RESUMO
Imprinting in chicks is a good model for elucidating the processes underlying neural plasticity changes during juvenile learning. We recently reported that neural activation of a telencephalic region, the core region of the hyperpallium densocellulare (HDCo), was critical for success of visual imprinting, and that N-Methyl-D-aspartic (NMDA) receptors containing the NR2B subunit (NR2B/NR1) in this region were essential for imprinting. Using electrophysiological and multiple-site optical imaging techniques with acute brain slices, we found that long-term potentiation (LTP) and enhancement of NR2B/NR1 currents in HDCo neurons were induced in imprinted chicks. Enhancement of NR2B/NR1 currents as well as an increase in surface NR2B expression occurred even following a brief training that was too weak to induce LTP or imprinting behavior. This means that NR2B/NR1 activation is the initial step of learning, well before the activation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors which induces LTP. We also showed that knockdown of NR2B/NR1 inhibited imprinting, and inversely, increasing the surface NR2B expression by treatment with a casein kinase 2 inhibitor successfully reduced training time required for imprinting. These results suggest that imprinting stimuli activate post-synaptic NR2B/NR1 in HDCo cells, increase NR2B/NR1 signaling through up-regulation of its expression, and induce LTP and memory acquisition. The study investigated the neural mechanism underlying juvenile learning. In the initial stage of chick imprinting, NMDA receptors containing the NMDA receptor subunit 2B (NR2B) are activated, surface expression of NR2B/NR1 (NMDA receptor subunit 1) is up-regulated, and consequently long-term potentiation is induced in the telencephalic neurons. We suggest that the positive feedback in the NR2B/NR1 activation is a unique process of juvenile learning, exhibiting rapid memory acquisition.
Assuntos
Galinhas/fisiologia , Retroalimentação Fisiológica/efeitos dos fármacos , Fixação Psicológica Instintiva/efeitos dos fármacos , Receptores de N-Metil-D-Aspartato/efeitos dos fármacos , Percepção Visual/efeitos dos fármacos , Animais , Animais Recém-Nascidos , Caseína Quinase II/antagonistas & inibidores , Estimulação Elétrica , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Antagonistas de Aminoácidos Excitatórios/farmacologia , Neurônios/efeitos dos fármacos , Estimulação Luminosa , Receptores de AMPA/efeitos dos fármacos , Receptores de N-Metil-D-Aspartato/genéticaRESUMO
Switching behaviors from aggression to submission in losers at the end of conspecific social fighting is essential to avoid serious injury or death. We have previously shown that the experience of defeat induces a loser-specific potentiation in the habenula (Hb)-interpeduncular nucleus (IPN) and show here that this is induced by acetylcholine. Calcium imaging and electrophysiological recording using acute brain slices from winners and losers of fighting behavior in zebrafish revealed that the ventral IPN (vIPN) dominates over the dorsal IPN in the neural response to Hb stimulation in losers. We also show that GluA1 α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits on the postsynaptic membrane increased in the vIPN of losers. Furthermore, these loser-specific neural properties disappeared in the presence of an α7 nicotinic acetylcholine receptor (nAChR) antagonist and, conversely, were induced in brain slices of winners treated with α7 nAChR agonists. These data suggest that acetylcholine released from Hb terminals in the vIPN induces activation of α7 nAChR followed by an increase in postsynaptic membrane GluA1. This results in an increase in active synapses on postsynaptic neurons, resulting in the potentiation of neurotransmissions to the vIPN. This acetylcholine-induced neuromodulation could be the neural foundation for behavioral switching in losers. Our results could increase our understanding of the mechanisms of various mood disorders such as social anxiety disorder and social withdrawal.
Assuntos
Habenula , Núcleo Interpeduncular , Receptores Nicotínicos , Animais , Núcleo Interpeduncular/metabolismo , Receptores Nicotínicos/metabolismo , Ácido Glutâmico , Acetilcolina/farmacologia , Habenula/fisiologia , Peixe-Zebra/metabolismoRESUMO
The habenula is among the evolutionarily most conserved parts of the brain and has been known for its role in the control of behavior to cope with aversive stimuli. Recent studies in zebrafish have revealed the novel roles of the two parallel neural pathways from the dorsal habenula to its target, the interpeduncular nucleus, in the control of behavioral choice whether to behave dominantly or submissively in the social conflict. They are modifiable depending on the internal state of the fish such as hunger and play another important role in orientation of attention whether to direct it internally to oneself or externally to others. These studies, therefore, are revealing a novel role for the habenula as the integrated switchboard for concertedly controlling behavior either as a winner with self-centered (idiothetic) attention or a loser with others-oriented (allothetic) attention.
Assuntos
Habenula , Núcleo Interpeduncular , Animais , Atenção , Vias Neurais , Peixe-ZebraRESUMO
Many animals fight for dominance between conspecifics. Because winners could obtain more resources than losers, fighting outcomes are important for the animal's survival, especially in a situation with insufficient resources, such as hunger. However, it remains unclear whether and how hunger affects fighting outcomes. Herein, we investigate the effects of food deprivation on brain activity and fighting behaviors in zebrafish. We report that starvation induces winning in social conflicts. Before the fights, starved fish show potentiation of the lateral subregion of the dorsal habenula (dHbL)-dorsal/intermediate interpeduncular nucleus (d/iIPN) pathway, which is known to be essential for and potentiated after winning fights. Circuit potentiation is mediated by hypothalamic orexin/hypocretin neuropeptides, which prolong AMPA-type glutamate receptor (AMPAR) activity by increasing the expression of a flip type of alternative splicing variant of the AMPAR subunit. This mechanism may underlie how hungry vertebrates win fights and may be commonly shared across animal phylogeny.
Assuntos
Processamento Alternativo/genética , Habenula/fisiologia , Fome/fisiologia , Orexinas/metabolismo , Receptores de AMPA/genética , Comportamento Social , Sequência de Aminoácidos , Animais , Animais Geneticamente Modificados , Comportamento Animal , Potenciais Pós-Sinápticos Excitadores , Masculino , Receptores de AMPA/metabolismo , Transdução de Sinais , Inanição/genética , Peixe-ZebraRESUMO
Spontaneous correlated neuronal activity during early development spreads like a wave by recruiting a large number of neurons, and is considered to play a fundamental role in neural development. One important and as yet unresolved question is where the activity originates, especially at the earliest stage of wave expression. In other words, which part of the brain differentiates first as a source of the correlated activity, and how does it change as development proceeds? We assessed this issue by examining the spatiotemporal patterns of the depolarization wave, the optically identified primordial correlated activity, using the optical imaging technique with voltage-sensitive dyes. We surveyed the region responsible for the induction of the evoked and spontaneous depolarization waves in chick embryos, and traced its developmental changes. The results showed that the wave initially originated in a restricted area near the obex and was generated by multiple regions at later stages. We suggest that the upper cervical cord/lower medulla near the obex is the kernel that differentiates first as the source of the correlated activity, and that regional and temporal differences in neuronal excitability might underlie the developmental profile of wave generation in early chick embryos.
Assuntos
Potenciais de Ação/fisiologia , Sistema Nervoso Central/fisiologia , Corantes/química , Neurônios/fisiologia , Óptica e Fotônica/métodos , Coloração e Rotulagem/métodos , Fatores Etários , Animais , Relógios Biológicos/fisiologia , Tronco Encefálico/embriologia , Tronco Encefálico/fisiologia , Comunicação Celular/fisiologia , Diferenciação Celular/fisiologia , Membrana Celular/fisiologia , Sistema Nervoso Central/embriologia , Embrião de Galinha , Vias Eferentes/embriologia , Vias Eferentes/fisiologia , Eletrofisiologia/instrumentação , Eletrofisiologia/métodos , Potenciais da Membrana/fisiologia , Vias Neurais/fisiologia , Neurogênese/fisiologia , Óptica e Fotônica/instrumentação , Formação Reticular/embriologia , Formação Reticular/fisiologia , Medula Espinal/embriologia , Medula Espinal/fisiologia , Fatores de TempoRESUMO
The midbrain roof is a retinorecipient region referred to as the optic tectum in lower vertebrates, and the superior colliculus in mammals. The retinal fibers projecting to the tectum transmit visual information to tectal retinorecipient neurons. Periventricular neurons are a subtype of these neurons that have their somata in the deepest layer of the teleostean tectum and apical dendrites ramifying at more superficial layers consisting of retinal fibers. The retinotectal synapses between the retinal fibers and periventricular neurons are glutamatergic, and ionotropic glutamate receptors mediate the transmission in these synapses. This transmission involves long-term potentiation, and is modulated by hormone action. Visual information processed in the periventricular neurons is transmitted to adjacent tectal cells and target nuclei of periventricular neuron axonal branches, some of which relay the visual information to other brain areas controlling behavior. We demonstrated that periventricular neurons play a principal role in visual information processing in the teleostean optic tectum; the effects of tectal output on behavior is discussed also in the present review.
Assuntos
Neurônios/metabolismo , Retina , Colículos Superiores , Vias Visuais , Animais , Comportamento Animal/fisiologia , Hormônio Liberador de Gonadotropina/metabolismo , Memória , Neurônios/citologia , Retina/citologia , Retina/metabolismo , Colículos Superiores/citologia , Colículos Superiores/fisiologia , Vias Visuais/anatomia & histologia , Vias Visuais/fisiologiaRESUMO
Using voltage-sensitive dye recording, we traced the ontogenetic expression of neural excitability related to the glossopharyngeal nerve (N. IX) and the vagus nerve (N. X) in the embryonic chick brainstem. At the 3.5-day embryonic stage, by averaging optical signals, we succeeded in recording very small action potential-related optical responses (DeltaI/I<10(-4)) induced by N. IX stimulation in the nucleus of the glossopharyngeal nerve (motor nucleus). This suggests that glossopharyngeal excitability in the motor nucleus is first generated no later than this developmental stage. On the other hand, action potential-related optical responses induced by N. X stimulation were first detected at the 4-day embryonic stage. Comparison with morphogenesis indicated that glossopharyngeal and vagal motoneurons acquire their excitability and send their axons to the periphery soon after they leave the proliferative pool.
Assuntos
Tronco Encefálico/embriologia , Nervo Glossofaríngeo/embriologia , Nervo Vago/embriologia , Potenciais de Ação/fisiologia , Animais , Tronco Encefálico/fisiologia , Embrião de Galinha , Corantes , Estimulação Elétrica , Nervo Glossofaríngeo/fisiologia , Técnicas de Cultura de Órgãos , Nervo Vago/fisiologiaRESUMO
We examined the intracellular Ca2+ ([Ca2+]i) elevation evoked by GABA in an 8-day embryonic chick brainstem slice using a Ca imaging technique with Ca green-1 AM. When small quantities of GABA were pressure-ejected on the surface of the slice, the [Ca2+]i elevation was clearly detected. The GABA-induced [Ca2+]i elevation was eliminated in a Ca2+-free solution, whereas the previously reported GABA-induced light-scattering change was independent of extracellular Ca2+. Although, micro-application of glycine or glutamate also induced [Ca2+]i elevation, these changes were smaller than that by GABA. These results suggest that the GABA-induced [Ca2+]i elevation is due to Ca2+ entry resulting from membrane depolarization and may play an important role in the development of the central nervous system (CNS).
Assuntos
Tronco Encefálico/efeitos dos fármacos , Cálcio/metabolismo , Líquido Extracelular/efeitos dos fármacos , Ácido gama-Aminobutírico/farmacologia , Animais , Tronco Encefálico/metabolismo , Embrião de Galinha , Líquido Extracelular/metabolismo , Técnicas In Vitro , Fatores de TempoRESUMO
The efferent connections and axonal and dendritic morphologies of periventricular neurons were examined in the optic tectum of rainbow trout to classify periventricular efferent neurons in salmonids. Among the target nuclei of tectal efferents, tracer injections to the following four structures labeled periventricular neurons: the area pretectalis pars dorsalis (APd), nucleus pretectalis superficialis pars magnocellularis (PSm), nucleus ventrolateralis of torus semicircularis (TS), and nucleus isthmi (NI). Two types of periventricular neurons were labeled by injections to the APd. One of them had an apical dendrite ramifying at the stratum fibrosum et griseum superficiale (SFGS), with an axon that bifurcated into two branches at the stratum griseum centrale (SGC), and the other had an apical dendrite ramifying at the SGC. Two types of periventricular neurons were labeled after injections to the TS. One of them had an apical dendrite ramifying at the boundary between the stratum opticum (SO) and the SFGS, and the other had dendritic branches restricted to the stratum album centrale or stratum periventriculare. Injections to the PSm and NI labeled periventricular neurons of the same type with an apical dendrite ramifying at the SO and a characteristic axon that split into superficial and deep branches projecting to the PSm and NI, respectively. This cell type also possessed axonal branches that terminated within the tectum. These results indicate that periventricular efferent neurons can be classified into at least five types that possess type-specific axonal and dendritic morphologies. We also describe other tectal neurons labeled by the present injections.
Assuntos
Neurônios Eferentes/classificação , Neurônios Eferentes/citologia , Colículos Superiores/citologia , Truta/anatomia & histologia , Vias Visuais/citologia , Animais , Feminino , MasculinoRESUMO
When animals encounter conflict they initiate and escalate aggression to establish and maintain a social hierarchy. The neural mechanisms by which animals resolve fighting behaviors to determine such social hierarchies remain unknown. We identified two subregions of the dorsal habenula (dHb) in zebrafish that antagonistically regulate the outcome of conflict. The losing experience reduced neural transmission in the lateral subregion of dHb (dHbL)-dorsal/intermediate interpeduncular nucleus (d/iIPN) circuit. Silencing of the dHbL or medial subregion of dHb (dHbM) caused a stronger predisposition to lose or win a fight, respectively. These results demonstrate that the dHbL and dHbM comprise a dual control system for conflict resolution of social aggression.
Assuntos
Agressão/fisiologia , Conflito Psicológico , Habenula/fisiologia , Negociação , Animais , Hierarquia Social , Núcleo Interpeduncular/fisiologia , Transmissão Sináptica , Peixe-ZebraRESUMO
Retinotectal transmission has not yet been well characterized at the cellular level in the optic tectum. To address this issue, we used a teleost, the rainbow trout, and characterized periventricular neurons as postsynaptic cells expected to receive the retinotectal inputs to the optic tectum. The somata of periventricular neurons are localized in the upper zone of the stratum periventriculare (SPV), whereas the lower zone of the SPV comprises the cell body layer of radial glial cells. Ca2+ imaging identified functional ionotropic glutamate receptors in periventricular neurons. We also cloned cDNAs encoding the NR1 subunit of N-methyl-D-aspartic acid (NMDA) receptors and the GluR2 subunit of (+/-)-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptors, and detected their mRNAs in periventricular neurons by in situ hybridization. The presence of the receptor subunit proteins was also confirmed in the dendrites of periventricular neurons by immunoblotting and immunohistochemistry. On the other hand, radial glial cells in the lower zone of the SPV did not respond to glutamate applications, and mRNA and immunoreactivities of ionotropic glutamate receptors were not detected in glial cells. The present findings suggest that glutamatergic transmission at synapses between retinotectal afferents and periventricular neurons is mediated by the functional NMDA and AMPA receptors.
Assuntos
Oncorhynchus mykiss/fisiologia , Retina/fisiologia , Colículos Superiores/fisiologia , Transmissão Sináptica/fisiologia , Sequência de Aminoácidos/genética , Animais , Ácido Glutâmico/farmacologia , Dados de Sequência Molecular , Retina/efeitos dos fármacos , Colículos Superiores/efeitos dos fármacosRESUMO
We examined synaptic plasticity in the optic tectum of rainbow trout by extracellular recordings. We found that the field-excitatory postsynaptic potential in the retinotectal synapses was potentiated by repetitive stimuli of 1.0 Hz for 20 s to the retinotectal afferents. The long-term potentiation (LTP) developed slowly, and was maintained for at least 2 h. Applications of an antagonist for N-methyl-D-aspartic acid (NMDA) receptors or Mg2+ -free saline showed that activation of NMDA receptors was required to form the LTP beyond the induction period. The present findings indicate that presynaptic stimulation in the retinotectal synapses causes LTP mediated by NMDA receptors in the optic tectum of rainbow trout.
Assuntos
Potenciação de Longa Duração/fisiologia , Colículos Superiores/fisiologia , Valina/análogos & derivados , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Anestésicos Locais/farmacologia , Animais , Cloreto de Cádmio/farmacologia , Cálcio/metabolismo , Estimulação Elétrica , Agonistas de Aminoácidos Excitatórios/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/efeitos da radiação , Potenciação de Longa Duração/efeitos dos fármacos , Potenciação de Longa Duração/efeitos da radiação , Oncorhynchus mykiss , Tetrodotoxina/farmacologia , Fatores de Tempo , Valina/farmacologiaRESUMO
Anticipation of danger at first elicits panic in animals, but later it helps them to avoid the real threat adaptively. In zebrafish, as fish experience more and more danger, neurons in the ventral habenula (vHb) showed tonic increase in the activity to the presented cue and activated serotonergic neurons in the median raphe (MR). This neuronal activity could represent the expectation of a dangerous outcome and be used for comparison with a real outcome when the fish is learning how to escape from a dangerous to a safer environment. Indeed, inhibiting synaptic transmission from vHb to MR impaired adaptive avoidance learning, while panic behavior induced by classical fear conditioning remained intact. Furthermore, artificially triggering this negative outcome expectation signal by optogenetic stimulation of vHb neurons evoked place avoidance behavior. Thus, vHb-MR circuit is essential for representing the level of expected danger and behavioral programming to adaptively avoid potential hazard.
Assuntos
Aprendizagem da Esquiva/fisiologia , Habenula/fisiologia , Vias Neurais/fisiologia , Núcleos da Rafe/fisiologia , Neurônios Serotoninérgicos/fisiologia , 5,7-Di-Hidroxitriptamina/metabolismo , Potenciais de Ação/fisiologia , Adaptação Psicológica/fisiologia , Animais , Animais Geneticamente Modificados , Condicionamento Clássico/fisiologia , Sinais (Psicologia) , Medo/fisiologia , Habenula/citologia , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Masculino , Neurotransmissores/metabolismo , Núcleos da Rafe/citologia , Serotonina/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteína Vesicular 2 de Transporte de Glutamato/genética , Proteína Vesicular 2 de Transporte de Glutamato/metabolismo , Peixe-Zebra , Proteínas de Peixe-Zebra/genética , Proteínas de Peixe-Zebra/metabolismoRESUMO
The encoding of long-term associative memories for learned behaviors is a fundamental brain function. Yet, how behavior is stably consolidated and retrieved in the vertebrate cortex is poorly understood. We trained zebrafish in aversive reinforcement learning and measured calcium signals across their entire brain during retrieval of the learned response. A discrete area of dorsal telencephalon that was inactive immediately after training became active the next day. Analysis of the identified area indicated that it was specific and essential for long-term memory retrieval and contained electrophysiological responses entrained to the learning stimulus. When the behavioral rule changed, a rapid spatial shift in the functional map across the telencephalon was observed. These results demonstrate that the retrieval of long-term memories for learned behaviors can be studied at the whole-brain scale in behaving zebrafish in vivo. Moreover, the findings indicate that consolidated memory traces can be rapidly modified during reinforcement learning.
Assuntos
Aprendizagem da Esquiva/fisiologia , Mapeamento Encefálico , Encéfalo/fisiologia , Rememoração Mental/fisiologia , Potenciais de Ação/genética , Animais , Animais Geneticamente Modificados , Biotina/metabolismo , Encéfalo/citologia , Encéfalo/cirurgia , Cálcio/metabolismo , Sinalização do Cálcio/genética , Sinais (Psicologia) , Proteínas ELAV/genética , Proteínas ELAV/metabolismo , Eletrólise , Reação de Fuga/fisiologia , Lateralidade Funcional/genética , Glutamato Descarboxilase/genética , Glutamato Descarboxilase/metabolismo , Neuroimagem , Neurônios/fisiologia , Parvalbuminas/metabolismo , Técnicas de Patch-Clamp , Natação/fisiologia , Fatores de Tempo , Proteínas Vesiculares de Transporte de Glutamato/genética , Proteínas Vesiculares de Transporte de Glutamato/metabolismo , Peixe-ZebraRESUMO
During development, correlated neuronal activity plays an important role in the establishment of the central nervous system (CNS). We have previously reported that a widely propagating correlated neuronal activity, termed the depolarization wave, is evoked by various sensory inputs. A remarkable feature of the depolarization wave is that it spreads broadly through the brain and spinal cord. In the present study, we examined whether the depolarization wave occurs spontaneously in the embryonic rat CNS and, if so, where it originates. In E15-16 rat embryos, spontaneous optically-revealed signals appeared in association with the rhythmic discharges of cranial motoneurons and propagated widely with similar characteristics to the evoked depolarization wave. At E15, the spontaneous wave mostly originated in the cervical to upper lumbar cords. At E16, the wave was predominantly generated in the lumbosacral cord although a wave associated with the second oscillatory burst was initiated in the rostral cord. At E16, a few waves also originated in the rostral ventrolateral medulla and the dorsomedial pons. When the influence of the caudal cord was removed by transecting the spinal cord, the contribution of the medulla and pons became more significant. These results show that the depolarization wave can be triggered by the spontaneous activity of multiple neuronal populations which are distributed widely from the pons to the lumbosacral cord, although the spinal cord usually plays a predominant role. This network possibly works as a self-distributing system that maintains the incidence and complicated patterns of the correlated activity in the developing CNS.
Assuntos
Mapeamento Encefálico , Sistema Nervoso Central/embriologia , Sistema Nervoso Central/fisiologia , Embrião de Mamíferos/fisiologia , Potenciais Evocados/fisiologia , Fatores Etários , Animais , Nervos Cranianos/fisiologia , Diagnóstico por Imagem , Estimulação Elétrica/métodos , Potenciais Evocados/efeitos da radiação , Técnicas In Vitro , Ratos , Ratos Wistar , Rodanina/análogos & derivados , Rodanina/metabolismo , Tiazolidinas/metabolismoRESUMO
Gonadotropin-releasing hormone (GnRH) is a hypophysiotropic decapeptide that stimulates the release of gonadotropins from the pituitary. In addition, there are extra-hypothalamic GnRH neurons that project to all regions of the brain and whose function remains unknown. Here, we investigated the effects of GnRH on retinotectal synaptic transmission, the synapses of which are formed between retinal fibers and tectal periventricular neurons that express GnRH receptor mRNA. We used rainbow trout as our study model. The excitatory postsynaptic currents (EPSCs), which were evoked by electrical stimulation of the retinal fibers and recorded in periventricular neurons, were suppressed by antagonists of ionotropic glutamate receptors. EPSCs were increased by application of each of two types of GnRH (GnRH2 and GnRH3) in the trout tectum. Such facilitation lasted for at least 10 min after application of the GnRH. To our knowledge, this is the first report of GnRH modulating conventional synaptic transmission in the brain, suggesting that tectal GnRH enhances tectal sensitivity for retinal inputs. Furthermore, such long-lasting facilitation might occur across all the brain regions innervated by GnRH neurons, and GnRH might simultaneously switch neuronal activities in the brain regions relevant to reproductive behaviors.
Assuntos
Hormônio Liberador de Gonadotropina/farmacologia , Retina/fisiologia , Colículos Superiores/citologia , Sinapses/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , 2-Amino-5-fosfonovalerato/farmacologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Animais , Relação Dose-Resposta a Droga , Antagonistas de Aminoácidos Excitatórios/farmacologia , Feminino , Técnicas In Vitro , Potenciais da Membrana/efeitos dos fármacos , Oncorhynchus mykiss , Técnicas de Patch-Clamp/métodosRESUMO
To map the functional synaptic organization over a wide area in the optic tectum, we directly monitored two-dimensional propagation of postsynaptic depolarization evoked by firing of retinotectal afferents in optic tectum slices prepared from rainbow trout (Oncorhynchus mykiss), using a voltage-sensitive dye and a photodiode array system. The postsynaptic responses to afferent stimulation first propagated in the stratum opticum and stratum fibrosum et griseum superficiale in an anterograde fashion in the afferents and then expanded vertically into the deep layers. This vertical propagation appeared to occur along a bundle-like structure that corresponded well with a cluster of neurons whose somata are located in the stratum periventriculare. Pharmacological studies showed that these postsynaptic responses were mediated by ionotropic glutamate receptors. On the other hand, the optical signals appeared to consist of at least two components (a transient signal and a slow signal). The second transient signal summated with the first slow signal by paired stimulation, suggesting that the transient and slow signals originated from different cell types. Taken together, these results showed that the functional synaptic organization of the teleost optic tectum comprises of two depolarization-signal propagating paths along a horizontal layer structure and a vertical bundle-like structure and that these synaptic responses occur via glutamatergic transmission.