Influence of Cannabinoids on Electrically Evoked Dopamine Release and Cyclic AMP Generation in the Rat Striatum

Abstract: Using the endogenous cannabinoid receptor agonist anandamide, the synthetic agonist CP 55940 {[1α,2β( R )5α]-(−)-5-(1,1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]phenol}, and the specific antagonist SR 141716 [ N -(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1 H -pyrazole-3-carboxamide hydrochloride], second messenger activation of the central cannabinoid receptor (CB1) was examined in rat striatal and cortical slices. The effects of these cannabinoid ligands on electrically evoked dopamine (DA) release from [³H]dopamine-prelabelled striatal slices were also investigated. CP 55940 (1 µ M ) and anandamide (10 µ M ) caused significant reductions in forskolin-stimulated cyclic AMP accumulation in rat striatal slices, which were reversed in the presence of SR 141716 (1 µ M ). CP 55940 (1 µ M ) had no effect on either KCl- or neurotransmitter-stimulated ³H-inositol phosphate accumulation in rat cortical slices. CP 55940 and anandamide caused significant reductions in the release of dopamine after electrical stimulation of [³H]dopamine-prelabelled striatal slices, which were antagonised by SR 141716. SR 141716 alone had no effect on electrically evoked dopamine release from rat striatal slices. These data indicate that the CB1 receptors in rat striatum are negatively linked to adenylyl cyclase and dopamine release. That the CB1 receptor may influence dopamine release in the striatum suggests that cannabinoids play a modulatory role in dopaminergic neuronal pathways.     

Characterization of CB1 Receptors on Rat Neuronal Cell Cultures: Binding and Functional Studies Using the Selective Receptor Antagonist SR 141716A

Abstract: This study was undertaken to characterize further the central cannabinoid receptors in rat primary neuronal cell cultures from selected brain structures. By using [³H]SR 141716A, the specific CB1 receptor antagonist, we demonstrate in cortical neurons the presence of a high density of specific binding sites ( B _max = 139 ± 9 fmol/mg of protein) displaying a high affinity ( K _D = 0.76 ± 0.09 n M ). The two cannabinoid receptor agonists, CP 55940 and WIN 55212-2, inhibited in a concentration-dependent manner cyclic AMP production induced by either 1 µ M forskolin or isoproterenol with EC₅₀ values in the nanomolar range (4.6 and 65 n M with forskolin and 1.0 and 5.1 n M with isoproterenol for CP 55940 and WIN 55212-2, respectively). Moreover, in striatal neurons and cerebellar granule cells, CP 55940 was also able to reduce the cyclic AMP accumulation induced by 1 µ M forskolin with a potency similar to that observed in cortical neurons (EC₅₀ values of 3.5 and 1.9 n M in striatum and cerebellum, respectively). SR 141716A antagonized the CP 55940- and WIN 55212-2-induced inhibition of cyclic AMP accumulation, suggesting CB1 receptor-specific mediation of these effects on all primary cultures tested. Furthermore, CP 55940 was unable to induce mitogen-activated protein kinase activation in either cortical or striatal neurons. In conclusion, our results show nanomolar efficiencies for CP 55940 and WIN 55212-2 on adenylyl cyclase activity and no effect on any other signal transduction pathway investigated in primary neuronal cultures.     

The δ-Opioid Receptor in SK-N-BE Human Neuroblastoma Cell Line Undergoes Heterologous Desensitization

Abstract: The human neuroblastoma cell line SK-N-BE expresses δ-opioid receptors negatively coupled to adenylyl cyclase. Prolonged treatment (2 h) of the cells with 100 n M etorphine leads to an almost complete desensitization (8.2 ± 5.9 vs. 45.8 ± 8.7% for the control). Other receptors negatively coupled to adenylyl cyclase, namely, D2-dopaminergic, α₂-adrenergic, and m2/m4-muscarinic, were identified by screening of these cells, and it was shown that prolonged treatment (2 h) with 1 µ M 2-bromo-α-ergocryptine or 1 µ M arterenol resulted in a marked desensitization of D2-dopaminergic and α₂-adrenergic receptors, respectively. Cross-desensitization experiments revealed that pretreatment with etorphine desensitized with the same efficiency the δ-opioid receptor and the D2-dopaminergic receptor, and pretreatment with 2-bromo-α-ergocryptine also desensitized both receptors. In contrast, pretreatment with etorphine desensitized only partly the α₂-adrenergic receptor response, whereas pretreatment with 1 µ M arterenol partly desensitized the δ-opioid receptor response. It is concluded that the δ-opioid receptor-mediated inhibitory response of adenylyl cyclase undergoes heterologous desensitization, and it is suggested that δ-opioid and D2-dopaminergic receptors are coupled to adenylyl cyclase via a G_i2 protein, whereas α₂-adrenergic receptor could be coupled to the enzyme via two G proteins, G_i2 and another member of the G_i/G_o family.     

Activation of phosphoinositide 3-kinase/PKB pathway by CB(1) and CB(2) cannabinoid receptors expressed in prostate PC-3 cells. Involvement in Raf-1 stimulation and NGF induction

Cannabinoids exert a variety of physiological and pharmacological responses in humans through interaction with specific cannabinoid receptors. Cannabinoid receptors described to date belong to the seven-transmembrane-domain receptor superfamily and are coupled through the inhibitory G(i) protein to adenylyl cyclase inhibition. However, downstream signal transduction mechanisms triggered by cannabinoids are poorly understood. We examined here the involvement of the phosphoinositide 3-kinase (PI3K)/PKB pathway in the mechanism of action of cannabinoids in human prostate epithelial PC-3 cells. Cannabinoid receptors CB(1) and CB(2) are expressed in these cells, as shown by RT-PCR, Western blot and immunofluorescence techniques. Treatment of PC-3 cells with either Delta(9)-tetrahydrocannabinol (THC), the major psychoactive ingredient of marijuana, or R-(+)-methanandamide (MET), an analogue of the endogenous cannabinoid anandamide, increased phosphorylation of PKB in Thr308 and Ser473. The stimulation of PKB induced by cannabinoids was blocked by the two cannabinoid receptor antagonists, SR 141716 and SR 144528, and by the PI3K inhibitor LY 294002. These results indicate that activation of cannabinoid receptors in PC-3 cells stimulate the PI3K/PKB pathway. We further investigated the involvement of Raf-1/Erk activation in the mechanism of action of cannabinoid receptors. THC and MET induced translocation of Raf-1 to the membrane and phosphorylation of p44/42 Erk kinase, which was reversed by cannabinoid receptor antagonists and PI3K inhibitor. These results point to a sequential connection between cannabinoid receptors/PI3K/PKB pathway and Raf-1/Erk in prostate PC-3 cells. We also show that this pathway is involved in the mechanism of NGF induction exerted by cannabinoids in PC-3 cells.     

Effects of cannabinoids on energy metabolism.

The present review summarizes the recent work carried out by our group on the link between signal transduction pathways and metabolic regulation systems as affected by cannabinoids. In cells such as astrocytes and lymphocytes, which express cannabinoid receptors, physiologically relevant doses of cannabinoids induce a remarkable metabolic stimulation as determined e.g. by enhanced glucose utilization. Studies performed in astrocytes show that the cannabinoid-evoked stimulation of glucose metabolism is independent of adenylyl cyclase inhibition, and seems to rely on the cascade CB1 cannabinoid receptor --> Sphingomyelin breakdown --> Ceramide --> Raf-1 --> Mitogen-activated protein kinase (MAPK) --> Glucose utilization. A role for phosphoinositide 3'-kinase in the stimulation of glucose utilization by cannabinoids is also put forward. In addition, ceramide generated upon CB1 cannabinoid receptor activation may enhance ketone body production by astrocytes independently of MAPK. Anandamide has also been shown to exert metabolic effects in hepatocytes, cells that do not express cannabinoid receptors. The biological role of cannabinoids as modulators of metabolism is as yet unclear.     

Coupling of Corticotropin-Releasing Hormone Receptors to Adenylyl Cyclase in Human Y-79 Retinoblastoma Cells

Abstract: In human Y-79 retinoblastoma cells, corticotropin-releasing hormone (CRH) stimulates adenylyl cyclase activity and increases cyclic AMP accumulation. Different CRH analogues mimic the CRH stimulation of adenylyl cyclase and show similar sensitivity to the CRH receptor antagonist α-helical CRH_9–41. Vasoactive intestinal peptide (VIP) also increases the enzyme activity but less potently than CRH, and its effect is counteracted by the VIP receptor antagonist [ d - p -Cl-Phe⁶,Leu¹⁷]VIP. The VIP antagonist does not affect the response to CRH. The CRH-stimulated adenylyl cyclase activity is amplified by Mg²⁺, is inhibited by submicromolar concentrations of Ca²⁺, and requires GTP. Moreover, the CRH stimulation is reduced by pretreatment of cells with cholera toxin and by incubation of membranes with the RM/1 antibody, which recognizes the C-terminus of the α subunit of G_s. In immunoblots, the RM/1 antibody identifies a doublet of 45 and 52 kDa. Two proteins of similar molecular weights are ADP-ribosylated by cholera toxin. These data demonstrate that in human Y-79 retinoblastoma cells, specific CRH receptors stimulate cyclic AMP formation by interacting with G_s and by affecting a Ca²⁺-inhibitable form of adenylyl cyclase.     

Epidermal Growth Factor Promotes Uncoupling from Adenylyl Cyclase of the Rat D2S Receptor Expressed in GH4C1 Cells

Abstract: In anterior pituitary cells or when transfected into host cell lines, the D₂ dopamine receptor inhibits adenylyl cyclase and activates potassium channels. The GH-3 pituitary tumor cell line, which lacks functional D₂ receptors, responds to epidermal growth factor (EGF) by expressing a D₂ receptor that, paradoxically, couples to potassium channel activation but poorly inhibits adenylyl cyclase; this was correlated with a pronounced increase in α subunit of the G protein G₁₃. In this study we have investigated the effects of EGF on the transduction mechanisms of D₂ receptors in GH4C1 cells transfected and permanently overexpressing the rat short D₂ receptor. Activation of D₂ receptors in these cells resulted in both inhibition of adenylyl cyclase and opening of potassium channels and inhibition of prolactin release by both cyclic AMP-dependent and independent mechanisms. Exposure of the transfected GH4C1 cells to EGF caused a dramatic decrease in the coupling efficiency of the D₂ receptor to inhibit cyclic AMP-dependent responses, leaving its activity toward potassium channels unchanged. The EGF treatment led to the concomitant increase in the membrane content of G₁₃ protein. These results suggest that the transmembrane signaling specificity of G protein-coupled receptors can be modulated by the relative amounts of different G proteins at the cell membrane.     

Regulation of Multiple Effectors by the Cloned δ-Opioid Receptor: Stimulation of Phospholipase C and Type II Adenylyl Cyclase

Abstract: The δ-opioid receptor is known to regulate multiple effectors in various tissues. When expressed in human embryonic kidney 293 cells, the cloned δ-opioid receptor inhibited cyclic AMP (cAMP) accumulation in response to the δ-selective agonist [ d -Pen², d -Pen⁵]enkephalin. The inhibitory response of [ d -Pen², d -Pen⁵]enkephalin was dependent on the expression of the δ-opioid receptor and exhibited an EC₅₀ of 1 n M . The receptor showed ligand selectivity and a pharmacological profile that is appropriate for the δ-opioid subtype. The inhibition was blocked by the opiate antagonist naloxone or by pretreatment of the cells with pertussis toxin. Cotransfection of the δ-opioid receptor with type II adenylyl cyclase and an activated mutant of α_s converted the δ-opioid signal from inhibition to stimulation of cAMP accumulation. It is interesting that when transfected into Ltk⁻ fibroblasts, the cloned δ-opioid receptor was able to stimulate the formation of inositol phosphates (EC₅₀ = 8 n M ). This response was sensitive to pertussis toxin. The opioid-mediated formation of inositol phosphates exhibited the same ligand selectivity as seen with the inhibition of cAMP accumulation. The ability of the δ-opioid receptor to couple to G proteins other than G_i was also examined. Cotransfection studies revealed that the δ-opioid receptor can utilize G_z to regulate cAMP accumulation and to stimulate the formation of inositol phosphates.     

Activation of Opioid and Muscarinic Receptors Stimulates Basal Adenylyl Cyclase but Inhibits Ca2+/Calmodulin- and Forskolin-Stimulated Enzyme Activities in Rat Olfactory Bulb

Abstract: In rat olfactory bulb, muscarinic and opioid receptor agonists stimulate basal adenylyl cyclase activity in a GTP-dependent and pertussis toxin-sensitive manner. However, in the present study, we show that in the same brain area activation of these receptors causes inhibition of adenylyl cyclase activity stimulated by Ca²⁺ and calmodulin (CaM) and by forskolin (FSK), two direct activators of the catalytic unit of the enzyme. The opioid and muscarinic inhibitions consist of a decrease of the maximal stimulation elicited by either CaM or FSK, without a change in the potency of these agents. [Leu⁵]Enkephalin and selective δ- and μ-, but not κ-, opioid receptors agonists inhibit the FSK stimulation of adenylyl cyclase activity with the same potencies displayed in stimulating basal enzyme activity. Similarly, the muscarinic inhibition of FSK-stimulated adenylyl cyclase activity shows agonist and antagonist sensitivities similar to those characterizing the muscarinic stimulation of basal enzyme activity. Fluoride stimulation of adenylyl cyclase is not affected by either carbachol or [Leu⁵]enkephalin. In vivo treatment of olfactory bulb with pertussis toxin prevents both opioid and muscarinic inhibition of Ca²⁺/CaM- and FSK-stimulated enzyme activities. These results indicate that in rat olfactory bulb δ- and μ-opioid receptors and muscarinic receptors, likely of the M4 subtype, can exert a dual effect on cyclic AMP formation by interacting with pertussis toxin-sensitive GTP-binding protein(s) and possibly by affecting different molecular forms of adenylyl cyclase.     

Opposite Regulation of Adenylyl Cyclase by Protein Kinase C in Astrocyte and Microglia Cultures

Abstract: We studied the regulation of cyclic AMP responses by protein kinase C (PKC) in purified astrocyte and microglia cultures obtained from the neonatal rat brain. In astrocytes, a 10-min treatment with the phorbol esters phorbol 12-myristate 13-acetate (PMA) and 4β-phorbol 12,13-didecanoate (4β-PDD) (but not with 4α-PDD) or with diacylglycerol, which activate PKC, dose-dependently enhanced cyclic AMP accumulation induced by the β-adrenergic agonist isoproterenol and the adenylyl cyclase activator forskolin. Such enhancement was prevented by the PKC inhibitors staurosporine and calphostin-C and by down-regulation of PKC and was not related to activation of membrane receptors or G_s proteins or to inhibition of G_i proteins or phosphodiesterases. Instead, the activity of adenylyl cyclase doubled in PMA-treated astrocytes. In microglia, a 10-min treatment with PMA or PKC inhibitors did not affect cyclic AMP accumulation, whereas longer treatments with PMA or 4β-PDD (but not 4α-PDD) inhibited the cyclic AMP response in a time- and dose-dependent manner. Such inhibition was mimicked by staurosporine and calphostin-C. Also, in the case of microglia, the modulation of cyclic AMP responses appeared to occur at the level of adenylyl cyclase, and not elsewhere in the cyclic AMP cascade. The inhibition of microglial adenylyl cyclase was apparently not due to aspecific cytotoxicity. A differential regulation of adenylyl cyclase by PKC in astrocytes and microglia may help to explain qualitative and quantitative differences in the response of these cells to various physiological and pathological stimuli.     

Effect of glutamate intake during gestation on adenosine A(1) receptor/adenylyl cyclase pathway in both maternal and fetal rat brain

Pregnant Wistar rats were orally treated with 1 g/L l -glutamate during the entire gestational period and the status of adenosine A₁ receptor (A₁R)/adenylyl cyclase transduction pathway from maternal and fetal brain was analyzed. Glutamate consumption, estimated from the loss of water from the drinking bottles, was 110 ± 4.6 mg/kg/day. In mother brains glutamate intake did not significantly alter the B _max value, although the K _d value was significantly decreased. However in fetus brain, a significant decrease in B _max was observed, without an alteration of K _d value. Similar results were observed by western blot assays using specific A₁R antibody, suggesting a down-regulation of A₁R in fetal brain. Concerning α subunits of inhibitory G proteins (Gi), αGi₃ protein was slightly but significantly decreased in maternal brain without alterations of either Gi₁ or Gi₂. In contrast, αGi₁ and αGi₂ isoforms were increased in fetal brain. On the other hand, basal, forskolin, and forskolin plus GTPγS-stimulated adenylyl cyclase activity was significantly decreased in both maternal and fetal brain, and this was more prominent in fetal than in maternal brain. Finally, A₁R functionality was significantly decreased in mother brain whereas no significant differences were detected in fetus brain. These results suggest that glutamate administered to pregnant rats modulates A₁R signaling pathways in both tissues, showing an A₁R down-regulation in fetal brain, and desensitization in maternal brain.     

Inhibition of Adenylyl Cyclase Activity by a Homogeneous Population of Dopamine Receptors: Selective Blockade by Antisera Directed Against Gi1 and/or Gi2

Abstract: The 7315c pituitary tumor cell expresses a homogeneous population of dopamine receptors that are functionally similar to brain dopamine D₂ receptors. [³H]-Sulpiride binding to 7315c cell homogenates was specific and saturable, and K _i values for compounds to compete for these sites were highly correlated with values for the same compounds at D₂ receptors in brain. Dopamine maximally inhibited ∼65% of forskolin-stimulated cyclase activity in cell membranes. Some D₂ agonists had lower efficacies, suggesting that some compounds are partial agonists at this receptor. Removal of GTP from the assay buffer or pretreatment of the tissue with pertussis toxin abolished the inhibition of adenylyl cyclase by dopamine. Immunodetection of most of the known Gα subunits revealed that G_i1, G_i2, G_i3, G_o, G_q, and G_s are present in the 7315c membrane. Pretreatment with the AS antibody (which recognizes the C-terminal regions of Gα_i1 and Gα_i2) significantly attenuated the inhibition of adenylyl cyclase activity by dopamine, whereas antibodies to C-terminal regions of the other Gα subunits had no effect. These findings suggest that the dopamine D₂ receptor regulates cyclase inhibition predominantly via G_i1 and/or G_i2 and that the 7315c tumor cells provide a useful model for studying naturally expressed dopamine D₂ receptors in the absence of other dopamine receptor subtypes.     

Participation of Tubulin in the Stimulatory Regulation of Adenylyl Cyclase in Rat Cerebral Cortex Membranes

Abstract: This study examined effects of tubulin on the activation of adenylyl cyclase in rat cerebral cortex membranes. Tubulin, prepared from rat brain by polymerization with the hydrolysis-resistant GTP analogue 5'-guanylylimidodiphosphate (GppNHp) caused significant activation of the enzyme by ∼156% under conditions in which stimulation rather than inhibition of the enzyme was favored. Tubulin-GppNHp activated isoproterenol-sensitive adenylyl cyclase, potentiated forskolin-stimulated activity of the enzyme, and reduced agonist binding affinity for β-adrenergic receptors. When tubulin, polymerized with the hydrolysis-resistant photoaffinity GTP analogue [³²P] P ³(4-azidoanilido)- P ¹-5'-GTP ([³²P]AAGTP), was incubated with cerebral cortex membranes, AAGTP was transferred from tubulin to G_sα as well as G_iα. These results suggest that, in rat cerebral cortex membranes, the tubulin dimer participates in the stimulatory regulation of adenylyl cyclase by transferring guanine nucleotide to G_sα, as well as affecting the G_i-mediated inhibitory pathway.     

Cannabinoid signalling

After their discovery, the two known cannabinoid receptors, CB(1) and CB(2), have been the focus of research into the cellular signalling mechanisms of cannabinoids. The initial assessment, mainly derived from expression studies, was that cannabinoids, via G(i/o) proteins, negatively modulate cyclic AMP levels, and activate inward rectifying K(+) channels. Recent findings have complicated this assessment on different levels: (1) cannabinoids include a wide range of compounds with varying profiles of affinity and efficacy at the known CB receptors, and these profiles do not necessarily match their biological activity; (2) CB receptors appear to be intrinsically active and possibly coupled to more than one type of G protein; (3) CB receptor signalling mechanisms are diverse and dependent on the system studied; (4) cannabinoids have other targets than CB receptors. The aim of this mini review is to discuss the current literature regarding CB receptor signalling pathways. These include regulation of adenylyl cyclase, MAP kinase, intracellular Ca(2+), and ion channels. In addition, actions of cannabinoids that are not mediated by CB(1) or CB(2) receptors are discussed.     

Dual Effects of Anandamide on NMDA Receptor-Mediated Responses and Neurotransmission

Abstract: Anandamide is an endogenous ligand of cannabinoid receptors that induces pharmacological responses in animals similar to those of cannabinoids such as Δ⁹-tetrahydrocannabinol (THC). Typical pharmacological effects of cannabinoids include disruption of pain, memory formation, and motor coordination, systems that all depend on NMDA receptor mediated neurotransmission. We investigated whether anandamide can influence NMDA receptor activity by examining NMDA-induced calcium flux (ΔCa²⁺_NMDA) in rat brain slices. The presence of anandamide reduced ΔCa²⁺_NMDA and the inhibition was disrupted by cannabinoid receptor antagonist, pertussis toxin treatment, and agatoxin (a calcium channel inhibitor). Whereas these treatments prevented anandamide inhibiting ΔCa²⁺_NMDA, they also revealed another, underlying mechanism by which anandamide influences ΔCa²⁺_NMDA. In the presence of cannabinoid receptor antagonist, anandamide potentiated ΔCa²⁺_NMDA in cortical, cerebellar, and hippocampal slices. Anandamide (but not THC) also augmented NMDA-stimulated currents in Xenopus oocytes expressing cloned NMDA receptors, suggesting a capacity to directly modulate NMDA receptor activity. In a similar manner, anandamide enhanced neurotransmission across NMDA receptor-dependent synapses in hippocampus in a manner that was not mimicked by THC and was unaffected by cannabinoid receptor antagonist. These data demonstrate that anandamide can modulate NMDA receptor activity in addition to its role as a cannabinoid receptor ligand.     

Long-Term Effect of Forskolin on the Activation of Adenylyl Cyclase in Astrocytes

Abstract: Long-term (48-h) forskolin treatment of rat astroglial cells led to a slight decrease (30–40%) in the response to isoproterenol, vasoactive-intestinal peptide, guanyl 5'-(βγ-imido)diphosphate, guanosine 5'- O -(3-thiotriphosphate) [GTP(S)], and AIF₄⁻ in crude membrane fractions. In contrast, the acute stimulatory effect of forskolin was increased by 1.25–1.5-fold. These two opposite effects of forskolin were mediated by a cyclic AMP-dependent mechanism. No changes in G_sα, G_iα, or Gβ protein levels could be determined by immunoblotting using specific antisera. No significant differences were observed in the ability of G proteins extracted from control and forskolin-treated cells to reconstitute a full adenylyl cyclase activity in membranes from S49 cyc⁻ cells, lacking G_sα protein. G_sα proteins were detected in two pools of membranes, one in the heavy sucrose fractions and the other in light sucrose fractions. Forskolin treatment of the cells shifted G_sα protein toward the light-density membranes. We did not find any significant change in the distribution of adenylyl cyclase. In contrast to the decreased stimulation of adenylyl cyclase activity by agonists acting via G_sα, observed in the crude membrane fraction, the responses of adenylyl cyclase to forskolin as well as to GTP(S) were increased in the purified plasma membrane fractions. These results may indicate that sensitization of the catalyst appears to be the dominant component in the astroglial cell response to long-term treatment by forskolin.     

Molecular Cloning and Characterization of a Lobster Gαs Protein Expressed in Neurons of Olfactory Organ and Brain

Abstract: We have isolated from an American lobster ( Homarus americanus ) olfactory organ cDNA library a clone, lobGα_s, with >70% identity to mammalian and arthropod Gα_s sequences. In genomic Southern blots, a fragment of lobGα_s detected only one band, suggesting the lobsters have a single Gα_s gene. In brain and olfactory organ, lobGα_s mRNA was expressed predominantly in neurons, including many of the neuronal cell body clusters of the brain. Gα_s protein was also expressed broadly, appearing on western blots as a band of 51.8 kDa in brain, eyestalk, pereiopod, dactyl, tail muscle, olfactory organ, and aesthetasc hairs. These results suggest that lobGα_s plays a role in a wide variety of signal transduction events. Its presence in the olfactory aesthetasc hairs, which are almost pure preparations of the outer dendrites of the olfactory receptor neurons, and the expression of lobGα_s mRNA in the olfactory receptor neurons of the olfactory organ indicate that lobGα_s may mediate olfactory transduction. That virtually all ORNs express lobGα_s mRNA equally predicts that hyperpolarizing odor responses mediated by cyclic AMP are a property of all lobster olfactory receptor neurons.