Occurrence and distribution of substance P-related immunoreactivity in the brain of adult lampreys, Petromyzon marinus and Entosphenus tridentatus

Neuronal mechanisms of respiratory pattern generation are evolutionary conserved

A brainstem region, the paratrigeminal respiratory group (pTRG), has been suggested to play a crucial role in the respiratory rhythm generation in lampreys. However, a detailed characterization of the pTRG region is lacking. The present study performed on isolated brainstem preparations of adult lampreys provides a more precise localization of the pTRG region with regard to both connectivity and neurochemical markers. pTRG neurons projecting to the vagal motoneuronal pool were identified in a restricted area of the rostral rhombencephalon at the level of the isthmic Müller cell I1 close to sulcus limitans of His. Unilateral microinjections of lidocaine, muscimol, or glutamate antagonists into the pTRG inhibited completely the bilateral respiratory activity. In contrast, microinjections of glutamate agonists enhanced the respiratory activity, suggesting that this region is critical for the respiratory pattern generation. The retrogradely labeled pTRG neurons are glutamatergic and surrounded by terminals with intense substance P immunoreactivity. Cholinergic neurons were seen close to, and intermingled with, pTRG neurons. In addition, α-bungarotoxin binding sites (indicating nicotinic receptors) were found throughout the pTRG area and particularly on the soma of these neurons. During apnea, induced by blockade of ionotropic glutamate receptors within the same region, microinjections of 1 μm substance P or 1 mm nicotine into the pTRG restored rhythmic respiratory activity. The results emphasize the close similarities between the pTRG and the mammalian pre-Bötzinger complex as a crucial site for respiratory rhythmogenesis. We conclude that some basic features of the excitatory neurons proposed to generate respiratory rhythms are conserved throughout evolution.

Cloning and expression of tachykinins and their association with kisspeptins in the brains of zebrafish

The tachykinins are a family of neuropeptides, including substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), that are encoded by the tac1 (SP and NKA) or tac2/3 (NKB) genes. Tachykinins are widely distributed in the central nervous system and have roles as neurotransmitters and/or neuromodulators. Recent studies in mammals have demonstrated the coexpression of NKB and kisspeptin and their comodulatory roles over the control of reproduction. We have recently identified two kisspeptin-encoding genes, kiss1 and kiss2, in teleosts. However, such relationship between tachykinins and kisspeptins has not been demonstrated in non-mammalian species. To determine the involvement of tachykinins in the reproduction in teleosts, we identified tac1 and two tac2 (tac2a and tac2b) sequences in the zebrafish genome using in silico data mining. Zebrafish tac1 encodes SP and NKA, whereas the tac2 sequences encode NKB and an additional peptide homologous to NKB (NKB-related peptide). Digoxigenin in situ hybridization in the brain of zebrafish showed tac1 mRNA-containing cells in the olfactory bulb, telencephalon, preoptic region, hypothalamus, mesencephalon, and rhombencephalon. The zebrafish tac2a mRNA-containing cells were observed in the preoptic region, habenula, and hypothalamus, whereas the tac2b mRNA-containing cells were predominantly observed in the dorsal telencephalic area. Furthermore, we examined the coexpression of tachykinins and two kisspeptin genes in the brain of zebrafish. Dual fluorescent in situ hybridization showed no coexpression of tachykinins mRNA with kisspeptins mRNA in hypothalamic nuclei or the habenula. These results suggest the presence of independent pathways for kisspeptins and NKB neurons in the brain of zebrafish.

Striatal cellular properties conserved from lampreys to mammals

The striatum of the lamprey, the first vertebrate group to appear in evolution, shows striking similarities to that of mammals with respect to histochemical markers, afferent and efferent projections and the effect of dopamine depletion, which leads to hypokinetic motor symptoms. The cellular properties of lamprey striatal neurons were studied here using patch-clamp recordings in acute striatal slices. Sixty-five per cent of recorded neurons were characterised by a prominent inward rectification due to a K+ conductance of the Kir type. They had a ramping response with a long delay to the first action potential due to activation of a low-voltage-activated A-type K+ current. Many such inwardly rectifying neurons (IRNs) had a hyperpolarised resting membrane potential and some had spiny dendrites. The remaining 35% of the neurons (non-IRNs) represent a heterogeneous group, including some with characteristics similar to the fast-spiking interneuron of the mammalian striatum. They showed short-lasting, large after hyperpolarisations (AHPs) and discharged action potentials at high frequency. None of the recorded neurons were spontaneously active but they received GABAergic and glutamatergic synaptic input. The fact that most lamprey striatal neurons display inward rectification indicates that this is a conserved characteristic of striatal neurons throughout vertebrate phylogeny. This is a cellular property of critical importance for the operations of the striatum in mammals.

Role of neurokinin receptors and ionic mechanisms within the respiratory network of the lamprey

We have suggested that in the lamprey, a medullary region called the paratrigeminal respiratory group (pTRG), is essential for respiratory rhythm generation and could correspond to the pre-Bötzinger complex (pre-BötC), the hypothesized kernel of the inspiratory rhythm-generating network in mammals. The present study was performed on in vitro brainstem preparations of adult lampreys to investigate whether some functional characteristics of the respiratory network are retained throughout evolution and to get further insights into the recent debated hypotheses on respiratory rhythmogenesis in mammals, such as for instance the "group-pacemaker" hypothesis. Thus, we tried to ascertain the presence and role of neurokinins (NKs) and burst-generating ion currents, such as the persistent Na(+) current (I(NaP)) and the Ca(2+)-activated non-specific cation current (I(CAN)), described in the pre-Bötzinger complex. Respiratory activity was monitored as vagal motor output. Substance P (SP) as well as NK1, NK2 and NK3 receptor agonists (400-800 nM) applied to the bath induced marked increases in respiratory frequency. Microinjections (0.5-1 nl) of SP as well as the other NK receptor agonists (1 microM) into the pTRG increased the frequency and amplitude of vagal bursts. Riluzole (RIL) and flufenamic acid (FFA) were used to block I(NaP) and I(CAN), respectively. Bath application of either RIL or FFA (20-50 microM) depressed, but did not suppress respiratory activity. Coapplication of RIL and FFA at 50 microM abolished the respiratory rhythm that, however, was restarted by SP microinjected into the pTRG. The results show that NKs may have a modulatory role in the lamprey respiratory network through an action on the pTRG and that I(NaP) and I(CAN) may contribute to vagal burst generation. We suggest that the "group-pacemaker" hypothesis is tenable for the lamprey respiratory rhythm generation since respiratory activity is abolished by blocking both I(NaP) and I(CAN), but is restored by enhancing network excitability.

The interplay between the pineal complex and the habenular nuclei in lower vertebrates in the context of the evolution of cerebral asymmetry

This paper presents an overview on the epithalamus of vertebrates, with particular reference to the pineal and to the asymmetrical organization of the habenular nuclei in lower vertebrates. The relationship between the pineal and the habenulae in the course of phylogenesis is here emphasized, taking data in the frog as example. Altogether the data support the hypothesis, put forward also in earlier studies, of a correlation of habenular asymmetry in lower vertebrates with phylogenetic modification of the pineal complex. The present re-visitation was also stimulated by recent data on the asymmetrical expression of Nodal genes, which involves the pineal and habenular structures in zebrafish. The comparative analysis of data, from cyclostomes to mammals, suggests that transformation of epithalamic structures may play an important role in brain evolution. In addition, in mammals, including rodents, a remarkable complexity has evolved in the organization of the habenulae and their functional interactions with the pineal gland. The evolution of these two epithalamic structures seems to open also new perspectives of knowledge on their implication in the regulation of biological rhythms.

The centrifugal visual system of vertebrates: a comparative analysis of its functional anatomical organization

The present review is a detailed survey of our present knowledge of the centrifugal visual system (CVS) of vertebrates. Over the last 20 years, the use of experimental hodological and immunocytochemical techniques has led to a considerable augmentation of this knowledge. Contrary to long-held belief, the CVS is not a unique property of birds but a constant component of the central nervous system which appears to exist in all vertebrate groups. However, it does not form a single homogeneous entity but shows a high degree of variation from one group to the next. Thus, depending on the group in question, the somata of retinopetal neurons can be located in the septo-preoptic terminal nerve complex, the ventral or dorsal thalamus, the pretectum, the optic tectum, the mesencephalic tegmentum, the dorsal isthmus, the raphé, or other rhombencephalic areas. The centrifugal visual fibers are unmyelinated or myelinated, and their number varies by a factor of 1000 (10 or fewer in man, 10,000 or more in the chicken). They generally form divergent terminals in the retina and rarely convergent ones. Their retinal targets also vary, being primarily amacrine cells with various morphological and neurochemical properties, occasionally interplexiform cells and displaced retinal ganglion cells, and more rarely orthotopic ganglion cells and bipolar cells. The neurochemical signature of the centrifugal visual neurons also varies both between and within groups: thus, several neuroactive substances used by these neurons have been identified; GABA, glutamate, aspartate, acetylcholine, serotonin, dopamine, histamine, nitric oxide, GnRH, FMRF-amide-like peptides, Substance P, NPY and met-enkephalin. In some cases, the retinopetal neurons form part of a feedback loop, relaying information from a primary visual center back to the retina, while in other, cases they do not. The evolutionary significance of this variation remains to be elucidated, and, while many attempts have been made to explain the functional role of the CVS, opinions vary as to the manner in which retinal activity is modified by this system.

Immunohistochemical distribution of tachykinins in the CNS of the lamprey Petromyzon marinus

The presence of tachykinins in the CNS of vertebrates has been known for many decades, and numerous studies have described their distribution in mammals. Tachykinins were also reported in the CNS of lampreys using immunohistochemistry, chromatography, and radioimmunoassay methods, but the use of substance P (SP)-specific antibodies to reveal those tachykinins could have led to an underestimation of their number in this genus. Therefore, we carried out a new immunohistochemical study on Petromyzon marinus using a commercial polyclonal antibody that binds not only to mammalian SP, but also to other neurokinins. This antibody labeled all previously described lamprey tachykinin-containing neuronal populations, but more important, labeled new populations in several parts of the brain. These include the dorsal gray of the rostral spinal cord, the dorsal column nuclei, the octavolateral area, the nucleus of the solitary tract, the medial rhombencephalic reticular formation, the lateral tegmentum of the rostral rhombencephalon, the torus semicircularis, the optic tectum, the habenula, the mammillary area, the dorsal thalamic area, the lateral hypothalamus, and the septum area. Preabsorption experiments confirmed the binding of the antibody to neurokinins and allowed us to propose that the CNS of P. marinus contains at least two different tachykinins.

Modulatory effect of substance P to the brain stem locomotor command in lampreys

Substance P initiates locomotion when injected in the brain stem of mammals. This study examined the possible role of this peptide on the supraspinal locomotor command system in lampreys. Substance P was bath applied or locally injected into an in vitro isolated brain stem, and the effects of the drug were examined on reticulospinal cells and on the occurrence of swimming in a semi-intact preparation. Bath applications of substance P induced sustained depolarizations occurring rhythmically in intracellularly recorded reticulospinal cells. Spiking activity was superimposed on the depolarizations and swimming was induced. The sustained depolarizations were abolished by tetrodotoxin, and substance P did not affect the membrane resistance of reticulospinal cells nor their firing properties, suggesting that it did not directly effect reticulospinal cells. To establish where the effects were exerted, successive lesions of the brain stem were made as well as local applications of the drug in the brain stem. Removing the mesencephalon abolished the sustained depolarizations, whereas large ejections of the drug in the mesencephalon excited reticulospinal cells and elicited bouts of swimming. More local injections into the mesencephalic locomotor region (MLR) also elicited swimming. After an injection of substance P, the current threshold needed to induce locomotion by MLR stimulation was decreased, and the size of the postsynaptic responses of reticulospinal cells to MLR stimulation was increased. Substance P also reduced the frequency of miniature spontaneous postsynaptic currents in reticulospinal cells. Taken together, these results suggest that substance P plays a neuromodulatory role on the brain stem locomotor networks of lampreys.

Distribution of thyrotropin-releasing hormone immunoreactivity in the brain of larval and adult sea lampreys, Petromyzon marinus L

This study investigated the distribution of thyrotropin-releasing hormone-immunoreactive (TRHir) neurons and fibers in the brain and retina of lampreys. Our results in the brains of large larvae and upstream-migrating adults of the sea lamprey showed the presence of TRHir neurons mainly in the preoptic region and the hypothalamus. A few TRHir neurons were also found in the striatum. The number and staining intensity of TRHir neurons increased from larval stages to adulthood, and the distribution of TRHir populations was wider in adults. The TRHir fibers were more easily traced in adults. Some TRHir fibers entered the neurohypophysis, although most fibers coursed in the different regions of the brain, mostly in the basal region, from the forebrain to the hindbrain. The presence of TRHir stellate cells was observed in the adenohypophysis. In the retina of adult lampreys, but not in that of larvae, TRHir amacrine cells are present.

Distribution of the orphan nuclear receptor Nurr1 in medaka (Oryzias latipes): cues to the definition of homologous cell groups in the vertebrate brain

The orphan nuclear receptor Nurr1 has been extensively studied in mammals and shown to contribute to the differentiation of several cell phenotypes in the nervous and endocrine systems. In this study, the gene homologous to the mammalian Nurr1 (NR4A2) was isolated in the teleost fish medaka (Oryzias latipes), and the distribution of its transcripts was analyzed within brains of embryos and adults. Nurr1 has a widespread distribution in the medaka brain. Large amounts of Nurr1 transcripts were found in the intermediate nucleus of the ventral telencephalon, preoptic magnocellular nucleus, ventral habenula, nucleus of the periventricular posterior tuberculum, and nuclei of glossopharyngeal and vagus nerves. To search for homologous cell groups between teleost fish and tetrapods brains, the co-localization of Nurr1 and tyrosine hydroxylase (TH) transcripts was analyzed. Neither Nurr1 nor TH expression was detected in the ventral midbrain, but both transcripts were present in the periventricular nucleus of the posterior tuberculum. This observation supports the hypothesis that this nucleus is homologous to dopaminergic mesencephalic nuclei of mammals. The presence of Nurr1 in the preoptic magnocellular nucleus of medaka and paraventricular hypothalamic nucleus of mammals reinforces the hypothesis of homology between these areas. TH and Nurr1 transcripts are also co-localized, among others, in the nucleus of the paraventricular organ and nucleus of the vagus nerve. This work suggests that the differentiating role of Nurr1 in the central nervous system is conserved in gnathostomes.

The distribution of lamprey GnRH-III in brains of adult sea lampreys (Petromyzon marinus)

In the sea lamprey, Petromyzon marinus, two forms of GnRH, lamprey GnRH-I and -III, have been demonstrated to be neurohormones regulating the pituitary-gonadal axis. The objective of the present study was to determine the distribution of lamprey GnRH-III in the brains of adult sea lampreys and to compare it to the distribution of lamprey GnRH-I. For this purpose, two kinds of immunostaining were employed: one was a single immunostaining by one of two GnRH antibodies using two successive sections; the other was double immunostaining of a single section. A dense accumulation of neuronal cells immunoreactive (ir) to antisera against either lamprey GnRH-I or -III was found in the arc-shaped preoptico-anterior hypothalamic area. Additional smaller numbers of irGnRH cells were found in the periventricular zone of the posterior hypothalamus. In the above-mentioned locations, the distribution of both irGnRH-I and -III cells was intermixed and very similar, but the cells exhibiting GnRH-III immunoreactivity were distinctly different from those exhibiting GnRH-I immunoreactivity. The relative numbers of irGnRH-III cells were larger than those of irGnRH-I cells in the preoptico-anterior hypothalamic area, and more than 90% of GnRH cells in the posterior hypothalamus were irGnRH-III cells. Both irGnRH-I and -III cells projected their fibers primarily into the neurohypophysis. The relative densities of the accumulated irGnRH-III fibers were similar to those of irGnRH-I fibers in the anterior neurohypophysis but higher than those of irGnRH-I fibers in the posterior neurohypophysis. The present study provides further immunocytochemical data to the already compelling physiological evidence that indicates that both lamprey GnRH-I and -III act through the hypothalamic-pituitary-gonadal axis to modulate reproductive processes in the sea lamprey.

Afferent and efferent connections of the parapineal organ in lampreys: a tract tracing and immunocytochemical study

The neural connections of the parapineal organ of two species of lampreys were studied with the fluorescent dye 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (DiI) and with immunocytochemistry. The lamprey parapineal organ consists of a vesicle and a ganglion that are connected to the left habenula. Labeling experiments included the application of DiI to the parapineal organ, left and right fasciculus retroflexus, left habenula, and the left pretectal region. Afferent parapineal fibers run in the left fasciculus retroflexus to the interpeduncular nucleus. The parapineal fibers of this fascicle arose from parapineal ganglion cells, whereas DiI application to the left habenula labeled both neurons of this ganglion and bipolar cells in the parapineal vesicle. Efferent neurons were observed in the left habenula, and bilaterally in the subhippocampal nucleus and the dorsal pretectum. Labeling with DiI also revealed a hippocampal projection. Immunocytochemical study of the parapineal vesicle revealed serotonin-immunoreactive cells in both species of lamprey, as well as substance P-immunoreactive (SP-ir) cells in sea lamprey and choline acetyltransferase-immunoreactive (ChAT-ir) cells in the river lamprey. The SP-ir cells and ChAT-ir cells formed a rich neuropil in the parapineal ganglion. Calretinin-ir cells were numerous in the ganglion. Neuropeptide Y-immunoreactive and gamma-aminobutyric acid-immunoreactive efferent fibers were observed in the parapineal organ. Neuropeptide Y-immunoreactive fibers originate in the subhippocampal nucleus, whereas gamma-aminobutyric acid-immunoreactive fibers might also arise in the pretectal nucleus. A few galanin-ir fibers were observed. These results indicate that the parapineal connections are completely different from those of the pineal organ. The possible homology between parapineal organs of vertebrates is discussed.

Structural and functional evolution of the basal ganglia in vertebrates

While a basal ganglia with striatal and pallidal subdivisions is 1 clearly present in many extant anamniote species, this basal ganglia is cell sparse and receives only a relatively modest tegmental dopaminergic input and little if any cortical input. The major basal ganglia influence on motor functions in anamniotes appears to be exerted via output circuits to the tectum. In contrast, in modern mammals, birds, and reptiles (i.e., modern amniotes), the striatal and pallidal parts of the basal ganglia are very neuron-rich, both consist of the same basic populations of neurons in all amniotes, and the striatum receives abundant tegmental dopaminergic and cortical input. The functional circuitry of the basal ganglia also seems very similar in all amniotes, since the major basal ganglia influences on motor functions appear to be exerted via output circuits to both cerebral cortex and tectum in sauropsids (i.e., birds and reptiles) and mammals. The basal ganglia, output circuits to the cortex, however, appear to be considerably more developed in mammals than in birds and reptiles. The basal ganglia, thus, appears to have undergone a major elaboration during the evolutionary transition from amphibians to reptiles. This elaboration may have enabled amniotes to learn and/or execute a more sophisticated repertoire of behaviors and movements, and this ability may have been an important element of the successful adaptation of amniotes to a fully terrestrial habitat. The mammalian lineage appears, however, to have diverged somewhat from the sauropsid lineage with respect to the emergence of the cerebral cortex as the major target of the basal ganglia circuitry devoted to executing the basal ganglia-mediated control of movement.

Organization of the lamprey striatum - transmitters and projections

The purpose of the present study is to characterize the striatum of the lamprey by immunohistochemical and tracing techniques. Cells immunoreactive for GABA and substance P (SP), and positive for acetylcholinesterase, are present in the lamprey striatum. Immunoreactive (ir) fibers were detected by antisera raised against SP, dopamine, enkephalin and serotonin. These immunoreactive fibers were mainly located in the periventricular neuropil that borders the striatum and in which GABAergic striatal neurons distributed their dendritic arbors. Putative connections between the striatum, the ventral part of the lateral pallium, and the diencephalic motor centers involved in the control of locomotion were studied by using fluorescein-coupled dextran amines (FDA) as a tracer. The striatum projects to the ventral part of the lateral pallium (lpv), where GABA-ir cells and SP-ir fibers were also present. The lpv in turn projects to the ventral thalamus, which has descending connections to the reticulospinal cells involved in the control of locomotion. These results, together with previous findings of histaminergic and neurotensin projections, suggest that the lamprey striatum and its inputs with regard to neurotransmitters/modulators are very similar to those of modem amniotes, including primates, and are thus conserved to a high degree.

Distribution of galanin-like immunoreactive elements in the brain of the adult lamprey Lampetra fluviatilis

Galanin is a brain-gut peptide present in the central nervous system of vertebrates and invertebrates. The distribution of galanin-like immunoreactive perikarya and fibers in the brain of the river lamprey Lampetra fluviatilis (Agnatha) has been studied immunocytochemically by using antisera against rat and porcine galanin. Galanin-like immunoreactive perikarya were seen in the telencephalon and mediobasal diencephalon. In the telencephalon, they were present in the nucleus olfactorius anterior, nucleus basalis, and especially, in the nucleus commissurae anterioris. The diencephalon contained most of the immunoreactive neurons. They were located in the nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus commissurae postinfundibularis, nucleus ventralis thalami, and nucleus dorsalis thalami pars medius. Most of the galanin-like immunoreactive infundibular neurons showed apical processes contacting the cerebrospinal fluid. Immunoreactive fibers and terminals were widely distributed throughout the neuraxis. In the telencephalon, the richest galaninergic innervation was found in the nucleus olfactorius anterior, lobus subhippocampalis, corpus striatum, and around the nucleus septi and the nucleus praeopticus. In the diencephalon, the highest density of galanin-like immunoreactive fibers was seen in the nucleus commissurae postopticae, nucleus commissurae praeinfundibularis, nucleus ventralis hypothalami, nucleus dorsalis hypothalami, and neurohypophysis. In the mesencephalon and rhombencephalon, the distribution of immunoreactive fibers was heterogeneous, being most pronounced in a region between the nucleus nervi oculomotorii and the nucleus interpeduncularis mesencephali, in the nucleus isthmi, and in the raphe region. A subependymal plexus of immunoreactive fibers was found throughout the ventricular system. The distribution of immunoreactive neurons and fibers was similar to that of teleosts but different to those of other vertebrate groups. The possible hypophysiotropic and neuroregulatory roles of galanin are discussed.

Distribution of substance P-like immunoreactivity in the brain of the elasmobranch Scyliorhinus canicula

Immunohistochemical methods were used to study the distribution of substance P in the brain of the small-spotted dogfish (Scyliorhinus canicula). Substance P-like immunoreactive (SP-IR) cell bodies and fibers were widely distributed. In the telencephalon, sparse populations of SP-IR neurons are present in the olfactory bulbs, pallium, and subpallium. In the subpallium numerous SP-IR boutons form unusual coats ("pericellular appositions") on SP-immunonegative neurons. In the diencephalon numerous SP-IR cerebrospinal fluid-contacting neurons are present in the preoptic recess organ and organon vasculosum hypothalami. Numerous SP-IR fibers also run in the hypothalamus, although no immunoreactivity was observed in the habenulo-interpeduncular system. A terminal field of SP-IR fibers is present in the median eminence. In the mesencephalic tegmentum, SP-IR neurons were observed in the Edinger-Westphal nucleus. SP-IR fibers are present at high density in the basal tegmentum, forming a conspicuous tract. In the hindbrain, numerous SP-IR fibers were observed in the isthmal region, the trigeminal descending root, the visceral sensory area and commissural nucleus, and the visceromotor column. SP-IR fibers occur at high density in the substantia gelatinosa of the rostral spinal cord.

Presumptive GABAergic centrifugal input to the lamprey retina: a double-labeling study with axonal tracing and GABA immunocytochemistry

The distribution of GABA-like immunoreactivity (GABA-LI) was performed in the lamprey retinopetal system which was previously identified by either anterograde or retrograde axonal tracing methods. This study was carried out at the ultrastructural level for the retina and under both the light and electron microscope for the mesencephalic retinopetal centers (M5 and RMA). The GABA-LI was distributed in about 40% of anterogradely HRP-labeled axon terminals in the inner retina. These made synaptic contacts upon either HRP-labeled ganglion cell dendrites or mostly on GABA-LI or on immunonegative amacrine cell dendrites and somata. The other immunonegative HRP-labeled axon terminals also established synaptic contacts on amacrine cell dendrites and somata. The mesencephalic retinopetal neurons, retrogradely labeled with HRP or [3H]proline, were GABA-LI in 65% of M5 somata and only in 15% of RMA neurons. M5 and RMA retinopetal neurons and dendrites, either GABA-LI or immunonegative, were contacted: (1) asymmetrically by HRP-labeled or unlabeled axon terminals containing rounded synaptic vesicles, always immunonegative and (2) symmetrically by HRP-unlabeled axon terminals containing pleiomorphic synaptic vesicles, which were either GABA-LI or immunonegative. The role of GABA as a putative neurotransmitter in the centrifugal visual system is discussed.

Substance P-like immunoreactivity in the brain of the gymnotiform fish Apteronotus leptorhynchus: presence of sex differences

The distribution of substance P-like immunoreactivity (SPli) was charted in the brain of the gymnotiform fish Apteronotus leptorhynchus, and correlated with the circuitry underlying intraspecific electrocommunication. Cell bodies were found predominantly in the lateral hypothalamus and in certain paraventricular organs: nucleus preopticus periventricularis, anterior subdivision; anterior hypothalamus; nucleus posterioris periventricularis; nucleus recessus lateralis, medial subdivision 2; nucleus recessus posterioris and nucleus recessus lateralis, lateral subdivision. Cell bodies were also found in the rostral olfactory nucleus, ventral telencephalon (ventral and central subdivisions), the habenula, the vagal sensory and motor nuclei and in the subtrigeminal nucleus. The distribution of SPli fibers was similar in some respects to that reported for other vertebrates. SPli was found in the rhombencephalon associated with vagal afferent fibers and in the funicular nucleus (possibly related to nociception). In the diencephalon and midbrain SPli fibers were found in the habenular-interpeduncular tract, in the hypothalamus and pituitary. SPli fibers were also found in preoptic and forebrain areas. The most striking result was the sexually dimorphic SPli innervation of certain hypothalamic and septal nuclei, and of the prepacemaker nucleus (PPn), a diencephalic cell group which controls communication ('chirping') in gymnotiforms. The PPn and septal/hypothalamic nuclei were densely innervated by SPli in males but devoid of SPli in females.

Comparative distribution of substance P (SP) and cholecystokinin (CCK) binding sites and immunoreactivity in the brain of the sea bass (Dicentrarchus labrax)

Specific binding sites for cholecystokinin (CCK) and substance P (SP) were detected in the brain of a marine teleost fish, the sea bass, after in vitro incubation of tissue sections with the tritiated peptides and light microscopic autoradiography. Specific binding sites for [3H]-CCK were detected in the dorsal and ventral telencephalon, in the preoptic, tuberal and posterior hypothalamus, in the optic tectum, in the valvulla cerebelli, in the vagal lobe and further in a dorsal location in the medulla oblongata. Areas rich in [3H]-SP binding were located in the ventral telencephalon, in the entire hypothalamic and thalamic region, in the midbrain tegmentum, in the optic tectum, in the valvulla cerebelli and in the medulla oblongata. The distribution of these binding sites seemed to match fairly well with the location of the corresponding immunoreactive elements, although some minor mismatches could be observed. These autoradiographic findings provide the first anatomical evidence for the presence of CCK-like and SP-like binding sites in the brain of a teleost fish.

Galanin-like immunoreactivity in the brain of teleosts: distribution and relation to substance P, vasotocin, and isotocin in the Atlantic salmon (Salmo salar)

The presence of galanin-like substances and their relation to substance P-, vasotocin-, and isotocin-immunoreactive neurons and fibers in the brain of teleosts was investigated with immunohistochemical methods. Two specific antisera against synthetic porcine galanin (GAL) revealed cell bodies and fibers in the brain of four different teleost species (Salmo salar, Carassius carassius, Gasterosteus aculeatus, and Anguilla anguilla). In all four species the main location of galanin immunoreactivity was in the hypothalamo-pituitary region. A detailed study of the distribution of galanin immunoreactivity in S. salar showed that galanin immunoreactive (GALir) perikarya were present in the nucleus preopticus periventricularis, an area that may be compared to the supraoptic nucleus in mammals, and in the nucleus lateralis tuberis, a nucleus involved in pituitary control in fishes that may be compared with the arcuate nucleus in mammals. GALir perikarya were found also in the nucleus recessus lateralis and in the nucleus recessus posterior. Numerous GALir fibers were present in the telencephalon and diencephalon, whereas only small numbers of fibers were found in the brainstem. In contrast to the situation in mammals, no GALir perikarya were observed in the brainstem areas corresponding to the noradrenergic locus coeruleus and serotonergic raphe nuclei in S. salar. We did not find any coexistence of GALir substances with arginine vasotocin or isotocin in neurosecretory neurons, as has been shown for galanin with the mammalian counterparts vasopressin and oxytocin. Also, the galanin-like substance(s) and their structurally closest related peptide family, the tachykinins, belong to separate neuronal systems in teleosts. The presence of GALir neurons in brain areas known to be involved in pituitary control, and a massive GALir innervation of the pituitary, strongly indicate a role for galanin-like substances in pituitary control also in teleosts. Furthermore, the presence of extrahypothalamic GALir fibers suggests involvement of galanin-like substances in other brain functions in teleosts. In conclusion, there are general similarities between teleosts and mammals concerning the distribution of galanin-like substances. However, there seem to be substantial differences in their distribution relative to functionally related peptides within the hypothalamo-pituitary system. Whereas galanin appears to be colocalized and released together with vasopressin and oxytocin in mammals, in teleosts the homologous substances are contained within different sets of neurons that innervate the same target, the pituitary.

Comparative distribution of neuropeptide-immunoreactive systems in the brain of the green molly, Poecilia latipinna

The comparative distribution of peptidergic neural systems in the brain of the euryhaline, viviparous teleost Poecilia latipinna (green molly) was examined by immunohistochemistry. Topographically distinct, but often overlapping, systems of neurons and fibres displaying immunoreactivity (ir) related to a range of neuropeptides were found in most brain areas. Neurosecretory and hypophysiotrophic hormones were localized to specific groups of neurons mostly within the preoptic and tuberal hypothalamus, giving fibre projections to the neurohypophysis, ventral telencephalon, thalamus, and brain stem. Separate vasotocin (AVT)-ir and isotocin (IST)-ir cells were located in the nucleus preopticus (nPO), but many AVT-ir nPO neurons also displayed growth hormone-releasing factor (GRF)-like-ir, and in some animals corticotrophin-releasing factor (CRF)-like-ir. The main group of CRF-ir neurons was located in the nucleus recessus anterioris, where coexistence with galanin (GAL) was observed in some cells. Enkephalin (ENK)-like-ir was occasionally present in a few IST-ir cells of the nPO and was also found in small neurons in the posterior tuberal hypothalamus and in a cluster of large cells in the dorsal midbrain tegmentum. Thyrotrophin-releasing hormone (TRH)-ir cells were found near the rostromedial tip of the nucleus recessus lateralis. Gonadotrophin-releasing hormone (GnRH)-ir cells were present in the nucleus olfactoretinalis, ventral telencephalon, preoptic area, and dorsal midbrain tegmentum. Molluscan cardioexcitatory peptide (FMRF-amide)-ir was colocalized with GnRH-ir in the ganglion cells and central projections of the nervus terminalis. Melanin-concentrating hormone (MCH)-ir neurons were restricted to the tuberal hypothalamus, mostly within the nucleus lateralis tuberis pars lateralis, and somatostatin (SRIF)-ir neurons were numerous throughout the periventricular areas of the diencephalon. A further group of SRIF-ir neurons extending from the ventral telencephalon into the dorsal telencephalon pars centralis also contained neuropeptide Y (NPY)-, peptide YY (PYY)-, and NPY flanking peptide (PSW)-like-ir. These immunoreactivities were, however, also observed in non-SRIF-ir cells and fibres, particularly in the mesencephalon. Calcitonin gene-related peptide (CGRP)-like-ir had a characteristic distribution in cells grouped in the isthmal region and fibre tracts running forward into the hypothalamus, most strikingly into the inferior lobes. Antisera to cholecystokinin (CCK) and neurokinin A (NK) or substance P (SP) stained very extensive, separate systems throughout the brain, with cells most consistently seen in the ventral telencephalon and periventricular hypothalamus. Broadly similar, but much more restricted, distributions of cells and fibres were seen with antisera to neurotensin (NT) and vasoactive intestinal peptide (VIP).(ABSTRACT TRUNCATED AT 400 WORDS)

Gut hormones in cyclostomes

The current state of knowledge about regulatory peptides in endocrine cells and nerves of the alimentary canal of lampreys and hagfishes is reviewed. Cyclostomes have a wide range of peptides similar immunochemically to those of higher vertebrates. They include, in the endocrine cells of the intestine, peptides resembling glucagon, gastrin/cholecystokinin, peptide YY (pancreatic polypeptide/neuropeptide Y), substance P, vasoactive intestinal peptide, somatostatin and, in the larval stages at least, insulin. The enteric nerves of some lamprey species contain peptides resembling bombesin (gastrin-releasing peptide) and calcitonin gene-related peptide, as well as serotonin. The occurrence of other peptides is less well documented.Little is known of the molecular structure or the biological roles of the enteric peptides in cyclostomes. Extraction, purification, sequencing and physiological experiments are greatly needed.