Substance P, but not TRH, modulates the 5-HT autoreceptor in ventral lumbar spinal cord

Neurodegenerative changes are prevented by Erythropoietin in the pmn model of motoneuron degeneration

Motoneuron diseases are fatal neurodegenerative disorders characterized by a progressive loss of motoneurons, muscle weakness and premature death. The progressive motor neuronopathy (pmn) mutant mouse has been considered a good model for the autosomal recessive childhood form of spinal muscular atrophy (SMA). Here, we investigated the therapeutic potential of Erythropoietin (Epo) on this mutant mouse. Symptomatic or pre-symptomatic treatment with Epo significantly prolongs lifespan by 84.6% or 87.2% respectively. Epo preserves muscle strength and significantly attenuates behavioural motor deficits of mutant pmn mice. Histological and metabolic changes in the spinal cord evaluated by immunohistochemistry, western blot, and high-resolution (1)H-NMR spectroscopy were also greatly prevented by Epo-treatment. Our results illustrate the efficacy of Epo in improving quality of life of mutant pmn mice and open novel therapeutic pathways for motoneuron diseases.

Calcitonin Gene-related Peptide (CGRP)-like Immunoreactivity and CGRP mRNA in Rat Spinal Cord Motoneurons after Different Types of Lesions

By use of the indirect immunofluorescence (IF) technique, radioimmunoassay (RIA) and in situ hybridization (ISH) histochemistry, the staining pattern, content and expression of calcitonin gene-related peptide (CGRP) in lumbar motoneurons of normal rats and rats subjected to sciatic nerve transection (SNT), ventral root transection (VRT), low thoracic spinal cord transection (SCT) alone or in combination with a subsequent SNT, as well as rats subjected to chemical lesioning of 5-hydroxytryptamine (5-HT) neurons by 5,7-dihydroxytryptamine (5,7-DHT), were studied. We here confirm that a large number of the lumbar motoneurons normally contain CGRP-like immunoreactivity (LI) and CGRP mRNA. SNT induced a transient increase in CGRP-LI, with a peak at days 2 - 5 after lesion, and normalized levels again after approximately 2 - 3 weeks. Comparable results were obtained with IF and RIA. This increase is probably a consequence of increased CGRP synthesis, since a parallel up-regulation of CGRP mRNA levels was seen. A normalization of CGRP mRNA did not occur during the period studied, despite an apparent normalization of peptide levels after 2 weeks, and this may in turn be due to an increased turnover and/or release of CGRP. The up-regulation of CGRP is probably caused by the axon injury itself, since a similar cellular reaction with respect to CGRP was observed in motoneurons subjected to VRT. However, SNT, which also lesions dorsal root afferents and causes a decline in CGRP-LI in the dorsal horn, induced an increase in CGRP-LI in motoneurons on the contralateral side also. Thus, it may be that severance of dorsal root afferents and/or changes in reflex activity may also influence the production of CGRP in motoneurons. SCT, which severs all descending synaptic input to the motor nucleus and causes a paralysis of muscles innervated by motoneurons below the lesion, resulted in a marked decline in both content of CGRP-LI (IF and RIA) and expression of CGRP mRNA. However, treatment with 5,7-DHT, which lesions 5-HT neurons, including those giving rise to the bulbospinal serotoninergic pathway, did not cause any dramatic changes in motor behaviour but induced an increase in both motoneuron content of CGRP-LI and expression of CGRP mRNA. In rats first subjected to SCT, which depresses CGRP, followed 2 weeks later by SNT, we found a marked increase in both content of CGRP-LI (IF and RIA) and expression of mRNA coding for CGRP. In summary our results show that the cellular production of the CGRP peptide, normally expressed in motoneurons, is influenced in a complex way by motoneuron injury as well as changes in the afferent input. There also appear to be important differences in the expression of CGRP in small (gamma) and large (alpha) motoneurons as well as between motoneurons of different nuclei, in normal as well as axotomized rats.

Synaptic control of motoneuronal excitability

Movement, the fundamental component of behavior and the principal extrinsic action of the brain, is produced when skeletal muscles contract and relax in response to patterns of action potentials generated by motoneurons. The processes that determine the firing behavior of motoneurons are therefore important in understanding the transformation of neural activity to motor behavior. Here, we review recent studies on the control of motoneuronal excitability, focusing on synaptic and cellular properties. We first present a background description of motoneurons: their development, anatomical organization, and membrane properties, both passive and active. We then describe the general anatomical organization of synaptic input to motoneurons, followed by a description of the major transmitter systems that affect motoneuronal excitability, including ligands, receptor distribution, pre- and postsynaptic actions, signal transduction, and functional role. Glutamate is the main excitatory, and GABA and glycine are the main inhibitory transmitters acting through ionotropic receptors. These amino acids signal the principal motor commands from peripheral, spinal, and supraspinal structures. Amines, such as serotonin and norepinephrine, and neuropeptides, as well as the glutamate and GABA acting at metabotropic receptors, modulate motoneuronal excitability through pre- and postsynaptic actions. Acting principally via second messenger systems, their actions converge on common effectors, e.g., leak K(+) current, cationic inward current, hyperpolarization-activated inward current, Ca(2+) channels, or presynaptic release processes. Together, these numerous inputs mediate and modify incoming motor commands, ultimately generating the coordinated firing patterns that underlie muscle contractions during motor behavior.

Multiple messengers in descending serotonin neurons: localization and functional implications

In the present review article we summarize mainly histochemical work dealing with descending bulbospinal serotonin neurons which also express a number of neuropeptides, in particular substance P and thyrotropin releasing hormone. Such neurons have been observed both in rat, cat and monkey, and may preferentially innervate the ventral horns of the spinal cord, whereas the serotonin projections to the dorsal horn seem to lack these coexisting peptides. More recent studies indicate that a small population of medullary raphe serotonin neurons, especially at rostral levels, also synthesize the inhibitory neurotransmitter gamma-amino butyric acid (GABA). Many serotonin neurons contain the glutamate synthesizing enzyme glutaminase and can be labelled with antibodies raised against glutamate, suggesting that one and the same neuron may release several signalling substances, causing a wide spectrum of post- (and pre-) synaptic actions.

Changes in receptor levels for thyrotropin releasing hormone, serotonin, and substance P in cervical spinal cord of Wobbler mouse: a quantitative autoradiography study during early and late stages of the motoneuron disease

Receptor levels for thyrotropin releasing hormone (TRH) measured by quantitative autoradiography in the Wobbler mouse cervical spinal cord show receptor losses that may relate to the inherited loss of motoneurons, most pronounced late (at Stage 4) in the motoneuron disease. An age-related decrease of TRH and serotonin (5-HT) receptors can be seen in the ventral horn of the control specimens (normal phenotype littermate and wild-type alike). However, this pattern is missing for substance P (SP) receptors from the wild-type specimens. Therefore the age-related decrease of SP receptors detected in the Wobbler mouse strain may identify a strain-related defect in SP neuronal/receptor developmental patterns. A higher level of TRH receptors was measured in the Wobbler dorsal horn at an early stage (Stage 1) in the motoneuron disease compared with the control specimens. The data are discussed in relation to an aberrant neuronal sprouting that occurs around the degenerating motoneurons in the ventral horn during the course of the motoneuron disease.

Met-enkephalin inhibits 5-hydroxytryptamine release from the rat ventral spinal cord via delta opioid receptors

The effect of opioid receptor agonists and antagonists on the electrically evoked release of endogenous serotonin (5-hydroxytryptamine, 5-HT) was studied in superfused slices of the rat ventral lumbar spinal cord. Met-ENK (1 x 10(-8)M-1 x 10(-6)M) and DPDPE (1 x 10(-8)M-1 x 10(-6)M) reduced the evoked 5-Ht release in a concentration dependent fashion. DAMGO (1 x 10(-8)-1 x 10(-6)) and (-)-trans-(1S,2S)-U-50488 (1 x 10(-6)M) had no effect on the 5-HT release. The inhibitory effect of met-ENK was completely abolished by ICI-174,864, but neither by naloxonazine nor nor-binaltorphimine. Following i.c.v. treatment with 5,7-dihydroxytryptamine (5,7-DHT), the tissue concentration of 5-HT was reduced by 97%, whereas the concentration of noradrenaline was reduced by only 5%. The tissue concentration of met-ENK, as measured by radioimmunoassay, was not significantly altered. The results suggest that met-ENK is present in the rat ventral spinal cord mainly in non-serotonergic nerve terminals and exerts an inhibitory action on 5-HT release via delta opioid receptors.

Serotoninergic, peptidergic and GABAergic innervation of the ventrolateral and dorsolateral motor nuclei in the cat S1/S2 segments: an immunofluorescence study

Indirect single- and double-staining immunofluorescence techniques were used to study the serotoninergic, peptidergic and GABAergic innervation of the ventrolateral (Onuf's nucleus) and dorsolateral (innervating intrinsic foot sole muscles) nuclei, located in the S1/S2 segments of the cat spinal cord. The relative density of 5-hydroxytryptamine-, thyrotropin-releasing hormone-, substance P- and gamma-aminobutyric acid-immunoreactive axonal varicosities was similar in both nuclei. The highest relative density was recorded for varicosities immunoreactive to gamma-aminobutyric acid, while those immunoreactive to 5-hydroxytryptamine or thyrotropin-releasing hormone yielded the lowest values. The density of enkephalin-immunoreactive varicosities was higher in the ventrolateral than in the dorsolateral nucleus. Calcitonin gene-related peptide-like immunoreactivity could be seen in neurons of the ventrolateral and dorsolateral nuclei. Occasionally, calcitonin gene-related peptide-immunoreactive axonal fibers were also encountered in these nuclei. Virtually all thyrotropin-releasing hormone-immunoreactive varicosities in the ventrolateral and dorsolateral nuclei also contained 5-hydroxytryptamine-like immunoreactivity, while a somewhat smaller number of them were co-localized with substance P. About 5-10% of the 5-hydroxytryptamine-immunoreactive varicosities were devoid of peptide-like immunoreactivity, and the number of 5-hydroxytryptamine-immunoreactive varicosities lacking thyrotropin-releasing hormone-like immunoreactivity was higher in the dorsolateral than in the ventrolateral nucleus. Finally, the free fraction of substance P-immunoreactive varicosities, i.e., those lacking both 5-hydroxytryptamine and thyrotropin-releasing hormone, was about 39% in the ventrolateral and 26% in the dorsolateral nucleus. Spinal cord transection at the lower thoracic level induced a depletion of 5-hydroxytryptamine and thyrotropin-releasing hormone-immunoreactive fibers from the ventrolateral and dorsolateral nuclei, indicating an exclusive supraspinal origin for these fibers. A reduction in substance P-like immunoreactivity following spinal cord transection alone or spinal cord transection combined with unilateral dorsal rhizotomy was also detected in both nuclei, suggesting a dual origin for substance P-immunoreactive fibers, i.e., both supra- and intraspinal. The decrease in number of substance P-immunoreactive fibers was however smaller than expected from the analysis of the fraction of substance P-immunoreactive fibers co-localized with 5-hydroxytryptamine, indicating thus that the experimental lesions may have triggered a sprouting of substance P-immunoreactive axons originating from spinal cord sources. The distribution of gamma-aminobutyric acid in the ventrolateral and dorsolateral nuclei was not affected by the different lesion paradigms. It is therefore assumed that these inputs are intrinsic to the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurokinin A coexists with substance P and serotonin in ventral medullary spinally projecting neurons of the rat

The coexistence of neurokinin A (NKA) with substance P (SP) and serotonin (5-HT) in ventral medullary neurons of the parapyramidal region and nucleus raphe pallidus of the rat was studied using multiple immunofluorescence labeling. Nearly all of the NKA-immunoreactive (IR) cells in the parapyramidal region and raphe pallidus were SP-IR nd 5-HT-IR, whereas about 70% of the SP-IR neurons and about 60% of the 5-HT-IR neurons contained NKA-IR. There were no apparent differences in the patterns of coexistence between parapyramidal and raphe pallidus neurons. NKA-IR neurons, which colocalized SP-IR and 5-HT-IR, were studied for projections to the lumbar and thoracic spinal cord by use of retrograde transport of fluorescent tracer. Whereas about 50% of the retrogradely labeled neurons of the parapyramidal region and raphe pallidus contained NKA-IR, nearly all of the NKA-IR neurons projected to the thoracic and lumbar spinal cord. In addition, some NKA-IR neurons in the ventral medulla were retrogradely labeled with tracer from localized injections into the thoracic intermediolateral cell column. In summary, this study demonstrated that NKA-IR is colocalized with SP-IR in bulbospinal serotonergic neurons of the parapyramidal region and raphe pallidus, which are known to regulate sensory, motor, and autonomic activities of the spinal cord.

Serotonergic regulation of the spinal cord content of thyrotropin releasing hormone in the cerebellar ataxia mutant mouse

The effects of serotonin (5-HT) and various serotonin receptor antagonists on the spinal cord thyrotropin releasing hormone (TRH) content were studied in the rolling mouse Nagoya (RMN) and in the unaffected C3H mouse. TRH was extracted from the cervical, thoracic, lumbar, and sacral cord, at 1 h after the intraperitoneal injection of a serotonin precursor, 2 serotonin agonists, and 5 serotonin receptor antagonists. Administration of 5-hydroxytryptophan and 2-methyl-5-hydroxytryptamine resulted in an increase of the spinal cord TRH content in C3H mice, but not in RMN. Parachlorophenylalanine decreased the spinal cord TRH content in C3H mice, while it increased TRH levels in all regions of the RMN spinal cord. The TRH contents were decreased in all regions of the spinal cord after 5,7-dihydroxytryptamine administration in both C3H mice and RMN. In C3H mice, methysergide, mianserin, ketanserin, and spiperone significantly decreased the TRH content in all regions of the spinal cord, while 3 alpha-tropanyl-1H-indole-3-carboxylic acid ester (ICS205-930) did not affect it. These antagonists paradoxically increased TRH levels in the cervical cord in RMN. The degradation of synthetic TRH by cord homogenates and the number and affinity of spinal cord serotonergic receptors (5-HT1 and 5-HT2) showed no significant difference between C3H mice and RMN. These results suggest that TRH turnover is abnormally regulated by serotonergic neurons in the RMN and that the dysfunction of the serotonergic nerves is attributable to the serotonin autoreceptor.

Regional distribution of serotonin and substance P co-existing in nerve fibers and terminals in the brainstem of the rat

Two-color fluorescence immunohistochemistry was used to identify and map the distribution of nerve processes immunoreactive for both serotonin and substance P in the rat brainstem. Doubly labeled fibers were observed throughout the brainstem, but tended to be densest in cranial nerve motor nuclei and in reticular regions of the ventral medulla. In the trigeminal motor nucleus, the facial nucleus and the spinal accessory nucleus, the majority of serotonergic varicosities also appeared to contain substance P; in the occulomotor nucleus and the hypoglossal nucleus the numbers of double-labeled and single-labeled serotonergic varicosities were roughly equal. Thus, co-existence of substance P with serotonin was common in many cell groups innervating skeletal muscle. The proportion of double-labeled varicosities was significantly lower in the nucleus of the solitary tract, wherein single-labeled varicosities were much more common. Double-labeled fibers and varicosities were also significantly less common in the spinal trigeminal nucleus. In addition, double-labeling appeared to be uncommon in regions involved in the processing of special sensory information (e.g. auditory, vestibular and visual pathways). These results demonstrate a subpopulation of serotonergic fibers immunoreactive for substance P in the brainstem of the rat. The consistently high density of double-labeled processes in cranial nerve motor nuclei suggests that, as may be the case in the spinal cord, neurons containing serotonin and substance P regulate the activity of motoneurons that innervate skeletal muscle. In addition, they may be involved in other aspects of the function of the brainstem.

Serotonin modulates the levels of mRNAS coding for thyrotropin-releasing hormone and preprotachykinin by different mechanisms in medullary raphe neurons

The serotonergic neurons of the medullary raphe also contain the peptide neurotransmitters substance P (SP) and thyrotropin releasing hormone (TRH). In this study we asked whether the manipulation of serotonin levels alters the levels of mRNA coding for pre-proTRH. Just like the mRNA coding for the precursor of SP (preprotachykinin, PPT), levels of TRH mRNA are increased when serotonin synthesis is inhibited by para-chlorophenylalanine (pCPA) and decreased when serotonin reuptake is blocked by zimelidine. However, subtle differences suggest that the mechanisms behind these changes are different. Levels of TRH mRNA are still decreased after 14 days of zimelidine treatment, a time when levels of PPT mRNA have returned to control values. In addition, the serotonin reuptake blocker fluoxetine lowers levels of TRH but not PPT mRNA. Finally, the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) induces a transient decrease in levels of PPT mRNA similar to that induced by zimelidine, but does not decrease levels of TRH mRNA even when 10-fold higher doses are administered. These results suggest that while some pharmacological manipulations appear to alter TRH and PPT mRNA levels coordinately, the mechanisms regulating the synthesis of these two colocalized neurotransmitters are different.

Serotonin-, substance P- and glutamate/aspartate-like immunoreactivities in medullo-spinal pathways of rat and primate

Serotonergic neurons of the medulla oblongata have been proposed to play a role in the control of sensory, motor and autonomic cells in the spinal cord. Many of these raphe neurons have been shown to contain the undecapeptide substance P as well as the tripeptide thyrotropin-releasing hormone, but evidence for the presence of an excitatory amino acid in these pathways has not yet been documented. In colchicine-treated rats, we have used a combination of retrograde tracing and tri-color immunohistofluorescence techniques to study co-localization of serotonin- and substance P- with glutamate- or aspartate-like immunoreactivities in medullary neurons and the possible spinal projections of these cells. In addition, the distributions of serotonin-, substance P- and glutamate-immunoreactive terminal fields in the dorsal, ventral and lateral horns of the spinal cord were examined with tri-color immunofluorescence in the rat and the primate Macaca fasciculata. In colchicine-treated rats, glutamate- and aspartate-like immunoreactivity was found in practically all serotonin- and substance P-immunoreactive neurons of the B1, B2 and B3 cell groups. Some of these neurons also contained wheat-germ agglutinin conjugated to inactivated horseradish peroxidase and colloidal gold particles retrogradely transported from the spinal cord. In the spinal cords of non-colchicine-treated monkeys and rats, striking co-localization of serotonin, substance P- and glutamate-like immunoreactivities was seen in large boutons, surrounding the dendrites and cell bodies of large alpha motor neurons in the ventral horn. These observations suggest the existence of spinally projecting serotonin/substance P neurons containing excitatory amino acids such as glutamate or aspartate.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical evidence for the coexistence of substance P, thyrotropin-releasing hormone, GABA, methionine-enkephalin, and leucin-enkephalin in the serotonergic neurons of the caudal raphe nuclei: a dual labeling in the rat

By means of dual immunohistochemical labeling on the same brain section examined with a light microscope, the present study reports the presence with serotonin (5-hydroxytryptamine; 5-HT) of gamma-aminobutyric acid (GABA), substance P (SP), thyrotropin-releasing hormone (TRH), leucin-enkephalin (LEU-enk), or methionine-enkephalin (MET-enk), within the same neuron in the nuclei raphe magnus, raphe obscurus, and raphe pallidus of the rat. On the one hand, peptides or GABA are detected with specific rabbit antibodies by indirect peroxidase labeling using peroxidase-conjugated Fab fragments, and on the other, 5-HT is detected with a rabbit antibody against the BSA-serotonin conjugate by radio-immunocytochemistry using [125I]-labeled protein A. The possible coexistence of TRH and SP in these neurons is also investigated by using peroxidase labeling and radio-immunocytochemical detection, respectively. In the whole caudal raphe nuclei the proportion of each coexisting peptide with 5-HT appears in decreasing order as: TRH greater than SP greater than MET-enk # LEU-enk greater than GABA. In all instances the level of coexistence differs considerably in B1-B2 vs. B3 cell groups. No SP/TRH dually labeled cells have ever been found in any of the serotonergic nuclei of the caudal raphe. Given the evidence that these raphe nuclei project possibly to the spinal cord, these data constitute an anatomical substrate for the several distinct physiological functions presumably subserved by 5-HT in the cord, namely the modulation of nociception, motor, and autonomic functions.

5-HT receptor-mediated regulation of thyrotropin-releasing hormone release in rat spinal cord

5-Hydroxytryptamine (5-HT, 10 microM) increased the veratridine-evoked release of thyrotropin-releasing hormone (TRH) from spinal cord slices. This effect of 5-HT was reduced by pre-exposure of the tissue to 10 microM ketanserin and methysergide, which both have 5-HT2 antagonistic activity. A 5-HT1 agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (10 microM), reduced the release of TRH. These results imply that 5-HT released from the terminals of descending fibers modulates the release of TRH, a cotransmitter contained in 5-HT fibers.

Ventral horn neuropeptides modulate the release of noradrenaline from tissue slices of rat brainstem and ventral thoracic spinal cord

The release of endogenous noradrenaline (NA) from slices of adult rat brainstem and ventral thoracic spinal cord was investigated using a fixed-volume incubation technique and HPLC with electrochemical detection. Incubation with potassium (15-50 mM) produced a dose-related increase in basal NA release that was calcium dependent. The potassium-evoked release of NA from spinal cord or brainstem slices was potentiated according to dose by preincubation with either (a) the selective alpha 2-adrenoceptor antagonist idazoxan (10(-6)-10(-4) M) or (b) the thyrotrophin-releasing hormone (TRH) analogue RX 77368 (pGlu-His-3,3'-dimethyl ProNH2; 10(-5) and 10(-4) M). Incubation of spinal cord slices with the NA uptake inhibitor maprotiline (1 microM) enhanced the effect of idazoxan but inhibited that of RX 77368. The effects of RX 77368 and potassium alone (15 mM) on NA release from both spinal cord and brainstem slices were reduced to basal levels with tetrodotoxin (10(-7) M). Similarly, preincubation of spinal cord, but not brainstem, slices with the insect neuropeptide proctolin (10(-4) M) significantly attenuated the potassium- or RX 77368-induced release of NA, whereas substance P (3 X 10(-5) and 1 X 10(-4) M) had no effect on either tissue. These results suggest that changes in NA release in the spinal cord and brainstem may mediate some of the actions of neuropeptides in ventral spinal cord, although the peptides may not be acting directly on the noradrenergic nerve terminals in these tissues.

Serotonergic response to spinal distraction trauma in experimental scoliosis

The effects of distraction injury to the spinal cord on serotonin (5HT) content and metabolism in a rat model of scoliosis were studied. Previous studies in this laboratory (Salzman et al., 1987a) have identified the 5HT response as a major component of the posttraumatic progression of spinal injury after impact trauma in the rabbit. The present study was designed to determine the universality of this response by examining a different model of injury in a different species. The results demonstrate that distraction trauma in the rat, like impact injury in the rabbit, is associated with a rapid and robust increase in the local spinal cord content and metabolism of 5HT and a long-term depletion of 5HT below the site of injury. The roles of the blood platelet and the raphe-spinal tract in the acute response and the disruption of axoplasmic transport during the chronic phase of injury are discussed.

The effect of selective serotonergic neurotoxin treatment on tachykinin levels in the rat ventral spinal cord

The levels of 5-hydroxytryptamine and tachykinin neuropeptides substance P, neurokinin A, neurokinin B and neuropeptide K were measured in the spinal cord of rats treated by intraventricular injection of the selective serotonergic neurotoxin 5,7-dihydroxytryptamine. The spinal cord levels of 5-hydroxytryptamine as measured by high performance liquid chromatography with electrochemical detection decreased by more than 90% in the ventral and dorsal cord compared to controls. The levels of substance P as measured by radioimmunoassay were significantly reduced (66%, P less than 0.01) in the ventral lumbar cord only. In this region, neurokinin A, neurokinin B and neuropeptide K levels were determined by combined high performance liquid chromatography and radioimmunoassay. The neurotoxin treatment also caused a significant reduction of neurokinin A (72% reduction, P less than 0.01) and a non-significant reduction of neuropeptide K, but virtually no change in the neurokinin B level. Immunohistochemical studies of the ventral lumbar cord of sham-operated animals showed immunoreactivity for 5-hydroxytryptamine as well as for substance P and neurokinin A in nerve fibres around motor neurons. In neurotoxin-treated rats this region was devoid of immunohistochemically detectable substance P- and neurokinin A-positive fibres and showed very sparse or no 5-hydroxytryptamine immunoreactivity. We conclude that among the tachykinins both neurokinin A and substance P, but probably not neurokinin B, co-exist with 5-hydroxytryptamine in nerve terminals in the rat ventral spinal cord.

In vivo release of serotonin in cat dorsal vagal complex and cervical ventral horn induced by electrical stimulation of the medullary raphe nuclei

Extracellular levels of serotonin (5-hydroxytryptamine; 5-HT) were monitored by microdialysis in the dorsal vagal complex (DVC) and the ventral horn of the spinal cord at the level of the phrenic motor nucleus in decerebrated cats. A selective serotonin uptake inhibitor, alaproclate (10(-4) M) was included in the dialysis probe perfusion fluid to increase basal and stimulated levels of 5-HT. Electrical stimulation (30 Hz, 10 V, 0.5 ms) in the nucleus raphe obscurus, containing neurons projecting to the DVC and to the ventral horn, induced a 2-3-fold increase of the 5-HT release in both these regions. After termination of the stimulation, the release gradually decreased during the following 60 min. Substance P, which coexists with 5-HT in descending neurons, did not significantly affect the 5-HT release when it was added (100 microM) to the probe perfusion fluid. The present findings are in accordance with the hypothesis that prolonged release of 5-HT is responsible for the previously demonstrated long-lasting facilitation of phrenic activity following raphe obscurus stimulation.

Autoradiographic visualization of NK-3 tachykinin binding sites in the rat brain, utilizing [3H]senktide

The autoradiographic distribution of the selective NK-3 tachykinin agonist [3H]senktide was investigated in rat brain. [3H]Senktide bound with high affinity (KD less than 2.5 nM) and high specificity (greater than 75%) to cerebral cortex and numerous subcortical sites, including the substantia nigra pars compacta. In addition, moderately dense binding was seen in the median but not the dorsal raphe nucleus, and this was disrupted by 5,7-dihydroxytryptamine (5,7-DHT)-induced destruction of 5-HT neurons. 5,7-DHT lesions did not affect the binding of [3H]senktide to forebrain regions, suggesting that 5-HT terminals are devoid of NK-3 receptors.

Presynaptic serotonin receptors in the central nervous system

Presynaptic 5-HT autoreceptors have been identified in any region of the mammalian CNS containing 5-HT nerve terminals that has been investigated for this purpose. They belong to the 5-HT1B receptor subclass in the rat and to the 5-HT1D subclass in the pig, guinea pig, and probably man. The presence and operation of presynaptic 5-HT autoreceptors have been proven by the ability of 5-HT receptor agonists to inhibit 5-HT release and of 5-HT receptor antagonists not only to competitively antagonize this effect but also to disclose the autoinhibitory effect of endogenous 5-HT by blocking the autoreceptor, thus interrupting the negative feedback loop. There is evidence that presynaptic 5-HT autoreceptors are operative in vivo. Presynaptic inhibitory 5-HT heteroreceptors have also been identified in various brain regions of the rat. DA nerve terminals in the striatum and nucleus accumbens as well as GLU nerve terminals in the cerebellum are endowed with such receptors, which were either not yet classified (DA neurone) or represent a not yet specified 5-HT1 subtype (GLU neurone). Release-inhibiting 5-HT receptors on the acetylcholine nerve terminals in the hippocampus are of the 5-HT1B subtype, and those in the striatum were not yet classified in detail. A 5-HT heteroreceptor mediating stimulation of release occurs on rat striatal DA nerve terminals; it belongs to the 5-HT3 class. Thus, presynaptic inhibitory 5-HT auto- and heteroreceptors as well as presynaptic excitatory 5-HT heteroreceptors are involved in the regulation of transmitter release in the brain.

Pharmacological characterization of the behavioural syndrome induced by the NK-3 tachykinin agonist senktide in rodents: evidence for mediation by endogenous 5-HT

The effects of various manipulations of brain 5-HT mechanisms on the behavioural responses induced by the selective NK-3 tachykinin agonist senktide in rodents were assessed. Senktide elicited wet dog shakes in the rat which were attenuated by the 5-HT1C/2 antagonist mianserin and the selective 5-HT2 antagonist altanserin. Senktide-induced forepaw treading was stereospecifically attenuated by the 5-HT1A + B antagonist (-)-alprenolol. Senktide also elicited chewing mouth movements and yawning, which were unaffected by mianserin, altanserin, (+)- or (-)-alprenolol, or the selective 5-HT3 antagonist ICS 205-930, but attenuated by the muscarinic antagonist scopolamine. Penile grooming elicited by senktide was attenuated by mianserin, but was unaffected by the other antagonists. Senktide-induced wet dog shakes were enhanced by the 5-HT reuptake inhibitors citalopram and fluoxetine, suppressed by the monoamine oxidase (MAO)-B inhibitor pargyline, but unaffected by the MAO-A inhibitor clorgyline. Forepaw treading was potentiated by citalopram and clorgyline, but not significantly altered by fluoxetine or pargyline. Depletion of 5-HT by p-chlorophenylalanine (PCPA) in the rat attenuated senktide-induced wet dog shakes and forepaw treading. Neither PCPA nor 5,7-dihydroxytryptamine affected senktide-induced behaviours in the mouse, but the degree of brain 5-HT depletion caused by these treatments in mice was relatively small. These findings indicate that stimulation of NK-3 tachykinin receptors by senktide results in a complex behavioural syndrome which is mediated by multiple 5-HT receptors, and dependent upon intact stores of endogenous 5-HT. Independent stimulation of brain cholinergic mechanisms by senktide is also confirmed.

Monoamine synaptic structure and localization in the central nervous system

The monoamines dopamine, noradrenaline, adrenaline, and serotonin as well as the diamine histamine have a widespread distribution in the central nervous system within synaptic terminals and nonsynaptic varicosities. In certain regions of the central nervous system the monoamines are contained in varicosities that have no synaptic specialization associated with them, suggesting a possible neuromodulatory role for some of the monoamines. The majority of monoamine labelled structures are synaptic terminals which are characterized by the presence of small, clear vesicles (40-60 nm) and large, granular vesicles (70-120 nm) within the terminal. A third population of vesicles--small, granular vesicles--which are visible only after histochemical staining, are probably the equivalent of the small, clear vesicles present after either autoradiographic or immunohistochemical labelling. Most monoamine containing terminals contact dendrites and dendritic spines and, less frequently, neuronal somata and other axons. Both asymmetrical and symmetrical membrane specializations are associated with monoaminergic terminals; however, asymmetrical contacts are the most frequent type found. These ultrastructural results indicate that monoamine containing terminals and varicosities in general share many common morphological features, but still have diverse functions.

Effects of short-term serotonin depletion on the efficacy of serotonin neurotransmission: electrophysiological studies in the rat central nervous system

The effects of short-term serotonin (5-HT) depletion by p-chlorophenylalanine (PCPA) on the firing activity of dorsal raphe nucleus 5-HT neurons, on the responsiveness of dorsal hippocampus pyramidal neurons to microiontophoretically applied 5-HT and on the efficacy of the electrical stimulation of the ascending 5-HT pathway in suppressing the firing activity of CA3 dorsal hippocampus pyramidal neurons were assessed in chloral hydrate-anesthetized rats. PCPA (250 mg/kg/day i.p. for 2 days) reduced the 5-HT content of the dorsal hippocampus by 90%. However, the number of spontaneously active 5-HT neurons per microelectrode trajectory through the dorsal raphe or their average rate of firing was unaltered. The effect of afferent 5-HT pathway stimulation was reduced in only 40% of treated rats, whereas the sensitivity of CA3 pyramidal neurons to microiontophoretic 5-HT was not modified. The function of the terminal 5-HT autoreceptor was assessed using methiothepin, an autoreceptor antagonist. Methiothepin (1 mg/kg, i.v.) significantly enhanced the efficacy of the stimulation in PCPA-treated rats, although the degree of enhancement was much less than in controls. A greater reduction of the effectiveness of the stimulation was obtained by increasing the dose of PCPA (350 mg/kg/day i.p. for 2 days). This regimen reduced the 5-HT content of the dorsal hippocampus by 95%. In these rats, the sensitivity of the terminal 5-HT autoreceptor was assessed by increasing the frequency of the stimulation from 1 to 5 Hz. This procedure reduced to a similar extent the efficacy of the stimulation in treated and control rats, suggesting that the reduced effectiveness of methiothepin in enhancing 5-HT synaptic transmission in PCPA-treated rats is due to a lower degree of activation of the terminal 5-HT autoreceptor. The present results showing that the 350 mg/kg/day regimen of PCPA, but not the 250 mg/kg/day regimen, reduced the efficacy of the stimulation of the ascending 5-HT pathway suggest that a greater than 90% depletion is required to affect 5-HT neurotransmission significantly. The reduced level of activation of terminal 5-HT autoreceptors in rats treated with the lower dose of PCPA may facilitate the release of the remaining 5-HT per stimulation-triggered action potential, ensuring a virtually unaltered synaptic efficacy.

5-Hydroxytryptamine, substance P, and thyrotropin-releasing hormone in the adult cat spinal cord segment L7: immunohistochemical and chemical studies

The terminal projections of the descending 5-hydroxytryptamine (5-HT) bulbospinal pathway and the coexistence among 5-HT-, substance P (SP)-, and thyrotropin-releasing hormone (TRH)-like immunoreactivities (LI) in fibers innervating the L7 segment in the cat spinal cord were studied quantitatively and semiquantitatively by use of the indirect double-staining immunofluorescence technique. The content of 5-HT, SP, and TRH in different parts of the spinal cord was determined by use of radioimmunoassay (RIA) (SP and TRH) and high-performance liquid chromatography with electrochemical detection (HPLC-ECD) (5-HT). For all three substances studied, immunoreactive (IR) axon terminals were found in all parts of the gray matter, but with clear regional variation in the density of innervation. Thus, all three substances showed a dense innervation in the motor nucleus, particularly in the ventral part of the nucleus, while the superficial dorsal horn was very densely innervated by SP-IR fibers (laminae I and II) and TRH-IR fibers (laminae II and III). In the motor nucleus, the studied substances coexisted to a very high degree, but some 5-HT-IR fibers (about 10%) lacked peptide-LI and some SP-IR fibers (about 10%) lacked 5-HT-LI while virtually all TRH-IR fibers also contained 5-HT-LI. In the superficial dorsal horn (laminae I-III), no coexistence was detected, while other parts of the gray matter displayed various degrees of coexistence in between those found in the motor nucleus and laminae I-III. The quantitative analysis of IR varicosities in the motor nucleus suggested that the unilateral L7 motor nucleus is innervated by about 55-110 x 10(6) 5-HT-IR nerve terminals, which may indicate as many as 4,000 boutons per descending 5-HT cell body in the brain stem only with this restricted projection. When combing these results with the biochemical data, it could be calculated that the concentration of 5-HT in IR varicosities is about 3-6 x 10(-3) M, while the corresponding figures for SP and TRH was 0.3-0.5 x 10(-3) M and 0.1-0.2 x 10(-3) M, respectively. In cats subjected to spinal cord transection at the lower thoracic level, all 5-HT-IR fibers in the L7 segment had disappeared 44 days after the lesion, indicating a strict suprasegmental origin of 5-HT-IR fibers in this segment.(ABSTRACT TRUNCATED AT 400 WORDS)

Alteration of substance P after trauma to the spinal cord: an experimental study in the rat

The distribution of substance P was determined in the rat spinal cord and brain after a focal traumatic injury to the thoracic region (T10-11) of the spinal cord. There was at 1 and 2 h after the injury a statistically significant increase of the substance P content not only in the injured segment but also in samples removed 5 mm proximal (T9) and distal (T12) to the lesion. At 5 h the substance P content of the injured segment of the cord was reduced by 30% compared with controls. However, there was a significant increase in the concentration of this peptide in segments located 5 mm cranial and caudal to the injury (65% and 22%, respectively). Interestingly, the whole brain content of substance P showed a statistically significant 22% increase from control values at 5 h after the injury. At 1 and 2 h after the spinal cord injury there was a significant decrease in whole brain substance P concentration by 25% and 65%, respectively. Pretreatment with p-chlorophenylalanine (a serotonin synthesis inhibitor) markedly reduced the endogenous content of substance P in whole brain of normal animals. In these animals, the spinal cord content of the peptide was elevated by 83-123% as compared to untreated control animals. Spinal cord trauma inflicted on p-chlorophenylalanine-treated animals did not affect the brain peptide level at all. However, a profound decrease was noted in all the spinal cord segments at 5 h as compared to the untreated traumatized group. The decrease in this peptide was more pronounced in the cranial and the injured segments as compared to the caudal one.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for co-existence of thyrotropin-releasing hormone, substance P and serotonin in ventral medullary neurons that project to the intermediolateral cell column in the rat

The present study was conducted to determine if substance P-, thyrotropin-releasing hormone- and/or serotonin-immunoreactivities coexist in ventral medullary neurons that project to the intermediolateral cell column in the rat. Neurons that projected to the intermediolateral cell column were identified by the presence of retrogradely transported rhodamine bead-labeled microspheres in the cell body after an injection of the microspheres into the intermediolateral cell column of the third thoracic spinal cord segment. Co-existence was determined by using a combination of dual color immunohistochemistry and serial 4-microns sections that were immunostained with different antibodies. Antibodies to substance P, serotonin, and pre-pro-thyrotropin releasing hormone160-169 were used to identify substance P, serotonin and thyrotropin-releasing hormone, respectively. Neurons that contained substance P-, thyrotropin-releasing hormone- and/or serotonin-immunoreactivities and that projected to the intermediolateral cell column were present in the nucleus raphe magnus, the nucleus raphe pallidus, the nucleus reticularis magnocellularis pars alpha, the paragigantocellular reticular nucleus and the parapyramidal region. Neurons that projected to the intermediolateral cell column, in each of these regions, were found to contain each of the following combinations of immunoreactive neurochemicals: substance P and thyrotropin-releasing hormone: substance P and serotonin; thyrotropin-releasing hormone and serotonin; or substance P, thyrotropin-releasing hormone and serotonin. In addition, most of the regions also contained neurons that appeared to contain only one of the neurochemicals and that also projected to the intermediolateral cell column. The greatest number of neurons that projected to the intermediolateral cell column and that also contained two or more co-existing neurochemicals was present in the midline regions. This study demonstrates the presence of neurons in the ventral medulla that project to the intermediolateral cell column and contain three co-existing neurochemicals. This study also demonstrates the use of a new method for the localization of three neurochemicals in single projection-specific neurons.

Substance P enhances the release of endogenous serotonin from rat ventral spinal cord

The effect of the tachykinin neuropeptides, substance P (SP), neurokinin A (NKA) and the neurokinin B (NKB) receptor agonist, senktide, on the potassium-evoked release of endogenous serotonin (5-hydroxytryptamine, 5-HT) was investigated in superfused tissue slices of rat ventral spinal cord, where 5-HT is known to coexist with SP. Endogenous 5-HT was assayed by HPLC with electrochemical detection. The evoked release of 5-HT was significantly enhanced by 10(-4) M SP (190% increase) and 10(-5) M SP (74% increase) but not by 10(-6) M SP, NKA (10(-5) and 10(-4) M) and senktide (10(-5) and 10(-4) M) had no significant effect on the 5-HT release. The results suggest that, in the rat ventral spinal cord, where most of the 5-HT and SP is stored in the same nerve endings. SP but not NKA nor NKB potentiates the evoked release of 5-HT in a dose-dependent manner.

Differential release of coexisting neurotransmitters: frequency dependence of the efflux of substance P, thyrotropin releasing hormone and [3H]serotonin from tissue slices of rat ventral spinal cord

In few systems has the release of coexisting classical and peptide neurotransmitters been studied. Here the release of substance P-like immunoreactivity (SP-LI), thyrotropin releasing hormone-like immunoreactivity (TRH-LI) and [3H]serotonin ([3H]5-HT) from tissue slices of rat ventral spinal cord was investigated in a superfusion system. The slices were stimulated electrically with field stimulation (900 pulses, 2 ms duration, 36 V) at frequencies between 0.25 Hz and 40 Hz. The evoked fractional release of SP-LI increased significantly from 0.46 to 1.24% of the total tissue store when the frequency of stimulation was changed from 3 to 10 Hz, while the evoked fractional release of TRH-LI increased significantly from 0.28 to 0.71% of the total tissue store with increasing frequency of stimulation between 0.5 and 3 Hz. The evoked fractional release of [3H]5-HT did not show any significant change when the frequency of stimulation was changed in the frequency range of 0.25-40 Hz but remained between 5.6 and 7.2% of the total tissue store. It appears that at frequencies lower than 0.5-1 Hz these 5-HT/SP/TRH neurons may function predominantly as serotonergic neurons. At 3 Hz stimulation with 900 pulses the extracellular Ca2+ concentration required for half-maximal release of [3H]5-HT was 1.2 mmol l-1, while for half-maximal release of SP-LI significantly higher concentrations of Ca2+ (4.2 mmol l-1) would be required.(ABSTRACT TRUNCATED AT 250 WORDS)

Co-existence between receptors, carriers, and second messengers on astrocytes grown in primary cultures

This overview deals with the current important problem of the expression by astrocytes of a set of functional and neurochemical properties which, until a few years ago, were thought to be specific for neurons. The interaction of different receptor functions and carrier systems in astrocytes and the functional importance of second messenger systems is discussed.

Effects of lysergic acid diethylamide (LSD) and adjuvant-induced inflammation on desensitization to and metabolism of substance P in the mouse spinal cord

We have previously shown that the caudally directed biting and scratching response to repeated intrathecal (i.t.) injections of substance P (SP) is decreased by the third injection of SP and that this apparent desensitization to SP is less pronounced in mice pretreated with Freund's adjuvant. This study was designed to study the mechanism of this desensitization to SP and to examine the effect of lysergic acid diethylamide tartrate (LSD) on desensitization. Our results indicate that while 25 micrograms of LSD/kg body weight i.p. in naive mice had no effect on the response to a single injection of SP, LSD decreased the development of desensitization to SP-induced behaviors. In contrast, identical injections of LSD in adjuvant-pretreated mice not only failed to prevent desensitization but enhanced the degree of apparent desensitization to SP. Tolerance developed to the effects of LSD on desensitization to SP-induced behaviors in both adjuvant- and saline-pretreated mice. When injected i.t. with SP, LSD failed to alter the degree of desensitization to SP-induced behaviors, suggesting that the effect of LSD is not produced at the spinal cord level. Separation and quantification of SP and its metabolites in the spinal cord using high performance liquid chromatography (HPLC) techniques indicated that either a single injection of LSD or pretreatment with Freund's adjuvant produced similar patterns of changes in the concentrations of SP-related peptides in mouse spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyrotropin-releasing hormone (TRH) effects on spinal cord neuronal excitability

TRH is found in terminals in the dorsal, lateral, and ventral horns of the spinal cord and apparently has at least a weak facilitatory effect on excitability of neurons in all these locations. These findings suggest that TRH may facilitate transmission in somatosensory pathways, enhance sympathetic outflow from the spinal cord, and facilitate somatic motoneuron excitability, at least transiently. All studies that have examined TRH effects on spinal neuronal excitability have used exogenously administered TRH. Virtually nothing is known about how spinal neuronal functioning might be affected by TRH released from terminals after activation of TRH-containing cell bodies. The acquisition of this knowledge awaits the development of specific TRH antagonists. Preliminary experiments suggest that TRH may have prolonged facilitatory effects on the excitability of developing or damaged spinal cord neurons. Further studies are necessary to determine how TRH interacts with other neuroactive peptides and monoamines to affect excitability of neurons in the developing, damaged, and normal adult spinal cord.

Distribution of TRH-like immunoreactivity with special reference to coexistence with other neuroactive compounds

During the last years, several important advancements have been made that are of importance for our understanding of the distribution and localization of neurons and cells producing TRH-LI. As detailed in other chapters in this volume, the precursor for TRH has been characterized that has allowed production of antibodies raised against specific sequences of this precursor. This, in turn, has provided new tools for the immunohistochemical elucidation of TRH systems in the CNS. The TRH precursor has also been cloned, leading to possibilities for studying the localization of TRH mRNA with in situ hybridization. Finally, as shown in this paper, improvement of the fixation technique has made it possible to visualize extensive TRH-immunoreactive cell body and fiber systems with antiserum raised against the TRH tripeptide. The results from the latter studies and those with antisera directed to the TRH precursor and in situ hybridization are in good agreement, with some minor exceptions. It should be pointed out that some of the systems described here, for example TRH positive-cell bodies in cortical areas and the hippocampal formation, contain only a very weak immunoreactivity. As always with immunohistochemical techniques, the possibility of crossreactivity with TRH-like peptides or TRH-like sequences within larger proteins must be considered. The present results confirm the presence of TRH-LI in the insulin-producing beta cells of the pancreas, which with the improved technique can be demonstrated also in early adulthood in rats and guinea pigs. Moreover, it could be established that TRH-LI is present in neurons in the gastrointestinal tract as well as in a population of endocrine cells in the antrum of the stomach of the guinea pig. These cells seem at least partly to be identical to the well-known gastrin-producing cells. TRH-LI has been observed to occur in neurons already containing a classical transmitter and/or other peptides. Of particular importance here seems to be a descending bulbospinal system that in addition to TRH co-contains 5-HT, substance P-LI, galanin-LI, human growth hormone immunoreactive material, and proctolin-like material. The significance of this coexistence is not well understood, but interesting interactions have been observed. Attempts to manipulate the TRH phenotype in these medullary neurons by transplantation to other sites in the brain has so far shown that the expression of this peptide seems fairly stable.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for colocalization of substance P and 5-hydroxytryptamine in spinally projecting neurons from the cat medulla oblongata

Substance P (SP)- and 5-hydroxytryptamine (5-HT)-like immunoreactivities were localized in bulbospinal neurons of the raphe nuclei and ventrolateral medulla (VLM). In raphe pallidus and raphe obscurus virtually all of the spinally projecting neurons contained SP and/or 5-HT. Furthermore, SP and 5-HT were colocalized in half of these spinal-raphe neurons. In raphe magnus few spinally projecting neurons contained either SP or 5-HT. Half of the bulbospinal neurons in the caudal VLM contained SP and/or 5-HT and in 50% of these SP and 5-HT were colocalized. However, no SP-containing neurons in the rostral VLM projected to the spinal cord.

Ultrastructural investigation of substance P-, leucine-enkephalin- and 5-hydroxytryptamine-like immunoreactive terminals in the area of cremaster motoneurons of the male rat

Studies were made on whether substance P-, leucine-enkephalin- and 5-hydroxytryptamine (serotonin)-like immunoreactive fibers exert a direct influence on the cremaster motoneurons of the male rat by immunocytochemistry combined with retrograde tracing at the light- and electron-microscopic levels. Horseradish peroxidase was used as a retrograde tracer. Two days after injection of horseradish peroxidase into the genitofemoral nerves, its accumulation in the cremaster motoneurons was demonstrated by the diaminobenzidine-nickel method. On immunocytochemical examination of the same sections immunoreactive end-products were detected by the peroxidase-antiperoxidase method. Two different kinds of reaction products were distinguishable at both the light- and electron-microscopical levels. The horseradish peroxidase-labeled cremaster motoneurons at the L1 and L2 levels of the spinal cord were surrounded by abundant immunoreactive terminals. Examination at the ultrastructural level showed that substance P-like immunoreactive terminals formed synaptic contacts almost exclusively with the proximal dendrites of these horseradish peroxidase-labeled cremaster motoneurons. On the other hand, in the leucine-enkephalin- and serotonin-like boutons, significant numbers of axosomatic contacts with horseradish peroxidase-labeled cells were seen although axodendritic contacts with horseradish peroxidase-labeled cells were predominant. Occasionally, leucine-enkephalin-like immunoreactive fibers with synapses on horseradish peroxidase-labeled neurons formed axoaxonic contacts with other leucine-enkephalin-like axonal terminals. Thus, substance P-, leucine-enkephalin- and serotonin-like fibers clearly regulate the function of cremaster motoneurons monosynaptically. The varied synaptic contacts of these fibers according to the neuroactive substances involved suggest different actions of these substances on the cremaster motoneurons.

Differential distribution of 5-hydroxytryptamine and substance P in synaptosomal vesicles of rat ventral spinal cord

The subcellular distribution of 5-hydroxytryptamine (5-HT) and substance P (SP) was investigated in rat ventral spinal cord using differential and density gradient centrifugation. 5-HT was determined by high performance liquid chromatography (HPLC) and SP by radioimmunoassay (RIA). Both substances were found to be stored within synaptosomes at high densities. After partial lysis of the synaptosomes, 5-HT was also recovered in low density fractions, while substance P was found also in a fraction of intermediate density. The results indicate that within synaptosomes from ventral spinal cord, most of the 5-HT is stored in small synaptic vesicles, while SP is only stored in large synaptic vesicles. A minor part of the 5-HT may in addition also be stored in large vesicles, as previously suggested by ultrastructural studies.

Spinal effects of chronic intrathecal administration of the thyrotrophin-releasing hormone analogue (CG 3509) in rats

The effect of repeated intrathecal administration of a thyrotrophin-releasing hormone (TRH) analogue (CG 3509; 2 micrograms twice daily for 5 days) on wet-dog shake (WDS) and forepaw-licking (FPL) behaviours and spinal cord TRH and indoleamine levels and choline acetyltransferase (ChAT) activity was examined in adult rats. A rapid behavioural tolerance developed to repeated intrathecal injections of CG 3509; WDS and FPL behaviours were reduced by 57% and 34%, respectively, following the fifth injection and remained reduced at the ninth injection. Repeated CG 3509 administration selectively elevated ChAT activity and the level of 5-hydroxytryptamine (5-HT) in the ventral but not in the dorsal horn of the spinal cord, while 5-hydroxyindoleacetic acid (5-HIAA) and TRH levels were unaltered in either region. As ventral horn ChAT activity is principally located within motoneurones this data implies that TRH exerts a trophic-like influence on mature rat motoneurones in vivo. The results also suggest that long-term intrathecal TRH administration may decrease the release of 5-HT from bulbospinal raphe neurones.

Interactions of substance P antagonists with serotonin in the mouse spinal cord

Administered intrathecally (IT) to mice, the putative substance P antagonist [D-Pro2,D-Trp7,9-substance P (DPDT) blocked substance P- and serotonin-induced reciprocal hindlimb scratching with ID50 values of 4.6 (2.9-6.9) and 3.0 (1.9-4.8) micrograms, respectively. The duration of this antagonistic effect was 90-120 min. In contrast, DPDT did not block bombesin-, somatostatin-, glycine- or glutamate-induced scratching. These data indicate that DPDT is an effective antagonist of serotonin-induced behaviors in the mouse spinal cord. Phenoxybenzamine (IT) also blocked substance P- and serotonin-induced scratching. Its onset of action was more rapid for serotonin than for DPDT implying differences in agonist-induced receptor activation. Methysergide (IT) blocked serotonin-induced scratching [ID50 = 0.7 (0.3-1.5) micrograms], but not substance P-induced scratching. Similar to DPDT, [D-Arg1,D-Trp7,9,Leu11]-substance P, [des-Arg1,D-Pro2, D-Trp7,9]-substance P(2-11) and [D-Pro4,D-Trp7,9]-substance P(4-11) blocked substance P and serotonin-induced scratching. In contrast, [D-Pro2,D-Phe7,D-Trp9]-substance P and [D-Pro4,D-Trp7,9,10]-substance P(4-11) blocked only substance P-induced scratching. Thus, some, but not all putative substance P antagonists may also be behavioral antagonists of serotonin in the mouse spinal cord.

The NK-3 tachykinin receptor agonist senktide elicits 5-HT-mediated behaviour following central or peripheral administration in mice and rats

The behavioural effects of the selective NK-3 tachykinin receptor agonist senktide were studied following intracisternal and subcutaneous administration in rodents. Behavioural manifestations of 5-hydroxytryptaminergic stimulation, including head twitches (mice), wet dog shakes (rats), forepaw treading, flat body posture, hindlimb splaying and Straub tail, were seen following the intracisternal (0.01-1.2 nmol) or subcutaneous (0.1-2.4 mumol kg-1) administration of senktide in both species. We conclude that stimulation of NK-3 receptors stimulates 5-hydroxytryptaminergic pathways in rodent brain, and that senktide may cross the blood-brain barrier in biologically significant amounts.

Localization of serotonin- and substance P-like immunofluorescence in the caudal spinal trigeminal nucleus of the rat

A double immunofluorescence labeling method was used to study the localization of serotonin (5-HT)- and substance P (SP)-like immunoreactivities within neuronal fibers in the caudal spinal trigeminal nucleus of the rat. The 5-HT- and SP-immunoreactive fibers share extensive topographical overlap within the superficial laminae of the caudal trigeminal nucleus; however, the majority of stained fibers are immunoreactive for either 5-HT or SP, but not both simultaneously. A small population of fibers in which 5-HT and SP are co-localized is present and restricted to the marginal zone as well as the inner and outer layers of the substantia gelatinosa. The results of the present study suggest that fibers containing coexistent 5-HT and SP may be involved in the processing of nociceptive somatic sensation in the medullary dorsal horn of rat.

Brainstem projections to spinal motoneurons: an update

1. The existence of direct projections to spinal motoneurons and interneurons from the raphe pallidus and obscurus, the adjoining ventral medial reticular formation and the locus coeruleus and subcoeruleus is now well substantiated by various anatomical techniques. 2. The spinal projections from the raphe nuclei and the adjoining medial reticular formation contain serotonergic and non-serotonergic fibres. These projections also contain various peptides, several of which are contained within the serotonergic fibres. Whether still other transmitter substances (e.g. acetylcholine) are present in the various descending brainstem projections to motoneurons remains to be determined. 3. The spinal projections from the locus coeruleus and subcoeruleus are mainly noradrenergic, but there also exists a non-noradrenergic spinal projection. 4. Pharmacological, physiological and behavioural studies indicate an overall facilitatory action of noradrenaline and serotonin (including several peptides) on motoneurons. This may lead to an enhanced susceptibility for excitatory inputs from other sources. 5. The brainstem areas in question receive an important projection from several components of the limbic system. This suggests that the emotional brain can exert a powerful influence on all regions of the spinal cord and may thus control both its sensory input and motor output.

An ultrastructural study of 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal boutons in the motor nucleus of spinal cord segments L7-S1 in the adult cat

The distribution and fine structure of 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive synaptic boutons and varicosities were studied in the motor nucleus of the spinal cord segments L7-S1 in the cat, using the peroxidase-antiperoxidase immunohistochemical technique and analysis of ultrathin serial sections. The 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive boutons had a similar ultrastructural appearance as judged from serial section analysis. The boutons could be classified into two types on the basis of their vesicular content, with one type containing a large number of small agranular vesicles together with only a few, if any large granular vesicles, while the other type contained a large number of large granular vesicles in addition to small agranular vesicles. The vesicles were spherical or spherical-to-pleomorphic. Postsynaptic dense bodies (Taxi bodies) were occasionally observed in relation to all three types of immunoreactive boutons, which almost invariably formed synaptic junctions with dendrites. Judged by the calibre of the postsynaptic dendrites, the boutons were preferentially distributed to the proximal dendritic domains of motoneurons. In one case, a substance P-immunoreactive bouton formed an axosomatic synaptic contact. In addition to synaptic boutons, 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal varicosities containing a large number of large granular and small agranular vesicles but lacking any form of conventional synaptic contact were observed. Such varicosities were either directly apposing surrounding neuronal elements or separated from the neurons by thin glial processes. The origin of the immunoreactive boutons was not traced, but it was thought likely that the main source of the boutons was neurons with their cell bodies located in the medullary raphe nuclei.

Lack of change in indoleamine metabolism in spinal cord of patients with amyotrophic lateral sclerosis

Indoleamine metabolism was determined by high-performance liquid chromatography with electrochemical detection in the cervical spinal cord of patients with amyotrophic lateral sclerosis (ALS) and controls with non-neurological diseases. The concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were the highest in the ventral horn compared with other regions of the spinal cord both in ALS and controls. There was no significant change in the concentration of 5-HT in any region of the spinal cord between ALS and controls. In addition, the concentration of 5-HIAA in ALS was lower than that in controls, however, no statistical significance was observed.

Thyrotropin-releasing hormone in spinal cord: coexistence with serotonin and with substance P in fibers and terminals apposing identified preganglionic sympathetic neurons

In this study we utilized the technique of simultaneous immunofluorescent double-labeling to investigate possible coexistence of the putative neurotransmitter thyrotropin-releasing hormone (TRH) with serotonin (5-HT) and with substance P (SP) in the intermediolateral cell column (IML) of rat spinal cord. We observed fibers and terminals immunoreactive for both TRH and 5-HT or TRH and SP in IML. In addition, this technique was used in animals in which we retrogradely labeled, with fluorescent tracer dyes, preganglionic sympathetic neurons within IML from either the adrenal medulla or the proximal cut end of the cervical sympathetic trunk. In these animals, fibers and terminals containing these combinations of neurotransmitters appeared to oppose identified preganglionic sympathetic neurons in IML. These data represent the first direct immunohistochemical demonstration of fibers and terminals in spinal cord which display coexistence of TRH- with either 5-HT- or SP-immunoreactivity. In addition, the proximity of TRH-immunoreactive fibers and terminals to sympathetic preganglionic neurons in IML support a role for TRH in the regulation of central sympathetic outflow.