Distribution of serotonin-immunoreactivity in the brain of the pigeon (Columba livia)

The distribution of serotonin (5-HT)-containing perikarya, fibers and terminals in the brain of the pigeon (Columba livia) was investigated, using immunohistochemical and immunofluorescence methods combined with retrograde axonal transport. Twenty-one different groups of 5-HT immunoreactive (IR) cells were identified, 2 of which were localized at the hypothalamic level (periventricular organ, infundibular recess) and 19 at the tegmental-mesencephalic and rhombencephalic levels. Ten of the cell groups were situated within the region of the midline from the isthmic to the posterior rhombencephalic level and constituted the raphe system (nucleus annularis, decussatio brachium conjunctivum, area ventralis, external border of the nucleus interpeduncularis, zona peri-nervus oculomotorius, zona perifasciculus longitudinalis medialis, zona inter-flm, nucleus linearis caudalis, nucleus raphe superior pars ventralis, nucleus raphe inferior). The 9 other cell populations belonged to the lateral group and extended from the posterior mesencephalic tegmentum to the caudal rhombencephalon [formatio reticularis mesencephali, nucleus ventrolateralis tegmenti, ectopic area (Ec) of the nucleus isthmo-opticus (NIO), nucleus subceruleus, nucleus ceruleus, nucleus reticularis pontis caudalis, nucleus vestibularis medialis, nucleus reticularis parvocellularis and nucleus reticularis magnocellularis]. Combining the retrograde axonal transport of rhodamine -isothiocyanate (RITC) after intraocular injection and immunohistofluorescence (fluoresceine isothiocyanate: FITC/5-HT) showed the centrifugal neurons (NIO, ec) to be immunonegative. Serotonin-IR fibers and terminals were found to be very broadly distributed within the brain and were particularly prominent in several structures of the telencephalon (archistriatum pars dorsalis, nucleus taeniae, area parahippocampalis, septum), diencephalon (nuclei preopticus medianus, magnocellularis, nucleus geniculatus lateralis pars ventralis, nucleus triangularis, nucleus pretectalis), mesencephalon-rhombencephalon (superficial layers of the optic tectum, nucleus ectomamillaris, nucleus isthmo-opticus and in most of the cranial nerve nuclei). Comparing the present results with those of previous studies in birds suggests some major serotonin containing pathways in the avian brain and clarifies the possible origin of the serotonin innervation of some parts of the brain. Moreover, comparing our results in birds with those obtained in other vertebrate species shows that the organization of the serotoninergic system in many regions of the avian brain is much like that found in reptiles and mammals.Abbreviations Ad Archistriatum pars dorsalis - alp area interpeduncularis - al ansa lenticularis - Ann nucleus annularis - APH area parahippocampalis - Av archistriatum pars ventralis - AVT area ventralis (Tsai) - bcd brachium conjunctivum descendens - BO bulbus olfactorius - ca commisssura anterior - CDL area corticoidea dorsolateralis - Cer cerebellum - cf fiber layer of the olfactory bulb - cg granular cell layer of the olfactory bulb - co chiasma opticum - ct commissura tectalis - dbc decussatio brachiorum conjunctivorum - DL nucleus dorsolateralis anterior thalami - DLP nucleus dorsolateralis posterior thalami - DM nucleus dorsomedialis thalami - dnt decussatio nervi trochlearis - E ectostriatum - Ec ectopic area of the nucleus isthmo-opticus - EM nucleus ectomamillaris - flm fasciculus longitudinalis medialis - fpl fasciculus prosencephali lateralis - FRL formatio reticularis lateralis mesencephali - FRM formatio reticularis medialis mesencephali - fu fasciculus uncinatus - GCt substantia grisea centralis - GLv nucleus geniculatus lateralis pars ventralis - gr granular cell layer of the cerebellum - HA hyperstriatum accessorium - HD hyperstriatum dorsale - HIS hyperstriatum intercalatus superior - HL nucleus habenularis lateralis - HM nucleus habenularis medialis - Hp hippocampus - HV hyperstriatum ventrale - ICo nucleus intercollicularis - i-flm inter fasciculus longitudinalis medialis - Imc nucleus ishmi pars magnocellularis - Ip nucleus interpeduncularis - Ipc nucleus isthmi pars parvocellularis - LA nucleus lateralis anterior thalami - La nucleus laminaris - LC nucleus linearis caudalis - LHy nucleus lateralis hypothalami - lm lemniscus medialis - LoC locus coeruleus - LPO lobus paraolfactorius - ls lemniscus spinalis - MLd nucleus mesencephalicus lateralis pars dorsalis - mo molecular layer of the cerebellum - MoV nucleus motorius nervi trigemini - Mp magnocellularis preopticus - N neostriatum - NIII nucleus nervi oculomotorii - nIII nervus oculomotorius - NIV nucleus nervi trochlearis - NV nucleus nervi trigemini nV nervus trigeminus - NVII nucleus nervifacialis - nVIII nervus octavus - NIO nucleus isthmo-opticus - om tractus occipitomesencephalicus - OPH hypothalamic periventricular organ - Os nucleus olivaris superior - Ov nucleus ovoidalis - PA paleostriatum augmentatum - Po nucleus pontis - POM nucleus preoticus medialis - PP paleostriatum primitivum - PrV nucleus sensorius principalis nervi trigemini - PT nucleus pretectalis - pu Purkinje cell layer - qf tractus quintofrontalis - Rai nucleus raphe inferior - RasV nucleus raphe superior pars ventralis - ReI recessus infundibularis - Rm nucleus reticularis magnocellularis - Rp nucleus reticularis parvocellularis - RPc nucleus reticularis pontis caudalis - RPO nucleus reticularis pontis oralis - Rt nucleus rotundus - Ru nucleus ruber - S septum - Sac stratum album centrale - SCH stratum cellulare hypothalami - Sgc stratum griseum centrale - Sgf stratum griseum et fibrosum superficiale - Sgfp stratum griseum et fibrosum periventriculare - Sop stratum opticum - SP nucleus subpretectalis - SPC nucleus superficialis parvocellularis - Spl nucleus spiriformis lateralis - Spm nucleus spiriformis medialis - SRt nucleus subrotundus - SuC nucleus subcoeruleus - to tractus opticus - Tn nucleus taeniae - TPc nucleus tegmenti pedunculo-pontinus pars compacta - Tr nucleus triangularis - tsm tractus septomesencephalicus - ttd nucleus et tractus descendens nervi trigemini - Tu nucleus tuberis - Vel nucleus vestibularis lateralis - Vem nucleus vestibularis medialis - Vlt nucleus ventrolateralis thalami - VT nucleus ventrolateralis tegmenti - Zp-flm zona perifasciculus longitudinalis medialis - Zp-NIII zona perinervus oculomotorius     

Pretectal connections in turtles with special reference to the visual thalamic centers: a hodological and gamma-aminobutyric acid-immunohistochemical study

Projections of the pretectal region to forebrain and midbrain structures were examined in two species of turtles (Testudo horsfieldi and Emys orbicularis) by axonal tracing and immunocytochemical methods. Two ascending gamma-aminobutyric acid (GABA)ergic pathways to thalamic visual centers were revealed: a weak projection from the retinorecipient nucleus lentiformis mesencephali to the ipsilateral nucleus geniculatus lateralis pars dorsalis and a considerably stronger projection from the nonretinorecipient nucleus pretectalis ventralis to the nucleus rotundus. The latter is primarily ipsilateral, with a weak contralateral component. The interstitial nucleus of the tectothalamic tract is also involved in reciprocal projections of the pretectum and nucleus rotundus. In addition, the pretectal nuclei project reciprocally to the optic tectum and possibly to the telencephalic isocortical homologues. Comparison of these findings with previous work on other species reveals striking similarities between the pretectorotundal pathway in turtles and birds and in the pretectogeniculate pathway in turtles, birds, and mammals.     

Quantitative immunogold evidence that glutamate is a neurotransmitter in afferent synaptic terminals within the isthmo-optic nucleus of the pigeon centrifugal visual system

A quantitative electron microscopic analysis of glutamate (GLU) immunoreactivity using the post-embedding immunogold technique was carried out within the isthmo-optic nucleus (ION) of the pigeon centrifugal visual system (CVS). Measurements were performed in each of eight different categories of axon terminals, including those that were GABA-immunoreactive (-ir), considered representing control profiles and identified using a single or double-label immunocytochemical procedure. The results demonstrated that the glutamate immunogold particle densities for both mitochondrial and vesicular pools and for total surface area of bouton profiles were significantly higher in P1a, P1b and P2b terminals and not significantly different in P4 and P5 terminals compared to those recorded in control GABA-ir terminals (P2a, P2c, P3). Moreover, the values measured in GLU-ir positive profiles were all significantly higher than in either P4 or P5 terminals. The results suggest that tectal neurons, which provide the main input to the ION cells, are either inhibitory GABA-ir possibly associated with P2c and/or P3 terminals or excitatory GLU-ir via P1a, P1b and P2b terminals. Such differential effects of tectal afferents may be the basis for the modulation of centrifugal activity and consequently of end target retinal ganglion cell responses. The data are relevant to hypotheses implicating the avian CVS in mechanisms of selective enhancement of visual attention to either novel or meaningful stimuli within the visual field.     

Presumptive FMRF-amide-like immunoreactive retinopetal fibres in Crocodylus niloticus

A small contingent of 30-50 of centrifugal visual fibres, showing FMRF-amide-like immunoreactivity, has been identified in C. niloticus; these fibres extend from the chiasmatic region into the retina. They do not take the marginal optic tract, but pass medially to the chiasmatic fascicles, from the preoptic region. The cells of origin of these fibres have not been identified. However, none of the retinopetal neurons of the brainstem [M. Medina, J. Reperant, R. Ward, D. Miceli, Centrifugal visual system of Crocodylus niloticus : a hodological, histochemical and immunocytochemical study, J. Comp. Neurol. 468 (2004) 65-85], labelled by retrograde transport of rhodamine beta-isothiocyanate after intraocular injection of this tracer, show FMRF-amide-like immunoreactivity; neither are any of the FMRF-amide-like immunopositive neurons in the crocodile brain, particularly those of the complex involving the terminal nerve and the septo-preoptic region, labelled by rhodamine after its intraocular injection.     

Axo–axonic GABA-immunopositive synapses on the primary afferent fibers in frogs

In three frog species Rana esculenta, Rana temporaria and Xenopus laevis, the contacts established by γ-aminobutyric acid and glutamate decarboxylase immunoreactive (-ir) terminals upon primary afferent fibers were studied using confocal and electron microscopy. For confocal microscopy, the primary afferent fibers were labeled through the dorsal root with Dextran–Texas Red, whereas γ-aminobutyric acid and glutamate decarboxylase immunoreactivity were revealed with fluorescein isothiocyanate. Appositions of γ-aminobutyric acid and glutamate decarboxylase immunoreactive profiles onto primary afferent fibers were observed and were considered as putative axo–axonic contacts of GABAergic terminals upon primary afferents. The latter was confirmed by the ultrastructural finding of axo–axonic synapses from γ-aminobutyric acid immunopositive boutons upon the HRP-labeled primary afferent fibers in postembedding immunoelectron microscopic study. Such synapses may represent the morphological basis of GABAergic presynaptic inhibition of primary afferent fibers.     

Fine structure of the optic fiber termination layer in the tectum of the teleost Rutilus: a stereological and morphometric study

The stratum fibrosum et griseum superficiale (SFGS) of the Rutilus optic tectum, which receives a massive fiber projection from the contralateral retina, was studied by electron microscopy. The qualitative and quantitative analysis of the laterodorsal (LD) portion of the stratum involved both a stereological examination of the different elements and a morphometric study of the various profiles containing synaptic vesicles (PCSVs). The relative volume of each element in the LD SFGS was as follows: myelinated and unmyelinated axons, 6.6%; PCSVs, 38%; dendrites without vesicles, spines, and cell bodies, 41.7%; glia, 10.5%. With the fixation employed, 35% of PCSVs showed spheroidal synaptic vesicles. These profiles could be subdivided into three types: (1) S1 (23.5%) represented optic terminals, since they degenerated after retinal ablation or were labeled after intraocular injection of HRP or [3H] proline. Three subgroups of S1 were identified: S1m--profiles containing clear mitochondria;S1c--profiles that were contiguous with S1m and lacked mitochondria;S1i--isolated profiles without mitochondria. (2) S2 (9.3%) were characterized mainly by their dark mitochondria. (3) S3 (2.2%) corresponded to small nonvisual terminals that were isolated and lacked mitochondria. The PCSVs with pleiomorphic synaptic vesicles (65%) were subdivided into three groups: P1 (38%), P2 (19%), and P3 (8%). P1 and P2 were axonal in nature; P2 could be distinguished from P1 by a greater density of synaptic vesicles. P3 was of dendritic origin. Analysis of synaptic patterns revealed a small number of serial synapses. The presynaptic elements were optic boutons, whereas the intermediate profiles were dendrites with synaptic vesicles (P3). Results are compared with ultrastructural data obtained in the superficial tectal layers of other teleosts and other vertebrate groups.     

Reorganization of GABAergic synapses in the viper optic tectum following retinal deafferentation

The immunocytochemical analysis of the viper optic tectum was carried out with an anti-gamma-aminobutyric acid (anti-GABA) antiserum following retinal deafferentation for survival times ranging from 10 to 90 days. The ultrastructure of the SGFS neuropil revealed that among the two types of axon terminals, namely pleiomorphic (P) and spherical (S) boutons, a subtype of the latter (S2), corresponding to the retinal terminals, was found to degenerate at varying rates. In most cases, this resulted in the glial engulfment of the presynaptic partner, leaving the postsynaptic differentiation free (FPSD). Beyond the two first months, the asymmetrical freed postsynaptic differentiations (FPSDs) were progressively and partly reafferented by GABA-positive P axon terminals through a sliding process. Three months postoperative, the number of GABA-positive P axon terminals which, in normal animals, establish asymmetrical contacts (1-2%), was found to increase to approximately 10%. The postsynaptic differentiation may represent a mismatched receptor area for the new competing presynaptic partners. The functional implications of such 'axonal terminal sprouting' are discussed.     

The anatomical organization of retinal projections in the shark Scyliorhinus canicula with special reference to the evolution of the selachian primary visual system

The retinal projections of the shark Scyliorhinus canicula were investigated using both the degeneration technique after eye removal and the radioautographic method following the intraocular injection of various tritiated tracers (proline, leucine, fucose, adenosine). The results showed contralateral projection via different optic tract components (TOM, AOT, TOm, TOI, ROVm, RODm) to various areas and nuclei of the hypothalamus (NSC), thalamus (NODLAT, NODMAT, NTTOM, NOVT, NODPT), pretectum (NOPC, NOCPd, NOCPv), tectum (SFGS, SGI) and mesencephalic tegmentum (AOTMd, NOTMv). Ipsilateral retinal projections were found to arborize within 7 distinct zones at the hypothalamic (NSC), thalamo-pretectal (NODLAT, NTTOM, NOVT. NOPC, NOCpd) and tectal (SFGS) levels.A comparison of the data with those previously obtained in different species of elasmobranchs and batoids indicate the existence of a common and consistent pattern of organization of the primary visual system in all selachians. Many of the discrepancies reported in studies on the organization of selachian retinal projection may be listed to methodological differences and/or interspecies variations in the cytoarchitecture of the different visual centers. Moreover, a comparison of the primary visual system of more primitive squalomorph sharks with that of the more advanced galeomorph sharks and batoids suggests that this system evolved through an increase in the neuronal density of the target structures and transformations in the dendritic configurations of the post-synaptic neurons rather than through an increase in the total number of projection zones.     

Eimeria involved in a case of coccidiosis in farmed red-legged partridges (Alectoris rufa) in France: oocyst isolation and gross lesion description after experimental infection

The aim of the present work was, after a coccidiosis outbreak in a farm rearing red-legged partridges (Alectoris rufa) in Brittany (France), to identify the Eimeria species and describe gross lesions induced by three of them (Eimeria kofoidi, Eimeria caucasica and Eimeria legionensis) after experimental infection. E. kofoidi oocysts measured 19.3 µm×16.3 µm on average; neither micropyle nor oocyst residuum were present, but one, two or more small polar granules were visible. After inoculation of 300,000 oocysts per partridge, severe gross lesions were observed in the duodenum and jejunum, characterized by thickened oedematous mucosa and lumen filled with thick mucus, gas and sometimes false-membrane due to sloughed epithelium. E. caucasica oocysts were on average 29.8 µm×19.5 µm in size; no oocyst residuum was observed, but a large granule was well visible. E. caucasica also invaded both the duodenum and jejunum, causing haemorrhagic points on the serosal surface, as well as mucoid duodenitis and catarrhal enteritis when 30,000 oocysts were inoculated per bird. E. legionensis oocysts measured 22.6 µm×14.9 µm on average; they presented a clear micropyle beneath which one or two granulations were present. E. legionensis mainly invaded the caeca; low mortality was observed at the dosage of 200,000 oocysts per bird. Caecal walls were thickened and caseous material was condensed into off-white cheesy cores. For each species, oocyst shedding started 5 days post inoculation, peaked at 9, 8 and 6 days post inoculation for E. kofoidi, E. caucasica and E. legionensis, respectively, then decreased and persisted until 15 days post inoculation (end of examinations).     

Synaptic circuitry in the retinorecipient layers of the optic tectum of the lamprey (Lampetra fluviatilis). A combined hodological, GABA and glutamate immunocytochemical study

The ultrastructure of the retinorecipient layers of the lamprey optic tectum was analysed using tract tracing techniques combined with GABA and glutamate immunocytochemistry. Two types of neurons were identified; a population of large GABA-immunonegative cells, and a population of smaller, highly GABA-immunoreactive interneurons, some of whose dendrites contain synaptic vesicles (DCSV). Five types of axon terminals were identified and divided into two major categories. The first of these are GABA-immunonegative, highly glutamate-immunoreactive, contain round synaptic vesicles, make asymmetrical synaptic contacts, and can in turn be divided into AT1 and AT2 terminals. The AT1 terminals are those of the retinotectal projection. The origin of the nonretinal AT2 terminals could not be determined. AT1 and AT2 terminals establish synaptic contacts with DCSV, with dendrites of the retinopetal neurons (DRN), and with conventional dendritic (D) profiles. The terminals of the second category are GABA-immunoreactive and can similarly be divided into AT3 and AT4 terminals. The AT3 terminals contain pleiomorphic synaptic vesicles and make symmetrical synaptic contacts for the most part with glutamate-immunoreactive D profiles. The AT4 terminals contain rounded synaptic vesicles and make asymmetrical synaptic contacts with DRN, with DCSV, and with D profiles. A fifth, rarely observed category of terminals (AT5) contain both clear synaptic vesicles and a large number of dense-core vesicles. Synaptic triads involving AT1, AT2 or AT4 terminals are rare. Our findings are compared to these of previous studies of the fine structure and immunochemical properties of the retinorecipient layers of the optic tectum or superior colliculus of Gnathostomes.