FMRFamide-like immunoreactivity in the brain of the honeybee (Apis mellifera). A light-and electron microscopical study

Peptide-FMRFamide-like immunoreactivity in the brain and suboesophageal ganglion of the honeybee Apis mellifera L. is demonstrated with the peroxidase-antiperoxidase technique. Immunoreactivity is found in about 120 perikarya of the brain and in about 30 of the suboesophageal ganglion. These cells are distributed in 13 paired clusters representing neurons of different types including neurosecretory neurons projecting to neurohemal organs. Immunoreactivity of different intensity is found in the non-glomerular neuropil around the mushroom bodies, in the lateral protocerebrum, the central body, the optic tubercles, the lobula and medulla of optic lobe, the ocellar neuropil, in multiglomerular elements of the antennal lobes and in the dorsal deuterocerebrum. In the mushroom bodies, immunoreactivity is located in layers of the lobes and stalks, corresponding to intrinsic fibre bundles of some Kenyon cell types. The somata of these intrinsic cells did not show FMRFamide-like immunoreactivity. Electron microscopy of immunostained somata and nerve fibres was performed employing a pre-embedding peroxidase-antiperoxidase technique. Fibres of optic lobes and the non-glomerular neuropil contain immunoreactive dense core vesicles (diameter 50-165 nm) accumulated in boutons besides small synaptic vesicles and synaptic membrane specializations. Immunoreactive layers of the mushroom body neuropil were analysed at the ultrastructural level. Axon profiles with dense-core vesicles of a small type (diameter 35-75 nm) show only faint immunoreactive products. Immunoreactivity of intrinsic mushroom body neurons does not appear to be specifically correlated with synaptic organelles. Our results indicate that FMRFamide or related peptides peptides may be neuroactive compounds in different classes of nerve cells in the bee brain.     

Morphological changes in the hypothalamic arcuate nucleus and median eminence in the golden hamster during the neonatal period

The purpose of the present investigation was to study the ultrastructure of the arcuate nucleus (ARC) and median eminence of hamsters on days 1–15 of the neonatal period. From days 1–6, the neurons of the ARC had large nuclei and a small amount of cytoplasm which contained polysomes, mitochondria, RER, lysosomes and Golgi complexes. From days 7–15 there was an increase in the amount of cytoplasm as well as more extensive Golgi complexes and RER. Astrocytes were the predominant glial component in both the ARC and median eminence. Astrocytic processes were in juxtaposition to unmyelinated axons, dendrites, and synapses. Axodendritic and axosomatic synapses containing clear vesicles were observed in the neuropil on day 1. There was an increase in the number of dense-core vesicles in the axonal endings beginning on day 4. Concomitantly, there were increasing numbers of clear and dense-core vesicles (64–70 nm) in terminals of the external layer of the median eminence, whereas larger dense-core vesicles (105–140 nm) were distinguishable by day 10 immediately dorsal to the external layer. The capillaries of the median eminence were composed of nonfenestrated endothelium from days 1–9. Fenestrae began to appear about day 10. Ependymal cells lining the third ventricle had pinocytotic vesicles, microvilli, and bleb-like protrusions on their apical surfaces. Ependymal processes were adjacent to nerve processes in the neuropil of the ARC and in the external layer of the median eminence, where they contacted the perivascular space. Two types of supraependymal cells were seen in animals throughout the neonatal period. One resembled a neuron which sent processes along the ependymal surface and often between cells. The second type was similar to a macrophage. The results of this study demonstrate the maturation of the neural elements in the ARC/median eminence area of the neonatal hamster.     

Serotonin immunoreactivity in the circumesophageal nervous system of Hermissenda crassicornis

Immunohistochemical techniques were used to examine the distribution of serotonin-immunoreactive (5-HT-IR) neurons and processes in the circumesophageal nervous system of Hermissenda. Both the pedal and the cerebropleural ganglia contained immunoreactive neuronal somata, with the majority occurring in the pedal ganglia. Immunoreactive fibers and varicosities were identified in portions of the central neuropil, where we noted a consistent and specific relationship between 5-HT-IR axons, the optic nerve and the synaptic region in the neuropil near the photoreceptor terminals.     

Dopamine-immunoreactive neurons in the blowfly visual system: light and electron microscopic immunocytochemistry

Dopamine-immunoreactive (DA-IR) neurons were mapped in detail in the visual system of the blowfly, Calliphora erythrocephala. Three types of DA-IR neurons could be identified in the optic lobes. One type constitutes a population of several thousand columnar small field amacrine neurons in the second neuropil region, the medulla. The other two types are large field projection neurons innervating the next, more central, synaptic region comprising the lobula and the lobula plate, as well as centres of the midbrain. Their cell bodies are located latero-ventrally in the brain. No DA-IR neurons were seen in the most peripheral visual synaptic neuropil, the lamina. The two types of projection neurons form overlapping wide field arborizations in the lobula and lobula plate and cannot be distinguished from each other in this region. Their central connections are different, however. One type of projection neuron, BOD1, consists of two neurons that bilaterally connect the optic lobes and neuropil on each side of the oesophageal foramen in the posterior protocerebrum. The other type, BOD2, also consists of two bilateral neurons similar to BOD1, but with their central processes posteriorly in the lateral protocerebrum. The amacrine DA-IR neurons form lateral processes in three layers of the medulla synaptic neuropil. These neurons were also investigated by means of electron microscopical immunocytochemistry. They contain predominantly clear vesicles, but a few dense core vesicles could be resolved. The synaptic connections of the DA-IR amacrines suggest that they form centrifugal feedback circuits between the inner and the outer portion of the medulla. The present results indicate that dopamine may be a neurotransmitter in functionally different classes of neurons of the blowfly visual system: amacrines and projection neurons.     

Fine structural survey of tyrosine hydroxylase immunoreactive terminals in the myenteric ganglion of the rat duodenum

We have examined whether the noradrenergic neurons have direct synaptic projections to the myenteric ganglion neurons of the duodenum and the ultrastructure of their terminals by using immunogold–silver labeling for tyrosine hydroxylase. In the neuropil of the myenteric ganglia, about half of the axon terminals contained round clear vesicles and the rest of them contained pleomorphic clear vesicles. The sizes of axon terminals contacting the dendrites as a whole were 1.62 ± 0.07 μm. All axon terminals formed asymmetric synaptic contacts with dendrites or somata. Immunohistochemical study revealed that the tyrosine hydroxylase-immunoreactive nerve terminals were distributed throughout the ganglia and contained exclusively pleomorphic clear synaptic vesicles (about 20–80 nm long). The tyrosine hydroxylase-immunoreactive terminals were generally large (1.99 ± 0.07 μm). A considerable number of the tyrosine hydroxylase-immunoreactive terminals made asymmetric synaptic contacts with small dendrites, spines or somata of the myenteric ganglion neurons. Serial ultrathin sections through the myenteric neurons revealed that about 16% of the total number of axosomatic terminals showed tyrosine hydroxylase immunoreactivity. These results indicated that the myenteric ganglion neurons of the duodenum receive direct synaptic projection of sympathetic noradrenergic neurons and that their terminals contain pleomorphic vesicles and form asymmetric synaptic contacts.     

Fine structural survey of tyrosine hydroxylase immunoreactive terminals in the myenteric ganglion of the rat duodenum

We have examined whether the noradrenergic neurons have direct synaptic projections to the myenteric ganglion neurons of the duodenum and the ultrastructure of their terminals by using immunogold–silver labeling for tyrosine hydroxylase. In the neuropil of the myenteric ganglia, about half of the axon terminals contained round clear vesicles and the rest of them contained pleomorphic clear vesicles. The sizes of axon terminals contacting the dendrites as a whole were 1.62 ± 0.07 μm. All axon terminals formed asymmetric synaptic contacts with dendrites or somata. Immunohistochemical study revealed that the tyrosine hydroxylase-immunoreactive nerve terminals were distributed throughout the ganglia and contained exclusively pleomorphic clear synaptic vesicles (about 20–80 nm long). The tyrosine hydroxylase-immunoreactive terminals were generally large (1.99 ± 0.07 μm). A considerable number of the tyrosine hydroxylase-immunoreactive terminals made asymmetric synaptic contacts with small dendrites, spines or somata of the myenteric ganglion neurons. Serial ultrathin sections through the myenteric neurons revealed that about 16% of the total number of axosomatic terminals showed tyrosine hydroxylase immunoreactivity. These results indicated that the myenteric ganglion neurons of the duodenum receive direct synaptic projection of sympathetic noradrenergic neurons and that their terminals contain pleomorphic vesicles and form asymmetric synaptic contacts.     

Synaptic organization of the nucleus of the optic tract in the rabbit: A combined Golgi-electron microscopic study

Summary The organization of the nucleus of the optic tract was investigated with light and electron microscopy in combination with Golgi impregnation.In Golgi material, neurons ranged in size from 10 to 25 m with three to seven principal dendrites extending predominantly parallel to the fibres of the optic tract, irrespective of their location within the nucleus. In some areas dendrites extended into the neuropil of the adjacent dorsal terminal nucleus of the accessory optic system and the posterior pretectal nucleus. Occasionally spines and appendages were observed. The fine structure of the nuclei, perikarya and the dendritic arborization did not allow a well-defined distinction between interneurons and projection neurons.The synaptic organization of the nucleus of the optic tract showed great resemblance to the neuropil of the lateral geniculate nucleus and the superior colliculus. Similar types of presynaptic terminals were noticed: (i) R-terminals were either large and scalloped or small and regular in outline with spherical vesicles and electron-lucent mitochondria, and showed asymmetric contact zones; (ii) F-terminals with flattened vesicles, opaque mitochondria and symmetric contact zones; (iii) RLD-terminals with spherical vesicles and electron-dense mitochondria and asymmetric contact zones; (iv) P-terminals with pleomorphic vesicles and electron-lucent or opaque mitochondria and asymmetric synaptic thickenings. These different types of terminal were found isolated in the neuropil or in clusters of synapses.The most striking differences between the nucleus of the optic tract and the lateral geniculate nucleus were the relative scarcity of F-terminals in the clusters, the paucity of triadic arrangements and the relatively small size of the R-terminals. The differences in ultrastructure may be related to retinal W-type ganglion cells, which form the main retinal input to the nucleus of the optic tract and could also be related to the physiologically identified direction-selective units within the nucleus of the optic tract.     

Immunocytochemical and electron microscopic study of serotonin neuronal organization in the dorsal raphe nucleus of the monkey

Serotonin neurons in the dorsal raphe nucleus were identified using an antibody to a serotonin-bovine serum albumin conjugate and the peroxidase anti-peroxidase method. Nerve cell bodies showing serotonin-like immunoreactivity ranged in size from 15 to 22 micron in diameter; their dendrites were also immunoreactive. Immunostaining was present in the cytoplasmic matrix, outer membranes of mitochondria, rough endoplasmic reticulum, multivesicular bodies and dense-cored vesicles. Heavily immunoreactive axonal varicosities contained small round vesicles (18-35 nm) and larger dense-cored vesicles (50-90 nm). Both unmyelinated (0.2-0.5 micron) and myelinated (0.8-1.1 micron) serotonin-like immunoreactive axons were found, often interspersed within bundles of similar caliber unlabeled axons. Serotonin-like immunoreactive somata and dendrites were postsynaptic to numerous unlabeled terminals that contained either (a) clear round vesicles (18-25 nm) with many small dense-cored vesicles (30-50 nm), (b) clear round vesicles (18-25 nm) with large dense-cored vesicles (90-110 nm) or (c) clear round vesicles (18-25 nm) with or without flat vesicles. In addition pairs of unlabeled terminals formed crest synapses onto serotonin-like immunoreactive dendritic spines. This variety of unlabeled terminals making contact with serotonin-like immunoreactive elements suggests that several neuronal systems with possibly different transmitters may regulate serotonin raphe neurons. We occasionally observed serotonin-like immunoreactive dendrites and terminals in apposition to other serotonin-like immunoreactive dendrites with membrane specializations at the site of contact. This might represent a possible site for the self inhibition of serotoninergic neurons reported in physiological studies of the serotonin system in the dorsal raphe nucleus.     

Electron microscopic study of intrinsic cardiac ganglia in the adult human

The aim of the present study was to describe in detail the ultrastructure of intrinsic cardiac ganglionic cells in the healthy human as these cells appear to be directly involved in the development of tachycardia, atrioventricular block, ventricular fibrillation, and sudden cardiac death. Tissues examined in this study were obtained from hearts of 10 adult humans of either sex aged 22-80 years at autopsy performed no more than 8 h after death. The examined human intrinsic cardiac nerve cells were in most respects typical autonomic neurons surrounded by a sheath of satellite cells that was either uni- or multilayered. In addition to regular unmyelinated axons, prominent large axon terminals containing lamellated dense bodies, mitochondria and vesicles in the cytoplasm were observed in the ganglion neuropil. Synaptic profiles were more common in the ganglion neuropil than on neuronal somata. According to axon terminal contents, synaptic profiles were of three types. The most common Type 1 synaptic profiles contained a predominance of small clear, with a few larger dense-cored vesicles and mitochondria. Type 2 synaptic profiles, in addition to the same components as in Type 1, had glycogen-like particles. Type 3 vesicle-containing profiles clearly differed from both the previous ones as they were the largest in diameter and included plentifiul large clear pleomorphic or dense-cored vesicles together with small clear and larger dense-cored vesicles, mitochondria, dense and multivesicular bodies. Independently of age of the human, the most frequent neuronal abnormality was an abundant accumulation of inclusions inside of somata and dendrites that, in profile, appeared like circular membranous or fine granular bodies variable in electron density. In addition to inclusions, some neuronal somata and dendrites had strongly swollen mitochondria filled up with granular material in spite of their close association with normal looking ganglionic neurons. Structures resembling an axon growth cone in profile were revealed inside of cardiac ganglia derived from an 80 year old man. In conclusion, the present results provide baseline information on the normal ultrastructure of intracardiac ganglia in healthy humans which may be useful for assessing and interpreting the degree of damage of ganglionic cells both in autonomic and sensory neuropathies of the human heart.     

Retrograde labelling of photoreceptors in different regions of the compound eyes of bees and ants

Summary The geometry of retinal receptor arrays and the projection patterns of photoreceptor axons are unravelled in the compound eyes of bees and ants by backfilling large populations of photoreceptors with horseradish peroxidase or Lucifer yellow. Such retrograde labelling techniques are applied in the insect retina for the first time. They brilliantly label populations of specific receptor types within more than 100 ommatidia. Such preparations are obtained in three distinctly different parts of the eye: (1) the part of the retina that is positioned at the uppermost dorsal margin of the eye and specialized for the detection of polarized skylight; (2) the remainder of the dorsal retina; and (3) the ventral retina. As shown by the large populations of labelled photoreceptors, the retinal receptor arrays differ strikingly between different parts of the eye. Furthermore, there exist similarities as well as marked differences between bees and ants. Former hypotheses concerning the location of photoreceptor terminals in the first and second visual neuropil have all been based on a few individual Golgi-labelled photoreceptors. The results presented in this paper, based on retrograde mass impregnations of selected types of photoreceptors, confirm some of the former hypotheses and reject others. The new findings are important for understanding how insects analyse polarized skylight.     

成年斑马鱼视神经再生期间顶盖表面纤维层和灰质层的突触形态学研究

目的研究斑马鱼视神经再生过程中神经递质的变化,探讨神经递质和神经再生的关系。方法应用斑马鱼视神经再生模型,通过电镜技术观察顶盖表面纤维和灰质层突触的形态变化。结果视神经损伤后顶盖突触变化过程大致可分4个时期：1．视神经损伤后早期顶盖突触结构的退变;突触密度和突触小泡密度均下降,空型终末密度增大,8d时突触小泡密度降到最低水平;而空型终末密度最高。2．损伤后14d再生纤维大量进入顶盖;这一时期大核小泡和小核小泡密度都大量增加,但进入顶盖的纤维还没有或很少形成突触,14d时突触密度降到最低。3．损伤后2ld的特征是突触大量形成和圆形清亮小泡、扁平清亮小泡密度增加。4．再生晚期突触形态和功能恢复及精确化;100d时突触密度和突触小泡密度都大体恢复正常,但大核小泡密度还很高。结论兴奋性神经递质和抑制性神经递质可能对早期神经再生的启动和突触的形成起重要作用,而肽类和胺类可能对再生轴突的投射和精确化有重要作用;神经递质促进神经再生有先后顺序。     

Ultrastructure of the nervous system.

Within the nervous system, five cell types were studied by the electron microscope: the neuron, astrocyte, oligodendroglia, microglia and ependymal cells. The neurons are characterized by the Nissl substance within the perikaryon, the neurotubules and the neurofilaments. The three types of glial cells can be distinguished from one another. The astrocyte has relatively lucent cytoplasm and contains filaments which extend into long cytoplasmic processes. The oligodendroglia has electron-dense cytoplasm with thin extensions wedged between the cellular processes of the neuropil. The microglia cytoplasm is similar to the oligodendroglia but can be differentiated by the peculiar convoluted outline of the nuclear membrane and the clear space which separate the nucleus from the cytoplasm. The ependymal cell has characteristic microvilli and cilia at its ventricular surface. The cytoplasm contain parabasal bodies and tight junctions between adjacent cells. In the peripheral nerve, the axon and the myelin sheath are located within the Schwann cells. The terminal nerve endings from enlargements filled with synaptic vesicles. Electron microscopy of the nervous system is not only essential for research, but is also helpful in diagnosis of certain diseases.     

The fine structure of the submucous plexus of the guinea-pig ileum. I. The ganglia, neurons, Schwann cells and neuropil

Summary A fine structural study was made of the ganglia, neurons, Schwann cells and neuropil of the submucous plexus of the guinea-pig ileum. The arrangement of the plexus as seen by light microscopy is briefly described. Submucous ganglia are small, containing an average of eight neurons per ganglion (compared with 43 in myenteric ganglia) and are connected with each other by fine nerve strands.The cell bodies of neurons and Schwann cells and a neuropil consisting of neuronal and Schwann cell processes form the ganglia. No other cell types or blood vessels are found within the ganglia. Ganglia are surrounded by a continuous basal lamina but lack a well-defined connective tissue investment. The glial investment of neurons is incomplete: many neurons lie directly beneath the basal lamina with no intervening Schwann cell processes, and the plasma membranes of adjacent neurons are often directly apposed over large areas. Other areas of apposition occur between the cell bodies and processes of neurons and Schwann cells. Desmosome-like membrane specializations may be seen between neurons and other neurons or Schwann cells. Submucous neurons could not be categorized according to size, shape, organelle content or types of processes. Processes emerging from nerve-cell bodies were placed into four broad categories on the basis of shape and microtubule content.Many bundles of closely apposed small nerve profiles lacking intervening Schwann processes are found in the neuropil in addition to a large number of vesiculated varicosities, some of which are directly apposed to the plasma membranes of nerve-cell bodies. A small proportion of vesiculated profiles form synapses with nerve cell bodies, their processes and profiles in the neuropil. From their structure, submucous neurons appear to form a more homogeneous population than myenteric neurons. Because of their incomplete investment they are more likely to be freely exposed to substances diffusing in the extraganglionic tissue than are neurons of sympathetic ganglia.     

The lateral vestibular nucleus of the toadfish Opsanus tau: Ultrastructural and electrophysiological observations with special reference to electrotonic transmission

The lateral vestibular nucleus of the toadfish Opsanus tau was localized by means of axonal iontophoresis of Procion Yellow. The ultrastructure of the lateral vestibular nucleus neurons was then correlated with their electrophysiological properties. The lateral vestibular nucleus consists of neurons of various sizes which are distributed in small clusters over a heavily myelinated neuropil. The perikarya and main dendrites of the large and the small neurons are surrounded by a synaptic bed, which is separated from the neighboring neuropil by a layer of thin astrocytic processes. The synaptic bed contains three main classes of axon terminals, club endings, large and small terminals, the first being quite infrequent. All the large terminals as well as the occasionally observed club endings contain a pure population of rounded synaptic vesicles. In some of the small axon terminals there are also rounded vesicles; however, the majority contain flattened vesicles or a pleomorphic population. These data indicate that the small terminals originate from different afferent sources. The synaptic interfaces of the large boutons and of the club endings bear three types of junctional complexes: attachment plates, gap junctions and active zones. Those showing both gap junctions and active zones were designated as morphologically ‘mixed synapses’. Gap junctions, although in large number, have only been observed at the synaptic interfaces between terminals with rounded vesicles and the perikarya or the dendrite of the lateral vestibular nucleus neurons. Therefore electrotonic coupling would only be possible by way of presynaptic fibers. Some axons observed in the neuropil were found to establish gap junctional complexes with two different dendritec profiles and this observation is in favour of electrotonic coupling by way of presynaptic terminals.Field and intracellular potentials were recorded in the lateral vestibular nucleus. The field potential evoked by stimulation of the vestibular nerve consisted of an early positive-negative wave followed by a slow negativity, and that evoked by spinal cord stimulation was composed of an antidromic potential followed by a slow negative wave. Vestibulo-spinal neurons were identified by their antidromic spikes. In these cells, stimulation of the ipsilateral vestibular nerve evoked an excitatory postsynaptic potential with two components. The short delay of the first component of this excitatory postsynaptic potential and its ability to follow paired stimulation at close intervals without reduction of the second response suggest that it is transmitted electrotonically from primary vestibular afferent fibers. By contrast the latency of the second peak of the vestibular evoked excitatory postsynaptic potential and its sensitivity to high stimulus frequencies are compatible with monosynaptic chemically mediated transmission from primary vestibular afferents. Spinal stimulation evoked graded antidromic depolarizations in vestibulo-spinal neurons. The latency of these potentials was too short to allow for chemical transmission through afferents or recurrent collaterals and suggests electrotonic spread of antidromic activity from neighboring neurons. An important finding is that the graded antidromic depolarizations can initiate spikes; thus coupling between neurons in the lateral vestibular nucleus is sufficiently close that a cell can be excited by activity spread from neighboring cells. Similar graded depolarizations were recorded in identified primary vestibular afferents; their latencies and time course indicate that they were brought about by electrotonic spread of postsynaptic potentials and spikes to the impaled presynaptic fibers; this confirms the morphological evidence that coupling between lateral vestibular nucleus neurons occurs, at least in part, by way of presynaptic vestibular axons. As the spinal stimulus strength was increased, these graded depolarizations became large enough to initiate spikes which presumably propagate to the vestibular receptors. Thus antidromic invasion of the presynaptic terminals may provide negative feedback by preventing their re-excitation at short intervals after a synchronous discharge of an adequate number of postsynaptic cells. Excitatory inputs to the neurons of the lateral vestibular nucleus were identified from the spinal cord and from the contralateral vestibular nerve. Long latency excitatory postsynaptic potentials large enough to excite the cells were recorded following spinal stimulation; the threshold intensity for evoking them was consistently higher than that adequate to generate the graded antidromic depolarizations. Field potentials recorded after stimulation of the contra lateral vestibular nerve consisted of an initial positive negative wave followed by a slow negative wave. the stimulus intensity for evoking these potentials was the same or slightly above the threshold for those evoked in the lateral vestibular nucleus on the stimulated side. Also lateral vestibular nucleus neurons exhibited excitatory postsynaptic potentials large enough to excite the cells following stimulation of the contralateral vestibular nerve. but no inhibitory postsynaptic potentials were detected. This lack of commissural inhibition indicates a qualitative difference between the central organization of these cells in the toadfish and in mammals.The presence of neurons in the lateral vestibular nucleus which send their axons to the labyrinth was confirmed by their heavy staining with Procion Yellow following axonal iontophoresis. In a number of vestibular neurons. abruptly rising spikes were evoked at short latencies after adequate stimulation of the ipsilateral vestibular nerve. Graded stimuli applied to the vestibular nerve evoked graded short latency depolarizations as well as long latency excitatory postsynaptic potentials in these presumed efferent neurons to the labyrinth; the former could indicate electrotonic coupling of the efferent cells or electrotonic transmission from primary afferents, resulting in a short latency feedback loop.From these studies, the synaptic organization of the lateral vestibular nucleus neurons is compared with that of the Mauthner cells of teleosts, and the possibility of a dual mode of transmission, electrical and chemical, by primary vestibular afferents is discussed.     

Exocytosis from large dense cored vesicles outside the active synaptic zones of terminals within the trigeminal subnucleus caudalis: a possible mechanism for neuropeptide release

It has been hypothesized that chemical interactions between neurons in the central nervous system can occur in the absence of well defined synaptic complexes, but morphological correlates have been difficult to find. The present study demonstrates exocytotic release from large (70-130 nm) dense cored vesicles at structurally nonspecialized areas along the plasmalemma of structurally different categories of terminals and occasionally from dendrites and axons within the neuropil of the trigeminal subnucleus caudalis. In rats, the marginal (lamina I) and substantia gelatinosa (lamina II) layers contain the central terminals of primary afferent fibers from the infraorbital nerve that supply the skin and whiskers (vibrissae). Different types of interneurons are also present and may modify the input being relayed to higher centers. While exocytotic profiles were present in control animals, they increased significantly (P less than 0.01) on the ipsilateral side 1-24 h after a unilateral skin lesion in the vibrissae area. A second increase (P less than 0.001) occurred 14-15 days after the lesion. Virtually all examples of large vesicle exocytosis were observed at structurally nonspecialized sites while those at the active synaptic zones involved small clear vesicles. Substance P-like immunofluorescence, present in controls and on the ipsilateral side during the first 6 days, subsequently declined until 4 weeks after surgery when some recovery was noted. The increase in large vesicle exocytosis and the decrease in substance P are interpreted to reflect functional adjustments of different neurons in response to the lesion. The exocytosis involving large dense cored vesicles may serve to deliver transmitters and/or neuropeptide modulators to appropriate receptors in a wider area than release into a specialized synaptic cleft would allow.     

Nerve growth factor effects on cholinergic neurons of neostriatum and nucleus accumbens in the adult rat

Following intraventricular nerve growth factor infusion in adult rats, the choline acetyltransferase immunostaining of the neuropil and neuronal cell bodies of the neostriatum (caudate-putamen) and nucleus accumbens was more intense on the side of the infusion. Furthermore, the average cross-sectional size (micron2) of the cholinergic somata was increased by about 40 and 20% in the striatum and accumbens, respectively. This unilateral response could be elicited in intact rats as well as in rats receiving a prior aspirative transection of the fimbria-fornix. The reported lack of (low-affinity) nerve growth factor receptor immunostaining in these neurons suggests that the nerve growth factor effects are most likely transduced by high-affinity receptors. The ability of these apparently undamaged cholinergic interneurons to respond to exogenous nerve growth factor with an increase in choline acetyltransferase content and cell body size suggests that they are benefiting from a less-than-maximal support by endogenous nerve growth factor in the normal young adult rat.     

Immunoelectron microscopic observations of hypothalamic TRH-containing neurons in rats

Summary Immunoreactive TRH-containing neurons and their synaptic associations were studied electron microscopically in the paraventricular nucleus (PVN) and dorsomedial nucleus (DMH) of the rat hypothalamus. In propylthiouracil (PTU)-treated rats, the immunoreactive cell bodies in the PVN appeared to be activated, showing a hypertrophic perikaryon, well developed Golgi bodies and numerous secretory granules. No such alterations were evident in the TRH neurons in the DMH. These findings suggest that the PVN-TRH neurons are involved in the hypothalamic-hypophysial-thyroid axis. Further, it was shown that unlabeled nerve terminals containing small and large clear vesicles make synaptic contacts with the TRH perikarya in the PVN. Thus it is likely that PVN-TRH neurons are regulated both by thyroid hormones and by other neuronal signals. In the DMH, unlabeled nerve terminals containing small and large clear vesicles, and immunoreactive terminals form synapses with TRH neurons. Thus the DMH-TRH neurons may be under dual neuronal control. It was further noted that in the DMH and PVN, TRH nerve terminals make synaptic contacts with other unlabeled neurons. It is evident that TRH acts as a neurotransmitter or neuromodulator, although the origin of TRH terminals should be elucidated.     

Ultrastructural localization and progressive formation of neuropil aggregates in Huntington's disease transgenic mice.

How aggregates of polyglutamine proteins are involved in the neurological symptoms of glutamine repeat diseases is unknown. We show that huntingtin aggregates are present in the neuronal processes of transgenic mice that express exon 1 of the Huntington's disease (HD) gene. Unlike aggregates in the nucleus, these neuropil aggregates are usually smaller and are not ubiquitinated. Electron microscopy reveals many neuropil aggregates in axons and axon terminals. Huntingtin aggregates in the axon terminal are co-localized with some synaptic vesicles, implying that they may affect synaptic transmission and neuronal communication. The formation of neuropil aggregates is highly correlated with the development of neurological symptoms. The present study raises the possibility that neuropil aggregates may cause a dysfunction in neuronal communication and con-tribute to the neurological symptoms of HD.     

Ultrastructure of photoreceptors in the eye of Hermissenda labelled with intracellular injections of horseradish peroxidase.

Summary The terminal processes of single and of pairs of identified photoreceptors in the eyes of the nudibranch molluscHermissenda crassicornis were studied by light and transmission electron microscopy after their somata were labelled by intracellular iontophoresis of horseradish peroxidase (HRP). The HRP spread from the somata into the axons and fine terminal processes within the neuropil of the cerebropleural ganglia. The photoreceptors ended in extensive secondary branches in the neuropil where previous electrophysiological studies had indicated the probable site of synaptic interactions between photoreceptors. Clear round vesicles (54–126 nm diameter) within labelled processes were similar to the vesicles found in the somata and axon hillocks. The terminal processes of pairs of type B photoreceptors contained different intensities of the HRP label. Uniform intensities of the HRP label were found in the terminal processes of single type B photoreceptors. These differences in intensity suggested that the terminal processes were from different type B photoreceptors. This finding suggests that the connections between type B photoreceptors are probably monosynaptic.