Future of the Roy model: challenge to redefine adaptation

Antibodies against the Drosophila gamma-aminobutyric acid (GABA) receptor subunit RDL were used to investigate the significance of inhibitory inputs to the mushroom bodies in the blowfly (Calliphora erythrocephala) brain. The pedunculus and the lobes of the mushroom body, which mainly consist of Kenyon cell fibers, revealed strong immunoreactivity against RDL. Pedunculi, alpha- and beta-lobe show characteristic unstained core structures with concentric labeling along the neuropile axis. The gamma-lobes in contrast exhibit a compartmentalized RDL-immunoreactive pattern. These data suggest an important role of GABAergic inhibition in the pedunculus and the lobes of insect mushroom bodies. It is most likely that the RDL-immunoreactivity in the mushroom bodies is closely related to Kenyon cell fibers suggesting that Kenyon cells are an inhomogeneous class of neurons, only part of which receive inhibitory GABAergic input from extrinsic elements. GABAergic inhibition, therefore, may play a substantial role in the process of learning and memory formation in the insect mushroom bodies.     

Morphology of feedback neurons in the mushroom body of the honeybee, Apis mellifera

The anatomy of gamma-aminobutyric acid (GABA)-immunoreactive, recurrent feedback neurons in the mushroom body (MB) of the honeybee, Apis mellifera, was investigated by using intraneuropilar injections of cobalt ions and light microscopic techniques. Each MB contains approximately 110 GABA-immunoreactive neurons, and approximately 50% of them are feedback neurons, i.e., they connect the MB output regions--the alpha-lobe, beta-lobe, and pedunculus--with its input regions--the calyces. Their somata are located in the lateral protocerebral lobe, and their primary neurites project medially and bifurcate near the alpha-lobe. In the alpha-lobe feedback neurons form narrow banded, horizontal arborizations in the dorsal and median alpha-lobe; each cell innervates a certain alpha-lobe layer. The neurons form additional branches in the pedunculus and the beta-lobe. All calycal subcompartments--the lip, collar, and basal ring--are innervated by feedback neurons. However, individual feedback neurons innervate exclusively a certain subcompartment in both the median and lateral calyx. Due to the arrangement of intrinsic Kenyon cells, each calycal subcompartment is connected to its specific, corresponding layer in the alpha-lobe. Feedback neurons interconnect the alpha-lobe and the calyces in either a corresponding or a noncorresponding fashion. With respect to their branching pattern in the alpha-lobe, the basal ring and the collar neuropil receive input from feedback neurons innervating the corresponding dorsal and median alpha-lobe layers. By contrast, the lip region, which receives olfactory antennal input, is innervated by feedback neurons with arborizations in a noncorresponding dorsal alpha-lobe layer.     

Anatomy of the mushroom bodies in the honey bee brain: the neuronal connections of the alpha-lobe

Neural connections between the mushroom body (MB) and other protocerebral areas of the honeybee's brain were studied with the help of cobalt chloride and Golgi staining methods. Focal injections of cobalt ions into the alpha-lobe neuropil of the MB reveal seven clusters of somata located in the protocerebrum and deutocerebrum of each brain hemisphere. These neurons connect the mushroom body neuropil with protocerebral areas and number approximately 400. They contact the layered organization of the alpha-lobe at different locations. Some project not only into the alpha-lobe, but also into the beta-lobe and pedunculus neuropils. Fifteen cell types which form intraprotocerebral circuits are morphologically described. They can be divided into three categories: 1) unilateral neurons, with projection fields restricted to the ipsilateral protocerebrum; these neurons connect the alpha-lobe with areas in the protocerebral lobe and ramify with densely layered arborisations arranged perpendicularly to the longitudinal axis of the alpha-lobe; 2) recurrent neurons, which interconnect subcompartments of the MB, forming loops at different levels of the neuropil; their arborisations are mainly restricted to the alpha-lobe, beta-lobe, pedunculus, and calyces of the ipsilateral MB; they also ramify sparsely around the neuropil of the alpha-lobe; and 3) bilateral neurons, which either interconnect both alpha-lobes or connect the ipsilateral alpha-lobe and protocerebral lobe with the dorsolateral protocerebral lobe of the contralateral hemisphere. The connections of different compartments of the MB with other parts of the protocerebrum as revealed in this study are discussed in the context of hypotheses about the functional role of MBs in the honeybee brain.     

Mushroom bodies of the cockroach: their participation in place memory

Insects and other arthropods use visual landmarks to remember the location of their nest, or its equivalent. However, so far, only olfactory learning and memory have been claimed to be mediated by any particular brain region, notably the mushroom bodies. Here we describe the results of experiments that demonstrate that the mushroom bodies of the cockroach (Periplaneta americana), already shown to be involved in multimodal sensory processing, play a crucial role in place memory. Behavioral tests, based on paradigms similar to those originally used to demonstrate place memory in rats, demonstrate a rapid improvement in the ability of individual cockroaches to locate a hidden target when its position is provided by distant visual cues. Bilateral lesions of selected areas of the mushroom bodies abolish this ability but leave unimpaired the ability to locate a visible target. The present results demonstrate that the integrity of the pedunculus and medial lobe of a single mushroom body is required for place memory. The results are comparable to the results obtained from hippocampal lesions in rats and are relevant to recent studies on the effects of ablations of Drosophila mushroom bodies on locomotion.     

Embryonic development of the Drosophila brain. I. Pattern of pioneer tracts

The neuropile of the late embryonic Drosophila brain can be subdivided into a vertical component (cervical connective), a transverse component (supraesophageal commissure), and a horizontal component for which we propose the term protocerebral connective. The core of each neuropile component is formed by numerous axon fascicles, the trajectory of which follows an invariant pattern. In the present study we have used an antibody against the adhesion molecule Fasciclin II (FasII) that is expressed in a large number of early differentiating neurons of the Drosophila embryo to follow the development of the axon tracts of the brain. The FasII antigen appears on the surface of clusters of neuronal somata prior to axon outgrowth. These clusters, for which we propose the term fibre tract founder clusters, are laid out in a linear pattern that forms an almost uninterrupted longitudinal track reaching from the ventral nerve cord to the "tip" of the brain. After expressing FasII on their soma, neurons of the fibre tract founder clusters extend axons that grow along the surface of the founder clusters and form a simple system of pioneer tracts for each of the components of the brain neuropile. We have reconstructed the FasII-positive fibre tract founder clusters and their axons from optical sections and generated digital 3-D models that illustrate the spatial relationships of the pioneer tracts. Three fibre tract founder clusters, D/T, P1, and P3m, pioneer the cervical connective. P21 and P2m form a transverse track that pioneers the supraesophageal commissure. P4m and P41/P51/VP5m form two tracts that pioneer a medial and a lateral component of the protocerebral connective, respectively. Because FasII expression continues uninterruptedly into the larval period when the "rudiments" of many parts of the adult neuropile are readily identifiable, it was possible to assign several of the embryonic pioneer tracts to definitive neuropile components, including the median bundle, antennocerebral tract, mushroom body, and posterior optic tract.     

Regional brain variations of cytochrome oxidase staining during olfactory learning in the honeybee (Apis mellifera).

Regional brain variations of cytochrome oxidase (CO) staining were analyzed in the honeybee (Apis mellifera) after olfactory conditioning of the proboscis extension reflex. Identification of brain sites where stimuli converge was done by precise image analysis performed in antennal lobes (AL) and mushroom bodies (MB). In Experiment 1, bees received 5 odorant stimulations that induced a transient decrease of CO activity in the lateral part of the AL. In Experiment 2, bees were trained with 5-trial olfactory conditioning. CO activity transiently increased in the lips of the MB calyces. There was also a delayed increase in the lateral part of the AL. An olfactory stimulus presented alone and an odor paired to a sucrose stimulation are treated by different pathways, including both AL and MB. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Identification of a secretomotor centre in the brain of Locusta migratoria, controlling the secretory activity of the adipokinetic hormone producing cells of the corpus cardiacum

After retrograde filling of axons terminating in the glandular lobe of the corpus cardiacum (CC) of Locusta migratoria with cobalt chloride, a paired group of about 15 cobalt containing cells was demonstrated in the lateral area of the protocerebrum. The axons of these cells run via the NCC II into the glandular lobe of the CC. These small neurons have the characteristics of secretory cells; they contain secretory granules of about 1000 A in diameter. The axon terminals in the glandular lobe, making synaptic contacts with the glandular cells, contain secretory granules of the same size. It is therefore concluded that the cell groups in the protocerebrum control the activity of the glandular cells which produce an adipokinetic hormone. Arborizations of fibers of the lateral secretomotor cells are present in the dorsal neuropile of the protocerebrum, ventral of the mushroom bodies and along the tracts of the NCC I within the brain. It is proposed that these arborizations are sites of synaptic input. It is discussed that the axons of these cells might receive additional synaptic input in the storage lobe of the CC. The localization of cell bodies, the axons of which enter the storage part of the CC is described. The course of the axon tracts of the various cell groups in the protocerebrum and their connections with the NCC I and NCC II are demonstrated.     

Relationship between afferent and central temporal patterns in the locust olfactory system

Odors evoke synchronized oscillations and slow temporal patterns in antennal lobe neurons and fast oscillations in the mushroom body local field potential (LFP) of the locust. What is the contribution of primary afferents in the generation of these dynamics? We addressed this question in two ways. First, we recorded odor-evoked afferent activity in both isolated antennae and intact preparations. Odor-evoked population activity in the antenna and the antennal nerve consisted of a slow potential deflection, similar for many odors. This deflection contained neither oscillatory nor odor-specific slow temporal patterns, whereas simultaneously recorded mushroom body LFPs exhibited clear 20-30 Hz oscillations. This suggests that the temporal patterning of antennal lobe and mushroom body neurons is generated downstream of the olfactory receptor axons. Second, we electrically stimulated arrays of primary afferents in vivo. A brief shock to the antennal nerve produced compound PSPs in antennal lobe projection neurons, with two peaks at an approximately 50 msec interval. Prolonged afferent stimulation with step, ramp, or slow sine-shaped voltage waveforms evoked sustained 20-30 Hz oscillations in projection neuron membrane potential and in the mushroom body LFP. Projection neuron and mushroom body oscillations were phase-locked and reliable across trials. Synchronization of projection neurons was seen directly in paired intracellular recordings. Pressure injection of picrotoxin into the antennal lobe eliminated the oscillations evoked by electrical stimulation. Different projection neurons could express different temporal patterns in response to the same electrical stimulus, as seen for odor-evoked responses. Conversely, individual projection neurons could express different temporal patterns of activity in response to step stimulation of different spatial arrays of olfactory afferents. These patterns were reliable and remained distinct across different stimulus intensities. We conclude that oscillatory synchronization of olfactory neurons originates in the antennal lobe and that slow temporal patterns in projection neurons can arise in the absence of temporal patterning of the afferent input.     

Acute effects of morphine on regional brain levels of acetylcholine in mice and rats

Electrophoretic injection of Procion Yellow M-R4 into the ocellar tract of the worker bee has revealed the following: Two types of giant axon run from the lateral ocellus to the circumesophageal neuropile, where one branches ipsilaterally and the other contralaterally. A third type comes from the median ocellus and can be traced into the cervical connectives. The largest dendritic complex is in the circumesophageal neuropile; in addition, fiber endings have been demonstrated in the following areas: in the subretinal region, along the optic commissure, in the medulla interna, in the subesophageal ganglion and between the neurosecretory cells of the pars intercerebralis. -- The giant fibers are enclosed in a glial sheath. Three types of cell body are described. One is associated with the glia; another, larger cell type comprises giant-axon somata. The third type of cell is small, and cannot yet be identified. Some of the histological results are discussed with respect to the possible function of the ocellus.     

Early formation of sexually dimorphic glomeruli in the developing olfactory lobe of the brain of the moth Manduca sexta

The antennal lobes (ALs), the primary olfactory centers, of the moth Manduca sexta are sexually dimorphic. Only ALs of males possess the macroglomerular complex (MGC), the site of primary processing of information about the female's sex pheromone. To understand the development of identified, odor-specific olfactory glomeruli, we investigated the cellular events involved in the morphogenesis of the MGC by means of various fluorescence staining techniques and laser-scanning confocal microscopy. The MGC lies near the entrance of the antennal nerve into the AL of the adult male and comprises three glomeruli, the globular cumulus and two toroidal structures. The MGC forms during early stages of metamorphic adult development through a stereotyped sequence of coordinated changes in MGC-specific receptor axons, glial cells, and early-ingrowing projection neurons of the medial group of AL neurons. The MGC divisions are the earliest glomeruli to form in the male AL, and their basic organization is established within about 3 days after ingrowth of the first sensory axons. Despite their special anatomical features, the MGC glomeruli develop in a manner similar to that of the ordinary glomeruli. Comparison of the ALs of males and females reveals that two relatively large and early-developing glomeruli that are situated dorsolaterally in the female AL appear to be female-specific. Development of the sexually dimorphic glomeruli diverges immediately after the ingrowth of the first olfactory receptor axons, resulting in the formation of these large glomeruli in females and the MGC in males.     

Continuous neurogenesis in the olfactory brain of adult shore crabs, Carcinus maenas

To scrutinize the common belief that the number of neurons in the CNS of adult decapod crustaceans stays constant, in spite of their dramatic postlarval increase in size, I counted olfactory projection neurons (OPNs) in the brains of differently-sized postlarval shore crabs, Carcinus maenas, and performed in vivo labeling of proliferating cells with 5-bromo-2'-deoxyuridine (BrdU) on brains of adults. The number of OPNs increases continuously throughout the postlarval life of shore crabs and approximately doubles from the very young to the oldest animals. Brain sections from adult crabs labeled with BrdU revealed ongoing proliferation of cells in the lateral soma cluster, which consists of OPN cell bodies, and in the cluster of somata of hemiellipsoid body local interneurons, which are the targets of the OPNs. Post-injection survival times from 5.5 to 120 h revealed a small but relatively constant number of labeled nuclei with neuronal morphology in both soma clusters of all specimens (31.3 +/- 9.5 S.D. nuclei per lateral cluster, n = 29; 20.1 +/- 4.5 S.D. nuclei per hemiellipsoid body cluster, n = 10). The labeled nuclei were located in a distinct proliferative zone in each cluster. There were significantly more labeled nuclei in both soma clusters after a prolonged post-injection survival time of 1 month (71.3 +/- 7.8 S.D. nuclei per lateral cluster, n = 4; 38.2 +/- 7.1 nuclei per hemiellipsoid body cluster, n = 6). In both soma clusters the labeled nuclei formed a compact group that was dislocated from the proliferation zone towards the outer edge of the cluster. In the proliferation zone of the lateral cluster histological stainings revealed cell bodies of typical neuronal shape that are slightly smaller and more intensely stained than the surrounding OPN somata. Some of these cell bodies were captured in various stages of mitosis. Collectively, these data indicate that continuous neurogenesis occurs in the central olfactory pathway of the brain of shore crabs throughout their entire adult life. This unexpected structural plasticity may enable long-lived decapod crustaceans to adapt to ever-changing olfactory environments.     

Transient lectin binding by white matter tract border zone microglia in the foetal rabbit brain

Axonal growth cones of developing white matter tracts are guided through the cerebrum by interactions with cell surface and extracellular matrix molecules expressed by glial cells that mediate cell adhesion and contact-dependent inhibition. Specific carbohydrates are considered essential for the proper functioning of these molecular complexes. We studied developmental aspects of complex carbohydrate expression by white matter glia in the foetal rabbit brain using the tomato lectin Lycopersicon esculentum, which has affinity for components of the extracellular matrix proteins and cell surface proteins (N-acetylglucosamine) and activated lysosomal membrane glycoproteins (N-acetyllactosamine). Concentrations of the lectin-positive glia were transiently found immediately adjacent to developing white matter tracts of the foetal rabbit brain from 22 to 32 days' gestation. The number of positive cells markedly diminished by the fourth post-natal day and in the adult brain. The lectin-positive glia did not react with antibody to glial fibrillary acidic protein. However, they did express the macrophage surface antigen, Mac-1, indicating that the lectin binding reflected the presence of microglial activated lysosomal membranes. These data suggest that, in addition to their role as central nervous system scavengers, microglia are involved in a specifically timed function in the neurodevelopmental programme of white matter tract formation.     

Olfactory ensheathing cells promote neurite extension from embryonic olfactory receptor cells in vitro

The role of ensheathing cells, a macroglial cell type with a unique presence in the olfactory system, in the outgrowth of olfactory receptor cell neurites was explored in vitro. Glial cell cultures harvested from both the olfactory bulb nerve layer and the hippocampus were established and immunocytochemically characterized. The expression of the p75 low-affinity nerve growth factor receptor by ensheathing cells was used to distinguish them from other macroglial subpopulations. Results indicated that ensheathing cell cultures were approximately 80% pure. Olfactory receptor cells were cocultured with ensheathing or hippocampal glial cells or were seeded on laminin or poly-L-lysine as controls. Olfactory receptor cells extended the longest primary neurites when cocultured with ensheathing cells. Neurite extension on hippocampal glia and laminin was less extensive than that observed on ensheathing cells but higher than that on poly-L-lysine. The neurite outgrowth-promoting effect of ensheathing cells was, at least in part, mediated by diffusible factors, because olfactory receptor cell neurite extension could also be facilitated when receptor cells were cultured in ensheathing cell-conditioned media. In contrast, cortical neurons extended neurites of equivalent lengths on ensheathing and hippocampal glia. The results suggest that ensheathing cells may release factors that support the continuous outgrowth of olfactory receptor cell axons and, therefore, the capacity of this pathway to recover from injury.     

Astroglial architecture of the carp (Cyprinus carpio) brain as revealed by immunohistochemical staining against glial fibrillary acidic protein (GFAP)

The present paper is the first comprehensive study on the astroglia of a teleost fish that is based on the immunohistochemical staining of GFAP (glial fibrillary acidic protein, an immunohistochemical marker of astroglia). The ray-finned fishes (Actinopterygii) and their largest group, the Teleostei, represent a separate pathway of vertebrate evolution. Their brain has a very complex macroscopic structure; several parts either have no equivalents in tetrapods or have a very different shape, e.g., the telencephalon. The results show that the teleost brain has a varied and highly specialized astroglial architecture. The primary system is made up of radial glia, which are of ependymal origin and cover the pial surface with endfeet. The tendency is, however, that the more caudal a brain area is, the less regular is the radial arrangement. A typical radial glia dominates some parts of the diencephalon (median eminence, lobus inferior and habenula) and the telencephalon. In the rest of the diencephalon and in the mesencephalon, the course of the glial fibers is modified by brain tracts. The most specialized areas of the teleost brain, the optic tectum and the cerebellum, display elaborate variations of the original radial system, which is adapted to their layered organization. In the cerebellum, an equivalent of the Bergmannglia can be found, although its fiber arrangement shows meaningful differences from that of mammals or birds. In the lower brain stem radial glia are confined to fibers separating the brain tracts and forming the midline raphe. A dense ependymoglial plexus covers the inner surface of the tectum and the bottom of the rhombencephalic ventricle, intruding into the vagal and facial lobes. The structure and the position of the rhombencephalic plexus suggest that it corresponds to a circumventricular organ that entirely occupies the bottom of the ventricle. Perivascular glia show an unusual form as they consist of long fibers running along the blood vessels. In the large brain tracts long glial fibers run parallel with the course of the neural fibers. At least in the diencephalon, these glial fibers seem to be modified radial fibers. Real astrocytes (i.e., stellate-shaped cells) can be found only in the brain stem and even there only rarely. The glial specialization in the various areas of the teleost brain seems to be more elaborate than that found either in amphibia or in reptiles.     

Olfactory epithelial organotypic slice cultures: a useful tool for investigating olfactory neural development

An in vitro slice culture was established for investigating olfactory neural development. The olfactory epithelium was dissected from embryonic day 13 rats; 400 microns slices were cultured for 5 days in serum-free medium on Millicell-CM membranes coated with different substrates. The slices were grown in the absence of their appropriate target, the olfactory bulb, or CNS derived glia. The cultures mimic many features of in vivo development. Cells in the olfactory epithelium slices differentiate into neurons that express olfactory marker protein (OMP). OMP-positive cells have the characteristic morphology of olfactory receptor neurons: a short dendrite and a single thin axon. The slices support robust axon outgrowth. In single-label experiments, many axons expressed neural specific tubulin, growth-associated protein 43 and OMP. Axons appeared to grow equally well on membranes coated with type I rat tail collagen, laminin or fibronectin. The cultures exhibit organotypic polarity with an apical side rich in olfactory neurons and a basal side supporting axon outgrowth. Numerous cells migrate out of the slices, of which a small minority was identified as neurons based on the expression of neural specific tubulin and HuD, a nuclear antigen, expressed exclusively in differentiated neurons. Most of the migrating cells, however, were positive for glial fibrillary acidic protein and S-100, indicating that they are differentiated glia. A subpopulation of these glial cells also expressed low-affinity nerve growth factor receptors, indicating that they are olfactory Schwann cells. Both migrating neurons and glia were frequently associated with axons growing out of the slice. In some cases, axons extended in advance of migrating cells. This suggests that olfactory receptor neurons in organotypic cultures require neither a pre-established glial/neuronal cellular terrain nor any target tissue for successful axon outgrowth. Organotypic olfactory epithelial slice cultures may be useful for investigating cellular and molecular mechanisms that regulate early olfactory development and function.     

Structural plasticity of identified glomeruli in the antennal lobes of the adult worker honey bee

Adult worker honey bees alter their behaviour with age but retain a strong reliance on sensory information from the antennae. The antennae house a diverse array of receptors, including mechanoreceptors, hygroreceptors, olfactory receptors, and contact chemoreceptors, which relay information to the brain. Antennal sensory neurons that project to the antennal lobes of the brain converge onto second-order interneurones to form discrete spheres of neuropil, called glomeruli. The spatial organisation of glomeruli in the antennal lobes of the honey bee is constant, but the central distribution of information from receptors tuned to different sensory modalities is unknown. Here we show that the glomerular neuropil of the antennal lobes undergoes constant modification during the lifetime of the adult worker bee. Changes in morphology are site specific and highly predictable. The total volume of the glomerular neuropil of the antennal lobe increased significantly during the first 4 days of adult life. Each of the five readily identifiable glomeruli examined in this study exhibited a unique pattern of growth. The growth of two of the five glomeruli changed dramatically with the shift to foraging duties. Furthermore, significant differences were identified between the antennal lobes of bees performing nectar- and pollen-foraging tasks. The highly compartmentalized nature of the antennal lobes, the ease with which specific glomeruli can be identified, and the predictability of changes to the antennal lobe neuropil make this an ideal system for examining the mechanisms and behavioural consequences of structural plasticity in primary sensory centres of the brain.     

Spatio-temporal patterns of ensheathing cell differentiation in the rat olfactory system during development

An immunocytochemical approach with specific glial markers was used to investigate the temporal and spatial patterns of differentiation of ensheathing glia wrapping axon fascicles along the primary olfactory pathway of the rat during development. The two glial markers tested, the proteins S-100 and glial fibrillary acidic protein, are known to be expressed at different stages of maturation in glial cells. The S-100 protein was first weakly expressed in cells accompanying the olfactory axons at embryonic day 14 (E14), while a first faint glial fibrillary acidic protein staining was detected along the olfactory axons at E15 and along the vomeronasal nerves at E16. A strong S-100 immunoreactivity was already present from E16 onwards along the axon fascicles through their course in both the nasal mesenchyme and the subarachnoid space before entering the olfactory nerve layer of the olfactory bulb. A gradual increase in glial fibrillary acidic protein expression was observed along this part of the developing olfactory pathway from E16 up to E20, when an adult-like pattern of staining intensity was seen. By contrast, most of the ensheathing cells residing in the olfactory nerve layer exhibited some delay in their differentiation timing and also a noticeable delayed maturation. It was only from E20 onwards that a weak to moderate S-100 expression was detected in an increasing number of cells throughout this layer, and only few of them appeared weakly glial fibrillary acidic protein positive at postnatal days 1 and 5. The immunocytochemical data indicate that there is a proximodistal gradient of differentiation of ensheathing cells along the developing olfactory pathway. The prolonged immaturity of ensheathing cells in the olfactory nerve layer, which coincides with the formation of the first glomeruli, might facilitate the sorting out of olfactory axons leading to a radical reorganization of afferents before they end in specific glomeruli.     

Posttraumatic olfactory dysfunction: MR and clinical evaluation

PURPOSE: To evaluate the sites of injury in patients with posttraumatic olfactory deficits and to compare damage with findings on clinical olfactory tests. METHODS: Twenty-five patients with posttraumatic olfactory dysfunction were examined by means of olfactory testing, endoscopy, and MR imaging. MR surface-coil scans through the olfactory bulbs and tracts and head-coil scans of the temporal lobes were evaluated. Quantitative and qualitative gradings of damage to the olfactory bulbs, tracts, subfrontal region, hippocampus, and temporal lobes were compared with results on tests of odor identification, detection, memory, and discrimination. RESULTS: Twelve patients were anosmic, eight had severe impairment, and five were mildly impaired. Injuries to the olfactory bulbs and tracts (88% of patients), subfrontal region (60%), and temporal lobes (32%) were found, but these did not correlate well with individual olfactory test scores. Volumetric analysis showed that patients without smell function had greater volume loss in olfactory bulbs and tracts than did those posttraumatic patients who retained some sense of smell. Qualitative and quantitative assessments of damage showed few significant correlations with olfactory tests, probably because of multifocal injuries, primary olfactory nerve damage, and the constraints of a small sample size on the detection of clinically significant differences. CONCLUSION: MR imaging shows abnormalities in patients with posttraumatic olfactory dysfunction at a very high rate (88%), predominantly in the olfactory bulbs and tracts and the inferior frontal lobes.     

Effects of fenvalerate on the development of olfactory perception in a beetle

Low doses of fenvalerate (a Type II pyrethroid) were applied to the beetle Tenebrio molitor at pupation, to ascertain its effects on the developing olfactory system. Doses of fenvalerate that prevent the formation of glomeruli in the primary olfactory neuropil (antennal lobes) also inhibit olfactory orientation behavior for different odors, despite the fact that sensory neurons developed responses to these odors. Even when lower amounts of fenvalerate that allowed glomeruli to develop were applied to pupae, the olfactory behavior was affected. Therefore, the formation of glomerular structures within the antennal lobe is not sufficient to establish olfactory behavior. A possible reason for this developmental effect of fenvalerate is a change in the odotopic arrangement of sensory axons within the glomeruli.