Raphe obscurus neurons participate in thermoregulation in rats / Neurônios do núcleo obscuro da rafe participam da termorregulação em ratos

In mammalian, several evidences suggest that central serotonin participates in thermoregulation. Nucleus raphe obscurus (NRO), a serotonergic nucleus, has been recognized to be the source of generation of various hemodynamic patterns in different behavioral conditions, but its involvement in thermoregulation is unclear. In the present study, extracellular action potentials of NRO neurons were recorded in anesthetized rats, which were submitted to cold and warm stimuli in the tail. The firing rate of the neurons was compared before and after each stimulation. It was found that 59% of the neurons submitted to a cold stimulus trial had a significant increase in their firing frequency, while 48% of the neurons submitted to warm stimulation trial were inhibited. The opposite responses in neuronal activity of NRO units to cooling or heating suggest that these cells are involved in producing the homoeothermic vascular adaptations secondary to changes in cutaneous temperature in the rat tail.

A termorregulação em mamíferos envolve a participação da serotonina. O núcleo obscuro da rafe (NRO), que é serotoninérgico, participa do controle autonômico, mas seu envolvimento na termorregulação é incerto. Neste estudo, registramos potenciais de ação extracelulares de neurônios do NRO em ratos anestesiados nos quais a cauda foi submetida a estímulos de calor ou frio. A frequência de disparo dos neurônios foi comparada antes e depois dos estímulos. O grupo controle não apresentou modificação da frequência de disparo, enquanto que 59% dos neurônios registrados em animais submetidos a estímulo de frio tiveram sua frequência aumentada. Por outro lado, 48% dos animais submetidos a estímulo de calor tiveram sua frequência de disparo diminuída. As respostas opostas da frequência de disparo em neurônios de animais submetidos à estimulação com frio e calor sugere que estes neurônios estejam envolvidos na geração de respostas hemodinâmicas, que são coerentes com a termorregulação nesta espécie.

Functional mapping of the cardiorespiratory effects of dorsal and median raphe nuclei in the rat

The dorsal (DRN) and median (MRN) raphe nuclei are important sources of serotonergic innervation to the forebrain, projecting to sites involved in cardiovascular regulation. These nuclei have been mapped using electrical stimulation, which has the limitation of stimulating fibers of passage. The present study maps these areas with chemical stimulation, investigating their influence on cardiorespiratory parameters. Urethane-anesthetized (1.2 g/kg, iv) male Wistar rats (280-300 g) were instrumented for pulsatile and mean blood pressure (MBP), heart rate, renal nerve activity, and respiratory frequency recordings. Microinjections of L-glutamate (0.18 M, 50-100 nl with 1 percent Pontamine Sky Blue) were performed within the DRN or the MRN with glass micropipettes. At the end of the experiments the sites of microinjection were identified. The majority of sites within the MRN (86.1 percent) and DRN (85.4 percent) evoked pressor responses when stimulated (DRN: deltaMBP = +14.7 ± 1.2; MRN: deltaMBP = +13.6 ± 1.3 mmHg). The changes in renal nerve activity and respiratory rate caused by L-glutamate were +45 ± 11 and +42 ± 9 percent (DRN; P < 0.05 percent), +40 ± 10 and +29 ± 7 percent (MRN, P < 0.05), respectively. No significant changes were observed in saline-microinjected animals. This study shows that: a) the blood pressure increases previously observed by electrical stimulation within the raphe are due to activation of local neurons, b) this pressor effect is due to sympathoexcitation because the stimulation increased renal sympathetic activity but did not produce tachycardia, and c) the stimulation of cell bodies in these nuclei also increases the respiratory rate.

Behavioral correlates of the activity of serotonergic and non-serotonergic neurons in caudal raphe nuclei

We investigated the behavioral correlates of the activity of serotonergic and non-serotonergic neurons in the nucleus raphe pallidus (NRP) and nucleus raphe obscurus (NRO) of unanesthetized and unrestrained cats. The animals were implanted with electrodes for recording single unit activity, parietal oscillographic activity, and splenius, digastric and masseter electromyographic activities. They were tested along the waking-sleep cycle, during sensory stimulation and during drinking behavior. The discharge of the serotonergic neurons decreased progressively from quiet waking to slow wave sleep and to fast wave sleep. Ten different patterns of relative discharge across the three states were observed for the non-serotonergic neurons. Several non-serotonergic neurons showed cyclic discharge fluctuations related to respiration during one, two or all three states. While serotonergic neurons were usually unresponsive to the sensory stimuli used, many non-serotonergic neurons responded to these stimuli. Several non-serotonergic neurons showed a phasic relationship with splenius muscle activity during auditory stimulation. One serotonergic neuron showed a tonic relationship with digastric muscle activity during drinking behavior. A few non-serotonergic neurons exhibited a tonic relationship with digastric and/or masseter muscle activity during this behavior. Many non-serotonergic neurons exhibited a phasic relationship with these muscle activities, also during this behavior. These results suggest that the serotonergic neurons in the NRP and NRO constitute a relatively homogeneous population from a functional point of view, while the non-serotonergic neurons form groups with considerable functional specificity. The data support the idea that the NRP and NRO are implicated in the control of somatic motor output

Involvement of the caudal raphe nuclei in the feeding behavior of rats

Involvement of the caudal raphe nuclei (raphe pallidus, RPa; raphe magnus, RMg, and raphe obscurus, ROb) in feeding behavior of adult rats was studied by measuring c-Fos protein expression, in animals submitted to the "meal-feeding" model of food restriction in which the rats were fed ad libitum only from 7:00 to 9:00 h, for 15 days. The experimental groups submitted to chronic fasting, named 'search for food' (SF), 'ingestion of food' (IF) and 'satiety of food' (SaF) were scheduled after a previous study in which the body weight and the general and feeding behaviors were evaluated by daily monitoring. Acute, 48-h fasting (AF) was used as control. In the chronic group, the animals presented a 16 percent reduction in body weight in the first week, followed by a continuous, slow rise in weight over the subsequent days. Entrainment of the sleep-wake cycle to the schedule of food presentation was also observed. The RPa was the most Fos immunopositive nucleus in the chronic fasting group, followed by the RMg. The ANOVA and Tukey test (P<0.05) confirmed these results. The IF group was significantly different from the other three groups, as also was the number of labeled cells in the RPa in SF and IF groups. Nevertheless, no significant difference was observed between RMg and RPa, or RMg and ROb in the SaF and AF. However, it is interesting to observe that the groups in which the animals were more active, searching for or ingesting food, presented a larger number of labeled cells. These results suggest a different involvement of the caudal raphe nuclei in the somatic and autonomic events of feeding behavior, corroborating the functions reported for them earlier

Electro-oscillographic correlation between dorsal raphe nucleus, neocortex and hippocampus during wakefulness before and after serotoninergic inactivation

Theta rhythm in many brain structures characterizes wakefulness and desynchronized sleep in most subprimate mammalian brains. In close relation to behaviors, theta frequency and voltage undergo a fine modulation which may involve mobilization of dorsal raphe nucleus efferent pathways. In the present study we analyzed frequency modulation (through instantaneous frequency variation) of theta waves occurring in three cortical areas, in hippocampal CA1 and in the dorsal raphe nucleus of Wistar rats during normal wakefulness and after injection of the 5-HT1a receptor agonist 8-OH-DPAT into the dorsal raphe. We demonstrated that in attentive states the variation of theta frequency among the above structures is highly congruent, whereas after 8-OH-DPAT injection, although regular signals are present, the variation is much more complex and shows no relation to behaviors. Such functional uncoupling after blockade demonstrates the influence of dorsal raphe nucleus efferent serotoninergic fibers on the organization of alertness, as evaluated by electro-oscillographic analysis.

Serotonergic neurons in the caudal raphe nuclei discharge in association with activity of masticatory muscles

There is a dense serotonergic projection from nucleus raphe pallidus and nucleus raphe obscurus to the trigeminal motor nucleus and serotonin exerts a strong facilitatory action on the trigeminal motoneurons. Some serotonergic neurons in these caudal raphe nuclei increase their discharge during feeding. The objective of the present study was to investigate the possibility that the activity of these serotonergic neurons is related to activity of masticatory muscles. Cats were implanted with microelectrodes and gross electrodes. Caudal raphe single neuron activity, electrocorticographic activity, and splenius digastric and masseter electromyographic activities were recorded during active behaviors (feeding and grooming), during quiet waking and during sleep. Seven presumed serotonergic neurons wer fied. These eurons showed a long duration action potential (> 2.0 msec), and discharged slowly (2-7 Hz) and very regularly (interspike interval coefficient of variation

Pressor effects elicited by stimulation within the medullary raphe nuclei of the golden hamster (Mesocricetus auratus)

The medullary raphe nuclei are involved in central autonomic regulation. In all species investigated, electrical stimulation of the raphe nuclei causes cardiovascular responses, although these changes vary between species. The present study was designed to investigate the participation of these nuclei in cardiovascular regulation in the hamster. We studied the effect on arterial blood pressure (BP) and heart rate (HR) of electrical stimulation (isolated cathodal square wave pulses for 10 sec at 100 Hz, 40-100 muA and 1-msec pulse duration) within the medullary raphe nuclei in urethane-anesthetized (1.2 g/kg, iv, after ether induction) golden hamsters (Mesocricetus auratus, 130 to 150 g, either sex). Electrical stimulation of the same sites was performed on a group of paralysed (Flaxedi1(, 1 mg/kg, iv) and artificially ventilated animals. Stimulation sites were histologically defined and maps of the stimuli were obtained for the effect of electrical stimulation on arterial blood pressure. In another series of experiments L-glutamate (0.18 M) was microinjected (75 to 150 nl) into the nucleus raphe obseurus. Electrical stimulation of the raphe nuclei produced predominantly pressor responses (delta =+ 12 to + 100 mmHg; 49.3 per cent of the stimulated sites). Hypotension (delta =-5 to -20 mmHg; 14.6 per cent of the stimulated sites) and no change in BP (35.3 per cent) were evoked from fewer stimulation sites. Pressor responses were also predominant in paralysed animals (delta =+ 15 to + 95 mmHg; 62.5 per cent of the stimulated sites), and after microinjection of L-glutamate into the raphe obscurus (delta = +35 to + 135 mmHg). The present results demonstrate that in the hamster the stimulation of these nuclei evokes mainly pressor responses. These responses are similar to those obtained in the rat and guinea pig but opposite to those observed in the cat and rabbit.

Mechanism of transmission and modulation of renal pain in cats; effect of nucleus raphe magnus stimulation on renal pain

Initially, when periaqueductal gray (PAG) is electrically stimulated, analgesia is induced, and this phenomenon is called stimulation-produced analgesia. Nucleus raphe magnus (NRM) as well as PAG are known to be the potent analgesic centers. NRM could modulate the nociceptive response of spinal cord neurons through spinally projecting fibers. However, as well as the above analgesic effects have been confined to the somatic pain, it was variable according to species, and the analgesic effect by NRM stimulation on the visceral pain was not yet clarified. In this study the analgesic effect by NRM stimulation on the visceral pain was examined through recording the activities of the dorsal horn neurons with renal input and renal pain, as a type of visceral pain. The renal pain was induced by ureteral occlusion or renal arterial occlusion, which in turn activated the renal mechanoreceptor or chemoreceptor. These cells had concomitant somatic input. In order to compare the effects of NRM stimulation on the renal pain with somatic pain, the somatic stimulation such as squeezing was conducted on the peripheral receptive field. The main results are summarized as follows: 1) After an electrical stimulation of NRM, spontaneous activities of dorsal horn neurons with renal input were reduced to 73.3 +/- 9.7% of the control value. 2) After an electrical stimulation of NRM, activities of dorsal horn neurons with renal input evoked by a brush, a type of non-noxious stimuli, did not change significantly. But the activities by a squeeze, a type of noxious stimuli, the activities were reduced to 63.2 +/- 7.2% of the control value. 3) After an electrical stimulation of NRM, activities of dorsal horn neurons with renal input evoked by occlusion of ureter or renal artery were reduced to 46.7 +/- 8.8% and 49.0 +/- 8.0% of the control value respectively. 4) The inhibitory effect of NRM on the dorsal horn neurons with renal input did not show any difference between renal A delta fiber and C fiber group. 5) By the electrical stimulation of NRM, the activities evoked by ureteral occlusion showed more reduction in the high threshold cell group than in the wide dynamic range cell group. These results suggest that activation of NRM can alleviate the renal pain as well as the somatic pain by modulating the dorsal horn neurons activities.

Role of the rostral ventrolateral medulla in the pressor response to stimulation of the nucleus raphe obscurus

1. Electrical stimulation of the nucleus raphe obscurus (NRO) in urethane-anesthetized rats increases arterial blood pressure (BP) between 20 and 95 mmHg (mean, 61.14 +/- 6.57; N = 30). 2. Unilateral electrolytic destruction of the rostral ventrolateral medulla (RVLM) did not reduce BP or heart rate (HR) but significantly reduced the pressor response to NRO stimulation (control, delta 76.0 +/- 5.4 mmHg; after lesion, delta 26.0 +/- 13.9 mmHg; P < 0.01, N = 5). 3. Bilateral destruction of the RVLM reduced basal BP (control, 104.1 +/- 11.4 mmHg; after lesion, 58.0 +/- 5.7 mmHg; P < 0.01) and the pressor response to NRO stimulation (control, delta 71.6 +/- 7.3; after lesion, delta 12.5 +/- 3.8 mmHg; P < 0.01, N = 6). 4. When topically applied to or microinjected into the RVLM, pentobarbital sodium (200 nl/1 microliters, 10 nmol) decreased BP, HR and the pressor response to NRO stimulation (control, delta 56.2 +/- 6.7 mmHg; after pentobarbital, delta 11.2 +/- 3.1 mmHg; P < 0.01, N = 13). Similar effects were obtained when glycine (200 nl, 50 nmol) was microinjected into RVLM (control, delta 40.5 +/- 5.9 mmHg; after glycine, delta 18.1 +/- 4.9 mmHg; P < 0.01, N = 6). 5. We conclude that RVLM is essential for the pressor response to NRO stimulation

Influence of median raphe nucleus lesions on neuroleptic-induced catalepsy and on the anticataleptic effect of buspirone

Catalepsy induced by neuroleptics in rats can be modified by 5-hydroxytryptaminergic (5-HTergic) manipulation. For example, buspirone (BUS) and other central 5-HT1A receptor ligands reduce neuroleptic-induced catalepsy (NIC). The dorsal (DRN) and median (MRN) raphe nuclei are reported to be important sources of 5-HTergic projections to the basal ganglia, the site of action of neuroleptics in producing NIC. A previous study showed that lesion of DRN did not affect NIC or the anticataleptic effect of BUS. The present study was designed to evaluate the participation of MRN in NIC and in the anti-NIC effect of BUS. Twenty-four male Wistar rats (N = 6/group) weighing 220-250 g were used. Electrolytic lesion of MRN was carried out in anesthetized rats along with sham operations (electrode inserted but no current applied). Ten days later, the rats were injected with BUS (5 mg/kg, ip) or saline (1 ml, ip). Catalepsy was induced 20 min later with haloperidol (H; 1 mg/kg, ip) and measured at 30-min intervals by means of a bar test. The Costall per cent Naylor method of scoring (range 0-5 points) was used. Saline-injected MRN-lesioned rats displayed significantly lower catalepsy scores than sham-lesioned rats (1.5 +/- 0.2 vs 3.8 +/- 0.3 at 90 min after H). In sham-lesioned rats, BUS significantly reduced the catalepsy scores in comparison with saline-treated animals (1.3 +/- 0.2 vs 3.8 +/- 0.3 at 90 min after H). However, BUS was not able to further reduce NIC in the MRN-lesioned animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Participation of the median raphe nucleus and central serotoninergic pathways in the control of water electrolyte excretion

1. The role of the median raphe nucleus (MRN) and of increased central serotonin (5HT) synthesis/release in the mediation of Na+ excretion (UNaV) and K+ excretion (UKV) and or urine output (UV) was evaluated for 120 min. 2. Male Wistar rats weighing 220-280g were used in each group of 12-13 animals. The rats implanted with a cannula in the MRN were injected with saline (0.5 µl) or with 5.0 and 15.0 ng/0.5 µl kainic acid (KA), an excitatory amino (EAA). Another group of rats was injected ip with 200 mg/Kg saline or tryptophan, the initial precursor of 5HT synthesis. 3. Injection of both kainic acid and tryptophan led to increased Na+ excretion, but the magnitude and time course were different for each treatment. Both KA doses were effective in increasing UNaV (0.061 ñ 0.08, mean ñ SEM, and 0.95 ñ 0.19 -Eq/min, respectively, vs 0.27 ñ 0.04 µEq/min for saline at 60 min). The effect on UKV was statistically significant with the 15.0 ng dose (0.44 ñ 0.05 µEq/min vs 0.25 ñ0.03 µEq/min for saline) at 20 min. 5. Tryptophan adminsitration caused an initial gradual increase in UNaV which became steady and significant after 60 min (1.02 ñ 0.15 µEq/min vs 0.36 ñ 0.06 µEq/min for saline), as well as an increase in UKV (0.58 ñ 0.06 µEq/min vs 0.26 ñ 0.04 µEq/min for saline) at 60 min and throught the remainder of the observation period. 6. KA-induced MRN stimulation and systemic tryptophan overload significantly increased UV at 60, 80 and 100 min (30 to 97% above control values). 7. These data show that kanic acid-mediated transmission at the MRN lellvel may play a modulatory role in hydromineral metabolism. The effects obtained after increased central availability of tryptophan suggest that the excretory response is associated with an increase in 5HT synthesis/release and with an increase in central transmission. 8. We conclude that the data obtained from CA-induced MRN stimulation and systemic tryptophan overload may possibly reflect an increased 5HT synaptic transmission at sites and efferent mechanisms that remain to be elucidated

Participation of nucleous raphe obscurus in the control of sympathetic activity in the anesthetized rat

The medullary raphe are involved in the control of sympathetic activity during desynchonized sleep and in the modulation of nocicepotive sensory inpts. To determine the particpation cholinergic and opiate mechanisms in the control of sympathetic activity, we microinjected eserine, morphine and naloxone into the nucleus raphe obscurus (NRO) of urethane-anesthetized rats. Arterial blood pressure (BP) and renal nerve activity (RN) were recorded. Eserine and morphine induced significant reductions of RN and BP, while naloxone had no effect. It is suggested that cholinergic and opiate mechanisms particpate in the control of sympathetic activity by th NRO

Responses of neurons of the nucleus raphe obscurus to noxious stimuli

Extracellular recordings were made from neurons located in the nucleous raphe obscurus (NRO), raphe magnus (NRM), and raphe pallidus (NRP) of urethane-anesthetized rats. Noxious cutaneous stimuli had excitatory, inhibitory or no effect on neurons of the nuclei. Most of the neurons were excited by noxious stimuli. The distribution of responses of noxiously activated units in the NRO is similar to that observed in the NRM. It is suggested that the NRO is also a component of the endogenous pain suppression system that originates in the NRM

Different behavioral reactivicty of 5-HT1 sites between killer and non-Killer rats after midbrain raphe lesion

Se realizaron estudios de la reactividad conductual de receptores serotoninérgicos de tipo 5-HTl y 5-HT2, en ratas "Killer" (K) y "non-Killer" (NK), obtenidos por aislamiento social o por lesión de los núcleos dorsal y medial del rafe. La reactividad de los receptores tipo 5-HTl fue medida en una escala de intensidad arbitraria para los síntomas de "forepaw treading" y "hindlimb abduction" luego de la administración de 5-MeODMT, mientras que la reactividad de los sitios 5-HT2 fue determinada a través del comportamiento de "wet dog shake", inducido por la administración de 5-hidroxitriptófano. No se observaron diferencias en las conductas mediadas por los sitios 5-HTl y 5-HT2 entre los animales aislados. De igual manera, se obtuvieron valores similares en el "wet dog shake" de ratas lesioandas K y NK. Por el contrario, 5- MeODMT indujo una menor respuesta conductual en las ratas lesionadas K en comparación con las lesionadas NK. Esta alteración en la respuesta conductual no es consecuencia de una desnervación neuronal diferente en el sistema serotoninérgico central, ya que no hubo modificaciones en el "uptake" de 5-Ht en las estructuras cerebrales analizadas entre estos dos grupos experimentales de ratas. Esta menor reactividad de los sitios 5-HTl podría reflejar una neurotransmisión serotoninérgica disminuida y aportaría una probable explicación a la aparición de la actvidad muricida en algunos pero no en todos los animales lesionados

Effects of physostigmine on the activity of medullary raphe neurons in anesthetized rats

Medullary raphe neurons are involved in the control of sympathetic activity during desynchronized sleep. To determine if cholinergic simulation of these sites has any effect on raphe unit activity, we administered physostigmine to urethane'anesthetized rats. Most of the neurons (68%) were excited by physostigmine, suggesting the existence of cholinergic synapses which are excitatory for the majority of medullary raphe neurons

Excitatory and inhibitory behavioral responses to the pharmacological stimulation of serotonergic function in dorsalis raphe lesioned rats

La lesion de neuronas 5-HT median te neurotoxinas induce supersensibilidad de receptores 5-HT1 sin afectar el "binding" de receptores 5-HT2. Este modelo fue utilizado en el presente trabajo para analizar el papel de ambos subtipos de receptores 5-HT en el mecanismo de control de las respuestas comportamentales excitatorias e inhibitorias provocadas por la estimulación farmacológica del sistema 5-HT. Las lesiones del rafe dorsales (RD) fueron hechas mediante inyección estereotáxica de ác. kaínico. Treinta días después las ratas RD y sus controles mostraron una actividad basal similar en "testes" de "hole board". Tres días después las ratas RD y sus controles fueron inyectadas ip con fluoxetina (5 y 10 mg/Kg) y 30 m después con 50HTP (15 y 30 mg/Kg). Imediatamente antes y después de cada inyección ip la respuesta excitatoria (síndrome mioclónico) fue evaluada. Las ratas RD y sus controles mostraron similares valores de mioclonías en respuesta a fluoxetina-5-HTP. La respuesta inhibitoria fue investigada en sesiones de "holeboard" a los 30 m de la segunda inyección ip. La lesión del RD potenció el efecto depresor de fluoxetina-5-HTP sobre el comportamiento. En concordancia con la literatura, la lesión del RD produjo una caída del 74.9% de la 5-HT del cerebro anterior y un incremento del 75% en el "bilding" de 3H-5HT en membranas corticales. En conclusión, los componentes de la respuesta excitatoria, que no se modificó por la lesión del RD, estarían relacionados principalmente con receptores 5-HT2. El aumento de la respuesta inhibitoria a la estimulación 5-HT observado en las rata lesionadas en RD estaría vinculado a la supersensibilidad de receptores 5-HT1

Involvement of a serotonergic control in the regulation of plasma levels of immunoreactive beta-endorphin

Se midió la concentración de beta-endorfina inmunoreactiva (B-E i.r.) en plasma e hipotálamo de ratas tratadas con alfa-metil-p-tirosina ( alfa -MT) (dos dosis de 200 mg/kg) o p-cloro-fenil-alanina (PCPA) (dos dosis de 150 mg/kg). Se determinó además la concentración de B-E i.r. en plasma después de una única dosis (5 mg/kg) de anfetamina o luego de la estimulación eléctrica del núcleo mediano del rafe (NMR). Los niveles plasmáticos de B-E i.r. disminuyeron por la administración de PCPA o aumentaron por la estimulación eléctrica del NMR. Tanto la adminsitración de alfa -MT como la de anfetamina fue inefectiva en modificar la concentración plasmática de B-E i.r. Los resultados sugieren un papel para la serotonina en la regulación del nivel plasmático de B-E i.r.