Parallel nociceptive reflex pathways with negative and positive feedback functions to foot extensors in the cat

1. Nociceptive reflex pathways to foot extensors were investigated with particular attention given to those not following a flexor reflex (FRA) or withdrawal pattern. 2. In anaemically decapitated, high spinal paralysed cats nociceptive afferents of the foot pad were activated by noxious radiant heat (48-60 degrees C), while for comparison non-nociceptive afferents were activated by weak mechanical stimulation of the skin or graded electrical nerve stimulation. The reflex action of the afferents on hindlimb motoneurones, innervating plantaris and intrinsic foot extensors (tibial nerve), was investigated by intracellular recording, by monosynaptic reflex testing and by recording of neurograms during fictive locomotion. A possible descending control of the nociceptive and non-nociceptive pathways was tested by application of opioidergic and monoaminergic compounds. 3. Beside the typical FRA pattern evoked in the majority of hindlimb motoneurone pools by nociceptive afferents from different skin areas of the foot, the results revealed parallel excitatory and inhibitory nociceptive reflex pathways from the central pad and partly from the toe pads to foot extensors. The excitatory pathways, which did not follow the FRA pattern, were predominantly to plantaris and intrinsic foot extensors. They were distinctly less depressed by opioids and monoaminergic compounds than FRA pathways. 4. While the nociceptive FRA pathways have a general nocifensive withdrawal function, the nociceptive excitatory non-FRA pathway to the foot extensors causes a movement of the affected area towards the stimulus or at least a resistance against the stimulus, i.e. it mediates a positive feedback.

Bulbospinal control of spinal cord pathways generating locomotor extensor activities in the cat

Intracellular recording of lumbosacral motoneurones in the decerebrate and partially spinalized cat injected with nialamide and L-dihydroxyphenylalanine (l-DOPA) was used to investigate the interneuronal convergence of two bulbospinal pathways and of the segmental pathways involved with the generation of extensor activities during locomotion. Deiter's nucleus (DN) or the medial longitudinal fasciculus (MLF) was stimulated in alternation with, and in combination with, stimulation of group I afferents from extensor muscles or of contralateral flexor reflex afferents (coFRA). The evoked polysynaptic EPSPs were recorded in extensor motoneurones when long-latency, long-lasting discharges were evoked by the stimulation of coFRA and when the group I autogenetic inhibition in extensors was reversed to polysynaptic excitation. Spatial facilitation was inferred when the amplitude of the EPSPs evoked by the combined stimuli was notably larger than the algebraic sum of the EPSPs evoked by individual stimulation. Both DN (16 motoneurones) and MLF inputs (8 motoneurones) showed spatial facilitation when preceded by coFRA stimuli and both could reset the rhythm of fictive stepping by triggering a precocious extensor phase. MLF showed spatial facilitation with extensor group I inputs in 69% of trials but DN failed to show spatial facilitation in any cells. These results indicate that DN and MLF project to the coFRA pathways of the extensor half-centre for locomotion and MLF, but not DN, converge on segmental interneurones of the extensor group I pathways. The implications of such convergence patterns on the functional organization of the extensor half-centre are discussed.

Serotonin receptor agonists that increase cyclic AMP positively regulate IGF-I in mouse mandibular mesenchymal cells

Evidence from the present study suggests that activation of both 5-HT(1A) and 5-HT(4) (5-hydroxytryptamine) receptor subtypes stimulates cyclic adenosine monophosphate (cAMP) synthesis in cultured embryonic mouse mandibular mesenchymal cells (micromass cultures). When these cells were grown in serum-free medium and treated with 10(-8) M agonist selective for either the 5-HT(1A) or 5-HT(4) receptor subtype (8-OH-DPAT and SC53116, respectively), this significantly stimulated cAMP synthesis and increased insulin-like growth factor I (IGF-I), but not IGF-II, protein levels compared to vehicle-treated controls, as measured by semi-quantitative immunobinding assays. Consistent with these results, IGF-I was significantly decreased when mandibular mesenchymal cells were grown in serum-containing medium (which contains micromolar amounts of 5-HT from fetal calf serum) and treated with 10(-8) M antagonist selective for the 5-HT(1A) or 5-HT(4) receptor subtype (NAN-190 on SDZ-205,557). Forskolin also stimulated cAMP and IGF-I (but not IGF-II) in both serum-containing and serum-free cultures. These results indicate that activation of 5-HT receptors that increase cAMP promotes synthesis of IGF-I. This may occur by activation of the cAMP response element sequence present in the IGF-I promoter region. Stimulation of the adenylyl cyclase pathway by activation of 5-HT(1A) or 5-HT(4) receptors may be one mechanism by which serotonin regulates IGF-I synthesis in developing craniofacial mesenchymal cells.

Sources of reactive oxygen species production in excitotoxin- stimulated cerebellar granule cells

Reactive oxygen species (ROS) production in rat cerebellar granule cells in the presence of the excitotoxins N-methyl-d-aspartate (NMDA) and kainic acid (KA) and by the protein kinase C activator phorbol myristate acetate (PMA) was Ca2+-dependent and resulted in decreased cell viability. Exposure of stimulated cells to rotenone (a respiratory chain inhibitor) did not decrease ROS levels and did not affect short-term cell viability. In cells stimulated by NMDA and KA, exposure to indomethacin (a cyclooxygenase inhibitor) and nialamide (a monoamine oxidase inhibitor) caused a decrease in ROS levels and increased cell viability occurred in NMDA-treated cells. In contrast, PMA-stimulated neurons did not show decreased ROS levels when exposed to indomethacin and nialamide. These studies suggest that there is a multiplicity of routes for Ca2+-dependent ROS production in neurons but that ROS generation by cyclooxygenase and monoamine oxidase is not controlled by protein kinase C.

Plasticity in reflex pathways controlling stepping in the cat

Previous studies have shown that stimulation of group 'I' afferents from ankle extensor muscles can prolong the cycle period in decerebrate walking cats and that the magnitude of these effects can be altered after chronic axotomy of the lateral-gastrocnemius/soleus (LGS) nerve. The effectiveness of LGS group I afferents in prolonging the cycle period decreases after axotomy, whereas the effectiveness of the uncut medial-gastrocnemius (MG) group I afferents is increased. The objectives of this investigation were to establish the time course of these changes in effectiveness and to determine whether these changes persist after transection of the spinal cord. The effects of stimulating the LGS and/or MG group I afferents on the cycle period were examined in 22 walking decerebrate animals in which one LGS nerve had been cut for 2 to 31 days. The effectiveness of LGS group I afferents declined progressively in the postaxotomy period, beginning with significant decreases at 3 days and ending close to zero effectiveness at 31 days. Large increases in the effectiveness of MG group I afferents occurred 5 days after axotomy, but there was no progressive change from 5 to 31 days. To test whether these changes in effectiveness were localized to sites within the spinal cord, the cord was transected in some decerebrate animals and stepping induced by the administration of L-DOPA L-3-4 dihydroxyphenylalanine (L-DOPA) and Nialamide. The effects of stimulating the MG and/or the LGS group I afferents on the cycle period were reexamined. In all four animals tested, stimulating the axotomized LGS group I afferents had a reduced effectiveness during locomotor activity in both the decerebrate and spinal states, whereas the increased effectiveness of the MG group I afferents was retained after transection of the spinal cord in two of five animals. Different mechanisms may be responsible for the changes in strength of the LGS and MG group I afferent pathways that project onto the rhythm generating sites in the spinal cord. This possibility follows from our observations of a linear relationship between the time after axotomy and decreased effectiveness of LGS group I afferents but no significant relationship between time postaxotomy and increased effectiveness of MG group I afferents; no significant relationship between the decreased effectiveness of LGS group I afferents and the increased effectiveness of MG group I afferents; and, after spinalization, consistent (4/4 cases) preservation of decreased LGS effectiveness but frequent (3/5 cases) loss of increased MG effectiveness.

Effects of tetrabenazine on methamphetamine-induced hyperactivity in mice are dependent on order and time-course of administration

The ambulation-increasing effect of methamphetamine (MAP: 2 mg/kg s.c.) in mice persisted for about 3 h. Tetrabenazine (TBZ: 4 mg/kg s.c.), a depleter of monoamines from the cytoplasmic pool did not increase ambulation on its own. Pretreatment with TBZ at 1.5 h before administration of MAP inhibited the stimulant effect of MAP. In contrast, combined administration of two drugs resulted in a transient but considerable enhancement of MAPs stimulant effect. Post-MAP treatment with TBZ at 0.5-2 h hardly modified MAPs behavioral effects. In contrast, 3-6 h post-MAP treatment with TBZ induced a transient increase in activity, although the stimulant effect of MAP had already disappeared. The maximum increase in ambulatory stimulation was produced by 4-h post-MAP treatment with TBZ. The inhibitory effect of TBZ pretreatment on MAP-induced hyperactivity, as well as the transient hyperactivity elicited by TBZ when administered along with MAP, or 4 h after MAP, was dose-dependent. Preliminary studies revealed that transient hyperactivity was never produced by combination of GBR-12909 (a selective dopamine reuptake inhibitor) with TBZ or MAP with oxypertine (a selective norepinephrine releaser/depleter), but produced by combination of nialamide (a monoamine oxidase inhibitor) with TBZ. Inhibition of MAPs effects by TBZ pretreatment suggests that enhancement of dopamine release from cytoplasmic pool, and inhibition of dopamine reuptake by MAP, are involved in MAPs acute behavioral effects. Further, the fact that neither TBZ administration following GBR-12909 pretreatment, nor oxypertine treatment following MAP pretreatment, elicited transient hyperactivity suggests that dopamine is involved in hyperactivity elicited by post-MAP treatment with TBZ. It is also suggested that inhibition of monoamine oxidase (MAO) by MAP and dopamine displacement by TBZ may be responsible for the transient stimulation produced by 3-6 h post-MAP treatment with TBZ. It is hypothesized that the MAO inhibitory action of MAP persists after cessation of its acute stimulant effect, possibly up to 6 h after administration.

Tyrosine hydroxylase-containing neurons in the spinal cord of the chicken. I. Development and analysis of catecholamine synthesis capabilities

1. The development of tyrosine hydroxylase-immunoreactive (TH-IR) neurons was examined in the spinal cord of the chick embryo and hatchling. 2. Two groups of TH-IR cells are described, both of which appear to reach their full complement in number relatively late in embryonic development. One group is comprised of numerous cells located ventral to the central canal which make direct contact with the lumen of the canal. The other group consists of large multipolar neurons that reside in the dorsal horn, more commonly along the outer margin of the gray matter within lamina I and II, and less frequently deeper in the dorsal horn within medial portions of laminae V, VI or VII. 3. TH-IR cells ventral to the central canal in the chick are comparable in location to dopamine (DA)-containing spinal cord cells in lower vertebrate species. In contrast, the dorsally-suited TH-IR cells in the chick are known only to occur in similar positions in higher vertebrates. Therefore, the chick is novel in that the presence of both groups of TH-IR cells appearing together in significant numbers within the spinal cord has not been shown in any other species studied to date. 4. The TH-containing cells in the chick cord do not appear to contain the catecholamine biosynthesis enzymes, DBH or PNMT. Moreover, using anti-DA immunocytochemistry, neither group of TH-IR cells demonstrated detectable levels of DA in control animals nor in animals pretreated with inhibitors of MAO (MAO-I). 5. However, a difference was noted though between the two TH-IR cell groups in terms of their responses to exogenously supplied L-DOPA, the immediate precursor to DA. With the administration of L-DOPA and a MAO-I to chick hatchlings, cells in the region ventral to the central canal stained intensely for DA. In contrast, the same treatment failed to produce DA-immunoreactive cells in the dorsal horn. 6. One reasonable hypothesis for these results is that the TH-IR cells ventral to the central canal contain an active form of AADC, the enzyme that converts L-DOPA to DA. With this interpretation, if these cells can produce DA from L-DOPA, yet do not appear to synthesize DA endogenously, it would appear that the TH enzyme contained in these cells occurs in an inactive form. Whether the TH enzyme in the dorsally located immunoreactive cells is also inactive is uncertain since it remains unclear whether they contain AADC.

Ultrastructural localization of sympathetic axons in experimental rat sciatic nerve neuromas

The ultrastructural localization of sympathetic axons was investigated in normal rat sciatic nerves and experimental sciatic nerve neuromas. The best ultrastructural localization of noradrenaline in the dense-cored vesicles of sympathetic axons was accomplished following pretreatment of rats with nialamide and 5-hydroxy dopamine, followed by fixation according to the modified chromaffin technique of Tranzer and Richards (1976). After such preparation, sympathetic axons containing 5-hydroxy dopamine-labelled dense-cored vesicles could be identified in normal sciatic nerve. Large accumulations of labelled dense-cored vesicles were also found in acute neuromas, up to 1 week after nerve section. Much smaller numbers of dense-cored vesicles could be identified in chronic neuromas from 2 to 3 weeks following nerve section. Sympathetic axons could also be identified following electron probe X-ray microanalysis of the tissue sections, using chromium detection as the marker for the noradrenaline-containing dense-cored vesicles. Unusual configurations of Schwann cell subunits, which enclosed myelinated fibres and sympathetic axon sprouts within the same basal lamina, were identified in the acute neuromas, 3-7 days after nerve section. Such configurations may be of relevance to the pathophysiological interaction which develops between sympathetic efferent and sensory fibres in peripheral nerve neuromas.

Exogenous gaseous superoxide potentiates the antinociceptive effect of opioid analgesic agents

The study examined the potentiation of the antinociceptive action of opioid analgesics produced by gaseous superoxide (GS) in the rat hind paw withdrawal test (PWT) and by GS or hydrogen peroxide (HP) in the formalin test. In the PWT, inhalation of GS for 50 minutes before i.p. injection of threshold doses of morphine (0.5 mg/kg) and trimeperidine (1.0 mg/kg) increased the threshold of nociception (TN) by a maximum of 43.0% (p < 0.05) and 113.4% (p < 0.01) respectively. The GS/trimeperidine-dependent increase in TN showed two peaks, the second of which could be suppressed by nialamide. Naloxone abolished the GS/ morphine-dependent increased in the TN. In the formalin test, a significant antinociceptive effect developed after GS inhalation or HP administration (intranasally, 2 x 5 microliters of 2 x 10(-5) mol/l solution in saline) in combination with low doses of Omnopon (0.06-0.75 mg/kg). These results suggest that both GS and HP potentiate the antinociceptive effects of opioid analgesics.

Rhythmic discharges recorded from tail muscle nerves after injection of nialamide and L-DOPA solution in spinalized cats

In 22 decapitated and high spinalized cats, rhythmic discharges were recorded from the nerves supplying the tail muscles, m. extensor caudae lateralis (ECL) and m. flexor caudae longus (FCL) after intravenous injection of Nialamide and L-DOPA solution. In 15 out of 22 cats, stable rhythmic discharges were recorded from tail muscle nerves. Two different discharge patterns were observed. The predominant pattern consisted of an alternating activation between left and right tail muscle nerves and a synchronous activation of ECL and FCL nerves on one side. The second pattern consisted of synchronous activity involving all four tail muscle nerves.

Influence of opioids and naloxone on rhythmic motor activity in spinal cats

The effects of L-DOPA, naloxone, and the opioids (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin (DAGO) and D-Ser2-Leu-enkephalin-Thr6 (DSLET) on spinal motor rhythm generation were compared in anemically decapitated high spinal cats. After premedication with nialamide, DOPA caused the well-known, slow rhythmic motor activity with a locomotor pattern. The cycle duration of the evoked rhythm was usually between 3.9 and 5.0 s. The opioids DAGO and DSLET, injected intravenously (1.2-2 mg/kg) or suffused over the lumbar spinal cord (10(-3)-10(-4) M in Ringer's solution), severely depressed the DOPA-induced rhythmic activity, sometimes completely abolishing efferent motor activity. Naloxone (0.5-1 mg/kg i.v.) exerted different rhythm-facilitating effects, depending on the experimental condition. In the acute phase after spinalization, without paralysis and without nialamide and DOPA, naloxone induced rhythmic movements with a main frequency of 1.2-2 Hz. In the same preparation with paralysis, naloxone induced a rhythmic motor activity with a distinctly higher frequency (main range 4.3-5.8 Hz). After premedication with nialamide and DOPA, naloxone facilitated or, if a rhythm was absent, induced the slow-frequency DOPA type of rhythm. Given after i.v. or topical opioid application, naloxone antagonized the rhythm-depressing action of the opioid and caused an additional facilitation of rhythmic activity. Dopa and naloxone facilitated the long-latency, segmental reflex pathways from flexor reflex afferents (FRA), while the opioids depressed them. The short-latency FRA pathways were depressed by DOPA and opioids but were facilitated by naloxone. The influence of the different drugs on spinal motor rhythm generation is discussed in relation to their influence on short- and long-latency segmental pathways from FRA. If the rhythm generation induced by DOPA is based on the release of the long-latency FRA pathways, as has been proposed before, the rhythm-depressing action of opioids may be due to the suppression of these pathways, and the particular rhythm-generating function of naloxone may be related to its facilitation of short- and long-latency FRA pathways.

5-Hydroxytryptamine-immunoreactive nerve fibers in the rat and porcine prevertebral sympathetic ganglia: effect of precursor loading and relation to catecholaminergic neurons

Localization of 5-hydroxytryptamine immunoreactivity was studied in the rat coeliac-superior mesenteric ganglion complex and in the porcine superior and inferior mesenteric ganglia by the indirect immunofluorescence technique. In normal rats, only 5-hydroxytryptamine immunoreactive SIF cells were seen in the coeliac-superior mesenteric ganglion complex. In the rats, pretreated with a 5-hydroxytryptamine precursor, L-tryptophan, and with a monoamine oxidase inhibitor, nialamide, a large number of 5-hydroxytryptamine-immunoreactive nerve fiber terminals were detected. In normal porcine superior and inferior mesenteric ganglia, intense 5-hydroxytryptamine immunoreactivity was found in numerous nerve fibers which were located around tyrosine hydroxylase-immunoreactive principal neurons. The origin and function of these fibers are discussed.

Effects of L-DOPA on fusimotor control of triceps surae muscle spindles in the cat

The experiments were performed on lightly alpha-chloralose anaesthetised and spinalized cats. Alterations in fusimotor activity were assessed by recordings from single spindle afferents (90 primary and 12 secondary) from the triceps surae muscle, before and after i.v. administration of L-beta-3,4-dihydroxyphenylalanine (L-DOPA). The effects of L-DOPA on fusimotor reflexes from ipsi- and contralateral hind limb afferents were investigated by using extensions of the intact contralateral hind limb and tonic stretches of the ipsilateral posterior biceps and semitendinosus muscles as reflex stimuli. Prior to injection of L-DOPA, a low reflex responsiveness was found to both the ipsi- and the contralateral stimulation. After administration of L-DOPA, the reflex responsiveness as well as the resting activity of the muscle spindle afferents were increased as a result of enhanced activity in mainly dynamic fusimotor neurones. The results indicate that changes in fusimotor activity elicited after administration of L-DOPA are caused by release of transmission in interneuronal pathways mediating ipsi- and contralateral reflexes to mainly dynamic fusimotor neurones. The possible role of monoaminergic descending control of fusimotor neurones in the regulation of muscle tone, tremor and rigidity is discussed.

Effect of various serotoninergically induced manipulations on audiogenic seizures in magnesium-deficient mice

The aim of our study was to analyse the possible implication of the serotoninergic system in the pathophysiology and the lethality of audiogenic seizures induced by magnesium deficiency, either by decreasing cerebral serotonin (5-HT) levels (p-chlorophenylalanine) or by increasing 5-HT levels in the brain (5-hydroxytryptophan, L-tryptophan, nialamide, fluoxetine). In magnesium-deficient mice, the percentages of audiogenic seizures and of fatal seizures were dependent on the time lapse between the p-chlorophenylalanine (PCPA) injection and the audiogenic test. The percentage was at least 24 h after the injection: in OF1 and C57BL/6 strains, PCPA fully protected the mice from seizure occurrence, whereas it only partially protected the animals of the other strains. 5-Hydroxytryptophan caused a decrease in the audiogenic seizures in magnesium-deficient OF1 mice as well as in control DBA/2 mice. In contrast L-tryptophan did not reduce the number of wild courses or of clonic and tonic seizures in either the magnesium-deficient OF1 strain or control DBA/2 mice. Nialamide and fluoxetine were only effective in decreasing the numbers of clonic and tonic convulsions of the audiogenic seizure without affecting the wild courses. The combination of nialamide and tryptophan caused a cessation of the audiogenic seizure phases in both magnesium-deficient OF1 and control DBA/2 mice. In contrast, the fluoxetine-tryptophan combination did not have the same effect on magnesium-deficient and non-magnesium-deficient mice. This work showed that the serotoninergic system plays a secondary role in the pathophysiology of audiogenic seizures in magnesium-deficient mice rather than in that of genetically audiosusceptible mice.

Effects of befloxatone, a new potent reversible MAO-A inhibitor, on cortex and striatum monoamines in freely moving rats

Single administration of befloxatone (0.75 mg/kg, i.p.) in the rat increased extracellular levels of DA (+300%) in striatum. In frontal cortex, befloxatone (0.75 mg/kg, i.p.) and nialamide (100 mg/kg, i.p.) increased NA by +100% but did not modify 5HT, whereas pargyline (100 mg/kg i.p.) increased extracellular NA and 5HT by 400 and 600%, respectively. At these doses, befloxatone inhibited totally and selectively MAO-A, pargyline inhibited totally MAO-A and MAO-B. Increases of tissue and extracellular concentrations of NA and 5HT were highest after Pargyline suggesting that both monoamines may be metabolized by MAO-A and MAO-B. Befloxatone and nialamide potentiated the effects of idazoxan (20 mg/kg, i.p.) on extracellular NA in frontal cortex, which increased from 350% to 2,000 and 1,500% respectively. These results suggest that alpha 2-adrenoceptors play a major role in the regulation of extracellular NA in frontal cortex.

Voltage-dependent excitation of motoneurones from spinal locomotor centres in the cat

Lumbar motoneurones were recorded intracellularly during fictive locomotion induced by stimulation of the mesencephalic locomotor region in decerebrate cats. After blocking the action potentials using intracellular QX-314, and by using a discontinuous current clamp, it is shown that the excitatory component of the locomotor drive potentials behaves in a voltage-dependent manner, such that its amplitude increases with depolarisation. As the input to motoneurones during locomotion is comprised of alternating excitation and inhibition, it was desirable to examine the excitatory input in relative isolation. This was accomplished in spinalised decerebrate cats treated with nialamide and L-dihydroxy-phenylalanine (L-DOPA) by studying the excitatory post-synaptic potentials (EPSPs) evoked from the "flexor reflex afferents" (FRA) and extensor Ib afferents, both of which are likely to be mediated via the locomotor network. As expected, these EPSPs also demonstrate a voltage-dependent increase in amplitude. In addition, the input to motoneurones from the network for scratching, which is thought to share interneurones with the locomotor network, also results in voltage-dependent excitation. The possible underlying mechanisms of NMDA-mediated excitation and plateau potentials are discussed: both may contribute to the observed effect. It is suggested that this nonlinear increase in excitation contributes to the mechanisms involved in the production of the high rates of repetitive firing of motoneurones typically seen during locomotion, thus ensuring appropriate muscle contraction.

Effects of two substituted hydrazine monoamine oxidase (MAO) inhibitors on neurotransmitter amines, gamma-aminobutyric acid, and alanine in rat brain

Time- and dose-response analyses were undertaken to investigate the effects of the substituted hydrazine monoamine oxidase (MAO) inhibitors iproniazid and nialamide on the following: MAO-A and -B activity; levels of gamma-aminobutyric acid (GABA), alanine (ALA), and the neurotransmitter amines dopamine, noradrenaline, and 5-hydroxytryptamine (serotonin) and their acid metabolites; and the activity of GABA-transaminase and ALA-transaminase. The results showed that these drugs are relatively potent MAO inhibitors but, unlike the unsubstituted hydrazine MAO inhibitor phenelzine, they do not produce increased GABA and ALA levels in brain. These experiments suggest that a free hydrazine group is necessary for MAO inhibitors to also have marked effects on GABA and ALA.

Serotonin and cardiac morphogenesis in the mouse embryo

The possible involvement of the neurotransmitter serotonin (5-HT) and its binding protein (SBP) in cardiac morphogenesis was studied using mouse whole embryo culture (together with immunocytochemistry or 3H-thymidine autoradiography) and a cell migration assay. Embryos were cultured before and during the period of endocardial cushion formation, embryonic (E) days 9-12, in the presence of 5-HT, the monoamine oxidase (MAO) inhibitor nialamide, or an uptake inhibitor (fluoxetine or sertraline). For the migration assay, cells from the outflow tracts of E12 embryos were dissociated and placed in a chemotaxis chamber together with different concentrations of 5-HT. E9 embryos cultured in the presence of 10 microM 5-HT and nialamide exhibited intense 5-HT immunoreactivity (5-HT IR) throughout the myocardium. This staining was greatly diminished by fluoxetine, sertraline, or the absence of nialamide. As morphogenesis proceeded, myocardial staining in embryos exposed to 5-HT became restricted to developing endocardial cushion forming regions and was more completely blocked by uptake inhibitors. No evidence for 5-HT synthesis by myocardium was found at any age studied using the precursor L-tryptophan. SBP was present in endocardial cushions in cultured and uncultured embryos. 3H-thymidine autoradiography demonstrated that both fluoxetine and sertraline inhibited proliferation of cardiac mesenchyme, endocardium, and myocardium. These effects were most pronounced when exposure began at E9 (prior to cushion formation). Dose-dependent effects of 5-HT on migration of outflow tract cells were also observed. Taken together, these results suggest that 5-HT may play a role in cardiac morphogenesis during endocardial cushion formation.

Differential expression of serotonin and [Met]enkephalin-Arg6-Gly7-Leu8 in neurons of the rat brain stem

The hypothesis that serotonin (5-HT) and [Met]enkephalin-Arg6-Gly7-Leu8 (MEAGL) coexist in the rat brain stem raphe nuclei was tested by a technique combining histofluorescence with immunocytochemistry, after treatment with colchicine and nialamide. In midbrain and pons serotonergic cell groups (B5-B9), no coexistence of 5-HT and MEAGL was detected. In serotonergic cell groups of the medulla oblongata (B1-B3), only 0.3-1.5% of 5-HT-fluorescent cells were MEAGL-immunoreactive. These findings suggest that putative 5-HT and MEAGL are mostly expressed in different populations of neurons in the rat raphe nuclei.

Nialamide, an MAO inhibitor, increases urinary excretion of endogenously produced bufotenin in man

Nialamide, an MAO inhibitor, was given per os (PO) to a normal man who volunteered in two separate trials (total intake 300 mg and 1000 mg, respectively), and his bufotenin excretion was followed by consecutive urine samples. In both experiments the excretion rose well above the values measured from the same test subject when not taking nialamide (median 0.089 nmol/mmol creatinine, range 0.002-1.78). At its highest, the excretion was 16.5 nmol/mmol creatinine, and the maximum urinary output was 495 nmoles (56 micrograms) in 24 hr. The levels of bufotenin in plasma required for the excretion of the latter amounts are not far from those that produce psychic symptoms in man.

Low-threshold, short-latency cutaneous reflexes during fictive locomotion in the "semi-chronic" spinal cat

Low-threshold, short-latency cutaneous reflexes evoked in ipsilateral hindlimb motor nerves were examined during fictive locomotion. Locomotion in 11 anaemically decerebrated spinal animals (1-3 weeks after transection at T13-L1) was induced by administration of clonidine, L-dopa and nialamide; by administration of the latter two drugs only; or by exteroceptive stimulation in the absence of any drugs. The caudal and lateral cutaneous sural, caudal cutaneous femoral, saphenous and superficial peroneal nerves were stimulated at low threshold (1.5-3 T). Pooled results from all combinations of cutaneous nerves stimulated and muscle nerves recorded show that the initial response was excitatory in 40 of 50 triceps surae and 17 of 20 semitendinosus (St) electroneurograms (ENGs). These excitatory responses occurred at latencies that ranged from 5 to 15 ms and tended to be maximal during the motor nerve's active period in the step cycle (i.e. they were modulated in a phase-dependent manner). Only three inhibitory responses (9-12 ms earliest latency) were encountered in total: in two St ENGs of one animal and in one lateral gastrocnemius-soleus ENG of a different animal. In two animals a "second" excitatory response (15-25 ms latency) was sometimes recorded in triceps surae and St nerves and, interestingly, could be modulated out of phase with the early response. Weak short-latency excitatory reflexes were also found in contralateral St ENGs when examined. Finally, among medial gastrocnemius, lateral gastrocnemius and soleus nerves, excitatory responses due to stimulation of any particular cutaneous nerve tended to be modulated similarly but were of consistently different amplitude among the three. This finding, together with the general observation that excitatory reflexes produced by stimulation of a particular cutaneous nerve were modulated similarly in extensors (or flexors) of different animals, suggests that spinal circuits generating locomotion may indeed exert a stereotypic control over interneurons in specific cutaneous reflex pathways to motoneurons. The results are primarily discussed in terms of the existing evidence for short-latency excitatory cutaneous reflexes in extensors in a variety of locomotive and non-locomotive preparations.

Serotonin promotes region-specific glial influences on cultured serotonin and dopamine neurons

To test the hypothesis that glia mediate interactions between embryonic serotonergic (5-HT) neurons and dopamine neurons, we studied the effects of 5-HT in co-cultures of E14 raphe neurons of mesencephalic dopamine neurons and radial glia/astrocytes derived from the same (homotypic) or opposite (heterotypic) brain region using a dose (10(-5) M) that would produce 5-HT uptake into glial cells as well as activate 5-HT receptors. Morphometric analysis of 5-HT and tyrosine hydroxylase (TH) immunoreactive neurons revealed regional differences in the effects of 5-HT (and nialamide) on survival, cell soma size, and dendrite-like neurite outgrowth in neuronal-glial co-cultures. In general, 5-HT had more significant effects on both types of monoamine neuron when they were cultured with mesencephalic glia (GSN). Stimulatory effects of 5-HT on growth of TH neurons in GSN cultures suggest that developing raphe axons, which reach the mesencephalon during the early differentiation of these neurons, may enhance the influence of local glial-derived trophic factors. Likewise, the promotion of 5-HT neuronal survival in these cultures suggests that glial factors in the mesencephalon may contribute to the support of 5-HT neurons in addition to the influences of raphe glia. The inhibitory effects of 5-HT on neurite outgrowth by raphe neurons in GSN co-cultures indicates enhanced sensitivity of these neurons to the inhibitory effects of 5-HT in the presence of mesencephalic glia. The region-specific effects of 5-HT and nialamide in glial co-cultures suggest that raphe and mesencephalic glia may express different capacities for 5-HT uptake, receptors, and/or monoamine oxidase (MAO) activities. These characteristics could be important for the specificity of growth-regulatory influences of glial cells on the development of brain monoamine neurons.

Characterization of dopamine autoreceptors in the amygdala: a fast cyclic voltammetric study in vitro

The present study has employed the technique of fast cyclic voltammetry to measure electrically-evoked dopamine release within the central amygdaloid complex in a rat brain slice. Local electrical stimulation caused the release of an electroactive substance which was identified, biochemically and pharmacologically, as being neuronal dopamine. Dopamine release could be inhibited by the dopamine D2 receptor agonist, quinpirole, but not by the D1 receptor agonist, SKF38393. Quinpirole-induced inhibitions were antagonized by sulpiride, metoclopramide and clozapine but not by SCH23390. It is concluded that dopamine release in the amygdala can be modulated by presynaptic D2 receptors which appear to be the same type as those found in striatum and nucleus accumbens.

Fictive motor patterns in chronic spinal cats

1. Fictive motor patterns were recorded in hind leg nerves of 10 adult chronic spinal cats (spinalized at T13). Four of these animals had been trained to step with their hind legs on a treadmill (late-spinal animals), whereas the remainder received no training and were examined a short time after spinalization (early-spinal animals). 2. A fictive pattern resembling the locomotor pattern for stepping was evoked in all animals in response to stimulation of the skin of the perineal region. (2-[2,6-Dichloroaniline]-2-imidazoline) hydrochloride (Clonidine) at doses ranging from 100 to 500 micrograms/kg iv facilitated the production of this pattern, particularly in early-spinal animals. 3. The fictive locomotor pattern in late-spinal animals was more complex than that occurring in early-spinal animals. In the latter the pattern consisted of an alternation of activity in flexor and extensor nerves, and changing leg position did not qualitatively alter the pattern, whereas in late-spinal animals the relative durations of the bursts in different flexors were usually not the same, and the pattern of flexor activity was dependent on leg position. 4. Moving the legs from extension to flexion progressively decreased the duration of flexor bursts, increased the cycle period, and decreased the ease with which the pattern could be evoked in both early- and late-spinal animals. 5. 1-beta-3,4-Dihydroxyphenylalanine (DOPA)/Isonocotinic acid 2-[(2-benzylcarbamoyl)ethyl]hydrazide (Nialamide) treatment following Clonidine in early-spinal animals increased the complexity of flexor burst activity. This, and other observations, indicates that DOPA and Clonidine do not have strictly identical actions on the locomotor pattern generator. 6. Stimulation of the paws in late-spinal animals produced two patterns of activity distinctly different from the locomotor pattern. of activity distinctly different from the locomotor pattern. One was a short sequence of high-frequency rhythmic activity (at approximately 8 c/s) in response to gently stimulating one paw with a water jet, and the other was a slow rhythm in flexor nerves in response to squeezing the paw. 7. The main conclusion of this investigation is that three distinctly different fictive motor patterns can be generated in chronic spinal cats depending on the method and site of stimulation. These patterns correspond to three different behaviors (locomotion, paw shake, and rhythmic leg flexion) that can be elicited in behaving chronic spinal cats in response to the same stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Serotonin and nialamide differentially regulate survival and growth of cultured serotonin and catecholamine neurons

In this morphometric analysis of immunoreactive serotonin (5-HT) and tyrosine hydroxylase (TH) neurons in culture, 5-HT and the MAO inhibitor nialamide influenced the survival, cell body size and neurite outgrowth of embryonic day 14 (E14) 5-HT neurons after treatment from 1-3 days in vitro (DIV), but did not significantly affect E14 or E15 TH neurons of either the noradrenergic or dopaminergic phenotype. These treatments had minimal effects on 5-HT neurons derived from E15 embryos. The stimulatory effects of 5-HT on survival and somal growth of E14 5-HT neurons was in contrast to its inhibitory effects on neurite outgrowth, suggesting trophic and inhibitory autoregulation of different cellular compartments of developing 5-HT neurons. The decreased sensitivity of E15 5-HT neurons to these treatments, despite similar viability and growth of these neurons in control cultures, suggests the existence of a critical period for this regulation during the initial period of serotonergic neurogenesis when these neurons are forming the bilateral B4-9 raphe complex. The lack of significant effects of 5-HT on TH neurons suggests differential sensitivities of 5-HT and TH neurons to developmental regulation by this neurotransmitter.

Corticosterone and prolactin response to TFMPP in rats during repeated antidepressant administration

The corticosterone and prolactin response to acute administration of the 5-HT agonist 1-(m-trifluoromethylphenyl) piperazine (TFMPP) (10 mg kg-1) was assessed in rats treated for 10 days with either saline, amitriptyline (20 mg kg-1 day-1) or nialamide (40 mg kg-1 day-1). For all groups, TFMPP significantly increased both serum corticosterone and prolactin concentrations compared with control animals challenged with saline. However, the corticosterone response to TFMPP was attenuated significantly by nialamide pretreatment, while the prolactin response to TFMPP was enhanced significantly by amitriptyline pretreatment. These results support previous reports that antidepressants differentially affect 5-HT-ergic systems involved in the regulation of corticosterone and prolactin secretion.

Phase-dependent modulation of primary afferent depolarization in single cutaneous primary afferents evoked by peripheral stimulation during fictive locomotion in the cat

Previous results from our laboratory have shown with intra-axonal recordings that hindfoot cutaneous primary afferents are subjected to rhythmic depolarizations during fictive locomotion (L-PAD) suggesting that cutaneous presynaptic mechanisms are activated by the central locomotor program. In this study, we examined the transmission in pathways responsible for primary afferent depolarizations (PAD) of cutaneous fibres during spontaneous fictive locomotion in decorticate cats and in spinal cats injected with nialamide and L-DOPA. PADs were evoked (E-PADs) by electrical stimulation of peripheral nerves and recorded intra-axonally with micropipettes in identified superficialis peroneal (SP; n = 7) and tibialis posterior (TP; n = 17) cutaneous primary afferents. Results showed that the amplitude of E-PADs, which were superimposed on the L-PAD, was deeply modulated throughout the locomotor cycle; decreasing to reach a minimum during the flexor phase and increasing to a maximum during the extensor phase. The results were not statistically different in fibres of the two nerves and in both types of preparation. The amplitude of E-PADs was always maximum during the extensor phase whether there was a large L-PAD or not during that phase. This suggests that the presynaptic mechanisms activated by central locomotor networks (L-PAD) and those activated by peripheral inputs (E-PAD) may in part be controlled differently. The results thus show that the transmission in PAD pathways activated by cutaneous inputs is phasically modulated by the central pattern generator for locomotion. This strongly suggests that the presynaptic inhibition in cutaneous fibres evoked by the movement-related feedback during real locomotion could be similarly modulated.

[Role of peripheral adrenergic links in the development of antidepressive effect in an experimental model of behavioral depression in rats]

The study was made on the reserpine model of behavioural depression in cats. The morphofunctional state of peripheral adrenergic nerves in control experiments and under action of antidepressants (befol and nialamid) was studied by fluorescent microscopic method. One definite correlation was shown between the state of somatovegetative changes and the level of neuromediator activity of the adrenergic structures. It was established that the used antidepressants (more expressive by befol) have protective effect in depressive conditions.

Effect of precursors on the synthesis of catecholamines and on neurotransmission in the superior cervical ganglion of the rat

Male Sprague-Dawley rats (325-350 g) were anesthetized with urethane (1.5 g/kg i.p.) and treated with physiological saline, Aspartame (APM; 552 mumols/kg), or tyrosine (Tyr; 552 mumols/kg). Ganglionic transmission and the synthesis of dopamine (DA) and norepinephrine (NE) were measured in the superior cervical ganglion (SCG) following electrical stimulation of the cervical sympathetic trunk (CST). When the CST was stimulated with single pulses, neither APM nor Tyr affected the synthesis of NE or DA. However, in response to low- (5 Hz, 20 s) and high- (20 Hz, 20 s) frequency pulses, the metabolism of DA was increased (p less than 0.05), but to the same extent after saline, APM, or Tyr. In rats stimulated with similar low- and high-frequency pulses, the synthesis of NE was increased significantly (p less than 0.05) after Tyr, but not after APM or saline. In saline-treated controls, ganglionic transmission was not changed in response to single pulses, or low- or high-frequency stimulation. However, after treatment with APM, ganglionic transmission was depressed significantly (p less than 0.01) in response to high-frequency stimulation (single: 0.46 +/- 0.09 mV; low: 0.39 +/- 0.07 mV; high: 0.27 +/- 0.07 mV). After treatment with Tyr, ganglionic transmission was depressed significantly (p less than 0.05) in response to both low- and high-frequency stimulation (single: 0.44 +/- 0.04 mV; low: 0.22 +/- 0.12 mV; high: 0.26 +/- 0.07 mV). In the nonstimulated SCG, L-3,4-dihydroxy-phenylalanine (25 mg/kg) caused a rapid, significant (p less than 0.01) increase in the synthesis and metabolism of DA, but not of NE.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of selective monoamine oxidase A and B inhibitors on footshock induced aggression in paired rats

Effects of a selective monoamine oxidase (MAO)--A inhibitor, clorgyline, a selective MAO-B inhibitor, deprenyl, and a non-selective MAO inhibitor, nialamide, were investigated on footshock-induced aggression (FIA) in paired rats. The doses and pretreatment times of the inhibitors used were based on an earlier reported in vivo dose-response and time-course study. In addition, apomorphine, a dopaminergic receptor agonist, and beta-phenylethylamine, a preferred substrate for MAO-B, were also used to garner corroborative evidence. The results of the study indicate that selective MAO-A inhibitors are likely to attenuate FIA by augmenting central serotonergic activity, while selective MAO-B inhibitors accentuate the behaviour by facilitating dopaminergic activity. A permissive role for noradrenaline could not be delineated by the available data.

Gangliosides enhance the anti-immobility response elicited by several antidepressant treatments in mice

Ganglioside pretreatment enhanced the anti-immobility effect induced in the forced swim test after a chronic treatment with desipramine, mianserin, clomipramine, nialamide or repeated electroconvulsive shock in mice. Gangliosides, which had no effect per se, showed a clear dose-response relationship in enhancing the anti-immobility effect of desipramine. These results suggest that, regardless of their mechanisms of action, gangliosides facilitate the behavioral response of several antidepressant treatments.

On the mechanism by which extracellular sodium depletion causes 5-hydroxytryptamine release from rat brain synaptosomes

The release of 3H-labelled 5-hydroxytryptamine (5-HT) from preloaded and superfused rat forebrain synaptosomes in response to extracellular Na+ depletion was studied. In the absence of monoamine oxidase inhibitors, the release of [3H]-5-HT caused by Na+ depletion was not affected by immobilizers of the plasma membrane 5-HT carrier. The release of [3H]-5-HT in response to Na+ depletion was also either independent of, or inversely related to the concentration of extracellular Ca2+ depending on the degree to which extracellular Na+ was reduced. The efflux of 45Ca2+ from prelabelled synaptosomes was decreased by Na+ reduction but the amplitude of the changes in 45Ca2+ efflux did not totally correlate with the changes in [3H]-5-HT efflux under the same experimental conditions. These results suggest that the release of [3H]-5-HT caused by Na+ depletion in drug-free synaptosomes is not mediated by 5-HT efflux through the plasma membrane carrier, nor to changes in cytosolic Ca2+ consequent to changes in Ca2+ fluxes across the plasma membrane. The results have been tentatively explained as an elevation of spontaneous 5-HT efflux caused by an increase in membrane fluidity mediated by the ionic manipulations used to produce the Na+-depleted media.

Effects of monoamine oxidase inhibitors on levels of catechols and homovanillic acid in striatum and plasma

Levels of homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC) and dihydroxyphenylglycol (DHPG) in plasma and the striatium were measured after inhibition of monoamine oxidase type A (MAO-A) by clorgyline (4 mg/kg i.p.), MAO-B by (-)deprenyl (1 mg/kg i.p.), both MAO-A and MAO-B by nialamide (75 mg/kg i.p.) or peripheral neuronal MAO by debrisoquin (40 mg/kg i.p.). Levels of HVA in plasma decreased by about 60% after single doses of nialamide or clorgyline, by about 80% after repeated doses of nialamide, by about 40% after a single dose of debrisoquin and by about 50% after repeated doses of debrisoquin. The administration of clorgyline, nialamide or debrisoquin significantly decreased concentrations of DOPAC and DHPG in plasma, whereas (-)deprenyl did not affect levels of DHPG or HVA. None of the MAO inhibitors produced more than about 80% depression of levels of any of the deaminated metabolites. The results suggest that most of the HVA in plasma is derived from deamination of DA by MAO-A in peripheral neurons; that DOPAC in plasma is derived from cells outside the central nervous system; that DHPG in plasma is derived virtually exclusively from the metabolism of norepinephrine in sympathetic nerve endings and that residual levels of HVA after treatment with debrisoquin provide an improved but limited indication of central dopaminergic activity.

Promotion by nialamide of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of nialamide, a monoamine oxidase inhibitor, on the incidence, number, and histology of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in male Wistar rats. Rats were given subcutaneously 50 mg/kg body weight of nialamide in depot form every other day after 25 weeks of oral treatment with MNNG. Prolonged alternate-day administration of nialamide caused a significant increase in the incidence and number of gastric cancers of the glandular stomach in week 52. However, it did not affect the histology of the cancers. Nialamide also caused a significant increase in tissue norepinephrine concentrations in the gastric wall and in the labeling indices of the gastric mucosae. However, nialamide had no influence on serum gastrin levels in the fasting state and after re-feeding. These findings indicate that nialamide promotes gastric carcinogenesis and that this may be related to its effects in increasing norepinephrine in the gastric wall and stimulating proliferation of gastric epithelial cells.

Nialamide-induced hypermotility in mice treated with inhibitors of monoamine uptake, 5-HT antagonists and lithium

When administered orally to mice 1 h before nialamide 100 mg/kg SC two non-selective and nine selective 5-HT uptake inhibitors enhanced the hypermotility produced by nialamide, whereas two inhibitors of NA uptake showed no influence on the nialamide response. Paroxetine was the most potent nialamide potentiator; 100% increase in motility response was obtained at 0.012 mg/kg. Pretreatment with the 5-HT2 antagonist ritanserin 1 and 10 mg/kg SC reduced the hypermotility produced by nialamide 200 mg/kg SC, but the 5-HT1 antagonist L-propranolol 10 mg/kg administered similarly was found inactive. Nialamide 100 mg/kg was given SC to groups of mice being treated for 4 weeks with paroxetine and lithium given through the diet. At daily intakes of paroxetine and lithium resulting in therapeutic plasma or serum levels a distinctive nialamide potentiation was found.