Amino acid neurotransmission between fimbria-fornix fibers and neurons in the lateral septum of the rat: a microiontophoretic study

Long-term depression of excitatory transmission in the lateral septum

Neurons in the lateral septum (LS) integrate glutamatergic synaptic inputs, primarily from hippocampus, and send inhibitory projections to brain regions involved in reward and the generation of motivated behavior. Motivated learning and drugs of abuse have been shown to induce long-term changes in the strength of glutamatergic synapses in the LS, but the cellular mechanisms underlying long-term synaptic modification in the LS are poorly understood. Here, we examined synaptic transmission and long-term depression (LTD) in brain slices prepared from male and female C57BL/6 mice. No sex differences were observed in whole cell patch-clamp recordings of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-R)- and N-methyl-d-aspartate receptor (NMDA-R)-mediated currents. Low-frequency stimulation of the fimbria fiber bundle (1 Hz 15 min) induced LTD of the LS field excitatory postsynaptic potential (fEPSP). Induction of LTD was blocked by the NMDA-R antagonist (d)-2-amino-5-phosphonovaleric acid (APV), but not the selective antagonist of GluN2B-containing NMDA-Rs ifenprodil. These results demonstrate the NMDA-R dependence of LTD in the LS. The LS is a sexually dimorphic structure, and sex differences in glutamatergic transmission have been reported in vivo; our results suggest sex differences observed in vivo result from network activity rather than intrinsic differences in glutamatergic transmission.NEW & NOTEWORTHY The lateral septum (LS) integrates information from hippocampus and other regions to provide context-dependent (top down or higher order) regulation of mood and motivated behavior. Learning and drugs of abuse induce long-term changes in the strength of glutamatergic projections to the LS; however, the cellular mechanisms underlying such changes are poorly understood. Here, we demonstrate there are no apparent sex differences in fast excitatory transmission and that long-term synaptic depression in the LS is NMDA-R dependent.

Dynamic changes in extracellular release of GABA and glutamate in the lateral septum during social play behavior in juvenile rats: Implications for sex-specific regulation of social play behavior

Social play is a motivated and rewarding behavior that is displayed by nearly all mammals and peaks in the juvenile period. Moreover, social play is essential for the development of social skills and is impaired in social disorders like autism. We recently showed that the lateral septum (LS) is involved in the regulation of social play behavior in juvenile male and female rats. The LS is largely modulated by GABA and glutamate neurotransmission, but their role in social play behavior is unknown. Here, we determined whether social play behavior is associated with changes in the extracellular release of GABA and glutamate in the LS and to what extent such changes modulate social play behavior in male and female juvenile rats. Using intracerebral microdialysis in freely behaving rats, we found no sex difference in extracellular GABA concentrations, but extracellular glutamate concentrations are higher in males than in females under baseline conditions and during social play. This resulted in a higher glutamate/GABA concentration ratio in males vs. females and thus, an excitatory predominance in the LS of males. Furthermore, social play behavior in both sexes is associated with significant increases in extracellular release of GABA and glutamate in the LS. Pharmacological blockade of GABA-A receptors in the LS with bicuculline (100 ng/0.5 μl, 250 ng/0.5 μl) dose-dependently decreased the duration of social play behavior in both sexes. In contrast, pharmacological blockade of ionotropic glutamate receptors (NMDA and AMPA/kainate receptors) in the LS with AP-5+CNQX (2mM+0.4mM/0.5 μl, 30 mM+3mM/0.5 μl) dose-dependently decreased the duration of social play behavior in females, but did not alter social play behavior in males. Together, these data suggest a role for GABA neurotransmission in the LS in the regulation of juvenile social play behavior in both sexes, while glutamate neurotransmission in the LS is involved in the sex-specific regulation of juvenile social play behavior.

Modulatory actions of steroid hormones and neuropeptides on electrical activity in brain

Electrophysiological studies over the past decades have shown that many compounds in addition to 'classical' neurotransmitters affect electrical activity in the brain. These compounds include neuropeptides synthesized in brain as well as compounds which are released from peripheral sources and subsequently enter the brain compartment, such as corticosteroid hormones from the adrenal gland. In the present review, this principle is illustrated by describing the effects of two substances, i.e. vasopressin and corticosterone. Neuropeptides and corticosteroid hormones add at least two essential aspects to information processing in the brain. First, they both act conditional, i.e. they modulate the actions of 'classical' neurotransmitters, rather than changing basal neuronal activity by themselves. Second, the time-frame in which modulation of electrical properties takes place differs from that generally seen with 'classical' neurotransmitters. Neuropeptides modulate electrical activity over a period of minutes, while effects of corticosteroid hormones usually become apparent after at least an hour but then last for hours. In this way, neuropeptides and steroid hormones expand the repertoire of responses through which the brain reacts to environmental challenges.

Role of corticotropin-releasing factor, vasopressin and the autonomic nervous system in learning and memory

Learning and memory are essential requirements for every living organism in order to cope with environmental demands, which enables it to adapt to changes in the conditions of life. Research on the effects of hormones on memory has focused on hormones such as adrenocorticotropic hormone (ACTH), glucocorticoids, vasopressin, oxytocin, epinephrine, corticotropin-releasing factor (CRF) that are released into the blood and brain following arousing or stressful experiences. Most of the information have been derived from studies on conditioned behavior, in particular, avoidance behavior in rats. In these tasks, an aversive situation was used as a stimulus for learning. Aversive stimuli are associated with the release of stress hormones and neuropeptides. Many factors play a role in different aspects of learning and memory processes. Neuropeptides not only affect attention, motivation, concentration and arousal or vigilance, but also anxiety and fear. In this way, they participate in learning and memory processes. Furthermore, neuropeptides such as CRF and vasopressin modulate the release of stress hormones such as epinephrine. In turn, systemic catecholamines enhance memory consolidation. CRF and vasopressin are colocalized in neurons from the nucleus paraventricularis, which project to nuclei in the brainstem involved in autonomic regulation. The objective of this paper is to discuss the role of CRF, vasopressin, and the autonomic nervous system (ANS) in learning and memory processes. Both CRF and vasopressin have effects in the same direction on behavior, learning and memory processes and stress responses (release of catecholamines and ACTH). These neuropeptides may act synergistically or in a concerted action aimed to learn to adapt to environmental demands.

Behavioral pharmacology of neuropeptides related to melanocortins and the neurohypophyseal hormones

Neuropeptides are peptides which affect the nervous system. They are derived from large precursor molecules. These are converted to neurohormones, neuropeptides of the "first generation", which can be further converted to neuropeptides of the "second generation". This review is a brief survey of the nervous system effects of neuropeptides derived from pro-opiomelanocortin (POMC) and the neurohypophyseal hormones. Processing of these molecules results in neuropeptides of the first and second generation which have similar, different, more selective or even opposite effects. Among those are effects on learning and memory processes, grooming, stretching and yawning, social, sexual and rewarded behavior, aging and nerve regeneration, thermoregulation, pain, sensitivity to seizures, and cardiovascular control. Results of animal studies as well as those of clinical studies suggest that these neuropeptides may be beneficial in aging, neuropathy, memory disturbances and schizophrenia. Most of these nervous system effects in animal studies were found before receptors in the nervous system for the various neuropeptides were detected. G-protein-coupled receptors for the neuropeptides of the "first generation", i.e., melanocortin receptors, opioid receptors, and neurohypophyseal hormone receptors have been found, in contrast to the receptors for neuropeptides of the "second generation", although there are indications that G-protein coupled receptors for these may be present in the brain.

Effects of vasopressin and related peptides on neurons of the rat lateral septum and ventral hippocampus

The effects of vasopressin (VP), VP fragments and propressophysin glycopeptide on neuronal activities in the septum-hippocampus complex of rats were studied in vitro and in vivo. The frequency of the hippocampus theta rhythm in Brattleboro rats homozygous for diabetes insipidus was significantly slower than that of heterozygous litter mates and normal rats. Intracerebroventricular micro-injection of des-glycine-amide vasopressin corrected for several hours the frequency deficit of the theta rhythm in the homozygous Brattleboro rats and the centrally administered VP slowed down theta rhythm in normal rats. Microinotophoretically administered VP excited single neurons in the lateral septum of ventral hippocampus, and/or facilitated the responses of these neurons to glutamate and to stimulation of the glutamatergic afferent fibers in the fimbria bundle. The excitatory effects of VP vanished within seconds after termination of the peptide administration, however, the peptide-induced enhancement of glutamate and syntatically induced excitations were sustained for up to 60 min after the peptide administration. In vitro, pM concentrations of VP, VP 4-8 and C-terminus glycopeptide of propresophysin facilitated for 30-60 min the glutamate-mediated EPSPs in neurons of the lateral septum or the ventral hippocampus. The EPSPs increase in the lateral septum neurons was not prevented by pretreatment with antagonist of the V1a type of the vasopressin receptor. The resting membrane potential and input resistance were not affected by the peptides. A low-frequency electrical stimulation in the diagonal Band of Broca or in the Bed nucleus of the stria terminals, sources of the vasopressinergic innervation of the septum, facilitated the negative wave of the filed potentials responses evoked in the lateral septum by stimulating the fimbria bundle fibers in control Long-Evans and Brattleboro rats heterozygous for diabetes insipidus. The field potential increase was sustained for several hours after the stimulation, and it was not occluded by long-term potentiation elicited by high frequency stimulation of the fimbria bundle afferent fibers. Brattleboro rats homozygous for diabetes insipidus failed to show the filed potential increase after the diagonal band stimulation. It is suggested that the long-lasting facilitation of glutamate-mediated excitations might be a physiological action of the propressophysin-derived peptides in the septum-hippocampus complex which, in concert with other forms of synaptic plasticity like the long-term potentiation, facilitates the hippocampus-mediated forms of learning and memory. This action is presumably related to the memory enhancing effect of the propressophysin-derived peptides.

Contextual conditioned fear blocks the induction but not the maintenance of lateral septal LTP in behaving mice

High-frequency stimulation (HFS) of the fimbria induces long-term potentiation (LTP) in the lateral septum. This study was aimed at investigating the effect of contextual fear conditioning on septal LTP with the use of behaving C57 BL/6 mice as subjects. For the acquisition of contextual fear conditioning, animals were placed in a conditioning chamber, where they were subjected to footshocks (FSs, 0.6 mA); the following day (retention), animals were reexposed to the chamber. Animals from the first group received HFS in their home cages before being submitted to conditioning; animals from the second group were first submitted to conditioning before receiving HFS during reexposure to the conditioning chamber; animals from the third group were submitted to the same regimen as those from the second group, except that no FS was delivered in the conditioning chamber; and animals from the fourth group received FS in the conditioning chamber but were maintained in their home cages the day after for LTP induction. Before conditioning, animals from the first group, placed in a familiar context (home cage), displayed an LTP of the N3 wave of septal field potential. After conditioning, reexposure of these animals to the conditioning chamber produced a transient decrease in the amplitude of N3 but did not interfere with the duration of maintenance of LTP. Conversely, in animals from the second group, when HFS was applied during reexposure to the conditioning chamber the induction of LTP was totally blocked. However, mice from the two other groups (3rd and 4th) displayed normal levels of LTP. Taken together with previous findings, these data suggest that contextual conditioned fear may interfere with certain forms of learning via blockade of hippocampal-septal LTP.

Effects of intraseptally injected glutamatergic drugs on hippocampal sodium-dependent high-affinity choline uptake in "naive" and "trained" mice

We have previously reported that spatial reference memory (RM) training-induced alterations in hippocampal cholinergic activity as measured by sodium-dependent high-affinity choline uptake (SDHACU). Each training session was found to induce an immediate (30 s) increase in SDHACU followed (30 s to 15 min posttest) by a deactivation and long-lasting inhibition (15 min to 24 h) of this cholinergic marker. The present experiments were designed to assess the role of septal glutamatergic receptors in this posttraining cholinergic deactivation. In the first experiment, the effects of intraseptal injections of different doses of glutamic acid and glutamatergic antagonists (kynurenic acid, KYN, and AP5) on hippocampal SDHACU were studied in awake but otherwise resting (i.e., naive) mice. The results showed that glutamic acid at the lowest dose used (5 ng) produced a decrease in SDHACU, whereas both glutamatergic antagonists produced a dose-related increase in this cholinergic marker. It was concluded that septal glutamatergic receptors mediate a tonic inhibitory input on the cholinergic cells. Hence, in a second experiment the effect of intraseptal injections of KYN (5 ng) on the training-induced changes in hippocampal cholinergic activity were assessed following variable amounts of radial maze RM training. Trained mice were injected 20 min before the first or the ninth training session and killed 30 s or 15 min posttraining for determination of SDHACU. KYN slowed the posttesting cholinergic deactivation (disinhibition), this effect being more marked in good learners than in bad learners. The present findings suggest that septal glutamatergic receptors mediate an inhibitory input on the cholinergic cells, and that this input could play a role in memory consolidation.

A theoretical and neurophysiological consideration on the pathogenesis of positive symptoms of schizophrenia: implications of dopaminergic function in the emotional circuit

The implications of the emotional circuit and the gating mechanism by dopamine (DA) proposed by Maeda in the pathogenesis of positive symptoms of schizophrenia were reconsidered based upon recent advances and findings in the fields of neurophysiology and neuropharmacology and in biological studies of schizophrenia. The gating mechanism by DA was partly supported by new evidence that glutamatergic or GABAergic neurotransmission, which mediates the hippocampo-lateral septal or the piriform cortico-amygdaloid neuronal connections, is likely to be modulated by DA. The compensation-facilitating or gating functions of DA was considered again to play an important role in producing positive symptoms in schizophrenics, who have been suggested to have morphological abnormalities in the limbic system or in the prefrontal cortex prior to the appearance of positive symptoms.

A comparative study of age-related changes in inhibitory processes and long-term potentiation in the lateral septum of mice

Anaesthetized C57 BL/6 mice of different ages (young: 5 months; middle-aged: 15 months; and old: 21 months) were used to determine whether aging alters the efficiency of synaptic inhibition and long-term potentiation (LTP) in the lateral septum (LS). Electrical stimulation of the fimbria induced field potentials in the ipsilateral LS comprising two initial negative components (N2 and N3) followed by a positive wave of low amplitude. Paired-pulse experiments showed a facilitation of the N2 component and a concomitant depression of the N3 components. Facilitation of the N2 component was stronger in both middle-aged and old mice as compared to young mice, whereas an inverse pattern of changes was observed for inhibition of the N3 component. High-frequency stimulation of the fimbria produced a persistent increase in the N3 amplitude. This LTP was of significantly higher amplitude in both young and middle-aged mice as compared to old mice. These results suggest that aging impairs both inhibitory processes and synaptic plasticity in the mouse LS, but that inhibitory processes appear to be affected earlier.

Catecholaminergic, GABAergic, and hippocamposeptal innervation of GABAergic "somatospiny" neurons in the rat lateral septal area

This study deals with the neurochemical characterization of the rat lateral septal area (LSA) somatospiny neurons and their innervation by hippocamposeptal, catecholaminergic, and GABAergic fibers. Electron microscopic single and double immunostaining methods were used to label catecholaminergic fibers and GABAergic cells and boutons. Axon terminals originating in the hippocampus were labeled by acute anterograde axon degeneration induced by fimbria-fornix transection 36 hours before sacrifice. Three types of experiments were performed. The convergent catecholaminergic and hippocamposeptal innervation of LSA somatospiny neurons was studied by combining immunostaining for tyrosine hydroxylase (TH) with fimbria-fornix transection. GABAergic neurons and their hippocamposeptal afferents were identified and characterized in colchicine pretreated animals immunostained for glutamic acid decarboxylase (GAD) combined with fimbria-fornix transection. The third experiment aimed at simultaneously visualizing the relationships between catecholaminergic boutons, hippocamposeptal excitatory amino acid containing axon terminals and GABAergic profiles by double immunostaining for TH (the PAP technique) and GAD (the immunogold method) combined with fimbria-fornix transection. The results are summarized as follows: 1) The same LSA somatospiny neurons receive synaptic inputs from the hippocampus and TH immunoreactive fibers which form pericellular baskets around these cells. 2) LSA somatospiny neurons are GABAergic and are postsynaptic targets of GABAergic boutons with unknown origin and hippocamposeptal axon terminals. 3) The double immunostaining experiment, finally, provided direct evidence that the same GABAergic somatospiny neurons are postsynaptic targets of both catecholaminergic and hippocamposeptal afferents. The synaptic interconnections described in this study provide anatomical basis for a better understanding of the action of catecholamines, excitatory amino acids, and GABA on the activity of LSA neurons.

The dose-response relationship for N-methyl-D-aspartate currents in cultured rat septal neurons: effects of magnesium ions and 2-amino-5-phosphonovaleric acid

Dose-response relations of the peak ionic current induced by N-methyl-D-aspartate (NMDA) under Mg-free vs normal saline (1.2 mM Mg) conditions were obtained in cultured neurons dissociated from septa of fetal rat brains using the single electrode voltage clamp method. The effect of D,L-2-amino-5-phosphonovalerate (APV) on the dose-response relationship was also studied. In the Mg-free condition, the response to NMDA increased progressively with dose up to 0.2 mM, at which point the response saturated up to 1 mM NMDA (ED50 was about 70 microM). At larger doses (1-3 mM) the response increased sharply. In normal saline the response increased up to doses of 10 mM, and there was no apparent plateau. In a comparison between the depressant effects of APV and Mg ions on the peak current value, the depression caused by APV (10-30 microM) at higher NMDA concentrations was larger than that caused by Mg.

Vasopressin facilitates excitatory transmission in slices of the rat dorso-lateral septum

The effect of vasopressin on neurons of the rat dorso-lateral septum (DLS) was studied in brain slices with intracellular microelectrodes. Two out of 13 neurons showed a small depolarization, spontaneous activity, and increased input resistances following a 15 min exposure to 10(-6) to 10(-8) M vasopressin (VP). These membrane effects disappeared completely within 3-5 min after the application. The remaining DLS neurons treated with these vasopressin concentrations showed an increase in glutamate-mediated excitatory postsynaptic potentials (EPSPs), evoked by stimulation of the fimbria fibers. As little as 10(-12) MVP increased these EPSPs markedly in nearly 80% of the cells studied. This increase in most of the cells disappeared within 15 min after the application period, whereas the increase in EPSPs induced by 10(-10) M VP outlasted the peptide application period for more than 30 min. Neither the blockade of GABA-ergic synaptic inhibition nor the pre-treatment of the neurons with d(CH2)5-Tyr(Me)-arginine vasopressin or 2-amino-5-phosphonovaleric acid (2-APV), antagonists for the V1 type of vasopressin receptor and NMDA receptors, respectively, interfered with the EPSPs potentiating effect of the peptide. It is concluded that a type of vasopressin receptor other then the V1 type is involved in the long-lasting potentiation of the primarily non-NMDA receptor mediated transmission in DLS neurons.

The C-terminal glycopeptide of propressophysin potentiates excitatory transmission in the rat lateral septum

Effects of peptides synthesized from the same precursor as vasopressin, i.e. the C-terminal 39-amino acid long glycopeptide and neurophysin II, were investigated for biological activities in electrophysiological experiments in brain slices of the rat lateral septum. These slices contained the glycopeptide as the predominant form and a fragment of it, amino acid sequence 22-39, as a minor form (8% of the glycopeptide 1-39), as shown by high performance liquid chromatography of extracts and by radioimmunoassay. None of the peptides, neurophysin II, the glycopeptide 1-39 and the fragment 22-39, tested in a concentration of 10(-12) M, had measurable effects on the resting membrane potential of the neurons. The glycopeptide and the fragment 22-39, however, increased, in some cells, for tens of minutes the excitatory postsynaptic potentials evoked in these neurons by stimulation of the fimbria fibers. The increase in input resistance, seen in many septal neurons treated with either of the peptides was not correlated with the excitatory postsynaptic potential increase. Neurophysin II affected neither the excitatory postsynaptic potentials nor the input resistance of the neurons. It is concluded that the glycopeptide 1-39 and the fragment 22-39 possess biological activities amongst which the facilitation of excitatory amino acid transmission on lateral septum neurons. Therefore, these peptides derived from the vasopressin precursor may act in concert with vasopressin to establish facilitation of excitatory transmission in the brain.

Vasopressin maintains long-term potentiation in rat lateral septum slices

In brain slices of normal Wistar and Long-Evans rats, brief high frequency stimulation of the fimbria fibers induced long-term potentiation (LTP) in excitatory transmission between these fimbria fibers and neurons of the lateral septum (LS). Slices prepared from diabetes insipidus (DI) Brattleboro rats, that contained no vasopressin (VP), consistently failed to maintain LTP in this excitatory transmission. Exogenous VP, administered to slices from DI Brattleboro rats shortly prior to the experiment or released from a subcutaneous depot in DI Brattleboro rats for several days prior to decapitation, corrected this failure. The maintenance of LTP in the LS in slices from Wistar and Long-Evans rats was prevented by D(CH2)5-Tyr(Me)-arginine VP, an antagonist for the V1 type of VP receptors. These results indicate an important role of VP in the maintenance of LTP in excitatory transmission in the LS. It is conjectured that the effects of VP on LS neurons are related to the role of the peptide in the maintenance of LTP and that these processes play a role in memory formation.

Excitatory amino acid-receptor-mediated EPSPs in rat dorsolateral septal nucleus neurones in vitro

1. Intracellular recordings were made from rat dorsolateral septal nucleus (DLSN) neurones in vitro. We investigated depolarizations resulting from pressure application of excitatory amino acids and compared these to synaptically evoked excitatory postsynaptic potentials (EPSPs). 2. EPSPs evoked by focal fimbrial afferent stimulation in saline with 30-50 microM-bicuculline and 1.2 mM-Mg2+ yielded a linear amplitude-voltage relationship: their reversal potential was -3 mV. These EPSPs exhibited little sensitivity to 2-amino-5-phosphonopentanoate (APV), an N-methyl-D-aspartate(NMDA)-receptor-specific antagonist, but were markedly depressed by kynurenic acid, a broad-spectrum excitatory amino acid antagonist. 3. In Mg2(+)-free solution, the amplitude and the duration of EPSPs were increased markedly masking the following inhibitory postsynaptic potential (IPSP) and the late hyperpolarizing potential (LHP). These facilitated and broadened EPSPs were sensitive to APV or Mg2+. The APV or Mg2(+)-sensitive component of the EPSP obtained by digital subtraction suggests a slower time course for the NMDA-receptor-mediated EPSP compared to the non-NMDA-receptor-mediated EPSP. On the other hand, in normal Mg2+ solution an EPSP evoked by either a single strong stimulus or by repetitive stimuli had APV-sensitive components. 4. The depolarizing potentials induced by pressure application of glutamate, kainate, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), quisqualate or NMDA were compared. The amplitude-voltage relationship of depolarizations induced by NMDA obtained in a normal Mg2+ solution was non-linear, but approached linearity when the same responses were recorded in a Mg2(+)-free solution. Depolarizations induced by kainate, AMPA and quisqualate were linear in their amplitude-voltage relationship in the presence or absence of Mg2+. APV blocked NMDA-induced depolarizations specifically, while kynurenic acid blocked all the depolarizations induced by NMDA, quisqualate, or kainate. 5. Our data demonstrate the existence of NMDA-receptor-mediated synaptic potentials in the rat DLSN, the characteristics of which are similar to those in other central nervous system regions.

Some properties of membrane current fluctuations induced by kainate, quisqualate, and NMDA in cultured septal neurons of rat

Ionic currents induced by glutamate, kainate, quisqualate, and N-methyl-D-aspartate (NMDA) in cultured septal neurons were analyzed by fluctuations analysis. The power spectrum (PWS) of NMDA current fluctuations always fitted a single Lorentzian. PWSs of the other agonists fitted the sum of two Lorentzians; however, the slopes of PWSs became larger and the PWSs became closer to single Lorentzians as the number of drug application increased. This may be explained in such a way that, in multiple conductance channels activated by these agonists, the high frequency component decreases the gating activity in later recordings, whereas the low frequency component keeps its gating kinetics.

N-acetyl-aspartylglutamate: binding sites and excitatory action in the dorsolateral septum of rats

In this study we examined the distribution of binding sites for [3H]N-acetyl-aspartylglutamate (NAAG) in the rat lateral septal nucleus (LSN) and the effect of iontophoretically applied NAAG on neuronal firing in this area. A high density of [3H]NAAG binding sites was found in the dorsolateral part of the LSN. Binding in the intermediate/ventral part of the LSN and medial septum was less dense. NAAG excited 75% of the dorsal neurons in the LSN, but only 36% of the cells in the intermediate/ventral part. Glutamic diethylester, an amino acid antagonist, depressed responses to NAAG to a similar extent as responses to quisqualate. The antagonist amino phosphonovaleric acid, which suppressed responses to N-methyl-D-aspartate almost completely, reduced NAAG-evoked responses only by 40%. A possible role of NAAG as excitatory transmitter in the LSN is discussed.

Rat lateral septum in slice preparation with viable transmission

A procedure is described which makes it possible to prepare slices from the rat brain that comprise nearly the entire lateral septum together with the major part of the fimbria-fornix afferent fibers to the lateral septum. The field potentials and monosynaptic excitation of lateral septal neurons elicited by electrical stimulation of the fimbria-fornix afferent fibers were employed to demonstrate that the neurophysiological features of the lateral septal neurons in vitro are similar to those found previously in vivo, and the synaptic transmission between fimbria-fornix afferent fibers and neurons of the lateral septum could be maintained in vitro without significant alterations for at least a 6-h period of incubation.

Effect of vasopressin, oxytocin and peptides derived from these hormones on field potential induced in lateral septum of rats by stimulation of the fimbria fornix

Superfusion of the dorsal surface of the septum with artificial cerebrospinal fluid containing 10(-10) M [Arg8]-vasopressin (VP) significantly increased the negative (N) wave in field potentials (FPs) elicited in the lateral septum (LS) of rats by stimulation of the fimbria-fornix. A similar increase in the FPs negativity was also observed following superfusion of the septum with [pGlu4, Cyt6] VP(4-9), [pGlu4, Cyt6] VP(4-8), [Cyt6] VP (5-9), desglycinamide9-VP and 1-deamino, 8-D-arginine-VP. However, for obtaining the effect with these peptides 10(3-4) times higher concentrations had to be used. Superfusion of the septum with 10(-8) M oxytocin (OX) elicited nearly the same N-wave increase as the 10(-8) M VP septal superfusion. The 10(-10) M concentration of OX as well as 10(-7) M [pGlu4, Cyt6] OX(4-9) and [pGlu4, Cyt6] OX(4-8) had little effect on the FPs negativity. The significance of these findings for the elucidation of the VP function in the LS is discussed.

Monoamine-induced responses in lateral septal neurons: influence of iontophoretically applied vasopressin

We examined the effect of iontophoretically applied noradrenaline (NA), dopamine (DA) and serotonin (5-HT) on the spontaneous activity of lateral septal neurons in rats and subsequently investigated if the observed responses to these monoamines were altered in the presence of arginine8-vasopressin (AVP). NA, DA and 5-HT induced a depression of the spontaneous activity in 70% of the spontaneously active neurons on which they were tested. Of the remaining neurons the majority was not affected by the monoamines. The responding cells differed from the non-responding cells in their localization in those parts of the lateral septum where dense monoamine-containing terminal networks have been visualized and in their significantly lower spontaneous activity. The effect of AVP on monoamine-induced responses was tested in neurons in which the spontaneous activity was not affected by the peptide itself. It appeared that in about 30% of these neurons, monoamine-induced inhibitions were reduced in presence of the peptide whereas in the majority of the neurons responses to the monoamines were not markedly altered by AVP. In contrast to this rather low occurrence of a clear AVP-effect on the monoamine responses, the peptide enhanced excitatory responses to glutamate in more than 75% of neurons tested during the same experiments. It was concluded that under these experimental conditions the effect of AVP on excitatory amino acid neurotransmission is more pronounced than on responses to putative monoaminergic neurotransmitters in the lateral septum.

Topographic organization of fimbria-fornix fibers projecting to the lateral septum of rats: a single and field response analysis

Single-unit and field potential responses, evoked by stimulation of restricted fimbria-fornix (fi-fx) segments, were recorded over the entire extent of the lateral septal complex (LSC) of rats in order to examine electrophysiologically the topographic organization of fi-fx fibers projecting to the LSC. We confirmed earlier studies showing that fi-fx fibers constitute a bilateral, monosynaptic excitatory projection to the LSC. The projection appeared to be topographically ordered in that medial fi-fx fibers innervated neurons in the mediodorsal part of the LSC whereas fibers coursing through progressively more lateral positions in the fi-fx activated neurons in gradually more lateral and ventral parts of the LSC. In addition to the topographic organization, a marked convergence of the fi-fx fibers on neurons located in the dorsolateral part of the LSC was apparent from both the single-unit and field potential experiments.

Arginine-vasopressin enhances the responses of lateral septal neurons in the rat to excitatory amino acids and fimbria-fornix stimuli

In the present study we investigated the effect of arginine-vasopressin (AVP) on responses induced in lateral septal neurons of the rat by iontophoretically administered excitatory and inhibitory amino acids and by synaptical stimuli delivered through fimbria-fornix (fi-fx) fibers. In the majority of the lateral septal neurons, iontophoretically applied AVP induced a marked increase in the excitatory responses to glutamate, aspartate, quisqualate and N-methyl-D-aspartate. The responses to excitatory amino acids frequently remained elevated several minutes after termination of the peptide administration. Inhibitory responses induced by GABA were not affected by AVP. The responsiveness of lateral septal single units to fi-fx stimuli was enhanced during iontophoretic administration of AVP. The enhanced responsiveness also appeared from experiments in which topically applied AVP induced a prolonged increase in the negative but not the positive wave of field potentials evoked in the lateral by fi-fx stimuli. The possible physiological significance of these findings is discussed.