Obese male mice (ob/ob) are normally sensitive to the satiating effect of CCK-8

The ob/ob mouse has a defect in short-term satiety mechanisms because ob/ob mice eat larger meals than leans and have abnormal postprandial behaviors. We suggested that this defect involved a failure to release CCK normally in response to ingested nutrients and/or decreased receptor sensitivity to CCK. McLaughlin and Baile reported that female obese mice were less sensitive to the satiating effect of CCK-8, a result consistent with the hypothesis of decreased receptor sensitivity. To investigate this possibility further, we determined the sensitivity to exogenous CCK-8 of obese and lean male mice. Adult male C57Bl/6J ob/ob and male +/+ controls were injected with CCK-8 (1, 2, 4, and 8 micrograms/kg, IP) 15 min prior to the presentation of solid food (Noyes pellets) after 4.5 hr food deprivation in the dark. Food intake (FI) was measured at 30 min and 150 min. CCK-8 decreased FI during the first 30 min in both obese and lean mice (p less than 0.01). The threshold dose for inhibition of FI was 2 micrograms/kg in obese and 4 micrograms/kg in lean. Since obese mice weighed approximately twice as much as lean mice, their total dose of CCK-8 was equal to that of lean mice. Thus, obese male mice were at least as sensitive to the satiating effect of CCK-8 as lean male mice. These results do not confirm McLaughlin and Baile's result in female mice eating in the light and they suggest that the defect in satiety in obese male mice is not the result of decreased sensitivity of CCK receptors.     

Dysregulation of the Hypothalamus-Pituitary-Adrenal Axis in Male and Female, Genetically Obese (ob/ob) Mice

The autosomal, recessive obesity of ob/ob mice is associated with hypercorticosteronemia and amelioration of most symptoms of obesity following adrenalectomy. Increased adrenocorticotropic hormone (ACTH) secretion has been hypothesized on the basis of several reports of higher pituitary ACTH content in ob/ob mice compared to lean littermates. However, the only measurement of ACTH blood concentration found lower levels in ob/ob mice than in leans suggesting that hypercorticosteronemia might result solely from an enhanced adrenal response to ACTH and also suggesting that the ob/ob's elevated pituitary ACTH content might be due to decreased ACTH secretion rather than increased ACTH synthesis. In our study, basal serum ACTH levels were higher in ob/ob males and females compared to sex-matched lean littermates. Anterior pituitary ACTH synthesis was also elevated as indicated by increased content of ACTH and proopiomelanocortin mRNA in obese mice of both sexes; however hypothalamic corticotropin-releasing factor content was not different in lean and obese mice. Basal serum ACTH and corticosterone (CS) levels showed normal circadian rhythm in both phenotypes and sexes, but the circadian increase in CS level was much greater in obese mice than in leans despite equal serum ACTH increases in the two phenotypes. Ether stress at both peak and trough of the circadian rhythm also stimulated much larger serum CS increases in obese mice even though ACTH increases were again equal in the two phenotypes. Taken together, these results strongly indicate that ob/ob mice have increased synthesis and secretion of pituitary ACTH despite the presence of chronically elevated serum CS. This hyperactivity of the hypothalamo-pituitary-adrenal axis appears to be most pronounced in ob/ob females since pituitary ACTH content was equal in obese males and females despite much higher circulating CS levels in the females. Furthermore, the results also indicate an enhanced response to ACTH by the adrenal cortex of the obese mouse. Thus, ob/ob mice exhibit abnormal hypothalamo-pituitary-adrenal axis function with hyperactivity occurring at the level of pituitary ACTH synthesis/secretion as well as at the level of adrenocortical response to ACTH.     

Increased binding at 5-HT1A, 5-HT1B, and 5-HT2A receptors and 5-HT transporters in diet-induced obese rats

5-Hydroxytryptamine (5-HT, serotonin), synthesized in midbrain raphe nuclei and released in various hypothalamic sites, decreases food intake but the specific 5-HT receptor subtypes involved are controversial. Here, we have studied changes in the regional density of binding to 5-HT receptors and transporters and the levels of tryptophan hydroxylase, in rats with obesity induced by feeding a palatable high-energy diet for 7 weeks. We mapped binding at 5-HT receptor subtypes and transporters using quantitative autoradiography and determined tryptophan hydroxylase protein levels by Western blotting. In diet-induced obese (DiO) rats, specific binding to 5-HT_1A receptors ([³H]8-OH-DPAT) was significantly increased in the dorsal and median raphe by 90% (P<0.01) and 132% (P<0.05), respectively, compared with chow-fed controls. 5-HT_1B receptor binding sites ([¹²⁵I]cyanopindolol) were significantly increased in the hypothalamic arcuate nucleus (ARC) of DiO rats (58%; P<0.05), as were 5-HT_2A receptor binding sites ([³H]ketanserin) in both the ARC (44%; P<0.05) and lateral hypothalamic area (LHA) (121%; P<0.05). However, binding to 5-HT_2C receptors ([³H]mesulgergine) in DiO rats was not significantly different from that in controls in any hypothalamic region. Binding to 5-HT transporters ([³H]paroxetine) was significantly increased (P<0.05) in both dorsal and median raphe, paraventricular nuclei (PVN), ventromedial nuclei (VMH), anterior hypothalamic area (AHA) and LHA of DiO rats, by 47%–165%. Tryptophan hydroxylase protein levels in the raphe nuclei were not significantly different between controls and DiO rats. In conclusion, we have demonstrated regionally specific changes in binding to certain 5-HT receptor subtypes in obesity induced by voluntary overeating of a palatable diet. Overall, these changes are consistent with reduced 5-HT release and decreased activity of the 5-HT neurons. Reduction in the hypophagic action of 5-HT, possibly acting at 5-HT_1A, 5-HT_1B and 5-HT_2A receptors, may contribute to increased appetite in rats presented with highly palatable diet.     

Differential modulation of I(h) by 5-HT receptors in mouse CA1 hippocampal neurons

CA1 pyramidal neurons of the hippocampus express various types of serotonin (5-HT) receptors, such as 5-HT(1A), 5-HT(4) and 5-HT(7) receptors, which couple to Galpha(i) or Galpha(s) proteins and operate on different intracellular signalling pathways. In the present paper we verify such differential serotonergic modulation for the hyperpolarization-activated current I(h). Activation of 5-HT(1A) receptors induced an augmentation of current-induced hyperpolarization responses, while the responses declined after 5-HT(4) receptors were activated. The resting potential of neurons hyperpolarized (-2.3 +/- 0.7 mV) after 5-HT(1A) receptor activation, activation of 5-HT(4) receptors depolarized neurons (+3.3 +/- 1.4 mV). Direct activation of adenylyl cyclase (AC) by forskolin also produced a depolarization. In voltage clamp, the Ih current was identified by its characteristic voltage- and time-dependency and by blockade with CsCl or ZD7288. Activation of 5-HT(1A) receptors reduced I(h) and shifted the activation curve to a more negative voltage by -5 mV at half-maximal activation. Activation of 5-HT(4) and 5-HT(7) receptors increased I(h) and shifted the activation curve to the right by +5 mV. Specific activation of 5-HT(4) receptors by BIMU8 increased membrane conductance and showed an increase in I(h) in a subset of cells, but did not induce a significant alteration in the activation curve. In order to verify spatial differences, we applied BIMU8 selectively to the soma and to the dendrites. Only somatic application induced receptor activation. These data are confirmed by immunofluorescence stainings with an antibody against the 5-HT(4) receptor, revealing receptor expression at the somata of the CA1 region. A similar expression pattern was found with a new antibody against 5-HT(7) receptors which reveals immunofluorescence staining on the cell bodies of pyramidal neurons.     

Increases in alpha-adrenergic receptors in the hypothalamus of the genetically obese mouse (ob/ob)

Despite significantly elevated hypothalamic norepinephrine levels, genetically obese mice (ob/ob) had more hypothalamic alpha-adrenergic receptors than their lean littermates. This receptor increase appeared to be specific to the alpha-receptors in the hypothalamus since no change was found in the number of alpha-receptors in the cortex or in the dopamine and muscarinic receptors in the cortex and striatum.     

Pre- and post-synaptic effects of the 5-HT3 agonist 2-Methyl-5-HT on the 5-HT system in the rat brain

Microiontophoretic applications of 5-HT and of the 5-HT₃ agonist 2-methyl-5-HT produced a current-dependent suppression of firing activity of both hippocampal (CA₁ and CA₃) and cortical neurons in anesthetized rats. Concomitant microiontophoretic applications of the 5-HT₃ antagonists BRL 46470A and S-zacopride, as well as their intravenous injection, did not antagonize the inhibitory effect of 5-HT and 2-methyl-5-HT. In contrast, the 5-HT_1A antagonist BMY 7378, applied by microiontophoresis or administered intravenously, significantly reduced the inhibitory action of 5-HT and 2-methyl-5-HT. The firing activity of dorsal raphe 5-HT neurons was also reduced by 5-HT, 2-methyl-5-HT and the 5-HT_1A agonist 8-OH-DPAT applied by microiontophoresis. While BRL 46470A (0.1 and 1 mg/kg, i.v.) did not antagonize the inhibitory effect of the three 5-HT agonists on 5-HT neuronal firing activity, only that of 8-OH-DPAT was attenuated by the 5-HT_1A antagonist (+) WAY 100135. R-zacopride significantly reduced the duration of suppression of firing activity of CA₃ pyramidal neurons induced by the electrical stimulation of the ascending 5-HT pathway, and this reducing effect was prevented by the three 5-HT₃/5-HT₄ antagonists renzapride, S-zacopride and tropisetron, but not by BRL 46470A. Finally, in in vitro superfusion experiments, both BRL 46470A and S-zacopride antagonized the enhancing action of 2-methyld-HT on the electrically-evoked release of [³H]-5-HT in both rat frontal cortex and hippocampus slices. These findings suggest that, in vivo, the suppressant effect of 2-methyl-5-HT on the firing activity of dorsal hippocampus pyramidal, somatosensory cortical, and dorsal raphe 5-HT neurons is not mediated by 5-HT₃ receptors, but rather by 5-HT_1A receptors. The attenuating effect of R-zacopride on the effectiveness of the stimulation of the ascending 5-HT pathway is not mediated by 5-HT₃ receptors. In contrast, in vitro, the enhancing action of 2-methyl-5-HT on the electrically-evoked release of [³H]5-HT in both frontal cortex and hippocampus slices is mediated by 5-HT₃ receptors. © 1995 Wiley-Liss, Inc.     

Autoradiographic analyses of 5-HT1A and 5-HT2A receptors after social isolation in mice

Social isolation of rodents is used to model human psychopathological processes. In the present study, the effects of intermediate and long term isolation housing on postsynaptic 5-HT_1A and 5-HT_2A receptors were analyzed in male mice housed in groups or isolation for 4 and 12 weeks. [³H]8-OH-DPAT and [³H]ketanserin were used to label 5-HT_1A and 5-HT_2A receptors. Four representative sagittal sections (planes 1–4) were scored by in vitro autoradiography. Whereas after 4 weeks of housing both receptor densities were lowered significantly in isolated mice, after 12 weeks of housing only marginal isolation effects were seen. Intermediate isolation reduced 5-HT_1A receptors especially in the lateral frontal, parietal and entorhinal cortex (−63%), in the lateral CA1–3 and dentate gyrus region of the hippocampus (−68%), in the basolateral, basomedial, central and medial amygdaloid nuclei (between −38 and −66%), and in the hypothalamus (−28%). 5-HT_2A receptors were strongly reduced in the frontal cortex (between −47 and −74%), in the hippocampus (between −47 and −95%), in the striatum (between −66 and −76%), and in the accumbens nucleus (between −59 and −73%) in comparison to group housed control mice. After 12 weeks of isolation in the hippocampus continuously decreased 5-HT_1A receptor densities were demonstrated (between −24 and −61%). But increased 5-HT_2A receptor densities were seen in the lateral striatum (+86%) compared to control mice. Age-dependent effects were also found. After 12 weeks of group housing the 5-HT_1A and 5-HT_2A receptor densities were decreased (between −28 and −54%) in all analyzed brain regions in comparison to 4 weeks of group housing. Isolated animals showed diminished 5-HT_1A receptor densities in the cortex (−14%) and hippocampus (−15%), but increased 5-HT_1A receptor densities in the amygdala (+33%) after 12 weeks. The 5-HT_2A receptor densities were increased in all analyzed regions (between +31 and +96%) after 12 weeks of isolation compared to 4 weeks. To explain these dynamic, time-dependent pattern of isolation-induced changes different regulation processes are supposed regarding 5-HT_1A and 5-HT_2A receptors. Besides metabolism-related adaptation processes also neurotransmitter and hormonal (e.g., glucocorticoid) interactions especially in limbic regions have to be considered.     

Increased beta-endorphin and dynorphin concentrations in discrete hypothalamic regions of genetically obese (ob/ob) mice.

Disturbances in hypothalamic beta-endorphin and dynorphin levels were investigated in non-fasted genetically obese (ob/ob) and homozygous lean mice at 14-15 weeks of age. Eight brain regions were microdissected from fresh, unfixed brain slices, and opioid peptide concentrations were determined in tissue micropunches by radioimmunoassay. A two-fold and five-fold increase in beta-endorphin levels in ob/ob versus lean mice were found in the ventromedial and dorsomedial hypothalamic nuclei respectively. Dynorphin levels were comparable between ob/ob and lean mice in the anterior, lateral, ventromedial and paraventricular hypothalamic areas, but a 5-fold increase in dynorphin concentrations was detected in the dorsomedial hypothalamic nucleus of the ob/ob mouse. These results demonstrate that increased concentrations of beta-endorphin and dynorphin occur in discrete hypothalamic nuclei, which are known to influence food intake and glucose homeostasis. This could signify an important central defect contributing to hyperphagia and glucoregulatory dysfunction in obese mice.     

Sex hormone-dependent desensitization of 5-HT1A autoreceptors in knockout mice deficient in the 5-HT transporter

The serotonin transporter (5-HTT) is the target of most antidepressant drugs, whose therapeutic action is related to their facilitatory influence on 5-HT neurotransmission. In this study, we investigated the functional adaptive properties of 5-HT1A autoreceptors, which regulate serotonergic neuronal firing, in knockout mice deficient in 5-HTT. Neurons of the dorsal raphe nucleus (DRN) were recorded extracellularly under chloral hydrate anaesthesia in male and female knockout 5-HTT mice and their wild-type counterparts. The inhibitory response of DRN neurons to intravenous injection of the 5-HT1A agonist 8-OH-DPAT was dramatically reduced in knockout 5-HTT compared with wild-type mice, especially in females. Changes in 8-OH-DPAT-induced hypothermia and autoradiographic labelling of 5-HT1A sites in the DRN confirmed a greater level of desensitization/down-regulation of 5-HT1A autoreceptors in female than in male knockout 5-HTT mice. After gonadectomy, the functional status of 5-HT1A autoreceptors was unchanged in wild-type mice, whereas in knockout 5-HTT, castrated males exhibited a down-regulation, and ovariectomized females an up-regulation of these receptors, as shown by electrophysiological recording and autoradiographic labelling in the DRN, as well as by changes in 8-OH-DPAT-induced hypothermia. Finally, in gonadectomized knockout 5-HTT mice, treatment with testosterone or estradiol restored the DRN neuronal firing sensitivity to 8-OH-DPAT back to sham control level in males or females, respectively. These data indicate that sexual hormones participate in the mechanisms responsible for the desensitization of 5-HT1A autoreceptors in knockout 5-HTT mice. The differential effects of testosterone and estradiol on 5-HT1A-mediated control of 5-HT neurotransmission might be related to the well-established gender differences in the vulnerability to depression.     

Nitrosative stress and peripheral diabetic neuropathy in leptin-deficient (ob/ob) mice

Nitrosative stress contributes to nerve conduction slowing, thermal hypoalgesia, and impaired nitrergic innervation in animal models of Type 1 diabetes. The role for reactive nitrogen species in Type 2 diabetes-associated neuropathy remains unexplored. This study evaluated the role for nitrosative stress in functional and structural neuropathic changes in ob/ob mice, a model of Type 2 diabetes with mild hyperglycemia and obesity. Two structurally diverse peroxynitrite decomposition catalysts, Fe(III) tetrakis-2-(N-triethylene glycol monomethyl ether)-pyridyl porphyrin (FP15) and Fe(III) tetra-mesitylporphyrin octasulfonate (FeTMPS), were administered to control and 8-week-old ob/ob mice for 3 weeks at the doses of 5 mg kg(-1) day(-1) (FP15) and 5 and 10 mg kg(-1) day(-1) (FeTMPS). The 11-week-old ob/ob mice developed motor nerve conduction velocity (MNCV) and hind-limb digital sensory nerve conduction velocity (SNCV) deficits, thermal hypoalgesia, tactile allodynia, and a remarkable ( approximately 78%) loss of intraepidermal nerve fibers. They also had increased nitrotyrosine and poly(ADP-ribose) immunofluorescence in the sciatic nerve, spinal cord, and dorsal root ganglion neurons. Treatment with two structurally diverse peroxynitrite decomposition catalysts was associated with restoration of normal MNCV and SNCV, and alleviation of thermal hypoalgesia. Tactile response thresholds increased in response to peroxynitrite decomposition catalyst treatment, but still remained approximately 2.7- to 3.2-fold lower compared with non-diabetic controls. Intraepidermal nerve fiber loss was not alleviated by either FP15 or FeTMPS. Nitrotyrosine and poly(ADP-ribose) immunofluorescence in sciatic nerve, spinal cord, and dorsal root ganglia of peroxynitrite decomposition catalyst-treated ob/ob mice were essentially normal. In conclusion, nitrosative stress plays an important role in functional abnormalities associated with large motor, large sensory, and small sensory fiber neuropathy, but not in small sensory nerve fiber degeneration, in this animal model. Peroxynitrite decomposition catalysts alleviate Type 2 diabetes-associated sensory nerve dysfunction, likely by mechanism(s) not involving arrest of degenerative changes or enhanced regeneration of small sensory nerve fibers.     

In vitro H-serotonin (5-HT) synthesis and release in BALBc and C57BL mice. II. Cell body areas

"In vitro" 3H-5-HT and 3H-5-HIAA, newly synthesized from 3H-TRP, are measured in the brainstem, the anterior raphe nuclei and the locus coeruleus of C57BL and BALBc mice. As found for the caudate nucleus and the hippocampus, higher synthesis and release are determined in C57BL than in BALBc, for the locus coeruleus and more globally, for the brainstem. But these differences disappear when the study is carried on the raphe dorsalis and the raphe centralis nuclei. Therefore the serotonergic activity could be independently regulated at the level of cell bodies and at those of terminals. However, the 5-HT metabolism of NRD of BALBc mice could be submitted to a specific autoinhibition which could explain a lower 5-HT synthesis and release at the corresponding terminal level, compared to C57BL.     

In vitro H-serotonin (5-HT) synthesis and release in BALBc and C57BL mice. I. Terminal areas

"In vitro," 3H-5-HT and 3H-5-HIAA newly synthesized from 3H-TRP are measured in the caudate nucleus and the hippocampus of C57BL and BALBc mice. Higher synthesis, utilization and release are to be found in C57BL than in BALBc strain. In the hippocampus of C57BL this higher synthesis is due both to higher tryptophan hydroxylase activity and to higher tryptophan uptake ability. But in the caudate nucleus the initial accumulation of tryptophan is similar in both strains. Finally the two forms of monoamine oxidase (A and B) show also similar activities in both strain. These data will be compared to those obtained at the nerve cell body level in the paper (II).     

Anxiolytic-like effects of 5-HT2 ligands on three mouse models of anxiety

The behavioural effects of 5-HT₂ receptor agonists, 5-HT_2A and 5-HT_2C receptor antagonists were investigated in the mouse four plates test (FPT), light/dark paradigm (L/D) and the elevated plus maze (EPM), in order to elucidate the role of the 5-HT₂ receptor subtypes in these models and to address the inconclusive results previously reported using rat psychopharmacological models. All compounds were administered intraperitoneally 30 min before each test. DOI, a preferential 5-HT_2A agonist (0.5–8 mg/kg) and BW 723C86, a 5-HT_2B agonist (8 and 16 mg/kg) provoked an anxiolytic-like response in the FPT. In the EPM, an anxiolytic-like effect was observed for DOI (0.5, 1 and 2 mg/kg), BW 723C86 (0.5, 4, 8 and 16 mg/kg), RO 60-0175 a 5-HT_2C agonist (4 mg/kg) and the non-selective 5-HT₂ receptor agonist mCPP (0.25 mg/kg.). Ketanserin, a 5-HT_2A/2C non-selective receptor antagonist (0.015 and 0.03 mg/kg), induced an anxiogenic-like effect in the L/D paradigm. The 5-HT_2C antagonists (RS 10-2221, SDZ SER082 and SB 206553) were without effect in all three tests. These behavioural results are indicative of an anxiolytic-like action of 5-HT₂ receptor agonists, an anxiogenic-like effect of 5-HT_2A receptor antagonism, whereas the blockade of 5-HT_2C receptors are without effect in the mouse models studied.     

Endogenous serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels in large regions and in discrete brain areas of C57BL and BALBc mice at three times of the day

The serotoninergic system has been analysed in the brainstem and the forebrain of adult C57BL and BALBc mice. Endogenous 5-HT and 5-HIAA levels have also been measured in the different raphe nuclei and in the caudate nucleus and the hippocampus of these strains, using the micropunch technique and the radioenzymatic method (for 5-HT) and a new radioimmunoassay (for 5-HIAA). This investigation was performed at three times of the day: 9:00 hr; 14:00 hr; 20:00 hr to underline the differences between the strains. Most of the time, higher 5-HT and 5-HIAA levels are found in the brainstem and the raphe nuclei of the BALBc strain compared to C57BL. In the forebrain the differences are reversed, except in the caudate nucleus and the hippocampus where the levels of 5-HT are identical in the two strains. Moreover the 5-HIAA/5-HT ratio shows a higher turn-over of the amine in the C57BL strain.     

Effects of sertraline and citalopram given repeatedly on the responsiveness of 5-HT receptor subpopulations

Summary The effect of repeated treatment (5 and 10 mg/kg,po, twice daily, 14 days) with sertraline and citalopram (antidepressants which selectively inhibit the reuptake of 5-hydroxytryptamine (5-HT)) on the responsiveness of different 5-HT receptors to their agonists, was examined in rats and mice. Sertraline and citalopram (both at a dose 5 and 10 mg/kg) antagonized (the first one more potently) the hypothermia induced in mice by 8-OH-DPAT (a 5-HT_1A agonist), but not the behavioural syndrome induced in rats by this substance. The m-chlorophenylpiperazine-induced hypothermia in mice (a 5-HT_1B effect) was increased by sertraline and citalopram (only in a dose of 10 mg/kg). Both antidepressants, given repeatedly (as well acutely) attenuated exploratory hypoactivity induced in rats by m-chlorophenylpiperazine (a 5-HT_1C effect). L-5-HTP-induced head twitches in mice (5-HT₂ effect) were antagonized dose-dependently by both repeated sertraline and citalopram. Both antidepressants (citalopram only in higher dose) reduced the fenfluramine-induced hyperthermia in rats (5-HT₂ effect).The results indicate that sertraline and citalopram given repeatedly decrease the responsiveness of 5-HT_1A (presynaptic) and 5-HT₂ receptors but increase the responsiveness of 5-HT_1B receptors to respective agonists.     

Contransmitters: differential effects of serotonin (5-HT)-depleting drugs on levels of 5-HT and TRH and their receptors in rat brain and spinal cord

Following codepletion of endogenous serotonin (5-HT, >90%) and thyrotropin-releasing hormone (TRH, 66%) by neonatal treatment with the serotonergic neurotoxin, 5,7-dihydroxytryptamine (DHT), a 33% (n = 12, P < 0.01) increase in specific TRH receptor binding was observed in adult rat spinal cord (SC) homogenates. A 20–21% increase in TRH receptors was also observed in the medulla/pons (MP) (n = 12, P < 0.05) and midbrain (MB) (n = 12, P < 0.02), but no changes were detected in 6 rostral brain regions. The depletion of 5-HT after DHT-treatment was also accompanied by a 34–42% increase in 5-HT₁ binding in the SC, MP and MB. Eadle-Hofstee analysis revealed that the changes in TRH receptor levels observed after DHT-lesions were due to an increase in receptor number rather than any significant changes in receptor affinity. Chronic treatment of adult rats with the 5-HT-depleting drugs, p-chlorophenylalanine (PCPA) and reserpine, produced a 90–97% decrease in 5-HT in the SC, MP and MB and elevated 5-HT₁ binding in any of these tissues. In conclusion, these results have provided further support for the coexistence of 5-HT and TRH in the MP and SC and revealed possible new areas of such colocalization in the MB. Furthermore, these data have demonstrated that only DHT-treatment, as apposed to PCPA or reserpine, can produce long-lasting codepletion of 5-HT and TRH with simultaneous compensatory up-regulation of their receptor systems in the SC and other caudal tissues.     

Differential effects of novel ligands for 5-HT receptor subtypes on nonopioid defensive analgesia in male mice

The effects of a number of 5-HT receptor ligands were examined on nonopioid defensive analgesia in male DBA/2 mice. MDL 73005EF (0.05-1.0 mg/kg), a selective 5-HT1A receptor agonist, potently and dose-dependently inhibited the analgesic consequences of social defeat. CGS 12066B (0.5-10.0 mg/kg) and MK-212 (0.3-10.0 mg/kg), selective agonists for 5-HT1B and 5-HT1C sites, respectively, failed to influence this particular form of adaptive pain inhibition. Two 5-HT2/1C receptor antagonists, ritanserin (0.05-10.0 mg/kg) and ICI 169.369 (0.3-10.0 mg/kg), were also devoid of specific effects upon defensive analgesia. Both ritanserin and ICI 169,369 were found to have intrinsic analgetic efficacy and to induce behavioural changes indicative of increased defensiveness. These data, together with previous findings, confirm the specific involvement of 5-HT1A receptor mechanisms in the analgesic consequences of social defeat in male mice. Results are discussed in relation to the role of anxiety in adaptive pain inhibition.     

Fluorescent histochemical demonstration of catecholamines in brown adipose tissue from obese (ob/ob) and lean mice acclimated at different temperatures

Fluorescent histochemistry was used to visualize catecholamines in brown adipose tissue (BAT) of lean and genetically obese mice after they had been acclimated at different temperatures. At all temperatures, strong catecholamine-dependent fluorescence, attributable to the sympathetic innervation, was seen around the blood vessels of BAT from both lean and obese animals. Additionally, catecholamine-dependent fluorescent varicosities, in direct contact with the adipocytes were seen in abundance in lean mice acclimated at 23 degrees, 13 degrees or 4 degrees C and in obese mice acclimated at 13 degrees C. This latter compartment was greatly reduced in lean mice acclimated at 33 degrees C and in obese mice acclimated at 23 degrees and 33 degrees C. Three acute treatments (pretreatment with a monoamine oxidase inhibitor; 24 h food deprivation; and short-term cold exposure followed by short-term warm exposure) all increased the varicose fluorescence associated with adipocytes in obese mice housed at 23 degrees C, which suggests that the low resting level in these animals is attributable, at least in part, to subthreshold concentrations of catecholamines in existing varicosities rather than the absence of sympathetic varicosities per se. These results are in accordance with the results from noradrenaline turnover studies which suggest that the difference in sympathetic nervous system (SNS) activity in BAT from lean and obese (ob/ob) mice is best demonstrated at normal environmental temperatures. The reduced SNS activity in BAT of obese mice (which our studies show to be at the 'cellular' level) is likely to be a major factor in their reduced non-shivering thermogenesis and resultant high efficiency of energy storage as previously suggested by other workers.     

Synthesis and evaluation of dimeric derivatives of 5-HT(2A) receptor (5-HT(2A)R) antagonist M-100907

It is now well accepted that at least some serotonin receptors exist in dimeric and oligmeric forms. The linking of receptor ligands has been shown to have potential in the development of selective agonists and antagonists for traditionally refractive receptors. Here we report the development of a dimeric version of the known 5-HT(2A)R antagonist, M-100907. Derivatives of M-100907 were synthesized to determine an appropriate site for the linker connection. Then, homodimers with polyether linkers of different lengths were functionally tested in a bioassay to determine the optimal linker length. Attachment at the catechol of M-100907 with linkers between 12 and 18 atoms in length proved to be optimal.