Spontaneous discharge of norepinephrine-containing locus coeruleus (NE- LC) neurons was examined during the sleep-walking cycle (S-WC) in behaving rats. Single unit and multiple unit extracellular recordings yielded a consistent set of characteristic discharge properties. (1) Tonic discharge co-varied with stages of the S-WC, being highest during waking, lower during slow wave sleep, and virtually absent during paradoxical sleep. (2) Discharge anticipated S-WC stages as well as phasic cortical activity, such as spindles, during slow wave sleep. (3) Discharge decreased within active waking during grooming and sweet water consumption. (4) Bursts of impulses accompanied spontaneous or sensory-evoked interruptions of sleep, grooming, consumption, or other such ongoing behavior. (5) These characteristic discharge properties were topographically homogeneous for recordings throughout the NE-LC. (6) Phasic robust activity was synchronized markedly among neurons in multiple unit populations. (7) Field potentials occurred spontaneously in the NE-LC and were synchronized with bursts of unit activity from the same electrodes. (8) Field potentials became dissociated from unit activity during paradoxical sleep, exhibiting their highest rates in the virtual absence of impulses. These results are generally consistent with previous proposals that the NE-LC system is involved in regulating cortical and behavioral arousal. On the basis of the present data and those described in the following report (Aston-Jones, G., and F. E. Bloom (1981) J. Neurosci.1: 887–900), we conclude that these neurons may mediate a specific function within the general arousal framework. In brief, the NE-LC system may globally bias the responsiveness of target neurons and thereby influence overall behavioral orientation.
The atypical excitation by opiates and opioid peptides of hippocampal pyramidal cells can be antagonized by iontophoresis of naloxone, the γ-aminobutyric acid antagonist bicuculline, or magnesium ion. The recurrent inhibition of these cells evoked by transcallosal stimulation of the contralateral hippocampus is blocked by enkephalin but only shortened by acetylcholine. The results suggest that the opioids excite pyramidal neurons indirectly by inhibition of neighboring inhibitory interneurons (probably containing γ-aminobutyric acid). This mechanism may be pertinent to the electrographic signs of addictive drugs.
Comparison by linear sucrose density gradient centrifugation showed that the rat heart contains a hitherto unrecognized major particulate fraction for norepinephrine storage, which sediments at a sucrose molarity exceeding 1 M and thus has sedimentation properties closely similar to the norepinephrine storage particles in bovine splenic nerves. By using special techniques it was possible to confirm reports of an additional norepinephrine-storing particulate fraction in the rat heart which peaks at 0.5 M sucrose. This light fraction was consistently absent from the splenic nerves. The heavy particles in the rat heart contained at least one-half of the total particle-bound norepinephrine in this tissue, in spite of changes in homogenization and in the composition of the medium. When light and heavy particles from the rat heart were layered on a second gradient, only the heavy particles formed a single peak in the same position as in the original gradient, while the light particles appeared to be more labile and had their activity dispersed throughout the gradient. Electron-microscopic analysis of the sedimented light and heavy particulate fractions fixed in glutaraldehyde—osmium tetroxide were strikingly homogeneous, and were composed of large empty bag-like forms and smaller vesicles of varying internal electron density. Comparison with biochemical data indicates that only the smaller vesicles may include the norepinephrine storage particles. Work is in progress on the possible functional significance of different amine storage structures in the same neuron and of differences in storage structures between different neurons.
The glyoxylic acid-induced fluorescence method for localization of brain catecholamine neurons has been modified. Fluorescence is developed rapidly in cryostat sections of brains fixed by perfusion with 0.5% depolymerized paraformaldehyde and 2.0% glyoxylic acid. Since neither freeze drying nor vibratome sectioning is required, total processing time can be less than 1 hr. Both perikarya and fine varicose axons of norepinephrine- and dopamine-containing neurons can be seen throughout the neuroaxis. The modified technique retains good cytologic integrity and may provide a useful alternative for methods combining histochemical approaches.
The mRNA encoding vasopressin has recently been documented within the magnocellular hypothalamo-neurohypophyseal projections of the rat such as the median eminence (ME) and the posterior pituitary (PP), suggesting the possibility of its axonal transport. To address the origin of this mRNA and to investigate the functional significance of this unexpected axonal transport of mRNA, we have examined its subcellular localization within both magnocellular perikarya and their axonal projections. For this purpose, we have used nonradioactive in situ hybridization techniques in order to localize the vasopressin mRNA with precision at the ultrastructural level in magnocellular perikarya, dendrites, and axons from control, salt-loaded, and lactating rats. This approach permitted us to demonstrate directly the axonal localization of vasopressin mRNA. Moreover, we were able to obtain novel information concerning vasopressin mRNA compartmentation within both perikarya and axons. At both light and electron microscopic levels, we observed vasopressin mRNA-containing cells in the hypothalamic magnocellular cell body groups, but not in the ME or in the PP. When vasopressin mRNA was detected in medium-size dendrites, it was always associated with the rough endoplasmic reticulum (RER). Within the labeled magnocellular perikarya, the abundant vasopressin mRNA was mainly associated with discrete areas of the RER. However, vasopressin mRNA was never detected in the Golgi apparatus or in association with neurosecretory granules, in perikarya or axons. These data suggest that vasopressin mRNA translation is restricted to certain segments within the RER, and that axonal transport of vasopressin mRNA does not involve the classical neurosecretory pathway, via the Golgi apparatus and the neurosecretory granules, as has been proposed. Within the magnocellular neuron axons, vasopressin mRNA could be detected only in a subset of axonal swellings, all of which were confined to the internal layer of the ME and the PP. The mRNA-containing swellings were numerous in 7 d salt-loaded animals, less abundant in lactating animals, and almost undetectable in control animals. In all groups of animals, no vasopressin mRNA was detectable in any other region of the magnocellular neuron axons, including undilated axonal segments or varicose swellings. These results strongly suggest that, under physiological activation such as chronic salt loading, axonal vasopressin mRNA is increased and becomes aggregated in a selected subset of swellings of the ME and the PP. Furthermore, these data indicate that along the magnocellular neuron axons, the swellings may differ in their biochemical and functional features. Further analysis focused on the mRNA-accumulating swellings may illuminate the function of RNA within the axonal compartment.
Adenylate cyclase activity in homogenates and particulate fractions of rat cerebellum, cerebral cortex, salivary gland, heart, and liver was inhibited by very low concentrations of lead ions (I50
