Autonomic and motor responses to electrical stimulation of the toad's septum

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.

Autonomic adjustments during avoidance and orienting responses induced by electrical stimulation of the central nervous system in toads (Bufo paracnemis)

Electrical stimulation of the central nervous system of conscious toads with permanently implanted electrodes in regions related to orienting and avoidance responses induces cardiovascular (hypertension and tachycardia) and respiratory (increased intrapulmonary pressure) changes together with the somato-motor effects typical of these responses. Sympathetic activation occurs and the main peripheral mediator involved may be adrenergic, since the cardiovascular effects are almost completely blocket by systemic pretreatment with phentolamine and DCI. The cardiovascular changes obtained by central stimulation are qualitatively similar to those recorded for toads whose orienting and avoidance behaviors are obtained by the presentation of visual stimuli (presentation of a prey and of a black card moved over the experimental box). Variations in heart rhythm may occur in both cases in the absence of visible somatic manifestations or of other neurovegetative changes, thus showing the importance of this parameter as an index of sensory reception of biologically significant stimuli. The results are compared to those obtained under similar conditions in other non-mammalian vertebrates.

Comparative aspects of central cardiovascular control with special reference to adrenergic mechanisms

1. The central nervous system probably serves as an overall cardiovascular regulatory centre in all vertebrates. 2. Electrical stimulation of the brain elicits haemodynamic effects in all vertebrate classes, but the quality of the responses may differ between different classes in some cases. 3. In the most "primitive" classes of vertebrates, i.e. fishes, the circulatory regulation may be exerted via mechanisms somewhat different from those in other vertebrates. 4. Amphibians, reptiles, birds and mammals display a similar cardiovascular response pattern to administration of drugs such as clonidine and L-DOPA.