Influences of the corticotropic axis and sympathetic activity on neurochemical consequences of 3,4-methylenedioxymethamphetamine (MDMA) administration in Fischer 344 rats

The respective influences of the corticotropic axis and sympathetic activity on 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) immediate effects on body temperature and long-term neurotoxicity, as assessed by decreases in hippocampal and striatal [(3)H]5-hydroxytryptamine ([(3)H]5-HT) reuptake, [(3)H]paroxetine binding at 5-HT transporters (5-HTT), and 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels, were examined in Fischer 344 rats. On each of the two injections of MDMA (5 or 10 mg/kg s.c. once a day for 2 consecutive days) body temperature rapidly increased in a dose-dependent manner. Six days after the last injection of 10 mg/kg MDMA, [(3)H]5-HT reuptake, [(3)H]paroxetine binding and 5-HT and 5-HIAA levels were decreased in the hippocampus and, to a lower extent, in striatum. Prior adrenalectomy (1 week beforehand), which weakened the immediate hyperthermic effect of MDMA, prevented the long-term MDMA-elicited reduction in hippocampal and striatal [(3)H]paroxetine binding. Supplementation of adrenalectomised Fischer 344 rats with corticosterone almost reinstated the immediate hyperthermic effect of MDMA and restored MDMA-elicited reduction in hippocampal and striatal [(3)H]paroxetine binding. In a final set of experiments, Fischer 344 rats were pretreated (30 min before each of the two injections of 10 mg/kg MDMA) with the ganglionic blocker chlorisondamine (2.5 mg/kg). This pretreatment markedly reduced the amplitudes of the immediate hyperthermia and long-term declines in hippocampal [(3)H]5-HT reuptake and [(3)H]paroxetine binding at 5-HTT, and in hippocampal and striatal 5-HT and 5-HIAA levels. These results suggest that sympathetic activity (possibly through its control of body temperature), but not corticotropic activity, plays a key role in MDMA-elicited neurotoxicity in Fischer 344 rats.     

Fox odour affects corticosterone release but not hippocampal serotonin reuptake and open field behaviour in rats

Group-housed Sprague-Dawley (SD) rats exposed for 1 h to 2,5-dihydro-2,4,5-trimethylthiazoline (TMT, a component of fox feces) did not display changes in hippocampal serotonin (5-HT) metabolism and [3H]5-HT reuptake, compared to water or butyric acid. Such an observation extended to isolated SD and Fischer 344 rats. When group-housed SD rats were tested 1 week after a 1-h exposure to TMT, hippocampal 5-HT metabolism, [3H]5-HT reuptake, and [3H]paroxetine binding at the 5-HT transporter remained unchanged. This study questions TMT as a specific predatory stimulus as both butyric acid and TMT increased plasma corticosterone levels whilst leaving intact open field behaviour (at least in group-housed SD rats).     

Compensatory responses in the aging hippocampal serotonergic system following neurodegenerative injury with 5,7-dihydroxytryptamine

This study utilized a multidisciplinary approach to examine injury-induced compensatory responses in the aging hippocampal serotonin transporter (5-HTT), a membrane protein implicated in a variety of neurodegenerative disorders. Age-dependent cellular, anatomical, and physiological changes of the 5-HTT were evaluated in female Fischer 344 rats (2 and 17 months) following denervation of the serotonergic afferents (fimbria-fornix and cingulum bundle) to the dorsal hippocampus using the neurotoxicant 5,7-dihydroxytryptamine (5,7-DHT). Seven days following 5,7-DHT administration, a uniform loss of the hippocampal 5-HTT immunoreactivity was observed in both age groups. However, at 21 days 5-HTT immunoreactivity in young 5,7-DHT-treated animals was similar to control levels, indicative of recovery, while older animals exposed to 5,7-DHT did not show recovery of hippocampal 5-HTT expression. 5-HTT binding site density, as determined by quantitative autoradiography ([3H]citalopram), supported the immunohistochemical results by demonstrating a recovery of 5-HTT binding sites in young, but not old animals, at 21 days following the lesion (P < 0.001). Furthermore, cellular electrophysiological function of hippocampal CA1 pyramidal neurons in 3- and 18-month-old F344 rats at 21 days following 5,7-DHT or vehicle treatment were assessed using in vivo microiontophoretic application of serotonin (5-HT). Independent of changes in sensitivity to the inhibitory effects of 5-HT application, the time to recovery of cell firing following application of 5-HT was significantly increased in the 18-month 5,7-DHT group compared to the 18-month vehicle and 3-month 5,7-DHT groups (60 and 59% increases, respectively; P < 0.05). Overall, these series of studies comprise a model which can be used to identify cellular events underlying both the formation of injury-induced compensatory processes in younger animals and the lack thereof with advancing age.     

Platelet serotonin uptake and paroxetine binding among allelic genotypes of the serotonin transporter in alcoholics

Expression rates of long (L) and short (S) alleles of the serotonin (5-HT) transporter (5-HTT) gene have been shown to differ under various circumstances. We compared 5-HTT uptake (function) level and paroxetine binding (density) in platelets of alcoholics as indices of 5-HTT expression rate among LL, LS, and SS genotypes. Concentration curves of [3H]5-HT and [3H]paroxetine were used to quantify the equilibrium constant (Km) and maximum 5-HT uptake rate (Vmax) for 5-HTT uptake into intact platelets and the dissociation constant (Kd) and maximum specific binding density (Bmax) for paroxetine binding to platelet membranes, respectively. Genotypes were determined using electrophoresis with fluorescent markers. Vmax for 5-HTT uptake did not correlate with Bmax for paroxetine binding (r=-0.095, P=0.415). Means of Vmax and Bmax did not differ in a statistically significant manner among LL, LS, and SS genotypes in these alcoholic subjects. However, Vmax for LL and SS appeared to have a bimodal distribution, so the percentage of subjects with Vmax <200 fmol/min-10(7) platelets was statistically significantly higher in LL than in SS (51.5% vs. 22.7%, respectively), with an odds ratio of 3.6 (P<0.05). The percentage of Vmax <200 fmol/min-10(7) platelets for LS was 39.3% (not significant vs. LL or SS). Previous studies of healthy human controls have shown that 5-HTT density in raphe nuclei and 5-HTT uptake in platelets are higher in the LL genotype than in S carriers. Our findings in currently drinking alcoholics support the hypothesis that those with the LL genotype of the 5'-HTTLPR region of the 5-HTT gene have reduced 5-HTT function.     

Neurogenetics of emotional reactivity to stress in animals

There is much evidence for the involvement of central monoaminergic systems, the key targets of stress, in the regulation of mood. Animal and human findings indicate that genetics play a role in the etiology of mood disorders, and so we selected divergent inbred rat strains according to their anxiety-related behaviors on exposure to novel environments. We compared these strains for psychoneuroendocrine response to stressors and/or antidepressants. Molecular genetic studies were also performed to localize the genomic regions associated with these strain-dependent anxiety profiles. We then examined human results indicating that allelic variations in the serotonin transporter (5-HTT) may play a role in the etiology of neuroticism and depression. Thus, we compared inbred rat strains for the 5-HTT, with regard to central and peripheral (platelet) protein expression and function, and the consequences of local application of a selective serotonin reuptake inhibitor (SSRI) on extracellular serotonin (5-HT) levels. Our results indicate that spontaneously hypertensive rats and Lewis rats (LEW) selectively diverge in terms of anxiety-related behaviors and that this divergence is located on chromosome 4. The use of social defeat in LEW and the analysis of its psychoneuroendocrine consequences strongly suggest that such a paradigm, which is sensitive to repeated SSRI treatment, models posttraumatic stress disorder. The Wistar-Kyoto rat may be an adequate model to study the consequences of a genetically driven hypersensitivity to stress and noradrenergic antidepressants. Our most recent findings show that the Fischer 344 and LEW strains differ in protein expression and function of hippocampal and platelet 5-HTT; the divergence in protein expression is not due to allelic variations in the gene-coding sequences and leads to marked differences in extracellular 5-HT levels under basal conditions or SSRI. These examples illustrate how the use of inbred rat strains may complement our knowledge on the genetics of behavior, in the same way as the use of transgenic mice.     

Increased hypothalamic [3H]flunitrazepam binding in hypothalamic-pituitary-adrenal axis hyporesponsive Lewis rats.

We have previously demonstrated that susceptibility of Lewis (LEW/N) rats to inflammatory disease, compared to relatively resistant Fischer (F344/N) rats, is related to deficient glucocorticoid counter-regulation of the immune response resulting from deficient corticotropin-releasing hormone (CRH) responsiveness to inflammatory and other stress mediators. The GABA/benzodiazepine receptor complex is an important negative modulator of CRH secretion and responsiveness to excitatory stimuli. In this study, we have examined in vitro binding of [3H]flunitrazepam to hypothalamic membrane preparations from LEW/N and F344/N rats. LEW/N rats had significantly more hypothalamic benzodiazepine binding sites (Bmax) than F344/N rats, but there were no differences in benzodiazepine binding affinities (Kd) between these two strains. The differences in benzodiazepine receptor number were consistent with the respective plasma corticosterone levels in the two strains, and with previous work indicating a negative correlation between corticosterone levels and benzodiazepine binding site number. Adrenalectomy of F344/N rats increased benzodiazepine binding to levels comparable to LEW/N animals and treatment of adrenalectomized F344/N rats with DEX resulted in lowering of benzodiazepine Bmax to levels that did not differ significantly from those of intact F344/N rats. There was no significant change in receptor number in either adrenalectomized or DEX-treated LEW/N rats. These findings suggest that basal benzodiazepine receptor differences between these strains may be partially related to strain differences in corticosterone levels, however that additional factors may contribute to maintenance of these differences in LEW/N rats. Since benzodiazepines attenuate hypothalamic CRH secretion through GABAergic inhibition, we suggest that strain differences in receptor number could also augment strain differences in hypothalamic-pituitary-adrenal axis function through differential sensitivity to GABA-mediated feedback.     

Increased hypothalamic [H]flunitrazepam binding in hypothalamic-pituitary-adrenal axis hyporesponsive Lewis rats

We have previously demonstrated that susceptibility of Lewis (LEW/N) rats to inflammatory disease, compared to relatively resistant Fischer (F344/N) rats, is related to deficient glucocorticoid counter-regulation of the immune response resulting from deficient corticotropin-releasing hormone (CRH) responsiveness to inflammatory and other stress mediators. The GABA/benzodiazepine receptor complex is an important negative modulator of CRH secretion and responsiveness to excitatory stimuli. In this study, we have examined in vitro binding of [³H]flunitrazepam to hypothalamic membrane preparations from LEW/N and F344/N rats. LEW/N rats had significantly more hypothalamic benzodiazepine binding sites (B_max) than F344/N rats, but there were no differences in benzodiazepine binding affinities (K_d) between these two strains. The differences in benzodiazepine receptor number were consistent with the respective plasma corticosterone levels in the two strains, and with previous work indicating a negative correlation between corticosterone levels and benzodiazepine binding site number. Adrenalectomy of F344/N rats increased benzodiazepine binding to levels comparable to LEW/N animals and treatment of adrenalectomized F344/N rats with DEX resulted in lowering of benzodiazepine B_max to levels that did not differ significantly from those of intact F344/N rats. There was no significant change in receptor number in either adrenalectomized or DEX-treated LEW/N rats. These findings suggest that basal benzodiazepine receptor differences between these strains may be partially related to strain differences in corticosterone levels, however that additional factors may contribute to maintenance of these differences in LEW/N rats. Since benzodiazepines attenuate hypothalamic CRH secretion through GABAergic inhibition, we suggest that strain differences in receptor number could also augment strain differences in hypothalamic-pituitary-adrenal axis function through differential sensitivity to GABA-mediated feedback.     

Occupancy of serotonin transporters by paroxetine and citalopram during treatment of depression: a [(11)C]DASB PET imaging study.

OBJECTIVE: Selective serotonin reuptake inhibitors are commonly used to treat major depression; however, the percentage of serotonin (5-HT) transporter (5-HTT) sites occupied during clinical dosing is unknown. This study measured the proportion of 5-HTT sites blocked during paroxetine and citalopram treatment of depression and assessed the relationship between serum paroxetine levels and the proportion of 5-HTT sites blocked. METHOD: Twelve medication-free depressed patients completed a 6-week trial of either paroxetine (N=8) or citalopram (N=4). Striatal 5-HTT binding potential was measured with [(11)C]DASB and positron emission tomography, before and after 4 weeks of treatment. The binding potential is proportional to receptor density. Striatal 5-HTT binding potential was measured twice in six healthy subjects and once in 11 healthy subjects. RESULTS: A significant decrease in striatal 5-HTT binding potential was found after either treatment, compared to changes found over a 4-week period in healthy subjects. For patients treated with 20 mg/day of paroxetine (N=7), the mean proportion of 5-HTT sites occupied was 83%. For patients treated with 20 mg/day of citalopram (N=4), the mean 5-HTT occupancy was 77%. 5-HTT occupancy increased in a nonlinear relationship with serum levels of paroxetine such that a plateau of occupancy around 85% occurred for serum paroxetine levels greater than 28 microg/liter. CONCLUSIONS: During treatment with clinical doses of paroxetine or citalopram, approximately 80% of 5-HTT receptors are occupied. This change in 5-HTT binding potential is greater than the known physiological range of changes in 5-HTT binding potential but may be necessary for some therapeutic effects.     

[3H]Paroxetine and [3H]citalopram as markers of the human brain 5-HT uptake site: a comparison study

Summary The binding of [3H]paroxetine and [3H]citalopram to the human brain serotonin (5-HT) uptake site has been characterized and compared. Our results reveal that the binding exclusively involved with the 5-HT uptake site is identical for both [3H]ligands. The selective 5-HT uptake inhibitor citalopram displays the highest affinity for this uptake site, as compared with the affinities obtained for desipramine and norzimeldine, which is in accordance with their respective blockage of 5-HT uptake. Similar Bmax values were obtained for both radioligands in the brain regions studied, indicating their binding to the same presynaptic membrane protein. Together these findings suggest that both [3H]paroxetine and [3H]citalopram are good markers of the 5-HT transporter as both bind selectively and with high affinity to the serotonin uptake sites. However, the higher affinity of [3H]paroxetine confirms that this compound is the best radioligand for the 5-HT uptake site available today.     

Methamphetamine differentially regulates hippocampal glucocorticoid and mineralocorticoid receptor mRNAs in Fischer and Lewis rats

Fischer 344 (F344) and Lewis (LEW) rats differ in physiological regulation of the limbic-hypothalamo-pituitary-adrenal (LHPA) axis, such that F344 rats exhibit greater LHPA axis responses to a variety of stimuli. Furthermore, LHPA axis activity has been implicated in the development of sensitization to abused drugs, and F344 rats exhibit greater behavioral sensitization to psychostimulants. Accordingly, we hypothesized that there may be some overlap between the neurobiological mechanisms that underlie these strain differences in LHPA axis activity and in behavioral sensitization to psychostimulants. We examined the effects of acute and repeated methamphetamine (4 mg/kg) treatments on the regulation of hippocampal glucocorticoid receptors (GR mRNA) and mineralocorticoid receptors (MR mRNA) in F344 and LEW rats. Our results showed that acute treatment with methamphetamine (MAP) does not alter the level of expression of GR or MR mRNA in both strains. However, repeated treatments with MAP decreased the expression of hippocampal GR, but not MR mRNA specifically in F344 rats. The same repeated treatments had no effect on either GR or MR mRNA in LEW rats. This selective MAP regulation of the level of expression of hippocampal GR mRNA in F344 suggests that these receptors may play a role in the development of behavioral sensitization to MAP in this strain. The lack of alteration in hippocampal GR mRNA in LEW rats suggests that plasticity of hippocampal GR may not be critical for the development of behavioral sensitization to MAP in this strain.     

Corticosterone regulation of serotonin transporter and 5-HT1A receptor expression in the aging brain

Hypercortisolemia is often observed in patients suffering from major depression. As the serotonergic (5-hydroxytryptamine; 5-HT) system plays a major role in the etiology of depression, a loss of endocrine and neurotransmitter system interactions, including corticosterone regulation of 5-HT transporter (5-HTT) and 5-HT receptor expression, may underlie age-related deficits in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis and correlate with an increased incidence of depression with advancing age. In this study, female Fischer 344 rats, ages 3, 13, and 18 months, were bilaterally adrenalectomized and supplemented for 3 weeks with corticosterone (0, 200, or 600 mg; LC, MC, or HC, respectively) containing 21 day sustained-release pellets implanted subcutaneously. Quantitative autoradiography of hippocampal and cortical regions using [3H]citalopram revealed a significant decrease in hippocampal 5-HTT binding in the 3-month HC treatment group compared to age-matched MC and LC groups; this loss was not present in the 13- or 18-month groups. Similarly, quantitative autoradiography using the radiolabeled 5-HT(1A) receptor agonist 8-hydroxy-2-(di-N-propylamino) tetralin demonstrated a significant decline in receptor density in 3- and 13-month MC and HC groups as compared to age-matched LC groups in the hippocampus. These hormone treatments (MC or HC), however, failed to alter hippocampal 5-HT(1A) binding site density in the 18-month groups as compared to the age-matched LC group. The 5-HT(2A) receptor was also evaluated using [3H]ketanserin and showed no age- or corticosterone-related changes in the cortex. Overall, an age-associated deficit in the regulation of the hippocampal serotonergic system by varied corticosterone treatment was revealed in the present study, which may underlie the increased incidence of depression and hypercortisolemia found with advancing age.     

3H]paroxetine binding and serotonin content of rat and rabbit cortical areas, hippocampus, neostriatum, ventral mesencephalic tegmentum, and midbrain raphe nuclei region.

The high-affinity binding of [3H]paroxetine to membranes was measured in different regions of the rat and rabbit brain: cingulate, frontal, parietal, piriform, entorhinal, and visual cortical areas; dorsal and ventral hippocampus; rostral and caudal halves of neostriatum (rat) or caudate nucleus and putamen (rabbit); ventral mesencephalic tegmentum; and midbrain raphe nuclei region. The tissue concentrations of serotonin (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxy-l-tryptophan (5-HTP) were also determined by high-performance liquid chromatography (HPLC) in the same brain samples. The regional density of [3H]paroxetine binding varied in both species; the highest values (Bmax) were found in the midbrain raphe region and ventral mesencephalic tegmentum. The cortical values ranged from moderate to low, with a significantly higher density in the cingulate cortex of the rat compared with rabbit. In the rat, there was also a higher density in the ventral than dorsal hippocampus, and the caudal than rostral neostriatum. In the rabbit, the hippocampal and neostriatal values were generally lower and more uniform. In both species, there was an excellent correlation between regional 5-HT levels and specific [3H]paroxetine binding (r = 0.87 in the rat and 0.96 in the rabbit). Considering the available quantitative data on the number of 5-HT nerve cell bodies and axon terminals in different regions of the rat brain, it appears likely that the high amount of [3H]paroxetine binding in the midbrain raphe region and ventral mesencephalic tegmentum reflects the presence of 5-HT uptake sites on 5-HT nerve cell bodies and dendrites as well as axon terminals. In other brain regions, the heterogeneous distribution of [3H]paroxetine binding parallels that of the number of 5-HT axon terminals, emphasizing the potential usefulness of this radioligand as a marker of 5-HT innervation density.     

Inhibition of hippocampal 5-HT synthesis by fluoxetine and paroxetine: evidence for the involvement of both 5-HT1A and 5-HT1B/D autoreceptors

Hippocampal serotonin (5-hydroxytryptamine, 5-HT) synthesis, as determined by the accumulation of 5-hydroxytryptophan (5-HTP) following inhibition of L-aromatic amino acid decarboxylase with NSD 1015, was inhibited by systemic administration of the selective serotonin reuptake inhibitors fluoxetine (10 mg/kg i.p.) and paroxetine (3 mg/kg i.p.). Pretreatment of rats with the selective 5-HT1A receptor antagonist WAY 100635 for a period of 7 days using subcutaneously implanted osmotic minipumps (1 mg/kg/day) was sufficient to block the inhibition of 5-HT synthesis following the 5-HT 1A receptor agonist 8-OH-DPAT (0.3 mg/kg s.c.), but failed to inhibit the decrease of hippocampal 5-HT synthesis by fluoxetine (10 mg/kg i.p.) or paroxetine (3 mg/kg i.p.). Similarly, pretreatment of rats with GR 127935 (5 mg/kg i.p.), an antagonist with high affinity for 5-HT1B/D receptors, blocked the reduction of hippocampal 5-HT synthesis following the 5-HT receptor agonist TFMPP (3 mg/kg s.c.) without affecting the reduction of hippocampal 5-HT synthesis by either fluoxetine or paroxetine. In contrast, pretreatment with WAY 100635 (1 mg/kg/day, for 7 days s.c. in osmotic minipumps) in combination with GR 127935 (5 mg/kg i.p.) significantly attenuated the decrease of hippocampal 5-HT synthesis by both fluoxetine and paroxetine. These results indicate that both 5-HT1A and 5-HT1B/1D receptors, which function in the rat as inhibitory somatodendritic and nerve terminal autoreceptors, independently regulate hippocampal 5-HT synthesis and must be simultaneously blocked to prevent the inhibition of 5-HT synthesis by selective serotonin reuptake inhibitors which increase 5-HT availability at both nerve terminals in hippocampus and 5-HT cell bodies in the raphe nuclei.     

Regional and subcellular localization in human brain of [3H]paroxetine binding, a marker of serotonin uptake sites

The characteristics of the binding of [3H]paroxetine, a selective serotonin (5-HT) uptake blocker, were investigated in human brain. The Kd value was 0.23 +/- 0.07 nM, and the Bmax value was 190 +/- 39 fmol/mg protein in the putamen. The capacity of various antidepressive drugs to inhibit [3H]paroxetine-specific binding in human brain was well correlated with their capacity to inhibit [3H]5-HT uptake in rat brain. The highest concentrations of [3H]paroxetine-specific binding sites were found in the substantia nigra, hypothalamus, and hippocampus. Lower values were obtained in the basal ganglia and the thalamus. The specific binding was very low in cerebral and cerebellar cortices. The regional distribution of [3H]paroxetine binding sites differs from that of [3H]ketanserin binding to S2 serotonin receptors. The subcellular distribution of the [3H]paroxetine-specific binding sites obtained by differential centrifugation revealed a synaptosomal enrichment in the frontal cortex and striatum, whereas an enrichment in the microsomal fraction was found in striatum. The results show that [3H]paroxetine is a ligand of choice to label the 5-HT uptake molecular complex in human brain.     

Plasticity and ontogeny of the central 5-HT transporter: effect of neonatal 5,7-dihydroxytryptamine lesions in the rat.

5,7-Dihydroxytryptamine (5,7-DHT) is unique as a serotonin (5-HT) neurotoxin in that i.p. injection of neonatal rats increases concentrations of 5-HT in brainstem while depleting 5-HT in cortex, hippocampus and spinal cord. To study the mechanism of this effect we measured the 5-HT transporter or uptake site, a presynaptic marker, using [3H]paroxetine binding. There were significant regional differences in Bmax of vehicle-injected rats: brainstem, diencephalon > striatum, cortex, spinal cord > hippocampus, cerebellum. There were also regional differences in the ontogeny of bindings sites: at postnatal day 7, [3H]paroxetine sites were 39% of adult levels in cortex compared to 63% in brainstem. Thirty days after 100 mg/kg 5,7-DHT i.p., Bmax of [3H]paroxetine binding was significantly increased in brainstem (+67%) and diencephalon (+136%), whereas it decreased in cortex (-59%), hippocampus (-94%) and spinal cord (-99%), striatum (-41%) and cerebellum (-37%). KD remained unaltered. In dose-response studies (0-200 mg/kg), 50 mg/kg was the threshold dose for Bmax effects and 200 mg/kg was lethal. In weekly time-course studies, changes were apparent 1 week after 5,7-DHT lesions. Binding site increases in diencephalon and brainstem were not maximal until 3 weeks after injection, whereas percent decreases in cortical sites remained unchanged at each week studied. Lesion effects on the ontogeny of [3H]paroxetine binding sites were region-dependent: cortical sites continued to increase with age but spinal sites did not. There was no significant recovery in spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)     

Brain 5-HT uptake sites, labelled with [3H]paroxetine, in antidepressant-free depressed suicides

Brain serotonin (5-HT) uptake sites were quantitated, by saturation binding of [3H]paroxetine, in 10 brain regions from 22 suicide victims and 20 control subjects. Suicide victims were restricted to those subjects in whom a firm retrospective diagnosis of depression was established and who had not recently been prescribed antidepressant drugs. The Kd and Bmax of [3H]paroxetine did not differ significantly between controls and depressed suicides in any of the brain regions. In putamen, Bmax values of suicides who died non-violently were lower than controls, whereas those who died by violent methods did not differ from controls. No significant differences between violent or non-violent suicides and their matched controls were found in other brain areas. These results offer little support for the view that suicide/depression is associated with an abnormality in 5-HT uptake.     

Aging regulates 5-HT(1B) receptors and serotonin reuptake sites in the SCN

Middle age is associated with changes in circadian rhythms (e.g., alterations in the timing of the circadian wheel running rhythm) which resemble changes induced by selective destruction of the serotonergic input to the suprachiasmatic nucleus (SCN), the principal mammalian circadian pacemaker. We hypothesized that serotonergic neurotransmission in the SCN is decreased in middle-aged hamsters, as compared to young adults. This hypothesis was tested indirectly by investigating the effect of aging on two markers of serotonin neurotransmission, 5-HT(1B) receptors and serotonin reuptake sites, which are regulated by serotonin. Previous studies have shown that experimentally induced decreases in serotonergic neurotransmission increase 5-HT(1B) receptors but decrease serotonin reuptake sites. Quantitative autoradiography was conducted using [125I]iodocyanopindolol ([125I]ICYP) and [3H]paroxetine, selective radioligands for the 5-HT(1B) receptors and the serotonin reuptake sites, respectively. Consistent with the hypothesis, specific ([125I]ICYP binding was significantly elevated in the SCN of middle-aged hamsters, as compared to young hamsters. The results also showed that serotonin reuptake sites in the SCN were significantly increased in both middle-aged and old hamsters, as compared to young controls. This result could not have been caused by decreased serotonin release. Alternatively, increased serotonin reuptake, which would reduce serotonin levels in the synaptic cleft, may cause or contribute to the increase in 5-HT(1B) receptor binding in the SCN in middle aged animals. These results show that the SCN exhibits changes in serotonergic function during middle age, which has been characterized by changes in the expression of circadian rhythms. Because these changes occur during middle age, they probably reflect the aging process, rather than senescence or disease.     

Different distributions of the 5-HT reuptake complex and the postsynaptic 5-HT(2A) receptors in Brodmann areas and brain hemispheres

The aim of the present study was to determine the distribution of the presynaptic 5-HT reuptake complex and the 5-HT(2A) receptors through Brodmann areas from two control subjects, together with the possible existence of laterality between both brain hemispheres. A left laterality was observed in the postsynaptic 5-HT(2A) binding sites, with significantly higher B(max) values in the left frontal and cingulate cortex. In frontal cortex, [3H]imipramine and [3H]paroxetine binding showed the highest B(max) values in areas 25, 10 and 11. In cingulate cortex, the highest [3H]imipramine and [3H]paroxetine B(max) values were noted in Brodmann area 33 followed by area 24, while postsynaptic 5-HT(2A) receptors were mainly distributed through Brodmann areas 23 and 29. In temporal cortex, the highest [3H]imipramine and [3H]paroxetine B(max) was noted in Brodmann areas 28 and 34, followed by areas 35 and 38. All Brodmann areas from parietal cortex (1, 2, 3, 4, 5, 6, 7, 39, 40 and 43) showed similar presynaptic and postsynaptic binding values. In occipital cortex no differences were observed with regard to the brain hemisphere or to the Brodmann area (17, 18 and 19). These results suggest the need to carefully define the brain hemisphere and the Brodmann areas studied, as well to avoid comparisons between studies including different Brodmann areas or brain hemispheres.     

Effect of chronic administration of duloxetine on serotonin and norepinephrine transporter binding sites in rat brain.

BACKGROUND: Chronic treatment of rats with certain selective serotonin or norepinephrine reuptake inhibitors produces significant decreases, respectively, in serotonin and norepinephrine transporter binding sites in brain. Duloxetine may be a dual serotonin/norepinephrine reuptake inhibitor, as it is only a slightly more potent inhibitor of serotonin than norepinephrine uptake in vitro. Consequently, we hypothesized that chronic duloxetine treatment, at doses producing serum levels within its therapeutic range, would affect both monoamine transporters dose-dependently, with a higher dose causing greater reductions of binding sites for both transporters. METHODS: Rats were treated with either 4 or 8 mg/kg/d of duloxetine, paroxetine, desipramine, or vehicle via subcutaneous osmotic minipumps for 21 days. Binding sites for serotonin and norepinephrine transporters were measured in amygdala and hippocampus using quantitative autoradiography. RESULTS: Both doses of duloxetine and paroxetine produced equivalent and significant decreases in [3H] cyanoimipramine binding to serotonin transporters, but only desipramine treatment significantly reduced [3H] nisoxetine binding to norepinephrine transporters. CONCLUSIONS: At doses producing rat serum concentrations in the range achieved in patients at recommended daily doses of the drug, duloxetine behaves in vivo more as a selective serotonin reuptake inhibitor than a dual reuptake inhibitor in its capacity to selectively reduce serotonin transporter density.     

Rat strain differences in sleep after acute mild stressors and short-term sleep loss

Genetic and physiological diversity amongst rodent strains provide the potential for developing models that may give insight into factors that regulate sleep in response to environmental challenges. We examined home cage activity, behavioral performance in the open field and sleep after a number of mild stressors (cage change [CC], open field [OF]) and after 1 and 4h of sleep deprivation (1hSD and 4hSD) in rat strains (Fischer 344 [F344], Lewis [LEW], Wistar [WST] and Sprague-Dawley [Sp-D], n=16 per strain) that differ in behavior and sleep. F344 and WST rats had greater home cage locomotion than LEW and Sp-D rats, but F344 rats exhibited the least relative locomotion in OF. In 24h baseline recordings of sleep, strain rankings were LEW=WST=Sp-D>F344 in rapid eye movement sleep (REM), and LEW=Sp-D>F344 and LEW>WST in non-REM (NREM). Compared to baseline, total sleep was reduced in all four strains after CC, OF and 1hSD, but not after 4hSD, in the first hour after treatment. Afterwards, increases in REM and NREM were seen after all treatments with the amount and time course varying across treatments and strains. CC induced the weakest and 4hSD the largest effects on sleep, whereas OF and 1hSD had intermediate effects. Among strains, the more anxious F344 rats exhibited the greatest sleep increases during the light period after OF, 1hSD and 4hSD. The results are discussed with respect to the relationship between behavioral and sleep responses to stressors, and to potential mechanisms underlying the strain differences.