expressed in proopiomelanocortin (POMC) neurons within the arcuate nucleus (ARC), a critical anorexigenic component of the hypothalamic energy balance circuitry. It inhibits POMC neurons by modifying neuronal excitability both pre- and postsynaptically. We tested the hypothesis that N/OFQ inhibits neurotransmission at synapses involving steroidogenic factor (SF)-1 neurons in the ventromedial nucleus (VMN) and ARC POMC neurons in a sex- and diet-dependent fashion.

METHODS

Electrophysiological recordings were done in intact male and in cycling and ovariectomized female NR5A1-Cre and eGFP-POMC mice. Energy homeostasis was assessed in wildtype animals following intra-ARC injections of N/OFQ or its saline vehicle.

RESULTS

N/OFQ (1 μM) decreased light-evoked excitatory postsynaptic current (leEPSC) amplitude more so in males than in diestrus or proestrus females, which was further accentuated in high-fat diet (HFD)-fed males. N/OFQ elicited a more robust outward current and increase in conductance in males than in diestrus, proestrus, and estrus females. These pleiotropic actions of N/OFQ were abrogated by the NOP receptor antagonist BAN ORL-24 (10 μM). In ovariectomized female eGFP-POMC mice, 17β-estradiol (E2; 100 nM) attenuated the N/OFQ-induced postsynaptic response. SF-1 neurons from NR5A1-Cre mice also displayed a robust N/OFQ-induced outward current and increase in conductance that was sexually differentiated and suppressed by E2. Finally, intra-ARC injections of N/OFQ increased energy intake and decreased energy expenditure, which was further potentiated by exposure to HFD and diminished by estradiol benzoate (20 μg/kg; s.c.).

CONCLUSION

These findings show that males are more responsive to the pleiotropic actions of N/OFQ at anorexigenic VMN SF-1/ARC POMC synapses, and this responsiveness can be further enhanced under conditions of diet-induced obesity/insulin resistance.

Endocannabinoid Signaling at Hypothalamic Steroidogenic Factor-1/Proopiomelanocortin Synapses Is Sex- and Diet-Sensitive

We tested the hypotheses that steroidogenic factor (SF)-1 neurons in the hypothalamic ventromedial nucleus (VMN) provide sexually disparate, endocannabinoid (EC)- and diet-sensitive glutamatergic input onto proopiomelanocortin (POMC) neurons. Electrophysiological recordings were performed in hypothalamic slices from intact and castrated guinea pigs, along with in vitro optogenetic experiments in intact male as well as cycling and ovariectomized female NR5A1-Cre mice. In slices from castrated male and female guinea pigs, depolarized-induced suppression of excitation (DSE) time-dependently reduced the amplitude of evoked excitatory postsynaptic currents (eEPSCs) in POMC neurons generated by electrically stimulating the dorsomedial VMN. Androgen stimulation rapidly enhanced this DSE, which was also found in insulin-resistant, high-fat diet (HFD)-fed males. By contrast, retrograde signaling at VMN/ARC POMC synapses was markedly attenuated in periovulatory females. HFD potentiated central cannabinoid-induced hyperphagia in both males and females, but exerted differential influences on cannabinoid-induced increases in energy expenditure. In NR5A1-Cre mice, the reduction in light-evoked EPSC amplitude caused by postsynaptic depolarization in cycling females was modest in comparison to that seen in intact males. Estradiol attenuated the DSE in light-evoked EPSC amplitude in slices from ovariectomized females. Moreover, the retrograde inhibition of transmission was further accentuated in HFD-fed males. Chemogenetic activation of SF-1 neurons suppressed appetite and increased energy expenditure in males, effects which were attenuated by HFD. Conversely, energy expenditure was increased in estradiol- but not vehicle-treated ovariectomized females. Together with our previous studies indicating that DSE in POMC neurons is EC-mediated, these findings indicate that VMN SF-1/ARC POMC synapses represent a sexually differentiated, EC- and diet-sensitive anorexigenic component within the hypothalamic energy balance circuitry.

Estradiol Protects Proopiomelanocortin Neurons Against Insulin Resistance

Insulin resistance is at the core of the metabolic syndrome, and men exhibit a higher incidence of metabolic syndrome than women in early adult life, but this sex advantage diminishes sharply when women reach the postmenopausal state. Because 17β-estradiol (E2) augments the excitability of the anorexigenic proopiomelanocortin (POMC) neurons, we investigated the neuroprotective effects of E2 against insulin resistance in POMC neurons from diet-induced obese (DIO) female and male mice. The efficacy of insulin to activate canonical transient receptor potential 5 (TRPC5) channels and depolarize POMC neurons was significantly reduced in DIO male mice but not in DIO female mice. However, the insulin response in POMC neurons was abrogated in ovariectomized DIO females but restored with E2 replacement. E2 increased T-type calcium channel Cav3.1 messenger RNA (mRNA) expression and whole-cell currents but downregulated stromal-interaction molecule 1 mRNA, which rendered POMC neurons more excitable and responsive to insulin-mediated TRPC5 channel activation. Moreover, E2 prevented the increase in suppressor of cytokine signaling-3 mRNA expression with DIO as seen in DIO males. As proof of principle, insulin [intracerebroventricular injection into the third ventricle (ICV)] decreased food intake and increased metabolism in female but not male guinea pigs fed a high-fat diet. The uncoupling of the insulin receptor from its downstream effector system was corroborated by the reduced expression of phosphorylated protein kinase B in the arcuate nucleus of male but not female guinea pigs following insulin. Therefore, E2 protects female POMC neurons from insulin resistance by enhancing POMC neuronal excitability and the coupling of insulin receptor to TRPC5 channel activation.

Testosterone Rapidly Augments Retrograde Endocannabinoid Signaling in Proopiomelanocortin Neurons to Suppress Glutamatergic Input from Steroidogenic Factor 1 Neurons via Upregulation of Diacylglycerol Lipase-α

Testosterone exerts profound effects on reproduction and energy homeostasis. Like other orexigenic hormones, it increases endocannabinoid tone within the hypothalamic feeding circuitry. Therefore, we tested the hypothesis that testosterone upregulates the expression of diacylglycerol lipase (DAGL)α in the hypothalamic arcuate nucleus (ARC) to increase energy intake via enhanced endocannabinoid-mediated retrograde inhibition of anorexigenic proopiomelanocortin (POMC) neurons. Energy intake, meal patterns, and energy expenditure were evaluated in orchidectomized, male guinea pigs treated subcutaneously with testosterone propionate (TP; 400 μg) or its sesame oil vehicle (0.1 mL). TP rapidly increased energy intake, meal size, O2 consumption, CO2 production, and metabolic heat production, all of which were antagonized by prior administration of the DAGL inhibitor orlistat (3 μg) into the third ventricle. These orlistat-sensitive, TP-induced increases in energy intake and expenditure were temporally associated with a significant elevation in ARC DAGLα expression. Electrophysiological recordings in hypothalamic slices revealed that TP potentiated depolarization-induced suppression of excitatory glutamatergic input onto identified ARC POMC neurons, which was also abolished by orlistat (3 μM), the CB1 receptor antagonist AM251 (1 μM), and the AMP-activated protein kinase inhibitor compound C (30 μM) and simulated by transient bath application of the dihydrotestosterone mimetic Cl-4AS-1 (100 nM) and testosterone-conjugated bovine serum albumin (100 nM). Thus, testosterone boosts DAGLα expression to augment retrograde, presynaptic inhibition of glutamate release onto ARC POMC neurons that, in turn, increases energy intake and expenditure. These studies advance our understanding of how androgens work within the hypothalamic feeding circuitry to affect changes in energy balance.

Modulatory influences of estradiol and other anorexigenic hormones on metabotropic, Gi/o-coupled receptor function in the hypothalamic control of energy homeostasis

The appetite suppressant actions of estradiol are due to its ability to attenuate orexigenic signals and potentiate anorexigenic signals. The work from my laboratory has shown that male guinea pigs are more sensitive to the hyperphagic and hypothermic effects of cannabinoids than their female counterparts. Cannabinoid sensitivity is further dampened by the activational effects of estradiol. This occurs via the hypothalamic feeding circuitry, where estradiol rapidly attenuates the cannabinoid CB1 receptor-mediated presynaptic inhibition of glutamatergic input onto anorexigenic proopiomelanocortin (POMC) neurons in the arcuate nucleus. This disruption is blocked by the estrogen receptor antagonist ICI 182,780, and associated with increased expression of phosphatidylinositol-3-kinase (PI3K). Moreover, the ability of estradiol to reduce both the cannabinoid-induced hyperphagia and glutamate release onto POMC neurons is abrogated by the PI3K inhibitor PI 828. The peptide orphanin FQ/nociceptin (OFQ/N) activates opioid receptor-like (ORL)1 receptors to hyperpolarize and inhibit POMC neurons via the activation of postsynaptic G protein-gated, inwardly-rectifying (GIRK) channels. We have demonstrated that the fasting-induced hyperphagia observed in ORL1-null mice is blunted compared to wild type controls. In addition, the ORL1 receptor-mediated activation of GIRK channels in POMC neurons from ovariectomized female rats is markedly impaired by estradiol. The estrogenic attenuation of presynaptic CB1 and postsynaptic ORL1 receptor function may be part of a more generalized mechanism through which anorexigenic hormones suppress orexigenic signaling. Indeed, we have found that leptin robustly suppresses the OFQ/N-induced activation of GIRK channels in POMC neurons. Furthermore, its ability to augment excitatory input onto POMC neurons is blocked by PI 828. Thus, estradiol and other hormones like leptin reduce energy intake at least partly by activating PI3K to disrupt the pleiotropic functions of Gi/o-coupled receptors that inhibit anorexigenic POMC neurons.

Estradiol Rapidly Attenuates ORL-1 Receptor-Mediated Inhibition of Proopiomelanocortin Neurons via Gq-Coupled, Membrane-Initiated Signaling

Estradiol rapidly regulates the activity of arcuate nucleus (ARH) proopiomelanocortin (POMC) neurons that project to the medial preoptic nucleus (MPN) to regulate lordosis. Orphanin FQ/nociceptin (OFQ/N) acts via opioid receptor-like (ORL)-1 receptors to inhibit these POMC neurons. Therefore, we tested the hypothesis that estradiol excites POMC neurons by rapidly attenuating inhibitory ORL-1 signaling in these cells. Hypothalamic slices through the ARH were prepared from ovariectomized rats injected with Fluorogold into the MPN. Electrophysiological recordings were generated in ARH neurons held at or near -60 mV, and neuronal phenotype was determined post hoc by immunohistofluorescence. OFQ/N application induced robust outward currents and hyperpolarizations via G protein-gated, inwardly rectifying K+ (GIRK) channels that were attenuated by pretreatment with either 17-β estradiol (E2) or E2 conjugated to bovine serum albumin. This was blocked by the estrogen receptor (ER) antagonist ICI 182,780 and mimicked by the Gq-coupled membrane ER (Gq-mER) ligand STX and the ERα agonist PPT. Inhibiting phosphatidylinositol-3-kinase (PI3K) blocked the estrogenic attenuation of ORL-1/GIRK currents. Antagonizing either phospholipase C (PLC), protein kinase C (PKC), protein kinase A (PKA) or neuronal nitric oxide synthase (nNOS) also abrogated E2 inhibition of ORL-1/GIRK currents, whereas activation of PKC, PKA, protein kinase B (Akt) and nNOS substrate L-arginine all attenuated the OFQ/N response. This was observed in 92 MPN-projecting, POMC-positive ARH neurons. Thus, ORL-1 receptor-mediated inhibition of POMC neurons is rapidly and negatively modulated by E2, an effect which is stereoselective and membrane initiated via Gq-mER and ERα activation that signals through PLC, PKC, PKA, PI3K and nNOS.

Sex differences in cannabinoid-regulated biology: A focus on energy homeostasis

Considerable strides have been made over the past 20 years in our understanding of the ligands, receptor subtypes, signal transduction mechanisms and biological actions comprising the endocannabinoid system. From the ever-expanding number of studies that have been conducted during this time, it has become increasingly clear that sex differences are the cornerstone of cannabinoid-regulated biology. Available evidence has demonstrated that these sex differences endure in the absence of gonadal steroids, and are modulated by the acute, activational effects of these hormones. This review focuses on select aspects of sexually differentiated, cannabinoid-regulated biology, with a particular emphasis on the control of energy balance. It is anticipated that it will lend impactful insight into the pervasive and diverse disparities in how males and females respond to cannabinoids--from the organismal level down to the molecular level. Additionally, it will furnish a newfound appreciation for the need to recalibrate our thinking in terms of how cannabinoids are used as therapeutic adjuvants for a broad range of clinical disorders and associated comorbidities, including body wasting and obesity.

The role of AMP-activated protein kinase in the androgenic potentiation of cannabinoid-induced changes in energy homeostasis

Orexigenic mediators can impact the hypothalamic feeding circuitry via the activation of AMP-dependent protein kinase (AMPK). Given that testosterone is an orexigenic hormone, we hypothesized that androgenic changes in energy balance are due to enhanced cannabinoid-induced inhibition of anorexigenic proopiomelanocortin (POMC) neurons via activation of AMPK. To this end, whole animal experiments were carried out in gonadectomized male guinea pigs treated subcutaneously with either testosterone propionate (TP; 400 μg) or its sesame oil vehicle (0.1 ml). TP-treated animals displayed increases in energy intake associated with increases in meal size. TP also increased several indices of energy expenditure as well as the p-AMPK/AMPK ratio in the arcuate nucleus (ARC) measured 2 and 24 h posttreatment. Subcutaneous administration of the CB1 receptor antagonist AM251 (3 mg/kg) rapidly blocked the hyperphagic effect of TP. This was mimicked largely upon third ventricular administration of AM251 (10 μg). Electrophysiological studies revealed that TP potentiated the ability of the cannabinoid receptor agonist WIN 55,212-2 to decrease the frequency of miniature excitatory postsynaptic currents in ARC neurons. TP also increased the basal frequency of miniature inhibitory postsynaptic currents. In addition, depolarization-induced suppression (DSE) is potentiated in cells from TP-treated animals and blocked by AM251. The AMPK inhibitor compound C attenuated DSE from TP-treated animals, whereas the AMPK activator metformin enhanced DSE from vehicle-treated animals. These effects occurred in a sizable number of identified POMC neurons. Collectively, these results indicate that the androgen-induced increases in energy intake are mediated via an AMPK-dependent augmentation in endocannabinoid tone onto POMC neurons.

Role of neuronal nitric oxide synthase in the estrogenic attenuation of cannabinoid-induced changes in energy homeostasis

Since estradiol attenuates cannabinoid-induced increases in energy intake, energy expenditure, and transmission at proopiomelanocortin (POMC) synapses in the hypothalamic arcuate nucleus (ARC), we tested the hypothesis that neuronal nitric oxide synthase (nNOS) plays an integral role. To this end, whole animal experiments were carried out in gonadectomized female guinea pigs. Estradiol benzoate (EB; 10 μg sc) decreased incremental food intake as well as O2 consumption, CO2 production, and metabolic heat production as early as 2 h postadministration. This was associated with increased phosphorylation of nNOS (pnNOS), as evidenced by an elevated ratio of pnNOS to nNOS in the ARC. Administration of the cannabinoid receptor agonist WIN 55,212-2 (3 μg icv) into the third ventricle evoked hyperphagia as early as 1 h postadministration, which was blocked by EB and restored by the nonselective NOS inhibitor N-nitro-L-arginine methyl ester hydrochloride (L-NAME; 100 μg icv) when the latter was combined with the steroid. Whole cell patch-clamp recordings showed that 17β-estradiol (E2; 100 nM) rapidly diminished cannabinoid-induced decreases in miniature excitatory postsynaptic current frequency, which was mimicked by pretreatment with the NOS substrate L-arginine (30 μM) and abrogated by L-NAME (300 μM). Furthermore, E2 antagonized endocannabinoid-mediated depolarization-induced suppression of excitation, which was nullified by the nNOS-selective inhibitor N5-[imino(propylamino)methyl]-L-ornithine hydrochloride (10 μM). These effects occurred in a sizable number of identified POMC neurons. Taken together, the estradiol-induced decrease in energy intake is mediated by a decrease in cannabinoid sensitivity within the ARC feeding circuitry through the activation of nNOS. These findings provide compelling evidence for the need to develop rational, gender-specific therapies to help treat metabolic disorders such as cachexia and obesity.

Gonadal steroids differentially modulate the actions of orphanin FQ/nociceptin at a physiologically relevant circuit controlling female sexual receptivity

Orphanin FQ/nociceptin (OFQ/N) inhibits the activity of pro-opiomelanocortin (POMC) neurones located in the hypothalamic arcuate nucleus (ARH) that regulate female sexual behaviour and energy balance. We tested the hypothesis that gonadal steroids differentially modulate the ability of OFQ/N to inhibit these cells via presynaptic inhibition of transmitter release and postsynaptic activation of G protein-gated, inwardly-rectifying K(+) (GIRK)-1 channels. Whole-cell patch clamp recordings were performed in hypothalamic slices prepared from ovariectomised rats. OFQ/N (1 μm) decreased the frequency of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs), and also caused a robust outward current in the presence of tetrodotoxin, in ARH neurones from vehicle-treated animals. A priming dose of oestradiol benzoate (EB; 2 μg) increased basal mEPSC frequency, markedly diminished both the OFQ/N-induced decrease in mEPSC frequency and the activation of GIRK-1 currents, and potentiated the OFQ/N-induced decrease in mIPSC frequency. Steroid treatment regimens that facilitate sexual receptivity reinstate the basal mEPSC frequency, the OFQ/N-induced decrease in mEPSC frequency and the activation of GIRK-1 currents to levels observed in vehicle-treated controls, and largely abolish the ability of OFQ/N to decrease mIPSC frequency. These effects were observed in an appreciable population of identified POMC neurones, almost one-half of which projected to the medial preoptic nucleus. Taken together, these data reveal that gonadal steroids influence the pleiotropic actions of OFQ/N on ARH neurones, including POMC neurones, in a disparate manner. These temporal changes in OFQ/N responsiveness further implicate this neuropeptide system as a critical mediator of the gonadal steroid regulation of reproductive behaviour.

Insulin excites anorexigenic proopiomelanocortin neurons via activation of canonical transient receptor potential channels

Proopiomelanocortin (POMC) neurons within the hypothalamic arcuate nucleus are vital anorexigenic neurons. Although both the leptin and insulin receptors are coupled to the activation of phosphatidylinositide 3 kinase (PI3K) in POMC neurons, they are thought to have disparate actions on POMC excitability. Using whole-cell recording and selective pharmacological tools, we have found that, similar to leptin, purified insulin depolarized POMC and adjacent kisspeptin neurons via activation of TRPC5 channels, which are highly expressed in these neurons. In contrast, insulin hyperpolarized and inhibited NPY/AgRP neurons via activation of KATP channels. Moreover, Zn(2+), which is found in insulin formulations at nanomolar concentrations, inhibited POMC neurons via activation of KATP channels. Finally, as predicted, insulin given intracerebroventrically robustly inhibited food intake and activated c-fos expression in arcuate POMC neurons. Our results show that purified insulin excites POMC neurons in the arcuate nucleus, which we propose is a major mechanism by which insulin regulates energy homeostasis.

The membrane estrogen receptor ligand STX rapidly enhances GABAergic signaling in NPY/AgRP neurons: role in mediating the anorexigenic effects of 17β-estradiol

Besides its quintessential role in reproduction, 17β-estradiol (E2) is a potent anorexigenic hormone. E2 and the selective Gq-coupled membrane estrogen receptor (Gq-mER) ligand STX rapidly increase membrane excitability in proopiomelanocortin (POMC) neurons by desensitizing the coupling of GABAB receptors to G protein-coupled inwardly rectifying K(+) channels (GIRKs), which upon activation elicit a hyperpolarizing outward current. However, it is unknown whether E2 and STX can modulate GABAB signaling in neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons. We used single-cell RT-PCR and whole cell patch clamping with selective pharmacological reagents to show that NPY/AgRP cells of mice express the GABAB-R1 and -R2 receptors and are hyperpolarized by the GABAB agonist baclofen in an E2-dependent manner. In males, E2 rapidly attenuated the coupling of GABAB receptors to GIRKs, which was blocked by the general PI3K inhibitors wortmannin and LY-294002 or the selective p110β subunit inhibitor TGX-221. The ERα-selective agonist propyl pyrazole triol mimicked the effects of E2. STX, in contrast, enhanced the GABAB response in males, which was abrogated by the estrogen receptor (ER) antagonist ICI 182,780. In gonadectomized mice of both sexes, E2 enhanced or attenuated the GABAB response in different NPY/AgRP cells. Coperfusing wortmannin with E2 or simply applying STX always enhanced the GABAB response. Thus, in NPY/AgRP neurons, activation of the Gq-mER by E2 or STX enhances the GABAergic postsynaptic response, whereas activation of ERα by E2 attenuates it. These findings demonstrate a clear functional dichotomy of rapid E2 membrane-initiated signaling via ERα vs. Gq-mER in a CNS neuron vital for regulating energy homeostasis.

Estradiol negatively modulates the pleiotropic actions of orphanin FQ/nociceptin at proopiomelanocortin synapses

Orphanin FQ/nociceptin (OFQ/N) inhibits the activity of proopiomelanocortin (POMC) neurons located in the hypothalamic arcuate nucleus (ARH) that regulate female sexual behavior and energy balance. We tested the hypothesis that estradiol modulates the ability of OFQ/N to pre- and postsynaptically decrease the excitability of these cells. To this end, whole-cell patch-clamp recordings were performed in hypothalamic slices prepared from ovariectomized rats, including some that were injected with the retrograde tracer Fluorogold in the medial preoptic nucleus (MPN) to label the POMC neurons regulating sexual receptivity. OFQ/N (1 µM) evoked a robust outward current in ARH neurons from vehicle-treated animals that was blocked by the opioid receptor-like (ORL)1 receptor antagonist UFP-101 (100 nM) and the G protein-gated, inwardly rectifying K⁺ (GIRK-1) channel blocker tertiapin (10 nM). OFQ/N also produced a decrease in the frequency of glutamatergic, miniature excitatory postsynaptic currents (mEPSCs), which was also antagonized by UFP-101. Estradiol benzoate (2 µg) increased basal mEPSC frequency and markedly diminished both the OFQ/N-induced activation of postsynaptic GIRK-1 channel currents and the presynaptic inhibition of glutamatergic neurotransmission. These effects were observed in identified POMC neurons, including eight that projected to the MPN. Taken together, these data reveal that estradiol attenuates the pleiotropic inhibitory actions of OFQ/N on POMC neurons: presynaptically through reducing the OFQ/N inhibition of glutamate release and postsynaptically by reducing ORL1 signaling through GIRK channels. As such, they impart critical insight into a mechanism for estradiol to increase the activity of POMC neurons that inhibit sexual receptivity.

Receptor subtypes and signal transduction mechanisms contributing to the estrogenic attenuation of cannabinoid-induced changes in energy homeostasis

We examined the receptor subtypes and signal transduction mechanisms contributing to the estrogenic modulation of cannabinoid-induced changes in energy balance. Food intake and, in some cases, O2 consumption, CO2 production and the respiratory exchange ratio were evaluated in ovariectomized female guinea pigs treated s.c. with the cannabinoid receptor agonist WIN 55,212-2 or its cremephor/ethanol/0.9% saline vehicle, and either with estradiol benzoate (EB), the estrogen receptor (ER) α agonist PPT, the ERβ agonist DPN, the Gq-coupled membrane ER agonist STX, the GPR30 agonist G-1 or their respective vehicles. Patch-clamp recordings were performed in hypothalamic slices. EB, STX, PPT and G-1 decreased daily food intake. Of these, EB, STX and PPT blocked the WIN 55,212-2-induced increase in food intake within 1-4 h. The estrogenic diminution of cannabinoid-induced hyperphagia correlated with a rapid (within 15 min) attenuation of cannabinoid-mediated decreases in glutamatergic synaptic input onto arcuate neurons, which was completely blocked by inhibition of protein kinase C (PKC) and attenuated by inhibition of protein kinase A (PKA). STX, but not PPT, mimicked this rapid estrogenic effect. However, PPT abolished the cannabinoid-induced inhibition of glutamatergic neurotransmission in cells from animals treated 24 h prior. The estrogenic antagonism of this presynaptic inhibition was observed in anorexigenic proopiomelanocortin neurons. These data reveal that estrogens negatively modulate cannabinoid-induced changes in energy balance via Gq-coupled membrane ER- and ERα-mediated mechanisms involving activation of PKC and PKA. As such, they further our understanding of the pathways through which estrogens act to temper cannabinoid sensitivity in regulating energy homeostasis in females.

Estradiol signaling in the regulation of reproduction and energy balance

Our knowledge of membrane estrogenic signaling mechanisms and their interactions that regulate physiology and behavior has grown rapidly over the past three decades. The discovery of novel membrane estrogen receptors and their signaling mechanisms has started to reveal the complex timing and interactions of these various signaling mechanisms with classical genomic steroid actions within the nervous system to regulate physiology and behavior. The activation of the various estrogenic signaling mechanisms is site specific and differs across the estrous cycle acting through both classical genomic mechanisms and rapid membrane-initiated signaling to coordinate reproductive behavior and physiology. This review focuses on our current understanding of estrogenic signaling mechanisms to promote: (1) sexual receptivity within the arcuate nucleus of the hypothalamus, (2) estrogen positive feedback that stimulates de novo neuroprogesterone synthesis to trigger the luteinizing hormone surge important for ovulation and estrous cyclicity, and (3) alterations in energy balance.

A comparative, developmental, and clinical perspective of neurobehavioral sexual dimorphisms

Women and men differ in a wide variety of behavioral traits and in their vulnerability to developing certain mental disorders. This review endeavors to explore how recent preclinical and clinical research findings have enhanced our understanding of the factors that underlie these disparities. We start with a brief overview of some of the important genetic, molecular, and hormonal determinants that contribute to the process of sexual differentiation. We then discuss the importance of animal models in studying the mechanisms responsible for sex differences in neuropsychiatric disorders (e.g., drug dependence) - with a special emphasis on experimental models based on the neurodevelopmental and "three hits" hypotheses. Next, we describe the most common brain phenotypes observed in vivo with magnetic resonance imaging. We discuss the challenges in interpreting these phenotypes vis-à-vis the underlying neurobiology and revisit the known sex differences in brain structure from birth, through adolescence, and into adulthood. This is followed by a presentation of pertinent clinical and epidemiological data that point to important sex differences in the prevalence, course, and expression of psychopathologies such as schizophrenia, and mood disorders including major depression and posttraumatic stress disorder. Recent evidence implies that mood disorders and psychosis share some common genetic predispositions and neurobiological bases. Therefore, modern research is emphasizing dimensional representation of mental disorders and conceptualization of schizophrenia and major depression as a continuum of cognitive deficits and neurobiological abnormalities. Herein, we examine available evidence on cerebral sexual dimorphism to verify if sex differences vary quantitatively and/or qualitatively along the psychoses-depression continuum. Finally, sex differences in the prevalence of posttraumatic disorder and drug abuse have been described, and we consider the genomic and molecular data supporting these differences.

Contribution of a membrane estrogen receptor to the estrogenic regulation of body temperature and energy homeostasis

The hypothalamus is a key region of the central nervous system involved in the control of homeostasis, including energy and core body temperature (Tc). 17β-Estradiol (E2) regulates Tc, in part, via actions in the basal hypothalamus and preoptic area. E2 primarily controls hypothalamic functions via the nuclear steroid receptors, estrogen receptor α/β. However, we have previously described an E2-responsive, Gq-coupled membrane receptor that reduces the postsynaptic inhibitory γ-aminobutyric acid-ergic tone and attenuates postovariectomy body weight gain in female guinea pigs through the administration of a selective Gq-mER ligand, STX. To determine the role of Gq-mER in regulating Tc, energy and bone homeostasis, ovariectomized female guinea pigs, implanted ip with temperature probes, were treated with STX or E2 for 7-8 wk. Tc was recorded for 4 wk, whereas food intake and body weight were monitored daily. Bone density and fat accumulation were determined postmortem. Both E2 and STX significantly reduced Tc in the females compared with controls. STX, similar to E2, reduced food intake and fat accumulation and increased tibial bone density. Therefore, a Gq-mER-coupled signaling pathway appears to be involved in maintaining homeostatic functions and may constitute a novel therapeutic target for treatment of hypoestrogenic symptoms.

Framework for sex differences in adolescent neurobiology: a focus on cannabinoids

This review highlights the salient findings that have furthered our understanding of how sex differences are initiated during development and maintained throughout life. First we discuss how gonadal steroid hormones organize the framework for sex differences within critical periods of development-namely, during those exposures which occur in utero and post-partum, as well as those which occur during puberty. Given the extensive precedence of sex differences in cannabinoid-regulated biology, we then focus on the disparities within the endogenous cannabinoid system, as well as those observed with exogenously administered cannabinoids. We start with how the expression of cannabinoid CB(1) receptors is regulated throughout development. This is followed by a discussion of differential vulnerability to the pathological sequelae stemming from cannabinoid exposure during adolescence. Next we talk about sex differences in the interactions between cannabinoids and other drugs of abuse, followed by the organizational and activational roles of gonadal steroids in establishing and maintaining the sex dependence in the biological actions of cannabinoids. Finally, we discuss ways to utilize this knowledge to strategically target critical developmental windows of vulnerability/susceptibility and thereby implement more effective therapeutic interventions for afflictions that may be more prevalent in one sex vs. the other.

The role of the NOP receptor in regulating food intake, meal pattern, and the excitability of proopiomelanocortin neurons

We evaluated the role of the nociceptin/orphanin FQ (NOP) receptor in regulating food intake, meal pattern and the activity of hypothalamic arcuate (ARC) neurons. The microstructural analysis of food intake and meal pattern was performed under both food-deprived and ad libitum conditions. Whole-cell patch clamp recordings were obtained using the in vitro hypothalamic slice preparation and biocytin-filled electrodes. NOP receptor knockout mice exhibited significantly reduced body weight. Fasting-induced hyperphagia was diminished for the first 2h of a 6-h re-feeding period, and was associated with decreased meal duration and size, as well as a biphasic effect on meal frequency. The genotype effect observed under ad libitum conditions was comparatively unremarkable. Orphanin FQ/nociceptin (OFQ/N) was able to decrease evoked excitatory postsynaptic current amplitude, increase the S(2):S(1) ratio via the paired-pulse paradigm, and decrease miniature excitatory postsynaptic current frequency in ARC neurons from wild type animals but not NOP receptor knockouts. In addition OFQ/N activated a reversible outward current that was antagonized by the G-protein activated, inwardly-rectifying K(+) (GIRK) channel blocker tertiapin in wild type but not NOP knockout animals. Both the presynaptic and postsynaptic actions of OFQ/N were observed in ARC neurons subsequently determined to be immunopositive for characteristic phenotypic markers of anorexigenic proopiomelanocortin (POMC) neurons. Taken together, these results demonstrate the contribution of the NOP receptor in controlling food intake and meal pattern, as well as glutamate release and GIRK1 channel activity at POMC synapses.

Sex differences in the cannabinoid regulation of energy homeostasis

This review highlights the progress made thus far in characterizing the behavioral and cellular mechanisms through which cannabinoids regulate energy homeostasis. We performed microstructural analysis of feeding behavior in gonadectomized guinea pigs and gonadally intact, transgenic CB1 receptor knockout mice to determine how cannabinoids affect circadian rhythms in food intake and meal pattern. We also implanted data loggers into the abdominal cavity to correlate the appetite-modulating properties of cannabinoids with changes in core body temperature. We then coupled the effects on feeding behavior and temperature regulation with synaptic changes in the hypothalamic feeding circuitry via whole-cell patch clamp electrophysiological recording from neurons in the arcuate nucleus (ARC), in order to gain a more global perspective on the cannabinoid modulation of energy homeostasis. We observed marked sex differences in cannabinoid effects on food intake and core body temperature--with male guinea pigs exhibiting a comparatively greater sensitivity to the hyperphagia and hypophagia, as well as the hypothermia and hyperthermia, produced by CB1 receptor agonists and antagonists, respectively. In addition, male but not female CB1 receptor knockout mice show a diminished nocturnal food intake and average daily body weight relative to their wildtype littermate controls. The disparity in the CB1 receptor-mediated hyperphagia is paralleled by sex differences in the cellular effects of cannabinoids at anorexigenic, guinea pig proopiomelanocortin (POMC) synapses. Postsynaptically, cannabinoids potentiate an A-type K+ current (I(A)) in POMC neurons from female guinea pigs, whereas in males the activation of an inwardly rectifying K+ current is observed. Presynaptically, while cannabinoids inhibit glutamatergic input onto POMC neurons in males and females to similar degrees, males are more refractory to the cannabinoid-induced inhibition of convergent GABAergic input than females. These data reveal pervasive sex differences in the cannabinoid regulation of energy homeostasis that are consistent with changes in the excitability of POMC neurons.

Estrogen rapidly attenuates cannabinoid-induced changes in energy homeostasis

We examined whether estrogen negatively modulates cannabinoid-induced regulation of food intake, core body temperature and neurotransmission at proopiomelanocortin (POMC) synapses. Food intake was evaluated in ovariectomized female guinea pigs abdominally implanted with thermal DataLoggers and treated s.c. with the cannabinoid CB(1)/CB(2) receptor agonist WIN 55,212-2, the CB(1) receptor antagonist AM251 or their cremephor/ethanol/0.9% saline vehicle, and with estradiol benzoate (EB) or its sesame oil vehicle. Whole-cell patch clamp recordings were performed in slices through the arcuate nucleus. WIN 55,212-2 produced dose- and time-dependent increases in food intake. EB decreased food intake 8-24h after administration, but rapidly and completely blocked the increase in consumption caused by WIN 55,212-2. EB also attenuated the WIN 55,212-2-induced decrease in core body temperature. The AM251-induced decrease in food intake was unaffected. The diminution of the WIN 55,212-2-induced increase in food intake caused by EB correlated with a marked attenuation of cannabinoid receptor-mediated decreases in glutamatergic miniature excitatory postsynaptic current frequency occurring within 10-15min of steroid application. Furthermore, EB completely blocked the depolarizing shift in the inactivation curve for the A-type K(+) current caused by WIN 55,212-2. The EB-mediated, physiologic antagonism of these presynaptic and postsynaptic actions elicited upon cannabinoid receptor activation was observed in arcuate neurons immunopositive for phenotypic markers of POMC neurons. These data reveal that estrogens negatively modulate cannabinoid-induced changes in appetite, body temperature and POMC neuronal activity. They also impart insight into the neuroanatomical substrates and effector systems upon which these counter-regulatory factors converge in the control of energy homeostasis.

Sex differences in the cannabinoid modulation of appetite, body temperature and neurotransmission at POMC synapses

We sought to determine whether sex differences exist for the cannabinoid modulation of appetite, body temperature and neurotransmission at pro-opiomelanocortin (POMC) synapses. Gonadectomized male and female guinea pigs were outfitted to monitor core body temperature and injected with either the CB1 receptor agonist WIN 55,212-2 (1 mg/kg s.c.), antagonist AM251 (3 mg/kg s.c.) or vehicle (1 ml/kg s.c.) and evaluated for changes in six indices of feeding behavior under ad libitum conditions for 7 days. WIN 55,212-2 elicited an overt, sexually differentiated hyperphagia in which males displayed larger increases in hourly and daily intake, consumption/gram body weight, meal size and meal duration. The agonist also produced a more robust acute hypothermia in males than in females. In addition, males were more sensitive to the hypophagic effect of AM251, manifested by comparatively sizeable decreases in hourly intake, consumption/gram body weight, meal frequency and hyperthermia. To gain additional insight into the cellular mechanism underlying cannabinoid regulation of energy homeostasis, we performed whole-cell patch clamp recordings in hypothalamic slices prepared from gonadectomized male and female guinea pigs, and monitored miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) in arcuate (ARC) neurons. ARC neurons from females exhibited a higher basal mEPSC frequency. WIN 55,212-2 dose-dependently reduced mEPSC and mIPSC frequency; however, cells from males were far less sensitive to the CB1 receptor-mediated decrease in mIPSC frequency. These effects were observed in neurons subsequently identified as POMC neurons. These data reveal pronounced sex differences in how cannabinoids influence the hypothalamic control of homeostasis.

Cannabinoid-induced hyperphagia: correlation with inhibition of proopiomelanocortin neurons?

We tested the hypothesis that cannabinoids modulate feeding in male guinea pigs, and correlated cannabinoid-induced changes in feeding behavior with alterations in glutamatergic synaptic currents impinging upon proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus. Feeding experiments were performed as follows: after a three-day acclimation period, animals were weighed and injected with either the CB1 receptor agonist WIN 55,212-2 (1 mg/kg, s.c.), antagonist AM251 (3 mg/kg, s.c.) or their cremophore/ethanol/saline vehicle (1:1:18; 1 ml/kg, s.c.) each day for seven days. WIN 55,212-2 increased, whereas AM251 decreased, the rate of cumulative food intake. The agonist effect was manifest primarily by increases in meal frequency and the amount of food eaten per meal. By contrast, the antagonist effect was associated with decreases in meal frequency, duration and weight loss. For the electrophysiological experiments, we performed whole-cell patch-clamp recordings from POMC neurons in hypothalamic slices. WIN 55,212-2 decreased the amplitude of evoked, glutamatergic excitatory postsynaptic currents (eEPSCs) and increased the S2:S1 ratio. Conversely, AM251 increased eEPSC amplitude per se, and blocked the inhibitory effects of the agonist. WIN 55,212-2 also decreased miniature EPSC (mEPSC) frequency; whereas AM251 increased mEPSC frequency per se, and again blocked the inhibitory effect of the agonist. A subpopulation of cells exhibited an agonist-induced outward current, which was blocked by AM251, associated with increased conductance and reversed polarity near the Nernst equilibrium potential for K(+). These data demonstrate that cannabinoids regulate appetite in the guinea pig in part through both presynaptic and postsynaptic actions on anorexigenic POMC neurons.

Estrogen differentially modulates the cannabinoid- induced presynaptic inhibition of amino acid neurotransmission in proopiomelanocortin neurons of the arcuate nucleus

The present study sought to determine whether cannabinoids inhibit glutamatergic and GABAergic synaptic input onto neurons of the hypothalamic arcuate nucleus (ARC), and whether estrogen modulates this process. Whole-cell patch clamp recordings were performed in hypothalamic slices prepared from ovariectomized female guinea pigs. CB1 receptor activation reduced the amplitude of excitatory postsynaptic currents (EPSCs) evoked by electrical stimulation that were sensitive to ionotropic glutamate receptor antagonists. The CB1 receptor antagonist AM251 increased evoked EPSC (eEPSC) amplitude, and reversed the agonist-induced decrease. CB1 receptor activation similarly decreased the amplitude of evoked inhibitory postsynaptic currents (eIPSCs). The cannabinoid-induced reduction in eEPSC and eIPSC amplitude correlated with a decrease in the frequency of miniature EPSCs (mEPSCs) and IPSCs (mIPSCs) that were abolished by ionotropic glutamate and GABA(A) receptor antagonists, respectively. AM251 increased mEPSC frequency, and antagonized the agonist-induced decrease. Compared to neurons obtained from vehicle-treated controls, estradiol benzoate (25 mug; s.c.) given 24 h prior to experimentation increased mEPSC frequency, and markedly decreased the potency of CB1 receptor agonists to decrease mEPSC frequency. Conversely, the steroid potentiated the cannabinoid-induced decrease in mIPSC frequency. These effects were observed in neurons subsequently identified as proopiomelanocortin (POMC) neurons. These data reveal that ARC neurons, including POMC neurons, receive glutamatergic and GABAergic synaptic inputs that are presynaptically inhibited by cannabinoids, and differentially modulated by estrogen. These opposing effects of estrogen on the cannabinoid regulation of amino acid neurotransmission excite POMC neurons, and lend additional insight into the mechanisms underlying estrogen-induced anorexia and negative feedback of the reproductive axis.

Expression of an RNAi-resistant SLBP restores proper S-phase progression

Metazoan histone mRNAs are unique in that they lack a 3'-polyadenylated tail, but instead end in a conserved stem loop that is bound by SLBP (stem-loop binding protein). SLBP is required for efficient histone mRNA synthesis and translation. Removal of SLBP by RNA interference causes an increase in the number of cells in S-phase and this effect can be reversed by expressing an exogenous SLBP resistant to the small interfering RNA. Cells with decreased SLBP levels progress slowly through S-phase when released from a double-thymidine block. Thus SLBP is required for efficient DNA replication probably because a decreased ability to assemble chromatin results in a decrease in the rate of DNA replication.

Sex differences in the cannabinoid modulation of an A-type K+ current in neurons of the mammalian hypothalamus

Cannabinoids regulate biological processes governed by the hypothalamus including, but not limited to, energy homeostasis and reproduction. The present study sought to determine whether cannabinoids modulate A-type K(+) currents (I(A)) in neurons of the hypothalamic arcuate nucleus (ARC). Whole cell patch-clamp recordings were performed in slices through the ARC prepared from castrated female and male guinea pigs. Forty percent of guinea pig ARC neurons exhibited a transient outward current that was antagonized by high (mM) concentrations of 4-aminopyridine and (100 nM) rHeteropodatoxin-2. Five of these neurons also were immunopositive for both beta-endorphin and the Kv4.2 channel subunit. Bath application of the CB1 receptor agonists WIN 55,212-2 (1 microM) or ACEA (1 microM) selectively induced a rightward shift in the inactivation curve for the I(A), significantly increasing the half-maximal voltage without affecting the peak current magnitude, in neurons from female but not male animals. The CB1 receptor antagonist AM251 (1 microM) reversed this action. Collectively, these data reveal that guinea pig ARC neurons, including proopiomelanocortin neurons, express a prominent I(A) that is positively modulated by cannabinoids in a sex-specific way by altering the voltage dependence of its inactivation. The resultant inhibitory effect on this neuronal population may shed some insight into the mechanism(s) by which cannabinoids influence hypothalamic function.

Rapid effects of estrogen on G protein-coupled receptor activation of potassium channels in the central nervous system (CNS)

Estrogen rapidly alters the excitability of hypothalamic neurons that are involved in regulating numerous homeostatic functions including reproduction, stress responses, feeding and motivated behaviors. Some of the neurons include neurosecretory neurons such as gonadotropin-releasing hormone (GnRH) and dopamine neurons, and local circuitry neurons such as proopiomelanocortin (POMC) and gamma-aminobutyric acid (GABA) neurons. We have elucidated several non-genomic pathways through which the steroid alters synaptic responses in these hypothalamic neurons. We have examined the modulation by estrogen of the coupling of various receptor systems to inwardly-rectifying and small-conductance, Ca(2+)-activated K(+) (SK) channels using intracellular sharp-electrode and whole-cell recording techniques in hypothalamic slices from ovariectomized female guinea pigs. Estrogen rapidly uncouples mu-opioid receptors from G protein-gated inwardly-rectifying K(+) (GIRK) channels in POMC neurons and GABA(B) receptors from GIRK channels in dopamine neurons as manifested by a reduction in the potency of mu-opioid and GABA(B) receptor agonists to hyperpolarize their respective cells. This effect is blocked by inhibitors of protein kinase A (PKA) and protein kinase C (PKC). In addition, after 24h following steroid administration in vivo, the GABA(B)/GIRK channel uncoupling observed in GABAergic neurons of the preoptic area is associated with reduced agonist efficacy. Conversely, estrogen enhances the efficacy of alpha(1)-adrenergic receptor agonists to inhibit apamin-sensitive SK currents in these preoptic GABAergic neurons, and does so in both a rapid and sustained fashion. Finally, we observed a direct, steroid-induced hyperpolarization of GnRH neurons. These findings indicate a richly complex yet coordinated steroid modulation of K(+) channel activity in hypothalamic (POMC, dopamine, GABA, GnRH) neurons that are involved in regulating numerous homeostatic functions.

Estrogen modulation of K(+) channel activity in hypothalamic neurons involved in the control of the reproductive axis

Here we report on the progress we have made in elucidating the mechanisms through which estrogen alters synaptic responses in hypothalamic neurons. We examined the modulation by estrogen of the coupling of various receptor systems to inwardly rectifying and small conductance, Ca(2+)-activated K(+) (SK) channels. We used intracellular sharp-electrode and whole-cell recordings in hypothalamic slices from ovariectomized female guinea pigs. Estrogen rapidly uncouples mu-opioid receptors from G protein-gated inwardly rectifying K(+) (GIRK) channels in beta-endorphin neurons, manifest by a reduction in the potency of mu-opioid receptor agonists to hyperpolarize these cells. This effect is blocked by inhibitors of protein kinase A and protein kinase C. Estrogen also uncouples gamma-aminobutyric acid (GABA)(B) receptors from the same population of GIRK channels coupled to mu-opioid receptors. At 24 h after steroid administration, the GABA(B)/GIRK channel uncoupling observed in GABAergic neurons of the preoptic area (POA) is associated with reduced agonist efficacy. Conversely, estrogen enhances the efficacy of alpha(1)-adrenergic receptor agonists to inhibit apamin-sensitive SK currents in these POA GABAergic neurons, and does so in both a rapid and sustained fashion. Finally, we observed a direct, steroid-induced hyperpolarization of both arcuate and POA neurons, among which gonadotropin-releasing hormone (GnRH) neurons are particularly sensitive. These findings indicate a richly complex yet coordinated steroid modulation of K(+) channel activity that serves to control the excitability of hypothalamic neurons involved in regulating the reproductive axis.

The noradrenergic inhibition of an apamin-sensitive, small-conductance Ca2+-activated K+ channel in hypothalamic gamma-aminobutyric acid neurons: pharmacology, estrogen sensitivity, and relevance to the control of the reproductive axis

The present study sought to determine whether small-conductance, Ca2+-activated K+ currents underlie the afterhyperpolarization (AHP) in neurons of the preoptic area (POA), a brain region important in controlling reproduction. We used an ovariectomized, female guinea pig model to test two hypotheses: 1) the current associated with the AHP (I(AHP)) regulates the firing rate of POA neurons and 2) amine neurotransmitters modulate it in a gonadal steroid-sensitive manner. Intracellular recordings followed by combined histofluorescence/in situ hybridization for glutamic acid decarboxylase, 65-kDa isomer, revealed that POA neurons, including gamma-aminobutyric acid (GABA)ergic neurons, exhibited an AHP and spike frequency adaptation. The corresponding I(AHP) was sensitive to antagonism by CdCl2 (200 microM), apamin (0.3-1 microM), and dequalinium (3 microM). The beta-adrenergic receptor agonist isoproterenol inhibited the I(AHP) in a dose-dependent, timolol-sensitive fashion. In addition, the alpha1-adrenergic receptor agonist methoxamine dose dependently inhibited the I(AHP) in a prazosin-sensitive manner and increased neuronal firing rate. Twenty-four-hour pretreatment with estradiol benzoate (EB; 25 microg, s.c.) markedly potentiated the inhibitory effect of methoxamine on the I(AHP), whereas that for isoproterenol was unaffected. Similarly, bath application of 17beta-estradiol (100 nM; 15-20 min) mimicked the effect of EB on the methoxamine-induced inhibition of the I(AHP). Thus, POA GABAergic neurons express an apamin-sensitive channel that mediates, at least in part, the I(AHP), and tempers the excitability of these cells. Furthermore, these studies demonstrate that estrogen enhances the alpha1-adrenergic receptor-mediated inhibition of this current.

Estrogen biphasically modifies hypothalamic GABAergic function concomitantly with negative and positive control of luteinizing hormone release

The principal role of estrogen is its control of the female ovulatory cycle via negative and positive feedback on gonadotropin secretion. However, a detailed, cohesive picture of how the steroid specifically regulates the excitability of hypothalamic neurons involved in the central control of gonadotropin secretion is still emerging. Here, we used an ovariectomized female guinea pig model to test the hypothesis that estrogen acts on GABAergic neurons in the preoptic area (POA) to elicit a biphasic profile of luteinizing hormone (LH) secretion. Intracellular electrophysiological recordings revealed that estradiol benzoate (EB; 25 microgram, s.c.) decreased the hyperpolarizing response of GABAergic neurons to the GABA(B) receptor agonist baclofen 24 hr after treatment. This effect of GABA(B) receptor stimulation in unidentified POA neurons was still depressed 42 hr after EB administration. By the use of a ribonuclease protection assay, however, EB reduced glutamic acid decarboxylase mRNA expression 42 hr but not 24 hr after its administration. Thus, estrogen attenuated the autoinhibition of GABAergic POA neurons during the initial LH suppressive (i.e., negative feedback) phase and subsequently reduced GABAergic function during the LH surge (i.e., positive feedback). These studies demonstrate that the effects of estrogen on hypothalamic GABAergic neurons coincide with the inhibitory and stimulatory actions, respectively, of the steroid on LH secretion. Furthermore, the data provide novel insights into the mechanism by which estrogen regulates hypothalamic GABAergic neurons, which are critical for the biphasic modulation of LH release observed over the course of the female ovulatory cycle.

The role of intrinsic and agonist-activated conductances in determining the firing patterns of preoptic area neurons in the guinea pig

Whole-cell and intracellular recordings were made in coronal hypothalamic slices prepared from ovariectomized female guinea pigs. 62% of preoptic area (POA) neurons fired action potentials in a bursting manner, and exhibited a significantly greater afterhyperpolarization (AHP) than did non-bursting POA neurons. The majority (70%) of POA neurons (n=76) displayed a time-dependent inward rectification (I(h)) that was blocked by CsCl (3 mM) or by ZD 7288 (30 microM). In addition, 51% of the cells expressed a low-threshold spike (LTS) associated with a transient inward current (I(T)) that was blocked by NiCl(2) (200 microM). A smaller percentage of POA neurons (29%) expressed a transient outward, A-type K(+) current that was antagonized by a high concentration of 4-aminopyridine (3 mM). Moreover, POA neurons responded to bath application of the mu-opioid receptor agonist DAMGO (93%) or the GABA(B) receptor agonist baclofen (83%) with a membrane hyperpolarization or an outward current. These responses were accompanied by a decrease in input resistance or an increase in conductance, respectively, and were attenuated by BaCl(2) (100 microM). In addition, the reversal potential for these responses closely approximated the Nernst equilibrium potential for K(+). These results suggest that POA neurons endogenously express to varying degrees an AHP, an I(h), an I(T) and an A-type K(+) current. The vast majority of these neurons also are inhibited upon mu-opioid or GABA(B) receptor stimulation via the activation of an inwardly-rectifying K(+) conductance. Such intrinsic and transmitter-activated conductances likely serve as important determinants of the firing patterns of POA neurons.

An intronic splicing silencer causes skipping of the IIIb exon of fibroblast growth factor receptor 2 through involvement of polypyrimidine tract binding protein

Alternative splicing of fibroblast growth factor receptor 2 (FGF-R2) transcripts involves the mutually exclusive usage of exons IIIb and IIIc to produce two different receptor isoforms. Appropriate splicing of exon IIIb in rat prostate cancer DT3 cells requires a previously described cis element (ISAR, for "intronic splicing activator and repressor") which represses the splicing of exon IIIc and activates the splicing of exon IIIb. This element is nonfunctional in rat prostate AT3 cells, which repress exon IIIb inclusion and splice to exon IIIc. We have now identified an intronic element upstream of exon IIIb that causes repression of exon IIIb splicing. Deletion of this element abrogates the requirement for ISAR in order for exon IIIb to be spliced in DT3 cells and causes inappropriate inclusion of exon IIIb in AT3 cells. This element consists of two intronic splicing silencer (ISS) sequences, ISS1 and ISS2. The ISS1 sequence is pyrimidine rich, and in vitro cross-linking studies demonstrate binding of polypyrimidine tract binding protein (PTB) to this element. Competition studies demonstrate that mutations within ISS1 that abolish PTB binding in vitro alleviate splicing repression in vivo. Cotransfection of a PTB-1 expression vector with a minigene containing exon IIIb and the intronic splicing silencer element demonstrate PTB-mediated repression of exon IIIb splicing. Furthermore, all described PTB isoforms were equally capable of mediating this effect. Our results support a model of splicing regulation in which exon IIIc splicing does not represent a default splicing pathway but rather one in which active repression of exon IIIb splicing occurs in both cells and in which DT3 cells are able to overcome this repression in order to splice exon IIIb.

Regional oral absorption, hepatic first-pass effect, and non-linear disposition of salmon calcitonin in beagle dogs

The dose-dependent disposition, first pass hepatic elimination, and absorption pharmacokinetics (PK) of salmon calcitonin (sCT) were investigated in a canine Intestinal Vascular Access Port (IVAP) model. The PK of sCT were determined after intravenous (IV), subcutaneous (SC), portal venous (PV), and oral (PO) administration of sCT. Regional oral absorption of unformulated sCT was also evaluated by direct administration into the duodenum (ID), ileum (IL), and colon (IC) by means of surgically implanted, chronic catheters. Plasma samples were collected and analyzed by radioimmunoassay (RIA). Salmon calcitonin PK were evaluated using 2-compartmental and model independent methods. Intravenous sCT PK were non-linear over the dose range studied. High dose groups (100-1000 microg) demonstrated higher total plasma clearance (CL) and V(dss) than the low dose groups (1-25 microg). However, the MRT did not change for doses ranging from 10 to 1000 microg. After SC administration, the absorption of sCT was rapid with bioavailability (BA) varying from 21.4 to 52.9%. However, the BA of sCT was low after ID, IL, and IC administration (0.039, 0.064, and 0.021%, respectively). The role of hepatic first-pass elimination was negligible. The results of these studies demonstrate that the elimination of sCT is rapid but does not occur in the liver. Enhanced sCT clearance at higher doses was indicated by increasing V(dss) values, and it is hypothesized that increased renal blood flow and/or saturated plasma protein binding may contribute to the non-linear behavior. The IVAP canine model was found to have utility for probing the absorption and disposition PK of sCT. The combination of high oral bioavailability variability and non-linear disposition of sCT may produce highly variable therapeutic effects. The practical impact of the non-linear disposition of sCT remains to be determined. Based on the current results it appears that the rate-limiting step to the successful oral administration of sCT is its delivery into the portal vein since hepatic metabolism was negligible.

A powerful GABA(B) receptor-mediated inhibition of GABAergic neurons in arcuate nucleus

We combined histofluorescence with in situ hybridization to identify GABAergic neurons in the arcuate nucleus (ARC) following electrophysiological recording, using GAD65 as a marker. Intracellular recordings 91 were made in hypothalamic slices prepared from ovariectomized guinea pigs. Over 90% of ARC neurons tested with the GABA(B) receptor agonist baclofen responded with a membrane hyperpolarization or an outward current. The hyperpolarization was dose dependent, and the GABA(B) receptor antagonist CGP 35,348 produced a rightward shift in the agonist dose-response curve. Agonist potency was lower, and the efficacy greater, in GAD-positive neurons. The use of this novel technique for identifying GABAergic neurons thus reveals differences in the pharmacodynamics of GABA(B) receptor activation between GABAergic and non-GABAergic ARC neurons.

Biopharmaceutical approaches for developing and assessing oral peptide delivery strategies and systems: in vitro permeability and in vivo oral absorption of salmon calcitonin (sCT)

PURPOSE

To evaluate a biopharmaceutical approach for selecting formulation additives and establishing the performance specifications of an oral peptide delivery system using sCT as a model peptide.

METHODS

The effect of formulation additives on sCT effective permeability and transepithelial electrical resistance (TEER) was evaluated in side-by-side diffusion chambers using rat intestinal segments. Baseline regional oral absorption of sCT was evaluated in an Intestinal and Vascular Access Port (IVAP) dog model by administration directly into the duodenum, ileum, and colon by means of surgically implanted, chronic catheters. The effect of varying the input rate and volume of the administered solution on the extent of sCT absorption was also evaluated. Citric acid (CA) was utilized in all studies to cause a transient reduction in local pH. In vitro samples and plasma samples were analyzed by radioimmunoassay (RIA). Two oral delivery systems were prepared based on the results of the in vitro and IVAP studies, and evaluated in normal dogs.

RESULTS

Maximal permeability enhancement of sCT was observed using taurodeoxycholate (TDC) or lauroyl carnitine (LC) in vitro. Ileal absorption of sCT was higher than in other regions of the intestine. Low volume and bolus input of solution formulations was selected as the optimal condition for the IVAP studies since larger volumes or slower input rates resulted in significantly lower sCT bioavailability (BA). Much lower BA of sCT was observed when CA was not used in the formulation. The absolute oral bioavailability (mean+/-SD) in dogs for the control (sCT + CA) and two proprietary sCT delivery systems was 0.30%+/-0.05%, 1.10+/-0.18%, and 1.31+/-0.56%, respectively.

CONCLUSIONS

These studies demonstrate the utility of in vitro evaluation and controlled in vivo studies for developing oral peptide delivery strategies. Formulation additives were selected, the optimal intestinal region for delivery identified, and the optimal release kinetics of additives and actives from the delivery system were characterized. These methods were successfully used for devising delivery strategies and fabricating and evaluating oral sCT delivery systems in animals. Based on these studies, sCT delivery systems have been fabricated and tested in humans with favorable results.

A novel isoform ratio switch of the polypyrimidine tract binding protein

In this report we present evidence for a novel switch in the ratio of the two major isoforms of the polypyrimidine tract binding protein (PTB) in two related prostate cancer cell lines. The existence of different isoforms of PTB is thought to be the result of alternative splicing. We used UV cross-linking to identify a PTB doublet in the DT3 cell line, which is a rat prostate epithelial cancer line that is androgen-dependent and nonmetastatic. The AT3 cell line, a metastatic, androgen-independent cell line derived from the same tumor as the DT3 cells, was noted here to have a different isoform ratio of PTB. The two most prevalent isoforms of PTB were found to bind to an RNA probe containing a pyrimidine stretch. Western blot analysis demonstrated that these isoforms are indeed expressed differently in the two cell lines and that the observed binding is the result of this differential expression. These two cell lines are derived from the original Dunning prostate tumor, which is a model for studying tumor progression in the prostate. This ratio switch may be an important event in tumor progression in this model system of prostate cancer.

Rapid effects of estrogen to modulate G protein-coupled receptors via activation of protein kinase A and protein kinase C pathways

17Beta-estradiol (E2) rapidly (<20 min) attenuates the ability of mu-opioids to hyperpolarize guinea pig hypothalamic neurons. We have used intracellular recordings from female guinea pig hypothalamic slices to characterize the receptor and intracellular pathway(s) mediating E2's rapid effects. E2 acts stereospecifically with physiologically relevant concentration-dependence (EC50 = 8 nM) to cause a fourfold reduction in the potency of the mu-opioid agonist (D-Ala2-N-Me-Phe4-Gly5-ol)-enkephalin and the GABA(B) agonist baclofen to activate an inwardly rectifying K+ conductance in hypothalamic neurons. Both the nonsteroidal estrogen diethylstilbestrol and the anti-estrogen ICI 164,384 blocked E2 actions to uncouple mu-opioid receptors. Using a pharmacological Schild analysis, we found that ICI 164,384 competed for this E2 receptor with a Ke of approximately 0.3 nM. The protein synthesis inhibitor cycloheximide did not block the estrogenic uncoupling of the mu-opioid receptor from its K+ channel, implying a rapid, nongenomic mechanism of E2 action. The effects of E2 were mimicked by the bath application of the protein kinase A (PKA) activators, forskolin and Sp-cAMP, and the protein kinase C (PKC) activator phorbol-12,13-dibutyrate. Furthermore, the selective PKA antagonists Rp-cAMP and KT5720, which have different chemical structures and modes of action, both blocked the effects of E2. In addition, the actions of E2 were blocked by the selective PKC inhibitor Calphostin C. Therefore, it appears that E2 can activate both PKA and PKC to cause a heterologous desensitization of both mu-opioid and GABA(B) receptors, which has the potential to alter synaptic transmission in many regions of the CNS.