The behavioral effects of lesions of the septum: a review

Glutamate, GABA, and glutamine are synchronously upregulated in the mouse lateral septum during the postpartum period

Dramatic structural and functional remodeling occurs in the postpartum brain for the establishment of maternal care, which is essential for the growth and development of young offspring. Glutamate and GABA signaling are critically important in modulating multiple behavioral performances. Large scale signaling changes occur in the postpartum brain, but it is still not clear to what extent the neurotransmitters glutamate and GABA change and whether the ratio of glutamate/GABA remains balanced. In this study, we examined the glutamate/GABA-glutamine cycle in the lateral septum (LS) of postpartum female mice. In postpartum females (relative to virgins), tissue levels of glutamate and GABA were elevated in LS and increased mRNA was found for the respective enzymes producing glutamate and GABA, glutaminase (Gls) and glutamate decarboxylase 1 and 2 (Gad1 and Gad2). The common precursor, glutamine, was elevated as was the enzyme that produces it, glutamate-ammonia ligase (Glul). Additionally, glutamate, GABA, and glutamine were positively correlated and the glutamate/GABA ratio was almost identical in the postpartum and virgin females. Collectively, these findings indicate that glutamate and GABA signaling are increased and that the ratio of glutamate/GABA is well balanced in the maternal LS. The postpartum brain may provide a useful model system for understanding how glutamate and GABA are linked despite large signaling changes. Given that some mental health disorders, including depression and schizophrenia display dysregulated glutamate/GABA ratio, and there is increased vulnerability to mental disorders in mothers, it is possible that these postpartum disorders emerge when glutamate and GABA changes are not properly coordinated.

Coupling of mesoscopic brain oscillations: recent advances in analytical and theoretical perspectives

Oscillatory brain activities have been traditionally studied in the context of how oscillations at a single frequency recorded from a single area could reveal functional insights. Recent advances in methodology used in signal analysis have revealed that cross-frequency coupling, within or between functional related areas, is more informative in determining the possible roles played by brain oscillations. In this review, we begin by describing the cellular basis of oscillatory field potentials and its theorized as well as demonstrated role in brain function. The recent development of mathematical tools that allow the investigation of cross-frequency and cross-area oscillation coupling will be presented and discussed in the context of recent advances in oscillation research based on animal data. Particularly, some pitfalls and caveats of methods currently available are discussed. Data generated from the application of examined techniques are integrated back into the theoretical framework regarding the functional role of brain oscillations. We suggest that the coupling of oscillatory activities at different frequencies between brain regions is crucial for understanding the brain from a functional ensemble perspective. Effort should be directed to elucidate how cross-frequency and area coupling are modulated and controlled. To achieve this, only the correct application of analytical tools may shed light on the intricacies of information representation, generation, binding, encoding, storage and retrieval in the brain.

Prenatal carbocyanine dye tracing of septo-hypothalamic connections

This is the first study of the prenatal development of septal projections to the hypothalamus in rats, using carbocyanine dyes (DiI and DiA) as retrograde tracers. First septal neurons send axons to the preoptic area and anterior hypothalamus on embryonic day 14,5 (E14,5) and on E15 numerous labeled neurons are visualized in the septum after DiI insertion into the preoptic region. On E18 and E20 these neurons develop numerous spiny dendrites that occupy all rostrocaudal extension of the septum with concentration in the ventral part of the septum. Only a few septal neurons send their axons to the mediobasal hypothalamus at E15 confirmed by double-labeling (DiI+DiA) experiments on E20-E21. All septo-hypothalamic connections are unilateral and the number of the neurons revealed in the septum correlates with the place and size of the DiI insertion in the hypothalamus: more lateral and anterior hypothalamic marker insertions always resulted in significant neuronal labeling in the septum. No septal connections with the posterior hypothalamus specifically, the mammillary bodies are formed prenatally. We have demonstrated that the development of septal projections to various rostrocaudal regions of the hypothalamus take place during different stages of development. Prominent parts of the septal projections are to the preoptic area and anterior hypothalamus while few connections with the mediobasal hypothalamus are formed prenatally. These data provide basic knowledge of early steps of the development of the septo-hypothalamic connections.

Postnatal development of septal projections to the midbrain central gray in female rats: tract-tracing analysis with DiI

The neural projection of the lateral septum (LS) to the rostral mesencephalic central gray (MCG) is sexually dimorphic and plays an important role in inhibiting female reproductive behavior. In this experiment, development of the LS-MCG connection from birth to 15 days after birth was examined in female rats by a tract-tracing method with DiI. On the birth day (D1 rat), and 5, 10 or 15 days after birth (D5, D10 or D15 rat, respectively) or 8 weeks after birth (adult), the brain was fixed by perfusion of a mixture of 4% PFA and 0.1% glutaraldehyde. DiI was pasted on the coronally cut-surface of the LS and the sample was incubated in PFA at 40 degrees C for up to 4 months. After incubation, 200-microm frozen parasagittal sections were prepared and observed by fluorescence microscopy. As a result, numerous DiI labeled fibers were found in the preoptic area, the anterior and posterior hypothalamus, and the MCG in adult rats. In D1 rats, several labeled axons extended caudal to the anterior hypothalamic area. In D5 rats, a few labeled fibers reached the MCG. Some labeled fibers were observed in the rostral MCG of D10 rats. In D15 rats, a considerable number of labeled fibers were seen to reach the rostral MCG and relative density of the fibers was comparable to that of adult. These results suggest that the neural pathway from the LS to the rostral MCG develops acutely during the period from 5-10 days up to more than 15 days after birth.

Pressor effects of noradrenaline injected into the lateral septal area of unanesthetized rats

The lateral septal area (LSA) is involved in central cardiovascular control. In the present study, we report on the cardiovascular effects of noradrenaline (NA) injection into the LSA of unanesthetized rats, as well as on local receptors and peripheral mechanisms involved in their mediation. Microinjections of NA (9, 15, 21, 27 or 45 nmol) caused long-lasting, dose-related pressor and bradycardic responses in unanesthetized rats. No responses were observed when the dose of 21 nmol of NA was microinjected into medial septal area or lateral ventricle suggesting a main action at the LSA. No changes were observed in arterial pressure and heart rate when NA was injected in the LSA of anesthetized rats. The effects of 21 nmol of NA were abolished by local pretreatment with 10 nmol of the specific alpha1-receptor antagonist WB 4101, but were not affected by pretreatment with 10 nmol of the specific alpha2-receptor antagonist RX 821002. The magnitude of pressor response to NA in the LSA was increased by i.v. pretreatment with the ganglion blocker pentolinium (10 mg/kg) and significantly reduced by i.v. pretreatment with the V1-vasopressin receptor antagonist dTyr (CH2)5(Me) AVP (50 microg/kg). No pressor response to NA was observed in hypophysectomized rats. The present observation of alpha1-adrenoceptor-mediated pressor responses after local injection of NA confirms earlier evidence of a LSA involvement in central cardiovascular control. Pretreatment with the alpha1-adrenoceptor antagonist WB-4101 did not affect baseline blood pressure or heart rate suggesting no tonic involvement of septal adrenergic mechanisms suggesting a modulatory LSA influence on cardiovascular control. Additionally, the blockade of the pressor response by the i.v. pretreatment with a V1-vasopressin antagonist indicates that noradrenergic LSA mechanisms modulate vasopressin release.

The septal complex of the fire-bellied toad Bombina orientalis: Chemoarchitecture

In order to investigate whether chemoarchitecture would support the subdivision of the anuran septum based on cytoarchitectonic and hodological studies, we performed enzyme-histochemical detection of NADPH-diaphorase and immunohistological demonstration of choline-acetyl transferase (ChAT), aspartate, calretinin, gamma-aminobutyric acid (GABA), 5-hydroxy-tryptamine, tyrosine hydroxylase, neuropeptide Y (NPY), somatostatin, Leu- and Leu + Met-enkephalin, and substance P in the fire-bellied toad Bombina orientalis. Labeling of cell bodies matched well the previously defined subnuclei: The dorsolateral septal nucleus contains enkephalin-immunoreactive (-ir) and weakly stained GABA-ir neurons; calretinin-ir and weakly labeled GABA-ir neurons are found in the ventrolateral septal nucleus. The medial septal nucleus is characterized by the presence of numerous ChAT-ir and some tyrosine hydroxylase-ir neurons, while the dorsal septal nucleus is outlined by its NPY-ir neurons. Many ChAT-ir and some aspartate-ir and somatostatin-ir neurons are found in the diagonal band of Broca, and the central septal nucleus contains some GABA-ir and ChAT-ir neurons. In contrast, labeled fibers form a pattern which does not match the boundaries of septal subnuclei. Comparing the anuran septal complex with that of other vertebrates reveals that the complexity of the lateral septum has increased during the evolution from anamniote to amniote vertebrates. In spite of this fact, many similarities in chemoarchitecture between anurans and other vertebrates are evident. Some basal septal functions such as involvement in learning and memory formation or inhibition of sexual behavior appear to have persisted during vertebrate evolution.

Hodological characterization of the septum in anuran amphibians: II. Efferent connections

The efferent connections of the septum of the gray treefrog Hyla versicolor were studied by combining anterograde and retrograde tracing with biotin ethylendiamine (Neurobiotin). The lateral septal complex projects mainly to the medial pallium, limbic regions (e.g., amygdala and nucleus accumbens), and hypothalamic areas but also to sensory nuclei in the diencephalon and midbrain. The central septal complex strongly innervates the medial pallium, limbic, and hypothalamic areas but also specific sensory (including olfactory) regions. The medial septal complex sends major projections to all olfactory nuclei and a weaker projection to the hypothalamus. Our results indicate that all septal nuclei may modify the animal's internal state via efferents to limbic and hypothalamic areas. Via projections to the medial pallium, lateral and central septal complexes may be involved in learning processes as well. Because of their connections to specific sensory areas, all septal areas are in a position to influence sensory processing. Furthermore, our data suggest that both the postolfactory eminence and the bed nucleus of the pallial commissure are not part of the septal complex, rather, the postolfactory eminence seems to be comparable to the mammalian primary olfactory cortex, whereas the bed nucleus may be analogous to the mammalian subfornical organ.

Norepinephrine-gamma-aminobutyric acid (GABA) interaction in limbic stress circuits: effects of reboxetine on GABAergic neurons

BACKGROUND

Reboxetine is a selective norepinephrine (NE) reuptake inhibitor that exerts significant antidepressant action. The current study assessed norepinephrine-gamma-aminobutyric acid (GABA)-ergic mechanisms in reboxetine action, examining glutamic acid decarboxylase (GAD) mRNA expression in limbic neurocircuits following reboxetine within the context of chronic stress.

METHODS

Male rats received 25 mg/kg reboxetine/day, p.o. Reboxetine and vehicle animals were exposed to 1 week of variable stress exposure or handling. Behavioral responses to stress (open field) were tested on day 7, and animals were killed on day 8 to assess neuroendocrine stress responses and limbic GAD65/67 mRNA regulation (in situ hybridization).

RESULTS

Reboxetine significantly decreased behavioral reactivity in the open field. Reboxetine administration did not affect expression of GAD65/67 mRNA in handled rats; however, administration to stressed animals reduced GAD67 (but not GAD65) mRNA in the medial amygdaloid nucleus, posteromedial bed nucleus of the stria terminalis, and dentate gyrus. In contrast, GAD65 mRNA expression was increased by reboxetine in the lateral septum of stressed animals.

CONCLUSIONS

Norepinephrine pathways appear to modulate synthesis of GABA in central limbic stress circuits. Decreases in GABA synthetic capacity suggest reduced activation of stress-excitatory pathways and enhanced activation of stress-inhibitory circuits, and is consistent with a role for GABA in the antidepressant efficacy of NE reuptake inhibitors.

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Pain responses, anxiety and aggression in mice deficient in pre-proenkephalin

Enkephalins are endogenous opioid peptides that are derived from a pre-proenkephalin precursor protein. They are thought to be vital in regulating many physiological functions, including pain perception and analgesia, responses to stress, aggression and dominance. Here we have used a genetic approach to study the role of the mammalian opioid system. We disrupted the pre-proenkephalin gene using homologous recombination in embryonic stem cells to generate enkephalin-deficient mice. Mutant enk-/- animals are healthy, fertile, and care for their offspring, but display significant behavioural abnormalities. Mice with the enk-/- genotype are more anxious and males display increased offensive aggressiveness. Mutant animals show marked differences from controls in supraspinal, but not in spinal, responses to painful stimuli. Unexpectedly, enk-/- mice exhibit normal stress-induced analgesia. Our results show that enkephalins modulate responses to painful stimuli. Thus, genetic factors may contribute significantly to the experience of pain.

Alterations in dendritic spine density in the rat brain associated with protein malnutrition

Rats that consume a high-protein diet are hyperactive, hyperresponsive to noxious stimuli, and demonstrate elevated basal arousal levels. Although the mechanism involved in dietary protein-induced changes in behavior is unclear, it may involve many changes including abnormal dendrite morphology in the brain. Three groups of rats were pair-fed with isocaloric diets containing 8%, 20% and 50% casein for 4 weeks. Their brains were processed for examination of dendritic spine densities in the frontal, parietal, and entorhinal cortices, the striatum, and the septum. Animals on the 50% casein diet showed increased spine densities in all areas investigated (P less than 0.05), compared to the animals on normal (20%) casein. In contrast, animals maintained on the 8% casein diet showed increased spine densities (P less than 0.05) only in the striatum and entorhinal cortex, and exhibited normal densities in the frontal and parietal cortices, and the medial septum.