The effects of 5-hydroxytryptamine-depleting drugs on peptides in the ventral spinal cord

Emetic action of the prostanoid TP receptor agonist, U46619, in Suncus murinus (house musk shrew)

The emetic action of the prostanoid TP receptor agonist, 11alpha,9alpha-epoxymethano-15S-hydroxyprosta-5Z,13E-dienoic acid (U46619; 300 microg/kg, i.p.), was investigated in Suncus murinus. The emetic response was reduced by 76% following bilateral abdominal vagotomy (P<0.001) and by reserpine (5 mg/kg, i.p., 24 h pretreatment; P<0.05) but U46619 administered i.c.v. (30-300 ng) was not emetic, suggesting a peripheral mechanism involving monoamines. However, fenfluramine (5 mg/kg, repeated treatment) and para-chlorophenylalanine (100-400 mg/kg) and ondansetron (0.3-3 mg/kg) were inactive (P>0.05) to reduce U46619-induced emesis precluding a role of 5-HT and 5-HT(3) receptors in the mechanism. Similarly, phentolamine (0.3-3 mg/kg), propranolol (3 mg/kg), and their combination, and metoclopramide (0.3-3 mg/kg), domperidone (0.3-3 mg/kg), droperidol (0.3-3 mg/kg), scopolamine (0.3-3 mg/kg) and promethazine (0.3-3 mg/kg) were inactive (P>0.05) to reduce the retching and vomiting response. However, the tachykinin NK(1) receptor antagonist, (+)-2S,3S(-3-(2-methoxy-5-trifluoromethoxybenzyl)amino-2-phenylpiperidine) (CP-122,721; 1-10 mg/kg) antagonized emesis (P<0.01). In conclusion, U46619-induced emesis appears to be mediated via a predominant peripheral mechanism sensitive to reserpine and is not likely to involve adrenoceptors, dopamine, 5-HT(3), muscarinic or histamine (H(1)) receptors. The action of CP-122,721 to reduce U46619-induced emesis extends the spectrum of anti-emetic action tachykinin NK(1) receptor antagonists to mechanisms involving TP receptors.

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.

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.

The effect of p-chloroamphetamine and p-chlorophenylalanine on the level of thyrotropin-releasing hormone and its receptors in some brain structures and lumbar spinal cord of the rat

The concentration of thyrotropin-releasing hormone (TRH) and the density and affinity of TRH receptors were examined in the ventral and dorsal lumbar spinal cord, nucleus accumbens and striatum of rats with the 5-hydroxytryptamine (5-HT) nerve terminal destroyed with p-chloroamphetamine (PCA), or in animals treated with the inhibitor of 5-HT synthesis p-chlorophenylalanine (PCPA). PCA (2 x 10 mg/kg i.p., 9 and 8 d before killing) and PCPA (3 x 300 mg/kg i.p., 72, 48 and 24 h before killing)--either of them dramatically diminishing the 5-HT and 5-HIAA concentrations in all the examined structures--reduced the TRH level and increased the density of TRH receptors in the ventral lumbar spinal cord. PCPA also reduced the TRH content in the nucleus accumbens. The PCA-induced reduction in the TRH level and increase in the density of TRH receptors in the ventral lumbar spinal cord were significantly attenuated by citalopram (2 x 20 mg/kg i.p., 30 min before PCA), a selective inhibitor of 5-HT uptake. Our results constitute a further proof that coexistence of TRH and 5-HT takes place in the ventral lumbar spinal cord and then indicate that other form(s) of relationship between 5-HT and TRH may exist in some parts of the central nervous system. They also suggest that an up-regulation of TRH receptors occurs in the spinal cord as a result of TRH depletion.

Alteration in the levels of thyrotropin releasing hormone, substance P and enkephalins in the spinal cord, brainstem, hypothalamus and midbrain of the Wobbler mouse at different stages of the motoneuron disease

The present study was undertaken to quantify selected neuropeptides (thyrotropin releasing hormone, substance P, methionine and leucine enkephalin) in the cervical spinal cord and other regions of the central nervous system of Wobbler mice by radioimmunoassays during several stages of the motoneuron disease compared with age- and sex-matched normal phenotype littermates. In Wobbler spinal cord, thyrotropin releasing hormone is higher early in the disease, whereas in the brainstem it is higher at a later stage. Substance P in spinal cord is also higher late in the disease. Leucine enkephalin levels are greater at all stages in diseased spinal cord and brainstem, but methionine enkephalin increases only late in the disease. Highly significant increases of the peptides (except thyrotropin releasing hormone) appear in hypothalamus and midbrain only late in the motoneuron disease. Regression analyses show that thyrotropin releasing hormone in spinal cord and brainstem decreases normally with age in the control mice and at a faster rate related to the extent of motor impairment in Wobbler mice. Thyrotropin releasing hormone and methionine enkephalin in the Wobbler brainstem correlate (P less than 0.05) with the progress of the motoneuron disease. Methionine enkephalin increases faster in Wobbler brainstem and decreases faster in control spinal cord with age. The increase of leucine enkephalin in the Wobbler spinal cord correlates significantly with age and with the progress of the disease, but leucine enkephalin declines slightly with age in the controls. The changes of substance P in spinal cord and brainstem do not correlate significantly with the progress of the disease. In the hypothalamus, increasing values for substance P in control specimens and enkephalins in Wobbler specimens are significantly correlated with age. However, in the midbrain, higher methionine and leucine enkephalin levels are significantly associated with age only in the control mice. Alterations of neuropeptides in the Wobbler mouse spinal cord and brainstem may result from the degeneration of bulbospinal raphe neurons projecting to the ventral spinal cord, or from primary afferent or interneuronal nerve terminals. The data imply that the neuronal degeneration process in the Wobbler motoneuron disease is not limited to motoneurons. In the spinal cord, the data support our previous hypothesis that neuronal sprouting presynaptic to the motoneurons may account for increased neuropeptide concentrations. Alternatively, synthesis and/or degradation of these peptides may be altered. In addition, it is proposed that enkephalinergic neurons may develop abnormally in Wobbler mice. The early increase of leucine enkephalin in the Wobbler spinal cord possibly indicates its importance in the etiology of the motoneuron disease.

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.

Serotoninergic denervation suppresses the sympathetic outflow induced by thyrotropin-releasing hormone in conscious rats

Intrathecal administration of thyrotropin-releasing hormone (TRH) resulted in an increase in plasma epinephrine (E) and glucose levels in conscious rats. To elucidate the mechanisms by which TRH stimulates the release of E, the animals were pretreated with 5,7-dihydroxytryptamine, parachlorophenylalanine, methysergide or ketanserin. Serotoninergic denervation suppressed the TRH-induced increase in plasma E and glucose levels, whereas inhibition of serotonin (5-HT) synthesis or blockade of 5-HT receptors did not suppress the responses. These findings suggest that the serotoninergic neurons, but not 5-HT itself, are involved in stimulating the sympathetic outflow by TRH at the spinal level.

Contribution of serotonin neurons to the functional recovery after spinal cord injury in rats

The contribution of serotonin neurons to the functional recovery after spinal cord injury was studied pharmacologically in rats with moderately severe neurologic impairment (complete paraplegia but responsive to tail pinching) 24 h after thoracic spinal cord (T11) compression-induced injury. Fourteen days after cord injury the levels of endogenous norepinephrine (NE, -33%), dopamine (DA, -50%) and serotonin (5-HT, -55%) in the lumbar cord in the injury control rats were decreased and there were significant correlations between the neurologic score and the NE level (rs = 0.562, P less than 0.01) and the 5-HT level (rs = 0.745, P less than 0.001) but not the DA level. Bilateral i.c.v. injection of 5,7-dihydroxytryptamine (200 micrograms/rat) 24 h after cord injury significantly retarded the neurologic recovery during the 14 days after injury, accompanied by a further reduction in the 5-HT level (-86%) but not in the NE or DA level. On the other hand, neither p-chlorophenylalanine (PCPA) (300 mg/kg, i.p., once daily starting 24 h after injury for 13 consecutive days) nor reserpine (1 mg/kg, i.p., 4 times, once 24 h after injury and then every fourth day) had any influence on the time course of the neurologic recovery during the 14 days after injury, although PCPA treatment further reduced the levels of NE (-50%) and 5-HT (-91%), and reserpine treatment further reduced the levels of NE (-95%), DA (-73%) and 5-HT (-85%).(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y and catecholamine synthesizing enzymes and their mRNAs in rat sympathetic neurons and adrenal glands: studies on expression, synthesis and axonal transport after pharmacological and experimental manipulations using hybridization techniques and radioimmunoassay

The effects of reserpine treatment (10 mg/kg, i.p.) on the content of neuropeptide Y-like immunoreactivity and catecholamines were compared with the levels of mRNA coding for neuropeptide Y, tyrosine hydroxylase and phenylethanolamine N-methyltransferase in rat sympathetic neurons and adrenal gland. A reversible depletion of neuropeptide Y-like immunoreactivity was observed in the right atrium of the heart, kidney and masseter muscle, while the immunoreactive neuropeptide Y content in the stellate and lumbar sympathetic ganglia and its axonal transport in the sciatic nerve increased following reserpine. The increase in the stellate ganglion was maximal at 48 h and absent 9 days after reserpine treatment. The expression of neuropeptide Y mRNA and tyrosine hydroxylase mRNA in both the stellate and the superior cervical ganglion increased earlier than the neuropeptide Y content, with a clear cut two-fold elevation at 24 h after reserpine. The increase in both mRNAs in the superior cervical ganglion and the depletion of neuropeptide Y, but not of noradrenaline, in terminal areas was prevented after pretreatment both with a nicotinic receptor antagonist (chlorisondamine) and with surgical preganglionic denervation. A marked (75-90%) depletion of neuropeptide Y-like immunoreactivity and adrenaline in the adrenal gland, concomitant with 3-4-fold increases in neuropeptide Y mRNA and tyrosine hydroxylase mRNA expression, was present at 24 h after reserpine treatment. Also in the adrenal gland, there was a reversal of the reserpine-induced increase in neuropeptide Y mRNA and tyrosine hydroxylase mRNA and depletion of neuropeptide Y and adrenaline following splanchnic denervation. Pharmacological, ganglionic blockade prevented the depletion of neuropeptide Y and the increased expression of neuropeptide Y mRNA, but not fully, the tyrosine hydroxylase mRNA elevation. In addition, a marked decrease in phenylethanolamine N-methyltransferase mRNA levels was noted after reserpine. This decrease was reversed by denervation and by ganglionic blockade. Denervation alone led to a small but significant decrease in all mRNAs examined both in the superior cervical ganglion and the adrenal medulla. The present data suggest that the depletion of neuropeptide Y-like immunoreactivity in sympathetic nerves and in the adrenal gland after reserpine is associated with a compensatory increase in neuropeptide Y synthesis and axonal transport, most likely due to increased nicotinic receptor stimulation. Whereas the reserpine depletion of neuropeptide Y in both sympathetic nerves and adrenal gland is related to neuronal activation, adrenal but not nerve terminal depletion of catecholamines can be prevented by the ganglionic blocker chlorisondamine.4+e difference in effect of pharmacological ganglionic

Effect of reserpine and colchicine on neuropeptide mRNA levels in the rat hypothalamic paraventricular nucleus

Using in situ hybridization and immunohistochemistry, we have studied mRNA and peptide levels in the hypothalamic paraventricular nucleus (PVN) 24 h after a single large dose of reserpine (10 mg/kg, i.p.) and 24 h after an intraventricular (i.c.v.) injection of colchicine (120 microliters/20 microliters saline). Sections of the PVN were hybridized using synthetic oligonucleotide probes complementary to mRNA for corticotropin-releasing hormone (CRH), neurotensin (NT), enkephalin (ENK), vasoactive intestinal polypeptide (VIP) and thyrotropin-releasing hormone (TRH). For immunohistochemistry rabbit antisera to CRH, NT, ENK, VIP and TRH were used. In situ hybridization showed a clear increase in CRH mRNA as compared to control rats after both treatments. Also NT and VIP mRNA could be seen in parvocellular neurons in reserpine and in colchicine-treated rats, whereas we so far have not been able to demonstrate these mRNAs in untreated rats. No changes in TRH mRNA could be detected after reserpine of colchicine. These results provide final evidence that subpopulations of parvocellular PVN neurons can synthesize not only CRH and ENK, but also NT and VIP, in agreement with earlier immunohistochemical results. With immunochemistry, after reserpine, many CRH-, but no NT- or VIP- positive neurons could be observed in the parvoecellular part of the PVN. The present results demonstrate that treatment with two drugs, the monoamine depleting drug reserpine and the mitosis inhibitor colchicine, causes increased levels of mRNA for several peptides in neurons of the PVN, located almost exclusively in its parvocellular part and being part of the hypothalamo-pituitary adrenal axis.

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.

The role of serotonin in non-cholinergic excitatory transmission in the guinea pig inferior mesenteric ganglion

The non-cholinergic late slow excitatory postsynaptic potential (ls-EPSP) of the guinea pig inferior mesenteric ganglion (IMG) was previously believed to be mediated by substance P (SP) or several other neuropeptides. Yet, the pharmacological evidence presented here indicates that serotonin (5-HT) may be another transmitter for the ls-EPSP in the guinea pig IMG. Repetitive stimulation of the presynaptic nerves elicited ls-EPSP in about half of the IMG neurons. Application of 5-HT or SP caused, in a portion of the IMG neurons, a slow depolarization similar to ls-EPSP. Fifty-six out of 88 (63.6%) neurons with ls-EPSP and 13 out of 35 (37.1%) neurons with ls-EPSP were sensitive to 5-HT and SP, respectively. Superfusion of the ganglia with 5-HT markedly suppressed the ls-EPSP evoked in 5-HT sensitive neurons. Similarly, exogenously applied SP attenuated the ls-EPSP of SP-sensitive neurons. However, prolonged superfusion of 5-HT or SP had no effect on the ls-EPSP elicited in 5-HT or SP-insensitive neurons, respectively. Furthermore, the ls-EPSPs elicited in 5-HT-sensitive neurons as well as the 5-HT-induced depolarization were reversibly suppressed by cyproheptadine, a 5-HT antagonist, and enhanced by fluoxetine, a 5-HT reuptake inhibitor. In contrast, the ls-EPSP of 5-HT insensitive neurons and SP-induced depolarization were not appreciably changed by those two drugs. Pretreatment with p-chlorophenylalanine, a 5-HT biosynthesis inhibitor, did not change the general electrophysiological characteristics of the neurons and did not suppress nicotinic neurotransmission, but markedly reduced the occurrence rate of ls-EPSP from 53.8% to 15.1% (P less than 0.005). Collectively, our results indicate that, besides SP, 5-HT may be involved in mediating the ls-EPSP in a subpopulation of neurons in the guinea pig IMG. The type of transmitter mediating ls-EPSP is apparently not limited to 5-HT and SP, as about 30% of the neurons with ls-EPSP were found to be insensitive to both 5-HT and SP and prolonged superfusion with both did not affect appreciably the ls-EPSP elicited in these neurons.

Tryptophan hydroxylase inhibition increases preprotachykinin mRNA in developing and adult medullary raphe nuclei

In order to study the regulation of co-localized monoamine and peptide neurotransmitters in the medullary raphe nuclei (MRN), we determined whether inhibition of serotonin (5-HT) synthesis affected levels of preprotachykinin (PPT; the prohormone precursor of substance P) mRNA in the MRN. Adult rats received p-chlorophenylalanine (pCPA), an irreversible inhibitor of tryptophan hydroxylase (TPH), via Alzet minipumps. TPH activity was inhibited by 70-80% for 3 weeks following pump implantation. During this period Northern mRNA analysis revealed that PPT mRNA levels in the MRN were increased 1.5-2-fold. The pCPA-induced increase was specific for PPT mRNA since no change was detected in mRNA coding for neuron-specific enolase (NSE; a constitutive neuronal protein) or 28 S ribosomal RNA. To determine whether fetal inhibition of 5-HT synthesis affected development of PPT mRNA in the MRN, pregnant rats were administered pCPA via Alzet minipump implanted on embryonic day 8. In pCPA-treated litters TPH activity was decreased by 60-70% from E16 to postnatal day 3 (P3), returning to control levels by P8. Northern mRNA analysis revealed that PPT mRNA levels increased 2.4-fold of control levels at P1. Infusion of pCPA for one week resulted in an earlier increase in PPT mRNA levels, suggesting that birth was not required to elicit the surge in PPT message. These results support the hypothesis that alterations in 5-HT metabolism have regulatory consequences for co-localized substance P formation in the MRN.

Measurement of neuropeptides in the brain and spinal cord of Wobbler mouse: a model for motoneuron disease

The Wobbler mouse (wr) exhibits the loss of motoneurons especially in the cervical spinal cord, and thus has been studied as a model for human motoneuron diseases. Wobbler mice selected at various ages and stages during the disease process show increased levels of thyrotropin releasing hormone and substance P in spinal cord and brainstem (medulla). Enkephalins (methionine and leucine) also increase in the spinal cord and brainstem. Somatostatin increases in hypothalamus, perhaps accounting partly for the small size of this mutant mouse via its effect on growth hormone.

Evidence for noradrenergic-purinergic cotransmission in the hepatic artery of the rabbit

1. Transmural electrical field stimulation produced a transient contraction of the isolated hepatic artery of the rabbit that was frequency-dependent up to 64 Hz. A contraction was rarely evoked at a stimulation frequency of less than 8 Hz and never at 4 Hz or less. All contractions were abolished in the presence of tetrodotoxin. 2. Neurogenic contractions were partially inhibited by prazosin. After desensitization of the P2X-purinoceptor with alpha, beta-methylene ATP, contractions in response to electrical stimulation were significantly reduced at all frequencies tested (4-64 Hz). In most cases, contractions were abolished by a combination of both drugs. 3. In vessels treated with 6-hydroxydopamine, no nerve-mediated contractile responses were observed. 4. In arteries from reserpine-treated rabbits, nerve stimulation evoked contractions that were resistant to prazosin. After desentization of the P2X-purinoceptor with alpha,beta-methylene ATP, no neurogenic contractile response remained. 5. The tissue contracted to exogenously applied noradrenaline and alpha,beta-methylene ATP. There was an increase in sensitivity to noradrenaline in 6-hydroxydopamine-treated vessels compared with control vessels, but no difference in potency to alpha,beta-methylene ATP was detected. The potency of noradrenaline and alpha,beta-methylene ATP was not significantly affected by reserpine treatment. 6. In control tissues, fluorescence histochemistry demonstrated the presence of noradrenergic nerve fibres. Noradrenaline-containing nerves were not observed in 6-hydroxydopamine-treated or reserpine-treated vessels. 7. It is concluded that noradrenaline and ATP are cotransmitters in the sympathetic nerves supplying the hepatic artery of the rabbit. In contrast to other vessels, the hepatic artery requires a relatively high frequency of stimulation to evoke contractions and the purinergic component is not frequency-dependent. The significance of this finding in terms of the physiological demands of blood flow to the liver are discussed.

The effect of fenfluramine on the thyrotropin-releasing hormone (TRH) content in the rat brain structures and lumbar spinal cord

The effect of fenfluramine (20 mg/kg i.p.) was studied on the thyrotropin-releasing hormone (TRH) content in several brain structures and the ventral part of the lumbar spinal cord of the rat. The effect of fenfluramine on the concentration of 5-hydroxytryptamine (5-HT) in some brain structures and the lumbar spinal cord was also examined. It was found that fenfluramine had no effect on the TRH level in the hypothalamus, hippocampus, occipital cortex, septum, nucleus accumbens and ventral part of the lumbar spinal cord, though the drug produced a profound depletion (by more than 60%) of 5-HT in the hypothalamus, nucleus accumbens, striatum and lumbar spinal cord. On the other hand, fenfluramine significantly increased the TRH content in the striatum, this effect was completely abolished by citalopram (20 mg/kg i.p.) or metergoline (10 mg/kg i.p.) Citalopram also prevented the fenfluramine-induced depletion of the striatal 5-HT. These results indicate a separate neuronal storage of TRH and 5-HT in the structures (ventral part of the lumbar spinal cord, nucleus accumbens, septum) in which the peptide and indoleamine coexist in 5-HT neurons. They also suggest that the fenfluramine-induced increase in the striatal TRH concentration is due to 5-HT release and stimulation of 5-HT receptors.

Tyrosine hydroxylase and galanin mRNA levels in locus coeruleus neurons are increased following reserpine administration

The neuropeptide galanin coexists in 80-90% of the norepinephrine-containing neurons in the locus coeruleus. In situ hybridization histochemistry was used to examine the effects of reserpine treatment or swim stress on tyrosine hydroxylase and galanin mRNA concentrations in locus coeruleus neurons. Reserpine administration significantly increased tyrosine hydroxylase and galanin mRNA levels in the locus coeruleus. The reserpine-induced increase in tyrosine hydroxylase mRNA was significantly correlated with the reserpine-induced increase in galanin mRNA. Three consecutive days of swim stress did not significantly alter either tyrosine hydroxylase or galanin mRNA concentrations in the locus coeruleus. These data suggest that both tyrosine hydroxylase and galanin gene expression in locus coeruleus neurons may be regulated by a reserpine-sensitive mechanism.

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)

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)

TRH and TRH receptors in the spinal cord

Over the past 12 years, substantial progress has been made in delineating the localization of TRH and TRH receptors in spinal cord. High concentrations of both the peptide and its receptor have been observed in the ventral horn in the region of the motoneurons and in the dorsal horn in the substantia gelatinosa. As noted, pharmacological effects of TRH administration on various parameters of spinal cord function have been reported in a number of studies. To date, however, substantial questions remain regarding the physiological role of TRH in the spinal cord. Nevertheless, it is hoped that the extensive information that has been obtained on localization of TRH and TRH receptors in spinal cord will provide a basis for answering these complex questions.

Preganglionic sympathetic neurones innervating the rat adrenal medulla: immunocytochemical evidence of synaptic input from nerve terminals containing substance P, GABA or 5-hydroxytryptamine

Sympathetic preganglionic neurones that innervate the adrenal medulla were identified for subsequent light and electron microscopic study by the retrograde transport of horseradish peroxidase (HRP) or a conjugate of HRP and cholera B-chain. Most labelled neurones were found in the intermediolateral column, but some occurred in the intercalated nucleus and in the lateral funiculus of the thoracic spinal cord. Three morphologically distinct types of neurone were retrogradely labelled, two of which had dendrites that extended medially towards the central canal and laterally across the entire lateral funiculus. A combination of retrograde labelling with pre-embedding immunocytochemistry allowed us to demonstrate synaptic contacts between boutons immunoreactive for substance P or 5-hydroxytryptamine (5-HT) and the cell bodies or proximal dendrites of sympathoadrenal neurones. The 5-HT-immunoreactive boutons appeared to be of two morphologically distinct types. Postembedding immunocytochemistry enabled us to show that sympathoadrenal neurones receive a heavy synaptic innervation from GABA-immunoreactive boutons: 32% of a random series of boutons in synaptic contact with cell bodies were GABA-immunoreactive. Proximal dendrites and also distal dendrites within the white matter were ensheathed in synaptic boutons, 37% of which were GABA-immunoreactive. It is concluded that sympathoadrenal neurones receive at least 4 distinct types of afferent synaptic input: from neurones containing substance P, or GABA and from two types of neurones containing 5-HT. The presence of synaptic inputs on distal dendrites that extend across the white matter adds further complexities to the control of the activity of sympathetic preganglionic neurones.

Intrathecal substance P modulates the depressant effect of 5-methoxy-N,N-dimethyltryptamine on a reflex response to radiant heat in mice

The effect of intrathecal (i.th.) substance P (SP) on antinociception elicited by the serotonin (5-HT) receptor agonist 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) was investigated in mice by means of the tail-flick method. Substance P (0.07, 0.7 or 7 micrograms) induced a behavioral syndrome for 1-2 min, but had no apparent toxic or neurologic effects and did not alter the tail-flick response to noxious radiant heat 30 min after injection. The depressant effect of 5-MeODMT (3 mg/kg) on tail-flick responses was, however, markedly attenuated when administered 30 min after SP. The tail skin temperatures of vehicle- and SP-injected mice were nearly identical 30 min after i.th. injection as well as after administration of 5-MeODMT. The results indicate a functional interaction between SP and 5-HT in spinal nociceptive processes, and it is suggested that i.th. SP modulates the function of 5-HT receptors.

Increased behavioural response to intrathecal substance P after intracerebroventricular 5,7-dihydroxytryptamine but not after p-chlorophenylalanine administration

The behavioural response to intrathecally injected substance P (SP, 1.25 ng) was investigated in mice after lesioning of serotonergic (5-HT) pathways by intracerebroventricular 5,7-dihydroxytryptamine (5,7-DHT, 80 micrograms base/mouse) and after 5-HT synthesis inhibition by p-chlorophenylalanine (PCPA, 400 mg kg-1 for 6 consecutive days). Pretreatment with 5,7-DHT and PCPA reduced the 5-HT level in the spinal cord to 6 and 7% of controls and the noradenaline (NA) level to 69 and 84% of controls, respectively. Intrathecally injected SP produced a response consisting of vigorous biting, licking and scratching of the caudal part of the body. The response to SP was significantly increased 5 days after injection of 5,7-DHT, but only a non-significant tendency towards enhancement of the response was found after 24 h. There was no change in the response to SP 24 h after the last injection of PCPA. It is suggested that 5,7-DHT but not PCPA induces receptor supersensitivity to SP, and that reduction in spinal SP by 5,7-DHT may be a factor in this change in receptor sensitivity.

5-HT depletion with 5,7-DHT, PCA and PCPA in mice: differential effects on the sensitivity to 5-MeODMT, 8-OH-DPAT and 5-HTP as measured by two nociceptive tests

Depletion of 5-hydroxytryptamine (5-HT) in mice was produced by intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT, 80 micrograms) or by systemic injections of p-chloroamphetamine (PCA, 3 X 40 or 4 X 40 mg/kg), p-chlorophenylalanine (PCPA, 5 X 400 or 14 X 400 mg/kg) or combined PCA (3 X 40 mg/kg) + PCPA (11 X 400 mg/kg). Neither of the pretreatments altered nociception in the increasing temperature hot-plate test, whereas hyperalgesia was demonstrated in 5,7-DHT lesioned animals in the tail-flick test. 5,7-DHT-pretreatment enhanced the antinociceptive effect of the 5-HT agonists 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-hydroxytryptophan (5-HTP). This effect was observed after 2, 5 and 8 days in the tail-flick test and after 5 and 8 days in the hot-plate test. However, pretreatment with PCPA or PCA failed to alter the antinociception elicited by the 5-HT agonists, although a tendency towards enhancement of antinociception was found after combined treatment with PCA and PCPA. It is suggested that the injection of 5,7-DHT induces denervation supersensitivity of post-synaptic 5-HT receptors. The lack of such supersensitivity after PCPA-pretreatment which induces similar 5-HT depletion to 5,7-DHT, may suggest that other factors than the absence of 5-HT may contribute to the development of denervation supersensitivity. Alternatively, the three 5-HT depleting agents may produce a qualitatively different reduction of 5-HT.

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.

Evidence for the co-localization of somatostatin- and methionine-enkephalin-like immunoreactivities in raphe and gigantocellularis nuclei

Somatostatin-like and methionine-enkephalin-like immunoreactivities were co-localized in neurons in the raphe nuclei and the nucleus gigantocellularis among immunoreactive cells stained for either one of these putative neurotransmitters. Their colocalization suggests that they form a subset of these two peptide populations and may serve as a major inhibitory system within the medullary reticular nuclei.

Raised thyrotrophin-releasing hormone, pyroglutamylamino peptidase, and proline endopeptidase are present in the spinal cord of wobbler mice but not in human motor neurone disease

The Wobbler mouse (wr) is a mutant that exhibits loss of anterior horn cells in the spinal cord and brainstem and subsequent muscle wasting, particularly of the forelimbs and neck. The wr mice, 2-3 months of age, were found to have increased levels of immunoreactive-thyrotrophin-releasing hormone (ir-TRH) in the spinal cord and pons and medulla, but not in other CNS areas. This increase was observed in dorsal and ventral cord and at cervical, thoracic, and lumbar levels and was confirmed by HPLC to be authentic TRH. The levels of immunoreactive-somatostatin, -neurotensin, and -substance P were not raised in the CNS of wr mice. The activities of two peptidases capable of degrading TRH, pyroglutamylaminopeptidase (PGAP, EC 3.4.11.8) and proline endopeptidase (PEP, EC 3.4.21.26), and the level of 5-hydroxyindoleacetic acid were also raised in the spinal cord of 2-3-month-old wr mice although the activities of alanine aminopeptidase and lactate dehydrogenase and the level of 5-hydroxytryptamine were not. Increased spinal cord levels of ir-TRH and PGAP and PEP activities were not observed in the 1-month-old wr mice. In addition, a pilot study using spinal cord obtained at autopsy from three patients with motor neurone disease and 12 control subjects indicated no increase in spinal cord ir-TRH, PGAP, or PEP in human motor neurone disease.

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.

Serotonergic and non-serotonergic raphe neurons projecting to the feline lumbar and cervical spinal cord: a quantitative horseradish peroxidase-immunocytochemical study

A quantitative study of raphe-spinal neurons and serotonergic neurons in 3 medullary raphe nuclei in the cat indicates that more than 80% of the raphe-spinal neurons that project to the spinal cord are serotonergic raphe-spinal neurons in each of the nuclei. More than 85% of the descending raphe-spinal neurons in the two caudal nuclei, nucleus raphe pallidus and nucleus raphe obscurus, are serotonergic, whereas 75% of the raphe-spinal neurons in the more rostrally placed nucleus raphe magnus contain serotonin (5-HT). These results are discussed in relation to descending systems containing both neuropeptides and 5-HT and collateralizing to several spinal segments.

Immunohistochemical analysis of the effects of cysteamine on somatostatin-like immunoreactivity in the rat central nervous system

The brain and spinal cord of untreated and cysteamine-treated rats were analyzed with immunohistochemistry using antisera raised against somatostatin (SOM)-28(1-14) and SOM-28(15-28). Sections incubated with increasing dilutions of antiserum were evaluated subjectively on coded slides and with computer-assisted image analysis. For control experiments, antisera raised against methionine-enkephalin, neuropeptide Y (NPY) and dynorphin (DYN)(1-13) were used. The latter antiserum does not visualize the conventional DYN systems in the brain, but reacts with an unknown epitope, which here could be shown to be present in SOM neurons. In cysteamine-treated rats a marked decrease in SOM-28(15-28)-like immunoreactivity (1.1) could be recorded subjectively at all antibody concentrations in fibers in several brain areas, including nucleus accumbens, tuberculum olfactorium and the hypothalamic ventromedial and arcuate nuclei. In these areas SOM-LI is fairly weak in untreated rats. In SOM-rich regions such as the median eminence and the dorsal horn of the spinal cord, the depleting effect of cysteamine could be recorded subjectively only when diluted antisera were used. Image analysis confirmed the subjective analysis, and, in addition, differences between controls and cysteamine-treated rats could be shown also at high antiserum concentrations. SOM-28(15-28)-immunoreactive cell bodies could be seen in the brains of either control or drug-treated rats. No effect of cysteamine could be observed when antiserum raised to SOM-28(1-14) was used. Cysteamine did not seem to affect enkephalin-LI, NPY-LI or an epitope in SOM neurons reacting with DYN(1-13) antiserum. After preabsorption of SOM-28(15-28) antiserum with SOM-28(15-28) peptide, the staining patterns described above disappeared completely. However, if the SOM-28(15-28) peptide was pretreated with a high concentration (1 M) of cysteamine before being used for absorption with SOM antiserum, no blocking effect could be observed. The present results demonstrate with immunohistochemistry that cysteamine causes depletion of SOM-28(15-28) in fibers but apparently not in cell bodies. No effects on SOM-28(1-14)-LI were observed. This supports earlier evidence that cysteamine interacts with the disulphide bond in the SOM-28(15-28) molecule. The present results also emphasize that when analyzing drug effects on peptide neurons with immunohistochemical techniques, it is important to use dilution series of antibodies and preferably to carry out the analysis with objective image analysis methods.

Regional distribution of immunoreactive-thyrotrophin-releasing hormone and substance P, and indoleamines in human spinal cord

The regional distributions of thyrotrophin-releasing hormone (TRH) and substance P in postmortem human spinal cord were determined by radioimmunoassay in fresh tissue taken from 22 patients who died without known neurological disease. Dorsal, ventral, and intermediolateral spinal cord regions were obtained from different segmental levels (lumbar L1, 2, 3, and 4; thoracic groups T1-3, T4-6, T7-9, and T10-12) together with selective regions of grey matter of lumbar spinal cord. The effects on peptide levels of the age of the patient, the postmortem time interval, and freezing the tissue samples prior to assay were assessed. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in regional lumbar and thoracic tissue using HPLC with electrochemical detection. Substance P was found in the highest concentration in the dorsal spinal cord, with no significant segmental differences. In contrast, TRH was present in higher levels in the ventral rather than the dorsal spinal cord, with segmental differences. There was a significant difference in the 5-HT/5-HIAA ratio between dorsal and ventral spinal cord, with the highest ratio in the ventral spinal cord. There were no significant differences in substance P, TRH, or 5-HT levels in spinal cords between 5 and 20 h postmortem or from patients aged between 65 and 90 years. Freezing the tissue (-80 degrees C for 24 h) prior to assay significantly reduced TRH and substance P levels compared to samples assayed immediately without prior freezing.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraventricular 5,7-dihydroxytryptamine increases thyrotropin-releasing hormone content in regions of rat brain

Rats received intraventricular (i.v.t.) injections of 5,7-dihydroxytryptamine (5,7-DHT) (100-600 micrograms). Some animals also received intraperitoneal injections of the 5-hydroxytryptamine uptake blocker fluoxetine (FX) (20 mg/kg) or the norepinephrine uptake blocker desmethylimipramine (DMI) (48 mg/kg) 30-90 min prior to i.v.t. 5,7-DHT. Rats were killed between 2 and 35 days following i.v.t. 5,7-DHT, brains were dissected, and regions were assayed for thyrotropin-releasing hormone (TRH) by radioimmunoassay. Dose-dependent increases in TRH content following i.v.t. 5,7-DHT were noted in the brainstem and hippocampus. DMI pretreatment blocked the increase in hippocampal TRH, but not in brainstem TRH. FX pretreatment was ineffective in blocking any increases in TRH content. These results suggest differential regulation of regional TRH content by interactions with specific neurotransmitter systems.

Mechanisms underlying changes in the contents of neuropeptide Y in cardiovascular nerves and adrenal gland induced by sympatholytic drugs

Neuropeptide Y (NPY) is a recently isolated vasoactive peptide, which is present, together with catecholamines, in sympathetic nerves and in the adrenal medulla. In the present study, we report that pretreatment with sympatholytic agents influences the tissue levels of NPY-like immunoreactivity (NPY-LI) in the guinea-pig. Thus, 24 h after reserpine not only noradrenaline (NA), but also NPY-LI, was depleted in the heart, spleen and the adrenal gland. The levels of NPY-LI in the vas deferens and stellate ganglia, however, were unaffected by reserpine in spite of marked depletions of NA. The reserpine-induced depletion of NPY-LI was probably caused by enhanced nerve-impulse flow and subsequent release from cardiovascular nerves in excess of resupply, since it could be prevented by the ganglionic-blocking agent chlorisondamine. Long-term (6 days) treatment with chlorisondamine reduced the levels of NPY-LI in the stellate ganglion. Short-term treatment (48 h) with guanethidine partially prevented the reserpine-induced depletion of NPY-LI, probably due to inhibition of NPY release. Long-term guanethidine treatment depleted not only NA, but also NPY-LI from the spleen. Pretreatment with the alpha-receptor antagonist phenoxybenzamine did not influence the NA levels but reduced the content of NPY-LI in the spleen via a mechanism that was dependent on intact ganglionic transmission. Since NPY has several cardiovascular actions, changes in NPY mechanisms may contribute to the pharmacological and therapeutical effects of sympatholytic agents.

Potentiation of motoneurone excitability by combined administration of 5-HT agonist and TRH analogue

Motoneurone field potentials have been recorded from the lumbar region of the spinal cord, to antidromic stimulation of a ventral root, in rats anaesthetised with urethane. Injection of the thyrotropin releasing hormone (TRH) analogue RX77368 (1mg/kg) plus the 5-hydroxytryptamine (5-HT) receptor agonist 5-methoxy-N, N-dimethyl-tryptamine (5MeODMT 0.4mg/kg) resulted in a potentiation of the increase in amplitude and duration of response, compared to when the drugs were given singly. These results are discussed in the context of possible interactions between 5-HT and TRH systems.

Differential effects of reserpine and 6-hydroxydopamine on neuropeptide Y (NPY) and noradrenaline in peripheral neurons

The effects of 6-hydroxydopamine (6-OHDA) and reserpine pretreatment on peripheral neuropeptide Y (NPY)- and noradrenaline (NA)-containing neurons were studied in guinea-pigs. Ten days after 6-OHDA pretreatment, a 60-80% reduction of the NA content was observed in the right atrium of the heart, stellate ganglion and spleen. The content of NPY-like immunoreactivity (LI) was reduced by about 50% in the heart, not changed in the spleen while it increased to 200% of control in the stellate ganglion. Immunohistochemistry showed a pronounced loss of NPY- and tyrosinehydroxylase (TH)-immunoreactive (IR) nerves in the heart but not in the spleen. Increased NPY-IR was seen in axons and cell bodies of the stellate ganglion. Reserpine pretreatment (thereshold dose 0.5 mg X kg-1) caused a dose- and time-dependent reduction of the content of NPY-LI in the heart. A maximal depletion of NPY-LI (about 80%) was observed 5 days after reserpine. Reserpine pretreatment also reduced the content of NPY-LI in the spleen, while no significant change was observed in the adrenal gland or vas deferens. The levels of NPY-LI increased in the stellate ganglion to about 180% of control 5 days after reserpine. Immunohistochemical analysis revealed an almost total loss of NPY-IR nerve fibres in the heart as well as around blood vessels in the lung and skeletal muscle. No detectable changes were observed in perivascular NPY-IR nerves in the spleen, vas deferens or kidney. TH-IR nerves remained unchanged after reserpine, thus indicating that the observed loss of NPY-IR nerves was due to a depletion of NPY and not a degeneration. No change in the levels of substance P-LI was observed in the right atrium 5 days after reserpine. NA was, in contrast to NPY, markedly depleted in all tissues investigated after reserpine treatment. The depletion of NA was more extensive, and occurred more rapidly and at much lower doses as compared to the effects on NPY-LI. Ligations of the sciatic nerve revealed that NPY-LI was transported axonally with a rapid rate (3 mm/h). Reserpine pretreatment significantly increased the amount of accumulated NPY-IR above the ligation, suggesting an increase in axonal transport. High performance liquid chromatography revealed that the NPY-LI consisted of two major peaks in the stellate ganglia, while only one peak closely corresponding to porcine NPY was seen in the right atrium. In conclusion, 6-OHDA pretreatment depletes NPY-LI in certain terminal regions and increases NPY-LI in ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)

A pivotal role for serotonin (5HT) in the regulation of beta adrenoceptors by antidepressants: reversibility of the action parachlorophenylalanine by 5-hydroxytroptophan

An acute reduction in the synaptic availability of serotonin (5HT) by p-chlorophenylalanine (PCPA) nullifies the decrease in the density of cortical beta adrenoceptors caused by desipramine (DMI) but does not appreciably alter the attenuation of the norepinephrine (NE) sensitive adenylate cyclase. The analysis of competition-binding curves of [3H]-dihydroalprenolol shows that the affinity of the agonist (-)-isoproterenol for cortical beta adrenoceptors is profoundly reduced following PCPA. This reduction in agonist affinity is enhanced by DMI. Resupplying 5HT by by-passing tryptophan hydroxylase inhibition, by administering 5-hydroxytryptophan, converts a DMI non-responsive to a DMI responsive beta adrenoceptor population and shifts the markedly decreased agonist affinity towards the affinity values found in control preparations. The results demonstrate the pivotal role of 5HT in the regulation of the density and agonist affinity characteristics of cortical beta adrenoceptors and contribute to the scientific basis of the 'serotonin-norepinephrine link hypothesis' of affective disorders.

LSD but not methysergide reduces the inhibitory effect of the medullary raphe stimulation on the spinal reflex in rats

Conditioning stimulation of the nucleus raphe in the rat medulla enhanced the monosynaptic reflex (MSR) and depressed the polysynaptic reflex (PSR) in separate time courses. The PSR decreasing effect was reduced in preparations pretreated with reserpine, PCPA, or 5,6-DHT. The MSR increasing effect was not altered by these three pretreatments. Intravenously administered LSD but not methysergide reduced the PSR decreasing effect with no influence on the MSR increasing effect. These two drugs had similar effects on the unconditioned responses; the MSR was decreased and the PSR was increased. Thus, the PSR decreasing effect seems to be mediated via a serotonergic pathway probably descending from the nucleus raphe.

Comparative effects of neonatal hypothyroidism and euthyroidism on TRH and substance P content of lumbar spinal cord in saline and PCPA-treated rats

The effects of neonatal thyroidectomy and thyroid hormone replacement therapy on the content of substance P and TRH in the lumbar segment of the rat spinal cord were studied. The peptide content of discrete spinal cord regions removed by punches of frozen serial slices was measured by RIA. Animals receiving T4 replacement therapy were indistinguishable from normal littermates. In hypothyroid animals without PCPA-treatment, levels of TRH and substance P were significantly increased by 100% in the ventral and the dorsal lumbar spinal cord, respectively. Inhibition of serotonin biosynthesis by PCPA increased by 90% the substance P content in the dorsal horn of euthyroid rats and abolished completely the stimulatory effect of hypothyroidism on the TRH content of the ventral horn. These findings suggest the existence of a physiological relationship between substance P and TRH with the serotoninergic system in the rat spinal cord and that thyroid hormone is implicated in the normal development of the peptide-containing neurons in the rat spinal cord.

Biochemical and autoradiographic studies of TRH receptors in sections of rabbit spinal cord

Receptors for thyrotropin-releasing hormone (pGlu-His-Pro-NH2, TRH) on thaw-mounted sections of rabbit spinal cord have been identified biochemically and visualized by light microscopic autoradiography. Binding of [3H] [3-Me-His2]TRH to 20 microns sections exhibited high apparent affinity and a pharmacological specificity almost identical to that previously demonstrated for spinal TRH receptors in membranes. In autoradiograms, the highest density of TRH receptors appeared in the substantia gelatinosa of the dorsal gray and around the central canal, with intermediate levels in the ventral gray.