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The effect of bulbectomy on amino acid levels in 5 regions of the rat primary olfactory cortex has been monitored. Glutamate levels were significantly lowered in the lateral olfactory tract only. In contrast, aspartate levels were significantly reduced in all regions except the periamygdaloid cortex. The results suggest transmitter heterogeneity of the tract fibres and confirm a likely transmitter role for aspartate for some tract terminals.

The connections of the medium (10–20 μm) and large (20–35 μm) cells of the islands of Calleja Complex (ICC) were studied in the albino rat with anterograde and retrograde transport of horseradish peroxidase (HRP) and fluorescent tracers. The medium and large size cells were found to project to the ipsilateral olfactory tubercle, ventral pallidum, septum, piriform cortex, periamygdaloid cortex, cortical nuclei of the amygdala, ventral endopiriform nucleus, lateral hypothalamic area, Forel's field H, ventral tegmental area, supramammillary complex, and nuclei gemini of the hypothalamus, midline, intralaminar and medial thalamic nuclei, and lateral habenula. Afferents of the ICC appear to include the same nuclei with the exception of the lateral habenula. In addition, the dorsal raphe projects to the ICC. These connections are consistent with the concept that the ICC is a striato-pallidal structure.

Previous studies have shown that the amygdala projects to both the mediodorsal thalamic nucleus (MD) and its cortical projection area, the prefrontal cortex (PFC). In this investigation rats received injections of different fluorescent retrograde tracers (true blue and diamidino yellow) into MD and either the lateral, polar, or medial PFC in order to examine the relationship of amygdaloid neurons with cortical and/or thalamic projections. PFC injections labeled neurons in the basolateral (BL), basomedial (BM), ventral endopiriform (Env), and rostral lateral nuclei as well as the periamygdaloid cortex (PAC) and the medial part of the amygdalohippocampal area (AHA). In BL, which contained the great majority of neurons projecting to PFC, most labeled cells were concentrated in particular parts of the nucleus and were topographically organized. The overwhelming majority of labeled neurons in BL were large pyramidal or piriform cells that correspond to class I neurons described in Golgi studies. Occasional small neurons with thin dendrites were also observed; these cells may be class II neurons. MD injections labeled numerous cells in the anterior division of the cortical nucleus, medial nucleus, and caudomedial part of the central nucleus. Moderate numbers of labeled cells were found in caudal portions of BM and PAC, whereas scattered cells were observed throughout the rest of the amygdala with the exception of the lateral nucleus. In BL and AHA many MD-projecting neurons were observed along nuclear boundaries and in the adjacent white matter. Neurons in BL, BM, and AHA usually had large elongated or irregular somata and two to four primary dendrites that branched sparingly. Other cells had smaller ovoid somata. The morphology and distribution of MD-projection cells in the basolateral amygdala indicate that they are primarily large class II neurons. Double-labeled amygdaloid neurons, labeled by both cortical and thalamic injections, were observed only in a small number of animals. Control experiments suggest that most of the double-labeled cells in these cases were artifacts caused by spread of the thalamic injectate into the third ventricle with subsequent uptake by fibers in the anterior commissure. Thus the findings of this study suggest that different neuronal populations in the amygdala project to the two poles of the MD-PFC system. In the basolateral amygdala class I neurons are the predominant cell type involved in PFC projections, whereas a subpopulation of class II neurons, hitherto thought to be primarily local-circuit neurons, project to MD.

The projections of the hypothalamus to the amygdala have been studied autoradiographically in a series of eleven cynomolgus monkeys (Macaca fascicularis) in which injections of [3H]amino acids had been made in different regions of the caudal two-thirds of the hypothalamus. The most prominent projection arises from the ventromedial nucleus of the hypothalamus and terminates most heavily in the medial, magnocellular division of the central nucleus. Injections confined to the ventromedial nucleus also result in labeling of the piriform cortex, the periamygdaloid cortex, the anterior amygdaloid area, the medial amygdaloid nucleus and the parvocellular divisions of both the basal and basal accessory nuclei. All these projections are bilateral (although the contralateral component is much smaller) and show evidence of a rostro-caudal topographic organization. Isotope injections that involve the caudal part of the lateral hypothalamic area label projections to the medial division of the central amygdaloid nucleus, to the medial and cortical nuclei and to the anterior amygdaloid area. When such caudally placed injections also involved the lateral mamillary nucleus, the lateral division of the central amygdaloid nucleus was additionally labeled. Although the medial mamillary nucleus does not project to the amygdala, there is evidence for a minor projection from the supramamillary region to the medial amygdaloid nucleus. The ventral tegmental area appears to project to the lateral division of the central nucleus and the medial portion of the substantia nigra has a small projection to both divisions of the central nucleus. All of these projections reach the amygdala by way of the so-called ventral amygdalofugal pathway, but at least some of the fibers that arise in the ventromedial nucleus run in the stria terminalis.

The temporal neocortical afferent connections to the amygdala were investigated in the rhesus monkey using the silver impregnation and autoradiographic tracing methods. A large topographically organized projection to the amygdala was found to originate from the anterior superior temporal gyrus (area TA), the anterior middle and inferior temporal gyri (area TE), and the medial and lateral aspects of the temporal pole (area TG). These projections terminate in discrete adjacent regions of the lateral and basal amygdaloid nuclei. The temporal pole projection terminates in the ventral two thirds of the medial one half of the lateral nucleus and in the accessory basal nucleus, the anterior superior temporal gyrus projection terminates in the ventral two thirds of the lateral one half of the lateral nucleus, and the anterior middle and inferior temporal gyri projection terminates in the dorsal parts of the lateral and lateral basal nuclei. A projection from the perirhinal cortex to the medial basal nucleus of the amygdala is also discussed. Our findings reveal that a far greater proportion of the temporal neocortex than previously described contributes afferents to the amygdala, further strengthening the view that the amygdala occupies a key anatomical position linking the neocortex with diencephalic structures.

The intrinsic amygdaloid connections of the cynomolgus monkey were investigated using the autoradiographic method. Additional evidence concerning the origin of some intra-amygdaloid connections was provided by a series of rhesus monkeys with injections of horseradish peroxidase (HRP) in the amygdaloid complex. The experiments indicated that each of the major amygdaloid nuclei possesses a unique, organized set of intrinsic projections. Furthermore, there were large differences in the magnitude of the internal connections arising from or terminating in the various nuclei. The heaviest intrinsic projections arose from the lateral and basal nuclei while the central, medial, cortical, and accessory basal nuclei received the greatest number of these afferents. Thus, there was a clear trend for the bulk of these connections to run dorsally and medially within the amygdala. One important function of these intrinsic connections may be the integration of afferent sensory information from the various association areas which project to the amygdala.

Axonal projections are described from the lateral and basolateral nuclei of the amygdaloid complex, and from the overlying periamygdaloid and prepiriform cortices and the endopiriform nucleus, to the lateral entohinal area, the ventral part of the subiculum, and the parasubiculum in the cat and rat. All of these projections have well-defined laminar patterns of termination, which are complementary to those of other projections to the same structure. Based on these results, and on cytoarchitectonic distinctions, the lateral entohinal area has been divided into dorsal, ventral, and ventromedial subdivisions. The olfactory bulb and prepiriform cortex project to layers IA and IB, respectively, of all three subdivisions, but the lateral amygdaloid nucleus has a restricted projection to layer III of the ventral subdivision only. The periamygdaloid cortex projects to layer II of the ventromedial and adjoining parts of the ventral subdivisions. The ventral part of the subiculum receives fibers from the posterior division of the basolateral nucleus, which terminate in the cellular layer and the deep half to one-third of the plexiform layer. The periamygdaloid cortex and the endopiriform nucleus also project to the same part of the subiculum, but these fibers terminate in the outer part of the plexiform layer. None of these projections extend into the dorsal part of the subiculum. The posterior division of the basolateral nucleus also projects to the posterodorsal part of the parasubiculum ("parasubiculum a" of Blackstad, '56). These fibers end in the deeper part of the plexiform layer and the superficial part of the cellular layer.

Using a polyclonal antibody directed against somatostatin, normal somatostatin-positive neurons and fibers were seen in the amygdala and periamygdaloid cortex of both young and aged macaques. In addition, immunoreactive structures, identical in appearance to neurites demonstrated by silver impregnation methods, were seen in the amygdala of one aged monkey that exhibited numerous senile plaques. Some of these immunoreactive neurites were associated with deposits of amyloid, as seen with thioflavin-T stains, suggesting that these were neurites of senile plaques. This study provides direct evidence for abnormalities in peptidergic neurons in brains of aged non-human primates.

The afferent projections to the primate amygdala were studied using horseradish peroxidase. The potential advantages of this technique are discussed compared with those previously used to determine amygdaloid afferents. The findings indicate that certain agranular or dysgranular cortical regions may project directly to the amygdala: in particular, the orbital frontal cortex, anterior cingulate gyrus, subcallosal gyrus, temporal pole and anterior insula. These projections probably terminate predominantly in either the lateral or accessory basal nuclei. Other cortical projections from the inferotemporal and superior temporal gyri are described. Evidence was found for a heavy projection from the superior temporal sulcus to the lateral nucleus. Subcortical afferents were found from the hypothalamus, substantia innominata, diagonal band, thalamus, periaqueductal central gray, peripeduncular nucleus and from a band of cells extending medially from the peripeduncular nucleus to the midline, just ventral to the thalamus. In the thalamus, labelled cells were restricted to the non-specific nuclei, and were common in the rostral midline nuclei. No projection was observed from the dorsomedial nucleus of the thalamus. We discuss the implications of these results for interpreting the functions of the amygdala.

1. Disturbance of the conditioned reflex activity after unilateral damage to the basolateral amygdala correlates as regards dates with the inhibition of the evoked responses of the dorsomedial nucleus of the thalamus to the stimulation of the periamygdaloid cortex. 2. The change in the evoked activity, reflecting the establishing of new functional interrelationships between the centers of the damaged system, as regards time considerably exceeds the duration of compensatory restoration of the characteristics of conditioned reflexes. 3. Three months after damage to the amygdala, in the dorsomedial nucleus evoked responses of the standard form and parameters are recorded which indicates the restoration of neurophysiological processes of bringing about incoming afferentation.

The cytoarchitectonic structure and divisions of the amygdaloid complex are described in the rat and cat, with special reference to the axonal connections of each of the amygdaloid nuclei, and to interspecies variations and similarities. Several intra-amygdaloid connections are also described, based on autoradiographic experiments with small injections of 3H-amino acids into the individual nuclei. Although it has probably not been possible to determine all of the intra-amygdaloid projections from these experiments, the connections which have been shown are very specific. The lateral nucleus projects to the basomedial nucleus, the lateral part of the central nucleus, and the periamygdaloid cortex, while the basolateral nucleus projects only to itself, the medial part of the central nucleus, and the nucleus of the lateral olfactory tract. The basomedial nucleus projects to the cellular layer of the medial nucleus and the amygdalo-hippocampal area, while the molecular layer of these structures and of the posterior cortical nucleus, receives projections from the periamygdaloid cortex or from the endopiriform cortex. There are also interconnections between the medial and posterior cortical nuclei, and commissural connections between the posterior cortical nuclei of the two sides.

Cholecystokinin (CCK) binding sites were localized in the hippocampus, amygdala, and medial temporal cortices of macaque monkeys by using techniques of in vitro receptor autoradiography. Binding sites were labeled with 3H-CCK-8 and 125I-CCK-33, and nonspecific binding was assessed in the presence of 1 μM CCK-8. Comparison of autoradiograms with Nisslstained sections allowed precise correlation of autoradiographic grain distribution with cytoarchitecture. CCK binding in the amygdala varied among nuclear subdivisions. It was dense in the lateral, basomedial, endopiriform, and cortical nuclei, in the parvicellular portion of the accessory basal nucleus, the periamygdaloid cortex, the cortical transition area, and in the amygdalohippocampal area. Labeling was sparse in the central, medial, and basolateral nuclei as well as in the magnocellular accessory basal nucleus. In the hippocampal formation, a single dense band of CCK binding was observed over the granule cell layer and adjacent few millimeters of the molecular layer of the dentate gyrus, while in the polymorph and remaining portions of this layer binding was of very low density. Prominent label over the pyramidal layer in the presubiculum clearly distinguished this region from the adjacent subiculum in which binding just exceeded background levels. Moderate to light label was observed in the hilus and stratum pyramidale of CA3, CA2, and CA1, while other hippocampal layers showed minimal specific binding. Variation in CCK binding in the medial temporal cortex showed close correspondence to cytoarchitectonic subdivisions. In entorhinal cortex, for example, binding was concentrated in layers III-VI while label in area 35 was prominent in all laminae except layer IV. Area TH of von Bonin and Bailey ('47) was distinguished from other regions by evenly distributed binding across all layers, while in area TF a bilaminar pattern of label in layers II and IV was observed. The highly specific patterns of CCK binding in amygdala and transitional cortices of the medial temporal lobe can be related to terminal fields of neo- and allocortical afferents to these regions, while label in the hippocampal formation coincides with the terminals of intrinsic neurons which ramify among the somata of cells that are targets of neocortical afferents. Thus, in all structures of the medial temporal lobe the disposition of peptidergic binding sites suggests that CCKergic systems may be important in the modulation of cortical afferents.

The organization of the cholinergic innervation of the macaque monkey amygdaloid complex was investigated by means of immunohistochemical techniques and either a polyclonal antiserum or a monoclonal antibody directed against the specific synthetic enzyme choline acetyltransferase (ChAT). Adjacent series of sections were processed histochemically for the demonstration of the degradative enzyme acetylcholinesterase (AChE) or for cell bodies with thionin. The density of ChAT immunoreactivity differed substantially among the various nuclei and cortical regions of the amygdala. In general, the distribution of ChAT immunoreactivity paralleled the pattern of AChE staining. One notable exception was the presence of AChE containing cell bodies in addition to AChE positive fibers within nearly all of the nuclear and cortical regions. In contrast, ChAT immunoreactivity was associated only with fibers and terminals. The highest density of ChAT immunoreactive fibers and terminals was consistently observed in the magnocellular subdivision of the basal nucleus. Staining was substantially less dense in the more ventrally situated parvicellular subdivision. Medially, in the adjacent accessory basal nucleus, immunoreactive fibers and terminals were densest in the magnocellular and superficial subdivisions and least prominent in the parvicellular subdivision. Of the deep nuclei, the lateral nucleus generally contained the least ChAT immunoreactive terminals and processes. Only its more densely cellular ventrolateral portion contained appreciable fiber and terminal staining. One of the more distinctive patterns of ChAT immunoreactivity was seen in the nucleus of the lateral olfactory tract. Here, ChAT positive fibers formed pericellular basket plexuses around unstained cell bodies. This unique pattern of staining was used to delineate the boundaries of the nucleus and indicated that it is present for much of the rostrocaudal extent of the amygdala. Another region of conspicuous staining on the medial surface of the amygdala was the sulcal portion of the periamygdaloid cortex. This region, associated with the sulcus semiannularis and bordering the entorhinal cortex, consistently contained dense immunoreactivity. The central nucleus also presented a somewhat idiosyncratic pattern of ChAT staining. The lateral subdivision had a diffuse distribution of immunoreactivity in which focal patches of more densely stained terminals and occasional fine fibers were embedded. In contrast, the medial subdivision contained a larger number of thicker, stained fibers without diffuse background labeling. Of the remaining amygdaloid nuclei, the amygdalohippocampal area contained dense ChAT staining, whereas progressively lighter staining was seen in anterior amygdaloid, posterior cortical, anterior cortical, and medial nuclei.

Summary Surface potentials were recorded in olfactory cortex of the guinea pig in vitro following stimulation of the lateral olfactory tract. In agreement with other investigators, stimulation of slices incubated at 37 °C evoked a surface negative wave in prepyriform cortex, olfactory tubercle and periamygdaloid cortex, but the surface-positive wave seen in vivo was absent. Variations in slice thickness indicated that the surface-negative wave was generated superficially since it could be evoked in slices as thin as 0.28 mm and that the surface-positive wave was generated from deeper layers since it could not be seen in slices less than 0.46 mm thick. To provide adequate oxygenation, the thicker slices were incubated at ambient temperatures. At these temperatures, 0.46–0.78 mm thick slices exhibited surface negative waves over the entire olfactory cortex, including entorthinal cortex, as well as sequential surface-negative and surface-positive waves over the periamygdaloid cortex. Optimum conditions were obtained with slices 0.52 mm thick, incubated in Krebs solution containing2.5m M Ca 2+ at 23–27 °C. Under these conditions evoked potentials were well maintained up to 1–2 days. Such slices demonstrated intracellular Na + , K + and water contents similar to those of thinner slices incubated at 37 °C. The surface positivity was sensitive to changes in calcium, magnesium and stimulus-frequency in a manner suggesting a synaptic potential.

[3H]D-aspartate ([3H]D-Asp) and [3H]gamma-aminobutyric acid ([3H]GABA) have been used as “transmitter specific”retrograde tracers to identify projections to the mediodorsal thalamic nucleus (MD) that may use glutamate and/or aspartate, or GABA as their neurotransmitter. Following injections of the “nonspecific” tracer WGA-HRP into MD, retrogradely labeled cells are found in a wide variety of forebrain and brainstem areas, including layer VI of the frontal and agranular insular cortex, the thalamic reticular nucleus, the ventral pallidum (including the polymorphic zone of the olfactory tubercle), the deepest layers of the piriform cortex, periamygdaloid cortex and entor-hinal cortex, the amygdaloid complex, the superior colliculus, substantia nigra, and dorsal raphe nucleus. Following injections of [3H]D-Asp or [3H] GABA, different subsets of these cells are labeled.

Publisher Summary The primate frontal lobe can be divided into three major parts: (1) the medial, defined by its projections from the anterior nuclear group; (2) the dorsolateral, defined by its projections from the microcellular portion of the medial thalamic nucleus; and (3) the posterior orbital, deriving projections from the midline of the thalamus and so heavily connected to the adjacent anterior insula, temporal pole, and periamygdaloid cortex. This chapter illustrates a model of inhibitory interactions that took place within the afferent channels. Collateral and recurrent afferent inhibitions were bucked against one another, forming a primary couplet of neural inhibition within afferent channels. Four forebrain mechanisms were assumed to provide efferent control on the primary couplet. Two of those—frontotemporal and sensory specific-intrinsic—influenced the couplet by regulating collateral inhibition whereas two others—hippocampal and polysensory motor—regulated recurrent inhibition. The frontal cortex appeared critically involved in implementing executive programs when those were necessary to maintain brain organization in the face of insufficient redundancy in input processing and in the outcomes of behavior.

Summary The amygdaloid complex of Ungulata is not so well developed in comparison with that of Carnivora, but a more or less high degree of differentiation than in Rodents, especially in the nucleus T, which likely comes out from the cortical element during the early embryonal period. Cells of this nucleus have a tendency in the adult to get segregated in small glomerulus-like groups, especially prominent in the cow. Another nuclei T' and M of amygdala proper are also well developed. But the central and medial nuclei E and D appear rather underdeveloped in comparison with those of Rodents. Although the small-celled nucleus K is generally well developed and separated in numerous groups, the correspondent to the nucleus intercalatus of Rodents can not be detected in Ungulata. The degree of differentiation of periamygdaloid cortex is rather advanced as it is divisible here into 3 parts, PA1, PAi and Pam, very likely corresponding to Pam1, Pam2 and Pam3 of Rose respectively. The nucleus B is here completely separated from the cortex Pam PAi of the horse is complicated in its cellular architecture as it is divisible into two subdivisions. In the cow the whole extept of periamygdaloid cortex is complicated as in the nucleus T, both showing glomerulus-like cell-islets. If these complicated features speak for the advanced degree of differentiation of this region with its functional significance parallel going, then the cow or bull might be most developed among the animals concerned, then follow the goat, horse and pig in developmental order downwards. In accordance with the classification in taxology in Ruminantia (cow and goat) and Non-Ruminantia (pig) of Archiodactyla and in Perissodactyla (horse), the cytoarchitectural patterns are each characteristic in these three groups. As to the fiber connection of the amygdaloid complex, the author has treated several fiber bundles of relatively well recognizable make-up. Their exact origin and termination have however to be determined by experimental investigation later on. In fact there must be numerous and complicated fibers hitherto untouched by the authors. Indication lies here in this study of Ungulata as it introduced several fiber bundles hitherto unkndwn, seemingly favored by larger form of brains studied. Concerning the islet-like groups of cells in the cow and goat, the author could not detect any specific fibrous characters even through application of certain axon-staining method, except that of compactly arranged capsule-like fibers. The assumption that the amygdala stands so intimately in relation with the cerebral cortex as the thalamus, or that it represents a vegetative centre or that it belongs to the extrapyramidal system, seems to be far from being entirely groundless as far as it concerns with the above mentioned anatomical investigation, but the lack of verification in experimental way leaves things to be entrusted to future researches.

Publisher Summary The central part of the mammalian olfactory system is made up by the olfactory bulb and those areas in the central nervous system that receive secondary olfactory fibers from the olfactory bulb. These structures are situated in the basal part of the telencephalon and show in the wide range of mammals, from macrosmatic opossum to microsmatic man, considerable variations in size and position. This chapter focuses on the cytoarchitectonics and fiber connections of the bulbar and retrobulbar areas. As to the structure of the other parts of the olfactory lobe, it is relevant to note that the cortical areas that receive secondary olfactory fibers—the prepyriform and periamygdaloid cortex and olfactory tubercle consist of three layers: (1) the plexiform or molecular layer, of which the superficial part is occupied by the fibers and collaterals of the lateral olfactory tract; (2) the pyramidal cell layer, consisting of small and medium-sized pyramidal cells; and (3) the polymorph cell layer, which contains fewer neurons than the preceding layer.

Summary A series of experiments was performed in an attempt to establish the anatomical localization of the effects upon uterine movements and ovulation due to the stimulation of the amygdaloid complex. A remarkable change in the uterine movements was recognized through electrical or chemical stimulation of delimitd parts of the amygdaloid nuclei in dogs, cats and rabbits. In pxtpartum and in non-pregnant matured animals, as well as in the latter half of pregnancy, an increase of tonus in uterine musculature and auginentation in frequency and amplitude of uterine motility can be evoked through unilateral stimulation of the medial principal amygdaloid nucleus (T of Volsch). These effects vary more or less according to the animal species and rather greatly by the stadium of sexual cycle at the time of experimentation. Stimulation of the lateral principal nucleus (M of VoZsch), the intermediate principal nucleus (T' of Vosch), the so-called cortical amygdaloid nucleus (B of Vosch), the medial amygdaloid nucleus (D of Vosch) and the central amygdaloid nucleus (E of Vosch) seems to be altogether ineffective. Stimulation of the periamygdaloid cortex gives an equally hardly effect upon the uterine motility. The impulse from the amygdala passes very likely through fibers corresponding to MV or MD fiber described by Fukuchi in Ungulata or through so-called medial forebrain bundle and is led to the viscero effective centre of the hypothalamus. The electrical stimulation of nuclei T and T' of the amygdala is capable of producing ovulation or hemorrhagic follicle in the ovary of the matured estrous rabbit. The impulse seems to go from the amygdala directly to the ventro medial nucleus of the hypothalamus leading further to the anterior pituitary lobe. The further effect to the ovary may be governed by the gonado tropic hormone released from the anterior pituitary lobe. In this latter case the estrous phase of the animals may also play an important role. (This work was aided in part by a grant from the Science Research Foundation of the Educational Department.

Summary 1) Through stimulation of the medial principal nucleus of amygdala proper (T of Volsch), most remarkable pupillary dilatation was called forth generally in both sides and in response to unilateral stimulation. Exophthalmus, abduction of eyeballs, retraction of the nictitating membranes, and nystagmus of small amplitude were also manifested. 2) Through stimulation of the lateral principal nucleus of amygdala proper (M of Volsch), there appeared in the most cases a slight degree of mydriasis. The movement of the nictitating membranes and nystagmus were also observed. 3) The stimulation of the intermediate principal nucleus of amygdala proper (T of Volsch prepared a causative also to the same phenomena, but owing to lesions in the neighboring nuclei, the results remained far from being eviding. Still, a small anterior part of nucleus T' seemed to stand in connection with pupillary constriction. 4) Functional bearing of the periamygdaloid cortex upon the pupillary dilatation was to be said quite weak, likely concerned with periamygdaloid area Pam2 of Rose. Unlike tremor of the eyelids which came out most remarkably and more frequently, nystagmus appeared upon periamygdaloid stimulation only in three cases out of 10 experiments and was of large amplitude, its quick component directed toward the operated side and making a good contrast to the excitatory case observable in cases of the nucleus T stimulation. The movement of eyes was not exactly recognizable. The nictitating membranes were protruded in about half of the cases, presumably to be concerned with fuxction of Pam1 of Rose. 5) Stimulation of Walker's ares 13 aroused a moderate till remarkable pupillary dilatation. The neuronal relationship of this area was to consider as definitely different from that of amygdala. It should be added that Brodmann's area 53 showed also dilatatory effect 6) Removal of the cervical sympathetic ganglion worked toward diminution of the dilatatory effect of amygdala. 8) The neuronal relationship of the dilatatory effect of amygdala was attacked through series of sectioning experiments and resulted in proving that the fiber path passed through the fibers correspondent to the M. V. and M. D. of Fukuchi in Ungulata.

Summary Through electrical or chemical stimulation of a limited part of the amygdaloid complex unilaterally, elevation of temperature of the animal body and inhibition of the gastrointestinal motility can be recognized. By histological investigation of experimented cases it was revealed that to the former effect the lateral amygdaloid nucleus of amygdala proper (M of Volsch) and to the latter the medial amygdaloid nucleus (T of Volsch) were precisely responsible. The peiiamygdaloid cortex stands definitely unparticipated in these phenomenon. Further it was conceivable that the impulse from the amygdala reaches to the visceroeffective center of the hypothalamus apparently without interruption of its neuronal connection to work inhibitory upon the gastrointestinal motility. These results certainly speak for our assumption that the amygdaloid complex comprises a link of the autonomic representation for regulation of visceral functions.

The fields of origin of the amygdalofugal pathways in the albino rat were studied by using the Fink-Heimer technique to stain degenerating fibers and terminals in brains of animals sacrificed four and seven days after small unilateral lesions of the amygdale. A surprisingly restricted field of origin was found for the supracommissural stria terminalis — the component projecting to the ventromedial nucleus of the hypothalamus Only a lesion in the most posterior part of the cortical nucleus produced degeneration in this pathway. The postcommissural stria terminalis which apparently distributes to the bed nucleus of the stria terminalis and preoptic area originates in a more widespread area including parts of both the basolateral and corticomedial complexes. Although intense terminal degeneration could be seen within the amygdala following all lesions, long fibers projecting into the anterior amygdaloid area, lateral preoptic area and lateral hypothalamus were found only after lesions in which fibers of passage from periamygdaloid cortex could have been interrupted. Convincing evidence, therefore, of a long axon ventral amygdalofugal pathway of the rat was not found in this study.

Summary We can produce movements of ears and eyelids Iiy stimulation of the anterior part of the cortex of the pyriform lobe. In their neuronal relationship it is different from those evoked from the lateral surface of the hemisphere or from the masticatory movement made excitible from the pyriform lobe. The impulse may apparently be transmitted from that part of the cortex directly, yerhnps through the medial parts T and T (Volsch) of the amygdaloid nuclei leading into the subrortical gray matters; thereby cortical face-area and thalamus seem to play no part in it. Exact histological investigation concerning the effective area was done by the melhod of Marchi and Nissl. From these experiments it is likely that we may ascertain that the amygdaloid and periamygdaloid areas are concerned with the extrapyramidal motor system in certain respects.

After lesions of the olfactory bulb, coarse degenerating fibers were traced by the method of Nauta and Gygax through the lateral olfactory tract to superficial terminations in the prepiriform and periamygdaloid cortex and olfactory tubercle. Fine degenerated fibers were traced from the bulb through the anterior limb of the anterior commissure to terminations among the less superficial cells of the prepiriform cortex and olfactory tubercle. No fibers from the bulb reached the hippocampus or entorhinal area in these three species. After lesions in the olfactory tubercle, prepiriform cortex, or preoptic area, however, degenerated fibers were traced to the entorhinal area, subiculum, and hippocampus. There were some species differences in the distribution of these fibers, but a clear anatomical basis was found for the relay of olfactory impulses to the hippocampus. Rabbit and rat brains with lesions affecting the medial forebrain bundle at various levels were examined. Degenerated fibers were found to ascend through the bundle to the septum and fornix, and to be distributed from the fimbria throughout the extent of the ipsilateral hippocampus, passing right down to the ventral pole.

Summary The stimulation on cats amygdala, either electrical or chemical, sometimes causes cessation of movements both of the stomach and small intestine and the lowering of tension therein, though there are also cases with negative effect. In case of marked change it deals with stimulation chiefly on the medial principal nucleus (nucleus T of Volsch); in case of no change, with stimulation chiefly on the other subnuclei. No change took place in the small intestine when stimulation partook the periamygdaloid cortex exclusively. Judged from the resubs of both severing and destruction experiments, the fibers instrumental for such change concerning gastro-intestinal motility of amygdalar origir, are assumed directly to run downward through the ipsilateral hypothalamus Trigonum olfactorium, area 13, hippocampus, fornix, stria terminalis and capsula externa do not participate in the course There are a large number of pressor pints in periamygdaloid cortex (PA) and the most marked focus thereof is situated in Pam2. Both the electrical and chemical stimulation on amygdala proper (A) causes the same blood pressure elevation as that on PA. However, the effect of chemical stimulation is generally less marked than that of the electrical one. Among the subnuclei of “ A”, that is laden with the most marked pressure acceleration, is the nucleus T, next come nuclei M, T‘, B and D. It is quite likely that the neumn pnjected from “ PA ” gets renewed at “ A” With regard to the blood pressure there seems to exist no connection between area 13 and “A” nor trigonum olfactorium and “ A.” Also, fiber connection by the way of the posterior and medial part of piriform lobe must be denied. Althongh both sides of amygdala stand in a close connection with each other, the commissural and association fibers running in these do not seem to go propagating the function at least so far-as blood pressure is concerned. The result of stimulation, especially following dissection of stria terminalis, speaks for that the pressure effect brought about by either “PA” or “A” stimulation goes propagating by the way of the said fibers Judging from the result of the simultaneous observation of respiratory movement and blood pressure, the two seem to go propagating by the way of different fibers as they react in evidently different ways. In the case of stimulation experiment performed with the destruction of hypothalamus aforegoing, there was no stimulation effect displayed ipsilateral to the destruction. Presumably, the blood pressure change reaches hypothalamus of the stimulated side by the way of the ipsilateral stria terminalis to be transmitted therefrom to the lower center.

Publisher Summary This chapter discusses the connections of the olfactory bulb and the anterior olfactory nucleus in some mammals. In 13 young and 18 adult guinea pigs surgical and electrolytic lesions are made in the bulbus olfactorius and the nucleus olfactorius anterior. The lateral olfactory tract forms the only projection bundle of the olfactory bulb and accessory olfactory bulb. Fibers from this tract terminate in the pars externa and pars lateralis of the anterior olfactory nucleus, prepiriform cortex, lateral part of the olfactory tubercle, anterior amygdaloid area, nucleus of the lateral olfactory tract, and periamygdaloid cortex. The area of distribution of the lateral olfactory tract in the amygdaloid complex is limited to the antero-lateral part of the cortical nucleus. The lateral olfactory tract plausibly receives fibers from the pars lateralis of the anterior olfactory nucleus. The pars rostralis of the anterior olfactory nucleus projects via the anterior limb of the anterior commissure to the pars externa of the heterolateral anterior nucleus. The pars dorsalis of this nucleus projects to the heterolateral main and accessory olfactory bulbs. The pars medialis of the anterior olfactory nucleus contributes its fibers principally, if not exclusively, to the medial forebrain bundle.