Identification and quantitative measurements of biogenic monoamines in the central nervous tissue of some gastropods

Investigations were carried out to determine levels of biogenic monoamines in the central nervous tissue of seven species of terrestrial gastropods (taxonomic family: Helicidae) using high-performance liquid chromatography (HPLC) with electrochemical detection (ELCD). The central nervous tissue of all species examined contained assayable amounts of dopamine (DA) and serotonin (5-HT). Noradrenaline (NA) was occasionally present; adrenaline (A) could not be detected. The central ganglia of two Mediterranean species generally contain 3-4 times more 5-HT relative to DA than the ganglia of the other species which contain amounts of 5-HT only slightly higher than DA.     

Modulation of swimming activity in the medicinal leech by serotonin and octopamine

1. The monoamines serotonin (5-HT) and octopamine (OA) enhance the expression of swimming activity in the medicinal leech (Willard, 1981; Belanger and Orchard, 1988). We explored further the effects of these monoamines and related agents on swimming activity observed in isolated leech nerve cords. 2. We confirmed that swimming activity is induced reversibly following exposure of the nerve cord to 5-HT (50 microM); the half-maximal rate of swimming activity develops in about 15 min. Swimming activity returns to control levels about 30 min after drug washout. 3. Swim-induction by 5-HT is blocked by the presence of 10 microM cyproheptadine (a 5-HT antagonist). 4. Although apparently less effective than 5-HT, OA application to nerve cords also induced swimming activity. 5. Depletion of endogenous amines from nerve cords by acute exposure to reserpine (10-150 microM) blocked stimulus-evoked swimming activity within 4 hr. 6. Subsequent application of 5-HT (50 microM) or OA (100 microM) reinstated stimulus-evoked swimming and induced repeated episodes of non-triggered swimming activity. 7. Application of cAMP and cAMP analogs, as well as phosphodiesterase inhibitors (theophylline and IBMX), mimicked the effects of the monoamines, suggesting that 5-HT and OA may activate swimming activity by increasing neuronal cAMP. 8. We obtained episodes of swim-like activity from individual, isolated ganglia exposed to 5-HT or OA. Such episodes were usually brief, with variable cycle period. 9. We conclude that individual nerve cord ganglia contain the complete neuronal circuitry required to generate the rudiments of swimming activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of steroid hormones on serotonin,norepinephrine and epinephrine contents in the pineal-paraphyseal complex of the soft-shelled turtle (Lissemys punctata punctata)

Summary Steroids (testosterone, oestrogen, progesterone, corticosterone, dexamethasone and deoxycorticosterone) were administered intramuscularly (0.1 mg · 100 g bw^-1) on seven consecutive days to juvenile male soft-shelled turtles. Serotonin, norepinephrine and epinephrine contents of the pineal-paraphyseal complex were measured spectrofluorometrically 24 h after the last injection. Testosterone and oestrogen decreased serotonin, norepinephrine and epinephrine levels. Progesterone treatment resulted in an increase of serotonin level and a fall in norepinephrine and epinephrine levels. Corticosterone treatment caused an increase of serotonin level and a decrease of norepinephrine and epinephrine levels. Dexamethasone failed to alter serotonin content, increased norepinephrine and decreased epinephrine levels. Deoxycorticosterone decreased serotonin and elevated epinephrine content.Abbreviations 5-HIAA 5-hydroxyindole-acetic acid - 5-MTOH 5-methoxytryptophol - ANOVA analysis of variance; bw body weight - COMT catecholamine-o-methyl transferase - E epinephrine - HIOMT hydroxyindole-o-methyl transferase - MAO monoamine oxidase - MS mean sum of squares - NAT N-acetyltransferase - NE norepinephrine - SR synaptic ribbon - SS sum of squares - SV source of variation     

Patterns of serotonin-immunoreactive neurons in the central nervous system of the earthworm Lumbricus terrestris L.

Summary The distribution patterns of serotonin-immunoreactive somata in the cerebral and subpharyngeal ganglion, and in the head and tail ganglia of the nerve cord of Lumbricus terrestris are described from whole-mount preparations. A small number of serotonin-immunoreactive neurons occurs in the cerebral ganglion, in contrast to the large population of serotonin-immunoreactive neurons that exists in all parts of the ventral nerve cord. From the arrangement of serotonin-immunoreactive somata in the subpharyngeal ganglion, we suggest that this ganglion arises from the fusion of two primordial ganglia. In head and tail ganglia, the distribution of serotonin-immunoreactive somata resembles that in midbody segments. Segmental variations in the pattern and number of serotonin-immunoreactive somata in the different body regions are discussed on the background of known developmental mechanisms that result in metameric neuronal populations in annelids and arthropods.Abbreviations CG1, CG2 cerebral soma group 1, 2 - CNS central nervous system - GINs giant interneurons - 5-HT 5-hydroxytryptamine, serotonin - 5-HTi 5-HT-immunoreactive - N side nerve - SG19 subpharyngeal soma group 1–9 - SN segmental nerve     

Biogenic monoamine levels in the central nervous system of the sea hare,Aplysia kurodai

1. By using a three-dimensional-coulometric HPLC system, biogenic monoamines and their metabolites were quantified simultaneously in the central nervous system of the sea hare, Aplysia kurodai.2. Precursor amino acids, tyrosine-4 (TYR-4) and tryptophan (TRP), and dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxytryptamine (5-HT) were detected in all the ganglia examined.3. Levels of these compounds in the cerebral, pedal and parieto-visceral ganglia were higher than those of the other ganglia examined.4. In some ganglia, epinephrine (E), 3-O-methyldopa (30MD), 3-methoxytyramine (3-MT), dihydroxyphenylethleneglycol (DOPEG), metanephrine (MN), vanillic acid (VA), octopamine (OCT), kynurenine (KYN) and 5-hydroxyindoleacetic acid (5-HIAA) were also detected.5. The main metabolic pathways of biogenic monoamines were shown to be TYR-4DADOPAC and TRP5-HT5-HIAA. Furthermore, following five pathways were also suggested to be present; TYR-4DAEMNVA, TYR-4TYRAOCT, TYR-43OMD, DA3-MT. EDOPEG and TRPKYN.     

Pharmacological Evidence for the Modulation of Monoamine Release by Adenosine in the Invertebrate Nervous System

An in vitro preparation from the pedal ganglia of the marine bivalve, Mytilus edulis, was used to examine the modulation of transmitter release by adenosine and its analogs from invertebrate nervous tissue. The ganglia of this organism contain the monoamines dopamine (DA), serotonin (5-HT), and norepinephrine (NE), and the presynaptic release of these substances is known to be calcium-dependent. This organism also contains a DA-sensitive adenylate cyclase system which resembles that seen in mammals. Neural tissue from the pedal ganglia was incubated with labeled monoamines, and release studies were then conducted in superfusion chambers; release of monoamines was evoked by the addition of 50 mM KCl. Addition to the superfusion medium of the adenosine analog, 5'-N-ethylcarboxamidoadenosine (NECA; 10 nM), inhibited the release of 5-HT and DA, and to a lesser extent NE, whereas 100-fold higher concentrations of adenosine itself and the adenosine analog, R-N6-phenylisopropyladenosine, were required to achieve comparable levels of inhibition. The inhibitory effects of NECA on neurotransmitter release were blocked by the adenosine receptor antagonist, theophylline (IC50 = 10-14 microM). The results from this study indicate for the first time the possible role of adenosine as a modulator of neurotransmitter release in the invertebrate nervous system.     

The nervous system of the tube-worm Chaetopterus variopedatus (Polychaeta)

Silver impregnation of serial histological sections of the tubeworm Chaetopterus variopedatus revealed the presence of a subepidermal nervous system. The anterior nervous system is delimited by the first 11 segments and comprises (1) two dorsolateral cerebral ganglia and lateral instead of ventral nerve cords which are widely separated and thus connected by unusually long commissures, (2) a pharyngeal ganglion in the fourth segment which is connected to the cerebral ganglia by pharyngeal nerves and constitutes along with the pharyngeal plexus a stomatogastric or enteric nervous system, and (3) small, presumably segmental ganglionic swellings along the lateral nerve cords from which emerge commissures and parapodial nerves. No subesophageal ganglion or periesophageal connective could be identified. The lateral nerve cords converge toward the midline in the 12th segment to form the posterior nervous system comprising a pair of ventromedian nerve cords with their repetitive segmental ganglia from which emerge numerous short commissures and three segmental nerves coursing toward the dorsal and ventral regions of parapods and toward the neuropod. Light and electron microscopic investigations of cerebral and segmental ganglia showed an arrangement of inner neuropile and of unipolar neuron somata at the periphery. The neuropile comprises numerous neurites ranging in diameter from 0.5 to 10 μm and making polarized or symmetrical synaptic junctions with each other. The pharyngeal ganglion consists of a similar neuropile and of a large mass of cell bodies which is traversed by an elaborate network of sinuses and harbors three types of neurosecretory cells in addition to the conventional neuron somata. These findings are interpreted in the framework of the highly specialized morphological features and habits of Chaetopterus, and the welldeveloped stomatogastric system is considered to be related to control of the feeding activities.     

Distribution of dopamine and octopamine in the central nervous system and ovary during the ovarian maturation cycle of the giant freshwater prawn, Macrobrachium rosenbergii

Dopamine (DA), octopamine (OA) and serotonin (5-HT) are the key neurotransmitters that control gonadal development in decapod crustaceans. 5-HT stimulates, while DA and OA delay gonadal development in Macrobrachium rosenbergii. In the present study, we have further investigated the distribution patterns of DA and OA in the central nervous system (CNS) and ovary during various stages of the ovarian maturation cycle of this giant freshwater prawn. DA- and OA-immunoreactive neurons and fibers were distributed extensively in several regions of the brain, subesophageal ganglion (SEG), thoracic ganglia and abdominal ganglia. In the brain, the two neurotransmitters were present in neurons of clusters 6, 7, 11, 17, and nearby neuropil regions. In the SEG, thoracic ganglia and abdominal ganglia, immunoreactive neurons and fibers were found along the midline and in several neuronal clusters around each neuropil region. Staining for DA and OA was more intense in the thoracic ganglia than in other parts of the CNS. In the ovary, DA- and OA-immunoreactivities were present at high intensity in early oocytes. The presence of DA- and OA-immunoreactivities in neural ganglia as well as ovary suggests that DA and OA may also be involved in the reproductive process, particularly ovarian development and differentiation of oocytes in this species.     

Aminergic neurons in the anterior nervous system of the rat acanthocephalan moniliformis dubius

The cerebral ganglion and nerve tracts of Moniliformis dubius show intense, specific, green fluorescence that is also associated with the lateral and apical sensory bulbs. Radioenzymatic assays showed that high levels of dopamine were present but only small amounts of the catecholamines norepinephrine and epinephrine were identified. Incubations of the proboscis sac in dilute solutions of dopamine increased fluorescence while incubations in reserpine resulted in loss of fluorescence. Nonfluorogenic amine octopamine was also detected radioenzymatically. Neutral red vitally stained a number of cells in the cerebral ganglion and the nerve tracts extending from the ganglion. Electron microscopy showed that many neurons contained electron-dense vesicles. The close association of the fluorescing, amine-containing nerve tracts with the sensory bulbs suggests that they may play a functional role in sensory reception and transmission in M. dubius. This is the first report on the presence of biogenic amines in the Acanthocephala.     

Immunohistochemical localization of serotonin,leu-enkephalin,tyrosine hydroxylase,and substance P within the visceral sensory area of cartilaginous fish

Summary We examined the distribution of immunoreactivity to serotonin (5-HT), leu-enkephalin (LENK), tyrosine-hydroxylase (TH), and substance P (SP) within the primary visceral sensory region of cartilaginous fish. Two genera of sharks, Squalus and Heterodontus, a skate, Raja, a ray, Myliobatis, and a holocephalian, Hydrolagus, were used. Cranial nerves, VII, IX, and X enter the visceral sensory complex from the lateral aspect and divide it into lobes. Based on sagittally cut sections, there are four lobes in Hydrolagus and five in Squalus, corresponding to the number of gill arches. The neurochemicals are differentially distributed within each lobe. LENK+ and 5-HT+fibers are located in all regions within the visceral sensory complex. SP+fibers are extremely dense in a dorsolateral subdivision and do not extend as far ventrally as 5-HT+ and LENK+fibers. The lobes lack 5-HT+cells, but contain a few LENK+ and SP+cells. Many TH+cells are distributed in dorsomedial portions of the complex, but there are few TH+fibers. Thus, the visceral sensory area of cartilaginous fish contains several divisions that can be distinguished by their neurochemical content.     

The serotoninergic system in Cryptomphalus aspersa. Immunocytochemical study with an anti-5-HT antiserum

This immunocytochemical study of 5-HT neurons and fibers in the nervous system of C. aspersa corroborate previous findings and describe new 5-HT neurons and their connections, mainly between the central nervous system and the tentacular sensory organs. We found a number of networks, fascicles, and neurons that show constant and symmetrical location. Three networks were found at the tip of the posterior tentacle: underlying the olfactory epithelium, in the neuropil of the tentacular ganglion (TG), and in the ocular capsule. The TG also contains a ventral 5-HT fascicle. A group of 30-40 serotoninergic fibers run through the tentacular connective from the postcerebrum to the tentacular ganglion. This 5-HT fascicle has a lateral position in the postcerebrum (lateral fascicle of the postcerebrum) and a subcortical location in the procerebrum (subcortical fascicle of the procerebrum). The optic nerve also has a small group of 5-HT fibers. Seven serotoninergic neurons were found in each cerebral ganglion: two giant neurons, one medium-sized, and four small neurons. Three different types of fascicles are in the postcerebrum: fascicles proceeding from the suboesophageal connectives, a lateral fascicle, and a commisural fascicle. Each cerebral ganglion region (pro-, meso- and postcerebrum) has a 5-HT network with a particular pattern of distribution and morphology. The suboesophageal ganglia show the highest concentration of 5-HT neurons (large, medium-sized, and small neurons).     

Monoamines and their metabolites in somatosensory,visual, and cingulate cortices of adult rat: Differences in content and lack of sidedness

Small areas of somatosensory, visual and cingulate cortex were microdissected and assayed for their monoamine content by high-performance liquid chromatography with electrochemical detection. No differences were found between the right and the left hemisphere for any area nor for any of the monoamines. The values averaged from left and right hemispheres for the sensory areas were significantly different from the cingulate in the content of norepinephrine, 4-hydroxy-3-methoxyphenylglycol, dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 5-hydroxyl-tryptophan, serotonin and 5-hydroxyindole-3-acetic acid. The two sensory cortices differed in their levels of norepinephrine, dopamine, 3–4-dihydroxyphenylacetic acid and homovanillic acid. In the latter comparison, the measured amounts were higher in somatosensory than in visual cortex. This biochemical heterogeneity in monoamine distribution may reflect specific innervation patterns for these compounds in these discrete cortical areas and allows differences in content to be related to functional specialization of the cerebral cortex.     

两种软体动物神经系统一氧化氮合酶的组织化学定位

运用一氧化氮合酶(NOS)组织化学方法研究了软体动物门双壳纲种类中国蛤蜊和腹足纲种类嫁Qi神经系统中NOS阳性细胞以及阳性纤维的分布。结果表明：在蛤蜊脑神经节腹内侧,每侧约有10-15个细胞呈强NOS阳性反应,其突起也呈强阳性反应,并经脑足神经节进入足神经节的中央纤维网中;足神经节内只有2个细胞呈弱阳性反应,其突起较短,进入足神经节中央纤维网中,但足神经节中,来自脑神经节阳性细胞和外周神经系统的纤维大多呈NOS阳性反应;脏神经节的前内侧部和后外侧部各有一个阳性细胞团,其突起分别进入后闭壳肌水管后外套膜神经和脑脏神经索。脏神经节背侧小细胞层以及联系两侧小细胞层的纤维也呈NOS阳性反应。嫁Qi中枢神经系统各神经节中没有发现NOS阳性胞体存在;脑神经节、足神经节、侧神经节以及脑—侧、脑—足、侧—脏连索中均有反应程度不同的NOS阳性纤维,这些纤维均源于外周神经。与已研究的软体动物比较,嫁Qi和前鳃亚纲其它种类一样,神经系统中NO作为信息分子可能主要存在于感觉神经。而中国蛤蜊的神经系统中一氧化氮作为信息分子则可能参与更广泛的神经调节过程。     

Extracellular Hypothalamic Monoamines Measured by In Vivo Microdialysis in a Rat Model of Dietary Fat-Induced Obesity

We tested two hypotheses about monoamine neurotransmitters in two strains of rats that differ in their sensitivity to obesity when eating a high-fat diet; 1) that the concentrations of norepinephrine and serotonin and of their metabolites differ in the extracellular fluid of tlie ventromedial hypothalamus of conscious, unrestrained Osborne-Mendel and S 5B/PI rats, and 2) that these monoamines are altered differently between strains by a high-fat diet. The monoamines were measured by HPLC in dialysate collected by in vivo microdialysis in rats eating a semisyntlietic low-fat diet (10% of kcal as fat) and again after either two or seven days of eating a high-fat diet (56 % of kcal as fat). Norepinephrine, serotonin (5-HT), and 5-hydroxyindole-3-acetic acid (5-HIAA) were lower in Osborne-Mendel rats than in S 5BR1 rats eating the low-fat diet. Norepinephrine and serotonin both increased in Osborne-Mendel rats with the onset of tlie high-fat diet so that Osborne-Mendel and S 5B/PI rats no longer differed in these neurotransmitters. By day 7 of high-fat feeding, the concentrations of 3-methoxy-4-hydroxyplienylglycol (MHPG), 5-HIAA and the 5-HIAA/5-HT ratio rose in both strains. Ambient extracellular monoamines in the medial hypothalamus are lower in Osborne-Mendel rats than in S 5B/PI rats and the response of these catecholamines to dietary fat was greater in Osborne-Mendel rats than in S 5B/PI rats.     

Structure of the nervous system of Myzostoma cirriferum (Annelida) as revealed by immunohistochemistry and cLSM analyses

The nervous systems of juvenile and adult Myzostoma cirriferum Leuckart, 1836, were stained with antisera against 5-HT (5-hydroxytryptamine, serotonin), FMRFamide, and acetylated alpha-tubulin in combination with the indirect fluorescence technique and analyzed by confocal laser scanning microscopy. The central nervous system consists of two small cerebral ganglia, connected by a dorsal commissure, a ventral nerve mass, and a pair of long circumesophageal connectives joining the former to the latter. The two neuropil cords within the ventral nerve mass curve outward and are joined to one another anteriorly and posteriorly. They are connected by 12 commissures, forming a ladder-like system. A single median nerve runs along the midventral axis. In addition to the circumesophageal connectives, 11 peripheral nerves arise from each main cord. The first innervates the anterior body region. The others form five groups of two nerves each, the first and thicker nerve of which is the parapodial nerve, innervating the parapodium and two corresponding cirri. Except for those in the most posterior group, the second nerves innervate the lateral organs and the body periphery. Serotonergic perikarya are arranged in six more or less distinct clusters, the first lying in front of and the other five between the main nerve cords. The distribution pattern of the FMRFamidergic perikarya is less clear and the somata lie between and outside the cords. One pair of dorsolateral longitudinal nerves was visualized by tubulin staining. Peripheral nerves and the commissures, in particular, demonstrate a segmental organization of the nervous system of M. cirriferum. Furthermore, their arrangement indicates that the body consists of six segments, the first of which is identifiable only by the first pair of peripheral nerves, the first two commissures, and the anteriormost ventral ganglion. The nervous system M. cirriferum thus exhibits several structures also found in the basic plan of the polychaete nervous system.     

THE EFFECT OF AMINO-OXYACETIC ACID ON BRAIN CATECHOLAMINES

Abstract— —Administration of amino-oxyacetic acid (AOAA) to rats induced a pronounced decrease of midbrain norepinephrine (NE) and adrenal epinephrine (E) after 30 min, at which time the GABA level of midbrain had increased to 117 per cent of the initial value. The concentrations of NE in the pons-medulla and of dopamine (DA) in the cerebral hemispheres were not changed.
Further increases in brain GABA were accompanied by a rise of NE in midbrain and pons-medulla beginning 1 hr after AOAA administration. A rise of cerebral DA level was observed only after 4 hr. Six hours after AOAA administration the levels of both NE and DA in brain were reduced.
From the results of these and other studies, where administration of small amounts of GABA were shown to affect brain NE and serotonin levels, it is suggested that monoamines may be involved in the physiological action of GABA in the brain.     

Effects of octopamine, dopamine, and serotonin on production of flight motor output by thoracic ganglia of Manduca sexta

Effects of biogenic amines on a centrally generated motor pattern in Manduca sexta were examined by pressure injecting nanomole to micromole amounts of octopamine, dopamine or serotonin into thoracic ganglia. Motor output was recorded extracellularly from a pair of antagonistic flight muscles and their motor neurons. The monoamines were found to alter production of a motor pattern that produces rhythmic wing flapping (10 Hz) and exhibits phase relationships similar to those in the flight pattern of intact moths. In mesothoracic ganglia with sensory nerves intact, octopamine (4 X 10(-9) mol) injected into lateral regions evoked regular firing of a single motor neuron, whereas a higher dose (4 X 10(-8) mol) often elicited the flight motor pattern. In the absence of sensory input, these doses of octopamine had little effect. Low doses (10(-10) mol) greatly enhanced motor responses to electrical stimulation of a wing sensory nerve. Dopamine (2 X 10(-10) mol) injected into the medial region of the mesothoracic ganglion elicited the flight motor pattern in the presence or absence of sensory input. Rhythmic output induced by dopamine (5 X 10(-10) mol) was suppressed by injecting serotonin (5 X 10(-10) mol) into the same region. These findings demonstrate that dopamine, octopamine, and serotonin have different effects on motor output in Manduca and suggest that these amines are involved in initiating, maintaining and terminating flight behavior, respectively. Octopamine may elicit flight production by enhancing the efficacy of sensory transmission thereby increasing excitability or arousal. Dopamine may act on interneurons involved in generating the flight motor pattern.     

Polyunsaturated fatty acids (PUFA) regulate neurotransmitter contents in rat brain

The effects of feeding of 6-propylthiouracil (6-PTU) and polyunsaturated fatty acids (PUFA) independently and in combination and administration (ip) of a single dose of triiodothyronine (T3) (2.5 microg/100 g body wt) along with feeding of 6-PTU and PUFA were studied in rat brain. Dopamine (DA), 5-hydroxytryptophan (5-HTP), serotonin (5-HT), 5-hydroxy indole acetic acid (5-HIAA), norepinephrine (NE) and epinephrine (EPI) contents were assayed in the hypothalamus and cerebral cortex regions. It was found that 6-PTU feeding resulted in decrease in dopamine, 5-HT, 5-HTP and 5-HIAA in both regions. In animals fed with PUFA followed by administration of T3, the DA level was found normal.     

Immunohistochemical demonstration of serotonin-containing nerve fibers in the cerebellum

Summary The localization of serotonin (5-HT)-immunoreactive nerve fibers in the cerebellum of the rat and cat was investigated by means of the peroxidase-anti-peroxidase (PAP) method using highly specific antibodies to 5-HT.Serotonin-containing nerve fibers were distributed throughout the entire cerebellum including the deep cerebellar nuclei, while 5-HT-positive neuronal somata were not detected in the cerebellum of either species. A different pattern of 5-HT innervation was found among the three layers of the cerebellar cortex. There were also interspecific differences in the pattern of distribution of 5-HT. In the rat, the pool of 5-HT nerve fibers mainly consisted of tangential elements, which were predominant in the molecular layer, while in the cat only a few 5-HT fibers were found in the molecular layer of the cerebellar cortex; dense networks of 5-HT nerve fibers were present in the granular layer. Some differences are evident in the pattern of distribution of 5-HT fibers in cerebellar regions classified on an anatomical and functional basis.This work was supported by a grant (No. 56440022) from the Ministry of Education, Science and Culture, Japan     

Microiontophoresis of 5-hydroxytryptamine, epinephrine, and prostaglandin E1 on spinal neurons in the frog.

5-Hydroxytryptamine (5-HT) and epinephrine were applied by microiontophoresis to single neurons in the isolated spinal cord of the frog. 5-HT depressed all but two of the responsive cells, whereas the response to epinephrine consisted exclusively of depression. 5-HT action was more marked than that of epinephrine on most cells. With either compound, responseve units were diffusely distributed throughout the tissue. While it was proven that prostaglandin E1 (PGE1) exerts a direct excitatory action on spinal neurons, no evidence of an antagonism between PGE1 and the monoamines was obtained. These findings provide additional support to the hypothesis that 5-HT and epinephrine are transmitters in the frog spinal cord. The possibility that PGE1 may 'modulate' the responsiveness of spinal neurons to the monoamines was not confirmed.