Fluoxetine elevates allopregnanolone in female rat brain but inhibits a steroid microsomal dehydrogenase rather than activating an aldo-keto reductase.

BACKGROUND AND PURPOSE: Fluoxetine, a selective serotonin reuptake inhibitor, elevates brain concentrations of the neuroactive progesterone metabolite allopregnanolone, an effect suggested to underlie its use in the treatment of premenstrual dysphoria. One report showed fluoxetine to activate the aldo-keto reductase (AKR) component of 3α-hydroxysteroid dehydrogenase (3α-HSD), which catalyses production of allopregnanolone from 5α-dihydroprogesterone. However, this action was not observed by others. The present study sought to clarify the site of action for fluoxetine in elevating brain allopregnanolone. EXPERIMENTAL APPROACH: Adult male rats and female rats in dioestrus were treated with fluoxetine and their brains assayed for allopregnanolone and its precursors, progesterone and 5α-dihydroprogesterone. Subcellular fractions of rat brain were also used to investigate the actions of fluoxetine on 3α-HSD activity in both the reductive direction, producing allopregnanolone from 5α-dihydroprogesterone, and the reverse oxidative direction. Fluoxetine was also tested on these recombinant enzyme activities expressed in HEK cells. KEY RESULTS: Short-term treatment with fluoxetine increased brain allopregnanolone concentrations in female, but not male, rats. Enzyme assays on native rat brain fractions and on activities expressed in HEK cells showed fluoxetine did not affect the AKR producing allopregnanolone from 5α-dihydroprogesterone but did inhibit the microsomal dehydrogenase oxidizing allopregnanolone to 5α-dihydroprogesterone. CONCLUSIONS AND IMPLICATIONS: Fluoxetine elevated allopregnanolone in female rat brain by inhibiting its oxidation to 5α-dihydroprogesterone by a microsomal dehydrogenase. This is a novel site of action for fluoxetine, with implications for the development of new agents and/or dosing regimens to raise brain allopregnanolone.

Temporal effects of dehydroepiandrosterone sulfate on memory formation in day-old chicks.

Dehydroepiandrosterone sulfate (DHEAS) has been shown to enhance memory retention in different animal models and in various learning paradigms. In the present study, we investigated the effect of peripherally administered DHEAS on the acquisition, consolidation and retention of memory using a weak version of the one-trial passive avoidance task in day-old chicks. Intraperitoneally administered DHEAS (20 mg/kg) either 30 min before or 30 min and 4.5 h after training on the weakly aversive stimulus, enhanced recall at 24 h following training, suggesting a potentiation of not only the acquisition but also the early and late phases of memory consolidation. In contrast, when DHEAS was administered at 30 min prior to the 24 h retention test there was no memory enhancement, indicating a lack of effect on memory retrieval. Memory recall was unaltered when DHEAS was administered at 30 min before training in a control group trained on a strongly aversive stimulus, confirming memory-specific effects. Interestingly, the memory enhancement appeared to be sex-specific as male chicks showed higher recall than females. These findings provide further evidence that DHEAS enhances memory and may be involved in the temporal cascade of long-term memory formation.

Identification of neuroactive steroids and their precursors and metabolites in adult male rat brain.

Steroids in the brain arise both from local synthesis and from peripheral sources and have a variety of effects on neuronal function. However, there is little direct chemical evidence for the range of steroids present in brain or of the pathways for their synthesis and inactivation. This information is a prerequisite for understanding the regulation and function of brain steroids. After extraction from adult male rat brain, we have fractionated free steroids and their sulfate esters and then converted them to heptafluorobutyrate or methyloxime-trimethylsilyl ether derivatives for unequivocal identification and assay by gas chromatography analysis and selected ion monitoring mass spectrometry. In the free steroid fraction, corticosterone, 3alpha,5alpha-tetrahydrodeoxycorticosterone, testosterone, and dehydroepiandrosterone were found in the absence of detectable precursors usually found in endocrine glands, indicating peripheral sources and/or alternative synthetic pathways in brain. Conversely, the potent neuroactive steroid 3alpha,5alpha-tetrahydroprogesterone (allopregnanolone) was found in the presence of its precursors pregnenolone, progesterone, and 5alpha-dihydroprogesterone. Furthermore, the presence of 3beta-, 11beta-, 17alpha-, and 20alpha-hydroxylated metabolites of 3alpha,5alpha-tetrahydroprogesterone implicated possible inactivation pathways for this steroid. The 20alpha-reduced metabolites could also be found for pregnenolone, progesterone, and 5alpha-dihydroprogesterone, introducing a possible regulatory diversion from the production of 3alpha,5alpha-tetrahydroprogesterone. In the steroid sulfate fraction, dehydroepiandrostrone sulfate was identified but not pregnenolone sulfate. Although pharmacologically active, identification of the latter appears to be an earlier methodological artifact, and the compound is thus of doubtful physiological significance in the adult brain. Our results provide a basis for elucidating the origins and regulation of brain steroids.

Lymphoscintigraphy and intraoperative lymphatic mapping of sentinel lymph nodes in melanoma patients.

Identification of sentinel lymph nodes (SLNs) using lymphoscintigraphy, the blue dye technique and intraoperative lymphatic mapping with a gamma-detecting probe has become the standard of care in diagnosing and treating melanoma. Numerous clinical studies have proven the reliability of predicting the histology of remaining lymph nodes in the lymphatic basin from the histologic evaluation of the SLNs. Technical and clinical factors presented in this paper have been shown to increase the accuracy of localization of SLNs. The nuclear medicine technologist shares a vital role in the radiopharmaceutical preparation and administration for preoperative lymphoscintigraphy and intraoperative lymphatic mapping in patients with melanoma.

Technical considerations for acquiring and processing indium-111 capromab pendetide images.

A diagnostic quality 111In capromab pendetide study depends on parameters such as the quality control of the camera, thorough patient preparation, adequate imaging time and accurate computer processing. Comparisons of different patient preparation methods, imaging times, and camera and processing parameters were evaluated to provide high-quality 111In capromab pendetide images and to develop acquisition and processing parameters for 111In capromab pendetide imaging. SPECT images provide the best views of metastatic pelvic nodal involvement. Volume rendered three-dimensional registration best differentiates between normal vasculature and metastatic disease. Optimal acquisition parameters for delayed imaging included 128 x 128 matrix and 65 sec/step. The LFOV dual-head SPECT camera required only one SPECT acquisition that encompassed both the pelvis and abdomen. Planar and SPECT positioning was critical in evaluating questionable lymph nodes. In processing these images, the most diagnostic results were obtained with a three-dimensional low-pass post filter. The most effective patient preparation consisted of an oral cathartic, enema and catheterization when needed.

Brain neurosteroids during the mouse oestrous cycle.

Concentrations of the neuroactive steroid 3alpha,5alpha-tetrahydroprogesterone (TH PROG or allopregnanolone) and its precursors progesterone (PROG) and 5alpha-dihydroprogesterone (DH PROG) have been measured in mouse brain throughout the oestrous cycle. Plasma PROG concentrations were also measured for comparison. At each stage, circadian fluctuations were found in the concentrations of brain PROG and its metabolites. Such fluctuations were greater than those attributable to any particular stage of the oestrous cycle. Over the entire cycle, a significant correlation was found between brain TH PROG (or DH PROG) and PROG concentrations but not between brain TH PROG (or DH PROG) and plasma PROG concentrations. There was also no correlation between endogenous TH PROG (or DH PROG) and activity of the 5alpha-reductase converting 3H-PROG to 3H-DH PROG in whole brain homogenates. Concentrations of another neuroactive steroid, pregnenolone sulphate (PREG S), in the brain during the oestrous cycle were in phase with plasma PROG but not brain PROG concentrations. Our results indicate that circadian and ovarian influences on the concentrations of PROG and its metabolite TH PROG in female whole mouse brain are caused predominantly by changes in the supply of PROG from within the tissue, whatever the contribution of peripheral sources.

Interactions of glycine and strychnine with their receptor recognition sites in mouse spinal cord.

Interactions between the inhibitory neurotransmitter glycine and its receptor antagonist strychnine have been studied in mouse spinal cord membranes and both agents employed to protect against residue selective protein modifying reagents in order to identify contact residues for ligand binding. Glycine was found to behave as a full competitive inhibitor of [3H]-strychnine binding, provided that precautions were taken to prevent radioligand binding to the glass-fibre filters used to terminate the assays. Hill coefficients for the glycine inhibition of [3H]-strychnine binding were not significantly different from one, indicating a lack of cooperative interactions. For the protection experiments, N-bromosuccinimide, tetranitromethane, diethylpyrocarbonate and 2,3-butanedione were used under conditions selective for tryptophan, tyrosine, histidine and arginine residues, respectively. Of these reagents, N-bromosuccinimide, tetranitromethane and diethylpyrocarbonate caused a decrease in total [3H]-strychnine binding without affecting the ability of unlabelled strychnine to compete. In contrast, the same reagents disrupted the ability of glycine to inhibit [3H]-strychnine binding. The presence of either excess glycine (10(-2) M) or strychnine (10(-4) M) during the above treatments was found to prevent the decrease in total and strychnine-specific [3H]-strychnine binding. However, only in the case of diethylpyrocarbonate treatment were both agonist and antagonist able to protect against the loss of glycine-specific [3H]-strychnine binding. The reagent 2,3-butanedione caused an increase in total and strychnine-specific [3H]-strychnine binding (which we have shown elsewhere to be at a site unrelated to the inhibitory glycine receptor). When the above protein modifying reagents were applied under the same conditions to specific strychnine binding antibodies, all four caused significant decreases in subsequent [3H]-strychnine binding. Strychnine was found to afford significant protection of the antibodies against N-bromosuccinimide, tetranitromethane and 2,3-butanedione, but not against diethylpyrocarbonate. Our results suggest that glycine and strychnine compete at overlapping but conformationally distinct sites on the receptor. Tyrosine, tryptophan, histidine and arginine residues are implicated as strychnine contact residues with a shared role for histidine in the recognition of glycine.

Evaluation of animal welfare by the self-expression of an anxiety state.

Although mental well-being has long been accepted as an important aspect of animal welfare, the subjective feelings of farm or laboratory animals are regarded as lying beyond the scope of scientific enquiry. We now report that pharmacological conditioning of pigs with a drug, pentylenetetrazole, known to induce anxiety in man, permits investigation of the presence or absence of this psychological state during exposure to a variety of environmental stimuli encountered during normal husbandry. Such pharmacological conditioning therefore provides a valuable means to assess and improve elements of animal welfare and should be applicable to other species that show operant behaviour.

Metabolism of progesterone in mouse brain.

Incubation of whole mouse brain homogenate with [3H]progesterone resulted in two metabolites: the 5 alpha-reduced product, 5 alpha-pregnane-3,20-dione and another metabolite at a 3-fold greater yield. This differed from rat brain, which produced predominantly the 5 alpha-reduced metabolite under the same conditions. Subcellular fractionation of mouse brain demonstrated a particulate location for the 5 alpha-reduction of progesterone and a cytosolic location for the production of the unknown major metabolite. Treatment of this unknown metabolite with chromium trioxide resulted in a reconversion to progesterone, indicating the presence of a hydroxyl at position 3 or 20. Comparison of the chromatographic behaviour of the unknown metabolite with that of authentic progesterone derivatives suggested that this metabolite corresponds to 20-hydroxy-4-pregnene-3-one.

A behavioural and pharmacological evaluation of the discriminative stimulus induced by pentylenetetrazole in the pig.

The anxiogenic nature of the interoceptive discriminative stimulus induced by pentylenetetrazole (PTZ) was investigated by examining the discriminatory behaviour of PTZ conditioned pigs during a conditioned emotional response (CER). A CER was induced in a nonoperant situation, by pairing a tone stimulus with the application of a mild, non-injurious electric shock. Subsequent presentation of the conditioned tone stimulus alone produced a generalisation to the PTZ cue. This generalisation of the conditioned emotional state (CES) to the PTZ cue was antagonised by pretreatment with diazepam (0.5 mg/kg, PO; 30 min). The PTZ stimulus was also antagonised by diazepam (0.5 mg/kg, PO; 30 min) but not by an anticonvulsant dose of ethosuximide (30 mg/kg, PO; 1-3 h), providing further confirmation of the anxiogenic nature of the PTZ cue. Our results demonstrate the validity of the PTZ discrimination paradigm in pigs as a test of anxiety.

The detection of changes in psychological state using a novel pharmacological conditioning procedure.

Using a novel pharmacological conditioning procedure, pigs were conditioned to discriminate the effects of a subconvulsant dose of the anxiogenic drug pentylenetetrazole (PTZ; 2.8-10 mg/kg, i.v.) from saline. The operant chamber provided two levers at which pigs were trained to press at a fixed ratio of 20 presses per food reward (FR 20). The animals were conditioned to select both levers alternately following saline treatment and to select one lever only following PTZ treatment. This procedure enabled the onset and offset of the PTZ stimulus to be detected within single test sessions; infusion of PTZ to animals already selecting both levers alternately after a saline pretreatment induced a period of response exclusive to the PTZ lever followed by a return to an alternation of lever selection response. The ability of the novel procedure to detect the time course of the drug cue should improve future evaluations of the psychological states induced by centrally acting drugs. With PTZ as the training drug, the novel procedure presents a valuable means to study the neurobiology of anxiety.

Fluctuations in responses to diazepam during the oestrous cycle in the mouse.

Administration of diazepam (0.28 mg/kg, IP; 60 min) to male mice or to female mice at oestrus or dioestrus increased the number of transitions made between the light and dark chambers of a test apparatus, a presumed anxiolytic action. However, the same dose of diazepam had no effect on light/dark transitions at late dioestrus, proestrus, or metoestrus II. At metoestrus I, this test dose of diazepam induced a decrease in the number of light/dark transitions and significant changes in other test parameters indicative of an increase in fearfulness or light aversion. Concentrations of diazepam in the brain after intraperitoneal injection were not influenced by the stage of the oestrous cycle, suggesting that the observed changes in responses to diazepam reflect changes in sensitivity to this drug rather than alterations in distribution or metabolism. The results indicate a physiological influence of ovarian steroid hormones on sensitivity to the benzodiazepine tranquilisers.

Polyclonal antibodies to the glycine receptor antagonist strychnine.

Polyclonal antibodies have been raised in rabbits against the glycine receptor antagonist strychnine, coupled through a 2-amino substituent to the antigenic protein key-hole limpet haemocyanin. Strychnine binding of the predominantly immunoglobulin G (IgG) class of antibodies was measured by incubation with [3H]strychnine, followed by adsorption of IgG onto Staphylococcus aureus cells and filtration through glass-fibre filters under vacuum. Only strychnine and structurally related alkaloids or derivatives were able to inhibit [3H]strychnine binding to the IgG. A significant rank correlation was found between the potencies of these compounds to inhibit [3H]strychnine binding to the antibodies and to the glycine receptor in mouse spinal cord membranes. In contrast, preincubation of strychnine antibodies with a variety of ligands at other neurotransmitter, drug, or hormone receptors in the CNS (at 10(-4) M) failed to inhibit binding significantly. The failure of glycine to inhibit strychnine antibody binding is consistent with previous suggestions that the recognition sites for this amino acid on the CNS receptor may be conformationally distinct from those for the antagonist alkaloid. Strychnine antibodies may now help in the identification and purification of possible endogenous ligands at this alkaloid binding site in the CNS.

Polyclonal antibodies to agonist benzodiazepines.

Benzodiazepine-binding, immunoglobulin G class antibodies have been raised in three rabbits immunised with a conjugate of kenazepine coupled to keyhole limpet haemocyanin. The antibodies were assayed by [3H]flunitrazepam binding, followed by adsorption onto Staphylococcus aureus cells. Measurement of the rates of association and dissociation of [3H]flunitrazepam binding, together with saturation analysis of equilibrium binding, revealed varying degrees of heterogeneity in the affinity constants of the three rabbit antisera (equilibrium KD values 0.18 to 4.13 nM at 20-22 degrees). Specificity of the antibodies was investigated by testing a wide variety of compounds (at concentrations of up to 10-100 microM) for their ability to inhibit [3H]flunitrazepam binding. Only benzodiazepines known to act as agonists at their receptor sites in the central nervous system (CNS) caused an inhibition of binding. The rank orders of the IC50 values of these drugs for inhibition of [3H]flunitrazepam binding to IgG from two out of the three rabbits correlated significantly with that previously published for displacement of CNS receptor binding. The agonist beta-carboline derivative ZK 93423, the anxiolytic cyclopyrrolones suriclone and zopiclone and the purines inosine and hypoxanthine all failed to inhibit antibody binding, supporting previous suggestions that these drugs may bind at non-benzodiazepine recognition sites on the CNS receptor. The antibodies described are expected to provide useful reagents for raising anti-idiotypic antibodies directed against the CNS receptor and for the identification and purification of possible endogenous benzodiazepine receptor agonists in the CNS.

On the location of gamma-aminobutyrate and benzodiazepine receptors in the cerebellum of the normal C3H and Lurcher mutant mouse.

Binding of gamma-aminobutyrate and benzodiazepine receptor ligands has been studied in the cerebellum of adult normal (C3H) and Lurcher mutant mice. The adult mutant has lost all Purkinje cells and more than 90% of the granule cells in the cerebellar cortex. When compared with their normal littermates Lurcher mice displayed large decreases in the number of high-affinity binding sites for [3H]muscimol, a synaptic gamma-aminobutyrate receptor ligand, in washed cerebellar homogenates. This observation was consistent with the extensive loss of gamma-aminobutyrate receptive Purkinje and granule cells from the Lurcher cerebellum. However, specific binding of the benzodiazepine-receptor ligand [3H]flunitrazepam to Lurcher cerebellum remained unchanged. Indeed quantitative autoradiography, employing [3H]flunitrazepam as a photoaffinity label, showed no significant differences in the density of labelling between Lurcher and normal littermate mice in any region of the cerebellum. These benzodiazepine binding sites in washed homogenates or tissue sections displayed a gamma-aminobutyrate-induced enhancement of [3H]flunitrazepam binding which occurred to the same extent in both Lurcher and normal cerebellum, a facilitatory effect which could be blocked by the addition of bicuculline methobromide. Our results suggest that a large proportion of the high-affinity, specific benzodiazepine binding sites in mouse cerebellum are not coupled to the synaptic gamma-aminobutyrate receptors thought to be labelled by high affinity [3H]muscimol binding. Further, that benzodiazepine binding sites do not appear to be enriched on either the soma or dendrites of Purkinje cells, as has been suggested from previous studies. Investigations at the electron microscope level are now required to elucidate the cellular location of benzodiazepine binding sites in the cerebellar cortex and to examine whether or not they are likely to be exposed to gamma-aminobutyrate in vivo.

Autoradiography of benzodiazepine receptor binding in the central nervous system of the normal C57BL6J mouse.

[3H]flunitrazepam has been used as a photoaffinity label for the specific, clonazepam-displaceable 1,4-benzodiazepine binding sites in sections of normal C57BL6J mouse brain and spinal cord. Binding was visualized by light microscope autoradiography and quantified by a simple microdensitometric procedure. Specific flunitrazepam binding was seen to be highest in the colliculi, cerebral cortex, hippocampal formation, interpeduncular nucleus, mamillary body, hypothalamus, olfactory tubercle, and in the molecular layer and deep nuclei of the cerebellum. The distribution of specific flunitrazepam binding sites in mouse brain and spinal cord is discussed in terms of the known actions of the benzodiazepines.

Changes in benzodiazepine receptor binding as seen autoradiographically in the central nervous system of the spastic mouse.

Quantitative light-microscope autoradiography has been used to compare the specific, clonazepam-displaceable binding of [3H]flunitrazepam, a photoaffinity label for the 1,4-benzodiazepine receptor, in different regions of the brain and spinal cord of spastic mice and their unaffected littermates. Specific binding of [3H]flunitrazepam in the central nervous system of the spastic mouse showed significant increases in the anterior colliculus and pretectal area and in all laminae of the grey matter in the lumbar spinal cord. These results confirm homogenate binding assays suggesting an increased number of benzodiazepine receptors in the spinal cord of the spastic mouse. Possible sites are therefore provided at which disorders of function could arise, associated with changes seen at the gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex in spinal cord homogenates from the mutant mouse spastic.