The Journal of comparative neurology
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Afferent connections of the anterior thalamic nuclei (ATN) are classically thought to originate in the mammillary body and limbic cortex. This study explores nonlimbic sources of ATN afferents by using retrograde transport of horseradish peroxidase (HRP) to ascertain the relative contribution of these connections. Spread of HRP into adjacent regions was prevented either by removing the overlying cortex or by injecting through permanently implanted cannulas. ⋯ In conclusion, ATN receive afferents from several nonlimbic regions. Of these inputs, the pretectum may be the primary route through which sensory information reaches ATN. In addition, cholinergic input may modulate activity in projections from the mammillary body to ATN through presynaptic muscarinic receptors.
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A population of intersegmental interneurones with axons extending from the meso- to the metathoracic ganglion of the locust is described. They receive specific mechanosensory inputs from one mesothoracic leg. Their cell bodies are in group at the posterior of the mesothoracic ganglion, lying over the lateral base of each connective, and their primary neurites emerge in one of four bundles. ⋯ Some interneurones have one to three axonal branches with sparse and varicose side branches in the mesothoracic ganglion, which resemble the metathoracic axonal branches. The metathoracic axonal branches are mostly restricted to the dorsal neuropil and the dorsal part of the intermediate neuropil where local non-spiking interneurones and motor neurones controlling movements of the hind leg also project. The overlap between the branches of the sensory afferents and the intersegmental interneurones in the mesothoracic ganglion and between those of the nonspiking local interneurones or motor neurones and intersegmental interneurones in the metathoracic ganglion suggest that these interneurones are responsible for transferring information about the action of one leg to an adjacent leg.
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Mitral cells of the olfactory bulb typically form reciprocal dendrodendritic synapses with anaxonic interneurons, granule cells, within a sublamina of the external plexiform layer. As a result of mitral cell loss in the murine mutant Purkinjie cell degeneration (PCD), subpopulations of these granule cells are denervated. The present report examines the capacity of these denervated interneurons to form new dendrodendritic microcircuits with a second population of olfactory bulb neurons, tufted cells. ⋯ In both the control and mutant mice the ratios of symmetrical:asymmetrical dendrodendritic synapses closely approached 1. This demonstrates that not only do the denervated spines receive new afferent input from tufted cell dendrites, but they also establish the reciprocal efferent projection. These data are discussed in terms of the sublaminar organization of dendrodendritic microcircuits in the olfactory bulb and their capacity of plasticity and reorganization following pertubation.