In vivo microdialysis of corticotropin releasing factor (CRF): calcium dependence of depolarization-induced neurosecretion of CRF.

Corticotropin releasing factor (CRF) is a large neuropeptide which functions as a major neurotransmitter in physiological stress responses. We have developed a microdialysis method for detecting CRF release from the median eminence of anesthetized rats. Depolarizing concentrations of KCl increased release of CRF into the perfusion media; this effect was inhibited by 100 microM verapamil. Our characterization of the physiologic conditions of KCl-induced release of neuronal CRF using the microdialysis technique provides evidence that the CRF release system is Ca(2+)-dependent and maintains its integrity over many hours in anesthetized rats.

Crossed receptive field components and crossed dendrites in cat sacrocaudal dorsal horn.

The hypothesis that sacrocaudal dorsal horn neurons with crossed receptive field components on the tail have dendrites which cross to the contralateral dorsal horn was tested in a combined electrophysiological and morphological study. Dorsal horn cells in the sacrocaudal spinal cord of anesthetized cats were penetrated with horseradish peroxidase-filled microelectrodes. After mapping their low threshold mechanoreceptive fields, cells were iontophoretically injected with horseradish peroxidase. A sample of 16 well-stained cells was obtained in laminae III and IV. Cells with receptive fields crossing the dorsal midline of the tail (n = 8) had somata in the lateral ipsilateral dorsal horn, and some of these cells (5/8) had dendrites which crossed to the lateral contralateral dorsal horn. Cells with receptive fields spanning the ventral midline (n = 2) were located near the center of the fused dorsal horn, and one of these had bilateral dendrites in this region. Cells with receptive fields on the lateral tail, crossing neither the dorsal nor the ventral midline (n = 6), had cell bodies in the middle of the ipsilateral dorsal horn; half had only ipsilateral dendrites, and half had crossed dendritic branches. Although the relationship between cell receptive field (RF) location (RF center, expressed as distance from tips of toes) and mediolateral location of the cell body was statistically significant, the correlation between crossed RF components and crossed dendritic branches was not significant.

Influence of map scale on primary afferent terminal field geometry in cat dorsal horn.

1. Thirty-one physiologically identified primary afferent fibers were labeled intracellularly with horseradish peroxidase (HRP). 2. A computer analysis was used to determine whether the distribution of cutaneous mechanoreceptive afferent terminals varies as a function of location within the dorsal horn somatotopic map. 3. An analysis of the geometry of the projections of these afferents has shown that 1) terminal arbors have a greater mediolateral width within the region of the foot representation than lateral to it, 2) terminal arbors have larger length-to-width ratios outside the foot representation than within it, and 3) the orientation of terminal arbors near the boundary of the foot representation reflects the angle of the boundary. Previous attribution of mediolateral width variations to primary afferent type are probably in error, although there appear to be genuine variations of longitudinal extent as a function of primary afferent type. 4. Nonuniform terminal distributions represent the first of a three-component process underlying assembly of the monosynaptic portions of cell receptive fields (RFs) and the somatotopic map. The other two components consist of the elaboration of cell dendritic trees and the establishment of selective connections. 5. The variation of primary afferent terminal distributions with map location is not an absolute requirement for development of the map; for example, the RFs of postsynaptic cells could be assembled with the use of a uniform terminal distribution for all afferents, everywhere in the map, as long as cell dendrites penetrate the appropriate portions of the presynaptic neuropil and receive connections only from afferent axons contributing to their RFs.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatotopic organization of single primary afferent axon projections to cat spinal cord dorsal horn.

Horseradish peroxidase injection of identified low threshold cutaneous mechanoreceptor (LTCM) primary afferent axons was used to assess the somatotopic organization of hindlimb projections to laminae III and IV of cat dorsal horn. Multiple injections in the same animals were used to assess bilateral symmetry and precision. Thirty-one axons were injected, with more than 1 axon injected in each of 8 animals (25 axons). Somatotopic relations between their receptive field (RF) centers and the centers of their dorsal horn projections were similar to the somatotopic relations between dorsal horn cell RF centers and cell locations. Very few reversals of mediolateral somatotopic gradients (proximodistal RF location as a function of mediolateral projection center) were observed. Two afferents with nearly identical RFs in 1 animal had nearly identical projections. These observations held for many different combinations of receptor types. A simple mathematical model was used to demonstrate that assembly of dorsal horn cell RFs via passive sampling of the presynaptic neuropil by dorsal horn cell dendrites cannot account for the sizes of dorsal horn cell LTCM RFs. Hypothesized mechanisms for assembly of dorsal horn cell RFs must take into account the functional selectivity of connections required to produce RFs smaller than those predicted by the passive assembly model.

Wheel-running activity after kainic acid injection into lateral hypothalamus of rats.

It has not been resolved whether the permanent decrease in wheel-running activity observed after the placement of bilateral electrolytic lesions in the ventrolateral hypothalamus of rats is due to local neuronal destruction or to disruption of fibers of passage within the lateral hypothalamus. To further explore this question, the changes in wheel-running activity following injections of a kainic acid (KA) solution into the ventrolateral hypothalamus of rats were studied. As was found with electrolytic lesions, KA induced lesions in the ventrolateral hypothalamus resulted in a permanent decrease in wheel-running activity. The uptake of 3H-dopamine (3H-DA) into crude synaptosomal preparations of striatal tissue was used as an index of the amount of damage done to fibers of passage by KA. 3H-DA uptake by striatal tissue from rats injected with KA did not significantly differ from that of control rats. These data support the hypothesis that the decrease in wheel-running activity following injection of KA into the ventrolateral hypothalamus is the result of damage to intrinsic neurons.

Locomotor activity and ingestive behavior after damage to ascending serotonergic systems.

The effects of electrolytic midbrain raphe lesions on ingestive behavior and locomotor activity of rats were compared to those produced by intracerebral injections of 5,7 dihydroxytryptamine (5,7 DHT) at various points along the ascending serotonergic pathways. Only electrolytic lesions of the median and/or dorsal raphe nuclei produced significant changes in food intake, water intake, body weight gain, and wheel running activity. Intracerebral injections of 5,7 DHT, a selective serotonergic neurotoxin, had no effect on any of these variables. However, 5,7 DHT induced lesions produced decreases in forebrain synaptosomal uptake of serotonin which were equivalent to, or greater than, those resulting from electrolytic lesions of the midbrain raphe nuclei. Failure of 5,7 DHT injections to replicate the behavioral changes resulting from electrolytic lesions of the midbrain raphe nuclei suggests that loss of ascending serotonergic projections was not responsible for the behavioral effects that followed the electrolytic lesions.

Serotonergic innervation of the lateral hypothalamus: evidence from synaptosomal uptake studies.

Uptake of tritiated serotonin by synaptosomes prepared from rat lateral hypothalamus was examined. Uptake of serotonin into lateral hypothalamic synaptosomes occurred by both saturable and non-saturable processes. The saturable process was a high affinity transport with kinetic parameters that agree closely with those previously reported for serotonin uptake into synaptosomes prepared from other brain regions. Fluoxetine, a selective inhibitor of uptake into serotonergic neurons, was a potent inhibitor of serotonin uptake into lateral hypothalamic synaptosomes. Desipramine and benztropine, noradrenergic and dopaminergic uptake inhibitors respectively, were much less effective. Damage to the ascending serotonergic system, by either electrolytic lesion of the dorsal or median raphe nucleus, or by 5,7 dihydroxytryptamine injections into the midbrain serotonergic pathways, significantly reduced the uptake of serotonin by lateral hypothalamic synaptosomes. Taken together, these data provide further evidence for a serotonergic terminal field within the lateral hypothalamus.

Effects of damage to median raphe nucleus on ingestive behavior and wheel running activity.

The effects of damage to the median raphe nucleus on the ingestive behavior and wheel running activity of rats were studied. This nucleus was damaged by the placement of either electrolytic or chemical (5,7-dihydroxytryptamine) lesions. After the placement of either type of lesion, wheel running activity was significantly decreased for the duration of the 8 week post-operative period. Although there were transient decreases in both food and water intakes after damage to the median raphe nucleus, these decreases did not appear to result from impairments in neuro-regulatory mechanisms. Rather, the decrease in food intake seemed to be related to the decrease in locomotor activity, and the decrease in water intake appeared to be linked to the decrease in food intake. In some rats with electrolytic lesions in the median raphe nucleus, the decrease in water intake was followed by a transient period of hyperdipsia.