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At least 793 records · Page 44Linked to original sources
PubMed1975

The distribution of the olfactory tracts in the bullhead catfish, Ictalurus nebulosus.

Using degeneration staining methods, central projections of the olfactory tracts in the bullhead catfish, Ictalurus nebulosus were studied. Seporate lesions were made of the lateral and medial olfactory tracts in an attempt to separate their zones of projection. Three major terminal fields were found: lateral, medial and central-posterior complex. Two additional minor projections were seen: interbulbar and hypothalamic. The lateral division of the olfactory tract terminates in lateral, central and hypothalamic terminal fields. The medial tract projects to lateral, meedial, posterior and hypothalamic fields. All terminal fields were found bilaterally; the lateral tract partly crossing in both the anterior commissure. A small intellbulbar commissure was also found to contain medial tract fibers. Evidence is given to show that the anterior olfactory nucleus, if present in catfish, may be located within the olfactory bulb itself. Similarities between mammalian and teleost olfactory systems are also discussed.

Animals↗
PubMed1996

Reciprocal and topographic connections between the piriform and prefrontal cortices in the rat: a tracing study using the B subunit of the cholera toxin.

In the present study, the reciprocal connections between the piriform cortex and the prefrontal areas are described on the basis of experiments using the anterograde and the retrograde transport of the cholera toxin B subunit (CTb). Following CTb injections placed in the anterior part of the piriform cortex, retrogradely labeled cells and anterogradely labeled fibers were mainly found in the ventrolateral and lateral orbital areas as well as in the anterior part of the agranular insular cortex. Following injections placed in the posterior part of the piriform cortex, the CTb labeling was primarily observed in the infralimbic area and the posterior part of the agranular insular cortex. Thus, we described a topographical organization of the direct reciprocal connections between the anterior and the posterior parts of the piriform cortex parts and some prefrontal areas. This could support a differential modulation of the olfactory processing along the rostrocaudal dimension of the piriform cortex.

Animals↗
PubMed2002

AMPA autoreceptors drive correlated spiking in olfactory bulb glomeruli.

Information processing in the brain may rely on temporal correlations in spike activity between neurons. Within the olfactory bulb, correlated spiking in output mitral cells could affect the odor code by either binding or amplifying signals from individual odorant receptors. We examined the timing of spike trains in mitral cells of rat olfactory bulb slices. Depolarization of mitral cell pairs elicited spikes that were correlated on a rapid timescale (< or =10 ms) for cells whose primary dendrites projected to the same glomerulus. Correlated spiking was driven by a novel mechanism that depended on electrical coupling at mitral cell primary dendrites; the specific synchronizing signal was a coupled depolarization ( approximately 20 ms) that was mediated by dendritic AMPA autoreceptors. We suggest that glomerulus-specific correlated spiking in mitral cells helps to preserve the fidelity of odor signals that are delivered to the olfactory cortex.

Action Potentials↗
PubMed1975

Neuroplasticity in the sparing or deterioration of function after early olfactory tract lesions.

Mating behavior in male hamsters depends on the sense of smell. Thus, complete transection of the lateral olfactory tract in adults eliminates mating. If the cut is made early in life, however, mating is spared. Partial section of the tract in adults does not affect mating, but similar cuts in the neonate lead to impaired mating performance later in life. Observed postsurgical rearrangements in the connections of axons in the lateral olfactory tract may explain both the sparing and the deterioration of function.

Age Factors↗
PubMed1986

Plasticity in the rat olfactory cortex.

The relationship of age to deafferentation plasticity was studied in the rat olfactory cortex (OC). Ablation of a single olfactory bulb (OB) was performed in each of several rats of selected postnatal (PN) ages: PN2.5, 6, 9, 13, and 21 days and in adults of PN100 days. Following survival times sufficient to remove the resultant degeneration, a cortical lesion was placed in the ipsilateral OC. The patterns of degeneration from the OC lesion were studied and mapped in the adjacent deafferented OC. The results show a spread or sprouting of the usually deep-lying afferents (interrupted by the OC lesion), onto the deafferented superficial dendrites (normally occupied by the OB afferents) in all of the ages. The spread is most striking at PN2.5 to PN9, gradually reduced by PN13 to PN21, and least in the adult (PN100). There is also an apparent increase of afferents to the deeper dendrites nearer the cell bodies in all cases except in the PN 100 group. Shrinkage of layer I is not seen in PN2.5 subjects, is minimal by PN9, but is most marked in the adult PN100 with total OB lesions. Incomplete OB lesions sparing some lateral olfactory tract (LOT) fibers greatly reduce the shrinkage of layer I and the spread of afferents in all ages. Thus, a capacity for reorganization of afferents occurs at least through PN9, with PN13-21 a possible "critical period" after which plasticity is limited and transneuronal effects are more permanent. The association, centrifugal, and olfactory-entorhinal pathways are possible origins for this plasticity. Factors contributing to limitations in this reorganization are discussed.

Age Factors↗
PubMed2006

Genetic manipulation of blood group carbohydrates alters development and pathfinding of primary sensory axons of the olfactory systems.

Primary sensory neurons in the vertebrate olfactory systems are characterised by the differential expression of distinct cell surface carbohydrates. We show here that the histo-blood group H carbohydrate is expressed by primary sensory neurons in both the main and accessory olfactory systems while the blood group A carbohydrate is expressed by a subset of vomeronasal neurons in the developing accessory olfactory system. We have used both loss-of-function and gain-of-function approaches to manipulate expression of these carbohydrates in the olfactory system. In null mutant mice lacking the alpha(1,2)fucosyltransferase FUT1, the absence of blood group H carbohydrate resulted in the delayed maturation of the glomerular layer of the main olfactory bulb. In addition, ubiquitous expression of blood group A on olfactory axons in gain-of-function transgenic mice caused mis-routing of axons in the glomerular layer of the main olfactory bulb and led to exuberant growth of vomeronasal axons in the accessory olfactory bulb. These results provide in vivo evidence for a role of specific cell surface carbohydrates during development of the olfactory nerve pathways.

Animals↗
PubMed1999

Cholinergic synaptic transmission in insect mushroom bodies in vitro.

The mushroom body of the bee brain is an important site for learning and memory. Here we investigate synaptic transmission in the mushroom body using extracellular recording techniques in a whole bee brain in vitro preparation. The postsynaptic response showed attenuation by cadmium and paired-pulse facilitation, similar to in vivo findings. This confirms the viability of the in vitro preparation and supports the isolated whole bee brain as a useful model of the in vivo preparation. Bath application of the acetylcholine receptor antagonists, D-tubocurarine and alpha-bungarotoxin attenuated the postsynaptic response by 61 and 62% of control, respectively. The glutamate receptor antagonists, (+)-2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitroquinoxaline-2,3-dione, had no effect. The invertebrate monoamine and neuromodulator, octopamine, transiently increased the postsynaptic response by 130% of control. These results suggest that synaptic transmission of the olfactory input pathway in the mushroom body is 1) mediated primarily by acetylcholine and 2) modulated by octopamine.

Acetylcholine↗
PubMed1988

Centrifugal regulation of neuronal activity in the olfactory bulb of the waking rabbit as revealed by reversible cryogenic blockade.

The influences of centrifugal projections to the olfactory bulb were examined on the bulbar EEG and mitral-tufted cell activity in waking rabbits. Each of 6 rabbits was implanted, under surgical anesthesia, with fine wire electrodes for recording of the EEG and mitral-tufted cell unit activity and for stimulating the lateral olfactory tract. Two cooling probes, for reversible cryogenic blockade, were implanted on either side of the left olfactory peduncle. Records of EEG and unit activity were taken for 200 s before, during and after cooling of the probes to 3 degrees centigrade. Antidromic evoked potentials were used to assess the efficacy of the blockade. During the cryogenic blockade bursts of EEG activity, evoked in the bulb by inspiration through the nose, were augmented in amplitude and reduced in frequency. Mitral-tufted cell unit activity was reduced in rate but was more highly correlated with the phase and amplitude of the EEG bursts. Analysis of individual EEG bursts revealed that the variance in frequency of bulbar activity was significantly reduced in the isolated state. The data demonstrate that oscillatory bursting activity in the olfactory bulb is intrinsically maintained within a relatively fixed frequency range during receptor input and does not depend on centrifugal projections for its electrogenesis. Changes in EEG frequency, amplitude and correlation with unit activity support the hypothesis that centrifugal projections act in part to inhibit mitral-tufted cell output by direct excitation of granule cells. These findings are supported by a theoretical model in which distributed feedback to the granule cells from more central olfactory structures acts to regulate the coherency of bulbar activity.

Action Potentials↗
PubMed2002

Projections from the posterior cortical nucleus of the amygdala to the hippocampal formation and parahippocampal region in rat.

The posterior cortical nucleus of the amygdala is involved in the processing of pheromonal information and presumably participates in ingestive, defensive, and reproductive behaviors as a part of the vomeronasal amygdala. Recent studies suggest that the posterior cortical nucleus might also modulate memory processing via its connections to the medial temporal lobe memory system. To investigate the projections from the posterior cortical nucleus to the hippocampal formation and the parahippocampal region, as well as the intra-amygdaloid connectivity in detail, we injected the anterograde tracer phaseolus vulgaris-leucoagglutinin into different rostrocaudal levels of the posterior cortical nucleus. Within the hippocampal formation, the stratum lacunosum-moleculare of the temporal CA1 subfield and the adjacent molecular layer of the proximal temporal subiculum received a moderate projection. Within the parahippocampal region, the ventral intermediate, dorsal intermediate, and medial subfields of the entorhinal cortex received light to moderate projections. Most of the labeled terminals were in layers I, II, and III. In the ventral intermediate subfield, layers V and VI were also moderately innervated. Layers I and II of the parasubiculum received a light projection. There were no projections to the presubiculum or to the perirhinal and postrhinal cortices. The heaviest intranuclear projection was directed to the deep part of layer I and to layer II of the posterior cortical nucleus. There were moderate-to-heavy intra-amygdaloid projections terminating in the bed nucleus of the accessory olfactory tract, the central division of the medial nucleus, and the sulcal division of the periamygdaloid cortex. Our data suggest that via these topographically organized projections, pheromonal information processed within the posterior cortical nucleus can influence memory formation in the hippocampal and parahippocampal areas. Also, these pathways provide routes through which seizure activity can spread from the epileptic amygdala to the surrounding region of the temporal lobe.

Acetylcholinesterase↗
PubMed1983

Basal telencephalic origins of the anterior commissure of the rat.

The cells of origin of the three limbs of the rat's anterior commissure (AC) have been identified by horseradish peroxidase histochemistry. Following transection of the corpus callosum and hippocampal commissure, rats were subjected to multiple, unilateral injections of horseradish peroxidase throughout one cerebral hemisphere. The cells of origin of the rat's AC are found in the anterior olfactory nucleus, the olfactory tubercles, the anterior piriform cortex, the nucleus of the lateral olfactory tract, the lateral, basolateral, basomedial and cortical nuclei of the amygdala, the posterior perirhinal cortex, and the entorhinal cortex. Anterogradely labeled fibers were also found in the olfactory bulbs and in the plexiform layer of the anterior and posterior piriform cortices.

Amygdala↗