Intrahypothalamic connections: An electron microscopic study in the rat

Summary Terminal degeneration within the hypothalamus was studied by electron microscopy 1 or 2 days (1) after carefully placed microlesions in the arcuate, anterior periventricular, ventromedial, premammillary and posterior hypothalamic nuclei and (2) after microlesions placed in the hypothalamus deafferented 3 weeks earlier.In the median eminence terminal degeneration was found after each of these lesions. Projections from the ventromedial nucleus reach the arcuate, suprachiasmatic, and anterior periventricular nuclei.Projections from the arcuate nucleus terminate in the medial preoptic, anterior periventricular, and ventromedial nuclei.After lesioning the premammillary nuclei degeneration was found in the supraoptic, arcuate, anterior hypothalamic and ventromedial nuclei.     

Intracellular analysis of excitatory-inhibitory synaptic interactions in crayfish stretch receptors.

1. To determine the membrane mechanisms underlying the interactions between inhibitory postsynaptic potentials (IPSPs) and excitatory inputs, we investigated, at the membrane potential level, the combined influences of low-frequency (0.05-0.50 Hz) imposed sinusoidal transmembrane currents (termed sine currents), representing the excitatory drive, and trains of regular (3-30/s) IPSPs. The two simplest possible neuron systems exemplified by the slowly and rapidly adapting stretch receptors of crayfish (RM1 and RM2, respectively) were used. 2. At constant elongation the RM1 and RM2 behaved as a pacemaker and a neuron without self-sustained oscillations, respectively, but in dynamic conditions uninhibited controls and IPSP sine current interactions were essentially identical in both RMs. Controls showed the usual smooth variation of the RM firing rate in response to the gradually varying excitatory input. IPSP effects were characterized by the expected overall reduction of the postsynaptic firing rate. More important, special effects were also present, such as the simple fixed alternations of IPSP and postsynaptic spikes (e.g., 1 IPSP, 1 postsynaptic or 1:1; 1 IPSP, 2 postsynaptic or 1:2; 2 IPSPs, 1 postsynaptic spike or 2:1), where interspike intervals were more constant than uninhibited controls and where the sensitivity to the excitatory input was reduced to small values, and the sudden firing rate discontinuities consisting of instantaneous discharge accelerations or decelerations (termed "jumps") between successive alteration ratios, where sensitivity increased to large values. Therefore with inhibition the RM firing rate varied discontinuously in response to the gradually changing input, and the discharge rate could take one of several discrete values by switching between different alteration ratios. 3. At the alternations the times elapsed between an IPSP and the closest spike before (phase, phi) or after it (cophase, theta) increased and decreased, respectively, with increasing excitation. The major membrane potential modification that accompanied the interactions at the alternations was the gradual increase of the post-IPSP slope as a function of excitatory drive, which reduced the time to reach the firing level or theta. 4. Inhibition introduced subtle and complex nonlinear modifications in the coding of convergent excitatory input. The most notable nonlinearity was the discontinuous variations of the firing rate as a function of the gradually changing excitatory input. Effects were due to voltage interactions occurring at the extrasynaptic membrane, with a decisive involvement of the spike generator and insignificant participation of the shunting action of IPSPs. The results provide yet another example of the predominant influence of intrinsic membrane properties in determining the effects of synaptic-evoked activity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Peripheral connections of FMRFamide-like immunoreactive neurons in the snail,Helix pomatia: an immunogold electron microscopic study

Summary Using a postembedding immunogold electron microscopic method, the ultrastructure and synaptic connections of FMRFamide-like immunoreactive varicosities were investigated in different peripheral organs of the snailHelix pomatia, including the heart (auricle), intestine, hepatopancreas, upper tentacle and salivary gland. The FMRFamide-like immunoreactive varicosities contained granules and vesicles as described in a previous study of the CNS of this species, and additionally, based on their granule content, two novel types of varicosities were found in the auricle. A selective accumulation of gold particles over the granules could be demonstrated. The FMRFamide-like immunoreactive varicosities formed unspecialized contacts with postsynaptic target cells in all peripheral organs investigated, with the exception of the tentacle retractor muscle. Both the neuro-muscular and the neuro-glandular contacts were characterized by either unspecialized close apposition of the pre- and postsynaptic membranes or the immunoreactive elements faced the target cell(s) across a relatively wide extracellular space. In the tentacle retractor muscle some of the neuromuscular contacts showed appositions of electron dense material along the presynaptic membrane, clustering of agranular synaptic vesicles and intersynaptic cleft material. The present observations support previous electrophysiological findings and suggest a versatile modulatory role of FMRFamide and related substances in theHelix PNS.Dedicated to Professor Rolf Elofsson on the occasion of his 65th birthday.     

Intestinal spirochaetosis: an electron microscopic study of an unusual case

An unusual case of intestinal spirochaetosis is described. The rectum of a 34-year-old male, suffering from Crohn's disease and ankylosing spondylitis, was heavily infested by spirochaetes. Both absorptive and goblet cells were colonized. Spiro-chaetes were found not only on the luminal surface of these cells, but also within the cytoplasm, in occasional macrophages within the lamina propria and, even more surprisingly, within the occasional Schwann cell. The significance of these findings is discussed.     

Graft rejection in earthworms: an electron microscopic study.

Graft rejection in the earthworm, Lumbricus terrestris, is mediated by granulocytic coelomocytes (neutrophils, by light microscopy). Within 1--3 days post-transplantation of body-wall xenografts, granulocytic coelomocytes migrate to the transplant site, penetrate the graft matrix, and actively phagocytize viable muscle fibers. Destruction of muscle tissues may be augmented by lymphocytic coelomocytes (basophils, by light microscopy), but these cells participate in a minor way and do so very late in the rejection process (days 11--13). Xenografts, autografts and sham-operated controls display generalized inflammatory reactions, including coelomyocyte infiltration into the grafted tissues. In autografts, however, granulocytes only penetrate the inner longitudinal muscle layers and extensive infiltration, persistence and complete destruction never occur. Lymphocytic coelomocytes are not observed in autografts or sham-operated controls. Grafts rejection by leukocytes in an advanced invertebrate confirms that aspects of cell-mediated immunity evolved early in phylogenetic history.     

An immunogold electron microscopic analysis of FMRFamide-like immunoreactive neurons in the CNS ofHelix pomatia: ultrastructure and synaptic connections

Summary The ultrastructure and synaptic connections of FMRFamide-like immunoreactive neurons were investigated in the CNS of the snailHelix pomatia, following the application of a post-embedding immunogold method. For comparison, first, we analyzed the ultrastructure and granule content of the identified FMRFamide-containing C3 neuron in the cerebral ganglion. Three types of unidentified immunoreactive neuronal perikarya, and five types of varicosities could be distinguished on the basis of granule content. The different granule types revealed a highly selective accumulation of gold particles. One granule type contained by one FMRFamide-like immunoreactive neuron type (N1) and by one varicosity type (T₂) showed similar ultrastructure to that of the granules seen in the C3 cell. In the neuropil, the majority of FMRFamide-like immunoreactive varicosities (four of the five varicosity types) established specialized synaptic contacts with unidentified postsynaptic profiles. In the connective tissue sheath around the ganglia, three types of FMRFamide-like immunoreactive varicosities were found to establish unspecialized contacts with smooth muscle fibres or to be free in the mass of collagen fibres. On the basis of these observations, we suggest (1) an extensive diversity of the localization of FMRFamide (and related substances) at the ultrastructural level; (2) the involvement of FMRFamide-like immunoreactive varicosities in synaptic, modulatory and neurohormonal regulatory processes in theHelix nervous system.     

Non-sympathetic synaptic innervation of the pinealocyte of the Mongolian gerbil (Meriones unguiculatus): an electron microscopic study

Summary Direct synaptic innervation of pinealocytes was observed in the superficial pineal gland of the Mongolian gerbil (Meriones unguiculatus) by electron microscopy. This innervation consisted of nerve fibres terminating in boutons with clear transmitter vesicles with a diameter of 40–60 nm. The boutons made synaptic junctions with the cell membrane of the pinealocyte displaying thickenings of both the pre- and postsynaptic membranes. Such boutons persisted in the gland 1 week after removal of both superior cervical ganglia. In contrast, all the sympathetic boutons containing transmitter vesicles with a small dense core disappeared after ganglionectomy. This direct synaptic innervation reveals a neuronal character of the pinealocyte and might underlie reports of action potentials in electrophysiological recordings from the gland.     

Synaptic connections of cortical and retinal terminals in the superior colliculus of the rabbit: an electron microscopic double labelling study

Summary Retinal and cortical afferents to the superior colliculus of the rabbit were labelled simultaneously by injecting ³H-leucine into the right eye and HRP into the left visual cortex. It could be shown that there is some convergence of retinal and cortical input onto common postsynaptic elements in the superficial grey, but these cases were found to be rather rare indicating that most afferents from the retina and the visual cortex terminate either on different postsynaptic cells or on different parts of common postsynaptic cells.     

Block of receptor response in the stretch receptor neuron of the crayfish by gadolinium

The trivalent lanthanide gadolinium was found to block the mechanotransducer response in the stretch receptor neuron of the crayfish. At normal calcium concentration (13.5 mm) a 50 per cent block of the receptor current was found at 395 ± 59 (mean ± SD), μM gadolinium. At a calcium concentration of 1.35 mm a 50 per cent block of the receptor current was obtained at 103 ± 14 (mean ± SD) μM gadolinium. The potential activated potassium current was also affected by gadolinium. At 200 μM the amplitude of the peak outward current as a result of a 90 mV positive potential step was decreased by about 40 per cent. The fast inward sodium current was decreased less than 10 per cent by gadolinium. It is concluded that in the crayfish stretch receptor gadolinium blocks the receptor current, reflecting block of stretch-activated channels, but at higher concentrations than have been described for other stretch-activated channels. In addition the outward rectifier potassium current is also blocked reflecting a block of potassium channels.