Changes in the auditory system of locusts (Locusta migratoria and Schistocerca gregaria) after deafferentation

Deafferentation experiments during postembryonic development show morphological and/or physiological changes of receptor fibers and of identified auditory interneurons in the CNS of the locusts Locusta migratoria and Schistocerca gregaria after unilateral ablation of one tympanic organ either in the larva or the adult animal.

Ascaris suum: Differential effects of Avermectin B1a on the intact animal and neuromuscular strip preparations

Avermectin B_1a, a novel antiparasitic agent, paralyzes Ascaris suum without causing either flaccid paralysis or a hypercontraction. It reduces the lengthening of the acetylcholine-preconditioned A. suum muscle strip caused by γ-aminobutyric acid. It does not affect the contraction of the isolated muscle strip preparation caused by applying acetylcholine. However, preinjection with Avermectin B_1a does significantly reduce the shortening caused by acetylcholine injection without affecting the paralysis of an intact ascarid worm. These results suggest that Avermectin B_1a may act on the central nervous system of Ascaris sp. nematodes.     

In Situ Analysis of Na,K-ATPase α1- and α3-Isoform mRNAs in Aging Rat Hippocampus

Abstract: Age-related changes in the expression of Na,K-ATPase α1- and α3-isoform mRNAs were analyzed by in situ hybridization in the Fischer-344 rat hippocampus. Quantification of signal density with cRNA probes in rat hippocampus at 3 months of age showed (a) α1 content is 1.5 times higher in granule than in pyramidal cell layers, whereas α3 content shows the opposite ratio and (b) α3 label is found in large clusters related to mossy cells and basket cells and in medium clusters corresponding to interneurons within the dendritic fields of CA1–3. In the 24-month-old rats as compared with the young animals, the α1 signal is increased more than sevenfold in the dendritic fields and is not significantly changed in perikaryal layers. The α3 signal is reduced about threefold ( p < 0.0001, ANOVA, n = 6) in perikaryal layers, is almost completely absent over the interneurons, basket cells, and mossy cells, and is not significantly changed in dendritic fields. These data indicate age-related, cell- and isoform-specific alterations in pretranslational regulation of Na,K-ATPase α isoforms. The striking changes in the dendritic fields, mossy cells, and GABAergic basket cells and interneurons may constitute early and sensitive markers for age-related alterations in hippocampal function, before cell loss.     

Histofluorescence and ultrastructural observations of small intensely fluorescent (SIF) cells in the superior sympathetic ganglion of the guinea pig

Summary Amine-containing small intensely fluorescent (SIF) cells are ubiquitous in vertebrate sympathetic ganglia and, in some species, SIF cells have been identified as interneurons. The hypothesis proposed in this study is that SIF cells in superior sympathetic ganglia of the guinea pig function as interneurons, with efferent connections characteristic for the species. Fluorescence (catecholamine) microscopy and 5-hydroxydopamine marker for electron microscopy were used to study SIF cells, their processes and connections in this ganglion.Brightly fluorescent fibers were seen attached to virtually all SIF cells, and were of two types. The first type, single or arranged in cords, interconnected elements of the SIF-cell system; these apparent linkages joined individual SIF cells as well as adjacent clusters. The electron-microscopic evidence for synaptic contacts between SIF cells warrants the claim that integrated action is a presumed function of these elements. The second type of SIF-cell process was generally of greater length. These individual, branching fibers made presumed connections with dendrites of most principal ganglionic neurons. This arrangement suggested by histofluorescence preparations was confirmed by electron microscopy to involve synaptic connections, and the postsynaptic element was shown to be continuous with the perikaryon of the principal ganglionic neuron. Ultrastructural evidence that collections of dense-cored vesicles occur within processes of both principal ganglionic neurons and SIF cells, in proximity to unsheathed portions of plasma membrane, leads to the conclusion that interstitial diffusion of catecholamine from both may occur; the finding of SIF cell processes adjacent to fenestrated blood vessels suggests that catecholamine may also be transported through capillaries.     

GABA-like immunoreactivity of identified interneurons in the flight system of the locust,Locusta migratoria

Summary The transmitter content of identified inhibitory interneurons in the flight system of the locust, Locusta migratoria, has been characterized using antibodies raised against protein-conjugated gamma aminobutyric acid. Identified flight neurons were filled with the fluorescent dye, Lucifer Yellow. Serial sections of dye-filled neurons were incubated with an antibody to gamma aminobutyric acid which was subsequently tagged with a fluorescent marker. Excitatory motoneurons to wing muscles and 13 flight interneurons (3 excitatory, 7 inhibitory, and 3 with unknown synaptic effect) were examined. Neither the moto-neurons nor any of the 3 excitatory interneurons contained immunoreactive material. Six of the 7 inhibitory interneurons did contain immunoreactive material. All the neurons which contained immunoreactive material and whose synaptic effect is known were inhibitory. We conclude that most of the inhibitory flight interneurons which have been described use gamma aminobutyric acid as their transmitter. Interestingly, at least 1 set of interneurons known to be inhibitory does not use gamma aminobutyric acid. We predict that the 2 interneurons which do contain immunoreactive material and whose synaptic effect is not yet known will be found to have inhibitory roles in the operation of the flight circuitry.     

Distribution of synapses on two types of ascending interneurons in the crayfish,Procambarus clarkii

Summary About 60 pairs of ascending interneurons are present in the terminal ganglion of the crayfish Procambarus clarkii (Girard). Some of these interneurons have been impaled intracellularly, characterized physiologically, and then labeled with horseradish peroxidase (HRP) to examine the distribution and ultrastructure of synapses. A close relationship between ultrastructure and physiological properties has been found between two types of interneurons, which either have a pre-motor effect upon motor neurons or have no such effect. In one interneuron with a pre-motor effect (6D2), input and output synapses are intermingled on thicker branches, whereas only input synapses are found on small diameter branches. Only input synapses have been observed on the branches in another interneuron with-out a pre-motor effect (6B1). No differences in branch morphology are found in these two interneurons. Interneuron 6D2 contains large numbers of small round agranular vesicles, but the same type of synaptic vesicles is rarely seen in interneuron 6B1, which has no output synapses. Our results indicate a good correlation between the synaptic distribution and pre-motor effects of interneurons in the terminal ganglion.Abbreviations A6, 7 Sixth and seventh abdominal segment of the terminal ganglion - AVC anterior ventral commissure - DC I dorsal commissure I - DIT dorsal intermediate tract - DMT dorsal medial tract - eLG extra lateral giant interneuron - LVT lateral ventral tract - LG lateral giant interneuron - LVT lateral ventral tract - MDT median dorsal tract - MG medial giant interneuron - MoG motor giant neuron - MVT median ventral tract - PVC posterior ventral commissure - R1s sensory fiber tract of nerve root 1 - R3m motor fiber tract of nerve root 3 - R4–7 nerve roots 4–7 - SC I,II sensory commissure I,II - VC I,III ventral commissure I, III - VIT ventral intermediate tract - VLT ventral lateral tract - VMT ventral medial tract     

Synaptic input to the axon hillock and initial segment of inhibitory interneurons in the cerebellar cortex of the rat

Summary The axon hillock (AH) and initial segment (IS) of 10 Golgi neurons and 6 basket cells in the cerebellar cortex of the rat were investigated by electron microscopy using serial sections. An average of 10.4 and 11.3 synaptic terminals were observed to establish synaptic contact with the axon hillock region of Golgi and basket cells, respectively. Most of these terminals were identified as the varicosities of the ascending parallel fibers. It is suggested that the focal innervation of AH regions represents an excitatory input pattern which is basically different from the randomly distributed, huge, parallel-fiber input onto the dendritic trees of Golgi and basket cells. In contrast to Golgi and basket neurons, no accumulation of parallel-fiber synapses was observed around the AH of stellate cells. The IS proper of the three neuronal types were devoid of true axo-axonal synapses.