William A. Hewlett

Binding of 3H-β-endorphin to rat brain membranes: Characterization of opiate properties and interaction with ACTH

The binding of tritiated beta-endorphin (3H-beta-EP) to brain homogenates is described. This has been difficult to achieve due to the lack of availability of 3H-beta-EP and to technical difficulties associated with high non-specific binding of beta-EP. We now report that 3H-beta-EP binding is saturable, stereospecific, has high affinity and is inhibited by sodium. Its dissociation rate is ten-fold longer than that of naloxone. Its regional distribution exhibits interesting differences from naloxone and enkephalin binding. ACTH1-24 appears to displace it more effectively than it displaces 3H-naloxone. The results are discussed in terms of multiple transmitter systems and the multiple opiate receptor hypothesis.

Clomipramine, clonazepam, and clonidine treatment of obsessive-compulsive disorder

Serotonergic reuptake inhibitors have been the primary medications for treatment of obsessivecompulsive disorder (OCD); however, other serotonergic and α2-adrenergic medications also have been reported to reduce obsessive-compulsive symptoms. In this study, we compare three medications with reported efficacy in OCD to a control medication, diphenhydramine, a medication without theoretical or demonstrated treatment benefit. The three active medications were clomipramine, a serotonergic reuptake inhibitor; clonazepam, a benezodiazepine with putative serotonergic properties; and clonidine, an α2-adrenergic agonist. Twenty-eight subjects with DSM-III-R diagnosis of OCD rotated through 6-week trials of each of the four medications in a randomized, double-blind, multiple crossover protocol. Clomipramine and clonazepam were both effective relative to the control medication in reducing OCD symptoms. There was a significant cross-response between these two medications; however 40% of subjects failing clomipramine trials had a clinically significant response to clonazepam treatment. The control medication, diphenhydramine, itself produced a significant decrement in symptoms, whereas clonidine was ineffective in reducing OCD symptoms. Clonazepam improvement was unrelated to changes in anxiety and occurred early in treatment. Clonazepam was significantly more effective than the other medications during the first 3 weeks of treatment. The results confirm the efficacy of clomipramine in the treatment of OCD and suggest that clonazepam might be a useful alternative treatment for patients with this disorder. (J Clin Psychopharmacol 1992; 12:420–430)

Fenfluramine stimulation of prolactin in obsessive-compulsive disorder

The success of serotonergic reuptake inhibitors in the treatment of obsessive-compulsive disorder (OCD) has suggested that serotonergic neurotransmission may play a role in the pathogenisis of this disorder. Prolactin responses to a 60-mg oral dose of fenfluramine in 26 medication-free patients with a DSM-III-R diagnosis of OCD were compared with those of 20 controls subjects. Fenfluramine produced a significant elevation of prolactin levels in both OCD patients and controls. Prolactin responses were significantly blunted in OCD patients compared with responses in control subjects. Female subjects in both groups showed greater prolactin responses to fenfluramine than did their male counterparts. There was a significant interaction between sex and the presence of OCD such that female patients had lower prolactin responses than their controls, while the difference between male patients and controls was not significant. Prolactin responses were not correlated with age, weight, drug level, depression, anxiety, or degree of OCD symptoms. The results are consistent with a relative reduction in serotonergic efficacy in the setting of OCD.

Regional interactions of opioid peptides at μ and δ sites in rat brain

Abstract Opiate binding sites in five brain regions were labeled with the μ and δ markers, 3 H-morphine and 3 H-[D-Ala 2 ,D-leu 5 ]enkephalin, respectively. The highest densities of both 3 H-morphine and 3 H-DADLE labeled sites are found in striatum and frontal cortex. Hypothalamus and midbrain contain predominantly 3 H-morphine labeled sites. The selectivity of the opioid peptides [D-Ala 2 ,D-leu 5 ]enkephalin, β-endorphin and dynorphin(1–13) for the two opiate sites was investigated by comparing the potency of these unlabeled compounds against the μ and δ markers in different brain regions. This determination has the effect of controlling for the breakdown of peptides within each region. While the enkephalin analogue shows a preference for the δ binding site and β-endorphin is more nearly equipotent towards the two binding sites, dynorphin(1–13) shows a high affinity and selective preference for the μ binding site over the δ site. The potency of the opioid peptides in displacing the μ and δ markers varies from region to region according to the relative densities of the two opiate binding site populations.

Opioid peptides as neuroregulators: Potential areas for the study of genetic-behavioral mechanisms

The opioid peptides have been related to behavior in both animal and human studies. Further investigation can be anticipated which could lead to the elucidation of genetic controls over enzymes which process these peptides and the receptors upon which the peptides act. The enzymes, both synthetic and degradative, can lead to the formation of different forms of the opiate peptides. Differential control of these enzymes or of the multiple forms of opiate receptors could lead to discrete changes in opiate status and subsequent behavioral changes. Conversely, genetically regulated behavioral modification could also lead secondarily to opiate changes.

CHARACTERIZATION OF 3H-β-ENDORPHIN BINDING IN RAT BRAIN

Summary 3 H-β-Endorphin (βEP) binding was characterized in rat brain homogenates. It exhibits many characteristics of opiate binding, including stereospecificity, inhibition by sodium, and displacement by all opiate agonists and antagonists tested. Interesting differences from 3 H-naloxone binding include some discrepancies in the profile of regional distribution and a significantly slower rate of dissociation of βP. Enkephalin and βEP exhibit a 25-fold difference in relative potency depending on which 3 H-Ligand they are competing against. These results may prove useful in exploring differences between subtypes of opiate receptors.

Tritiated ethylketocyclazocine binding in rat brain: Differential distribution of binding sites across brain regions

Abstract In rat brain, 3 H-EKC shows a relative regional distribution of binding which parallels that of 3 H-morphine. Dynorphin(1–13) has a pattern similar to morphine and dissimilar to EKC in displacing the three labels. Dynorphin(1–13) is more potent against 3 H-morphine than against 3 H-EKC across brain regions while β-endorphin competes better against 3 H-EKC.

MULTIPLE OPIATE BINDING SITES IN RAT BRAIN: DIFFERENTIAL DISPLACEMENT OF 3H-NALOXONE BINDING BY DIFFERENT OPIATE LIGANDS

The ability of ethylketocyclazocine methane sulfonate (EKC) and SKF 10,047 (SKF) to displace 3H-naloxone binding was examined in a washed membrane preparation of rat brain. Scatchard analysis of 3H-naloxone binding yields a curvilinear plot which can be resolved into high and low affinity components. Both EKC and SKF displace high affinity naloxone binding but at concentrations up to 10 μM are unble to displace low affinity binding. The low affinity binding is displacable by morphine and naltrexone.

DIFFERENTIAL INTERACTIONS OF DYNORPHIN(1–13), β-ENDORPHIN, AND ENKEPHALIN-RELATED PEPTIDES AT μ AND δ SITES IN DIFFERENT BRAIN REGIONS

Dynorphin-(1–13) shows a selective preference for 3H-morphine-labeled binding sites over those labeled by 3H-[D-ala2, D-leu5]enkephalin (DADLE)