Ervin W. Powell

Connections of cerebral structures functioning in neurohypophysial hormone release

Summary Connections to the paraventricular and supraoptic nuclei from cerebral structures rostral to the pons related to neurohypophysial hormones release were determined by milk-ejection, pressor, evoked potential and degeneration techniques. Milk-injection (oxytocic) responses were readily obtained from stimulating the hippocampal rudiment and nucleus accumbens. Oxytocic and vasopressor responses resulted from stimulation of the midbrain central gray, subthalamus and posterior hypothalamus. Evoked potentials having a latency of 7 msec or less were recorded from the paraventricular and supraoptic nuclei following stimulation of the former structures. Responses and latencies greater than 7 msec were registered in the supraoptic nucleus when the cingulate cortex, claustrum, putamen, medial lemniscus, superior colliculus and prectum were stimulated. Degeneration patterns from lesions in the hippocampal rudiment reveal direct projections to the paraventricular nucleus via the superior fornix anf fornix column but not to the supraoptic nucleus. Following lesions in the midbrain central gray, connections were traced to the hypothalamus and subthalamus via the dorsal longitudinal fasciculus, mammillary peduncle and medial forebrain bundle. From lesions in the subthalamus and posterior hypothalamus, degenerated fibers entered the medial forebrain bundle and projected to the supraoptic and paraventricular nuclei, respectively. These results show that the hippocampal rudiment, central gray, subthalamus and posterior hypothalamus are intimately involved in mechanisms of

Limbic projections to the thalamus.

SummaryDegeneration density and topography in the thalamus of the squirrel monkey was studied following lesions in the septal area, fornix, and cingulate gyrus. It was found that the hippocampus projects more fibers to the anteroventral nucleus of the thalamus and the cingulate gyrus projects fewer fibers to it than does the septal area. The septal fibers to the anteromedial nucleus were more marked than were its projections to the anteroventral nucleus. The hippocampus and cingulate gyrus did not show this preferential projection. The thalamus is a more prominent target of limbic connections than heretofore realized. They appear to quantitatively rival known limbic-hypothalamic pathways. Therefore, in order to understand the total influence of the limbic system on cerebral function, one must consider its effects on thalamic perceptive mechanisms as well as effects on the hypothalamus.

The limbic system: An interface

Much work has related limbic structure with hypothalamic function rather than with higher nervous system function. Most studies have dealt with single limbic structures rather than with several as interrelated functional systems. Upon consideration of the total limbic-structure complex it would appear that the septum-hippocampus-amygdala form an interface between the isocortex and the thalamus. Our work relating to projections of the limbic system, especially the septal area, has directed our attention to the thalamus as a particularly important target of limbic system projections. Furthermore, our work on projections of the cingulate gyrus reveals that this cortical area projects strongly to other cortical regions as well as to thalamic nuclei. The orbital frontal cortex, cingulate gyrus, and hippocampal gyrus are isocortical areas which then link the limbic system with other corticothalamic systems. This feature, plus strong thalamic connections from the hippocampus, septum, and amygdala provide a basis for considering the limbic system as an interface between the overlying cerebral isocortex and thalamic structures. This interface may be a key integrating system related to selective modulation of emotion and sensory mechanisms of the brain via a number of feedback circuits wherein recycling could be effected through the temporal and/or the frontal cortex.

Silver Impregnation of Degenerating Axons; Comparisons of Postoperative Intervals, Fixatives and Staining Methods

By introducing variations in procedures and comparing density and patterns of degeneration exhibited, we found that: (1) in the rat, cat, and monkey, the optimum survival time was about 1 wk; this period yielding the maximum amount of argyrophilic reaction and the most consistent staining among several different parts of the brain. Survival times of up to 3 wk did not seriously impair the interpretation of argyrophilial patterns; (2) some qualitative changes in the nuclear patterns of degeneration suggested that the use of a range of survival times may provide useful data; (3) staining differences and similarities in different neural systems of known connections were about the same in the 3 species of animals; (4) formalin, buffered formalin, and a 4%:1% paraformaldehyde-glutaraldehyde mixture were satisfactory perfusion solutions; however, staining was less intense when the Nauta-Gygax method followed the last fixative mixture; (5) The Fink-Heimer I method yielded more consistent results than did the Fin...

Differential conditioning of septum and hippocampus

Abstract Electrical stimulation of septum and hippocampus was used as a discriminative stimulus for bar-pressing behavior in the rat. Stimulation of septum was easier to establish as a discriminative cue than was stimulation of hippocampus. A differential conditioned response could be established between the stimulations of septum and hippocampus and this differential response could be reversed by appropriately reversing the reinforcing contingencies associated with the stimulations. The results suggest that electrical stimulation of septum and hippocampus can be used to control behavior in a manner similar to that exerted by exteroceptive stimuli. Thus, the excitatory or inhibitory behavioral effects of brain stimulation may be more related to the reinforcing contingencies present during stimulation than to some intrinsic function of the structures stimulated.

An evoked potential study of limbic projections to nuclei of the cat septum

Abstract A study of the relationship between connections of limbic structures and septal nuclei of the cat was conducted with the evoked potential technique. 1. 1. Limbic structures project via a variety of imputs, differentially to a number of septal nuclei. Some of the nuclei of the septum are activated by more than one limbic structure. 2. 2. The dorsal hippocampus projects to dorsal nuclei of the septum especially to the n. medialis pars anterior via the fornix and diagonal band. 3. 3. Connections to n. dorsalis pars intermedia, n. medialis pars anterior and n. accumbens from the ventral hippocampus and hippocampal gyrus would appear to be multisynaptic via the diagonal band and perhaps fornix. 4. 4. The antero-ventral nucleus of the thalamus has connections with the n. septalis fimbrialis and n. septalis medialis pars anterior via the fornix and diagonal band. 5. 5. The amygdala projects to ventral posterior structures of the septum, especially the n. accumbens and olfactory tubercle via the longitudinal association bundle, stria terminalis and diagonal band. 6. 6. The mammillary body projects to the n. septalis medialis pars anterior via the fornix.

Influence of the septum and inferior colliculus on medial geniculate body units

Abstract The septum has been found to have direct projections to the medial geniculate body (MGB) and the inferior colliculus; this study was undertaken to determine whether or not the septum might influence the function of the MGB. Excitatory and inhibitory effects on MGB unit firing were observed after stimulation of the septum and inferior colliculus. In addition, interacting effects between the septum and inferior colliculus on MGB units were observed using a focus in each in turn as a test or conditioning stimulus origin. Ablation of the inferior colliculus or removal of the posterior reticular formation did not eliminate MGB unit activation. 1. 1. A tungsten micro-electrode was used to record from units of the MGB, and small concentric bipolar electrodes were used to stimulate the septum and inferior colliculus. 2. 2. Single shocks of 40 V, 0.1 msec pulse duration were delivered at a frequency of 0.5 /sec. 3. 3. Units in the MGB were excited from 15 foci and inhibited from 2 other foci after stimulation of the septum. 4. 4. Units in the MGB were excited from 45 foci and inhibited from 11 other foci after stimulation of the inferior colliculus. 5. 5. Both the septum and inferior colliculus, when used respectively as a conditioning and a test stimulus, were found either to excite or to inhibit unit firing produced by the test stimulus. From this and similar evidence it is likely that the septum modulates auditory inputs or their subsequent impact on cerebral function via the MGB and temporal lobe cortex.

A Comparison of Fixation by Formaldehyde and Glutaraldehyde-Formaldehyde for Combined Light and Electron Microscopy of Axonal Degeneration in the Mammillary Body

Mammillary body (Mb) cell structures were compared following four different procedures for fixation, in order to find one procedure which would be suitable both for silver impregnation methods and electron microscopy. Fixatives compared were: (1) formaldehyde (4% pH 5.5), Mb from a frozen-section; (2) formaldehyde (4% pH 7.2.), Mb from a frozen-section; (3) glutaraldehyde-formaldehyde (1%-4% pH 6.0), Mb from a frozen-section; and (4) glutaraldehyde-formaldehyde (3%-2% pH 7.2), unfrozen Mb. All solutions were perfused into the left ventricle of the heart of anesthetized rats, except for the animal from which the unfrozen tissue was obtained. The Mb was excised from the fresh brain and immediately placed in a fixative solution. After aldehyde fixation, the tissues were further fixed in 1% OsO4 (pH 7.4), dehydrated, embedded in Epon-Araldite and double-stained with uranyl acetate and lead citrate. Comparisons of mitochondria, myelin, synapses, neurofilaments and synaptic membranes indicated that the perfusio...