Divergent projections of projecting neurons of the inferior colliculus to the medial geniculate body and the contralateral inferior colliculus in the rat.

The present paper shows, by means of the combination of two fluorescent tracers, that a significant number of neurons of the three divisions of the inferior colliculus in the rat project to the contralateral inferior colliculus and the ipsilateral medial geniculate body. The topographic distribution of double-labeled cells depends on the location of injections in each case. According to the soma size and the dendritic stem, different neuron types may be distinguished. Our results suggest that the inputs that converge in individual neurons of the inferior colliculus can diverge again.

Effects of postnatal administration of ethanol on the M. gastrocnemius of the albino mouse.

A combined morphometric-histochemical (mATPase) study of the effects of ethanol during postnatal development on the m. gastrocnemius has been performed in the albino mouse. The experimental group received ethanol in the drinking water until sacrifice at the age of 40 days. Based on the fiber composition, three different areas are distinguished in the m. gastrocnemius of the mouse. The typical location of these areas does not change after ethanol administration. However, postnatal administration of ethanol produces a selective atrophy and a decrease of the number of type IIb (fast glycolytic) fibers. Concurrently, the number of type IIa (fast oxidative-glycolytic) fibers increases.

The spiny stellate neurons in layer IV of the human auditory cortex. A Golgi study.

The spiny stellate neurons have been studied by the Golgi method in the auditory koniocortex and parakoniocortex of man. Spiny stellate cells are a consistent though not very common component of layer IV. They are not confined to specific sublayers but occur at all depths of layer IV, and also in layer IIIc. Spiny stellate cells in the auditory areas show a great variety of their dendritic arborization pattern. The presence of all intermediate forms between small pyramidal cells--which constitute the dominant cell type in layer IV and which display an extraordinary heteromorphism--and spiny stellate cells shows the close kinship between both neuronal types. The morphology and distribution of spines along the dendrites of spiny stellate neurons are similar to those of the small pyramidal cells of the same layer. The axons, which were impregnated only in their proximal portions, mostly descend, giving rise to recurrent ascending collaterals, but initially ascending axons do also occur. Spiny stellate neurons are present in the different cytoarchitectonic areas examined, and thus they are not confined to the auditory koniocortex.

Direct projections from the medulla oblongata to selective cortical areas in the rat.

Injections of horseradish peroxidase into different cortical areas reveal that neurons located in the rostroventral medulla oblongata innervate restricted cortical areas: the anterior and posterior cingulate cortex and the insular cortex. Other cortical areas do not receive medullary projections. Neurons projecting to both the anterior and the posterior cingulate cortex lie scattered throughout a wide territory of the ventrorostral medulla, whereas neurons projecting to the insular cortex are restricted to more medial regions.

Development of neuronal types and laminar organization in the central nucleus of the inferior colliculus in the cat.

The development of neuronal morphology and laminar organization in the central nucleus of the inferior colliculus has been studied with the different Golgi methods in kittens and cats of 1 day-2 years of age. The different Golgi methods used allowed us to selectively visualize the axonal or dendritic component of the fibrodendritic laminae. The characteristic lamination of the central nucleus defined by the fiber system of the lateral lemniscus is already present at birth. The axonal component of the laminae is constituted by parallel condensations of varicose terminals, myelinated axons, and preterminal fibers, oriented from ventrolateral to dorsomedial. The laminae are smaller in the dorsolateral edge of the nucleus. Neurons are classified mainly on the basis of their dendritic trees and the axonal ramification patterns. Three main types are distinguished: spinous disk-shaped neurons, aspinous to sparsely spinous disk-shaped neurons, and large or giant multipolar neurons. Our results suggest that the basic structures of the central nucleus--neuronal types and lamination of the lemniscal fibers--are already established at birth. The different neuronal types can be distinguished from the first days of life according to the ramification pattern of dendritic and axonal arbors. The characteristics of the different cell types, such as the density and distribution of dendritic spines, and the presence of varicose dendritic branchlets, are recognizable from the second week. At the end of the first month, neurons display an adult-like morphology, although the density of dendritic spines is higher than in the adult. Our morphological data can be related to the development of response properties in the inferior colliculus.

Afferent connections of the inferior colliculus in the albino mouse.

We have studied the afferent connections of the inferior colliculus of the albino mouse. Our results show: First, the afferent connections of the inferior colliculus in the mouse are similar to those of other species, however, some differences exist. Second, there is a different projection pattern to the dorsal cortex and the central nucleus of the inferior colliculus; the dorsal cortex receives fibers essentially from auditory centers, while the central nucleus also receives afferents from other structures not related to the auditory system. Third, an interesting parallel may be established between the connections of the inferior colliculus and those of the superior colliculus.

The commissural interconnections of the inferior colliculus in the albino mouse.

In the inferior colliculus of the mouse, 4 cell types project across the collicular commissure: small to medium sized spiny cells, small to medium sized spineless cells, medium sized sparsely spinous neurons and large cells. The axons of large cells give rise to a great number of ipsi- and contralateral collaterals terminating in nests of fine varicose fibers. The anterograde transport of HRP revealed that following injections into the central nucleus, the axonal terminals are arranged in a fixed, ipsi- and contralateral banding pattern across the central, pericentral and external nucleus irrespective of the location of the injection. On the contrary, the position of projecting cells varies with the location of the injection, though the area emitting commissural fibers is not completely homotopic to the injection site but subordinated to the axonal banding pattern.