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A Transcriptional Signature of Induced Neurons Differentiates Virologically Suppressed People Living With HIV from People Without HIV.

Neurocognitive impairment is a prevalent and important co-morbidity in virologically suppressed people living with HIV (PLWH), yet the underlying mechanisms remain elusive and treatments lacking. Here, we explored for the first time, use of participant-derived directly induced neurons (iNs) to model neuronal biology and injury in PLWH. iNs retain age- and disease-related features of the donors, providing unique opportunities to reveal novel aspects of neurological disorders. We obtained primary dermal fibroblasts from six virologically suppressed PLWH (range: 27 - 64 years, median: 53); 83% Male; 50% White) and seven matched people without HIV (PWOH) (range: 27 - 66, median: 55); 71% Male; 57% White). iNs were generated using transcription factors NGN2 and ASCL1, and validated by immunocytochemistry and single-cell-RNAseq. Transcriptomic analysis using bulk-RNAseq identified 29 significantly differentially expressed genes between iNs from PLWH and PWOH. Of these, 16 genes were downregulated and 13 upregulated in PLWH iNs. Protein-protein interaction network mapping indicates that iNs from PLWH exhibit differences in extracellular matrix organization and synaptic transmission. IFI27 was upregulated in iNs from PLWH, which complements independent post-mortem studies demonstrating elevated IFI27 expression in PLWH-derived brain tissue, indicating that iN generation reconstitutes this pathway. Finally, we observed that expression of the FOXL2NB-FOXL2-LINC01391 genome locus is reduced in iNs from PLWH and negatively correlates with neurocognitive impairment. Thus, we have identified an iN gene signature of HIV through direct reprogramming of skin fibroblasts into neurons revealing novel mechanisms of neurocognitive impairment in PLWH.

HAND

Techniques for converting Golgi precipitate in CNS neurons into stable electron microscopic markers.

Direct electron microscopy of nervous tissue stained with the Golgi impregnation method is unsatisfactory because the cytoplasm of the cell bodies and processes of the impregnated neurons are completely filled with a compact precipitate of electron dense silver chromate. This precipitate entirely obscures the cytological details of the impregnated neurons. Because of its solidity and instability in aqueous solutions, the silver chromate is also a source of inconvenience during the preparation of the ultrathin sections. This review summarizes methods that have been developed with the aim of replacing the Golgi precipitate in CNS neurons with a more convenient electron dense material--for example, heavy metal salts or metallic particles. Conversion of the precipitate into a stable electron dense marker is done before the material is embedded for electron microscopy. The methods include lead, gold, and bromide substitution, treatment with ammonia, direct chemical reduction into metallic silver, and photoreduction of the silver chromate into silver through irradiation with ultraviolet light.

Aminophenols

Mutations in the channel domain of a neuronal nicotinic receptor convert ion selectivity from cationic to anionic.

Introduction by site-directed mutagenesis of three amino acids from the MII segment of glycine or gamma-aminobutyric acid (GABAA) receptors into the MII segment of alpha 7 nicotinic receptor was sufficient to convert a cation-selective channel into an anion-selective channel gated by acetylcholine. A critical mutation was the insertion of an uncharged residue at the amino-terminal end of MII, stressing the importance of protein geometrical constraints on ion selectivity.

Acetylcholine

Modifications induced by neonatal steroids in reproductive organs and behavior of male rats.

Male rats injected on Day 3 neonatally with .01, .1, 1, 10, 100, or 1,000 micrograms of estradiol benzoate (EB), 10,000 microgram of testosterone propionate (TP), or sesame oil were subsequently examined for testicular, penile, and accessory organ development. Sexual behavior was evaluated during therapy with fluoxymesterone (FM) and then with TP. Estradiol benzoate in dosages greater than 1.0 micrograms delayed testicular descent, reduced the size and hormone responsiveness of reproductive organs, and decreased sexual behavior in a dose-dependent manner. The 10,000-microgram dosage of neonatal TP delayed testicular descent and reduced sexual behavior to levels near those of the 10--100 micrograms EB groups, but it produced no significant penile or accessory organ changes. Neither reduced peripheral organ development nor inhibited neonatal testicular secretions fully explain reductions in male behavior following large dosages of neonatal TP. Neonatal androgen may reduce the responsiveness of central nervous system neurons governing male sexual behavior after being converted to estrogen or by directly altering steroid receptor systems.

Animals

Metabolism of acetylcholine in the nervous system of Aplysia californica. III. Studies of an indentified cholinergic neuron.

[3H] choline and [3H] acetyl CoA were injected into the cell body of an identified cholinergic neuron, the giant R2 of the Aplysia abdominal ganglion, and the fate and distribution of the radioactivity studied. Direct eveidence was obtained that the availabliity of choline to the enzymatic machinery limits synthesis. [3H] choline injected intrasomatically was converted to acetylcholine far more efficiently than choline taken up into the cell body from the bath. Synthesis from injected [3H] acety CoA was increased more than an order of magnitude when the cosubstrate was injected together with a saturating amount of unlabeled choline. In order to study the kinetics of acetylcholine synthesis in the living neuron, we injected [3H] choline in amounts resulting in a range of intracellular concentrations of about four orders of magnitude. The maximal velocity was 300 pmol of acetylcholine/cell/h and the Michaelis constant was 5.9 mM [3H] choline; these values agreed well with those previously reported for choline acetyltransferase assayed in extracts of Aplysia nervous tissue. [3H] acetylcholine turned over within the injected neuron with a half-life of about 9 h. The ultimate product formed was betaine. Subcellular distribution of [3H] acetylcholine was studied using differential and gradient centrifuagtion, gel filtration, and passage through cellulose acetate filters. A small portion of acetylcholine was contained in particulates the size and density expected of cholinergic vesicles.

Acetyl Coenzyme A

Metabolism of [3H]serotonin in the marine mollusc, Aplysia californica.

The fate of serotonin was studied in several tissues of the marine mollusc, Aplysia californica. When isolated nervous tissue was bathed in [3H]serotonin, two radioactive derivatives were formed; both appeared to be sugar conjugates: the first, possibly of glucuronic acid, and the second, of a more complex sugar moiety. When [3H]serotonin was injected directly into cell bodies of identified neurons, both serotonergic and non-serotonergic, only the conjugate which behaved as the glucuronide was formed. [3H]Serotonin was also converted only to this substance during incubation with isolated heart, kidney and hemolymph. Metabolic activity of the blood resided within cellular elements. No evidence of oxidative deamination was found in any tissue. In contrast to serotonin, however, [3H]tryptamine was readily oxidized to indoleacetic acid by nervous tissue.

Acetylation

A proposed mechanism for the biphasic vasoconstrictor responses to 5-hydroxytryptamine and methysergide in the rabbit ear artery.

Rabbit ear arteries were isolated and perfused at a constant flow rate so that the perfusate flowed into the fluid bathing the adventitial surface of the artery. Submaximal doses of intraluminally applied noradrenaline injected as a bolus into the perfusion fluid produced transient monophasic vascoconstrictor responses. In contrast, similarly administered 5-hydroxytryptamine (5-HT) or methysergide caused prolonged biphasic vascoconstrictor responses. The extraluminal/intraluminal potency ratios for noradrenaline, 5-HT and methysergide were 230, 15 and 6 respectively, which indicates that 5-HT methysergide are relatively more potent when administered extraluminally than noradrenaline. Cocaine (3-0 X 10(-5) mol litre-1) markedly increased the potency of extraluminally administered noradrenaline and converted the monophasic responses produced by noradrenaline to biphasic responses. It is concluded that under the experimental conditions used 5-HT and methysergide produced biphasic responses by an action on the medial smooth muscle firstly via the intraluminal surface and secondly an additional direct action via the adventitial surface. Noradrenaline's extraluminal potency is low because of its neuronal uptake and hence the responses are normally monophasic.

Animals

Epinephrine and the genesis of hypertension.

Several lines of evidence suggest a psychophysiological link between stress, adrenomedullary activation, and the genesis of hypertension. Experimental data support four important concepts: 1) epinephrine stimulates prejunctional beta 2-adrenergic receptors that facilitate norepinephrine release from sympathetic nerve endings; 2) epinephrine can be converted into a cotransmitter by neuronal uptake and on subsequent release augment the simultaneous discharge of norepinephrine; 3) exogenous epinephrine can induce sustained hypertension in rats; and 4) there is a period of critical sensitivity to endogenous epinephrine in a genetic model of rat hypertension. Plasma epinephrine concentrations are elevated in many young subjects with borderline or mild hypertension. The hypothesis that intermittent surges in epinephrine could initiate or promote the development of primary hypertension by amplifying peripheral neurotransmission, both directly (facilitative effect) and indirectly (cotransmitter action), is supported by reports that hemodynamic and noradrenergic responses to sympathetic activation can be augmented by increases in endogenous epinephrine or by its local or systemic (up to 30 ng/kg/min) infusion. Such responses have been documented in both normotensive and hypertensive subjects and can be blocked by propranolol. Although the weight of evidence (mostly indirect) indicates that epinephrine can augment norepinephrine release in humans, the epinephrine hypothesis, itself, remains unproven. Expression of hypertension by this mechanism may be restricted to a specific epinephrine-sensitive subset of individuals with a genetic predisposition to high blood pressure.

Animals

The pinealocyte--a paraneuron? A review.

The pineal complex develops from a tubular evagination of the diencephalic roof. In amphibians a proliferation zone is the source of the pinealocytes and of the cells of the subcommissural organ. The pinealocytes are not real nerve cells, but derived likewise from the embryonic neural epithelium. The pinealocytes of lower vertebrates are directly photosensitive; however, the morphological structures for direct light perception are gradually lost in the phylogenetic development and are absent in the pinealocytes of mammals. A secretory function is shown in the pinealocytes of all vertebrates, but it is more pronounced in the pinealocytes of reptiles, birds and mammals; dense-cored vesicles originate in the Golgi complex and are transported to and accumulated in the terminals of the basal processes near the perivascular space. Nerve cells are in synaptic ribbon contact with pinealocytes in lower vertebrates and their axons give a rise to the tractus pinealis. The nerve cells and nervous connection with the brain are absent in the pineal organ of mammals. Only few autonomic fibers reach the pineal organ of lower vertebrates, but the sympathetic and parasympathetic innervation are well developed in the pineal organ of most species of birds and mammals. The transmitter release from the sympathetic fibers is influenced by environmental light; light mediates in this way the activity of hormone producing enzymes in the pinealocytes. The synthesis of indolderivates, like melatonin, is confirmed and the presence of a polypeptide hormone is discussed. Accordingly, the pineal organ functions as a "neuro" chemical, "neuro" endocrine transducer or photo-"neuro" endocrine organ, which converts a light input (direct in lower vertebrates, via transmitter release by sympathetic fibers in mammals) into a hormonal output. The pineal organ thus provides the animal with a "biological clock", which is geared to the lighting environment. The pineal organ is a regulator (or a regulator of regulators) for several body functions. In mammals, the influence on the synchronization of the gonadal activity is best known. The pinealocyte is a hormone producing cell, which shows common features with the liquor contacting neurons and with the neurosecretory cells; after the definition of FUJITA (1976) the pinealocyte is said to be a paraneuron, also.

Animals

Effects of changes in cortical excitability upon the epileptic bursts in generalized penicillin epilepsy of the cat.

Previous studies had suggested that the epileptic bursts of feline generalized penicillin epilepsy represent the response of hyperexcitable cortex to thalamocortical volleys normally evoking spindles. If this were the case, it should be possible to convert the epileptic bursts of generalized penicillin epilepsy into spindles by decreasing the excitability of cortical neurons. In cats exhibiting the EEG signs of feline generalized penicillin epilepsy cortical excitability was decreased by hypoxia, by the topical application to the cortex of KCl (inducing spreading depression), barbiturates, GABA, AMP or noradrenaline. During generalized penicillin epilepsy, hypoxia and KCl-induced spreading depression abolished epileptic bursts which were replaced by spindles. When spindles and epileptic complexes occurring in the same animal were compared, a direct correlation between the frequencies of these two rhythms could be demonstrated, that of the epileptic complexes being about half that of the spindle waves. These observations support the hypothesis that the epileptic bursts of feline generalized penicillin epilepsy are induced by thalamocortical volleys normally involved in spindle genesis. Topical cortical applications of barbiturates, GABA, AMP and noradrenaline reduced or inverted the negative spikes of the spike and wave complexes, while augmenting the negative slow waves, or revealing them clearly in instances in which they had been poorly developed. This effect is interpreted as being due to a selective inactivation of the superficial cortical layers. That topical cortical application of barbiturates, GABA, AMP and noradrenaline was capable of transforming into typical spike and wave complex epileptic bursts, which had not previously conformed to this pattern, indicates that the intracortical electrophysiological events of typical and atypical epileptic bursts in feline generalized penicillin epilepsy are fundamentally the same and reflect an alternation between excitatory and inhibitory sequences.

Adenosine Monophosphate

Genetic alteration of catecholamine specificity in transgenic mice.

Epinephrine-producing cells are characterized by the presence of phenylethanolamine N-methyltransferase (PNMT), which catalyzes the formation of epinephrine from norepinephrine. We generated a line of transgenic mice carrying a chimeric gene containing human PNMT cDNA fused to the 4-kilobase fragment of the human dopamine beta-hydroxylase (DBH) gene promoter, to switch catecholamine phenotype in the nervous and endocrine systems. Human PNMT transcripts and immunoreactivity were mainly detected in norepinephrine neurons in brain and sympathetic ganglion as well as in norepinephrine-producing cells in adrenal medulla of transgenic mice, indicating that the human DBH gene promoter of 4 kilobases is sufficient to direct expression of the gene in norepinephrine-producing cells. Analysis of catecholamines in the various tissues showed that the expression of human PNMT in transgenic mice induced the appearance of epinephrine in sympathetic ganglion and dramatic changes in norepinephrine and epinephrine levels in brain, adrenal gland, and blood. These results indicate that the additional PNMT expression in norepinephrine-producing cells can convert these cells to the epinephrine phenotype, and suggest that norepinephrine-producing cells normally possess the basic machinery required for the synthesis of epinephrine except for PNMT. Thus it appears that the only major difference between norepinephrine- and epinephrine-producing cells is the expression of PNMT. Our transgenic animals provide an experimental model to investigate the functional differences between norepinephrine and epinephrine.

Animals

In vivo imaging of calcium accumulation in fly interneurons as elicited by visual motion stimulation.

The computation of motion plays a central role in visual orientation. The fly has been successfully used as a model system for analyzing the mechanisms underlying motion detection. Thereby, much attention has been paid to a neuronal circuit of individually identifiable neurons in the third visual ganglion that extracts different types of retinal motion patterns and converts these patterns into specific components of visual orientation behavior. The extended dendritic trees of these large cells are the sites of convergence of numerous spatially distributed local motion-sensitive elements. As is revealed by in vivo microfluorometric imaging, these cells accumulate calcium during activation by visual motion stimulation. The spatiotemporal pattern of calcium distribution shows the following characteristics: (i) calcium accumulation is first spatially restricted to those dendritic branches that are depolarized by the retinotopic input, (ii) during ongoing motion stimulation calcium may also accumulate throughout the cell and, in particular, in regions that do not receive direct synaptic input. These experiments successfully monitor the intracellular distribution of activity-dependent ions in visual interneurons of living animals stimulated by their natural synaptic input.

Animals

Peptone stimulates gastrin secretion from the stomach by activating bombesin/GRP and cholinergic neurons.

The mechanism by which partly digested protein (peptone) stimulates gastrin secretion was examined in isolated antral tissues with intact intramural innervation. In the isolated vascularly perfused rat stomach, luminal perfusion with 0.5% peptone increased gastrin (62 +/- 14 pg/min; P less than 0.01) and decreased somatostatin (74 +/- 19; P less than 0.01) secretion. The axonal blocker tetrodotoxin (TTX) abolished the gastrin and somatostatin responses indicating that the responses were neurally mediated. Atropine partly inhibited the gastrin response (50%) and converted the somatostatin response to an increase above basal level. The selective bombesin/gastrin-releasing peptide (GRP) antagonist [Leu13-psi(CH2NH)-Leu14]-bombesin partly inhibited the gastrin response (65%) and caused a further decrease in somatostatin secretion. A combination of atropine and the bombesin/GRP antagonist, like TTX, abolished the gastrin and somatostatin responses. The pattern of response to peptone in superfused antral segments was identical to that in the vascularly perfused stomach. In fundic segments that do not secrete gastrin, the somatostatin response to peptone alone and with various antagonists was identical to that in antral segments. The results indicate that peptone stimulates gastrin secretion by activating stimulatory cholinergic and bombesin/GRP neurons. Cholinergic neurons stimulate gastrin directly as well as indirectly by eliminating the inhibitory paracrine influence of somatostatin.

Animals

CRISPR-Enabled functional genomics in hPSCs-derived neural models for autism spectrum disorder.

Autism Spectrum Disorder (ASD) is a genetically heterogeneous neurodevelopmental condition in which hundreds of individually rare risk variants converge on a small number of shared biological pathways, including synaptic scaffolding, chromatin remodeling, excitation-inhibition balance, and cellular energy metabolism. Translating this genetic heterogeneity into mechanistic insight requires experimental systems capable of interrogating individual gene functions in human-relevant neural contexts at scale. CRISPR-enabled functional genomics in human pluripotent stem cell (hPSC)-derived neural models, spanning neural progenitors, cortical and inhibitory neurons, astrocytes, microglia, and brain organoids, provides precisely this capability. By integrating pooled perturbation screens with multimodal readouts including single-cell and spatial transcriptomics, chromatin accessibility profiling, proximity labeling proteomics, multi-electrode array electrophysiology, and metabolic flux analysis, these platforms enable systematic, causal mapping of ASD gene function at system resolution. Early applications have already revealed convergent mechanisms: BAF complex disruption expands the ventral progenitor pool and biases its fate toward oligodendrocyte and interneuron lineages; ADNP loss impairs microglial synaptic pruning through altered endocytic trafficking; and mTOR pathway dysregulation in PTEN- and TSC2-perturbed models links genetic risk directly to metabolic and mitochondrial dysfunction. Computational frameworks including MIMOSCA and SCEPTRE enable causal network reconstruction and pseudotime inference from these datasets, moving the field from gene lists toward pathway-level models of ASD pathobiology. Translational applications leverage isogenic iPSC panels and variant-level base and prime editing to stratify ASD variants by functional impact, informing gene therapy design for haploinsufficient targets such as CHD8 and SCN2A via AAV or antisense oligonucleotide delivery. Remaining challenges, including model developmental immaturity, batch variability, and the difficulty of modeling polygenic risk, are addressed by a roadmap integrating spatial perturbomics, AI-driven causal inference, and population-scale standardized biobanks. This review synthesizes the current state of CRISPR-based functional genomics in human stem cell neural models as a coherent experimental framework for converting ASD genetic associations into mechanistic understanding and therapeutic opportunity.

Humans

Inward current caused by sodium-dependent uptake of GABA in the crayfish stretch receptor neurone.

A two-microelectrode current-voltage clamp and Cl(-)-selective microelectrodes were used to examine the effects of gamma-aminobutyric acid (GABA) on membrane potential, current and intracellular Cl- activity (aiCl) in the crayfish stretch receptor neurone. All experimental solutions were CO2-HCO3- free. 2. GABA (500 microM) produced a mono- or biphasic depolarization (amplitude < or = 10 mV), often with a prominent initial depolarizing component followed by a transient shift to a more negative level. In some neurones, an additional depolarizing phase was seen upon washout of GABA. Receptor desensitization, being absent, played no role in the multiphasic actions of GABA. 3. The pronounced increase in membrane conductance evoked by GABA (500 microM) was associated with an increase in aiCl which indicates that the depolarizing action was not due to a current carried by Cl- ions. 4. The currents activated by GABA under voltage clamp conditions were inwardly directed when recorded at the level of the resting membrane potential, and they often revealed a biphasic character. The reversal potential of peak currents activated by pulses of 500 microM-GABA (EGABA) was 9-12 mV more positive than the reversal potential of the simultaneously measured net Cl- flux (ECl). ECl was 2-7 mV more negative than the resting membrane potential. 5. EGABA (measured using pulses of 500 microM-GABA) was about 10 mV more positive than the reversal potential of the current activated by 500 microM-muscimol, a GABA agonist that is a poor substrate of the Na(+)-dependent GABA uptake system. 6. In the absence of Na+, the depolarization and inward current caused by 500 microM-GABA were converted to a hyperpolarization and to an outward current. Muscimol produced an immediate outward current both in the presence and absence of Na+. 7. Following block of the inhibitory channels by picrotoxin (100-200 microM), the depolarizing effect of 500 microM-GABA was enhanced and the transient hyperpolarizing shifts were abolished. 8. In the presence of picrotoxin, GABA (> or = 2 microM) produced a concentration-dependent monophasic inward current which had a reversal potential of +30 to +60 mV. This current was inhibited in the absence of Na+ and by the GABA uptake blocker, nipecotic acid. Unlike the channel-mediated current, the picrotoxin-insensitive current was activated without delay also at low (2-10 microM) concentrations of GABA.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals

A double scanning microphotometer for image analysis: hardware, software and biomedical applications.

A new image processing system designed for densitometry and pattern analysis of microscopic specimens is described with special regard to the hardware, the software and the biologic applications. The data acquisition procedure involves the combination between the scanning of the preparation by means of a motorized stage and the scanning of successive fields by a mechanical device. The signal provided by the photomultiplier is converted into digital values which are directed to an on-line computer. The data processing is based on a one-pass computation involving automata theory and therefore it avoids the storage of the image in the computer memory. In so doing, an entire and continuous image of the whole preparation can be processed at the highest magnification of the microscope whatever the size of the analyzed specimen may be. A biologic application of the system is reported and concerns the automatic identification and counting of cells in the various phases of the mitotic cycle.

Animals

Smooth pursuit disorders.

Smooth pursuit is a relatively recent eye movement which has developed in frontal-eyed species. The smooth pursuit system is involved during foveal smooth pursuit, the 'rapid' component of OKN slow phase and VOR suppression. The cortical areas controlling smooth pursuit (at the temporo-parieto-occipital junction and in the FEF) send ipsilateral projections onto the pontine nuclei, mainly the DLPN, passing through the anterior part of the midbrain. A midbrain or DLPN lesion results in ipsilateral smooth pursuit impairment (i.e. decreased gain) (Table 1). After the pontine nuclei, all smooth pursuit pathways pass through the cerebellum. They project onto the flocculus, mainly contralaterally (first decussation of the lateral smooth pursuit circuitry), and bilaterally onto the posterior vermis. Eye velocity is encoded in the activity of the floccular Purkinje cells, whereas target velocity is encoded in that of the vermal Purkinje cells. Unilateral floccular lesions and posterior vermal lesions (involving both sides of this structure) result in ipsilateral and bilateral smooth pursuit impairment, respectively. The flocculus sends an ipsilateral inhibitory projection onto the MVN, the y-group nucleus and the SVN, controlling contralateral, upward and perhaps downward smooth pursuit, respectively. Alternatively, the downward smooth pursuit pathway could pass through the dentate nuclei. The MVN sends a contralateral excitatory projection onto the abducens nucleus (second decussation of the lateral smooth pursuit circuitry). These anatomical and physiological characteristics of lateral smooth pursuit pathways, in addition to the results of lesion studies, suggest that, besides the floccular inhibitory Purkinje cell, there is another inhibitory neurone in the circuitry preceding this cell, perhaps within the flocculus itself. The posterior vermis projects onto the fastigial nuclei, which also control smooth pursuit. These nuclei could send efferents to those periabducens cells involved in ipsilateral smooth pursuit. The final part of the pathways involved in vertical smooth pursuit could pass mainly through the BC, originating in the y-group nucleus for upward movement and in the SVN or the dentate nuclei for downward movement. Alternatively, a ventral tegmental tract could transmit upward smooth pursuit signals between the y-group nucleus and the oculomotor nucleus. The MLF also belongs to this vestibulo-oculomotor circuitry, but does not appear to be crucial for vertical smooth pursuit since this eye movement is only partially impaired after MLF lesions. Lastly, parallel to the direct vestibulo-ocular motor nuclei pathways, there are other pathways passing through the brain stem integrators, converting eye velocity signals to eye position signals during all eye movements, including smooth pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals

Effects of 5-hydroxytryptamine on the lower esophageal sphincter in vivo: evidence for multiple sites of action.

Intravenous administration of 5-hydroxytryptamine (5-HT) caused a dose-dependent contraction in the lower esophageal sphincter in the opossum. The smallest dose of 5-HT which caused a detectable contraction of the sphincter was 0.5 mug/kg, and a maximal sphincter contraction was produced by a dose of 40 mug/kg. Methysergide converted the contractile effect of 5-HT to a dose-dependent fall in the sphincter pressure; maximal inhibition of 77.2 +/- 7.2% of the resting pressure occurred with a dose of 40 mug/kg. The inhibitory effect of 5-HT was antagonized by tetrodotoxin, 5 MeO-DMT, and 5-HT tachyphylaxis. 5 MeO-DMT enhanced 5-HT-induced contraction of the sphincter. In the presence of 5 MeO-DMT and methysergide, 5-HT still caused a brief contraction of the sphincter; this contraction appeared to be due to stimulation of postganglionic cholinergic neurons as it was antagonized by tetrodotoxin or atropine. Reserpinization caused enhancement of the sphincter contraction by 5-HT. In the reserpinized animals in the presence of methysergide, 5-HT caused a small initial contraction followed by prolonged inhibition; atropine antagonized the initial contraction, while inhibition was antagonized by 5 MeO-DMT. These studies are consistent with the view that 5-HT exerts several different effects on the sphincter. 5-HT causes contraction of the sphincter by its direct action on the muscle and also by stimulation of cholinergic excitatory neurons. In addition, 5-HT inhibits the sphincter by stimulation of nonadrenergic inhibitory neurons.

5-Methoxytryptamine