Ultrastructural characterization of axonal endings in the substantia gelatinosa which take up [3H]serotonin

Mechanisms of orofacial pain control in the central nervous system

Recent advances in the study of pain have revealed somatotopic- and modality-dependent processing and the integration of nociceptive signals in the brain and spinal cord. This review summarizes the uniqueness of the trigeminal sensory nucleus (TSN) in structure and function as it relates to orofacial pain control. The oral nociceptive signal is primarily processed in the rostral TSN above the obex, the nucleus principalis (Vp), and the subnuclei oralis (SpVo) and interpolaris (SpVi), while secondarily processed in the subnucleus caudalis (SpVc). In contrast, the facial nociceptive signal is primarily processed in the SpVc. The neurons projecting to the thalamus are localized mostly in the Vp, moderately in the SpVi, and modestly in the ventrolateral SpVo and the SpVc. Orofacial sensory inputs are modulated in many different ways: by interneurons in the TSN proper, through reciprocal connection between the TSN and rostral ventromedial medulla, and by the cerebral cortex. A wide variety of neuroactive substances, including substance P, gamma-aminobutyric acid, serotonin and nitric oxide (NO) could be involved in the modulatory functions of these curcuits. The earliest expression of NO synthase (NOS) in the developing rat brain is observed in a discrete neuronal population in the SpVo at embryonic day 15. NOS expression in the SpVc is late at postnatal day 10. The neurons receiving intraoral signals are intimately related with the sensorimotor reflexive function through the SpVo. In summary, a better understanding of the trigeminal sensory system--which differs from the spinal system--will help to find potential therapeutic targets and lend to developing new analgesics for orofacial-specific pain with high efficacy and fewer side effects.

Subdural engraftment of serotonergic neurons following spinal hemisection restores spinal serotonin, downregulates serotonin transporter, and increases BDNF tissue content in rat

Spinal hemisection injury at T13 results in development of permanent mechanical allodynia and thermal hyperalgesia due to interruption and subsequent loss of descending inhibitory modulators such as serotonin (5-HT) and its transporter (5-HT(T)). We hypothesize that lumbar transplantation of non-mitotic cells that tonically secrete 5-HT and brain-derived neurotrophic factor (BDNF) will restore alterations in 5-HT and 5-HT(T) systems within the spinal dorsal horn. We used an immortalized rat neuronal cell line derived from E13 raphe (RN46A-B14) which is shown to secrete 5-HT and BDNF in vitro and in vivo. Three groups (n=35) of 30 day old male Sprague-Dawley rats were spinally hemisected at T13 and 28 days later received either lumbar RN46A-V1 control empty-vector (n=15) or RN46A-B14 (n=15) intrathecal grafts, or no transplant. Twenty-eight days following transplantation, animals were perfused and tissue examined for changes in 5-HT, 5-HT(T), and BDNF at the site of transplantation or at lumbar enlargements (L5). Immunohistochemistry revealed that RN46A-B14, but not RN46A-V1 cells, increased 5-HT tissue staining at L5 in the dorsal white matter as well as in superficial dorsal horn laminae I and II on both ipsilateral and contralateral sides, results confirmed by ELISA. Transplantation of RN46A-B14 cells significantly reduced ipsilateral 5-HT(T), upregulated after injury. Significantly increased levels of BDNF were also observed after RN46A-B14 transplantation but were not localized to particular spinal laminae. These results are consistent with recovery of locomotor function and reductions in chronic pain behaviors observed behaviorally after RN46A-B14 transplantation and supports the pragmatic application of cell-based therapies in correcting damaged circuitry after spinal cord injury.

Serotonin transporters in adult rat brain astrocytes revealed by [3H]5-HT uptake into glial plasmalemmal vesicles

Cultured astrocytes derived from neonatal rat brain exhibited high affinity, Na+-dependent, paroxetine and fluoxetine sensitive [3H]5-HT uptake. Reverse transcriptase-PCR demonstrated that astrocytes in culture expressed messenger RNA for the cloned serotonin transporter protein which has been characterised as the neuronal serotonin transporter. Although the serotonin transporter in cultured astrocytes displayed a Km value approximately 10 times greater than found in adult brain synaptosomes, these observations indicated that astrocytes in vitro may express the same serotonin transporter as neurons. Reverse transcriptase-PCR demonstrated the presence of serotonin transporter mRNA in the adult rat cerebral cortex, suggesting that astrocytes in vivo may express low levels of this mRNA. To investigate whether astrocytes in the adult CNS express functional serotonin transporters, glial plasmalemmal vesicles were prepared from cerebral cortex, representing a subcellular fraction composed primarily of vesicles derived from astrocytes. These vesicles were characterised by [3H]-glutamate and [3H]-dopamine uptake and by immunoblot analysis, using glial and synaptic markers: glutamate synthase, SNAP-25 and synaptobrevin. [3H]5-HT was taken up into glial plasmalemmal vesicles in a high affinity (Km approximately 40 nM), Na+ dependent, paroxetine-sensitive manner. The [3H]5-HT uptake capacity (Vmax) in these vesicles was approximately one quarter of that observed in synaptosomes. These data indicate that astrocytes in culture and in vivo are capable of 5-HT uptake via the previously characterised 'neuronal' serotonin transporter.

Serotonergic axonal contacts on identified cat trigeminal motoneurons and their correlation with medullary raphe nucleus stimulation

The innervation of the trigeminal motor nucleus by serotonergic fibers with cell bodies in the raphe nuclei pallidus and obscurus suggests that activation of this pathway may alter the excitability of trigeminal motoneurons. Thus, we recorded intracellular responses from cat jaw-closing (JC) andjaw-opening (JO) alpha-motoneurons evoked by raphe stimulation and used a combination of intracellular staining of horseradish peroxidase (HRP) and immunohistochemistry at the light and electron microscopic levels to examine the distribution of contacts made by serotonin (5-HT)-immunoreactive boutons on the two motoneurons types. Electrical stimulation applied to the nucleus raphe pallidus-obscurus complex induced a monosynaptic excitatory postsynaptic potential (EPSP) in JC (masseter) alpha-motoneurons and an EPSP with an action potential in JO (mylohyoid) alpha-motoneurons. The EPSP rise-times (time to peak) and half widths were significantly longer in the JC than in the JO motoneurons. The EPSPs were suppressed by systemic administration of methysergide (2 mg/kg). Six JC and seven JO alpha-motoneurons were well stained with HRP. Contacts were seen between 5-HT-immunoreactive boutons and the motoneurons. The JC motoneurons received a significantly larger number of the contacts than did the JO motoneurons. The contacts were distributed widely in the proximal three-fourths of the dendritic tree of JC motoneurons but were distributed on more proximal dendrites in the JO motoneurons. At the electron microscopic level, synaptic contacts made by 5-HT-immunoreactive boutons on motoneurons were identified. The present study demonstrated that JC motoneurons receive stronger 5-HT innervation, and this correlates with the fact that raphe stimulation caused larger EPSPs among these neurons than among JO motoneurons.

Localization of the serotonin transporter in rat spinal cord

The spinal cord is richly innervated by serotoninergic fibres originating from the raphe nuclei. The localization of the terminating component of serotoninergic neurotransmission, the serotonin transporter SERT1, was found in both the dorsal and ventral horns, especially at the level of the cervical and lumbar segments. Within the thoracic region, we observed a heavily labelled bundle in the intermediolateral nucleus of lamina VII. A low density of stained fibres was encountered in the sacral spinal cord. In contrast to homogeneous staining of motor nuclei, a differential labelling of laminae was seen in the dorsal horn, with laminae I, III and IV exhibiting a higher density of immunopositive terminals than the medial part of lamina II. High magnification revealed a preferential accumulation of serotonin transporter staining within nerve endings and varicosities of thin fibres. Double immunofluorescence staining demonstrated a co-localization of serotonin and its uptake system within these varicosities. These results show that the serotonin transporter is highly expressed in the rat spinal cord and that its distribution parallels the serotoninergic innervation. They also reinforce the view that varicosities are important neuronal structures, which modulate the function of dorsal and ventral horn neurons by releasing serotonin.

Autoradiographic studies on the uptake of 3H-noradrenaline and 3H-serotonin by neurones and astrocytes in explant and primary cultures of rat CNS: effects of antidepressants

Autoradiographic studies were made on the uptake of 3H-noradrenaline and 3H-serotonin in explant cultures and primary astrocyte cultures from various regions of rat central nervous system (cortex, cerebellum, locus coeruleus, nucleus raphé, spinal cord). In explant cultures from locus coeruleus and nucleus raphé cell bodies and processes of many neurones revealed intense labelling by 3H-noradrenaline and 3H-serotonin, respectively. In cultures from cortex, cerebellum and spinal cord the cell bodies of neurones did not show labelling by the monoamines but many nerve fibres in the outgrowth zone had taken up 3H-noradrenaline and 3H-serotonin. Astrocytes in explant cultures did not take up 3H-noradrenaline and 3H-serotonin whereas astrocytes in primary cultures showed heavy uptake of both monoamines. In contrast, amino acid transmitters such as 3H-GABA and 3H-glutamate were accumulated by astrocytes in explant as well as in primary cultures. Uptake of both 3H-noradrenaline and 3H-serotonin by neurones and astrocytes was considerably reduced or inhibited in Na(+)-free incubation medium or at low temperature, suggesting an active uptake mechanism. Addition of the antidepressants maprotiline and (+)oxaprotiline inhibited the uptake of 3H-noradrenaline by neuronal cell bodies and fibres in explant cultures and by astrocytes in primary cultures. The uptake of 3H-serotonin by neurones and astrocytes was blocked by citalopram and paroxetine. Our studies demonstrate that astrocytes in primary cultures are able to actively take up 3H-noradrenaline and 3H-serotonin whereas there was no uptake of monoamines into astrocytes in explant cultures, suggesting that there is a difference between astrocytes in different culture systems (explant cultures vs primary cultures) with respect to the uptake of monoamine transmitters.

Synaptic organization of the interstitial subdivision of the nucleus tractus solitarii and of its laryngeal afferents in the rat

The nucleus tractus solitarii, the first central relay for gustatory and a variety of visceral afferents, is also an integrative center for numerous functions. Its interstitial subdivision is involved in swallowing and respiratory reflexes. The ultrastructural characteristics of this subdivision and of its laryngeal afferents were investigated in adult rat by a serial-section study and by application of wheat germ agglutinin-horseradish peroxidase conjugate to the peripheral afferent fibers. The interstitial subnucleus contained scattered small neuronal cell bodies with such ultrastructural features as a large nucleus with deep indentations and an organelle-poor cytoplasm. On the basis of their size and vesicular content, the axon terminals were classified into three categories. Group I and group II terminals were small or large, respectively, and contained mainly small, round, and clear synaptic vesicles. Group III terminals were also small but contained small, pleomorphic, and clear vesicles. Axodendritic synapses were the most numerous. They were either asymmetrical, comprised of group I and II terminals, or symmetrical, comprised of group III terminals. More than 50% were part of complex synaptic arrangements in the form of rosettes or glomeruli. Axosomatic contacts involved both group I and group III terminals and were always symmetrical. A high frequency of axoaxonic synapses was found. They were symmetrical, comprised of group III terminals on group I or II terminals. Different types of symmetrical synaptic contacts made by dendrites were also found. This study indicates also that the ipsilateral interstitial subdivision constitutes the preferential site of termination for superior laryngeal afferents. The labeled axon terminals belonged exclusively to groups I and II and were involved in both axodendritic and axoaxonic synapses. Some of the axodendritic synapses were part of rosettes or glomeruli. All these synaptic arrangements may be considered a morphological substrate for important processing of afferent information in the nucleus tractus solitarii. They may account for some of the integrative functions of the interstitial subnucleus such as physiological processes triggered from the superior laryngeal nerve.

Serotonergic synaptic input to cholinergic neurons in the rat mesopontine tegmentum

Serotonergic synaptic inputs to cholinergic neurons in the laterodorsal and pedunculopontine tegmental nuclei were examined with pre-embedding dual-label immunoelectron microscopy. Numerous serotonin-immunoreactive axon terminals visualized with a silver-enhanced immunogold method were present in both of these tegmental nuclei. Serotonergic terminals occasionally made synaptic contacts with the soma and proximal dendrites of cholinergic tegmental neurons labelled with a choline acetyltransferase-immunoreactive peroxidase-anti-peroxidase diaminobenzidine reaction product. In the rostralmost region of the laterodorsal tegmental nucleus, a few serotonergic neurons of the dorsal raphe nucleus were interspersed among cholinergic neurons. Some dendrites of these serotonergic neurons appeared to contain synaptic vesicles. Both myelinated and unmyelinated serotonergic axons were present in the mesopontine tegmentum. The presence of serotonergic synapses onto tegmental cholinergic neurons is consistent with previous behavioral and electrophysiological findings suggesting an inhibitory role of serotonin in the induction of rapid eye movement sleep and its phenomenology through an action on cholinergic neurons in the mesopontine tegmentum.

Monoamine oxidase: distribution in the cat brain studied by enzyme- and immunohistochemistry: recent progress

Localization of MAO-containing neurons, fibers and glial cells has been described by recent progress in MAO histochemistry and immunohistochemistry. It does not necessarily correspond to those containing monoamines. MAO-A is demonstrated in many noradrenergic cells, but it is hardly detectable in DA cells. Increase of 5-HT and DA concentration after inhibition of MAO-A indicates the possible existence of MAO-A in such neuronal structures. MAO-A is also undetectable in neurons containing 5-HT, a good substrate for MAO-A. These neurons contain MAO-B. There still remain contradictions to be solved in future. MAO is present in astroglial cells, in which monoamines released in extracellular space may be degraded. In glial cells, MAO may also play a role to regulate concentration of telemethylhistamine and trace amines. Such cells appear to transform MPTP to MPP+, a neurotoxin for nigral DA neurons.

Periterminal synaptic organization of primary afferents in laminae I and IIo of the rat spinal cord, as shown after anterograde HRP labelling

The fine structure and periterminal synaptology of the primary afferent terminations in laminae I and IIo are examined in the rat, following anterograde labelling with horseradish peroxidase applied to the right C5-dorsal root. Labelled varicosities observed along the terminal arbors in parasagittal thick sections were relocated in ultrathin sections by electron microscopy. The labelled terminal profiles generated by the three primary afferent plexuses which can be identified by light microscopy in laminae I-IIo had similar fine structural features, except that axo-axonal contacts, although rare, were more frequent in the medial network plexus. Primary boutons were packed with agranular spherical vesicles and some large granular vesicles, and were mostly presynaptic to profiles of dendritic trunks of marginal cells. Unlabelled axonal profiles, either light with some flattened vesicles, or dense with round vesicles, were also presynaptic at symmetrical or asymmetrical contacts, respectively, to those dendritic profiles. It is suggested that such knobs of intrinsic origin are responsible for postsynaptic modulation of the primary noxious input. Although the 20 microns wide lamina IIo belongs cytoarchitectonically to lamina II and can be distinguished from lamina I by a decreased amount of myelinated fibres and large dendritic profiles, the periterminal synaptology was here found to be the same as in lamina I.

Gating of transmission to motoneurones by stimuli applied in the locus coeruleus and raphe nuclei of the cat

1. Neuronal systems activated by stimulation in the region of the locus coeruleus/subcoeruleus (LC/SC) and raphe nuclei have previously been shown to depress transmission from group II muscle afferents in regions of the midlumbar spinal segments in which premotor interneurones are located. The aim of the present investigation was to determine the extent to which such depression is paralleled by depression of the reflex actions of group II afferents on motoneurones. 2. The effects of short trains of conditioning electrical stimuli applied within the LC/SC and raphe nuclei were examined on postsynaptic potentials (PSPs) evoked by group I and group II muscle afferents in hindlimb motoneurones. The effects were examined over a wide range of conditioning-test intervals but particular emphasis was placed on the effects produced at long intervals (> 100 ms) since such effects are more likely to be mediated by the descending noradrenergic and serotonergic neurones of the LC/SC and raphe nuclei which are of slow conduction velocity. In addition, conditioning stimuli alone evoked PSPs in motoneurones (with latencies of 7-15 ms and a duration of 50-80 ms) and effects evoked at short conditioning-test intervals might therefore have been secondary to changes in motoneurone membrane properties. 3. At conditioning-test intervals between 100 and 350 ms synaptic actions of group II origin were strongly and consistently depressed. Both EPSPs and IPSPs were affected, two-thirds of those tested being reduced in amplitude by 50% or more. A similar depression was exerted on PSPs evoked from the quadriceps and deep peroneal nerves mediated predominantly by interneurones located in the midlumbar segments and on PSPs evoked from the hamstring and triceps surae nerves mediated by interneurones located in more caudal segments. It is thus concluded that neuronal systems activated by stimuli applied in the LC/SC and raphe nuclei are capable of gating transmission in all those interneuronal pathways which mediate the reflex actions of group II afferents on motoneurones in anaesthetized animals.

Uptake of [3H]serotonin and [3H]glutamate by primary astrocyte cultures. I. Effects of different sera and time in culture

Na(+)-dependent, fluoxetine-sensitive high-affinity uptake of serotonin and Na(+)-dependent uptake of glutamate were studied in primary astrocyte cultures from 1-day-old rat neocortex. This uptake was independent of time in culture from 1 to 6 weeks. High-affinity serotonin uptake was decreased when cells were grown in horse serum as compared to fetal bovine serum and was almost absent when cells were grown in chemically defined medium. In contrast, glutamate uptake was unaffected by the composition of the medium in which the cultures were grown. The serum effect on serotonin uptake was not due to the greater level of serotonin in the fetal bovine serum and was only reversed by a change of serum over a time period of days.

Responses of neurons in the caudal medullary raphe nuclei of the cat to stimulation of the vestibular nerve

In the decerebrate cat, recordings were made from neurons in the caudal medullary raphe nuclei to determine if they responded to electrical stimulation of the vestibular nerve and thus might participate in vestibulosympathetic reflexes. Many of these cells projected to the upper thoracic spinal cord. The majority (20/28) of raphespinal neurons with conduction velocities between 1 and 4 m/s received vestibular inputs; 13 of the 20 were inhibited, and 7 were excited. Since many raphespinal neurons with similar slow conduction velocities are involved in the control of sympathetic outflow, as well as in other functions, these cells could potentially relay vestibular signals to sympathetic preganglionic neurons. The onset latency of the vestibular effects was long (median of 15 ms), indicating the inputs were polysynaptic. In addition, 34 of 42 raphespinal neurons with more rapid conduction velocities (6-78 m/s) also received long-latency (median of 10 ms) labyrinthine inputs; 26 were excited and 8 were inhibited. Although little is known about these rapidly-conducting cells, they do not appear to be involved in autonomic control, suggesting that the function of vestibular inputs to raphe neurons is not limited to production of vestibulosympathetic reflexes. One hypothesis is that raphe neurons are also involved in modulating the gain of vestibulocollic and vestibulospinal reflexes; this possibility remains to be tested.

Uptake of [3H]serotonin and [3H]glutamate by primary astrocyte cultures. II. Differences in cultures prepared from different brain regions

Regional astrocyte cultures were derived by dissecting six regions; brain stem, cerebellum, mesencephalon, basal ganglia plus diencephalon, cerebral cortex, and hippocampus, from 3 to 4-day-old neonatal rat brains. Glial fibrillary acidic protein (GFAP) immunocytochemistry was used to confirm the astrocyte composition of the cultures. The percentage of GFAP (+) cells between regions varied from 75% to 100%. Once confluent these cultures were incubated with radiolabeled serotonin or glutamate for uptake and autoradiographic studies. For the different brain regions Na(+)-dependent, [3H] L-glutamate, and fluoxetine-sensitive [3H] 5-HT uptake varied markedly. The relative order of uptake for [3H] 5-HT was MS (mesencephalon) greater than CC (cerebral cortex) greater than BG + DI (basal ganglia + diencephalon) greater than HP (hippocampus) greater than BS (brain stem) greater than CB (cerebellum). For [3H] L-glutamate the order was HP greater than CC greater than BG + DI greater than MS = BS greater than CB. For [3H] 5-HT this essentially corresponds to the reported order of binding in situ of the [3H] 5-HT-specific uptake ligand [3H] citalopram. For [3H] L-glutamate regional variation of the uptake for the different cultures corresponds to the regional uptake reported for different regions of rat brain. Double-label studies with GFAP and radiolabeled neurotransmitters were also used to study uptake into GFAP(+) astrocytes by autoradiography. Flat GFAP cells with or without processes comprised 65-98% of the cultures and represented most of the uptake. The percentage of all GFAP(+) cells that were positive for uptake of ARG varied from 50% to 90% and also showed differences in grain density both intra- and inter-regionally. These differences in transmitter uptake by GFAP(+) astrocytes in primary culture, which are dependent on the region of origin and correspond to regional differences in situ, suggest that such uptake in vitro may reflect uptake by astrocytes in vivo. Implied in this is that uptake by astrocytes represents a significant component of serotonin uptake in vivo.

Serotonin uptake by astrocytes in situ

Co-localization of glial fibrillary acidic protein (GFAP) and radioactivity was examined after intraventricular injection of [3H]5-HT in adult rat brains. Radioactivity localized over GFAP-positive astrocytes was seen, especially when image-enhancing techniques were applied to the data. Also slices prepared from astrogliotic hippocampi of rats pretreated with kainic acid showed a twofold increased uptake of [3H]5-HT compared to control slices. This indicates that the uptake of [3H]5-HT seen in primary astrocyte cultures also occurs for astrocytes in situ. Also, as with astrocyte cultures, only some of the GFAP(+) astrocytes in situ showed localization of radioactivity, supporting the concept of intraregional heterogeneity of astrocyte functions.

Role of spinal serotonin1 receptor subtypes in thermally and mechanically elicited nociceptive reflexes

The ability of 5-HT1A and 5-HT1B agonists to alter a spinal animal's nociceptive threshold was examined using two analgesiometric tests. In the spinal withdrawal reflex test, administration of the selective 5-HT1A agonists ipsapirone, gepirone and PAPP resulted in significant dose-dependent increases in receptive field (RF) area for withdrawal reflexes when compared to predrug baseline values, indicating an increase in nociceptive sensitivity. The average overall percent maximal increase in RF area following administration of 5-HT1A selective compounds was: 80 +/- 16% for the ventroflexion reflex, 90 +/- 6% for the dorsiflexion reflex and 87 +/- 8% for the lateral flexion reflex. Similar to the effects noted with 5-HT1A agonists, administration of 5-HT1B agonists RU24969, mCPP and TFMPP resulted in a hyperalgesic response with an overall percent maximal increase of 43 +/- 6% for the ventroflexion reflex, 51 +/- 6% for the dorsiflexion reflex and 38 +/- 9% for the lateral flexion reflex. In the tail-flick analgesiometric test, administration of the 5-HT1A agonists 8-OH-DPAT and ipsapirone and the 5-HT1B agonists RU24969 and mCPP resulted in a significant dose-dependent increase in tail-flick latencies when compared to predrug baseline values, indicating a decrease in nociceptive sensitivity to noxious thermal stimuli. No differences in magnitude of the effect of the two receptor subtypes were found, indicating that stimulation of either 5-HT1A or 5-HT1B receptors was equipotent in producing the antinociceptive tail-flick response.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural organization of the interstitial subnucleus of the nucleus of the tractus solitarius in the cat: identification of vagal afferents

This electron microscopic study, based on serial section analysis, describes the synaptic organization of the interstitial subnucleus of the nucleus of the solitary tract and identifies the terminals of the vagal primary afferents utilizing degeneration and HRP transport. The interstitial subnucleus contains sparsely scattered cell bodies, numerous dendrites and axon terminals, and bundles of unmyelinated and myelinated axons. The cell bodies which are small in diameter have an organelle poor cytoplasm and a large invaginated nucleus. Axon terminals can be classified into two main types according to their vesicular shape. The first type contains clear, round vesicles and can be further subdivided into two subgroups on the basis of their morphology and the size of their vesicles. In the first subgroup the terminals are small, contain a few mitochondria and their vesicles are densely packed with an homogeneous size. In the second subgroup the terminals which vary from small to large, contain many mitochondria and contain round vesicles which are heterogeneous in size. The second main terminal type consists of axon terminals containing pleomorphic vesicles which are associated with asymmetrical or symmetrical synaptic contacts on dendrites. Axo-axonic contacts are present in the interstitial subnucleus. In general, the presynaptic axon terminals contain pleomorphic vesicles and the postsynaptic elements contain round vesicles of varying size. In some dendrites, identified by the presence of ribosomes, groups of round and/or pleomorphic vesicles are found associated with synaptic contacts. These dendrites are presynaptic to conventional dendrites and postsynaptic to axon terminals. After removal of the nodose ganglion, degenerative alterations are seen only at the caudal and middle levels of the interstitial subnucleus. Degeneration occurs in a few myelinated axons and in axon terminals which usually contain a mixture of small and larger round, clear vesicles. After HRP injection into the vagus nerve, the HRP reaction product is visible in axon terminals filled with clear, round vesicles which are heterogeneous in size. The labelled axon terminals establish single or multiple synaptic contacts. This study demonstrates that terminals of vagal primary afferents consist principally of terminals of the second subgroup. The morphology of these terminals are compared to primary afferents in the brainstem and spinal cord.

Autoradiographic mapping of 5-HT1, 5-HT1A, 5-HT1B and 5-HT2 receptors in the rat spinal cord

The distribution of 5-HT1, 5-HT1A, 5-HT1B and 5-HT2 receptors in the rat spinal cord was investigated with quantitative autoradiography. Receptors were labeled respectively with [3H]serotonin (5-[3H]HT),8- hydroxy-2-[N-dipropylamino-3H]tetralin (8-OH-[3H]DPAT), [125I]iodocyanopindolol and [3H]ketanserin. It is shown that 5-HT1, 5-HT1A and 5-HT1B receptors are distributed within the spinal cord according to a rostro-caudal gradient. Both 5-HT1 and 5-HT1A receptors are mainly present in the dorsal horn and 5-HT1B is present throughout the spinal cord, exhibiting high densities in the caudal-most part of the dorsal horn in lamina X and in the sacral parasympathetic area. On the other hand, 5-HT2 receptors are shown mostly in the thoracic sympathetic area and in the thoracic ventral horn; the dorsal horn exhibits few 5-HT2 receptors. The differential involvement of 5-HT through different receptors in nociception, autonomous nervous system control and motility are discussed.

Serotonergic innervation of the dorsal horn of rat spinal cord: light and electron microscopic immunocytochemical study

The ultrastructure of serotonergic projections to the dorsal horn of the rat spinal cord has been investigated, using a highly specific polyclonal antiserum. The highest concentrations of immunoreactive profiles were found in lamina I and the outer part of lamina II (IIo). Intermediate concentrations were found in laminae III and IV, while the inner part of lamina II (IIi) was almost devoid of immunoreactivity. Whereas 60% of the profiles show at least one varicosity studded with synaptic vesicles, only one-fifth of the latter contributes to classical synapses, the remaining profiles being devoid of a facing postsynaptic density. The results are compared with those in the literature and our own results relative to other regions of the cord. It is concluded that the pauci-synaptic projections to the dorsal horn could correspond to a diffuse influence of serotonin, the targets for which are determined by the corresponding serotonergic receptors.

Differential uptake of HRP by intact axon terminals versus transected axons: a study on bulbospinal fibers in the dorsolateral funiculus

A comparison was made of the amount of HRP uptake from transected versus intact axonal endings of rostral ventromedial medulla (RVMM) and locus coeruleus cells projecting via the dorsolateral funiculus in the rat. We found that retrograde labelling in the RVMM was reliably different between treatments, while locus coeruleus retrograde labelling was highly variable and not reliably different. HRP applied to intact endings retrogradely labelled approximately twice as many RVMM cells, including 25 times as many 5-hydroxytryptamine (B3) cells, as HRP applied to transected axons. In this first quantitative assessment of HRP uptake from transected versus intact endings, reliable differences have been found. These results have implications for the neural circuitry involved in pain modulatory systems.

Monoamine synaptic structure and localization in the central nervous system

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

Involvement of descending monoaminergic systems in the transmission of dental pain in the trigeminal nucleus caudalis of the rabbit

Perfusates were taken from the superficial layers of the subnucleus caudalis of the trigeminal sensory nuclear complex (SpVc), the first relay station of dental pain, with a push-pull cannula system and were assayed for endogenous serotonin (5-HT) and catecholamines by high-pressure liquid chromatography with an electrochemical detection. Spontaneous release of 5-HT and epinephrine was observed, while that of norepinephrine was not. Tooth pulp stimulation (ST) tended to increase the level of 5-HT in the perfusates. Pretreatment with morphine at a dose of 10 mg/kg (i.v.) significantly enhanced the release of 5-HT. However, there was no significant difference in morphine effect on the 5-HT level between stimulated and non-stimulated animals. Systemic administration of morphine (10 mg/kg i.v.) completely inhibited the release of immunoreactive substance P from the superficial layers of SpVc evoked by ST, and this inhibition was antagonized by local application of methysergide (10(-4) M). These results suggest that in the superficial layers of SpVc, morphine may primarily activate the descending 5-HT pathway which serves to modulate dental pain transmission.

Serotonin-containing axon terminals in the hypoglossal nucleus of the rat. An immuno-electronmicroscopic study

The morphology and distribution of serotonin-containing axon terminals in the rat hypoglossal nucleus (XII) was investigated immunocytochemically at the electron microscopic level. Serotonin-positive profiles were found throughout all regions of XII and included unmyelinated axons, varicosities and axon terminals. Most labeled profiles (68.1%) were nonsynaptic unmyelinated axons and varicosities, while synaptic profiles, ending on dendrites and somata, were seen less frequently (28.7%). The majority of labeled axon terminals (76.9%) ended on small-to-medium-sized dendrites. Most axodendritic terminals contained small, round agranular vesicles (20-55 microns), several large (60-100 microns) dense core vesicles, and were associated with a pronounced asymmetric postsynaptic specialization. By contrast, labeled axosomatic terminals were seen less often than those ending on dendrites (23.0%). Axosomatic terminals typically contained small, round, agranular and large dense core vesicles and were associated with a symmetric or no postsynaptic specialization. These results provide the structural substrates for elucidating the functional role of serotonin in tongue control.

Serotonin-like immunoreactive cells and fibres in the rat ventromedial mesencephalic tegmentum

The distribution and morphology of serotonin-like immunoreactive (5HT-IR) nerve cells, fibres and terminals in the rat ventromedial mesencephalic tegmentum (VMT) was studied using qualitative and quantitative immunohistochemical methods at light and electron microscopic levels. All five component nuclei were examined and the size, number and density of immunoreactive neurons and terminals determined. Thirty percent of all neurons in the caudal linear nucleus and 1% in the interfascicular nucleus were immunoreactive for serotonin. Different regions of the VMT had morphologically distinct 5HT-IR fibres and quantitative differences between the VMT nuclei were seen in the density of 5HT-IR terminals. In the lateral VMT, many thick, nonvaricose 5HT-IR fibres were found in the parabrachial pigmented nucleus while many fine, varicose 5HT-IR fibres were found in the paranigral nucleus. Fine, varicose 5HT-IR fibres were also seen in the rostral and caudal linear nuclei. Many 5HT-IR axon profiles formed synapses with small calibre dendrites. 5HT-IR fibres in the interfascicular nucleus were thick with variable sized varicosities at irregular intervals. Few 5HT-IR axon profiles formed synapses in this nucleus. A comparison between the number of 5HT-IR terminals and the total number of axon terminals in the VMT (25) reveals that the majority of all terminals in the paranigral and rostral linear nuclei can be labelled with serotonin. The effect of serotonin on VMT cells is therefore likely to be mediated by different types of 5HT-IR fibres which preferentially innervate particular VMT nuclei.

5-hydroxytryptamine3 receptors in the human brain: autoradiographic visualization using [3H]ICS 205-930

The distribution of 5-hydroxytryptamine receptors of the 5-hydroxytryptamine3 type was examined in human brain post mortem tissue, using quantitative in vitro autoradiography. The selective and potent 5-hydroxytryptamine3 receptor antagonist [3H]ICS 205-930 [(3 alpha-tropanyl)-1H-indole-3-carboxylic acid ester] was used as ligand. Highest levels of labelling were found in discrete nuclei of the lower brainstem. At all levels of the spinal cord the substantia gelatinosa was also densely labelled. In contrast, specific binding in the forebrain was very low and concentrated in some regions of the limbic system. The enrichment of [3H]ICS 205-930 binding sites in nuclei of the dorsal medulla and spinal cord is in good agreement with the proposed role for 5-hydroxytryptamine in sensory processing. High densities of 5-hydroxytryptamine3 binding sites in the area postrema support a central site of action for 5-hydroxytryptamine in emesis. Finally, the presence of [3H]ICS 205-930 binding sites in the limbic system provides an anatomical substrate for the behavioural effects of 5-hydroxytryptamine3 receptor antagonists.

The interstitial system of the spinal trigeminal tract in the rat: anatomical evidence for morphological and functional heterogeneity

Utilizing cyto-, myelo-, and chemoarchitecture as well as connectional criteria, the present study reveals the interstitial system of the spinal trigeminal tract (InSy-SVT) in the rat to be composed of five morphologically and functionally distinct components that are distributed within spatially restricted regions of the lateral medulla. The first component is represented by scattered interstitial cells and neuropil, which extend laterally into SVT from the superficial laminae of the medullary dorsal horn (MDH). The second component, the dorsal paramarginal nucleus (PaMd), consists of a small group of marginal (lamina I)-like neurons and neuropil situated within the dorsolateral part of SVT at the rostral pole of MDH. The third component represents a trigeminal extension of the parvocellular reticular formation (V-Rpc) into the ventromedial aspect of SVT at levels extending from rostral MDH to the caudal part of trigeminal nucleus interpolaris (Vi). The fourth component, the paratrigeminal nucleus (PaV), consists of a large accumulation of neurons and neuropil situated within the dorsal part of SVT throughout the caudal half of Vi. The fifth component is the insular trigeminal-cuneatus lateralis nucleus (iV-Cul), which is a discontinuous collection of neurons and neuropil interspersed among fibers of SVT as well as wedged between it and the spinocerebellar tract. Thalamic projection neurons are located in PaMd and V-Rpc, whereas cerebellar projecting neurons are confined to iV-Cul.

A survey of the cytology and synaptic organization of the insular trigeminal-cuneatus lateralis nucleus in the rat, including an identification of spinal afferent inputs

The cytology and synaptic organization of the insular trigeminal-cuneatus lateralis (iV-Cul) nucleus was examined in the rat. In addition, the ultrastructural morphology and synaptic connectivity of anterogradely labeled spinal afferent axons terminating in iV-Cul were examined following injection of horseradish peroxidase (HRP) into the cervical spinal cord. The uniformity of the ultrastructural features of iV-Cul neurons supports the presence of a homogeneous neuronal population. The most prominent feature of the iV-Cul neuropil is the presence of numerous interdigitating astrocytic processes, which extensively isolate neuronal somata and processes. iV-Cul contains a heterogeneous population of axonal endings that can be separated into three categories, depending upon whether they contain predominantly spherical-shaped agranular synaptic vesicles (R endings), predominantly pleomorphic-shaped agranular synaptic vesicles (P endings), or a heterogeneous population of dense-core vesicles (DC endings). The R endings represent the majority of axonal endings in iV-Cul and establish asymmetrical axodendritic and axospinous synaptic contacts, primarily along the distal portions of the dendritic tree. P endings establish symmetrical axosomatic, axodendritic, and axospinous synaptic contacts and exhibit a more generalized distribution along the somadendritic tree. DC terminals establish asymmetrical axodendritic synaptic contacts with distal dendritic processes and are the least frequently observed endings in the iV-Cul neuropil. Numerous synaptic glomeruli, exhibiting a single large central R bouton that establishes multiple axodendritic or axospinous synapses, characterize the iV-Cul neuropil. Axoaxonic synapses are conspicuously absent from the iV-Cul neuropil and glomeruli. The anterograde HRP labeling of spinal afferent axons that terminate in iV-Cul indicates that the terminals along these fibers are of the R type and that they are engaged predominantly in synaptic glomeruli. The results of this study indicate that the synaptic organization of iV-Cul is distinctly different from that of neighboring somatosensory nuclei, and supports the recent suggestion that this nucleus should be considered a separate precerebellar spinal relay nucleus in the lateral medulla.

Turning responses evoked by stimulation of visuomotor pathways

Lateral eye, head, and body movements are produced by electrical stimulation of many brain regions from frontal cortex to pons. A new collision method shows that at least 5 separate axon bundles mediate stimulation-elicited lateral head and body movements in rats. One bundle passes between the rostromedial tegmentum and medial pons, with conduction velocities of 0.8-18 m/s. A second bundle passes between the superior colliculus and contralateral medial pons, with conduction velocities of 1.7-13 m/s. A third bundle passes between the superior colliculus and ventrolateral pons, with conduction velocities of 1.3-20 m/s. A fourth bundle passes between the internal capsule and medial substantia nigra, with conduction velocities of 0.9-4.4 m/s. A fifth bundle passes between the anteromedial cortex and rostral striatum, with conduction velocities of 2.4-36 m/s. Collision effects have not been observed between the anteromedial cortex and the internal capsule, medial substantia nigra, superior colliculus, rostromedial tegmentum, or medial pons, which suggests that these sites are not connected by axons mediating turning. Possible synaptic linkages between the 5 bundles and possible transmitters are discussed.

Absence of tonic supraspinal control of substance P release in the substantia gelatinosa of the anaesthetized cat

Antibody microprobes were used to measure immunoreactive substance P (irSP) release in the substantia gelatinosa of the lower lumbar spinal cord of barbiturate-anaesthetized cats. Release of irSP was produced by noxious peripheral stimuli. Such release was not altered by blocking spinal conduction at the first lumbar segment by cooling or transecting the spinal cord. The results suggest that the release of irSP from the central terminals of nociceptors is not subject to tonic supraspinal inhibition.

Morphology and distribution of serotoninergic and oculomotor internuclear neurons in the cat midbrain

Serotoninergic fibers have been reported in both the abducens and facial nuclei of the cat. Furthermore, serotoninergic dorsal raphe and oculomotor internuclear neurons occupy similar locations in the periaqueductal gray overlying the oculomotor and trochlear motor nuclei. To resolve the issue of whether these two populations of neurons overlap, serotoninergic fibers were assayed in the abducens and facial nucleus; then the morphologies and distributions of identified serotoninergic neurons and oculomotor internuclear neurons were determined. Both the abducens and facial nuclei contained varicosities labelled with antibody to serotonin, but a much higher density of immunoreactive fibers was present in the latter, especially in its medial aspect. Distinct synaptic profiles labelled with antibodies to serotonin were observed in both nuclei. In both cases, terminal profiles contained numerous small, predominantly spheroidal, synaptic vesicles as well as a few, large, dense-core vesicles. These profiles made synaptic contacts onto dendritic and, in the facial nucleus, somatic profiles that occasionally displayed asymmetric, postsynaptic, membrane densifications. Following injection of horseradish peroxidase into either the abducens or facial nuclei, double-label immunohistochemical techniques demonstrated that the serotoninergic and oculomotor internuclear neurons form two distinct cell populations. The immunoreactive serotoninergic cells were distributed within the dorsal raphe nucleus, predominantly caudal to the retrogradely labelled oculomotor internuclear neurons. The latter were located in the oculomotor nucleus along its dorsal border and in the adjacent supraoculomotor area. Intracellular injection of horseradish peroxidase revealed that oculomotor internuclear neurons have multipolar somata with up to ten long, tapering dendrites that bifurcate approximately five times. Their dendritic fields were generally contained within the nucleus and adjacent supraoculomotor area. In contrast, putative serotoninergic neurons were often spindle-shaped and exhibited far fewer primary dendrites. Many of these long, narrow, sparsely branched dendrites crossed the midline and extended to the surface of the cerebral aqueduct. In the vicinity of the aqueduct they branched repeatedly to form a dendritic thicket. The axons of the intracellularly stained serotoninergic neurons emerged either from the somata or the end of a process with dendritic morphology, and in some cases they produced axon collaterals within the periaqueductal gray. Thus the oculomotor internuclear and serotoninergic populations differ in both distribution and morphology.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural organization of regenerated serotonin axons in the dorsomedial hypothalamus of the adult rat

The ultrastructural organization of regenerated serotonin (5-HT) axons was examined in the dorsomedial hypothalamus (DMH) of the adult rat using high-resolution radioautography after intraventricular infusion of [3H]5-HT. An analysis of the microenvironment of the [3H]5-HT-labelled terminals in the DMH was made 30 and 50 days after unilateral injection of 5,7-dihydroxytryptamine (5,7-DHT) or vehicle solution into the dorsolateral hypothalamus. In sham-treated animals [3H]5-HT-labelled axons were small, contained many small clear vesicles, one or more large granular vesicles, and showed only rare synaptic specializations. In 5,7-DHT-treated animals the internal organization of [3H]5-HT-labelled profiles resembled that of sham-treated animals. A tendency toward increased synaptic frequency was found for [3H]5-HT-labelled terminals in the 5,7-DHT-treated group 50 days post-lesion, and an increase in the number of [3H]5-HT-labelled terminals abutting unlabelled perikarya was found in both 30- and 50-day post-lesion groups as compared to sham-treated groups. No other differences in ultrastructural environment were found between sham- and 5,7-DHT-treated animals at either 30 or 50 days post-lesion. These results suggest that 5-HT fibres in the hypothalamus regenerate with a great deal of cellular specificity.

Serotonin axon terminals in the ventral tegmental area of the rat: fine structure and synaptic input to dopaminergic neurons

The serotoninergic (5-hydroxytryptamine, 5-HT) innervation of the rat ventral tegmental area (VTA) was examined by light and electron microscopic radioautography following intraventricular infusion of [3H]5-HT. The [3H]5-HT labeled processes were characterized with respect to their regional distribution, ultrastructure and relationships with all neurons, including dopaminergic neurons, identified in the same sections using immunocytochemistry for the localization of the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH). By light microscopy, [3H]5-HT labeled axons and axonal varicosities were detected throughout the interfascicular nucleus and ventral portion of the VTA. By electron microscopy, [3H]5-HT-labeled axons were found to be mainly small and unmyelinated, although a few showed several lamellae of myelin. The labeled varicosities measured 0.6 micron in mean diameter and contained many small, round or flattened agranular vesicles and a few large granular vesicles. More than 18% showed synaptic specializations in single thin sections. Most of these synapses were asymmetric and established on dendritic shafts. Based on the probability of seeing such synaptic specializations in single thin sections, it was estimated that as many as 50% of the labeled 5-HT terminals formed synaptic contacts in the VTA. In dually labeled light microscopic sections, [3H]5-HT-accumulating processes often appeared adjacent to TH-immunoreactive perikarya and proximal dendrites. Electron microscopy demonstrated that terminals with radioautographic labeling for 5-HT formed conventional synapses both with TH-labeled and unlabeled dendrites in the VTA. Many additional 5-HT terminals lacking recognizable synaptic densities were directly apposed to TH-labeled dendrites and were isolated from the rest of the neuropil by thin glial leaflets. These results suggest that 5-HT neurons innervate both dopaminergic and non-dopaminergic neurons in the VTA and may influence mesocortical and mesolimbic efferent systems through synaptic as well as non-synaptic mechanisms.

On the relationship between chronic pain and depression when there is no organic lesion

Patients suffering from pain without evidence of either depression or organic lesions, or of any pathophysiological process to which the pain might be attributed, may be diagnosed as suffering from 'indeterminate pain.' The evidence in the literature which suggests that some of these cases might be due to a 'depressive equivalent' is examined. It is suggested that it is difficult, if not impossible, to formulate a diagnosis of depressive illness in patients who do not have clear symptoms of depression. However, there is evidence in the literature that a relatively high percentage of patients with chronic indeterminate pain appear to have a family history of depression and depressive spectrum disorders. Biological markers of depression also give some indication that certain of these patients may have a link with depressive illness as well as with pain. It is suggested that there is a need to explore the existence of a sub-group of patients with indeterminate pain in whom the mechanism of the pain may be related to the mechanism of depressive illness even though formal depressive symptoms are not found.

Effects of midbrain stimulation and iontophoretic application of serotonin, noradrenaline, morphine and GABA on electrical thresholds of afferent C- and A-fibre terminals in cat spinal cord

We have used the single-fibre excitability testing method to investigate whether electrical stimulation in midbrain periaqueductal gray or lateral reticular formation, as well as intraspinal iontophoretic application of the suspected inhibitory neurotransmitters serotonin (5-hydroxytryptamine), noradrenaline, the opiate morphine, or gamma-aminobutyric acid (GABA), exert presynaptic actions at the central terminals of cutaneous afferent unmyelinated or myelinated fibres. Thresholds to antidromically excited 42 single unmyelinated and 18 myelinated fibres in the sural nerve by intraspinal microstimulation were determined before and during periaqueductal gray or lateral reticular formation stimulation (3 100 ms trains/s at 100 Hz; 100-900 microA) or intraspinal iontophoretic application (40-300 nA) of 5-hydroxytryptamine, noradrenaline, morphine or GABA from a multibarrel micropipette. Periaqueductal gray or lateral reticular formation stimulation had mixed effects on unmyelinated and myelinated fibre thresholds, with most threshold measurements within +/- 10% of control. There was a tendency for thresholds to increase more during periaqueductal gray than lateral reticular formation stimulation. Thresholds of unmyelinated fibres were predominantly raised during iontophoretic application of 5-hydroxytryptamine (20/29 fibres), noradrenaline (10/13) and morphine (15/21), while GABA had mixed effects; thresholds of nearly all myelinated fibres were raised by each drug. Both periaqueductal gray or lateral reticular formation stimulation and application of 5-hydroxytryptamine, noradrenaline or morphine tended to raise thresholds in the majority of the 53 unmyelinated and myelinated fibres tested. Methodological problems in interpreting the physiological significance of these results for presynaptic modulation are discussed.

Brainstem projections to lumbar motoneurons in rat--I. An ultrastructural study using autoradiography and the combination of autoradiography and horseradish peroxidase histochemistry

In 11 rats the descending projections from the ventrolateral medullary medial reticular formation, the medullary raphe nuclei and the area of the nucleus coeruleus and subcoeruleus to lumbar motoneuronal cell groups were studied by means of electron microscopical autoradiography after [3H]leucine injections in the respective brainstem areas. The distribution of the transported radioactivity in the autoradiographs was determined using the circle method [Williams (1977), in Practical Methods in Electron Microscopy, Vol. 6, pp. 85-173] which showed that the vast majority of the silver grains was located over terminal profiles. In the motoneuronal cell groups six different types of terminals were distinguished. After injections in the ventrolateral medial reticular formation the majority of the silver grains was located over F-type terminal profiles while many fewer silver grains were found over S- and G-types. After injections in the raphe nuclei and the adjoining medial reticular formation approximately equal numbers of silver grains were found over F- and G-type terminals while fewer were found over S-type. A small proportion of silver grains was present over C-type terminals and only after injections in the ventrolateral medial reticular formation. After [3H]leucine injections in the area of the nucleus coeruleus and subcoeruleus the majority of silver grains were located over E- and S-type terminals whereas relatively few were located over F-type terminals. The E-type terminal, which has not been described before in the motoneuronal cell groups, is characterized by the fact that it contains relatively small vesicles and occasionally elongated or canaliculi-like structures. In the three groups of experiments approximately 40-50% of the labelled S- and F-type terminal profiles established synaptic contacts, but only approximately 10% of the labelled E- and G-type terminal profiles did so. In all cases these synaptic contacts were established mainly with proximal dendrites. In the autoradiographs some of the silver grains were concentrated into clusters. The vast majority of these clusters, consisting of six or more silver grains, were centred over terminal profiles. The differential distribution of these clusters over the different types of terminal profiles in the various experiments was roughly the same as found by means of the circle method. In two rats [3H]leucine injections in the ventrolateral medial reticular formation were combined with horseradish peroxidase injections in the ipsilateral hindleg muscles, resulting in retrograde labelling of the corresponding motoneurons as visualized by means of the tetramethyl benzidine incubation method.(ABSTRACT TRUNCATED AT 400 WORDS)

Transmitter localization and vesicle turnover at a serotoninergic synapse between identified leech neurons in culture

An electron microscopic study has been made of chemical synapses that develop between identified nerve cells isolated from the CNS of the leech and maintained in culture. Structures resembling synapses were observed in pairs of Retzius cells and P sensory cells at which chemical transmission had been demonstrated by recording with microelectrodes. Vesicle recycling was shown by following the uptake of extracellular markers after stimulation. The membrane separation between the presynaptic Retzius cell (which is known to liberate serotonin) and the postsynaptic P cell was wider in synaptic than in extrasynaptic regions. The Retzius cell contained clusters of clear vesicles apposed to thickenings of the presynaptic membrane. These clear vesicle clusters were capped by a layer of dense core vesicles that did not contact the presynaptic membrane thickenings. Subsynaptic cisternae were found in the postsynaptic cell opposite the presynaptic membrane thickenings. Occasional slight postsynaptic membrane thickenings were seen. Extracellular material was observed within the synaptic cleft. Similar synaptic structures developed between pairs of Retzius cells in culture; even a single Retzius cell was able to form autapses upon itself. Structures resembling transmitter release sites were found in Retzius cells at a distance from any postsynaptic membranes. These are presumed to be locations for the diffuse release of transmitter. Presynaptic structures resembling release sites were never observed in P cells apposed to Retzius cells. Antibody to serotonin (5-HT) labelled with colloidal gold showed serotonin to be localized in the dense core vesicles in Retzius cells. Stimulation of pairs of Retzius and P cells by raised concentrations of K+ resulted in uptake of extracellular markers. Only Retzius cells became labelled. Ferritin was found in cisternae, in dense core vesicles, and in clear vesicles. HRP was found in cisternae and in clear vesicles. Colloidal gold was taken up by coated vesicles and was occasionally found in both clear and dense core vesicles. The uptake of extracellular markers following stimulation was blocked by high Mg++. These results show that structures develop between pairs of cells at which chemical transmission develops and that transmitter release leads to turnover of dense core and clear vesicles.

Ultrastructure of marginal zone during prenatal development of human spinal cord

Electron microscopic studies were conducted in the marginal zone (lamina I) in human fetuses ranging from 8-25 weeks of gestational age. At 8 weeks the neurons have indented nuclei and sparse organelles in the cytoplasm. The neuropil shows contacts between the axons and dendritic profiles. Some of them are well defined synapses with post synaptic thickening and agranular spherical vesicles in the presynaptic terminal. At 18 weeks compactly packed organelles with long cisternae of rough endoplasmic reticulum could be visualized in the neuronal cytoplasm. At 25 weeks the neurons have heterochromatin patches in the nuclei. Axosomatic, dendrodendritic, axoaxonic, symmetrical, asymmetrical and multisynaptic contacts with agranular and dense core vesicles are seen at different sequential age periods.

Regional differences in 5-hydroxytryptamine and catecholamine uptake in primary astrocyte cultures

The uptake of 3H-labelled 5-hydroxytryptamine (5-HT, serotonin) norepinephrine ([3H]NE), and 3,4-dihydroxyphenylethylamine ([ 3H]dopamine, [3H]DA) was studied in primary astrocyte cultures prepared from the cerebral cortex, corpus striatum, and hippocampal regions of neonatal rat brain. Na+-dependent uptake showed marked regional differences. For [3H]5-HT the magnitude of uptake was corpus striatum greater than or equal to cerebral cortex greater than hippocampus, whereas for [3H]NE the order was hippocampus greater than corpus striatum greater than cerebral cortex. For [3H]DA, only the hippocampal cultures showed significant Na+-dependent uptake. [3H]5-HT uptake was specifically inhibited by 10(-7) M fluoxetine whereas [3H]NE uptake was preferentially inhibited by 10(-7) M desipramine. These results may reflect regional brain specialization and/or different developmental patterns of high affinity uptake of serotonin and catecholamines by astrocytes in situ.

Bulbospinal projections in the primate: a light and electron microscopic study of a pain modulating system

The projections of the nucleus raphe magnus (NRM) and the immediately adjacent reticular formation were studied in the macaque monkey following injections of the rostroventral medulla with 3H-leucine and examination of the resultant labeled axons and terminals by light and electron microscopic autoradiography. Five monkeys had accurately placed injections, which resulted in fiber pathway labeling that coursed caudally, laterally, and dorsally to project to laminae I, II, and V of subnucleus caudalis of the trigeminal and then traveled in the dorsolateral funiculus of the cord and terminated in similar laminae of the spinal dorsal horn at cervical levels. The pathway was only lightly labeled caudal to the cervical enlargement and could not be readily discerned above background in the thoracic or lumbar cord. Electron microscopy revealed that axons and terminals serving this system constitute a heterogeneous population. Large-diameter myelinated axons (3-6-micron diameter), small myelinated axons (0.75-3-micron diameter), and clusters of nonmyelinated axons were labeled. Terminals in laminae I, II, and V contained mixtures of clear round and granular vesicles or clear pleomorphic and granular vesicles or formed the central element in synaptic glomeruli. The labeled profiles formed asymmetrical or symmetrical synapses on medium and small dendrites; labeled axosomatic synapses were not observed. In rare instances there were contacts between labeled profiles and vesicle-containing structures, which were probably dendritic, but whether the NRM axon was pre- or postsynaptic to such structures could not be determined. It was concluded that the NRM in the monkey is organized in a manner quite similar to that previously described in the cat. The wide variety of fiber types and synaptic terminals serving this system suggests that different classes of neurons participate in it, probably using several transmitter substances that result in varying postsynaptic effects on neurons located in the trigeminal complex and dorsal horn.

Monoamine innervation of the oculomotor nucleus in the rat. A radioautographic study

The serotonin and noradrenaline innervations of the rat oculomotor nucleus were examined by high resolution radioautography after in vivo labeling with tritiated 5-hydroxytryptamine and dopamine, respectively. Noradrenaline as well as serotonin endings (axonal varicosities) pervaded the entire nucleus, but the latter were at least six times more numerous (1.3 X 10(6) per mm3 of tissue) and were often found in the immediate vicinity of neuronal somata and proximal dendrites. The axon terminals of both types were of similar size and exhibited some large dense-cored vesicles in association with aggregated small and clear vesicles. The dense-cored vesicles were, however, more frequent and the content in clear vesicles more pleomorphic in serotonin than noradrenaline endings. In single thin sections, the proportion of noradrenaline and serotonin profiles exhibiting a synaptic junction was relatively small (15%). These were either symmetrical or asymmetrical when made on dendritic branches but invariably symmetrical on spines. In addition, a significant number of serotonin terminals were seen in close apposition or synaptic contact with neuronal perikarya and large dendrites, allowing for a direct, "proximal" action of serotonin. Moreover, many such terminals appeared to be coupled with unlabeled endings of another category, characterized by dispersed, uniformly round and clear synaptic vesicles, providing an alternate route for a proximal effect of serotonin in the oculomotor nucleus. In line with previous investigations on other motor nuclei, these data support the likelihood of a close involvement of both noradrenaline and serotonin in the control of motoneuronal activity.