Single Synapse Information Coding in Intraburst Spike Patterns of Central Pattern Generator Motor Neurons

Burst firing is ubiquitous in nervous systems and has been intensively studied in central pattern generators (CPGs). Previous works have described subtle intraburst spike patterns (IBSPs) that, despite being traditionally neglected for their lack of relation to CPG motor function, were shown to be cell-type specific and sensitive to CPG connectivity. Here we address this matter by investigating how a bursting motor neuron expresses information about other neurons in the network. We performed experiments on the crustacean stomatogastric pyloric CPG, both in control conditions and interacting in real-time with computer model neurons. The sensitivity of postsynaptic to presynaptic IBSPs was inferred by computing their average mutual information along each neuron burst. We found that details of input patterns are nonlinearly and inhomogeneously coded through a single synapse into the fine IBSPs structure of the postsynaptic neuron following burst. In this way, motor neurons are able to use different time scales to convey two types of information simultaneously: muscle contraction (related to bursting rhythm) and the behavior of other CPG neurons (at a much shorter timescale by using IBSPs as information carriers). Moreover, the analysis revealed that the coding mechanism described takes part in a previously unsuspected information pathway from a CPG motor neuron to a nerve that projects to sensory brain areas, thus providing evidence of the general physiological role of information coding through IBSPs in the regulation of neuronal firing patterns in remote circuits by the CNS.

Atrophy and Neuron Loss: Effects of a Protein-Deficient Diet on Sympathetic Neurons

Protein deficiency is one of the biggest public health problems in the world, accounting for about 30-40% of hospital admissions in developing countries. Nutritional deficiencies lead to alterations in the peripheral nervous system and in the digestive system. Most studies have focused on the effects of protein-deficient diets on the enteric neurons, but not on sympathetic ganglia, which supply extrinsic sympathetic input to the digestive system. Hence, in this study, we investigated whether a protein-restricted diet would affect the quantitative structure of rat coeliac ganglion neurons. Five male Wistar rats (undernourished group) were given a pre- and postnatal hypoproteinic diet receiving 5% casein, whereas the nourished group (n = 5) was fed with 20% casein (normoproteinic diet). Blood tests were carried out on the animals, e.g., glucose, leptin, and triglyceride plasma concentrations. The main structural findings in this study were that a protein-deficient diet (5% casein) caused coeliac ganglion (78%) and coeliac ganglion neurons (24%) to atrophy and led to neuron loss (63%). Therefore, the fall in the total number of coeliac ganglion neurons in protein-restricted rats contrasts strongly with no neuron losses previously described for the enteric neurons of animals subjected to similar protein-restriction diets. Discrepancies between our figures and the data for enteric neurons (using very similar protein-restriction protocols) may be attributable to the counting method used. In light of this, further systematic investigations comparing 2-D and 3-D quantitative methods are warranted to provide even more advanced data on the effects that a protein-deficient diet may exert on sympathetic neurons. (C) 2009 Wiley-Liss, Inc.

The reactions of specific neuron types to intestinal ischemia in the guinea pig enteric nervous system

Damage following ischemia and reperfusion (I/R) is common in the intestine and can be caused during abdominal surgery, in several disease states and following intestinal transplantation. Most studies have concentrated on damage to the mucosa, although published evidence also points to effects on neurons. Moreover, alterations of neuronally controlled functions of the intestine persist after I/R. The present study was designed to investigate the time course of damage to neurons and the selectivity of the effect of I/R damage for specific types of enteric neurons. A branch of the superior mesenteric artery supplying the distal ileum of anesthetised guinea pigs was occluded for 1 h and the animals were allowed to recover for 2 h to 4 weeks before tissue was taken for the immunohistochemical localization of markers of specific neuron types in tissues from sham and I/R animals. The dendrites of neurons with nitric oxide synthase (NOS) immunoreactivity, which are inhibitory motor neurons and interneurons, were distorted and swollen by 24 h after I/R and remained enlarged up to 28 days. The total neuron profile areas (cell body plus dendrites) increased by 25%, but the sizes of cell bodies did not change significantly. Neurons of type II morphology (intrinsic primary afferent neurons), revealed by NeuN immunoreactivity, were transiently reduced in cell size, at 24 h and 7 days. These neurons also showed signs of minor cell surface blebbing. Calretinin neurons, many of which are excitatory motor neurons, were unaffected. Thus, this study revealed a selective damage to NOS neurons that was observed at 24 h and persisted up to 4 weeks, without a significant change in the relative numbers of NOS neurons.

Immunohistochemical analysis of neuron types in the mouse small intestine

The definition of the nerve cell types of the myenteric plexus of the mouse small intestine has become important, as more researchers turn to the use of mice with genetic mutations to analyze roles of specific genes and their products in enteric nervous system function and to investigate animal models of disease. We have used a suite of antibodies to define neurons by their shapes, sizes, and neurochemistry in the myenteric plexus. Anti-Hu antibodies were used to reveal all nerve cells, and the major subpopulations were defined in relation to the Hu-positive neurons. Morphological Type II neurons, revealed by anti-neurofilament and anti-calcitonin gene-related peptide antibodies, represented 26% of neurons. The axons of the Type II neurons projected through the circular muscle and submucosa to the mucosa. The cell bodies were immunoreactive for choline acetyltransferase (ChAT), and their terminals were immunoreactive for vesicular acetylcholine transporter (VAChT). Nitric oxide synthase (NOS) occurred in 29% of nerve cells. Most were also immunoreactive for vasoactive intestinal peptide, but they were not tachykinin (TK)-immunoreactive, and only 10% were ChAT-immunoreactive. Numerous NOS terminals occurred in the circular muscle. We deduced that 90% of NOS neurons were inhibitory motor neurons to the muscle (26% of all neurons) and 10% (3% of all neurons) were interneurons. Calretinin immunoreactivity was found in a high proportion of neurons (52%). Many of these had TK immunoreactivity. Small calretinin neurons were identified as excitatory neurons to the longitudinal muscle (about 20% of neurons, with ChAT/calretinin/+/- TK chemical coding). Excitatory neurons to the circular muscle (about 10% of neurons) had the same coding. Calretinin immunoreactivity also occurred in a proportion of Type II neurons. Thus, over 90% of neurons in the myenteric plexus of the mouse small intestine can be currently identified by their neurochemistry and shape.

Recording from Two Neurons: Second-Order Stimulus Reconstruction from Spike Trains and Population Coding

We study the reconstruction of visual stimuli from spike trains, representing the reconstructed stimulus by a Volterra series up to second order. We illustrate this procedure in a prominent example of spiking neurons, recording simultaneously from the two H1 neurons located in the lobula plate of the fly Chrysomya megacephala. The fly views two types of stimuli, corresponding to rotational and translational displacements. Second-order reconstructions require the manipulation of potentially very large matrices, which obstructs the use of this approach when there are many neurons. We avoid the computation and inversion of these matrices using a convenient set of basis functions to expand our variables in. This requires approximating the spike train four-point functions by combinations of two-point functions similar to relations, which would be true for gaussian stochastic processes. In our test case, this approximation does not reduce the quality of the reconstruction. The overall contribution to stimulus reconstruction of the second-order kernels, measured by the mean squared error, is only about 5% of the first-order contribution. Yet at specific stimulus-dependent instants, the addition of second-order kernels represents up to 100% improvement, but only for rotational stimuli. We present a perturbative scheme to facilitate the application of our method to weakly correlated neurons.

Automatic contour extraction from 2D neuron images

This work describes a novel methodology for automatic contour extraction from 2D images of 3D neurons (e.g. camera lucida images and other types of 2D microscopy). Most contour-based shape analysis methods cannot be used to characterize such cells because of overlaps between neuronal processes. The proposed framework is specifically aimed at the problem of contour following even in presence of multiple overlaps. First, the input image is preprocessed in order to obtain an 8-connected skeleton with one-pixel-wide branches, as well as a set of critical regions (i.e., bifurcations and crossings). Next, for each subtree, the tracking stage iteratively labels all valid pixel of branches, tip to a critical region, where it determines the suitable direction to proceed. Finally, the labeled skeleton segments are followed in order to yield the parametric contour of the neuronal shape under analysis. The reported system was successfully tested with respect to several images and the results from a set of three neuron images are presented here, each pertaining to a different class, i.e. alpha, delta and epsilon ganglion cells, containing a total of 34 crossings. The algorithms successfully got across all these overlaps. The method has also been found to exhibit robustness even for images with close parallel segments. The proposed method is robust and may be implemented in an efficient manner. The introduction of this approach should pave the way for more systematic application of contour-based shape analysis methods in neuronal morphology. (C) 2008 Elsevier B.V. All rights reserved.