TL;DR: The highly polarized AQP4 expression indicates that these cells are equipped with specific membrane domains that are specialized for water transport, thereby mediating the flow of water between glial cells and the cavities filled with CSF and the intravascular space.
Abstract: Membrane water transport is critically involved in brain volume homeostasis and in the pathogenesis of brain edema. The cDNA encoding aquaporin-4 (AQP4) water channel protein was recently isolated from rat brain. We used immunocytochemistry and high-resolution immunogold electron microscopy to identify the cells and membrane domains that mediate water flux through AQP4. The AQP4 protein is abundant in glial cells bordering the subarachnoidal space, ventricles, and blood vessels. AQP4 is also abundant in osmosensory areas, including the supraoptic nucleus and subfornical organ. Immunogold analysis demonstrated that AQP4 is restricted to glial membranes and to subpopulations of ependymal cells. AQP4 is particularly strongly expressed in glial membranes that are in direct contact with capillaries and pia. The highly polarized AQP4 expression indicates that these cells are equipped with specific membrane domains that are specialized for water transport, thereby mediating the flow of water between glial cells and the cavities filled with CSF and the intravascular space.
TL;DR: The distribution of GABAA receptor subunits deriving from 13 different genes in the adult rat brain was investigated using immunocytochemistry, and striking examples of complementary distribution of certain subunit-immunoreactivities were observed.
TL;DR: The retinohypothalamic tract in the rat appears to arise from the ganglion cells of the retina and to terminate on the smaller dendritic branches of the neurons of the suprachiasmatic nucleus.
Abstract: A direct projection from the retina to the hypothalamus was demonstrated in the rat. Following injection of tritiated leucine or proline into the posterior chamber of the eye, labelled protein was shown autoradiographically in the suprachiasmatic nuclei of the medial hypothalamus, both ipsilateral and contralateral to the injected eye. The labelling of the nucleus was heaviest in its ventral portion but extended throughout the nucleus. No evidence for a projection to the supraoptic nucleus or any other hypothalamic nucleus was observed. All of the known terminal nuclei of the primary and accessory optic tracts were heavily labelled. The projection to the suprachiasmatic nucleus could not be clearly confirmed in material prepared using the Fink-Heimer method for the demonstration of degenerating axon terminals. Electron microscopic study of the suprachiasmatic nucleus following orbital enucleation showed degenerating endings making synaptic contacts with small dendrites of the suprachiasmatic nucleus cells. These first appeared at three days after operation and were nearly gone by seven days. Thus, the retinohypothalamic tract in the rat appears to arise from the ganglion cells of the retina and to terminate on the smaller dendritic branches of the neurons of the suprachiasmatic nucleus.
TL;DR: The autoradiographic material, and additional double-labeling experiments, were used to identify and to characterize projections that interconnect the A1, A2 and A6 regions, as well as possible projections from these cell groups to the spinal cord.
TL;DR: Simultaneous recording from two extracellular electrodes indicated neural activity at two sites in the brain, one of which is in or near the suprachiasmatic nucleus and the other in one of many other brain locations, which indicated clear circadian rhythmicity of spontaneous neural activity.
Abstract: The experimental work described tested the prosposition that the suprachiasmatic nucleus of the hypothalamus is an autonomous circadian pacemaker. Simultaneous recording from two extracellular electrodes indicated neural (multiple unit) activity at two sites in the brain, one of which is in or near the suprachiasmatic nucleus and the other in one of many other brain locations. Both sites in intact rats displayed clear circadian rhythmicity of spontaneous neural activity. In experimental animals, a Halasz knife was used to create an island of hypothalamic tissue that contained the suprachiasmatic nuclei. In such animals that were also blinded by bilateral ocular enucleation, circadian rhythmicity was lost at all brain locations recorded outside the island, but it persisted within the island that contained the suprachiasmatic nuclei. The rhythmicity of the island is thus not dependent on afferent inputs from elsewhere in the brain.