D. Miceli

Pain modulating and reward systems: A single brain mechanism?

Abstract The hypothesis that brain rewarding and pain modulating systems could involve a common opiate system, identically blocked by naloxone, has been tested in three experiments. The preferences or aversions for sapid solutions in rats have been employed as reliable measures of responses to rewarding or nociceptive stimulations. In the first experiment, it was shown that the spontaneous aversion to a quinine HCl solution was enhanced when rats were offered the solution 30 min after naloxone at a dose of 1 mg/kg. The same enhanced aversion was observed in the second experiment towards a sweet solution previously made aversive through a conditioned taste aversion paradigm. In the third experiment, by using two different procedures and saccharin or glucose solutions, it was found that naloxone acutely abolished the preference for sweet solutions versus water in rats. It is concluded that: (1) the enhancement by naloxone of the aversion to a sapid solution, similar to the naloxone induced hyperalgesia, allows to assimilate this aversion to other responses to nociceptive stimulations; (2) this suggests that, like other responses to nociceptive stimulations, this aversion is normally attenuated through the release of brain or pituitary opiates; (3) the suppressant effect of naloxone upon both this attenuation of aversion and a preference for a sapid solution supports the notion of a biochemical and functional community between rewarding and pain modulating systems.

Decrease in ethanol consumption by naloxone in naive and dependent rats

Acute effects of the opiate antagonist, naloxone, on alcohol intake have been examined and compared in naive and behaviorally dependent rats. In naive rats the aversion to an 8% alcohol solution exhibited in a 30 min presentation was selectively augmented by an IP administration of naloxone (1 mg/kg) 30 min before a morning drinking session. In other rats, behavioral dependence was established by 15 days of IG administration of intoxicating doses of alcohol. This dependence was exhibited by a sustained preference for ethanol for 6 days. Naloxone (1 mg/kg) abolishes the acquired preference for ethanol tested during an 8 hour day time presentation. These effects of naloxone on alcohol intake in ethanol naive and dependent rats are interpreted in relation to a general non-specific action of naloxone on preferred or aversive flavoured solutions.

The Centrifugal Visual System of Vertebrates: A Century-Old Search Reviewed

Publisher Summary This chapter reviews a comparative perspective from both anatomical and functional points of view, group by group, from the most primitive vertebrates to the most evolved vertebrates. The centrifugal system of birds is considered because of the large volume and diversity of work done in this vertebrate class. Extrinsic axons to the retina are found in most of the large taxonomic groups of vertebrates, from the lamprey to the human. These fibers always terminate upon amacrine cells, more rarely upon ganglion cells, and upon interplexiform cells (IPC). However, upon entering the retina, they show a considerable degree of collateralization and thus may be considered to be divergent. These fibers are generally of small diameter and unmyelinated (except in the human). These axons are usually of large diameter and myelinated. It is also demonstrated that the retinopetal fibers are predominantly convergent in birds. In teleosts, several neuropeptides are colocalized within retinopetal fibers, including luteinizing hormone-releasing hormones (LHRH)-like, molluscan cardioexcitatory tetrapeptide (FMRF) amide-like, and substance P-like peptides.

An anatomical study of ipsilateral retinal projections in the quail using radioautographic, horseradish peroxidase, fluorescence and degeneration techniques

The topographical organization of ipsilateral retinal projections was investigated in the pigmented quail using different anatomical tracing techniques. The orthograde labeling patterns were examined after intraocular injections of tritiated tracers (autoradiography), horseradish peroxidase (HRP) either alone or combined with wheat germ agglutinin (WGA), the fluorescent tracer rhodamine beta-isothiocyanate (RITC) and after unilateral retinal ablations using degeneration methods where the material was observed at both light and electron microscope levels. The different techniques provided extremely variable results with regard to demonstrating ipsilateral retinal projections. Whereas the latter could not be revealed in the radioautographic preparations, the results derived using the degeneration and HRP methods were fragmentary. The RITC method was found to be the most effective and made it possible to accurately define the different ipsilateral optic contingents and their terminal arborizations within various thalamic, pretectal and tegmentomesencephalic centers. The contradictory data in the literature regarding the existence of ipsilateral retinal projections in various avian species may be explained by differences in methodology based upon the relative degrees of resolution offered by the different techniques.

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 β-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.

The distribution of GABA-immunoreactive neurons in the brain of the silver eel (Anguilla anguilla L.).

The distribution of GABA-immunoreactivity was studied in the brain of the silver eel (Anguilla anguilla) by means of antibodies directed against GABA. Immunoreactive neuronal somata were distributed throughout the brain. Positive perikarya were detected in the internal cellular layer of the olfactory bulb, and in all divisions of the telencephalon, the highest density being observed along the midline. Numerous GABA-reactive cell bodies were found in the diencephalon, particularly in the preoptic and tuberal regions of the hypothalamus, and the dorsolateral, dorsomedial and ventromedial thalamic nuclei. In the optic tectum, the majority of GABApositive cell bodies were located in the periventricular layer. A number of immunolabelled cell bodies were observed in different tegmental structures, notably the torus semicircularis. In the cerebellum, the Purkinje cells were either very intensely or very weakly immunoreactive. In the rhombencephalon, reactive cell bodies were observed in the eminentia granularis, the valvula cerebellaris, the octavolateral nucleus, the lobus vagus and in the vagal and glossopharyngeal motor nuclei. Intensely immunoreactive axons and terminals were observed in the external granular layer and internal cellular layer of the olfactory bulb. In the telencephalon, the highest density of reactive fibres and boutons was found in the fields of the medial wall. Many immunolabelled fibres were seen in the medial and lateral forebrain bundles. In the diencephalon, intense labelling of fibres and terminals were observed in the nuclei situated close to the midline. In the optic tectum the highest density of reactive fibres was seen in the sfgs, the layer to which the retina projects massively. Finally, in the rhombencephalon the strongest labelling of neurites was observed in the nuclei of the raphé, the nucleus octavocellularis magnocellularis and the nuclei of the IXth and Xth cranial nerves. The GABAergic system of the eel, which is well developed, appears to be generally comparable to that described in tetrapod vertebrates.

The serotoninergic system of the brain of the lamprey, Lampetra fluviatilis: an evolutionary perspective

The distribution of serotonin(5HT)-immunoreactive cell bodies, nerve fibers and terminals was investigated by light microscopy in the lamprey Lampetra fluviatilis. Twenty-three distinct groups of 5HT neuronal somata were identified from diencephalic to rhombencephalic levels in the brain. The diencephalon contained a subependymal population of immunoreactive cells in contact with the cerebrospinal fluid (CSF), which could be subdivided into five separate groups situated in the hypothalamus and ventral thalamus; five additional groups of immunoreactive diencephalic neurons, situated in the dorsal thalamus and thalamo-pretectum, which were not in contact with the CSF, were also identified. In the midbrain, in addition to a few labelled neurons in the optic tectum, two structures containing immunoreactive cells were identified in the tegmentum mesencephali. None of these 5HT cells corresponded to the retinopetal neurons which are situated in the same region. A very large number of 5HT neurons were observed in the hindbrain which could be divided into seven groups in the isthmus rhombencephali and a further three in the rhombencephalon proper. Immunoreactive fibers and terminals were widely distributed throughout the neuraxis. In the telencephalon two 5HT fibers assemblies, lateral and medial, could be identified which terminated in both pallial and subpallial structures. The richest serotoninergic innervation in the telencephalon was found in the lateral portion of the primordium hippocampi and the medial part of the corpus striatum. In the diencephalon, the distribution of immunoreactive fibers and terminals was heterogeneous, being most pronounced in the lateral hypothalamic area and in the infundibulum. The densest arborization of fibers in the mesencephalon was found in the stratum fibrosum et cellulare externum of the optic tectum, a major site of retinal projection, and in the nucleus interpeduncularis mesencephali as well as in the oculomotor nuclei. The rhombencephalon is richly endowed with serotoninergic fibers and terminals, many labelled arborizations being found in the nuclei isthmi rhombencephali and around the nucleus motorius nervi trigemini. Comparative analysis of the serotoninergic systems of petromyzontiforms and gnathostomes indicates that the evolution of this system involves a progressive elimination of the rostral immunoreactive cells and an increasing complexity of the caudal population of serotoninergic neurons.

An anatomical and electrophysiological study of the centrifugal visual system in the lamprey (Lampetra fluviatilis)

The centrifugal visual system of the lamprey Lampetra fluviatilis was investigated using various neurohistophysical methods: intraocular injections of [3H]adenosine, fluorescent tracer (Evans Blue) and the iontophoretic deposit of HRP on the optic nerve. Retrogradely labeled neurons were identified bilaterally within the nucleus M5 of Schober and contralaterally in the reticular mesencephalic area (RMA). Comparison of the various orthograde and retrograde labeling results indicated that the neurons of M5 and RMA were labeled via retrograde axonal transport of the different tracers in the retinopetal system and not by orthograde transneuronal processes or from extraretinal pathways. Part of the anatomical data regarding RMA as a site of origin of the centrifugal visual system was confirmed using electrophysiological techniques involving evoked potential and unit cell recordings in RMA following electrical stimulation of the optic nerve. The experiments were performed in the curarized animal under conditions of either normal blood circulation, perfusions of adapted physiological saline, or with a solution known to block chemical synaptic transmission. Various electrophysiological criteria, including the results obtained during the conditions of reversible chemical synaptic blockade, indicated that the responses in RMA reflect an antidromic process. The anatomical organization of the centrifugal visual system in the lamprey is compared to that found in different gnathostome vertebrate species. Several hypotheses concerning the marked interspecies differences related either to the number and the topographical location of the centrifugal neurons as well as the evolution of this system are advanced.

Projections of the dorsolateral anterior complex and adjacent thalamic nuclei upon the visual Wulst in the pigeon.

The distinctive patterns of thalamic input to the rostral (R), intermediate (I) and caudal (C) divisions of the pigeon Wulst were determined using the retrograde multiple label technique following concomitant injections of various fluorescent tracers into different Wulst loci. The results showed topographical projections from components of the visual thalamic n. dorsolateralis anterior complex. Major ipsilateral and contralateral projections upon the R and I Wulst stem from the pars lateralis ventralis and dorsalis nuclei, respectively. The nuclei pars lateralis rostralis, pars magnocellularis and n. suprarotundus provide weak bilateral projections to all of the Wulst divisions sampled. Lastly, bilateral connections from the n. superficialis parvocellularis upon I and C, and from n. dorsolateralis posterior upon the posterior C Wulst were also demonstrated. Based upon their patterns of terminal distribution upon the Wulst, some of these thalamic nuclei are compared to specific components of the mammalian geniculate and extrageniculate visual systems.

Audition differently activates the visual system in neonatally enucleated mice compared with anophthalmic mutants.

The occipital cortex, normally visual, can be activated by auditory or somatosensory tasks in the blind. This cross‐modal compensation appears after early or late onset of blindness with differences in activation between early and late blind. This could support the hypothesis of a reorganization of sensory pathways in the early blind that does not occur in later onset blindness. Using immunohistochemistry of the c‐Fos protein following a white noise stimulus and injections of the anterograde tracer dextran‐biotin in the inferior colliculus, we studied how the occurrence of blindness influences cross‐modal compensation in the mutant anophthalmic mouse strain and in C57BL/6 mice enucleated at birth. We observed, in mutant mice, immunolabeled nuclei in the visual thalamus – the dorsal lateral geniculate nucleus – in the primary visual area (V1) and a few labeled nuclei in the secondary visual area (V2). In enucleated mice, we observed auditory activity mainly in V2 but also sparsely in V1. No labeled cells could be found in the visual thalamus. Tracing studies confirmed the difference between anophthalmic and birth‐enucleated mice: whereas the first group showed inferior colliculus projections entering both the dorsal lateral geniculate and the latero‐posterior nuclei, in the second, auditory fibers were found only within the latero‐posterior thalamic nucleus. None was found in controls with intact eyes. We suggest that the prenatal period of spontaneous retinal activity shapes the differences of the sensory reorganization in mice.