Membrane properties of identified guinea-pig paraventricular neurons and their response to an opioid mu-receptor agonist: evidence for an increase in K+ conductance

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.

Cellular and synaptic adaptations mediating opioid dependence

Although opioids are highly effective for the treatment of pain, they are also known to be intensely addictive. There has been a massive research investment in the development of opioid analgesics, resulting in a plethora of compounds with varying affinity and efficacy at all the known opioid receptor subtypes. Although compounds of extremely high potency have been produced, the problem of tolerance to and dependence on these agonists persists. This review centers on the adaptive changes in cellular and synaptic function induced by chronic morphine treatment. The initial steps of opioid action are mediated through the activation of G protein-linked receptors. As is true for all G protein-linked receptors, opioid receptors activate and regulate multiple second messenger pathways associated with effector coupling, receptor trafficking, and nuclear signaling. These events are critical for understanding the early events leading to nonassociative tolerance and dependence. Equally important are associative and network changes that affect neurons that do not have opioid receptors but that are indirectly altered by opioid-sensitive cells. Finally, opioids and other drugs of abuse have some common cellular and anatomical pathways. The characterization of common pathways affected by different drugs, particularly after repeated treatment, is important in the understanding of drug abuse.

Quantitative opioid withdrawal signs in rats: effects exerted by clothiapine administration

An opioid withdrawal syndrome, which causes alteration of several physiological signs, was induced in rats by repeated morphine administration and final naloxone injection. The aim of this study was prevention of the altered physiological profiles by utilising clothiapine, which is capable of affecting fecal and urinary excretion, rectal temperature, pain threshold levels and salivatory behaviour. Morphine was administered in three daily intraperitoneal (ip) injections for 4 days at doses of 9, 16 and 25 mg/kg (d 1), 25, 25 and 50 mg/kg (d 2), 50, 50 and 50 mg/kg (d 3) and 50, 50 and 100 mg/kg (d 4). Naloxone was injected (30 mg/kg) ip 180 min after the last morphine injection. Clothiapine was administered orally 0.7, 2 and 6 mg/kg 2 hours before the naloxone administration. Signs such as fecal and urine excretion, rectal temperature and latency times to thermal stimulus salivation, jumping and wet dog shakes were affected in different ways by morphine, naloxone, clothiapine and combination of them. Notably the administration of clothiapine in rats receiving morphine and naloxone decreased the intensity of certain withdrawal symptoms, such as altered excretion of feces, temperature values, salivation, jumping and wet dog shakes behaviour, and elevated the nociceptive threshold values. The effects exhibited by clothiapine administration may be explained through its antimuscarinic, antiadrenergic and antidopaminergic activities interfering with the mechanisms involved in the regulation of these previously mentioned withdrawal symptoms. The use of this drug is thus suggested as a possible control of the acute phase of opioid withdrawal in heroin addicts.

Kappa-selective agonists decrease postsynaptic potentials and calcium components of action potentials in the supraoptic nucleus of rat hypothalamus in vitro

To investigate the effects of the endogenous kappa-receptor agonists dynorphin and leumorphin on neurons of the supraoptic nucleus in the rat hypothalamus, intracellular recordings were made from 62 supraoptic neurons in slice preparations. Bath application of dynorphin and leumorphin at 10(-7) M to 3 x 10(-6) M decreased the spontaneous firing rate with slight hyperpolarization of the membrane potential (-3.8 +/- 0.5 mV, mean +/- S.E.M.) but did not detectably change input resistance. The inhibitory effects were blocked by the relatively selective kappa-antagonist MR-2266. The synthetic kappa-receptor agonist U-50,488H had similar inhibitory effects on supraoptic neurons. Postsynaptic potentials evoked by electrical stimulation dorsal or dorsolateral to the supraoptic nucleus were suppressed by dynorphin and leumorphin. Morphine and [D-Ala, D-Leu]enkephalin, which are relatively selective to mu- and delta-receptors, respectively, influenced the postsynaptic potentials less. Dynorphin and leumorphin also decreased the duration of action potentials that were prolonged by either bath application of tetraethylammonium chloride at 5-10 mM or intracellular injection of Cs ions from the recording electrodes which were filled with 3 M cesium citrate. The prolongation was blocked by 1 mM MnCl2 and 2 mM CoCl2, which suggested that the components were due to voltage-dependent Ca2+ influx. The results suggest that endogenous kappa-receptor agonists inhibit neurosecretory cells of the supraoptic nucleus to suppress synaptic events and Ca2+ components of action potentials.

Endogenous opiates: 1993

This paper is the sixteenth installment of our annual review of research concerning the opiate system. It is restricted to papers published during 1993 that concern the behavioral effects of the endogenous opiate peptides, and does not include papers dealing only with their analgesic properties. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; development; immunological responses; and other behaviors.