Localization Of Enkephalin Research Articles

Immunohistochemical localization of enkephalin in the human striatum: A postmortem ultrastructural study

Within the basal ganglia, the functionally defined region referred to as the striatum contains a subset of GABAergic medium spiny neurons expressing the neuropeptide enkephalin. Although the major features of ultrastructural enkephalin localization in striatum have been characterized among various species, its ultrastructural organization has never been studied in the human brain. Human striatal tissue was obtained from the Maryland and Alabama Brain Collections from eight normal controls. The brains were received and fixed within 8 h of death allowing for excellent preservation suitable for electron microscopy. Tissue from the dorsal striatum was processed for enkephalin immunoreactivity and prepared for electron microscopy. General morphology of the dorsal striatum was consistent with light microscopy in human. The majority of neurons labeled with enkephalin was medium-sized and had a large nonindented nucleus with a moderate amount of cytoplasm, characteristic of medium spiny neurons. Of the spines receiving synapses in dorsal striatum, 39% were labeled for enkephalin and were of varied morphologies. Small percentages (2%) of synapses were formed by labeled axon terminals. Most (82%) labeled terminals formed symmetric synapses. Enkephalin-labeled terminals showed no preference toward spines or dendrites for postsynaptic targets, whereas in rat and monkey, the vast majority of synapses in the neuropil are formed with dendritic shafts. Thus, there is an increase in the prevalence of axospinous synapses formed by enkephalin-labeled axon terminals in human compared with other species. Quantitative differences in synaptic features were also seen between the caudate nucleus and the putamen in the human tissue.

Distribution of methionine and leucine enkephalin neurons within the social behavior circuitry of the male Syrian hamster brain

Enkephalin plays a role in the social behaviors of many species, but no corresponding role for this peptide has been investigated in the male Syrian hamster, a species in which brain nuclei controlling social behaviors have been identified. Previous studies have shown the distribution of dynorphin and beta-endorphin throughout social behavior circuits within the male hamster brain. To date, the only studies of enkephalin in the hamster brain address the distribution of this peptide in the olfactory bulb and hippocampus. The present study provides a complete map of enkephalinergic neurons within the forebrain and midbrain of the male Syrian hamster and addresses the question of whether enkephalin immunoreactive (Enk-ir) cells are found within brain regions relevant to male hamster social behaviors. Following immunocytochemistry for either methionine enkephalin (met-enkephalin) or leucine enkephalin (leu-enkephalin), we observed enkephalin localization consistent with data that have previously been reported in the rat, with notable exceptions including lateral septum, ventromedial nucleus of the hypothalamus and cingulate gyrus. Additionally, met- and leu-enkephalin localization patterns largely overlap. Consistent with the post-translational processing of preproenkephalin, met-enkephalin was more abundant than leu-enkephalin both within individual cells (darker staining), and within given brain nuclei (more met-enkephalin immunoreactive cells). Two exceptions were the posterointermediate bed nucleus of the stria terminalis, containing more neurons heavily labeled for leu-enkephalin, and the main olfactory bulb, where only met-enkephalin was observed. Of most interest for this study was the observation of Enk-ir cells and terminals in areas implicated in both sexual and agonistic behaviors in this species.

Differences in opioidergic inhibition of spinal reflexes and Fos expression evoked by mechanical and chemical noxious stimuli in the decerebrated rabbit

Noxious mechanical and chemical stimuli were applied to the toes of the left hind limb of decerebrated, spinalized rabbits and their effects on a hind limb spinal withdrawal reflex and expression of Fos-like immunoreactivity in the spinal cord were measured. The animals were prepared so as to minimize nociceptive inputs arising from surgery. A single crush stimulus applied with a pair of haemostatic forceps caused long-lasting ( c. 20 min) inhibition of reflexes evoked in medial gastrocnemius motoneurons by electrical stimulation of the skin at the heel. Naloxone (0.25 mg/kg i.v.) increased reflexes to more than 1000% of pre-drug controls and reversed crush-evoked inhibition. Mustard oil applied to the toes had no consistent effects on the heel–gastrocnemius reflex before or after naloxone. Both crush and mustard oil stimuli gave rise to unilateral increases in the number of Fos-immunopositive profiles in the superficial dorsal horn of spinal segments L7 and S1. There were significantly more Fos-immunoreactive elements in the central and lateral parts of lamina I of both segments in animals receiving the crush stimulus than there were in animals receiving the mustard oil stimulus. Immunochemical localization of enkephalins in rabbit spinal cord showed a dense network of fibres and terminals in laminae I and II, accompanied by infrequent but distinctly stained neuronal cell bodies. The same pattern, with increased numbers of visible cell bodies, was seen after treatment with colchicine. The present data show that tonic and stimulus-evoked opioidergic inhibition of the heel–gastrocnemius reflex of the rabbit are not epiphenomena of surgical preparation of the hindlimb. Opioid-mediated inhibition of the heel–gastrocnemius withdrawal reflex of the rabbit was evoked by noxious mechanical but not by chemical stimulation of the toes. Of these stimuli, the former gave rise to greater activation of neurons in central and lateral lamina I of segments L7 and S1, the region of termination of afferent fibres from the heel and the location of some enkephalin-positive neuronal cell bodies. Thus, noxious mechanical stimulation of the toes elicits inhibition of the heel–gastrocnemius withdrawal reflex, probably via activation of enkephalinergic neurons in the lateral half of lamina I in the L7 and S1 segments.

Immunocytochemical localization of enkephalins in the brain of the African lungfish, Protopterus annectens, provides evidence for differential distribution of Met‐enkephalin and Leu‐enkephalin

The distribution of various opioid peptides derived from proenkephalin A and B was studied in the brain of the African lungfish Protopterus annectens by using a series of antibodies directed against mammalian opioid peptides. The results show that both Met-enkephalin- and Leu-enkephalin-immunoreactive peptides are present in the lungfish brain. In contrast, enkephalin forms similar to Met-enkephalin-Arg-Phe, or Met-enkephalin-Arg-Gly-Leu, as well as mammalian α-neoendorphin, dynorphin A (1–8), dynorphin A (1–13), or dynorphin A (1–17) were not detected. In all major subdivisions of the brain, the overwhelming majority of Met-enkephalin- and Leu-enkephalin-immunoreactive cells were distinct. In particular, cell bodies reacting only with Leu-enkephalin antibodies were detected in the medial subpallium of the telencephalon, the griseum centrale, the reticular formation, the nucleus of the solitary tract, and the visceral sensory area of the rhombencephalon. Cell bodies reacting only with Met-enkephalin antibodies were found in the lateral subpallium of the telencephalon, the caudal hypothalamus, and the tegmentum of the mesencephalon. The preoptic periventricular nucleus of the hypothalamus exhibited a high density of Met-enkephalin-immunoreactive neurons and only a few Leu-enkephalin-immunoreactive neurons. The distribution of Met-enkephalin- and Leu-enkephalin-immunoreactive cell bodies and fibers in the lungfish brain showed similarities to the distribution of proenkephalin A-derived peptides described previously in the brain of land vertebrates. The presence of Met-enkephalin- and Leu-enkephalin-like peptides in distinct regions, together with the absence of dynorphin-related peptides, suggests that, in the lungfish, Met-enkephalin and Leu-enkephalin may originate from distinct precursors. J. Comp. Neurol. 396:275–287, 1998. © 1998 Wiley-Liss, Inc.

Immunocytochemical localization of enkephalins in the brain of the African lungfish,Protopterus annectens, provides evidence for differential distribution of Met-enkephalin and Leu-enkephalin

Immunocytochemical localization of enkephalins in the brain of the African lungfish,Protopterus annectens, provides evidence for differential distribution of Met-enkephalin and Leu-enkephalin

Immunocytochemical localization of enkephalins in the brain of the African lungfish, Protopterus annectens, provides evidence for differential distribution of Met‐enkephalin and Leu‐enkephalin

The distribution of various opioid peptides derived from proenkephalin A and B was studied in the brain of the African lungfish Protopterus annectens by using a series of antibodies directed against mammalian opioid peptides. The results show that both Metenkephalin- and Leu-enkephalin-immunoreactive peptides are present in the lungfish brain. In contrast, enkephalin forms similar to Met-enkephalin-Arg-Phe, or Met-enkephalin-Arg-Gly-Leu, as well as mammalian alpha-neoendrophin, dynorphin A (1-8), dynorphin A (1-13), or dynorphin A (1-17) were not detected. In all major subdivisions of the brain, the overwhelming majority of Met-enkephalin- and Leu-enkephalin-immunoreactive cells were distinct. In particular, cell bodies reacting only with Leu-enkephalin antibodies were detected in the medial subpallium of the telencephalon, the griseum centrale, the reticular formation, the nucleus of the solitary tract, and the visceral sensory area of the rhombencephalon. Cell bodies reacting only with Met-enkephalin antibodies were found in the lateral subpallium of the telencephalon, the caudal hypothalamus, and the tegmentum of the mesencephalon. The preoptic periventricular nucleus of the hypothalamus exhibited a high density of Metenkephalin-immunoreactive neurons and only a few Leu-enkephalin-immunoreactive neurons. The distribution of Met-enkephalin- and Leu-enkephalin-immunoreactive cell bodies and fibers in the lungfish brain showed similarities to the distribution of proenkephalin A-derived peptides described previously in the brain of land vertebrates. The presence of Met-enkephalin- and Leu-enkephalin-like peptides in distinct regions, together with the absence of dynorphin-related peptides, suggests that, in the lungfish, Met-enkephalin and Leu-enkephalin may originate from distinct precursors.

Immunohistochemical localization of enkephalin in peripheral sensory axons in the rat

Dorsal root ganglia (DRG) contain measurable amounts of met-enkephalin (ENK), and a significant number of DRG cells contain mRNA for the manufacture of ENK. Yet almost no DRG cells are immunostained for ENK and dorsal rhizotomy does not diminish ENK staining in the dorsal horn. A hypothesis which would explain these seemingly discrepant results is the phenomenon of differential transport, where DRG cells making ENK rapidly transport the peptide only to their peripheral sensory axons. Evidence consistent with this hypothesis would be the demonstration of ENK-containing peripheral sensory axons. The present study demonstrates that approximately 17% of peripheral cutaneous axons label for ENK. The presence of a significant number of ENK-containing axons suggests an endogenous neural source of opiate ligand in the periphery and, in addition to ENK-containing inflammatory cells, this neural source may be functionally important in responses to physiologic as well as inflammatory pain.

Expression and localization of enkephalin, substance P, and substance P receptor genes in the rat carotid body.

Peripheral chemoreceptors in the carotid body sense changes in arterial oxygen, carbon dioxide tension and pH and play a critical role in modulating ventilation. The major components of the carotid body involved in chemoreception are the chemosensitive Type 1 cell which contains vesicles that store and release excitatory and inhibitory neurotransmitters, the supportive Type 2 cell, blood vessels and fibers from the carotid sinus nerve, the output from the carotid body. Dopamine, Met-enkephalin and substance P are three putative neurotransmitters/neuromodulators that have been identified in the carotid body (for review see Gonzalez et al, 1995).KeywordsCarotid BodySuperior Cervical GanglionCarotid Sinus NerveSodium PolyacrylateSubstance PreceptorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Immuno-electron-microscopic localization of enkephalin in the secretory granules of C cells in the chicken ultimobranchial glands

In the chicken, enkephalin-immunoreactive cells and nerve fibers are distributed in the ultimobranchial glands, which consist of C-cell groups and cyst structures. Ultrastructural features of the enkephalin cells and nerve fibers were examined by immuno-electron microscopy using both the streptavidin-biotin-peroxidase method and the protein A-colloidal gold method. Immunoreactivity for enkephalin was located on the secretory granules of C cells. In 1-day-old chickens, three types of C cells were distinguished on the basis of their granule size. Type-I cells were filled with large secretory granules (200-600 nm in diameter). These elements represented a majority of the C-cell population. Type-II cells contained medium-sized granules (100-280 nm in diameter). Type-III cells displayed small secretory granules (60-200 nm in diameter). The latter cells were elongate or irregular in shape and frequently extended cytoplasmic processes into the connective tissue stroma or contacted other C cells. Enkephalin-immunoactivity was revealed by dense deposits of immunogold particles on the secretory granules of type-II and type-III cells. There were only a few type-I cells showing immunoreactivity for enkephalin. A double immunogold labeling procedure demonstrated that calcitonin and enkephalin were colocalized in the same secretory granules of type-I and type-II cells. Type-III cells were devoid of immunoreactivity for calcitonin. Enkephalin-immunoreactive nerve fibers were characterized by the presence of granular vesicles, 60-160 nm in diameter, and frequently established direct contact with the surface of C cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of enkephalin and substance P in the nucleus caudalis of the spinal trigeminal V in the medulla oblongata of the human fetus

The distribution of enkephalin-positive neurons, substance P-positive and enkephalin-positive fibers was studied in the nucleus caudalis of the trigeminal spinal V in the medulla oblongata regions of developing humans (12 weeks gestation to 40 weeks gestation). Enkephalin-positive neurons were identified in all the subnuclei of the nucleus caudalis as early as 12 weeks of gestation and increased in number as the fetus aged. Substance P-positive neurons were absent in this area throughout development. On the other hand, substance P-positive and enkephalin-positive fibers were present in all the subnuclei, again commencing as early as 12 weeks of gestation. These fibers tended to be linked to each other in the different subnuclei and to the reticular formation in this area and to increase significantly in quantity by the latter quarter of pregnancy. These results show the early presence of these neurons and fibers in the first trimster of development.

Dual ultrastructural localization of enkephalin and tyrosine hydroxylase immunoreactivity in the rat ventral tegmental area: multiple substrates for opiate-dopamine interactions

Endogenous opiates modulate activity in the mesocorticolimbic dopaminergic system, and this interaction is thought to underlie major aspects of motoric, reward-seeking, and stress-coping behaviors. We sought to determine the ultrastructural substrate for this modulatory action at the level of dopaminergic perikarya in the rat ventral tegmental area (VTA). Using a dual-labeling, immunoperoxidase and immunogold-silver method, we localized antisera directed against leu5-enkephalin (ENK) and the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) in acrolein-fixed sections through the VTA. ENK-like immunoreactivity (ENK-LI) was visualized within unmyelinated axons and in axon terminals. In terminals, ENK-LI was densely localized to one or more dense-cored vesicles and either densely or lightly detected surrounding small clear vesicles. Immunoreactive dense-cored vesicles were occasionally associated with the presynaptic specialization but were more frequently detected at distant sites along the plasmalemmal surface, often in apposition to astrocytic processes. ENK-immunoreactive terminals formed both symmetric and asymmetric synapses, most frequently on large proximal dendrites. Direct appositions without glial separation were also detected between terminals containing ENK-LI and other ENK-labeled or unlabeled terminals. In contrast to ENK-LI, immunolabeling for TH was primarily detected within perikarya and dendrites in the VTA. Of the ENK-immunoreactive terminals that formed synaptic contacts in single sections, approximately 50-60% were in association with TH-labeled dendrites. The remainder formed synapses on dendrites lacking detectable immunoreactivity for TH. Multiple ENK-immunoreactive terminals occasionally formed convergent synaptic contacts on single TH-labeled or unlabeled dendrites. Furthermore, individual ENK-labeled terminals sometimes formed divergent contacts on two TH-labeled or unlabeled dendrites. When a single ENK-immunoreactive terminal made dual synaptic contacts on TH-labeled dendrites, the latter were usually in close apposition to one another. These findings represent the first ultrastructural demonstration that opioid peptide-containing terminals provide a direct synaptic input to dopaminergic, as well as nondopaminergic, neurons in the VTA. In addition, the morphological evidence suggests that endogenous opioid peptides (1) may be released from nonsynaptic sites, (2) may modulate the release of transmitters from other terminals, and/or (3) may synchronize the activity of multiple neuronal targets in the VTA. These results provide a number of morphological substrates through which opiates may directly or indirectly regulate activity in mesocorticolimbic dopaminergic pathways.

Comparative Distribution of Neurons Containing FLFQPQRFamide-like (morphine-modulating) Peptide and Related Neuropeptides in the Rat Brain.

FLFQPQRF-NH2 (F8Famide; morphine-modulating peptide), isolated from bovine brain, is an FMRFamide-like peptide with opioid analgesia modulating effects. In the rat brain, F8Famide is immunohistochemically localized in neurons of the medial hypothalamus and medulla oblongata. Neuropeptide Y (NPY) is structurally related to F8Famide and the mammalian FMRFamide-like immunoreactivity (LI) was once thought to be due to an NPY-like peptide. We compared the anatomical distribution of F8Famide-LI with the localization of enkephalin- and NPY-LI-containing structures in the rat brain to find out if NPY or enkephalins coexist with F8Famide-LI. Cryostat sections of colchicine-treated Wistar rat brains were incubated with specific antisera against F8Famide, NPY, YGGFMRGL (Met-enkephalin-Arg-Gly-Leu), or YGGFMRF (Met-enkephalin-Arg-Phe) raised in rabbits. The immunoreactivity was visualized by the peroxidase - antiperoxidase or immunofluorescence method. The light microscopic mirror method was applied to study the colocalization of F8Famide and NPY. The F8Famide-immunoreactivity was concentrated in smaller areas of medial hypothalamus and nucleus of the solitary tract than that of enkephalins and NPY. In all brain areas, the distributions of F8Famide-, enkephalin- and NPY-immunoreactive neurons were distinct. F8Famide-, NPY- and enkephalin-LI-containing nerve terminals were seen in the nucleus of the solitary tract and in the lateral parabrachial nucleus. These results show that the neuronal systems containing F8Famide-, enkephalin- or NPY-LI are anatomically separate in all brain regions. However, there are terminal areas in which more than one type of these immunoreactivities are detected. These results have anatomical correlation with pharmacological reports, suggesting modulatory functions for these peptides on regulation of blood pressure, feeding behaviour and endocrine functions.

Immunohistochemical and ultrastructural studies of the various nuclei of the trigeminal complex in the human newborn

The various nuclei of the trigeminal complex were studied by immunohistochemical (enkephalin localization) and ultrastructural means in the brainstems of eight newborn human babies that died within 24 h after birth. Positive enkephalin neurons were detected in the chief sensory and spinal trigeminal nuclei as well as in some fibers of the trigeminal nerve. Ultrastructurally, two morphologically distinct types of neuron were observed, respectively, in the motor nucleus, the spinal nucleus and the mesencephalic nucleus of the trigeminal complex, whereas three morphologically distinct types of neuron were observed in the chief sensory nucleus. “Glomerulus” formation was a frequently observed feature in the chief sensory nucleus. In the spinal nucleus, rolls of synaptic terminals stacking up one on top of another and synapsing onto the final synaptic element were very much in evidence. Axosoniatic, axodendritic, dendrodendritic and dendroaxonic synapses were demonstrated in all the different nuclear areas of the trigeminal complex but axoaxonic synapses were absent in the mesencephalic nucleus. Some of the findings in the present human study were similar to those reported in the rats and cats.

Production of a bi-specific monoclonal antibody recognizing mouse kappa light chains and horseradish peroxidase

The production of a bi-specific monoclonal antibody that simultaneously recognizes mouse kappa light chains and horseradish peroxidase (HRP) for use as a general developing reagent in a wide variety of immunobased techniques is described. This antibody, named McC10, was produced by the fusion of an aminopterin-sensitive interspecies hybridoma which secretes rat monoclonal antibodies against HRP (RAP2.Ag) and splenocytes from a rat immunized with whole mouse immunoglobulin (Ig)G. The hybrid-hybridoma generated from this fusion expresses and secretes rat Igs of the IgG1 and IgG2a subclasses, as determined by radial immunodiffusion. In competitive binding solid-phase enzymatic assays, McC10 was found to cross-react with all four mouse IgG subclasses as well as mouse kappa light chains. In contrast, in this type of assay, McC10 did not appear to recognize mouse IgA, IgM or lambda light chains. However, IgM-bearing kappa light chains were recognized by immunocytochemistry. Epitope specificity of this bi-specific antibody was more clearly determined on immunoblots where McC10 was found to exclusively recognize mouse kappa light chains and display no cross-reactivity with mouse Ig heavy chains nor with kappa light chains from rat or rabbit. In addition, McC10 was used successfully in two-step immunocytochemistry (ICC) for the localization of enkephalin, nerve growth factor (NGF) receptor and paired helical filament-immunoreactive sites in rat brain, rat skin and human brain, respectively, using mouse IgG's and IgM's as primary antibodies. McC10 compared favourably with peroxidase-anti-peroxidase (PAP) ICC with respect to sensitivity but was markedly superior with respect to specificity when used in fixed human brain or rat skin.(ABSTRACT TRUNCATED AT 250 WORDS)

Development and localization of enkephalin and substance P in the nucleus of tractus solitarius in the medulla oblongata of human fetuses

The presence of enkephalin and substance P-positive neurons and fibers were studied by immunohistochemistry (peroxidase-antiperoxidase or avidin-biotin-peroxidase complex methods) in 26 human fetuses ranging from 11 weeks of gestation to 40 weeks of gestation. Enkephalin-positive neurons were localized in the commissural, medial and intermediate subnuclei as early as 11–12 weeks' gestation. Positive enkephalin fibers were localized around 12 weeks' gestation and in many subnuclei, notably the medial, commissural, intermediate, ventrolateral, ventral and dorsolateral subnuclei. Substance P-positive neurons were localized in the commissural and medial subnuclei around gestation age 13 weeks. Positive substance P fibers appeared even earlier, around 11 weeks of gestation in many subnuclei, notably the medial, intermediate, ventral, ventrolateral and dorsolateral subnuclei. Increase in both enkephalin- and substance P-positive fibers was evident in the later stages of development (e.g. around 26 weeks of gestation). The importance of the early appearance of enkephalin and substance P neurons and fibers of the pain pathways in the major subnuclei connecting with the cardiovascular, gastrointestinal and respiratory functions in the human has to be stressed.

Golgi and immunocytochemical analysis of neurons in trigeminal subnucleus interpolaris: Correlations with cellular localization of enkephalin

Recent electrophysiological evidence shows that rostral levels of the trigeminal spinal complex are concerned with pain processing from receptive fields in the face and oral cavity. The ventrolateral quadrant of the subnucleus interpolaris contains concentrations of enkephalin, dynorphin, serotonin, substance P and GABA [Matthews M.A. Hernandez T.V. and Liles S.L. (1987) Synapse 1, 512–529; Matthews M.A., McDonald G.K. and Hernandez T.V. (1988) Somatosensory Res. 5, 205–217]. These transmitters have also been localized to the fusiform and stalked cells in Laminae I and II of the subnucleus caudalis [Basbaum A.I. and Fields H.L. (1984) A. Rev. Neurosci. 7, 309–338]. The present study compares Golgi impregnations of the subnucleus interpolaris with sections at the same levels immunoreacted against enkephalin to determine if comparable cells exist in the subnucleus interpolaris and if they occur predominantly in the ventrolateral quadrant of the subnucleus. Twelve, young adult cats were killed by perfusion, the brainstems removed and either processed for rapid Golgi impregnation or sectioned and immunoreacted for enkephalin using the avidin-biotin Vectastain method. Golgi impregnated tissue was sectioned in the coronal, transverse or sagittal plane to insure the most advantageous visualization of cells with a directional bias in their dendritic arbors. The subnucleus interpolaris contained several distinctive cell types. The predominant neuron throughout the subnucleus was the smooth pyramidal cell or multipolar cell, characterized by a large round soma (15–25 μm diameter) and a spherical dendritic arborization which allowed its identification in all planes of section. The second cell type was the fusiform cell which had a smaller ovoid soma (10–15μm) with narrow, less ramified, dendritic arbors oriented dorsoventrally, thus giving a bipolar appearance. Fusiform cells were most concentrated along the lateral margin of the subnucleus interpolaris. Examination of sections at the same level reacted for enkephalin revealed cells with a bipolar appearance in these same locations. An additional cell population which tended to predominate in the lateral zone was the stalked cell. These displayed a rounded soma (12–20 μm) and were evident only in the transverse or sagittal plane. Two to four primary dendrites arose from the soma and extensively ramified into a dense spiny arbor directed into the body of the subnucleus interpolaris. Many examples contained enkephalin. Islet cells, characterized by a very small oval soma (6–12 μm) and dense, rostrocaudally oriented dendrites, were less common than stalked cells and were located deeper in the nucleus. These cells displayed recurrent dendritic branches in common with the spiny pyramidal cell, which was noted by Gobel [Gobel S. (1978) J. comp. Neurol. 180, 378–394; Gobel S. (1978) J. comp. Neurol. 180, 395–414] in the subnucleus caudalis and which was occasionally seen in our preparations. Spiny pyramidal cells had a triangular and distinctive basal and apical dendrites. Arboreal cells represented the last neuronal category noted in the subnucleus interpolaris. These were only infrequently encountered and displayed an extensively branched, laterally directed, dendritic arbor. Occasional arboreal cells were found to contain enkephalin. Finally, an extensive axonal plexus was observed along the lateral margin of the subnucleus interpolaris throughout its length. Axons arising from fusiform, stalked and arboreal cells had branches which either ramified in this plexus, recurred into the dendritic arbor of the parent cell or coursed into the spinal V tract. In conclusion, these findings indicate that the ventrolateral quadrant and lateral margin of the subnucleus interpolaris contains populations of neurons comparable in structure and enkephalin affinity to those neurons located in the superficial laminae of the subnucleus caudalis. These data provide additional support for a functional subdivision of the subnucleus interpolaris involved principally in pain processing.

Localization of enkephalin- and neurotensin-like immunoreactivities in cat adrenal medulla.

Enkephalin (ENK)- and neurotensin (NT)-immunoreactivities (IR) were localized in cat adrenal medulla using immunocytochemistry. ENK was localized mainly in adrenaline cells, 70%-80% of which were heavily labelled. About 5%-10% of the noradrenaline cells were ENK-immunoreactive (IR). A dense network of ENK-IR nerves was localized among adrenaline cells. NT was localized only in the noradrenaline cells, 60%-70% of which were immunoreactive. NT- and ENK-IR were localized in separate noradrenaline cells. A dense network of NT-IR nerves was restricted among noradrenaline cells. The present findings confirm that ENK- and NT-like peptides are localized in separate adrenal medullary cells and demonstrate that also the preganglionic nerves are divided in subpopulations according to their neuropeptide content. These nerves have a selective localization among adrenaline and noradrenaline cells and may have physiological significance in the control of secretion of catecholamines and neuropeptides from adrenal medulla.

The ultrastructural localization of enkephalin and substance P immunoreactivities in the nucleus tractus solitarii of the cat.

In the medial and commissural subdivisions of the nucleus tractus solitarii enkephalin and substance P immunoreactivities were localized within synaptic terminals, unmyelinated axons, and neuronal cell bodies. Both enkephalin and substance P immunoreactivities were contained within synaptic terminals which had a mixture of small clear vesicles and dense core vesicles. The presence of dense core vesicles within both the enkephalin- and substance P-immunoreactive terminals was a consistent feature, although they were not associated with the actual synaptic junction. While enkephalin- and substance P-immunoreactive terminals shared a similar morphology, their respective distributions along the dendritic tree were quite distinct. Enkephalin-immunoreactive terminals contacted mainly the cell body and proximal portions of the dendritic tree. In contrast, substance P-immunoreactive terminals synapsed predominantly with spines and shafts of small to medium-sized dendrites. Few substance P-immunoreactive terminals contacted proximal dendrites and they were never presynaptic to the neuronal cell body. This apparent segregation of synaptic terminals on neurons suggests that enkephalin synapses have a more pronounced effect than substance P terminals.

Localization of enkephalins in adrenaline cells and the nerves innervating adrenaline cells in rat adrenal medulla.

The coexistence of met5- and leu5-enkephalin-like immunoreactivities with catecholamines in the rat adrenal medulla was studied with combined fluorescence microscopy and immunocytochemistry. Both met5- and leu5-enkephalin-like immunoreactivities were localized in few heavily stained adrenaline cells and in a population of nerves innervating adrenaline cells and as well as ganglion cells among the adrenaline cells. Only occasionally single noradrenaline cells exhibited light immunostaining for both enkephalins but no positive fibers could be found around the noradrenaline cells. In electron microscope the immunoreaction was seen in the granules of the adrenaline cells and in the large synaptic vesicles of the nerve terminals around the adrenaline cells. The present findings suggest that enkephalin-like immunoreactivity coexists mainly with adrenaline in rat adrenal medulla and that the enkephalin immunoreactive terminals regulate secretion of adrenaline from rat adrenal medulla.

Localization of enkephalin and cholecystokinin immunoreactivities in the perforant path terminal fields of the rat hippocampal formation

The distribution of enkephalin immunoreactivity (EI) in the molecular layer of the hippocampal formation corresponded to the terminal field of the lateral perforant path and the lateral temporoammonic tract. The distribution of cholecystokinin immunoreactivity (CI) in the molecular layer of the hippocampal formation corresponded to the established terminal field of the medial temporoammonic tract. The exception was a CI band at the deep part of the molecular layer throughout the regio superior. Accordingly, an additional terminal field of the medial temporoammonic tract is suggested. Selective lesion of the entorhinal afferents to the hippocampus and the area dentata resulted in a disappearance of EI throughout the molecular layer with no affection of CI and vice versa. Neonatally X-ray irradiated hippocampi were examined as they appear in the adult animal. These animals are known to possess an altered relation between the granule cells of area dentata and the perforant path zones extending beyond a reduced medial blade into the stratum oriens of the regio inferior. In such animals EI and CI revealed the same pattern of changes by following the perforant path zones into stratum oriens due to neonatal X-ray irradiation. Accordingly, the perforant path may contain EI and CI independent of the granule cell dendrites. Based on a discussion of these observations we conclude that enkephalin immunoreactivity is localized in terminals of the lateral perforant path and the lateral temporoammonic tract and that cholecystokinin immunoreactivity is localized in the terminals of the medial perforant path and the medial temporoammonic tract.