Jon D. Dunn

Plasma corticosterone responses to electrical stimulation of the bed nucleus of the stria terminalis

The effect of ventral septal stimulation on pituitary-adrenal function was assessed by evaluating plasma corticosterone obtained prior to and following sham or electrical stimulation of the bed nucleus of the stria terminalis (BNST) of female rats anesthetized with urethane (1.3 g X kg-1). Hippocampal EEG, ECG, heart rate, blood pressure and respiration were routinely monitored; timed blood samples (0.2 ml) for determining plasma corticosterone (RIA) were obtained from a catheterized tail artery. Samples were taken at 0.5 min prior to and at 5, 10, 15 and 30 min after initiation of stimulation. Whereas increased plasma corticosterone levels followed stimulation of the medial aspect of the BNST, lateral stimulation resulted in decreased plasma corticosterone levels. The overall increase in plasma corticosterone following medial stimulation was 24%; the overall decrease was 13%. The largest increase in plasma corticosterone (36%) occurred at 30 min poststimulation; the largest decrease (22%) occurred at 15 min. Stimulation of the most rostral aspect of the BNST produced plasma corticosterone responses similar to that observed following medial stimulation. In contrast, no changes in corticosterone levels were observed following either sham stimulation or stimulation of the corpus callosum, fornix or anterior commissure.

Plasma Corticosterone Responses to Electrical Stimulation of the Amygdaloid Complex: Cytoarchitectural Specificity

To pursue the possibility that subdivisions within the amygdaloid complex are differentially involved in adrenocortical function, plasma samples obtained prior to and following electrical stimulation of the amygdala of urethane (1.30 g/kg) anesthetized female rats were assessed for corticosterone concentration. Hippocampal EEG, ECG, heart rate, mean arterial pressure, and respiration routinely were monitored, and timed blood samples (0.2 ml) were obtained from a catheterized artery. Blood samples were taken 0.5 min prior to and at 5, 10, 15, and 30 min after initiation of stimulation. Whereas stimulation of the central and lateral nuclei produced a decrease (p less than 0.05) in plasma corticosterone, stimulation of the basomedial, medial and posterior corticomedial nuclei resulted in increased plasma corticosterone levels (p less than 0.05). In contrast, no change in corticosterone levels were observed following sham stimulation or stimulation of several nonamygdaloid sites. Collectively, these data support the hypothesis that subdivisions within the amygdaloid complex are differentially involved in adrenocortical function.

Neurotransmitter Microchemistry of the Cochlear Nucleus and Superior Olivary Complex

The complex function of the nervous system is made possible by its underlying chemistry. One aspect of this chemistry involves the primary mechanism by which neurons communicate with each other, chemical neurotransmission. It is likely that the neurons of the auditory system are organized chemically as well as structurally and functionally. We may therefore look for populations of neurons employing particular neurotransmitters. These neuronal populations may serve specific functions in the auditory system, just as specific functions are served by cholinergic spinal motoneurons or dopaminergic nigrostriatal neurons.

Effects of trapezoid body and superior olive lesions on choline acetyltransferase activity in the rat cochlear nucleus.

Using a microdissection and quantitative microassay approach, choline acetyltransferase activities were mapped in the cochlear nuclei of rats having either transection of the trapezoid body or destruction of the superior olivary complex on one side in the brain stem. Lateral trapezoid body transection resulted in dramatic loss of choline acetyltransferase activity in all parts of the ipsilateral cochlear nucleus, while more medial transection had little effect. Destruction of the superior olivary complex resulted in dramatic loss of choline acetyltransferase activity in the ipsilateral cochlear nucleus, and detectable loss also contralaterally. The results suggest that most of the centrifugal cholinergic projections to the rat cochlear nucleus derive from or traverse the vicinity of the superior olivary complex bilaterally and enter the cochlear nucleus ventrally from the region of the trapezoid body.

Effect of olivocochlear bundle transection on choline acetyltransferase activity in the rat cochlear nucleus

Using a microdissection and quantitative microassay approach, choline acetyltransferase activities were mapped in the cochlear nuclei of rats having complete transections of the olivocochlear bundle on one side in the brain stem. In rats in which the trapezoid body was not significantly damaged by the lesion, consistent reductions of choline acetyltransferase activity in subregions of the lesion-side cochlear nucleus, as compared to the control side, averaged about 20%. Nevertheless, a profound lesion-side reduction of choline acetyltransferase activity was found in a branch connection from the olivocochlear bundle to the cochlear nucleus. The results suggest that branches from the olivocochlear bundle are cholinergic, but contribute a relatively minor proportion of the cholinergic synapses in all regions of the rat cochlear nucleus. In the light of previous results with more extensive lesions, it can be proposed that synapses in all regions of the rat cochlear nucleus. In the light of previous results with more extensive lesions, it can be proposed that most cholinergic input into the rat cochlear nucleus enters by a ventral route along the trapezoid body. It is noted that this represents a quantitatively somewhat different situation from that in the cat.

Effects of large brain stem lesions on the cholinergic system in the rat cochlear nucleus

Large lesions were made medial to one cochlear nucleus in rats, in order to cut virtually centrifugal pathways to it. To estimate the contribution of these centrifugal pathways to cholinergic synapses in the cochlear nucleus, choline acetyltransferase and acetylcholinesterase activities were mapped, by quantitative histochemical procedures, in lesion and control side cochlear nuclei. Choline acetyltransferase activities were reduced by 85-90% in most regions of the lesion side cochlear nucleus and by 65-75% in granular regions. Acetylcholinesterase activities were reduced by 50% or less in the same regions. The choline acetyltransferase results are consistent with a conclusion that by far most cholinergic synapses in the rat cochlear nucleus derive from centrifugal pathways. Additionally, the effects of the lesions on enzyme activities in the lateral superior olivary nucleus and ventral nucleus of the trapezoid body, and in the facial, motor trigeminal, and spinal trigeminal nuclei were examined. In the lesion side facial nucleus, 60% and 40% decreases in choline acetyltransferase and acetylcholinesterase activities, respectively, were apparently consequences of facial root transection. Lesion-control enzyme activity differences in the other nuclei were much smaller.

Differential cytolysis of murine spleen, bone-marrow and leukemia cells by melittin reveals differences in membrane topography

L1210 leukemia cells are 2-4 fold more sensitive to the cytolytic effects of melittin, the membrane-active toxin of bee venom, than normal DBA/2 mouse spleen and bone-marrow cells. Lysis of the normal cells was abolished when either 75 mM galactosamine, glucosamine or 100 microM beta-lactoglobulin was added to the melittin-cell reaction, but lysis of the leukemia cells was unaffected. The amino-groups appeared necessary for blocking melittin-mediated lysis since glucose, galactose and the N-acetyl derivatives were not inhibitory. Bone-marrow cells were more readily protected from lysis than spleen cells. Since melittin-inhibitor complexes were not detected by gel chromatography and the inhibitor could be added to the cell suspension after melittin, the evidence suggests that bone-marrow cells are rich in membrane binding sites for carbohydrates that decrease in mature spleen cells and are virtually absent after neoplastic transformation.

Contribution of centrifugal innervation to choline acetyltransferase activity in the cat cochlear nucleus

Using a quantitative microchemical mapping approach combined with surgical cuts of fiber tracts, the contributions of centrifugal pathways to choline acetyltransferase activity were mapped three-dimensionally in the cat cochlear nucleus. Large reductions of choline acetyltransferase activity, averaging 70%, were measured in almost all parts of the lesion-side nucleus following transection of virtually all its centrifugal connections. More superficial cuts, penetrating just through the olivocochlear bundle, also led to significant reductions of enzyme activity, especially most rostrally in the anteroventral cochlear nucleus and superficial granular region, where the reductions were similar to those following the complete cuts. Lesions encroaching upon the superior olivary complex gave bilateral effects. Transverse cuts between rostral and caudal parts of the cochlear nucleus gave some small effects. The results suggest that, as in rats, most choline acetyltransferase activity in the cat cochlear nucleus is associated with its centrifugal innervation. However, unlike the situation in rats, the enzyme activity in cats is related more to olivocochlear branches than to ventral fibers in the trapezoid body region. Also, the choline acetyltransferase activity related to olivocochlear collateral innervation is much less uniformly distributed within the cochlear nucleus in cats than in rats.

Quantitative distributions of aspartate aminotransferase and glutaminase activities in the rat cochlea

The intra-cochlear distributions of aspartate aminotransferase and glutaminase, prominent enzymes of aspartate and glutamate metabolism, have been studied by quantitative microchemical techniques. Also measured was choline acetyltransferase, the enzyme synthesizing acetylcholine, and a marker for the olivocochlear bundle. Aspartate aminotransferase activity was highest in the stria vascularis, about half this high in the organ of Corti synaptic (hair cell) zones, somewhat lower in the organ of Corti non-synaptic (Hensens cell) zones, lower yet in Reissners and lowest in the tectorial membrane. Glutaminase, on the other hand, had its highest activity in synaptic zones, about a third of that activity in the organ of Corti non-synaptic zones, and a barely detectable activity in Reissners and tectorial membranes, and stria vascularis. Seven days after transection of the olivocochlear bundle, no significant difference was found between lesion- and control-side aspartate aminotransferase or glutaminase activities, even though no choline acetyltransferase activity remained in the lesion-side of the organ of Corti. Both the distribution of aspartate aminotransferase activity and the lesion results would seem to implicate it in energy more so than neurotransmitter metabolism. The distribution of glutaminase activity could be consistent with a role in neurotransmission; however, the lesion data were unable to demonstrate a specific association with the olivocochlear bundle.

Differential Plasma Corticosterone Responses to Electrical Stimulation of the Medial and Lateral Septal Nuclei

To pursue the possibility that subdivisions within the medial and lateral septal nuclei are differentially involved in adrenocortical function, plasma samples obtained prior to and following electrical stimulation of the septal nuclei of urethane (1.30 g/kg)-anesthetized female rats were assessed for corticosterone concentration. Hippocampal EEG, ECG, heart rate (HR), mean arterial pressure (MAP) and respiration were routinely monitored, and timed blood samples (0.15 ml) were obtained from a catheterized tail artery. Blood samples were taken 0.5 min prior to and at 5, 10, 15 and 30 min after initiation of stimulation. Whereas no change in Cpd B levels were observed following sham stimulation or stimulation of the corpus callosum, fornix or anterior commissure, stimulation of the medial septal nuclei produced differential responses. Decreased plasma Cpd B responses followed stimulation of the medial septal nucleus (MS); increases in plasma Cpd B followed stimulation of the dorsal (LSD) and ventral (LSV) division of the lateral septal nucleus. The overall increase in plasma Cpd B levels following LSD and LSV stimulation was 16 and 32%, respectively. The overall decrease in corticosterone concentration subsequent to MS stimulation was 18%. The largest increases in Cpd B levels occurred at 5 min (36%) and 10 min (24%) for LSV and LSD groups, respectively; the largest decrease was noted at 15 min (25%). Plasma Cpd B responses to stimulation of the intermediate area of the lateral septal nucleus produced varying and inconsistent responses. Collectively, these data support the hypothesis that subdivisions within the septal nuclei are differentially involved in adrenocortical function.