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Theta activity has been related to the processing of spatial information and the formation of hippocampus-dependent memory. The medial septum (MS) plays an important role in the control and coordination of theta activity, as well as in the modulation of learning. It has been established that increased serotonergic activity may desynchronize theta activity, while reduced serotonergic activity produces continuous and persistent theta activity in the hippocampus. We investigate whether serotonin acting on the medial septum could modify spatial learning and the functional relationship between septo-hippocampal and septo-mammillary theta activity. The serotonin was depleted (5HT-D) from the medial septum by the injection of 5,7 DHT (5,7- dihydroxytryptamine). Theta activity was recorded in the dorsal hippocampus, MS and mammillary nuclei (SUM, MM) of Sprague-Dawley male rats during spatial learning in the Morris water maze. Spatial learning was facilitated, and the frequency of the hippocampal theta activity during the first days of training increased (to 8.5Hz) in the 5HT-D group, unlike the vehicle group. Additionally, the coherence between the MS-hippocampus and the MS-mammillary nuclei was higher during the second day of the test compared to the vehicle group. We demonstrated that septal serotonin depletion facilitates the acquisition of spatial information in association with a higher functional coupling of the medial septum with the hippocampus and mammillary nuclei. Serotonin, acting in the medial septum, modulates hippocampal theta activity and spatial learning.

Summary Serotonin (5-HT) has been shown to exert antiepileptic effects in a variety of generalized convulsive seizure models, particularly the genetically epilepsy-prone rat (GEPR). The present study was designed to identify the region/site(s) where 5-HT exerts anticonvulsant effects in the GEPR-9, a model in which sound-evoked generalized tonic–clonic seizures (GTCS) are highly sensitive to manipulations in 5-HT concentration. Because the 5-HT reuptake inhibitor, fluoxetine, was known to exert anticonvulsant effects in GEPR-9s via a 5-HT-dependent mechanism, we utilized selective regional 5-HT depletion in combination with systemic fluoxetine administration to find the site where a 5-HT deficit would prevent the anticonvulsant action of fluoxetine. Widespread destruction of serotonergic terminal fields or regionally specific terminal field destruction was achieved using intracerebroventricular and more target specific infusions of 5,7-dihydroxytryptamine. The capacity of fluoxetine to suppress seizures in GEPR-9s following a loss of 5-HT was then examined. The present findings show the anticonvulsant action of fluoxetine is markedly attenuated following the loss of midbrain 5-HT, particularly in the region of the superior colliculus, while forebrain and spinal cord 5-HT do not appear to play a role in the action of fluoxetine. The importance of the deep layers of the SC was confirmed by demonstrating that direct microinfusion of fluoxetine into the SC can suppress seizures in rats pretreated with the 5-HT 1A receptor antagonist pindolol.

Background Innervation of the hypothalamus and median eminence arise from the dorsal and medial raphe nuclei (DRN and MRN, respectively). The hypothalamus regulates the secretion of gonadotropins, which in turn regulate the reproductive function of males and females. However, it is not known the role of raphe nuclei in male reproductive function. Our goal was to investigate the role of the DRN and MRN in the regulation of the testicular function and secretion of gonadotropins in prepubertal rats. Methods Dihydroxytryptamine (5,6-DHT) in ascorbic acid was used to chemically lesion the DRN or MRN. Rats were treated at 30 days-of-age and sacrificed at 45 or 65 days-of-age. Sham-treated controls were injected with ascorbic acid only. Negative controls were untreated rats. The damage induced by the 5,6-DHT was monitored in coronal serial sections of DRN and MRN; only the animals in which lesion of the DRN or MRN was detected were included in this study. As output parameters, we measured the concentrations of noradrenaline (NA), dopamine (DA) and serotonin (5-HT) in the anterior (AH) and medial (MH) hypothalamus by high performance liquid chromatography (HPLC); whereas, circulating concentrations of gonadotropins and sexual steroids were measured by radioimmunoassay. Seminiferous epithelium and sperm quality were also evaluated. Results Lesion of DRN or MRN does not induced changes in concentrations of LH, progesterone, and testosterone. Compared with the control group, the sham or lesion of the DRN or MRN did not modify noradrenaline or dopamine concentrations in the AH and MH at 45 or 65 days of age. Meanwhile, serotonin concentrations decreased significantly in lesioned rats. Lesion of DRN induced significantly lower concentrations of FSH regardless of age; similar lesion in the MRN had no impact on FSH levels. Sperm concentration and motility were significantly decreased in the same animals. The lesion of the MRN does not induced changes in the seminiferous epithelium or gonadotropin levels. Our results suggest that raphe nuclei regulate differentially the male reproductive functions. Conclusions The DRN but not the MRN regulates the secretion of gonadotropins and testicular function. Electronic supplementary material The online version of this article (doi:10.1186/s12958-015-0130-0) contains supplementary material, which is available to authorized users.

To investigate the role of G proteins in denervation supersensitivity of the CNS serotonergic system, we examined the effect of lesioning serotonergic neurons on the abundance of cerebral cortical membrane G protein subunits in rats. Three weeks after intracisternal injection of 5,7-dihydroxytryptamine (5,7-DHT), which significantly reduced cortical 5-hydroxytryptamine (5-HT; -90%) and 5-hydroxyindoleacetic acid (approximately 98%) levels, no statistically significant differences were observed for G alpha s-1, G alpha s-s, G alpha i1, G alpha i2, G alpha q/11, G alpha 0, G beta 1 and G beta 2 immunoreactivity levels between sham-lesioned and 5,7-DHT lesioned rats. These data suggest that the functional supersensitivity of 5-HT neuronal system often observed following lesions of 5-HT fibers may not involve changes at the level of G proteins but may instead encompass other downstream elements of the 5-HT receptor signaling cascade.

The 5,6-dihydroxytryptamine (5,6-DHT) derivatives 4-fluoro- and 7-fluoro-5,6-DHTs (26a,b) and 4,7-difluoro-5,6-DHT (26c) were synthesized from 3-fluoroanisole (1) and 1,4-difluoro-2,3-dimethoxybenzene (13), respectively. Efficient methods were developed for the conversion of 1 to 4-fluoro- and 7-fluoro-5,6-bis(benzyloxy)indoles (12a,b, respectively), and 13 to 4,7-difluoro-5,6-[( diphenylmethylene)dioxy]indole (19) via reductive cyclization of 2-nitro-beta-(dialkylamino)styrenes prepared in situ from 2-nitrotoluenes. Indoles 12a,b and 19 were then converted to 26a-c via the corresponding indole-3-acetonitriles. The fluorine-substituted 5,6-DHTs displayed increased phenol acidities, determined spectrophotometrically, and decreased inherent potential to undergo oxidation as determined by cyclic voltammetry. Fluorine substitution did not have a significant adverse effect on the cytotoxic potential as judged from the IC50 values of 117, 125, 135, and 92 microM for 26a,c and 5,6-DHT, respectively, for the inhibition of incorporation of [3H]thymidine into the DNA of neuroblastoma clone N-2a cells in culture. Surprisingly, 26a-c exhibited 32-, 23-, and 13-fold higher affinities, respectively, compared to 5,6-DHT for the serotonergic uptake system of N-2a cells as measured by the ability of 26a-c and 5,6-DHT to antagonize the uptake of [3H]5-HT into the N-2a cells. These desirable chemical and biological properties of 26a-c should make them useful tools for the study of the molecular mechanism of neurodegenerative action of 5,6-DHT.

In conscious rats, we investigated the change of nociceptive paw withdrawal reflexes elicited by mechanical and heat stimuli during intramuscular (i.m.) 5.8% hypertonic (HT) saline elicited muscle nociception. i.m. injection of HT saline caused rapid onset, long lasting (around 7 days), bilateral mechanical hyperalgesia, while it induced bilateral, slower onset (1 day after the HT saline injection), long-term (about 1-2 weeks) heat hypoalgesia. Ipsilateral topical pre-treatment of the sciatic nerve with 1% capsaicin significantly prevented the occurrence of both the bilateral mechanical hyperalgesia and the contralateral heat hypoalgesia. Intrathecal administration of either 6-hydroxydopamine hydrobromide (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT), and intraperitoneal injection of naloxone all markedly attenuated the HT saline induced bilateral heat hypoalgesia, but not the mechanical hyperalgesia. Combined with experiments with lesioning of the rostroventral medulla with kainic acid, the present data indicate that unilateral i.m. injection of HT saline elicits time-dependent bilateral long-term mechanical hyperalgesia and heat hypoalgesia, which were modulated by descending facilitatory and inhibitory controls, respectively. We hypothesize that supraspinal structures may function to discriminate between afferent noxious inputs mediated by Aδ- and C-fibres, either facilitating Aδ-fibre mediated responses or inhibiting C-fibre mediated activities. However, this discriminative function is physiologically silent or inactive, and can be triggered by stimulation of peripheral C-fibre afferents. Importantly, in contrast to the rapid onset of descending facilitation, the late occurrence of descending inhibition suggests a requirement of continuous C-fibre input and temporal summation. Thus, a reduction of C-fibre input using exogenous analgesic agents, i.e. opioids, may counteract the endogenous descending inhibition.

p-Chloroamphetamine (PCA) is a useful pharmacologic tool for selectively increasing brain serotonin function acutely by release of serotonin into the synaptic cleft. PCA produces behavioral, neurochemical and neuroendocrine effects believed due to serotonin release after doses in the range of 0.5-5 mg/kg. At higher doses and at longer times, PCA causes depletion of brain serotonin. The mechanisms of this depletion are not well understood but require the serotonin uptake carrier. Antagonism of PCA-induced depletion of brain serotonin is a useful means of assessing the ability of a compound to block the serotonin uptake carrier on brain serotonin neurons. PCA can also be used as a neurotoxic agent to deplete brain serotonin in functional studies, apparently by destroying some serotonergic nerve terminals. Used in this way, PCA has an advantage over 5,6- and 5,7-dihydroxytryptamines in being effective by systemic injection, and it affects brain serotonergic projections with a different neuroanatomic specificity than the dihydroxytryptamines.

In the 1950s, the discovery of anti-nerve growth factor, an immunotoxin stunting sympathetic neural development, signaled the advent of neurotoxins as research modalities. Other selective neurotoxins were discovered in rapid succession. In the 1960s, 6-hydroxydopamine and 6-hydroxydopa were shown to destroy noradrenergic and dopaminergic nerves. Excitotoxins (glutamate, aspartate, and analogs) were discovered in the 1970s. DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] proved to be selective for noradrenergic destruction, while 5,6- and 5,7-dihydroxytryptamines were relatively selective for serotonin neurons. Additional neurotoxins were discovered, but it was MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) that predominated neurotoxicity research in the 1980s. Eventually, Clostridium botulinum neurotoxin (BoNT), discovered as a "poisonous" principle in the late 1800s, resurfaced in purified and standardized forms as a clinically useful drug. Neurotoxins represent chemical tools, useful not only for discerning neuronal mechanisms and animal modeling of neurological disorders, but also for their use in medicine and potential as treatments for medical disorders. This unit reviews the early discovery of neurotoxins, describes categories of neurotoxins, and finally characterizes their usefulness--first as research tools, and eventually as clinical therapeutic agents.

Intrathecal administration of the neurotoxins 5,6-dihydroxytryptamine (5,6-DHT) and 6-hydroxydopamine (6-OHDA) in rats selectively lesioned the descending spinal serotonergic and noradrenergic pathways, respectively. Four days after neurotoxin administration the behaviour was evaluated in the formalin test. Several behavioural variables were recorded. The statistical analysis of the results was supplemented using a multivariate statistical method (partial least squares projection to latent variables, PLS) in addition to traditional analysis of variance. The described methods for recording and statistical analysis of behaviour appear to be useful in describing drug-induced differences in behavioural patterns in the formalin test. Both types of lesion reduced the pain-related behaviour in the formalin test (protection of the paw, biting and licking). The results indicate that the descending monoaminergic pathways are parts of a network which maintains adequate nociceptive responses to a chemical stimulus, or to stimuli lasting several minutes, as in the formalin test.

The 5,6-dihydroxytryptamine (5,6-DHT) derivatives 4-fluoro- and 7-fluoro-5,6-DHTs (26a,b) and 4,7-difluoro-5,6-DHT (26c) were synthesized from 3-fluoroanisole (1) and 1,4-difluoro-2,3-dimethoxybenzene (13), respectively. Efficient methods were developed for the conversion of 1 to 4-fluoro- and 7-fluoro-5,6-bis(benzyloxy)indoles (12a,b, respectively), and 13 to 4,7-difluoro-5,6-[( diphenylmethylene)dioxy]indole (19) via reductive cyclization of 2-nitro-beta-(dialkylamino)styrenes prepared in situ from 2-nitrotoluenes. Indoles 12a,b and 19 were then converted to 26a-c via the corresponding indole-3-acetonitriles. The fluorine-substituted 5,6-DHTs displayed increased phenol acidities, determined spectrophotometrically, and decreased inherent potential to undergo oxidation as determined by cyclic voltammetry. Fluorine substitution did not have a significant adverse effect on the cytotoxic potential as judged from the IC50 values of 117, 125, 135, and 92 microM for 26a,c and 5,6-DHT, respectively, for the inhibition of incorporation of [3H]thymidine into the DNA of neuroblastoma clone N-2a cells in culture. Surprisingly, 26a-c exhibited 32-, 23-, and 13-fold higher affinities, respectively, compared to 5,6-DHT for the serotonergic uptake system of N-2a cells as measured by the ability of 26a-c and 5,6-DHT to antagonize the uptake of [3H]5-HT into the N-2a cells. These desirable chemical and biological properties of 26a-c should make them useful tools for the study of the molecular mechanism of neurodegenerative action of 5,6-DHT.

Learning in rats trained in the Stone 14-unit T-maze, a complex, positively reinforced spatial discrimination task was assessed following cytotoxic (5,7-dihydroxytryptamine; 5,7-DHT) deafferentation of the serotonergic inputs to the hippocampus. Serotonergic deafferentation was accomplished by infusing the cytotoxin in to the fornix-fimbria/cingulum bundle. Lesioned rats reached criterion (i.e. learned) in significantly fewer trials and made significantly fewer errors throughout training than either vehicle-injected or sham-operated controls. This represents the first time that the effects of selective chronic destruction of serotonergic inputs to the hippocampus have been investigated. The present results provide, therefore, evidence in support of a neuromodulatory role for serotonin (5-HT) within the rat hippocampus in the mediation of the processes underlying learning and memory for this task. Other studies are, therefore, warranted in order to determine whether hippocampal 5-HT also plays a role in the mediation of the processes underlying learning and memory in other types of tasks.

To study the involvement of serotonin (5-HT) receptor subtypes in behavioral supersensitivity following neonatal 5,7-dihydroxytryptamine (5,7-DHT) lesions, we measured acute behavioral responses to a single dose of selective 5-HT1A (8-OH-DPAT) or 5-HT2,1C (DOI) agonist compared to 5-hydroxytryptophan (5-HTP) in rats injected with 5,7-DHT intraperitoneally or intracisternally 14 weeks earlier. Only intraperitoneal 5,7-DHT injection resulted in brainstem 5-HT hyperinnervation, but cortical 5-HT depletions were also less. Effects of DOI, such as shaking behavior and forepaw myoclonus, were enhanced by 5,7-DHT lesions made intracisternally not intraperitoneally, whereas 8-OH-DPAT-evoked behaviors, such as forepaw myoclonus and head weaving, were enhanced more by the intraperitoneal route. The main consequence of intraperitoneal compared to intracisternal 5,7-DHT injection on supersensitivity to 5-HT agonists was increased presynaptic 5-HT1A responses and decreased 5-HT2,1C responses. In contrast, 5-HTP evoked more shaking behavior and less of the serotonin syndrome with the intraperitoneal compared to the intracisternal route of 5,7-DHT injection. Behavioral supersensitivity to 5-HTP, which was attributable to 5-HT1A, 5-HT2,1C, and possibly to other 5-HT receptors, was orders of magnitude greater than that elicited by direct receptor agonists and more clearly differentiated between rats with 5,7-DHT lesions and their controls, and between routes of 5,7-DHT injections, than responses to 5-HT agonists at the dose studied. 5,7-DHT induced dysregulation of 5-HT receptors, including both presynaptic and postsynaptic changes and altered interactions between receptor subtypes, better explains these data than postsynaptic changes alone.

The role of the serotonergic system in the regulation of hamster circadian rhythms was analyzed using intraventricular injection of the selective neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT). Sixty days after 5,7-DHT administration, immunoreactive serotonin in the forebrain, particularly the suprachiasmatic nuclei and intergeniculate leaflets, was severely depleted in 16 animals, moderately depleted in four and only slightly affected in four. 5,7-DHT produced an immediate and sustained advance of the onset of running wheel activity relative to the 24 h light-dark (LD) cycle. Activity onset occurred0.7 ± 0.07 h before lights out among, 5,7-DHT-treated animals compared with0.18 ± 0.04 h after lights out for vehicle-infused controls. This new, advanced phase angle of entrainment was maintained throughout the 60-day period of the study while the animals remained in a LD cycle, including after an 8-h phase advance of the light cycle. 5,7-DHT treatment also delayed the offset of wheelrunning in 16 of 24 animals and reduced the likelihood of a smooth pattern of reentrainment to the shifted LD cycle. The drug treatment did not affect circadian period in constant darkness, the rate of reentrainment to an 8-h phase advance or the amount of wheelrunning activity per day. In addition, 5,7-DHT treatment had no effect on the ability of triazolam, a short-acting benzodiazepine, to accelerate the rate of reentrainment to an 8-h phase advance. These observations show that ascending projections of midbrain raphe serotonin neurons participate in the regulation of the circadian activity phase but are not required for triazolam-induced acceleration of reentrainment to a phase-advanced LD cycle.

Catecholamines, indolealkylamines and their analogues are oxidized at neutral or alkaline pH, producing hydrogen peroxide, quinones and free radicals. Several of these amines were tested for trypanocidal effects on Trypanosoma brucei, which possess a well-documented vulnerability to such oxidation products. Dopamine, 5-hydroxydopamine (5-OHDA), 6-hydroxydopamine (6-OHDA), 5-hydroxytryptamine (5-HT), 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT) killed the parasites in vitro, using a fibroblast feeder layer cell culture system, in four to 48 hours at concentrations of 10(-5)-10(-7) M. The 5-OHDA, 6-OHDA, 5,6-DHT and 5,7-DHT were also effective in vivo when tested by intraperitoneal injection of infected mice.

Intraperitoneal injection of benzodiazepine receptor agonists (estazolam, zopiclone, triazolam: 0.03–0.24 mmol/kg) induces the head twitch response (HTR). The present study was undertaken to examine the possible participation of the serotonergic system in the mechanism of head twitches induced by benzodiazepine receptor agonists (BZ-RAs). The HTR induced by BZ-RAs was suppressed by pretreatment with ketanserine (1 mg/kg, i.p.), a selective 5-HT2 receptor antagonist. Pretreatment with fluoxetine (10 mg/kg, i.p.), a 5-HT reuptake inhibitor, and 8-hydroxy-2-(di-n-propylamino)tetralin, a 5-HT1A receptor agonist, also suppressed the HTR induced by BZ-RAs. These results suggest that the HTR induced by BZ-RAs may be the result of an activation of postsynaptic 5-HT2 receptors, probably due to direct action.

The role of tyrosinase and peroxidase in melanogenesis of 5-hydroxytryptamine, 5,6- and 5,7-dihydroxytryptamines was investigated by matrix-assisted laser desorption/ionization mass spectrometry. Each enzyme was incubated with the tryptamine derivatives and samples were drawn at various times, ultrafiltered and immediately lyophilized.

It has been proposed that a defect in the metabolism of 5-hydroxytryptamine or serotonin (5-HT) leads to the formation of more highly hydroxylated indoleamines (Udenfriend et al., 1956; Mclsaac and Page, 1959; Eriksen et al., 1960) such as 5,6- and 5,7-dihydroxytryptamine (5,6-DHT and 5,7-DHT), powerful serotoninergic neurotoxins (Baumgarten et al, 1971; 1972a; 1972b; Baumgarten and Lachenmeyer, 1972; Bjorklund et al., 1973a; 1973b; Saner et al, 1974). The discovery of this oxidative pathway from 5-HT may provide a chemical basis for understanding certain neurological and psychotic disorders.

The relation between electroacupuncture (EA) analgesia (A) and substance P (SP) level in the brain stem (BS) and lumbar spinal cord (LSC) of arthralgic rats was investigated. The rats were divided into three groups: 1)5.7-dihydroxytryptamine (5.7-DHT) + EA, 2) vehicle (V) + EA, and 3)5.7-DHT. All the animals were induced arthralgesia by injecting Freund's adjuvant 7 days after cisterna injection of 5.7-DHT or vehicle. The SP level in the BS and LSC was determined by RIA. The results indicated that in V + EA group the EA could prolong tail flick latency by 39.6%, but in other two groups did not. The SP level in LSC of V + EA group (179.1 +/- 11.5 pmol/g) was higher than that in the 5.7-DHT + EA (135.9 +/- 9.3pmol/g) and 5.7-DHT (125.8 +/- 10.0 pmol/g) groups. It suggested that both EA and arthralgia could activate the descending 5-HTergic inhibitory system to inhibit the release of SP in LSC. When the 5-HTergic system was destroyed by 5.7-DHT, the EAA was attenuated, and the SP level in LSC was lowered due to its release was decreased by EA and arthralgia.

5,6-dihydroxytryptamine was microinjected into the nucleus raphe magus (NRM) of rats. The sections of upper cervical segments were processed for immunoreactive substance P (SP). The degenerated axon terminals and immunoreactive fibers were identified by electron microscopy. The results show that the degenerated axon terminals and immunoreactive positive dendrites and axons were found in the laminae I and II of the dorsal horn. The electron-dense axon terminals were in contact with unlabelled dendrites, some also in contract with immunoreactive dendrites. In lamina II, one of degenerated axon terminals as a center was contacted by several unlabelled axonal boutons. SP labelled terminals were synapsed with unlabelled dendrites and dendritic spine; in addition, unlabelled axo-axonal synapse was found in lamina II. These results suggest that 5-HT axon terminals from NRM directly innervate SP and non-SP neurons in the laminae I and II.

The present study was conducted (a) to determine if cross-supersensitivity at spinal noradrenergic receptors could be demonstrated in antinociceptive tests following depletion of spinal cord 5-hydroxytryptamine (5HT) by the intrathecal (i.t.) and intracerebroventricular (i.c.v.) administration of 5,7-dihydroxytryptamine (5,7DHT), and (b) to compare the pattern of supersensitivity at spinal 5HT receptors following these manipulations and 5,7DHT microinjected into the ventral raphe (VR) region and the nucleus raphe magnus (NRM). Both i.t. and i.c.v. administration of 5,7DHT produced a marked depletion of spinal cord 5HT (greater than 75%) and supersensitivity to the i.t. injection of 5HT in the tail flick and hot plate tests. No supersensitivity to the i.t. injection of noradrenaline (NA) was observed. Microinjection of 5,7DHT into the VR and NRM produced less depletion of spinal cord 5HT (40-57%), and supersensitivity to the i.t. injection of 5HT was observed only in the hot plate test following microinjection of 5,7DHT into the VR. An increased incidence of signs of the 5HT behavioural syndrome, particularly tremor and Straub tail, was observed in all 5,7DHT-pretreated groups. These results indicate that cross-supersensitivity to spinal NA receptors does not occur following depletion of spinal cord 5HT. In addition, responses mediated by 5HT receptors show a differential pattern of development of supersensitivity. Thus, the 5HT behavioural syndrome (presumably mediated by 5HT1A receptors) more readily reflects the development of supersensitivity than the tail flick test (presumably mediated by 5HT2 receptors), while the hot plate test (uncharacterized subtype) shows an intermediate development of supersensitivity.

The effects of intrabrainstem injections of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) into the B3 raphe region (nucleus raphe magnus and nucleus reticularis paragigantocellularis) on early ingestive behavior and nociception were assessed in Sprague-Dawley rat pups during the first postnatal week. Lesions resulted in a marked depletion of serotonin (5HT) in hindbrain without influencing 5HT levels in forebrain. Pretreatment with desipramine (DMI) resulted in a sparing of noradrenergic neurons from neurotoxic effects. The B3 lesion resulted in significant hyperalgesia as reflected by decreased latencies in tail flick testing. Although nipple attachment latencies in suckling tests were slightly increased by the lesion, no notable effects on mouthing or other ingestive-related behaviors were observed in testing conducted in an independent ingestion paradigm. These results suggest that whereas B3 serotonergic neurons may be functioning in an adult-typical manner to regulate analgesia during the early postnatal period, this raphe region may play only a slight role in the modulation of ingestion-related behaviors early in life.

The sequential course of uptake by retinal cells of intravitreally injected 5,7-dihydroxytryptamine (5,7-DHT) together with dopamine (DA) was investigated in juvenile carp retinas, which were removed at various intervals (1-24 h) after injection. The cells taken up 5,7-DHT were visualized immunohistochemically with anti-serotonin (5-HT) antibody and FITC-conjugated IgG. After a mixture of 5,7-DHT and DA (2.5, 10 or 20 micrograms each) was given, large-sized indoleamine (IA) amacrine cells first (1-4 h), and then small-sized indoleamine-accumulating amacrine amacrine (IAA) cells (4-12 h), bipolar cells (8-12 h) and in some cases photoreceptor cells (12-24 h) were sequentially observed, and finally the immunoreactive structures almost disappeared around 24 h after injection. When the mixture of 5,7-DHT and DA (10 micrograms each) was injected into the eyes of reserpinized fish, the same sequential uptake of 5,7-DHT was seen in a faster time course, but additionally various classes of retinal cells (horizontal, ganglion and Muller cells) became visible as irregular clusters. However, DA cells were never visualized at any stages of all the experiments, indicating that DA cells do not take up 5,7-DHT in the carp retina, which was further confirmed by double labeling of 5-HT- and tyrosine hydroxylase-like immunoreactive cells. Double labeling also revealed that 5,7-DHT-accumulating bipolar cells appear to represent a subclass different from that of protein kinase C-like immunoreactive bipolar cells.

"Denervation supersensitivity" of serotonin (5-HT) receptors has been proposed to explain the behavioral supersensitivity to 5-hydroxytryptophan (5-HTP) which develops after lesions of indoleamine neurons with 5,7-dihydroxytryptamine (5,7-DHT). To examine the possible role of receptor recognition sites and second messenger activity in supersensitivity, we measured regional 5-HT2 receptor ligand binding and 5-HT-stimulated phosphoinositide turnover in adult rats with 5,7-DHT lesions made by intracisternal injection and their saline-treated controls. In [3H]ketanserin binding studies of fresh brain tissue two weeks after 5,7-DHT injection, there were no significant changes in frontal cortex, brainstem, or spinal cord in Bmax, Kd, or nH of 5-HT2 receptors, 5,7-DHT lesions did not affect basal levels of [3H]inositol phosphate (IP) accumulation but significantly increased 5-HT-stimulated [3H]IP accumulation in the brainstem (+27%) and cortex (+23%). Because brainstem rather than cortex is involved in 5-HTP-evoked myoclonus, increased 5-HT-stimulated phosphoinositide hydrolysis in brainstem following 5,7-DHT lesions in the rat may be relevant to serotonergic behavioral supersensitivity.

In 62 male Wistar rats the influence was studied of the transplanted embryonal tissue of raphe nuclei (NR) on the mechanisms of compensation of disturbances of exploratory activity, sensory attention, learning and emotional reactivity induced by neonatal injection of 5,7-DHT. In histochemical studies by Falk-Hillarp method the presence of yellow fluorescence confirmed the specificity of transplanted 5-HT neurones. It is found that NR transplantation causes in animals after 3 months recovery of orienting reaction to sensory stimuli, reduces rats reactivity in the open field, restores the ability to discrimination of emotionally positive influence, disturbed by neonatal injection of 5,7-DHT. The obtained data show the possibility of compensation of behaviour disturbances caused by chronic deprivation of 5-HT system activity by transplantation in the neocortex parenchyma of the embryonal tissue, containing serotoninergic neurones.

The role of the hippocampal 5-hydroxytryptamine (5-HT) terminals in the control of locomotor activity was investigated by lesioning 5-HT axons in the fimbria with 5,7-dihydroxytryptamine (5,7-DHT). Rats pretreated with desimipramine (10 mg/kg, i.p.) received microinjections of 5,7-DHT (0, 1, 3, 5 or 10 micrograms in 0.4 microliter ascorbic Ringer's solution) into the fornix-fimbria. On the fourteenth to twenty-first nights after operation, nocturnal locomotor activity was measured in photocell cages. Twenty-eight to thirty days after operation degeneration of 5-HT terminals was assessed by measuring in vitro [3H]5-HT re-uptake in slices of dorsal hippocampus, ventral hippocampus and the septum. Groups injected with 5,7-DHT showed hyperactivity in the night period and increased decrements of activity between tests, both of which were related to the dose of neurotoxin. A reduction of [3H]5-HT re-uptake was found in dorsal hippocampus which was related to the dose of 5,7-DHT), but ventral hippocampal and septal [3H]5-HT re-uptake were not systematically reduced. For each rat, levels of dorsal and ventral hippocampal [3H]5-HT re-uptake were negatively correlated with the mean nocturnal activity from the 7 nights of testing. Levels of dorsal, but not ventral hippocampal [3H]5-HT re-uptake were negatively correlated with the mean nightly decrement of activity. No correlations were found between septal [3H]5-HT and these activity measures. These results, indicate that the increase in nocturnal locomotor activity caused by generalized depletion of 5-HT in the brain may be due to disruption of hippocampal 5-HT terminals supplied by the fornix-fimbria.

The analgesia induced by 30-s footshock (1 mA) is enhanced and attenuated by decreasing and increasing the extraneuronal availability of serotonin (5-HT), respectively. In the present work we have shown the effect to be mediated by spinal 5-HT systems as the response was increased by depletion of spinal but not brain 5-HT following injection of 5,7-dihydroxytrptamine into the spinal cord or raphe magnus. Injection of 5,7-DHT into the medial raphe which depleted brain but not spinal 5-HT was without effect.

The effect of intracerebral injections of 5,7-dihydroxytryptamine (5,7-DHT) and 6-hydroxydopamine (6-OHDA) on the serotonin (5-HT)-immunoreactive (IR) cell bodies 11 and fibers in the adult rat hypothalamus was studied with 5-HT immunocytochemistry. In rats pretreated with pargyline and l-tryptophan, 5-HT-IR cells were seen in the ventromedial part of the dorsomedial nucleus (DMN) and 5-HT-IR fibers in all hypothalamic areas. In the ventrolateral part of the DMN the 5-HT-IR fibers were of a much finer type than those seen in other hypothalamic areas. Five days after unilateral injection of 5,7-DHT into the dorsolateral hypothalamus, the 5-HT-IR cells were absent from the DMN, and there was a decrease in the number of 5-HT-IR fibers throughout the hypothalamus ipsilateral to the injection. Contralateral to the injection there was evidence of selective 5-HT fiber degeneration but the 5-HT-IR cells and the group of fine fibers in the ventrolateral DMN remained. Unilateral injection of 6-OHDA into the dorsolateral hypothalamus had no effect on the 5-HT-IR fibers or cell bodies in the hypothalamus. Twelve days after unilateral injection of 5,7-DHT into the rostral midbrain, the majority of 5-HT-IR fibers in the ipsilateral hypothalamus had disappeared. The 5-HT-IR cell bodies in the DMN and the group of fine 5-HT-IR fibers in the ventrolateral DMN remained on both sides of the hypothalamus. These results support our previous finding of a group of 5-HT-IR cell bodies in the ventromedial DMN of the hypothalamus, and suggest that these cells innervate the ventrolateral part of the same nucleus. Evidence that these cells constitute a new 5-HT cell group, B-10, is discussed.

1. The highest spinal cord levels of 5-hydroxytryptamine (5-TH) and thyrotropin releasing hormone (TRH) were found in the ventral lumbar cord, in contrast to substance P which was found predominantly in the dorsal cord. 2. 5,6- and 5,7-dihydroxytryptamine, administered into the lateral ventricles reduced 5-HT in the dorsal and ventral spinal cord by up to 90%. 3. There was a parallel reduction in substance P and TRH in ventral spinal cord while methionine-enkephalin and somatostatin in ventral and dorsal cord increased. 4. Reserpine and tetrabenazine depleted 5-HT and partially depleted substance P and TRH in the ventral cord, but had no effect on either methionine-enkephalin or somatostatin. 5. The rates of loss and recovery, after reserpine and tetrabenazine, of 5-HT were different from those of the two peptides. 6. Endogenous 5-HT and TRH release from slices of lumbar cord was enhanced by high potassium. 7. p-Chloroamphetamine and fenfluramine increased 5-HT release but reduced or had no effect on TRH release. The effect of p-chloroamphetamine on TRH release was not dependent on either the presence of 5-HT or 5-HT receptor activity. 8. The results are discussed in terms of the possible co-existence, co-storage and release of 5-HT, substance P and TRH in descending bulbospinal neurones.

Rats were implanted with cannulae in the median raphe nucleus (MR). 5,7-Dihydroxytryptamine (5,7-DHT) or vehicle was infused either directly through the MR cannula, or bilaterally into the medial forebrain bundle (MFB). The MR 5,7-DHT lesions completely blocked the hyperactivity elicited by injections into the MR of the neurokinin (NK) 3 agonists, DiMe-C7 and senktide, and the NK-2 agonist, neurokinin A. In contrast, the MFB 5,7-DHT lesions did not affect the locomotor hyperactivity produced by intra-MR administration of DiMe-C7 and senktide, but appeared to attenuate the effects of NKA. The data indicate that intra-raphe neurokinin-induced hyperactivity is mediated by 5-HT neurons, and that 5-HT projections to the forebrain may be involved in the behavioral activation induced by intra-raphe neurokinin A administration, but not that induced by intra-MR NK-3 agonists.

Proteins which are apparently regulated in concentration in two different areas of the rat brain by the indole neurotransmitter serotonin were identified using two-dimensional gel electrophoresis combined with computerized scanning densitometry. Reduction in central serotonin levels produced a decrease in the concentration of 3 different proteins (2 in the parietal cortex, 1 in the hippocampus). Two proteins, both in the hippocampus, were elevated in concentration following serotonin depletion. These results demonstrate that there exist in the brain a limited number of proteins whose concentration is influenced by serotonin.

Rats were treated as neonates or adults with desmethylimipramine (DMI) followed by intraventricular 6-hydroxydopamine (6-HDA) or 5,7 dihydroxytryptamine (5,7-DHT). Locomotor activity of treated rats was measured in photocell cages. Neonatal treatment with 5,7-DHT produced hypoactivity during development while neonatal 6-HDA led to hyperactivity. Treatment of adult rats with 5,7-DHT or 6-HDA, while resulting in equivalent monoamine depletions, was without effect on locomotor activity. The dose response function for caffeine was determined in these rats. Depletion of dopamine by either neonatal or adult treatment with 6-HDA decreased caffeine stimulation of locomotor activity. The adenosine receptor agonist 1-phenylisopropyladenosine (L-PIA) decreased locomotor activity in all rats in a dose-dependent fashion.

The tail vasomotor tone in rats is reduced by the intraventricular injection of 5,7-dihydroxytryptamine but not by 6-hydroxydopamine. Central serotonergic but not noradrenergic neurons participate in vasoconstriction of the tail.

Thyrotropin-releasing hormone (TRH), present in high concentrations in the mammalian spinal cord, exerts excitatory effects on the alpha-motorneuron (AMN) via axodendritic contacts. We used the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) to deplete TRH from the ventral horn of the spinal cord of adults rats to determine whether the tripeptide may be trophic to the AMN. The rats were studied blindly and sequentially for 11 weeks. Motor performance remained normal by clinical and electrophysiologic assessments. AMN counts were not reduced in the lumbar cord, and gastrocnemius muscle showed no evidence of denervation in treated rats. We conclude that in the adult rat chronic ventral horn TRH deficiency does not lead to AMN degeneration and is not associated with a significant alteration of AMN function.

The present study sought to determine whether rats, treated neonatally with 5,7-dihydroxytryptamine (5,7-DHT), have an increased sensitivity to the respiratory and cough-depressant effects induced by dihydrocodeine. The serotonin (5-HT) levels in the whole brain of 5,7-DHT-treated rats were reduced to 19% of the corresponding control values. The 5,7-DHT-treated rats were supersensitive to the depression in frequency of respiration and cough reflex produced by i.p. administration of dihydrocodeine. The increased sensitivity to dihydrocodeine in terms of the depression of frequency of respiration and the cough reflex in 5,7-DHT-treated rats could possibly have been due to changes in the sensitivity of serotonergic receptors.

The regeneration of central adrenergic axons has been followed between 5 days and 18 months after 5,7-dihydroxytryptamine(5,7-DHT)-induced axotomy in the adult rat, using fluorescence histochemistry in combination with noradrenaline (NA) determinations and [3H]NA uptake measurements. The axonal and terminal degeneration caused by the 5,7-DHT treatment (150 micrograms intraventricularly) was, by 1--2 weeks after injection, accompanied by a 70% reduction of NA in the forebrain and 30% reduction in the brain stem, and by 43--85% reductions in the [3H]NA uptake capacity in various regions of the brain and spinal cord. Signs of sprouting of the drug-lesioned axons were evident along the terminal axon segments at 5 days after treatment. The sprouts increased rapidly in length and number during the subsequent weeks and by 2--6 months after injection new NA terminal systems of relatively normal density and distribution had been re-established in many initially denervated regions. In parallel there was a recovery of endogenous NA and [3H]NA uptake to the pre-injection levels in the brain, and to levels 50--75% of normal in the cervical and thoracic spinal cord. Four successive phases of the regeneration process are distinguished: (1) primary sprouting from the lesioned NA axon stumps, occurring within the first week after treatment; (2) seemingly random growth and proliferation of the newly formed sprouts during the second and third weeks; (3) directed, forward growth of some of the sprouts leading to a partial restoration of the original fibre paths, branching patterns and terminal networks within 3--6 months; (4) a concomitant removal of at least part of the abnormally directed sprouts. Although the original fibre architecture was quite accurately restored in many areas the regeneration was not always correct. Hyperinnervation patterns and abnormal terminal arrangements were often formed, and in the spinal cord the down-growth of the regenerating axons occurred predominantly along a route that is inconspicuous in the normal rat. It is concluded that at least certain types of central neurons regenerate very efficiently provided the conditions are favourable, and that under such conditions axonal regeneration in the mammalian CNS is subjected to regulatory mechanisms that can be very precise. The results provide evidence that the adult mammalian CNS possesses mechanisms for axonal guidance which allow the accurate regeneration of lesioned axonal tracts and branching patterns, as well as mechanisms of recognition making possible the re-establishment of the original terminal connections.

The effects of chronic depletion of serotonin on feminine sexual behavior (lordosis), cytosolic progestin receptors and estradiol nuclear receptors were investigated. Intrahypothalamic administration of 5,7-dihydroxytryptamine (5,7-DHT) markedly enhanced lordotic responding in estradiol benzoate (EB)-primed, 5,7-DHT-treated female rats and in EB-progesterone primed, 5,7-DHT-treated male rats. Cytosolic progestin receptors were measured in preoptic-hypothalamic nuclei related to reproductive function in sham and 5,7-DHT-treated rats after EB priming. In both sexes, no differences between sham and 5,7-DHT-treated subjects were noted for progestin binding in the medial preoptic nucleus, ventromedial nucleus or arcuate-median eminence area. Estrogen-nuclear complexes were measured in the same brain nuclei of female rats following EB priming, and no differences between sham and 5,7-DHT-treated rats were found. Under the conditions employed, it would appear that, despite marked elevations in lordotic responsivity, the accumulation of estrogen nuclear receptors and the levels of estrogen inducible progestin receptors remain unaltered after chronic depletion of serotonin. Thus, serotonergic influences on lordosis do not appear to involve changes in the expression of steroid receptor levels in preoptic-hypothalamic nuclei known to mediate hormone-dependent neuroendocrine processes.

The i.p. administration of reserpine daily for 4 days to rats brought about an increase of adrenal phenylethanolamine N-methyltransferase (PNMT) activity. However, the combination of the systemic administration of p-chlorophenylalanine (PCPA) and reserpine for 3 days produced an earlier increase in this adrenal enzyme. The effect was reduced significantly in the denervated gland. Prior administration of 5,7-dihydroxytryptamine (DHT) i.c.v. to rats greatly potentiated the inducing effect of reserpine. On the other hand, the depletion of catecholamines by giving rats alpha-methyl-p-tyrosine (AMPT) i.p. or 6-hydroxydopamine (6-OHDA) i.c.v. did not alter the action of reserpine on adrenal PNMT. PCPA, DHT, AMPT and 6-OHDA did not have any effect by themselves on adrenal PNMT, but the combination of PCPA and AMPT, each given i.p., caused increased adrenal PNMT activity. The administration of dopamine agonists, a treatment that increases adrenal TH, did not modify adrenal PNMT. We conclude that the induction of PNMT by reserpine involves depletion of catecholamines and serotonin, the depletion of serotonin having the more powerful effect. A monoaminergic (serotonergic) inhibitory pathway is involved in the central regulation of adrenal PNMT activity.

The conditioned place preference (CPP) paradigm was used to determine a role for serotonin in the nucleus accumbens in the mediation of the rewarding properties of d -amphetamine morphine and diazepam. The effect of these drugs on CPP was examined in controls and in animals with 5,7-dihydroxytryptamine lesions of the nucleus accumbans. The results from control animals confirmed that d -amphetamine (1.5 mg/kg, i.p.), morphine (2.0 mg/kg, i.p.) and diazepam (1.0 mg/kg, i.p.) produced place preference for a distinctive environment that had previously been paired with injections of the drug. In animals with 80% reduction of 5-hydroxytryptamine content of the nucleus accumbens, d -amphetamine CPP was unchanged and morphine CPP was attenuated compared with controls. Diazepam CPP was not apparent in animals with the lesion. In separate experiments, characteristic behavioural effects of the drugs under study were examined in control and in animals with lesion. The results showed a tendency for increased amphetamine hyperlocomotion, enhanced morphine activity and analgesia and decreased diazepam anti-anxiety effect in animals with lesions. Thus, the 5,7-dihydroxytryptamine lesions of the nucleus accumbens differently influenced the CPP induced by the drugs studied and, with the exception of diazepam, the various behavioural effects elicited by each drug. The findings suggest that serotonin-containing neurones of the nucleus accumbens are a component of the neural circuitry that mediates the rewarding properties of morphine, probably of diazepam, but not of d -amphetamine.

Intrahemocoelial administration of 5,7-dihydroxytryptamine (5,7-DHT) to Aplysia californica induces a transient (less than 4 h) behavioral alteration. About 5 weeks after 5,7-DHT treatment, 5-hydroxytryptamine (5-HT)-containing neurons develop dark brown pigmentation. These labeled 5-HT neurons have normal physiological and pharmacological properties when investigated electrophysiologically. This contrasts with the long-term neurotoxic effect of 5,7-DHT on vertebrate neurons. This technique will greatly facilitate visual identification of 5-HT-containing neurons and study of their physiology and actions.

In order to establish a more complete behavioral profile on animals induced to kill mice following serotonin depletion, naturally non-mouse-killing male Long-Evans rats were administered 5,7-dihydroxytryptamine (5,7-DHT) in a saline-ascorbic acid vehicle or vehicle alone to the left lateral ventricle through a chronically indwelling cannula. Following a postsurgical delay, animals were tested for mouse killing, food and water consumption, spontaneous motor activity, and exploratory behavior. 5,7-DHT treatment resulted in a significant increase in the incidence of mouse killing over vehicle-injected controls in the absence of effects on the other behaviors investigated. In a second experiment, 5,7-DHT-treated rats from Experiment I were administered small doses of serotonin intraventricularly. An additional group of spontaneously mouse-killing rats also received intraventricular injections of serotonin. This manipulation led to a significant increase in the latency of both groups to kill mice over both preinjection latencies and vehicle-injected control animals. Since serotonin depletion resulted in the induction of mouse killing in naturally nonkilling rats without affecting other potentially contributory behaviors and since the mouse killing could be reversed by intraventricular administration of serotonin an inhibitory role for serotonin in the mediation of mouse killing is suggested.

In order to assess the role of the serotonergic system in the development of tolerance to ethanol in the mouse, serotonin neurons in the CNS were lesioned with an intracerebroventricular injection of the neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT). Mice injected with 5,7-DHT responded to an acute dose of ethanol with a longer sleep time and greater fall in body temperature than CSF-treated mice. The increased response to acute administration of ethanol was accompanied by higher circulating levels of ethanol in mice pretreated with 5,7-DHT. When mice were fed an ethanol-containing liquid diet for five days, a higher mortality rate was observed in the 5,7-DHT group compared to the CSF pretreated group of mice. When the groups of mice were tested for tolerance 24 hours after withdrawal, the 5,7-DHT group was less tolerant than the CSF group. Therefore, damage to the serotonin neurons results in altered ethanol disposition, altered initial sensitivity to ethanol, and an inhibition in the development of tolerance in the mouse.

Rat pups were injected intracisternally (i.c.) or intraperitoneally (i.p.) with 5,7-dihydroxytryptamine (5,7-DHT) or saline and challenged 2 and 14 weeks later with the 5-HT precursor, 5-hydroxytryptophan (5-HTP), which evokes behavioral supersensitivity in adult rats. 5,7-DHT induced transient postinjection convulsions in rats injected i.c. but not i.p. Rats with either type of 5,7-DHT lesions displayed supersensitive behavioral responses to 5-HTP. However, rats lesioned by i.p. injections exhibited significantly greater shaking behavior (+1445%) in response to 5-HTP than their i.c. counterparts, who instead showed more forepaw myoclonus (+250%) and head weaving (+270%), the core features of the 5-HT syndrome. Differences in 5-HT syndrome behaviors were already present 2 weeks after lesioning, whereas the difference in shaking behavior was not. After 14 weeks, 5-HT was selectively depleted (−43 to −92%) in hippocampus, spinal cord, and frontal cortex, and differences between i.c. and i.p. 5,7-DHT routeswere insignificant except in frontal cortex. Brainstem 5-HT concentrations were significantly increased (+35%) after i.p. 5,7-DHT injections in contrast to reduction (−89%) after i.c. 5,7-DHT; 5-hydroxyindole acetic acid/5-hydroxytryptamine (5-HIAA/5-HT) ratios were decreased (−20%) with either route. These data suggest that brainstem 5-HT hyperinnervation following i.p. 5,7-DHT injection modifies the functional consequences of injury in abating the 5-HT syndrome, but does not result in complete recovery since shaking behavior is enhanced. Loss of presynaptically mediated autoregulation or receptor dysregulation may play a major role in behavioral supersensitivity induced by 5-HTP in rats with 5,7-DHT lesions. To the extent that the 5-HT syndrome is mediated by 5-HT 1A , receptors and shaking behavior by 5-HT 2 sites, differential responses to injury of 5-HT 1A and 5-HT 2 receptors may contribute to these behavioral differences.

Infant rats, treated intracisternally with 6-hydroxydopamine or 5,7-dihydroxytryptamine, alone or in combination with desmethylimipramine or pargyline, at 5 to 7 days of age, had significant specific depletions of brain norepinephrine, dopamine, both of these amines, or serotonin at 2.5 months of age. Despite apparent long-term depletions of brain biogenic amines, susceptibility to audiogenically-induced seizures following chronic ethanol withdrawal in these animals was similar to that of controls. Amine-depleted rats also displayed spontaneous withdrawal-induced tremors, spastic motor activity and irritability. The interpretation of these preliminary findings with regard to the proposed role of the biogenic amines in the development of physical dependence on ethanol is discussed.