Olfactory Peduncle Research Articles

The anatomy of the brain of the bottlenose dolphin (Tursiops truncatus). Rhinic lobe (rhinencephalon). I. The paleocortex.

AbstractThe bottlenose dolphin, Tursiops truncatus, lacks olfactory bulbs and peduncles as do the other members of the odontocete suborder of Cetacea. Nevertheless the dolphin as well as the other cetacean species studied possess a rhinencephalon or rhinic lobe consisting of prominent olfactory lobes and a very reduced hippocampus covered over, respectively, by small epistriatal (frontal, especially orbital lobes and insula) and huge epihippocampal (parietal, occipital and temporal lobes) Portions of the hemisphere.In the dolphin the demarcation of the rhinic lobe from each hemisphere bilaterad to it is particularly clear and consists of a continuous circular groove (rhinic cleft) composed of posterior parolfactory, anterior and posterior rhinal, rhinohippocampal, hippocampal and callosal segments. Along the trajectory of the rhinic cleft, the cytoarchitectonic demarcation of the paleocortex (olfactory lobes) and archicortex (hippocampus) from the neocortex in the border (limbus) of each hemisphere is equally clear. The rhinic lobe in Tursiops and other Cetacea so far examined thus appears to be a formation of the telencephalon whose distinctness in these species is dramatically emphasized.Topographic disposition of the cytoarchitectonic areas of the paleocortex in Tursiops, Which have not heretofore been described, has been found in this study to be essentially similar to that of other placental mammals. These areas of the paleocortical division of the rhinic lobe (Prepyriform, tubercular, diagonal and periamygdalar areas) are as easily differentiated from one another in this species as in many other mammalian forms.

Impaired mating performances in male rats after anosmia induced peripherally or centrally.

The olfactory epithelium and the afferent nerve fibers to the olfactory lobes were destroyed in one group of rats, while in another the olfactory peduncle was destroyed bilaterally. Following either o

Phase and Electron Microscopy of Olfactory Bulb After Sectioning of its Peduncle

The unilateral section of the olfactory peduncle was made in adult albino rats in order to produce axonal and terminal degeneration of the whole system of centrifugal projections. This experiment was carried out with a double purpose. First, to tipify the different structural modes of axonal and terminal degeneration in a correlative light and electron microscopy study. Second, to study the distribution of these central projections to the bulb. The animals were sacrificed by fixation-perfusion 4 to 7 days post-operation and samples of olfactory bulbs were processed as routinely for electron microscopy observation. Thick sections stained with paraphenylenediamine (PPDA)(1) were utilized for phase observation.

Projections of the olfactory tract fibers in the nurse shark ( Ginglymostoma cirratum)

Summary Five nurse sharks were killed between 6 and 43 days after the olfactory tract had been cut unilaterally. Whereas the axon degeneration was demonstrated best with the Nauta-Laidlaw technique after 3–4 weeks survival time, the terminal degeneration, as identified in Fink-Heimer preparations, was best seen in a 13-day specimen. The distribution of olfactory tract fibers is entirely ipsilateral to the lesion, the majority terminating near the attachment of the olfactory peduncle to the hemisphere. Terminal degeneration is restricted caudally to a tongue-like extension of the lateral olfactory area on the ventral surface of the hemisphere with a spill-over into the area superficialis basalis of Johnston. The results indicate that the distribution of olfactory bulb fibers in the shark is much more restricted than had been suggested by most earlier descriptions based on studies of normal material.

The lateral olfactory tract, the anterior commissure and the cells of the olfactory bulb

The respective relations of the cells of the olfactory bulb to the lateral olfactory tract and the anterior commissure were studied in the rabbit by the use of the Nauta and Fink-Heimer techniques. The following observations were made. 1. The origin of the anterior commissure in the bulbar area is limited to the pars rostralis of the anterior olfactory nucleus. In the rabbit this nucleus extends up to the rostral end of the olfactory bulb. 2. The commissural fibers arising in the cucleus olfactorius anterior pars rostralis terminate in the pars externa of the contralateral anterior olfactory nucleus. No interbulbar connection could be demonstrated. 2. The lateral olfactory tract is composed of axons of both mitral and tufted cells of the main olfactory formation. 4. This fiber bundle projects to the olfactory cortex as defined by White and Heimer, with the exception of the medial portion of the nucleus olfactoriusanterior pars dorsalis. The latter nucleus is supplied by fibers which originate in the medial part of the olfactory formation and pass caudally along the medial side of the olfactory peduncle. 5. In contrast to all other portions of the anterior olfactory nucleus the pars rostralis receives no afferents from the main olfactory formation. 6. The synaptic distribution of the tufted cell axons in the olfactory cortex appears to be considerably more limited than that of the mitral cell axons. 7. No areal localization could be detected in the projection of the olfactory bulb via the lateral olfactory tract to the ipsilateral forebrain regions. This appears to apply to the projections of the mitral cells as well as to those of the tufted cells.

The effects of central stimulation and nasal air flow on induced activity of olfactory structures

This study investigated the effects of brainstem stimulation (Mes RF, Med RF and Mes CG) and nasal air flow on induced activity recorded from olfactory structures. In acute, artificially respirated, curarized cats, it was possible to observe the influence of this stimulation upon olfactory bulb induced activity without confounding by air flow changes normally elicited by the effect of such stimulation on brainstem respiratory centers. Nasal air flow was manipulated independently by pumping air in puffs through a cannula placed in one naris. With nasal air flow held constant from puff to puff, stimulation in the Mes RF, Med RF and Mes CG produced a strong augmentation of olfactory bulb induced activity. Stimulation in the absence of nasal air flow, however, produced no observable increases in pre-existing olfactory bulb activity. This augmentation was completely eliminated by severing the olfactory peduncle showing that the augmentation was effected via centrifugal fibers running in the olfactory peduncle to the olfactory bulb. Increases in nasal air flow in the absence of brain-stem stimulation caused augmentation of the olfactory bulb induced activity without significant changes in neocortical arousal. These results show that olfactory bulb induced activity varies in amplitude and duration as a function of nasal air flow and centrifugal input. The effect of brain-stem stimulation is, however, one of modulation of a response elicited by nasal air flow, while variations associated with changes in nasal air flow alone probably reflect recruitment of different numbers of olfactory receptors. Additional observations of the effects of nasal air flow and central stimulation on prepyriform and amygdala induced activity are presented and discussed.

Septal efferents in the cat

Four selected cases were studied following placement of 1–2 mm lesions in the septum of the cat. Degeneration of nerve fibers and terminals was observed in the olfactory peduncle, olfactory tubercle, gyrus rectus and overlying gyrus cinguli. Projections to posterior cortex occurred over the fornix longus and body of the fornix to the gyrus cinguli, subiculum and hippocampal gyrus. Other projections occurred downstream via three pathways. A dorsal route was traced over the stria medullaris to thalamic nuclei and midbrain. A central pathway coursed through the internal medullary lamina and zona incerta into the prerubral field. Ventrally, degeneration traveled over the diagonal band, medial forebrain bundle and ventral tegmental tract into the midbrain. The over-all degeneration preferential was to the anterior thalamic nuclei, lateral reticular nucleus of the thalamus and hippocampus. Differential projections evidenced by terminals occurred in the septum, anterior and other thalamic nuclei, hypothalamus and midbrain reticular nuclei. Degeneration was noted differentially within the columns of the fornix, diagonal band and medial forebrain bundle. These differential topographic projections of the septum are proposed as a possible structural basis for diverse effects reported in the literature concerning septum studies. The septum is considered as part of an accessory thalamus functioning within a larger system referred to as a “dynamic scale”. It is also implied that this functional concept could be true of other cerebral structures.

Some olfactory pathways in the rabbit brain.

AbstractThe degeneration pattern in the rabbit following transection of the olfactory bulb or peduncle at various levels was studied by the Laidlaw method of Nauta. Degenerating axons were observed in the crossing of the anterior limb of the anterior commissure and in the lateral olfactory tract following olfactory bulb lesions which did not damage the anterior olfactory nucleus. Evidence was found for termination of the olfactory tract fibers over all parts of the anterior olfactory nucleus, the rostral and lateral parts of the olfactory tubercle, the anterior continuation of the hippocampus, the nucleus of the lateral olfactory tract, and the prepyriform areas 1, 2, and 3, the periamygdaloid areas 1, 2, part of 3, and 5, and the entorhinal axeas 1, 2, and 4 of Maximillian Rose. When the anterior olfactory nucleus was damaged degeneration was found in the contralateral olfactory bulb and anterior olfactory nucleus and parts of the ipsilateral neocortex adjacent to the rhinal fissure, limbic system (medial septal nucleus and anterior continuation of the hippocampus), pyriform lobe cortex, and lateral preoptic area. The results differ in particulars from those of previous investigators.

A Monograph of Orycteropus afer.—II. Nervous System, Sense‐organs and Hairs

Summary. The external and internal anatomy of the brain have been described. Characters suggesting Ungulate affinities have been found in the gyrus ambiens, in the fissuration of the cortex and in the distribution of the cortical areas. Despite the high degree of osmatism, the brain as shown by the amount of cortical differentiation is by no means a very primitive one. On the other hand, it is much nearer the generalized type of Proto‐Oarnivore or Ungulate brain than is Sus communis, for instance. The brain of Orycteropus has advanced sufficiently far from the generalized type to suggest that it was advancing along the line of the Ungulates. The anterior olfactory nucleus appears to be the same structure which previous writers called the olfactory peduncle with its prolongation into the bulb. Since its cell type differs from the other secondary olfactory centres, and it is continuous with the cellular laminæ of the bulb, it more properly belongs to this structure than to the olfactory cortex. It is thought that the wide extent and pattern of the secondary olfactory cortex needs no other explanation than the response to the macrosmatism. The constitution of the amygdaloid nucleus conforms to the account given by Johnstone for other mammals.