Modulation of spontaneous firing in rat subthalamic neurons by 5-HT receptor subtypes

The subthalamic nucleus (STN) is considered to be one of the driving forces in the basal ganglia circuit. The STN is innervated by serotonergic afferents from the raphe nucleus and expresses a variety of 5-HT receptor subtypes. We investigated the effects of 5-HT and 5-HT receptor subtype agonists and antagonists on the firing properties of STN neurons in rat brain slices. We used cell-attached, perforated-patch, and whole cell recording techniques to detect changes in firing frequency and pattern and electrical membrane properties. Due to the depolarization of membrane potential caused by reduced potassium conductance, 5-HT (10 microM) increased the firing frequency of STN neurons without changing their firing pattern. Cadmium failed to occlude the effect of 5-HT on firing frequency. 5-HT had no effect on afterhyperpolarization current. These results indicated that the 5-HT action was not mediated by high-voltage-activated calcium channel currents and calcium-dependent potassium currents. 5-HT had no effect on hyperpolarization-activated cation current (I(H)) amplitude and voltage-dependence of I(H) activation, suggesting that I(H) was not involved in 5-HT-induced excitation. The increased firing by 5-HT was mimicked by 5-HT(2/4) receptor agonist alpha-methyl-5-HT and was partially mimicked by 5-HT2 receptor agonist DOI or 5-HT4 receptor agonist cisapride. The 5-HT action was partially reversed by 5-HT4 receptor antagonist SB 23597-190, 5-HT2 receptor antagonist ketanserin, and 5-HT2C receptor antagonist RS 102221. Our data indicate that 5-HT has significant ability to modulate membrane excitability in STN neurons; modulation is accomplished by decreasing potassium conductance by activating 5-HT4 and 5-HT2C receptors.     

5-HT inhibits synaptic transmission in rat subthalamic nucleus neurons in vitro

The subthalamic nucleus (STN) plays a pivotal role in normal and abnormal motor function. We used patch pipettes to study effects of 5-HT on synaptic currents evoked in STN neurons by focal electrical stimulation of rat brain slices. 5-HT (10 microM) reduced glutamate-mediated excitatory postsynaptic currents (EPSCs) by 35+/-4%. However, a much higher concentration of 5-HT (100 microM) was required to inhibit GABA-mediated inhibitory postsynaptic currents (IPSCs) to a comparable extent. Concentration-response curves showed that the 5-HT inhibitory concentration 50% (IC50) for inhibition of IPSCs (20.2 microM) was more than fivefold greater than the IC50 for inhibition of EPSCs (3.4 microM). The 5-HT-induced reductions in EPSCs and IPSCs were accompanied by increases in paired-pulse ratios, indicating that 5-HT acts presynaptically to inhibit synaptic transmission. The 5-HT1B receptor antagonist NAS-181 significantly antagonized 5-HT-induced inhibitions of EPSCs and IPSCs. These studies show that 5-HT inhibits synaptic transmission in the STN by activating presynaptic 5-HT1B receptors.     

5-羟色胺对正常大鼠丘脑底核神经元放电的双向效应

目的观察5-HT对正常大鼠丘脑底核神经元放电频率的影响及其作用机制。方法用多管微电极在体细胞外电生理记录观察5-HT及5-HT1B、5-HT2C、5-HT4和5-HT1A受体激动剂对丘脑底核神经元的电生理效应,免疫组织化学法观察丘脑底核神经元4种受体亚型的表达情况。结果 5-HT既可使丘脑底核神经元的自发放电频率明显升高(P0.001),也可使其明显降低(P0.05)。作为5-HT受体激动剂,CP-93129、RO-600175和ML-10302可明显增加丘脑底核神经元的放电频率(CP-93129:P0.001;RO-600175:P0.01;ML-10302:P0.001),8-OHDPAT则使其放电频率明显降低(P0.01)。正常大鼠丘脑底核表达丰富的5-HT1B、5-HT2C、5-HT4和5-HT1A受体。结论 5-HT可以改变正常大鼠丘脑底核神经元的兴奋性,产生使放电频率升高和降低的双向效应。5-HT的这种兴奋效应主要是通过激活5-HT1B、5-HT2C和5-HT4受体实现的,而抑制效应则与5-HT1A受体的激活有关。     

Changes on 5-HT2 receptor mRNAs in striatum and subthalamic nucleus in Parkinson's disease model

Abnormal interactions between the serotonin and dopamine systems may underlie the high prevalence of non-motor complications in Parkinson's disease (PD). Here, we demonstrate that the genes encoding serotonin 5-HT2A and 5-HT2C receptors are differently regulated by dopamine in the 6-hydroxydopamine (6-OHDA) rat model of PD. Nigrostriatal cell loss causes an up-regulation of 5-HT2AR mRNA, but a down-regulation of 5-HT2CR mRNA, in striatum. Repeated injections with L-DOPA/benserazide reverse the effect of 6-OHDA lesioning on 5-HT2AR, but not on 5-HT2CR, gene expression. Neither 6-OHDA-lesioning nor L-DOPA/benserazide treatment had any effect on 5-HT2AR mRNA in cortex or on 5-HT2CR mRNA in nucleus subthalamicus. These data suggest that the regulation of 5-HT2AR in striatum, in the 6-OHDA rat model of PD, is mainly dependent upon alterations in dopamine levels. 5-HT2CR, on the other hand, are regulated by nigrostriatal cell loss and by the accompanied reduction of factor(s), other than dopamine, that are normally co-expressed with dopamine. The apparent imbalance between 5-HT2AR and 5-HT2CR levels in this PD model indicates a potential role for these receptors in the pathophysiology of neuropsychiatric symptoms, such as depression and L-DOPA-induced hallucinations, which are co-morbid with PD. The fact that 5-HT2CR are differentially regulated as compared to 5-HT2AR to alterations in the dopamine tone predicts that pharmacological manipulations at 5-HT2CR, but not at 5-HT2AR, will result in similar effects in PD patients whether they are treated or not with dopamine replacement.     

Characterization of outward currents induced by 5-HT in neurons of rat dorsolateral septal nucleus

Properties of the 5-hydroxytryptamine (5-HT)-induced current (I(5-HT)) were examined in neurons of rat dorsolateral septal nucleus (DLSN) by using whole cell patch-clamp techniques. I(5-HT) was associated with an increase in the membrane conductance of DLSN neurons. The reversal potential of I(5-HT) was -93 +/- 6 (SE) mV (n = 7) in the artificial cerebrospinal fluid (ACSF) and was changed by 54 mV per decade change in the external K(+) concentration, indicating that I(5-HT) is carried exclusively by K(+). Voltage dependency of the K(+) conductance underlying I(5-HT) was investigated by using current-voltage relationship. I(5-HT) showed a linear I-V relation in 63%, inward rectification in 21%, and outward rectification in 16% of DLSN neurons. (+/-)-8-Hydroxy-dipropylaminotetralin hydrobromide (30 microM), a selective 5-HT(1A) receptor agonist, also produced outward currents with three types of voltage dependency. Ba(2+) (100 microM) blocked the inward rectifier I(5-HT) but not the outward rectifier I(5-HT). In I(5-HT) with linear I-V relation, blockade of the inward rectifier K(+) current by Ba(2+) (100 microM) unmasked the outward rectifier current in DLSN neurons. These results suggest that I(5-HT) with linear I-V relation is the sum of inward rectifier and outward rectifier K(+) currents in DLSN neurons. Intracellular application of guanosine-5'-O-(3-thiotriphosphate) (300 microM) and guanosine-5'-O-(2-thiodiphosphate) (5 mM), blockers of G protein, irreversibly depressed I(5-HT). Protein kinase C (PKC) 19-36 (20 microM), a specific PKC inhibitor, depressed the outward rectifier I(5-HT) but not the inward rectifier I(5-HT). I(5-HT) was depressed by N-ethylmaleimide, which uncouples the G-protein-coupled receptor from pertussis-toxin-sensitive G proteins. H-89 (10 microM) and adenosine 3',5'-cyclic monophosphothioate Rp-isomer (300 microM), protein kinase A inhibitors, did not depress I(5-HT). Phorbol 12-myristate 13-acetate (10 microM), an activator of PKC, produced an outward rectifying K(+) current. These results suggest that both 5-HT-induced inward and outward rectifying currents are mediated by a G protein and that PKC is probably involved in the transduction pathway of the outward rectifying I(5-HT) in DLSN neurons.     

Expression of the 5-HT1B receptor by subtypes of rat trigeminal ganglion cells

The type of trigeminal ganglion cells that express 5-HT1B receptors has not been well characterized, despite the fact that these receptors are important targets for anti-migraine drugs. We have therefore used combined in situ hybridization and immunofluorescence to examine the expression of 5-HT1B receptor messenger RNA in identified subpopulations of rat trigeminal ganglion cells. 5-HT1B-expressing cells accounted for 15% of all trigeminal ganglion cells, were medium sized, and showed immunoreactivity for either 200,000 mol. wt neurofilament, calcitonin gene-related peptide, or nerve growth factor receptor (trkA). In contrast few 5-HT1B cells showed immunoreactivity for substance P or binding of the lectin Griffonia simplicifolia IB4. Our results are consistent with 5-HT1B receptors acting to control the release of calcitonin gene-related peptide from trigeminal neurons with finely myelinated axons. 5-HT1B receptor agonists may reduce neurogenic vasodilation by activating such receptors. However many nociceptive trigeminal neurons, including the substance P and IB4-binding populations, do not express the 5-HT1B receptor.     

AMPA receptors are modulated by tachykinins in rat cerebellum neurons

The peptides of the tachykinin family are widely distributed within the mammalian peripheral and central nervous systems and play a well-recognized role as neuromodulators, although their direct action on cerebellum granule cells have not yet been demonstrated. We have examined the effect of the best known members of the family, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors from rat cerebellar granule cells in culture to assess the ability of these peptides to regulate the glutamatergic input. Both NKA and NKB, but not SP, produce a significant enhancement of ionic current through AMPA receptors activated by the agonist kainate in 53.5 and 46% of patched neurons, respectively. This effect was not observable in the presence of MEN 10,627 and Trp(7)betaAla(8), NKA and NKB competitive antagonist receptors, respectively, indicating that the current modulations were mediated by the respective receptors. NKB also produces a significant enhancement of ionic current through the AMPA receptors activated directly by its agonist AMPA and cyclothiazide, an allosteric modulator that selectively suppresses desensitization of AMPA receptors. The presence of NK3 receptors was demonstrated in these neurons by RT-PCR amplification of total RNA extracted from cerebellar granule cells, using NK3-specific primer pairs. Immunocytochemistry experiments, using a specific polyclonal antibody directed against NK3, also confirmed the presence of NK3 receptors and their co-localization with the GLUR2 AMPA subunit in about 54% of cerebellar granule neurons. This study adds the tachykinins to the list of neuromodulators capable of exerting a excitatory action on cerebellar granule cells.     

Membrane resonance and its ionic mechanisms in rat subthalamic nucleus neurons

The oscillatory activity in the basal ganglia is believed to have an important function, but little is known about its actual mechanisms. We studied the resonance characteristics of subthalamic nucleus (STN) neurons and their ionic mechanisms using whole-cell patch-clamp recordings in rat brain slices. A swept-sine-wave current with constant amplitude and linearly increasing frequency was applied to measure the resonance frequency (f_res) of STN neurons. We also used single-frequency sine wave current to evoke firing. We found that the resonance of STN neurons was temperature- and voltage-dependent. The f_res of STN neurons was about 4 Hz when the temperature was maintained at 38 °C and holding potential was at −70 mV. The f_res increased with more negative holding potentials and decreased with lower temperature. Action potentials fired most readily when the input frequency was near f_res. After application of drug ZD7288 (20 μM), the resonance of STN neurons was blocked and the spikes evoked by both impedance amplitude profile (ZAP) current and single-frequency sine wave current arose readily at the lowest frequencies, indicating that hyperpolarization-activated cation current (I_h) generated the resonance and mediated a preferential coupling at frequencies near f_res between inputs and firing. In conclusion, there is a θ-frequency resonance mediated by I_h in STN neurons. The resonance characteristics are temperature- and voltage-dependent. The resonance mediates a frequency-selective coupling between inputs and firing.     

5-HT(2) receptor subtypes mediate different long-term changes in GABAergic activity to parasympathetic cardiac vagal neurons in the nucleus ambiguus

Serotonin (5-HT), and in particular 5-HT(2) receptors, play an important role in cardiorespiratory function within the brainstem. In addition, abnormalities in the 5-HT system have been implicated in many cardiorespiratory disorders, including sudden infant death syndrome. However, little is known about the mechanisms of action of 5-HT(2) receptors in altering the activity of parasympathetic cardiac neurons in the brainstem. In this study we examined the effects of activation of different subtypes of 5-HT(2) receptors on spontaneous and respiratory-evoked GABAergic neurotransmission to cardioinhibitory vagal neurons within the nucleus ambiguus as well as rhythmic fictive inspiratory-related activity in rats. A single application of alpha-Me-5-hydroxytryptamine maleate (alpha-Me-5-HT), a 5-HT(2) receptor agonist, did not significantly alter the frequency of spontaneous or respiratory-evoked GABAergic inhibitory postsynaptic currents (IPSCs) in cardiac vagal neurons. However, repetitive successive applications of alpha-Me-5-HT elicited a long-lasting (>/=1 h) decrease in the frequency of spontaneous as well as inspiratory-related GABAergic IPSCs to cardiac vagal neurons. This study demonstrates multiple, but not single applications of the 5-HT(2) receptor agonist alpha-Me-5-HT caused a long-lasting inhibition of both spontaneous and fictive inspiratory-related GABAergic neurotransmission to CVNs, which can be prevented by the 5-HT(2B) receptor antagonist SB204741, but persisted with the 5-HT(2A/2C) receptor antagonist ketanserin. The 5-HT(2) receptor agonist alpha-Me-5-HT also reversibly and transiently excited central fictive inspiratory activity, which was abolished by ketanserin, but was unaffected by the 5-HT(2B) receptor antagonist SB204741.     

The discharge of subthalamic neurons is modulated by inhibiting the nitric oxide synthase in the rat

The effects induced on the discharge of subthalamic spontaneously active neurons by inhibiting the enzyme nitric oxide synthase was studied in two groups of urethane-anesthetized rats. In the first group of animals (n = 10), the activity of subthalamic single units was recorded before and after the systemic administration of 7-nitro-indazole (7-NI, 50 mg/kg i.p.), a selective inhibitor of neuronal nitric oxide synthase. In the second group of rats (n = 15), Nomega-nitro-L-arginine methyl ester (L-NAME), another inhibitor of nitric oxide synthase, was iontophoretically administered while performing single unit extracellular recordings. The activity of most tested spontaneously discharging neurons (8/10) was influenced by 7-NI administration, which always caused a statistically significant decrease in the firing rate of the responsive cells. In contrast, the iontophoretic administration of L-NAME, although influencing many cells (24/32), did not have univocal effects: in fact, 18 cells were inhibited while 6 neurons were excited in a statistically significant manner. We hypothesize that nitric oxide neurotransmission could exert a tonic modulatory influence upon spontaneously discharging subthalamic neurons, with a prevalent excitatory effect.     

5-HT excites globus pallidus neurons by multiple receptor mechanisms

Anatomical and neurochemical studies indicated that the globus pallidus receives serotonergic innervation from raphe nuclei but the membrane effects of 5-HT on globus pallidus neurons are not entirely clear. We address this question by applying whole-cell patch-clamp recordings on globus pallidus neurons in immature rat brain slices. Under current-clamp recording, 5-HT depolarized globus pallidus neurons and increased their firing rate, an action blocked by both 5-HT(4) and 5-HT(7) receptor antagonists and attributable to an increase in cation conductance(s). Further experiments indicated that 5-HT enhanced the hyperpolarization-activated inward conductance which is blocked by 5-HT(7) receptor antagonist. To determine if 5-HT exerts any presynaptic effects on GABAergic and glutamatergic inputs, the actions of 5-HT on synaptic currents were studied. At 10 microM, 5-HT increased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) but had no effect on both the frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs). However, 5-HT at a higher concentration (50 microM) decreased the frequency but not the amplitude of the mIPSCs, indicating an inhibition of GABA release from the presynaptic terminals. This effect was sensitive to 5-HT(1B) receptor antagonist. In addition to the presynaptic effects on GABAergic neurotransmission, 5-HT at 50 microM had no consistent effects on glutamatergic neurotransmission, significantly increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) in 4 of 11 neurons and decreased the frequency of mEPSCs in 3 of 11 neurons. In conclusion, we found that 5-HT could modulate the excitability of globus pallidus neurons by both pre- and post-synaptic mechanisms. In view of the extensive innervation by globus pallidus neurons on other basal ganglia nuclei, this action of 5-HT originated from the raphe may have a profound effect on the operation of the entire basal ganglia network.     

Alpha4 containing nicotinic receptors are positioned to mediate postsynaptic effects on 5-HT neurons in the rat dorsal raphe nucleus

Nicotinic acetylcholine receptors containing the alpha4 and beta2 subunits constitute the most abundant high-affinity binding site of nicotine in the brain and are critical for the addictive qualities of nicotine. 5-HT neurotransmission is thought to be an important contributor to nicotine addiction. Therefore in this study it was examined how alpha4-containing receptors are positioned to modulate the function of 5-HT neurons using ultrastructural analysis of immunolabeling for the alpha4 receptor subunit in the dorsal raphe nucleus (DR), a primary source of forebrain 5-HT in the rat. Of 150 profiles labeled for the alpha4 subunit, 140 or 93% consisted of either soma or dendrites, these were often small-caliber (distal) dendrites <1.5 μm in diameter (63/150 or 42%). The majority (107/150 or 71%) of profiles containing labeling for alpha4 were dually labeled for the synthetic enzyme for 5-HT, tryptophan hydroxylase (TPH). Within dendrites immunogold labeling for alpha4 was present on the plasma membrane or near postsynaptic densities. However, labeling for alpha4 was commonly localized to the cytoplasmic compartment often associated with smooth endoplasmic reticulum, plausibly representing receptors in transit to or from the plasma membrane. Previous studies have suggested that nicotine presynaptically regulates activity onto 5-HT neurons, however alpha4 immunolabeling was detected in only 10 axons in the DR or 7% of profiles sampled. This finding suggest that alpha4 containing receptors are minor contributors to presynaptic regulation of synaptic activity onto 5-HT neurons, but rather alpha4 containing receptors are positioned to influence 5-HT neurons directly at postsynaptic sites.     

Characterization of Ca(2+) channels in rat subthalamic nucleus neurons

The subthalamic nucleus (STN) plays a key role in motor control. Although previous studies have suggested that Ca(2+) conductances may be involved in regulating the activity of STN neurons, Ca(2+) channels in this region have not yet been characterized. We have therefore investigated the subtypes and functional characteristics of Ca(2+) conductances in STN neurons, in both acutely isolated and slice preparations. Acutely isolated STN cells were identified by retrograde filling with the fluorescent dye, Fluoro-Gold. In acutely isolated STN neurons, Cd(2+)-sensitive, depolarization-activated Ba(2+) currents were observed in all cells studied. The current-voltage relationship and current kinetics were characteristic of high-voltage-activated Ca(2+) channels. The steady-state voltage-dependent activation curves and inactivation curves could both be fitted with a single Boltzmann function. Currents evoked with a prolonged pulse, however, inactivated with multiple time constants, suggesting either the presence of more than one Ca(2+) channel subtype or multiple inactivation processes with a single channel type in STN neurons. Experiments using organic Ca(2+) channel blockers revealed that on average, 21% of the current was nifedipine sensitive, 52% was sensitive to omega-conotoxin GVIA, 16% was blocked by a high concentration of omega-agatoxin IVA (200 nM), and the remainder of the current (9%) was resistant to the co-application of all blockers. These currents had similar voltage dependencies, but the nifedipine-sensitive current and the resistant current activated at slightly lower voltages. omega-Agatoxin IVA at 20 nM was ineffective in blocking the current. Together, the above results suggest that acutely isolated STN neurons have all subtypes of high-voltage-activated Ca(2+) channels except for P-type, but have no low-voltage-activated channels. Although acutely isolated neurons provide a good preparation for whole cell voltage-clamp study, dendritic processes are lost during dissociation. To gain information on Ca(2+) channels in dendrites, we thus studied Ca(2+) channels of STN neurons in a slice preparation, focusing on low-voltage-activated channels. In current-clamp recordings, a slow spike was always observed following termination of an injected hyperpolarizing current. The slow spike occurred at resting membrane potentials and was sensitive to micromolar concentrations of Ni(2+), suggesting that it is a low-threshold Ca(2+) spike. Together, our results suggest that STN neurons express low-voltage-activated Ca(2+) channels and several high-voltage-activated subtypes. Our results also suggest the possibility that the low-voltage-activated channels have a preferential distribution to the dendritic processes.     

Taste responses of neurons in the hamster solitary nucleus are modulated by the central nucleus of the amygdala

Previous studies have shown a modulatory influence of forebrain gustatory areas, such as the gustatory cortex and lateral hypothalamus, on the activity of taste-responsive cells in the nucleus of the solitary tract (NST). The central nucleus of the amygdala (CeA), which receives gustatory afferent information, also exerts descending control over taste neurons in the parabrachial nuclei (PbN) of the pons. The present studies were designed to investigate the role of descending amgydaloid projections to the NST in the modulation of gustatory activity. Extracellular action potentials were recorded from 109 taste-responsive cells in the NST of urethan-anesthetized hamsters and analyzed for a change in excitability following electrical and chemical stimulation of the CeA. Electrical stimulation of the CeA orthodromically modulated 36 of 109 (33.0%) taste-responsive NST cells. An excitatory response was observed in 33 (30.28%) cells. An initial decrease in excitability to electrical stimulation of the CeA, suggestive of postsynaptic inhibition, was observed in three (2.75%) NST taste cells. NST cells modulated by the CeA were significantly less responsive to taste stimuli than cells that were not. Many of these cells were under the modulatory influence of the contralateral CeA (28/36 = 77.8%) as well as the ipsilateral (22/36 = 61.1%); 14 (38.9%) were excited bilaterally. Latencies for excitation were longer after ipsilateral than after contralateral CeA stimulation. Microinjection of DL-homocysteic acid (DLH) into the CeA mimicked the effect of electrical stimulation on each of the nine cells tested: DLH excited eight and inhibited one of these electrically activated NST cells. Application of subthreshold electrical stimulation to the CeA during taste trials increased the taste responses of every CeA-responsive NST cell (n = 7) tested with this protocol. These effects would enhance taste discriminability by increasing the signal-to-noise ratio of taste-evoked activity.     

The role of 5-HT receptor subtypes in the ventrolateral orbital cortex of 5-HT-induced antinociception in the rat

The present study examined the involvement of 5-HT in the ventrolateral orbital cortex (VLO) on descending antinociception and determined which subtypes of 5-HT receptors mediated this effect. This study focused on the effects of 5-HT microinjection in the VLO of lightly anesthetized male rats on the radiant heat-evoked tail flick (TF) reflex, as well as the influence of 5-HT(1A), 5-HT(2), 5-HT(3), and 5-HT(4) receptor subtype antagonists on the effect of 5-HT. Results showed that 5-HT microinjection (2, 5, 10 microg, in 0.5 microl) into the VLO depressed the TF reflex in a dose-dependent manner. Pretreatment with 5-HT receptor antagonists (1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl] piperazine hydrobromide (NAN-190), cyproheptadine hydrochloride (CPT) and 1-methyl-N-(8-methyl-8-azabicyclo[3.2.3]-oct-3-yl)-1H-indazole-3-carboxamide maleate salt (LY-278,584)), specific for 5-HT(1A), 5-HT(2) and 5-HT(3) receptors, respectively, partially reversed the 5-HT-evoked inhibition. In contrast, the 5-HT(4) receptor antagonist, 1-[2-[(methylsulfonyl)-amino]ethyl]-4-piperidinyl]methyl1-methyl-1H-indole-3-carboxylate (GR 113808), had no effect on the inhibition of 5-HT. Microinjections of NAN-190, CPT and LY-278,584 alone into the VLO had no effect on the TF reflex. These results suggest that 5-HT(1A), 5-HT(2) and 5-HT(3), but not 5-HT(4) receptors, are involved in mediating 5-HT-induced antinociception in the VLO. According to different properties and distribution patterns of the 5-HT receptor subtypes on neurons, the possible mechanism of 5-HT activation of the VLO-periaqueductal gray (PAG) descending antinociceptive pathway is discussed.     

Ptychodiscus brevis toxin-induced depression of spinal reflexes involves 5-HT via 5-HT3 receptors modulated by NMDA receptor

The involvement of 5-hydroxytryptaminergic (5-HT) system for the Ptychodiscus brevis toxin (PbTx)-induced depression of spinal reflexes was evaluated. The reflex potentials were recorded at ventral root by stimulating the corresponding dorsal root in neonatal rat spinal cord in vitro. Superfusion of PbTx (2.8-84microM) depressed the monosynaptic (MSR) and polysynaptic (PSR) reflexes in a concentration-dependent manner. The depression of the reflexes was maximal with 84microM of the toxin. Ondansetron (0.1microM), a 5-HT(3) receptor antagonist, blocked the PbTx-induced depression of MSR and PSR. Spiperone (a 5-HT(2A) antagonist) or ketanserin (5-HT(2A/2C) antagonist and also at 5-HT(1B/1D)) failed to block the PbTx-induced depression of the reflexes. The 5-HT concentration of the cords was increased by four-fold after exposure to PbTx (28microM) and the increase was not seen in the cords pretreated with dl-2 amino-5-phosphonovaleric acid (APV, a NMDA receptor antagonist). Superfusion of 5-HT or phenylbiguanide (PBG, a 5-HT(3) receptor agonist) also produced depression of the spinal reflexes in a concentration-dependent manner. The 5-HT-induced depression of reflexes was blocked by ondansetron but not by spiperone. The results demonstrate that the PbTx-induced depression of spinal reflexes involves 5-hydroxytryptamine via 5-HT(3) receptors modulated by NMDA receptor.     

大鼠海马内5-羟色胺及其受体5-HT2A的表达

目的:观察5-羟色胺(5-HT)纤维和5-HT2A受体在大鼠海马CA1、CA2和CA3三个区域的分布特点.方法:用5-HT递质和5-HT2A受体特异性抗体的免疫组织化学显色以及图像处理与分析.结果:在海马内,抗5-HT2A受体的免疫反应阳性产物主要位于锥体细胞的细胞膜和树突,树突染色较深;5-HT2A受体的阳性胞体在C...