El Hassan Hamdani

Bio: El Hassan Hamdani is an academic researcher from University of Oslo. The author has contributed to research in topics: Olfactory system & Olfactory bulb. The author has an hindex of 16, co-authored 20 publications receiving 934 citations. Previous affiliations of El Hassan Hamdani include Oslo University Hospital.

Specific projection of the sensory crypt cells in the olfactory system in crucian carp, Carassius carassius.

Abstract: To study the projection of a special type of sensory neuron called crypt cells in the olfactory system in crucian carp, Carassius carassius, we applied the neural tracer 1,1-dilinoleyl-3,3,3#,3#-tetramethylindocarbocyanine perchlorate (DiI) in the olfactory bulb (OB). Small crystals of DiI were applied in a small area at the synaptic region at the ventral part of the OB, where a population of secondary neurons specific for sex pheromones has been identified. In those samples (4 out of 24) where only axons in the lateral bundle of the medial olfactory tract were stained, the majority (50–66%) of olfactory sensory neurons stained were crypt cells situated in the peripheral layer of the olfactory epithelium. Because this bundle of the tract mediates reproductive behavior, it is conceivable that crypt cells express olfactory receptors for sex pheromones.

Alarm reaction in the crucian carp is mediated by the medial bundle of the medial olfactory tract

Abstract: Experiments were performed to determine which bundles of the olfactory tracts were essential for mediating alarm reaction in crucian carp (Carassius carassius L.). The fish were maintained in physiological saline after surgery to preserve the remaining tracts and postoperative inspections revealed the functionality of the intact tracts. Operations on the tracts were performed symmetrically on both sides. Sham-operated and non-operated fish showed the typical alarm behaviour of fast swimming to the bottom, dashing movements and aggregation when exposed to skin extract which contain alarm substance. Fish with only the medial bundle of the medial olfactory tract intact also displayed the alarm behaviour upon exposure; however, these fish did not react to the amino acid, L-alanine with either feeding response or alarm reaction. Crucian carp which had the medial bundle of the medial olfactory tract cut, leaving both the lateral bundle of the medial olfactory tract and the lateral olfactory tract intact, did not display any alarm reaction to skin extract; however, these fish reacted to exposure to L-alanine with feeding behaviour. There were statistically significant differences between the behaviour scores for the fish subject to different treatments. The present study demonstrates that the medial bundle of the medial olfactory tract appears to be both necessary and sufficient for mediation of the alarm reaction. The results also show that the sensory neurons which respond to alarm substance terminate and make synaptic connections with the secondary neurons that make up the medial bundle of the medial olfactory tract; thereby demonstrating the specificity of the spatial aspect of olfactory processing. The results are discussed with respect to the spatial aspect of organization within the olfactory system, the pattern of generalization across orders of fish, and the functional implications of the spatial arrangement of information transmission between the peripheral olfactory organ and the brain.

Projection of sensory neurons with microvilli to the lateral olfactory tract indicates their participation in feeding behaviour in crucian carp.

Abstract: In the olfactory system of vertebrates, a large number of primary sensory neurons terminate in glomeruli in the olfactory bulb, where they make synapses with a significantly smaller number of secondary neurons. We applied small amounts of a lipophilic neural tracer (Dil) in the glomerular regions of the lateral olfactory bulb in crucian carp, and investigated the centrifugal migration of this stain through the secondary neurons towards the brain and peripherally to the sensory neurons of the olfactory epithelium. In preparations where only the secondary neurons of the lateral olfactory tract (LOT) were stained, the majority (76%) of sensory neurons had cell bodies in the intermediate layer of the olfactory epithelium. Scanning electron microscopy revealed that most of the sensory neurons with cell bodies in the intermediate layers of the olfactory epithelium feature microvilli. Based on observations that the secondary neurons of the LOT mediate feeding behaviour, we feel that there is strong evidence to indicate that the sensory neurons that exhibit microvilli are responsible for mediating the behavioural patterns related to feeding. These results are discussed in relation to physiological experiments on the properties of the sensory neurons and to studies of the innervation pattern of sensory neurons.

Is feeding behaviour in crucian carp mediated by the lateral olfactory tract

Abstract: Experiments were performed to investigate which bundle of the olfactory tract was essential for mediating feeding behaviour in crucian carp. Fish were divided in three groups: control fish, fish with only the lateral olfactory tracts (LOTs) intact and fish with the LOTs cut. The fish were maintained in physiological saline after surgery to preserve the remaining tracts and postoperative inspections revealed the functional status of the remaining tracts. With the injection of food odour into the aquaria the scores for various feeding behaviours—biting, snapping, mouth openings and vertical posture—were not significantly different between those of the control fish and the fish with the LOT intact. Those fish that had the LOT cut but the medial and lateral parts of the medial olfactory tract (mMOT, lMOT) intact had significantly lower feeding-related scores than the other two groups of fish. The results of the present study indicate that the LOT is necessary to maintain the full qualitative and quantitative extent of feeding behaviour in crucian carp.

Glutamate as a neurotransmitter in the healthy brain.

Abstract: Glutamate is the most abundant free amino acid in the brain and is at the crossroad between multiple metabolic pathways. Considering this, it was a surprise to discover that glutamate has excitatory effects on nerve cells, and that it can excite cells to their death in a process now referred to as “excitotoxicity”. This effect is due to glutamate receptors present on the surface of brain cells. Powerful uptake systems (glutamate transporters) prevent excessive activation of these receptors by continuously removing glutamate from the extracellular fluid in the brain. Further, the blood–brain barrier shields the brain from glutamate in the blood. The highest concentrations of glutamate are found in synaptic vesicles in nerve terminals from where it can be released by exocytosis. In fact, glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. It took, however, a long time to realize that. The present review provides a brief historical description, gives a short overview of glutamate as a transmitter in the healthy brain, and comments on the so-called glutamate–glutamine cycle. The glutamate transporters responsible for the glutamate removal are described in some detail.

Odor Coding by a Mammalian Receptor Repertoire

Abstract: Deciphering olfactory encoding requires a thorough description of the ligands that activate each odorant receptor (OR). In mammalian systems, however, ligands are known for fewer than 50 of more than 1400 human and mouse ORs, greatly limiting our understanding of olfactory coding. We performed high-throughput screening of 93 odorants against 464 ORs expressed in heterologous cells and identified agonists for 52 mouse and 10 human ORs. We used the resulting interaction profiles to develop a predictive model relating physicochemical odorant properties, OR sequences, and their interactions. Our results provide a basis for translating odorants into receptor neuron responses and for unraveling mammalian odor coding.

Pheromones and Animal Behavior: Chemical Signals and Signatures

Abstract: Pheromones and other kinds of chemical communication underlie the behavior of all animals Building on the strengths of the first edition, widely recognized as the leading text in the subject, this is a comprehensive overview of how pheromones work Extensively revised and expanded to cover advances made over the last ten years, the book offers a thorough exploration of the evolutionary and behavioral contexts of chemical communication along with a detailed introduction to the molecular and neural basis of signal perception through olfaction At a time of ever increasing specialization, Wyatt offers a unique synthesis, integrating examples across the animal kingdom A final chapter critically considers human pheromones and the importance of olfaction to human biology Its breadth of coverage and readability make the book an unrivaled resource for students and researchers in a range of fields from chemistry, genetics, genomics, molecular biology and neuroscience to ecology, evolution and behavior

Pheromones and signature mixtures: defining species-wide signals and variable cues for identity in both invertebrates and vertebrates.

Abstract: Pheromones have been found in species in almost every part of the animal kingdom, including mammals. Pheromones (a molecule or defined combination of molecules) are species-wide signals which elicit innate responses (though responses can be conditional on development as well as context, experience, and internal state). In contrast, signature mixtures, in invertebrates and vertebrates, are variable subsets of molecules of an animal’s chemical profile which are learnt by other animals, allowing them to distinguish individuals or colonies. All signature mixtures, and almost all pheromones, whatever the size of molecules, are detected by olfaction (as defined by receptor families and glomerular processing), in mammals by the main olfactory system or vomeronasal system or both. There is convergence on a glomerular organization of olfaction. The processing of all signature mixtures, and most pheromones, is combinatorial across a number of glomeruli, even for some sex pheromones which appear to have ‘labeled lines’. Narrowly specific pheromone receptors are found, but are not a prerequisite for a molecule to be a pheromone. A small minority of pheromones act directly on target tissues (allohormone pheromones) or are detected by non-glomerular chemoreceptors, such as taste. The proposed definitions for pheromone and signature mixture are based on the heuristic value of separating these kinds of chemical information. In contrast to a species-wide pheromone, there is no single signature mixture to find, as signature mixtures are a ‘receiver-side’ phenomenon and it is the differences in signature mixtures which allow animals to distinguish each other.

Parallel Olfactory Systems in Insects: Anatomy and Function

Abstract: A striking commonality across insects and vertebrates is the recurring presence of parallel olfactory subsystems, suggesting that such an organization has a highly adaptive value. Conceptually, two different categories of parallel systems must be distinguished. In one, specific sensory organs or processing streams analyze different chemical stimuli (segregate parallel systems). In the other, similar odor stimuli are processed but analyzed with respect to different features (dual parallel systems). Insects offer many examples for both categories. For example, segregate parallel systems for different chemical stimuli are realized in specialized neuronal streams for processing sex pheromones and CO2. Dual parallel streams related to similar or overlapping odor stimuli are prominent in Hymenoptera. Here, a clear separation of sensory tracts to higher-order brain centers is present despite no apparent differences regarding the classes or categories of olfactory stimuli being processed. In this paper, we review...