Selective Depletion of Dopamine, Octopamine, and 5-Hydroxytryptamine in the Nervous Tissue of the Cockroach (Periplaneta americana)

High-performance liquid chromatography with electrochemical detection was used to measure the concentrations of 3,4-dihydroxyphenylethylamine (dopamine), 5-hydroxytryptamine (5-HT), p-hydroxyphenylethanolamine (octopamine), alpha-methyl-p-tyrosine, and tryptophan in the cerebral ganglia of cockroaches (Periplaneta americana) after peripheral administration of alpha-methyl-p-tyrosine and alpha-methyltryptophan. In addition, the levels of dopamine, 5-HT, octopamine, alpha-methyl-p-tyrosine, and tryptophan were determined after injection of alpha-methyl-p-tyrosine, 6-hydroxydopamine, or 5,7-dihydroxytryptamine directly into the cerebral ganglia by means of microinjection needles. Peripheral administration of alpha-methyl-p-tyrosine (400-1,600 micrograms/insect) caused a reduction in dopamine and 5-HT concentrations in cockroach cerebral ganglia, although the reduction in dopamine concentrations was more pronounced. Peripheral injections of alpha-methyl-p-tyrosine also reduced octopamine levels in the cerebral ganglia. Peripheral injection of alpha-methyltryptophan (400-1,600 micrograms/insect) caused a marked reduction in 5-HT and tryptophan concentrations in cockroach cerebral ganglia without altering dopamine or octopamine concentrations. Central injections of alpha-methyl-p-tyrosine (80 micrograms/insect) reduced dopamine concentrations in the cerebral ganglia. However, neither 6-hydroxydopamine (20 micrograms/insect) nor 5,7-dihydroxytryptamine (20 micrograms/insect) caused reductions in amine levels when applied near or directly into the cerebral ganglia. The results suggest that specific lesions of aminergic neurons in insects by either 6-hydroxydopamine or 5,7-dihydroxytryptamine are impractical. The specific, long-lasting depletion of 5-HT by alpha-methyltryptophan suggests that this chemical may be useful in elucidating the functions of 5-HT in insects.     

Effect of Intranigral Administration of 6-Hydroxydopamine and 5, 7-Dihydroxytryptamine on Rat Brain Tryptamine

Earlier experiments have shown that unilateral electrolytic lesions of the substantia nigra result in significant reductions in the rate of accumulation of rat striatal tryptamine. For elucidation of the type of neuronal degeneration that is associated with tryptamine depletion, the effects of intranigral injections of 6-hydroxydopamine or 5,7-dihydroxytryptamine, which would affect, respectively, dopamine- or indoleamine-containing neurons, have been assessed. Nigral 6-hydroxydopamine lesions resulted in an ipsilateral reduction in the rate of accumulation of striatal tryptamine, but no changes were observed after nigral injections of 5,7-dihydroxytryptamine. The present results suggest that decreases in the pargyline-induced accumulation of striatal tryptamine may be associated with lesions of the nigral dopamine-containing cell bodies. Alternatively, there may exist specific tryptamine-containing neurons that are damaged by 6-hydroxytryptamine and unaffected by 5,7-dihydroxytryptamine.     

Effect of intracerebroventricular injection of 6-hydroxydopamine and 5,6-dyhydroxytryptamine on the phasic secretion of luteinizing hormone (author's transl)]

In ovariectomized rats carrying an estradiol sylastic implant the effect of the intraventricular administration of the serotonin neurotoxin 5,6-dihydroxytryptamine and of the norepinephrine neurotoxin 6-hydroxydopamine on the circadian secretion of the luteinizing hormone (LH) was studied. The decrease of 5-HT after injection of 5,6-dihydroxytryptamine reduced the a.m. and p.m. values and suppressed the phasic rhythm of LH. The diminution of noradrenaline after administration of 6-hydroxydopamine increased the a.m. and did not alter the p.m. values, resulting in a partial abolition of the rhythm.     

The mechanism of action of neurocytotoxic compounds

In 1967 Tranzer and Thoenen (1,2) recognized that 6-hydroxydopamine has the capacity for selectively destroying adrenergic nerve terminals. Two hydroxyserotonin isomers have a similar effect on the serotonin-containing neurons (3,4,5,6). Since the discoveries of these phenomena, 6-hydroxydopamine and 5,6 and 5,7-dihydroxytryptamine have become valuable pharmacological tools in the selective degeneration of noradrenergic and respectively serotonergic nerve terminals. In low doses, 6-hydroxydopamine is taken up into adrenergic nerve terminals without producing any detectable damage, acting as a false neurotransmitter. The administration of large doses of 6-hydroxydopamine results in very long-lasting sympathomimetic effects which are accompanied by a gradual deterioration of various specific functions of the neuronal membrane of the adrenergic nerve terminal (7,8,9). Repeated administration of high doses of 6-hydroxydopamine leads to an extensive destruction of adrenergic nerve terminals in all species studied so far (10). In general, the cell bodies of adrenergic neurons seem to be very resistant to the destructive effect of 6-hydroxydopamine compared to the nerve terminals. The two dihydroxylated indoleamines, 5,6-dihydroxytryptamine and 5,7-dihydroxytryptamine, produce long-lasting depletions in brain serotonin (3,11,12). Biochemical and morphological evidence suggests that these severe reductions of serotonin level are the result of degeneration of the axons and terminals of central serotonin containing neurons (13,14,15). These neurocytotoxic agents exhibit many pharmacological and biochemical properties which are beyond the scope of this short review which aims to cover only the various approaches reported in the literature dealing with the mechanism of action of above compounds.     

The stimulation of 6-hydroxydopamine autoxidation by bivalent copper: Potential importance in the neurotoxic process

Copper sulfate (Cu²⁺, 10^?6M to 10^?5M) stimulated the rate of autoxidation of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) as judged both by absorbancy measurements at 490 nm and oxygen consumption. This stimulation of 6-OHDA autoxidation by Cu²⁺ was prevented by the copper chelating agent EDTA. In other experiments, Cu²⁺ stimulated the rates of autoxidation of dopamine and norepinephrine as well as the neurotoxic agents 6-aminodopamine, 5,6-dihydroxytryptamine and 5,7-dihydroxytryptamine. It is suggested that intraneuronal levels of copper, by virtue of controlling the rates of autoxidation reactions, might be important in vivo.     

Selective Neurotoxic Lesions of Descending Serotonergic and Noradrenergic Pathways in the Rat

The ability of neurotoxic substances to induce selective lesions of the descending monoaminergic pathways in rats was investigated. Saline, 6-hydroxydopamine, 5,6-dihydroxytryptamine, or 5,7-dihydroxytryptamine were administered into the lumbar subarachnoid space through a chronically indwelling catheter. The lesions were evaluated 2-3 weeks later by in vitro uptake of [3H]noradrenaline and [14C]5-hydroxytryptamine into synaptosomal preparations from the frontal cortex, brainstem, cervical spinal cord, and lumbar spinal cord of each animal. There was no difference in uptake between saline-injected and noncatheterized controls and no significant changes in cortical uptake after any of the treatments (dose range of neurotoxins: 0.6-80 micrograms). In the lumbar spinal cord, 6-hydroxydopamine (5-80 micrograms) reduced the [3H]noradrenaline uptake by approximately 90% with no effects on [14C]5-hydroxytryptamine uptake, whereas 5,6-dihydroxytryptamine reduced the uptake of [14C]5-hydroxytryptamine by 90% (20-80 micrograms). [3H]Noradrenaline uptake was unaffected by lower doses of 5,6-dihydroxytryptamine but fell by 45-55% after 40-80 micrograms. 5,7-Dihydroxytryptamine (10-80 micrograms) reduced [3H]noradrenaline uptake by 90-95% and [14C]5-hydroxytryptamine uptake by approximately 80% (5-80 micrograms) in the lumbar cord. It is concluded that intrathecal administration of suitable doses of neurotoxins may produce extensive selective lesions of descending noradrenergic and serotonergic pathways.     

Monoamine precursor uptake in ganglia of a mollusc Anodonta cygnea L. (Bivalvia)

Summary In vitro-uptake and localization of ³H-5-hydroxytryptophan and ³H-dihydroxyphenylalanine have been investigated by means of light microscopic autoradiography in the central nervous system of the freshwater mussel, Anodonta cygnea L. Accumulation of the labelled monoamine precursors could be observed both over neuronal perikarya and neuropil in the ganglia. ³H-5-hydroxytryptophan and ³H-dihydroxyphenylalanine were taken up by neurons characterized by a small size (10–20 m), a polygonal form and an intense staining with toluidine blue. Labelled axon branches situated either in the neuropil or between nerve cells in the cortex exhibited only a moderate activity, frequently of a diffuse character.After pretreatment for 24 h with colchicine, silver grains were also seen over the neuronal perikarya and some axon profiles. This shows that local uptake of the monoamine precursors and, presumably, the synthesis of the monoamines takes place both at perikaryal and axonal/terminal level.The nerve cells accumulating the monoamine precursors contain a nucleus with rich chromatin content and a deeply invaginated nuclear envelope. Further ultrastructural characteristics of these neurons are their well-developed rough endoplasmic reticulum system, a great number of mitochondria and glycogen granules, and the presence of dense-cored vesicles of different types. All these features are responsible for the electron-dense appearance of the cytoplasm.     

Innervation of the intestine in the bivalve mollusc Chione stutchburyi

Summary The innervation of the gut of the venerid bivalve mollusc, Chione stutchburyi, has been examined by fluorescence histochemistry, electron microscopy and autoradiography. Specific green and yellow varicose fluorescent fibres indicate the presence of dopaminergic and serotonergic axons, respectively. Three different types of axons can be distinguished by the morphological characteristics of their vesicles. Type I axons contain predominantly small granular vesicles (average diameter 65 nm), Type II axons possess large granular vesicles (average diameter 100 nm) and Type III axons contain large opaque vesicles (average diameter 150 nm). The granular vesicles in both Types I and II axons react positively to dichromate, and their granularity is reduced by reserpine indicating that they are monoaminergic. Only Type I axons accumulate tritiated dopamine and are selectively damaged by 6-hydroxydopamine. It is concluded that Type I axons are dopaminergic. Type II axons are serotonergic: they alone take up tritiated 5-hydroxytryptamine, and 5,7-dihydroxytryptamine selectively causes degenerative changes in these axons. Type III axons contain an unidentified neurotransmitter substance. The large opaque vesicles of these axons do not react to dichromate and are unaffected by reserpine, 6-hydroxydopamine or 5,7-dihydroxytryptamine.     

Release of dopamine and serotonin from Limax ganglia in vitro

1. We wish to establish the kinetics of serotonin and dopamine release from Limax cerebral and buccal ganglia and find selective treatments to modify their release kinetics.2. The release of dopamine and serotonin from isolated ganglia was stimulated by high potassium exposure with and without prior treatment of ganglia with 6-hydroxydopamine (6-OHDA).3. Single ganglia release significant quantities of monoamines during a single 5 min high K⁺ exposure. Multiple high K⁺ exposures deplete a readily releasable transmitter store with little effect on storage pools.4. 6-OHDA exposure depletes readily releasable DA with little effect on total ganglion DA content or on serotonin.5. Feeding motor program responsiveness is suppressed reversibly by whole ganglion high K⁺ treatment.     

An Ultrastructural and Fluorescence Histochemical Study of the Myenteric Plexus of the Stomach of the Rainbow Trout Salmo gairdneri

The myenteric plexus of the rainbow trout Salmo gairdneri is enclosed within an incomplete Schwann-like sheath which allows bundles of unmyelinated axons to pass into the adjacent smooth muscle layers. Neuronal and non-neuronal constituents of the myenteric plexus are divided into smaller units by endoneurial collagen which in places condenses to form a perineurial covering. The myenteric plexus is avascular but arterioles and fenestrated capillaries are present close to the plexus in the intermuscular space. Small groups of neurones constitute the ganglia of the plexus but as yet few ultrastructural indications of differing neurone types have been observed. Within the neuropil of the ganglia five types of axon profile, characterised by their vesicle content, have been identified. One of these types was only recognisable following the administration of 5-hydroxydopamine. Axo-somatic and axo-dendritic synaptic contacts were only made by Type 1 axons but these were uncommon. The presence of an adrenergic component of the myenteric plexus was confirmed ultrastructually following 6-hydroxydopamine-induced degeneration and also by Falck-Hillarp fluorescence histochemistry which revealed an extensive distribution of adrenergic nerves in the plexus. The structural organisation of the plexus, the comparatively few ultrastructurally recognisable axon and neurone types and the sparsity of synaptic contacts all indicate that the teleost myenteric plexus is less complex than its mammalian counterpart.     

Temporal Changes of CB1 Cannabinoid Receptor in the Basal Ganglia as a Possible Structure-Specific Plasticity Process in 6-OHDA Lesioned Rats

The endocannabinoid system has been implicated in several neurobiological processes, including neurodegeneration, neuroprotection and neuronal plasticity. The CB1 cannabinoid receptors are abundantly expressed in the basal ganglia, the circuitry that is mostly affected in Parkinson’s Disease (PD). Some studies show variation of CB1 expression in basal ganglia in different animal models of PD, however the results are quite controversial, due to the differences in the procedures employed to induce the parkinsonism and the periods analyzed after the lesion. The present study evaluated the CB1 expression in four basal ganglia structures, namely striatum, external globus pallidus (EGP), internal globus pallidus (IGP) and substantia nigra pars reticulata (SNpr) of rats 1, 5, 10, 20, and 60 days after unilateral intrastriatal 6-hydroxydopamine injections, that causes retrograde dopaminergic degeneration. We also investigated tyrosine hydroxylase (TH), parvalbumin, calbindin and glutamic acid decarboxylase (GAD) expression to verify the status of dopaminergic and GABAergic systems. We observed a structure-specific modulation of CB1 expression at different periods after lesions. In general, there were no changes in the striatum, decreased CB1 in IGP and SNpr and increased CB1 in EGP, but this increase was not sustained over time. No changes in GAD and parvalbumin expression were observed in basal ganglia, whereas TH levels were decreased and the calbindin increased in striatum in short periods after lesion. We believe that the structure-specific variation of CB1 in basal ganglia in the 6-hydroxydopamine PD model could be related to a compensatory process involving the GABAergic transmission, which is impaired due to the lack of dopamine. Our data, therefore, suggest that the changes of CB1 and calbindin expression may represent a plasticity process in this PD model.     

Specific effect of 5,6-dihydroxytryptamine on the monoamine fluorophore of the frog's gustatory cells

Summary A specific formaldehyde-induced yellow fluorescence, suggesting the presence of serotonin-like monoamine has been demonstrated in the gustatory cells of the frog.The fungiform papillae of frogs were examined fluorescence-histochemically after intraperitoneal injection of 5,6-dihydroxytryptamine. The results indicated that the fluorophore of gustatory cells was affected selectively by the drug injection: the yellow fluorescence was transiently enhanced 3 hours after the drug injection, thereafter being reduced rapidly. The effect of 5,6-dihydroxytryptamine was long-lasting with the reduction of the yellow fluorophore persisting at least for the experimental duration of 14 days. A single injection of 6-hydroxydopamine induced a complete depletion of noradrenaline fluorescence from adrenergic nerve terminals, while the fluorescence of gustatory cells was not affected by a high dose of the drug.The present results with pharmacologic treatments further support the view that the gustatory cell of the frog contains a serotonin-like monoamine.     

Enhanced glutamate,IP3 and cAMP activity in the cerebral cortex of Unilateral 6-hydroxydopamine induced Parkinson's rats: Effect of 5-HT,GABA and bone marrow cell supplementation

Parkinson's disease is characterized by progressive cell death in the substantia nigra pars compacta, which leads to dopamine depletion in the striatum and indirectly to cortical dysfunction. Increased glutamatergic transmission in the basal ganglia is implicated in the pathophysiology of Parkinson's disease and glutamate receptor mediated excitotoxicity has been suggested to be one of the possible causes of the neuronal degeneration. In the present study, the effects of serotonin, gamma-aminobutyric acid and bone marrow cells infused intranigrally to substantia nigra individually and in combination on unilateral 6-hydroxydopamine induced Parkinson's rat model was analyzed. Scatchard analysis of total glutamate and NMDA receptor binding parameters showed a significant increase in B_max (P < 0.001) in the cerebral cortex of 6-hydroxydopamine infused rat compared to control. Real Time PCR amplification of NMDA2B, mGluR5, bax, and ubiquitin carboxy-terminal hydrolase were up regulated in cerebral cortex of 6-hydroxydopamine infused rats compared to control. Gene expression studies of GLAST, ά-Synuclien and Cyclic AMP response element-binding protein showed a significant (P < 0.001) down regulation in 6-OHDA infused rats compared to control. Behavioural studies were carried out to confirm the biochemical and molecular studies. Serotonin and GABA along with bone marrow cells in combination showed reversal of glutamate receptors and behaviour abnormality shown in the Parkinson's rat model. The therapeutic significance in Parkinson's disease is of prominence.     

Involvement of peripheral noradrenaline and 5-hydroxytryptamine in carrageenin-induced pedal oedema in rats

Role of peripheral and central noradrenaline and 5-hydroxytryptamine in the carrageenin-induced pedal oedema in rats was studied using agents which influence catecholamine synthesis and receptor activity of noradrenaline and 5-hydroxytryptamine. Reserpine, guanethidine, α-methyl-p-tyrosine, diethyldithiocarbamate, 6-hydroxydopamine, phenoxybenzamine, phentolamine, chlorpromazine and yohimbine markedly inhibited carrageenin-induced pedal oedema. However, 6-hydroxydopamine given intracerebroventricularly, 5,6-dihydroxytryptamine,p-chlorophenylalanine, lower dose of yohimbine, pro pranolol, haloperidol, cyproheptadine and mepyramine did not alter the carrageenin-induced oedema, whereas, cyproheptadine and mepyramine given simultaneously, markedly inhibited carrageenin-induced oedema. Our studies indicate that the process of oedema formation in rats by carrageenin involves both the peripheral noradrenaline and 5-hydroxytryptamine Communication No. 58 from IDPL Research Centre, Hyderabad.     

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.     

The ultrastructure of the intestinal nerve of Remak in the domestic fowl

Summary An ultrastructural study was made of the neurons, satellite cells and vesiculated axons of the intestinal nerve of the domestic fowl. Broad membrane-to-membrane contacts between adjacent nerve cell bodies were sometimes observed. The cell bodies and processes were not always separated from the extracellular space by a capsule of satellite cells. Following fixation using potassium permanganate, catecholamine (CA)-containing neurons in the intestinal nerve, unlike those in the lumbar parasympathetic ganglia, did not possess any small granular vesicles (SGV). Following exposure to noradrenaline, SGV could be demonstrated in the cell bodies of the juxta-ileal ganglia but not the juxta-rectal ganglia of the intestinal nerve. Non-CA axons were examined in tissue from birds that had been pretreated with 6-hydroxydopamine. Approximately one half of the non-CA axons formed axo-somatic contacts. Most of the non-CA axons contained varying proportions of small clear vesicles, large clear vesicles and large granular vescles. Statistical analysis showed that the non-CA axons could not be subdivided according to their vesicle content. CA-axons contained many SGV and were found in close apposition to neuronal somata and processes, and in the neuropil.     

Neural and vascular provisions of rat interscapular brown adipose tissue

The innervation of rat interscapular brown adipose tissue has been studied by light and fluorescence microscopy and electron microscopy after treatment with "false" adrenergic neurotransmitters 5- and 6-hydroxydopamine. The vascular markers neoprene latex and thioflavin S were used to define the blood vascular arrangements within the around the tissue. Catecholaminergic innervation was revealed by fluorescence microscopy at both parenchymal and vasomotor sites. In animals injected with 6-hydroxydopamine, this catecholaminergic fluorescence was extinguished in the parenchymal nerve distribution and markedly reduced in the vasomotor plexus. Identification of an extensive network of noradrenergic vasomotor and parenchymal nerve terminals was established by electron microscopy after 5- and 6-hydroxydopamine administration, but unmarked terminals were also observed in both distributions. These unmarked terminals might represent an additional nonnoradrenergic nerve supply to interscapular brown adipose tissue. The thoracodorsal veins draining the fat pads are directly tributary to a large median perforating vein, which joins the azygos vein, and are also continuous with the axillary vein. In addition to the recognized vascular distribution pattern of lobular arteries supplying an abundant capillary plexus drained by lobular veins, direct arteriovenous anastomoses were observed within the interscapular brown fat pad. It is postulated that these additional vascular arrangements are determinant in the phenomenal increase in blood flow through brown adipose tissue during metabolic stimulation.     

Neuroanatomy of the central nervous system of the wandering spider,Cupiennius salei (Arachnida,Araneida)

Summary In Cupiennius salei (Ctenidae), as in other spiders, the central nervous system is divided into the supraoesophageal ganglion or brain and the suboesophageal ganglia (Fig. 1). The two masses are interconnected by oesophageal connectives. The brain gives off four pairs of optic and one pair of cheliceral nerves. From the suboesophageal ganglia arise a pair of pedipalpal, four pairs of leg, and several pairs of opisthosomal nerves (Fig. 2). 1. Cell types. In the brain a total of 50900 cells were counted, in the suboesophageal ganglia 49000. They are all monopolar cells, found in the ganglion periphery and may be classified into four types: (a) Small globuli cells (nuclear diameter 6–7 m) forming a pair of compact masses in the protocerebrum (Fig. 10b); (b) Small and numerous cells (cell diameter 12–20 m) with processes forming the bulk of the neuropil in the brain and suboesophageal ganglia; (c) Neurosecretory cells (cell diameter ca. 45 m) in the brain and suboesophageal ganglia; (d) Large motor and interneurons (cell daimeter 40–112 m), mostly in the suboesophageal ganglia (Figs. 10a and c). 2. Suboesophageal mass. The cell bodies form a sheet of one to several cell layers on the ventral side of each ganglion and are arranged in groups. Three such groups were identified as motor neurons, four as interneurons. At the dorsal, dorso-lateral, and mid-central parts of the ganglion there are no cell somata. The fibre bundles arising from them form identifiable transverse commissural pathways (Fig. 9b). They form the fibrous mass in the central part of the suboesophageal mass.Neuropil is well-formed in association with the sensory terminations of all major nerves (Fig. 9a). As these proceed centrally they break up into five major sensory tracts forming five layers one above the other. There are six pairs of additional major longitudinal tracts arranged at different levels dorsoventrally (Fig. 8). They ascend into the brain through the oesophageal connectives and terminate mostly in the mushroom bodies and partly in the central body. 3. Protocerebrum. Fine processes of the globuli cells form the most important neuropil mass in the fibrous core, called the mushroom bodies. These consist of well developed glomeruli, hafts, and bridge which are interconnected with the optic masses of the lateral eyes and most fibre tracts from the brain and suboesophageal mass (Fig. 7). The median eye nerves form a small optic lamella and optic ganglia, connected to the central body through an optic tract. Each posterior median and posterior lateral eye nerve ends in large optic lamellae (Fig. 13a). These are connected through chiasmata to a large optic mass where fibres from globuli cells form conspicuous glomeruli. There are 10–12 large fibres (diameter 9 m) of unknown origin on each side, terminating in the optic lambella of the posterior lateral eye.The central body, another neuropil mass (Fig. 13b) in the protocerebrum, is well developed in Cupiennius and located transversely in its postero-dorsal region (Fig. 10d). It consists of two layers and is interconnected with optic masses of the median and lateral eyes through optic tracts. Fibre tracts from the brain and suboesophageal mass join the central body.     

Some parasympathetic neurons in the guinea-pig heart express aspects of the catecholaminergic phenotype in vivo

Summary In a histochemical study of intrinsic cardiac ganglia of the guinea-pig in whole-mount preparations, it was found that some 70–80% of the neurons express aspects of the catecholaminergic phenotype. These neurons have an uptake mechanism for L-DOPA, and contain the enzymes for converting L-DOPA, (but not D-DOPA) to dopamine and noradrenaline, i.e. aromatic L-aminoacid decarboxylase and dopamine -hydroxylase. Monoamine oxidase is also present within some of the neurons. In these respects, the neurons resemble noradrenergic neurons of sympathetic ganglia, so we refer to them as intrinsic cardiac amine-handling neurons. However, these neurons do not contain tyrosine hydroxylase and show little or no histochemically detectable uptake of -methyldopa, dopamine or noradrenaline, even after depletion of endogenous stores of amines by pre-treatment with reserpine. Noradrenergic fibres from the sympathetic chain form pericellular baskets around nerve cell bodies. The uptake of L-DOPA into nerve cell bodies is not prevented by treatment with 6-hydroxydopamine sufficient to cause transmitter-depletion or degeneration of the extrinsic noradrenergic fibres. Such degeneration experiments suggest that axons of the amine-handling neurons project to cardiac muscle, blood vessels and other intrinsic neurons. The cardiac neurons do not show any immunohistochemically detectable serotonergic characteristics; there is no evidence for uptake of the precursors L-tryptophan and 5-hydroxytryptophan or 5-HT itself, whereas the extrinsic noradrer ergic nerve fibres within the ganglia can take up 5-HT when it is applied in high concentrations.Abbreviations AChE acetylcholinesterase - DBH-IR dopamine -hydroxylase-like immunoreactivity - L-DOPA L-dihydroxyphenylalamine - 5-HT-IR 5-hydroxytryptamine-like immunoreactivity - 6-OHDA 6-hydroxydopamine - methyldopa L--methyl-dihydroxyphenylalanine - MAO monoamine oxidase - NPY neuropeptide Y - SIF small intensely fluorescent cells - TH-IR tyrosine hydroxylase-like immunoreactivity - VIP vasoactive intestinal polypeptide     

Indoleamines and the eccentric cells of the Limulus lateral eye

The lateral eye of the horseshoe crab, Limulus polyphemus, was studied by fluorescence microscopy according to Falck and Hillarp and microspectrofluorometry for identifying neuronal monoamines. After the formaldehyde treatment, the eccentric cells and their axons have a yellowish, rapidly fading fluorescence, such as is seen with 5-hydroxytryptamine. The microspectrofluorometric analysis was compatible with the fluorescence being caused by an indole, which could not be definitely identified, however. The eccentric cells have the ability to accumulate indoleamines such as 5-hydroxytryptamine, 6-hydroxytryptamine and 5,6-dihydroxytryptamine. Their axons were best demonstrated after being loaded with 6-hydroxytryptamine. Characteristic varicose terminals were seen in the neuropil, often arranged in clusters. Other terminals, possibly originating from the eccentric cells, were also seen among the pigment cells in the basal part of the ommatidia.