A wealth of data supports the hypothesis that the neurotransmitter serotonin regulates the intake of ethanol, and is involved in the development of alcoholism in humans. Reduced functioning of the serotonergic system hypothetically increases alcohol intake in both animals and humans. In this thesis, it was proposed that the effect of lowered serotonergic function on alcohol intake is mediated by an increase in disinhibition. The hypothesis that lowered serotonin increases disinhibition was tested in separate groups of individuals at high risk for the development of psychopathology: nonalcoholic young men with a strong family history of paternal alcoholism, and adolescent men with previous histories of physically aggressive behavior. Lowered serotonergic synthesis (and thus presumably function) was experimentally induced through a transient dietary reduction in the availability of the amino add precursor of serotonin, tryptophan. Disinhibition was quantified using a go/no-go task previously shown to characterize psychopaths and children with attention deficit hyperactivity disorder as disinhibited. In the first study, acute tryptophan depletion had no effect on aggressive responding on a modified competitive reaction time aggression task, but increased disinhibition in young men at risk for alcoholism. This effect was independent of the tryptophan depletion-induced mood alterations. The effect tryptophan depletion on disinhibition was not replicated in the second study with previously aggressive adolescent men. A number of explanations for this were posited, including the presence of a ceiling effect. An association between disinhibition and executive functioning (cognitive abilities associated with proper functioning of the prefrontal cortex, such as working memory, planning abilities) was demonstrated in the second study. In a third preliminary study, no association between disinhibition on the go/no-go task and allelic polymorphisms of the dopamine D4 receptor

Both chronic psychosocial stress and chronic administration of corticosterone have been shown to alter serotonergic type 2A (5-HT2A) receptor activity. A non-invasive behavioural index of 5-HT2A receptor activity is the frequency of "wet dog shakes" (WDS) or serotonergic stereotypy. In addition to WDS, 5-HT2A receptors mediate effects on sexual behaviour in the rat, in particular, inhibition in the male and stimulation in the female. In the present series of experiments, the potential involvement of stress and corticosterone in the regulation of WDS and sexual behaviour in the male and female rat was investigated. In Experiments 1-4, chronic exposure to several different forms of psychosocial stress was found to facilitate female and inhibit male rat sexual behaviour while concurrently increasing the display of WDS in both sexes. In Experiment 5, nefazodone, an antidepressant with 5-HT2A antagonistic properties, blocked the effects of stress on WDS but not sexual behaviour in female rats. In Experiments 6-7, the corticosterone synthesis inhibitor, metyrapone, blocked the effects of stress on sexual proceptivity and WDS in female rats. Metyrapone blocked the effects of stress on WDS but not sexual behaviour in male rats. In Experiments 8-9, high doses of corticosterone administered chronically facilitated female and inhibited male rat sexual behaviour while concurrently increasing WDS in both sexes. In Experiments 10-11, the 5-HT2A antagonist ketanserin was found to completely attenuate the effects of corticosterone on sexual behaviour and WDS in both male and female rats. In Experiments 12-13, the acute administration of corticosterone was found to exert no effect on either sexual behaviour or WDS in male or female rats. The present results indicate that both chronic corticosterone treatment and exposure to chronic stress inhibit male and facilitate female sexual behaviour while concurrently increasing WDS behaviour. The stress-induced facilitation of WDS appears to be related to elevated corticosterone levels and is suggestive of increased 5-HT2A activity. Both corticosterone and stress exerted effects on sexual behaviour in the direction that would be predicted by increased 5-HT2A activity. While the effects of corticosterone on sexual behaviour appear to be mediated by 5-HT2A activity, the effects of stress on sexual behaviour do not appear to be related to either elevations in corticosterone levels or alterations in 5-HT2A activity.

Serotonin (5-HT) and noradrenalin (NA) increase persistent inward currents mediated by sodium and calcium channels on the dendrites of motoneurons. The ability of 5-HT and NA to modulate these channels depends on the distributions of 5-HT and NA synapses. Recent studies of the distribution of 5-HT and NA synapses on motoneurons innervating the neck muscle splenius reported that these synapses are rare on the somata and have a strong bias to dendrites with small diameters. It is unknown whether this distribution pattern represents a general principle of organization (1) for all motoneuron groups or (2) for all types of modulators. To address the first question, we have examined the distribution of 5-HT and NA synapses on flexor motoneurons, which unlike extensor motoneurons, are not able to generate self-sustained discharges known to involve the activation of persistent inward currents. To answer the second question, we have mapped the distribution dopamine (DA) synapses. The dendrites of motoneurons that innervate the neck flexor rectus capitis anterior (RCA) were stained. Synapses containing 5-HT, NA and DA were identified using immunohistochemical techniques. Observations based on five RCA motoneurons indicate that the average densities of 5-HT and NA contacts are 2.3 and 1.4 times less dense than the average densities of 5-HT and NA contacts on splenius motoneurons, respectively. Moreover, pairs of 5-HT contacts and pairs of NA contacts were found to be 3.0 and 1.8 times closer together on splenius compared to RCA motoneurons, respectively. These observations may reflect the inability of flexor motoneurons to generate self sustained discharges. Similar to splenius motoneurons, 5-HT and NA synapses were found to preferentially innervate dendrites with diameters less than 2 µm. Thus, 5-HT and NA synapses facilitate channels in regions where excitatory or inhibitory signals undergo the largest attenuations. DA synapses on the dendritic tree were sparse (0.2 and 0.1 contacts per 1000 µm2), suggesting that the actions of DA synapses are confined to local regions on the dendritic tree. These results highlight that motoneurons do not all share the same intrinsic properties, and the distribution of modulatory synapses have a crucial role in determining these properties. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2011-09-28 15:17:54.335

No description available.

While selective serotonin (5-HT) reuptake inhibitors (SSRIs) are utilized as the first-line strategy in treating depression, new approaches are still desired. Using in vivo electrophysiological techniques, the effects of co-administration of bupropion with the SSRI escitalopram on the firing rate of dorsal raphe 5-HT and locus coeruleus norepinephrine (NE) neurons were investigated. Escitalopram significantly decreased the firing of 5-HT and NE neurons at day 2. The 5-HT firing rate, unlike that of NE, recovered after the 14-day escitalopram regimen. Bupropion did not increase 5-HT firing but decreased that of NE after 2 days. Following 14-day bupropion, 5-HT firing was markedly enhanced, and NE firing was back to baseline. Co-administration of escitalopram and bupropion doubled 5-HT firing after 2 and 14 days, whereas NE neurons were inhibited after 2, but partially recovered after 14 days. Although sustained bupropion administration did not alter the sensitivity of 5-HT1A receptors in hippocampus, the tonic activation of postsynaptic 5-HT1A receptors was enhanced in 14-day bupropion-treated rats to a greater extent than in the 2-day and control rats. The function of terminal 5-HT1B autoreceptors was not changed. The inhibitory action of α2-adrenergic receptors on 5-HT terminals was, however, diminished. The function of terminal α2-adrenergic autoreceptors was also attenuated in rats given bupropion for 14 days. Administration of the antidepressant trazodone suppressed the 5-HT firing at day 2, which recovered to baseline following 14 days. Prolonged trazodone-administration enhanced the tonic activation of postsynaptic 5-HT1A receptors in hippocampus, and decreased the function of terminal 5-HT1B autoreceptors. Finally, a novel psychotropic agent asenapine showed potent antagonistic activity at 5-HT2A, D2, and α2-adrenoceptors. Asenapine, however, acted as a partial agonist at 5-HT1A receptors in dorsal raphe and hippocampus. Overall, the therapeutic effects of various antidepressants may be, at least in part, due to the enhancement of 5-HT and/or NE neurotransmission.

We studied the expression of c-fos in medullary serotonergic neurons after a locomotor task on a treadmill in adult mice. We used a transgenically modified line in which serotonergic cells expressed enhanced yellow fluorescent protein (eYFP). We counted and plotted cells using Micro Bright Field Co. software. We determined the location of the serotonergic cells in this mouse line in the adult. We found an increase in the number of eYFP-positive cells expressing c-fos after a locomotor task in the raphe and PPR between bregma -6.8 and bregma -6.48 in the mouse (flanked rostrally by the seventh cranial nerve and caudally by the inferior olive). The percentage of eYFP-positive cells that expressed c-fos after the locomotor task in the raphe was 4%, whereas in the PPR the percentage was13.3%. Our results corroborate the observation that a specific group of serotonergic neurons located in the PPR are involved in locomotion.

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Bibliography: leaves 167-198. / xv, 198 leaves : ill, ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The principle aim of the studies was to characterise the responses to 5-Hydroxytryptamine (5-HT) occuring in the aorta of a primate species, the common marmoset. Further aims were to determine whether the 5-HT- induced response of the aorta is representative of the serotonergic responses of other vessels from the marmoset, in particular the coronary artery. Studies were extended to vascular disease states following a high lipid diet and aortic balloon-catheterisation. Results are discussed. / Thesis (Ph.D.)--University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 1999

5-HT powerfully affects gastrointestinal function. However, the study of these effects is complicated because 5-HT from both mucosa and a subset of enteric neurons acts on multiple receptor subtypes in enteric tissues. The role of neural 5-HT has been difficult to isolate with current techniques. This thesis aimed to elucidate the role of 5-HT neurons in motility using anatomical and functional methods. In Chapter 2, confocal microscopy was used to examine over 95% of myenteric neurons in guinea pig jejunum, categorized neurochemically, to identify neurons that received anatomically-defined input from 5-HT interneurons. The data showed that cholinergic secretomotor neurons were strongly targeted by 5-HT interneurons. In another key finding, excitatory motor neurons were surrounded by 5-HT terminals; this could provide an anatomical substrate for the descending excitation reflex. Subgroups of ascending interneurons and neurons with immunoreactivity for NOS, were also targeted by 5-HT interneurons. Thus, subtypes of these neurons might act in separate reflex pathways. Despite strong physiological evidence for 5-HT inputs to AH/Dogiel type II neurons, few contacts were identified. In Chapter 3, the confocal microscopy survey was extended to the three other interneuron classes (VIP/NOS and SOM descending interneurons; calretinin ascending interneurons) of guinea pig small intestine. A high degree of convergence between the otherwise polarized ascending and descending interneuron pathways was identified.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.