The effect of raphe nuclei lesions on the rat ovarian cycle

The effects of lesions of the median raphe or dorsal raphe nuclei on ovarian cycle were studied in rats. Lesions involving raphe nuclei decreased forebrain 5-HT and 5-hydroxyindole acid (5-HIAA) concentrations. Rats with lesions of the raphe showed prolonged estrous phase as well as an increase in both the eosinophilic index and karyopycnotic index of the vaginal smears. Histological examinations revealed that lesions of both the dorsal and median raphe produced marked increase in the number of maturing and mature follicles as well as an increase in corpora lutea. The increase in uterine weight was also observed. Present results indicate that lesions of the ascending 5-HT neurons stimulate ovulation and cause an increase in the estrogenic activity. Thus, the 5-HT neurons of the raphe nuclei seem to inhibit ovulation probably due to inhibiting of the hypothalamic releasing hormones.     

Firing of 5-HT neurones in the dorsal and median raphe nucleus in vitro shows differential alpha1-adrenoceptor and 5-HT1A receptor modulation

The median raphe nucleus and dorsal raphe nucleus together are the major source of ascending 5-HT projections. Here, using in vitro extracellular single unit electrophysiology we examined the responses of individual neurones in the rat median raphe nucleus and dorsal raphe nucleus to alpha(1)-adrenoceptor and 5-HT(1A) receptor activation and made comparisons between the two nuclei. In the presence of the alpha(1)-adrenoceptor agonist phenylephrine (1microM) all spontaneously active neurones recorded in the median and dorsal raphe nuclei fired slowly (<5Hz) and regularly. Most were inhibited by 5-HT (10-50microM), although a few were excited by 5-HT. 5-HT-induced inhibition was attenuated by the 5-HT(1A) receptor antagonist, WAY100635 (100nM). Compared to those in the dorsal raphe nucleus, the neurones in the median raphe nucleus which were inhibited by 5-HT had: (1) lower basal firing rates in the continuous presence of phenylephrine (1microM), (2) smaller excitatory responses to higher concentrations of phenylephrine (3-10microM), (3) smaller excitatory responses to brief application of norepinephrine (10-100microM) and (4) smaller inhibitory responses to 5-HT (10-50microM). The lower sensitivity of median raphe neurones to alpha(1)-adrenoceptor excitation and 5-HT(1A) receptor inhibition will have consequences for 5-HT neurotransmission in forebrain regions innervated by the two nuclei.     

Tryptamine Concentrations in Areas of 5-Hydroxytryptamine Terminal Innervation After Electrolytic Lesions of Midbrain Raphe Nuclei

The possible existence of tryptamine-containing neurons originating in the midbrain raphe is suggested by several reports of tryptamine-mediated responses to electrical stimulation of the raphe nuclei. To assess this hypothesis, we have investigated the effects of electrolytic lesions of the median and dorsal raphe nuclei on striatal, hypothalamic, and hippocampal concentrations of tryptamine, 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid. In addition, the rat striatal tryptophan concentrations were also determined. No changes in the concentrations of tryptamine were observed at 1 or 2 weeks after lesioning the dorsal and median raphe nuclei, at which time the other 5-hydroxyindoles were markedly reduced; furthermore, no reductions were observed in tryptamine concentrations in the striatum, hypothalamus, or hippocampus of rats pretreated with a monoamine oxidase inhibitor. The only change observed in these rats was a limited increase in striatal tryptamine and tryptophan observed at 1 day after lesioning. The results indicate that tryptamine concentration is independent of the integrity of 5-HT-containing neurons of the midbrain raphe nuclei. Furthermore, if tryptamine-containing neurons that have terminal projections to the striatum, hypothalamus, and hippocampus exist, their cell bodies are located in regions outside the dorsal and median raphe nuclei. Another possibility could be that tryptamine is located in glial cells.     

Differential Effects of Ipsapirone on 5-Hydroxytryptamine Release in the Dorsal and Median Raphe Neuronal Pathways

Abstract: Serotonergic neurons of the dorsal and median raphe nuclei are morphologically dissimilar. Recent results challenge previous evidence indicating a greater inhibition of dorsal raphe neurons after 5-hydroxytryptamine_1A (5-HT_1A) autoreceptor activation. As both nuclei innervate different forebrain territories, this issue is critical to understanding the changes in brain function induced by anxiolytic and antidepressant drugs. Using microdialysis, we examined the modifications of 5-HT release induced by the selective 5-HT_1A agonist ipsapirone in both neuronal pathways. Maximal and minimal basal 5-HT values (in the presence of 1 µ M citalopram) were 45.0 ± 4.8 fmol/fraction in the median raphe nucleus and 8.4 ± 0.4 fmol/fraction in the dorsal hippocampus. Ipsapirone (0.3, 3, and 10 mg/kg s.c.) reduced dose-dependently 5-HT in the two raphe nuclei and four forebrain areas. Maximal reductions (to ∼25% of predrug values) were observed in cortex and striatum and in median raphe nucleus. The effects were more moderate in dorsal and ventral hippocampus (to 66 and 50% of baseline, respectively). These results are consistent with a higher sensitivity of dorsal raphe neurons to 5-HT_1A autoreceptor activation. Yet the differential reduction of 5-HT release in the median raphe nucleus and hippocampus suggests the presence of complex mechanisms of control of 5-HT release in these neurons.     

Distribution of serotonin immunoreactive neurons in the brainstem of the hamster, guinea pig, rabbit, and rat

Immunohistochemical techniques were employed to study the distribution of serotonin (5-HT) immunoreactive neurons in the brainstem of the hamster, guinea pig, rabbit and rat. 5-HT neurons were principally found to be concentrated in the midline raphe nuclei, particularly, the raphe pallidus, raphe obscurus, raphe magnus, raphe median, raphe pontis and raphe dorsalis nuclei. Characteristically, these cell bodies are displayed in bands or wing-like patterns which extend laterally from the raphe into reticular formations. The formations often appear to blend with the catecholamine system. They are particularly evident in the brainstems of the rabbit and hamster which contain wider and more lateral extensions of the serotonergic (5-HT) neurons than those observed in the brainstems of the rat and guinea pig. The widespread distribution of 5-HT immunoreacted cell bodies in the brainstem shows that there are significant prospects of 5-HT in neuronal activities.     

大鼠脑内5-HT能神经元对咽肌的支配及调控

用ＰＲＶ和５－ＨＴ免疫组织化学双标记方法研究脑内５－ＨＴ能神经元对咽肌的神经支配及调控。观察到中缝核群的中缝苍白核、中缝隐核、中缝大核、中缝桥核、中缝正中核、中缝背核、和中缝尾侧线形核等部位有ＰＲＶ和５－ＨＴ双标记细胞,直接证明中缝核群的５－ＨＴ能神经元投射到支配咽肌的疑核运动神经元和孤束核中的前运动神经元,调控咽肌的运动。并推测脑干中缝核群中的５－ＨＴ能神经元对咽肌运动的调控可能经由５ＨＴ３和５ＨＴ１Ａ两种受体介导。     

In Vivo Brain Dialysis Study of the Somatodendritic Release of Serotonin in the Raphe Nuclei of the Rat: Effects of 8-Hydroxy-2-(Di-n-Propylamino)tetralin

Abstract: The characteristics of the serotonin (5-HT) output in the dorsal and median raphe nuclei of the rat were studied using in vivo microdialysis. The basal output of 5-HT increased after KC1 was added to the perfusion fluid. In contrast, neither the omission of calcium ions nor the addition of 0.5 nM tetrodotoxin affected dialysate 5-HT or 5-hy-droxyindoleacetic acid (5-H1AA). Reserpine did not decrease the output of 5-HT and 5-HIAA 24 h later and p-chloroamphetamine increased 5-HT in both vehicle- and reserpine-treated rats severalfold. 8-Hydroxy-2-(di-n-pro-pylamino)tetralin (8-OH-DPAT), at 1 or 10 μM, perfused into the raphe did not change the outputs of 5-HT or 5-HIAA. Higher doses (0.1, Land 10 mM) increased extracellular 5-HT in the raphe, probably via an inhibition of uptake. In animals bearing two probes (raphe nuclei and ventral hippocampus), only the 10 vaM dose of 8-OH-DPAT perfused into the raphe decreased the hippocampal output of 5-HT and 5-HIAA. The systemic injection of 0.1 mg/kg 8-OH-DPAT decreased dialysate 5-HT and 5-HIAA in the raphe and hippocampus. These results suggest that extracellular 5-HT in raphe nuclei originates from a cytoplasmic pool and is not dependent on either nerve impulse of 5-HT neurons or local activation of 5-HT_1A receptors.     

GABAB receptor mRNA in the raphe nuclei: co-expression with serotonin transporter and glutamic acid decarboxylase

We have used double-label in situ hybridization techniques to examine the cellular localization of GABAB receptor mRNA in relation to serotonin transporter mRNA and glutamic acid decarboxylase mRNA in the rat dorsal raphe, median raphe and raphe magnus nuclei. The degree of cellular co-localization of these markers notably varied among the different nuclei. In the dorsal raphe, cell bodies showing GABAB receptor mRNA were very abundant, the 85% being also labelled for serotonin transporter mRNA, and a low proportion (5%) showing glutamic acid decarboxylase mRNA. In the median raphe, the level of co-expression of GABAB receptor mRNA with serotonin transporter mRNA was significantly lower. Some cells were also identified that contained GABAB receptor mRNA in the absence of either one of the other mRNA species studied. Our results support the presence of GABAB receptors in serotonergic as well as GABAergic neurones in the dorsal and median raphe, providing the anatomical basis for the reported dual inhibitory/disinhibitory effect of the GABAB agonist baclofen on serotonergic function.     

Serotonin-mediated cardiovascular responses to electrical stimulation of the raphe nuclei in the rat.

The dorsal and median raphe nuclei in rats were electrically stimulated and blood pressure and heart rate were recorded. Stimulation of each raphe nucleus caused an increase in blood pressure without affecting heart rate. The size of the increase in blood pressure depended upon the stimulus-intensity.Significant increases were already obtained with 5 sec. trains of 0.3 msec., 200 μA stimuli given at a frequency of 50 Hz. The increases in blood pressure could be obtained with electrodes within the raphe nuclei.Pretreating rats with para-chlorophenylalanine (pCPA, 100 mg/kg.day for 3 days) significantly diminished the increases in blood pressure obtained during electrical stimulation of the median raphe nucleus. However, similar pretreatment did not affect blood pressure rises induced by dorsal raphe stimulation.These data are discussed in relation to the role of central serotoninergic mechanisms in cardiovascular control.     

大鼠延髓网状背侧亚核内5-羟色胺能、P物质样和脑啡肽样阳性终末的中枢起源

研究用荧光金（ＦＧ）逆行追踪与免疫荧光组化染色相结合的双标技术对大鼠脑干向延髓网状背侧亚核（ＳＲＤ）的５┐羟色胺（５┐ＨＴ）能、Ｐ物质（ＳＰ）能和亮氨酸┐脑啡肽（Ｌ┐ＥＮＫ）能投射进行了观察。将ＦＧ注入ＳＲＤ后,ＦＧ逆标神经元主要见于中脑导水管周围灰质、脑干中缝核簇（中缝背核、中缝正中核、中缝桥核、中缝大核、中缝隐核和中缝苍白核）、巨细胞网状核α部、延髓网状结构的内侧部和外侧部、延髓外侧网状核、三叉神经脊束核尾侧亚核和孤束核。５┐羟色胺（５┐ＨＴ）样、Ｐ物质（ＳＰ）样和亮氨酸脑啡肽（Ｌ┐ＥＮＫ）样阳性神经元主要见于中脑导水管周围灰质、脑干中缝核簇和巨细胞网状核α部;此外,ＳＰ样和Ｌ┐ＥＮＫ样阳性神经元还见于臂旁核、背外侧被盖核和孤束核。ＦＧ逆标并呈５┐ＨＴ样、ＳＰ样或Ｌ┐ＥＮＫ样阳性的双标神经元也主要见于中脑导水管周围灰质、脑干中缝核簇和巨细胞网状核α部,尤其是位于延髓中缝核团内的双标神经元数量较多。本研究的结果说明ＳＲＤ内的５┐ＨＴ样、ＳＰ样和Ｌ┐ＥＮＫ样阳性终末主要来自中脑导水管周围灰质、脑干中缝核簇和巨细胞网状核α部,向ＳＲＤ发出５┐ＨＴ能、ＳＰ能和Ｌ┐ＥＮＫ能投射的上述核团对ＳＲＤ发挥“弥漫性伤害抑     

Habenular modulation of raphe indoleamine metabolism

Anatomical and neurophysiological findings have demonstrated neuronal connections between the diencephalic habenular nuclei and brain stem serotonergic raphe nuclei. Therefore we examined some neurochemical consequences of habenular lesions. Sixteen hours and one week after bilateral lesions serotonin metabolism (as reflected by concentrations of its metabolite, 5-hydroxyindoleacetic acid) was significantly increased in the dorsal but not the median raphe nuclei. Unilateral lesions produced a proportionally smaller augmentation. Motron locomotor activity was enhanced during the light and dark illumination phases in lesioned animals but only attained statistical significance during the day.     

Comparative distribution of nitric oxide synthase- and serotonin-containing neurons in the raphe nuclei of four mammalian species

 Monoclonal antibodies were generated against serotonin (5-HT) and the C-terminal portion of the neuronal form of nitric oxide synthase (nNOS), the enzyme producing nitric oxide in neurons. These antibodies were used to compare the distribution of 5-HT- and nNOS-containing neurons in the raphe nuclei of four animal species (rat, mouse, guinea pig, and cat). It was found that the rat was the only species in which the raphe nuclei contain a substantial number of nNOS-immunoreactive (IR) cell bodies. In this species and as observed by other authors, all mesencephalic raphe nuclei contained nNOS-IR cells, the largest group being located in the nucleus raphe dorsalis. The coexistence of nNOS and 5-HT immunoreactivities in these nuclei was visualized by double labeling. In the medulla, the nuclei raphe magnus and obscurus displayed a rather low number of nNOS-IR neurons. In the other species, nNOS-IR cell bodies were found in very low numbers, whatever raphe nucleus was considered. The rostral pole of the nucleus raphe dorsalis and the nuclei raphe magnus and obscurus contained a few nNOS-IR neurons which did not show any coincidence with the 5-HT neurons. In addition, nNOS-IR axons were rare. It is concluded that in the mouse, guinea pig, and cat the involvement of nitric oxide in functions subserved by 5-HT within the raphe nuclei might be minimal. Accepted: 5 May 1998     

Evidence for the localization of 5HT1A binding sites on serotonin containing neurons in the raphe dorsalis and raphe centralis nuclei of the rat brain

Precise anatomical distribution of 5HT1 binding sites has been investigated in the nuclei raphe dorsalis, raphe centralis and locus caeruleus of the rat brain. An original pattern of distribution was observed in the raphe nuclei, closely correlated to the already known distribution of 5HT containing elements. This pattern, more pronounced when 5HT1A sites were labelled, completely disappeared after lesioning by 5, 7DHT indicating the presence of this subtype of 5HT1 binding sites on 5HT containing neurons. It is postulated that these 5HT1A sites correspond in these raphe nuclei to 5HT autoreceptors.     

Regional distribution and cellular expression of tryptophan hydroxylase messenger RNA in postmortem human brainstem and pineal gland

The characterization and cellular localization of tryptophan hydroxylase mRNA in the human brainstem and pineal gland were investigated by using northern blot analysis and in situ hybridization histochemistry. Northern analysis of human pineal gland revealed the presence of two mRNA species that were absent in RNA isolated from human raphe. In situ hybridization experiments revealed very dense hybridization signal corresponding to tryptophan hydroxylase mRNA in cells throughout the pineal gland. In contrast, tryptophan hydroxylase mRNA was heterogeneously distributed in neurons in the dorsal and median raphe nuclei. Within the dorsal raphe, the ventrolateral and interfascicular subnuclei contained the greatest number of tryptophan hydroxylase mRNA-positive neurons. Also, the cellular concentration of tryptophan hydroxylase mRNA varied widely within the dorsal and median raphe. Comparison of the cellular concentration of tryptophan hydroxylase mRNA between the pineal gland and the raphe nuclei revealed an 11- and 46-fold greater average grain density of tryptophan hydroxylase mRNA positive cells in the pineal gland compared with the dorsal and median raphe, respectively. These findings are the first to demonstrate the cellular localization of tryptophan hydroxylase mRNA in the human brain and pineal gland as well as heterogeneity in the cellular concentration within and between these tissues.     

Extracellular 5-Hydroxytryptamine in Median Raphe Nucleus of the Conscious Rat Is Decreased by Nanomolar Concentrations of 8-Hydroxy-2-(Di-n-Propylamino)tetralin and Is Sensitive to Tetrodotoxin

Abstract: Extracellular 5-hydroxytryptamine (5-HT) in the median raphe and dorsal hippocampus was measured using in vivo microdialysis. Administration of 60 m M K⁺ through the probe into the median raphe region significantly increased 5-HT output from the median raphe and the right dorsal hippocampus. Local infusion of 10 µ M tetrodotoxin into the median raphe region substantially decreased 5-HT in the median raphe and left and right dorsal hippocampus. Systemic administration (0.3 mg/kg s.c.) of 8-hydroxy-2-(di- n -propylamino)tetralin (8-OH-DPAT) decreased the 5-HT levels in the dialysates from both the median raphe region and dorsal hippocampus. Administration of 30 n M 8-OH-DPAT through the dialysis probe into the median raphe region decreased 5-HT output from the median raphe and dorsal hippocampus significantly, whereas at concentrations from 60 n M to 10 µ M , no significant effects were found in either region. With 100 µ M 8-OH-DPAT, a significant increase was seen in the median raphe region, but not in dorsal hippocampus. Similar findings were obtained following microinjections of different doses of the compound into the median raphe region. The results of this study indicate that the somatodendritic release of 5-HT is impulse flow-dependent. Moreover, the decrease of 5-HT in the median raphe region by low nanomolar concentrations of 8-OH-DPAT supports the notion that somatodendritic 5-HT release is subject to a local negative feedback mechanism through 5-HT_1A autoreceptors.     

Developmental changes in the brain-stem serotonergic nuclei of teleost fish and neural plasticity

Summary 1. During early ontogeny, the serotonergic neurons in the brain stem of the three-spined stickleback shows a temporal and spatial developmental pattern that closely resembles that of amniotes.2. However, in the adult fish, only the midline nuclei of the rostral group (dorsal and median raphe nuclei) and the dorsal lateral tegmental nucleus are consistently serotonin-immunoreactive (5-HTir), whereas the groups of the upper and lower rhombencephalon (raphe pontis, raphe magnus, and raphe pallidus/obscurus nuclei) are variable and, when present, contain relatively small numbers of 5-HTir neurons.3. Using specific antisera against tryptophan 5-hydroxylase and aromaticl-amino acid decarboxylase, we have shown that the lateral B9 group and the groups of the upper and lower rhombencephalon are consistently present in adult sticklebacks. The results are discussed in relation to other known instances of neurotransmitter plasticity or transient neurotransmitter expression in teleost fish.4. While there are several instances of transient expression of neurotransmitter markers by discrete neuronal populations, there is so far no evidence of changes from one neurotransmitter phenotype to another in the brain of teleost fish. However, there are indications of plasticity of expression of catecholamines and indoleamines, and their respective synthesizing enzymes, as reflected in age-dependent changes and variation between individuals of different physiological status.5. As the brain grows continuously in teleost fish, and new neurons are added from proliferative regions, synaptic connections may be expected to undergo remodeling in all brain regions throughout life. Thus, the teleostean brain may be considered a suitable model for experimental studies of different aspects of neural plasticity.     

Demonstration of direct olfactory projections in the hypothalamus, the mesencephalon and the metencephalon of Microcebus murinus (Primate, Lemurian)

The efferent projections of the olfactory bulb in Microcebus murinus were identified after transection of the olfactory peduncle and after the revelation of the degenerating fibers by different silver staining methods. Total and partial sections have allowed demonstrating the importance of the two olfactory tracts in the olfactory projection areas. Degenerated fibers and endings were evidence not only in the different telencephalic regions, as classically known, but also in various hypothalamic nuclei (lateral hypothalamus, the suprachiasmatic, posterior supraoptic and mammillary nuclei and in the median eminence) and in several mesencephalic and metencephalic nuclei (ventral tegmental area, interpeduncular and raphe nuclei, and locus coeruleus). In all these structures the degenerate fibers were seen on both sides. The olfactory projections appeared not to be limited to the telencephalic areas. Moreover, the olfactory bulbs seem to be directly connected especially with the vegetative and integrative areas localized in the hypothalamus and the brainstem and particularly with the major aminergic nuclei that play an essential role in the neurovegetative, neuroendocrine and behavioral regulations.     

Preliminary observations on the distribution of serotoninergic and cerebellar-projecting neurons of the raphe nuclei of the brain stem

Cerebellar projection from raphe nuclei were investigated in rabbit by using retrograde transport of HRP and serotonergic mapping by direct fluorescence. A close topographical correlation between the HRP labeled cells and the serotonergic neurons has been observed. The current study has demonstrated the presence of paramedian and lateral cells whose cytoarchitecture is identical with midline cells of many raphe nuclei. All of the raphe nuclei except the linear nuclei, contained serotonergic perikarya. The midline and paramedian portions of the nuclei raphe obscurus, pallidus, magnus, and nucleus raphe dorsalis contained principally serotonergic neurons; the lateral portions of the medullary raphe nuclei and the nuclei raphe pontis and centralis superior contained a significant number of non-fluorescent cells. In these regions, fluorescent sections often revealed the size, shape, and orientation of the perikarya and dendrites; further verification of cytoarchitectural characteristics of these neurons depended heavily upon these clues.     

Caudal Brainstem Raphe Nuclei: Neural Substrate for their Involvement in the Expression of Some Biological Rhythms

Nucleus raphe pallidus (RPa) lies ventrally in the caudal brainstem, where it is coextensive rostrally with the nucleus raphe magnus (RMg) and caudally with the nucleus raphe obscurus (ROb). Retrograde neuronal tracing studies of our laboratory, carried out in rats and presented elsewhere, with fluorogold, true-blue or fast-blue, iontophoretically injected or by crystalline deposit, along the RPa extent, displayed many labeled pericaria at the preoptic area (POA), as well as lateral (LH) and dorsomedial (DMH) hypothalamus; paraventricular nucleus (PVN) and dorsal (DR) and median (MnR) raphe nuclei among others structures. In addition, RPa, which projects to the intermediolateral column, has been demonstrated to bear relation to many of the somatic-visceral functions also reported for POA. Iontophoretic injections of PHA-L, an anterograde tracer, in the POA subnuclei, presented terminal and varicose labeled fibers in RPa, as well as in the RMg, ROb, paraventricular thalamic (PVA), PVN and supraoptic nucleus (SO), LH, subparaventricular zone (sPVZ) and locus coeruleus (LC). Interestingly, POA, PVA, PVN, LH and SO have been described as retino- and suprachiasmatic-recipients. Taken together, these neuronal connections between brainstem raphe nuclei and POA, the similarity of functions to which they are related, as well as connections with other retino-suprachiasmatic-recipient structures, suggest that these caudal brainstem raphe nuclei could be part of the output system for the expression of some biological rhythms.     

Caudal Brainstem Raphe Nuclei: Neural Substrate for their Involvement in the Expression of Some Biological Rhythms

Nucleus raphe pallidus (RPa) lies ventrally in the caudal brainstem, where it is coextensive rostrally with the nucleus raphe magnus (RMg) and caudally with the nucleus raphe obscurus (ROb). Retrograde neuronal tracing studies of our laboratory, carried out in rats and presented elsewhere, with fluorogold, true-blue or fast-blue, iontophoretically injected or by crystalline deposit, along the RPa extent, displayed many labeled pericaria at the preoptic area (POA), as well as lateral (LH) and dorsomedial (DMH) hypothalamus; paraventricular nucleus (PVN) and dorsal (DR) and median (MnR) raphe nuclei among others structures. In addition, RPa, which projects to the intermediolateral column, has been demonstrated to bear relation to many of the somatic-visceral functions also reported for POA. Iontophoretic injections of PHA-L, an anterograde tracer, in the POA subnuclei, presented terminal and varicose labeled fibers in RPa, as well as in the RMg, ROb, paraventricular thalamic (PVA), PVN and supraoptic nucleus (SO), LH, subparaventricular zone (sPVZ) and locus coeruleus (LC). Interestingly, POA, PVA, PVN, LH and SO have been described as retino- and suprachiasmatic-recipients. Taken together, these neuronal connections between brainstem raphe nuclei and POA, the similarity of functions to which they are related, as well as connections with other retino-suprachiasmatic-recipient structures, suggest that these caudal brainstem raphe nuclei could be part of the output system for the expression of some biological rhythms.