Lateral septal projections onto tubero-infundibular neurons in the hypothalamus of the guinea pig

Sucrose modifies c-fos mRNA expression in the brain of rats maintained on feeding schedules

Food intake is regulated according to circadian activity, metabolic needs and the hedonic value of food. Rodents placed on a fixed feeding schedule show behavioral and physiological anticipation of mealtime referred to as food-anticipatory activity (FAA). FAA is driven by the food-entrainable oscillator (FEO), whose anatomical substrate is not yet known. Recent data have shown that restricted feeding schedules for regular chow and daily limited access to palatable food in free-feeding rats activate distinct brain regions during FAA. The combination of a deprivation regimen and scheduled access to palatable food may give rise to a more global anticipatory mechanism because the temporal cycles of energy balance would be strongly modulated by the incentive properties of palatable food; however, the neuronal response to this combined treatment is not yet known. The present study investigated how adding palatable sucrose to feeding schedules affects the pattern of brain c-fos mRNA expression during FAA (0-3 h) and 1 h following feeding. The rats maintained on scheduled chow access increased their daily chow intake, while the rats maintained on scheduled sucrose and chow mainly increased their daily sucrose intake. Adding sucrose to scheduled feeding displaced c-fos mRNA expression from the dorsomedial and paraventricular hypothalamic nuclei and posterior lateral hypothalamus (LH) to the prefrontal cortex, lateral septum, nucleus accumbens and anterior LH. During refeeding, the rats on scheduled sucrose demonstrated higher activation of the nucleus of the solitary tract. The present results suggest that palatable sucrose combined with restricted feeding schedules activate a distinct neuronal network compared to neuronal activation produced by scheduled access to regular chow. These data provide evidence that the brain may contain different food-oscillatory systems and that food palatability may shift the neuronal activity from the medial hypothalamus to the limbic and reward-related areas even at the negative metabolic state.

Intermittent access to sucrose increases sucrose-licking activity and attenuates restraint stress-induced activation of the lateral septum

Intermittent access to palatable food can attenuate anorectic and hormonal responses to stress in rats. The neuronal mechanisms of modulation of stress response by diets are not fully understood. The present study was conducted to create rat models with intermittent access to sucrose that demonstrate resistance to stress-induced hypophagia, to study the pattern of sucrose consumption by these rat models, and to investigate in which brain structures intermittent sucrose regimens modify stress-induced neuronal activation. The obtained results demonstrate that 6-wk intermittent access to sucrose without food restriction (4 day/wk ad libitum access to sucrose in addition to chow, and following 3 day/wk exclusive feeding of chow; SIA rats) and combined with food restriction (4 day/wk access to chow and sucrose restricted to 2 h/day, and following 3 days/wk on unrestricted chow; SIR rats) increased sucrose-licking activity. The alterations in the rats' feeding behavior were accompanied by a resistance of their body weight gain and food intake to 1-h restraint stress applied once per week. The chronic intermittent sucrose consumption significantly lowered, in the SIA and SIR rats, the levels of expression of corticotropin-releasing factor type 2 receptor and restraint stress-induced expression of c- fos mRNA in the medioventral part of the lateral septum. Conversely, the levels of the corticotropin-releasing factor type 2 receptor transcript in the ventromedial hypothalamic nucleus were decreased only in the food-restricted SIR rats. The lower stress-induced neuronal activation in the medioventral part of the lateral septum may contribute to the attenuated anorectic stress response in the rats maintained on intermittent sucrose regimens.

Forebrain projections to the hypothalamus are topographically organized in anurans: conservative traits as compared with amniotes

The organization of the forebrain in amphibians (anamniotes) is currently being re-evaluated in terms of evolution and several evidences have corroborated numerous traits shared by amphibians and amniotes, such as the organization of the basal ganglia and the amygdaloid complex. In the present study we have analysed the organization of forebrain afferent systems to the hypothalamus of the frog Rana perezi. In vivo and in vitro tract-tracing techniques with dextran amines and immunohistochemistry for localizing nitric oxide synthase (NOS) in a series of single or combined experiments were used as NOS labelling reveals hypothalamic afferents arising from the lateral amygdala and the combination allowed analysis of the relationship between fibers of different origins in the same section. The results showed a large segregation of afferents in the hypothalamic region depending on their site of origin in the forebrain. Four highly topographically organized prosencephalic tracts reaching the anuran hypothalamus were observed: (i) the medial forebrain bundle, from the medial pallium and septal complex; (ii) the caudal branch of the stria terminalis formed by fibers arising in the lateral and medial amygdala; (iii) part of the lateral forebrain bundle with fibers from the central amygdala and (iv) the dorsal thalamo-hypothalamic tract. Fibers coursing in each tract reach the hypothalamus and terminate in distinct fields. The resemblance in pattern of forebrain-hypothalamic organization between amphibians and amniotes suggests that this feature represents an important trait conserved in the evolution of all tetrapods and therefore essential for the hypothalamic function.

Efferent connections of septal nuclei of the domestic chick (Gallus domesticus): An anterograde pathway tracing study with a bearing on functional circuits

Small iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin were placed in different subregions of the septum of domestic chicks. The main targets of septal projections comprised the ipsi- and contralateral septal nuclei, including the nucleus of the diagonal band, basal ganglia, including the ventral paleostriatum, lobus parolfactorius, nucleus accumbens, and olfactory tubercle, archistriatum, piriform cortex, and anterior neostriatum. Further diencephalic and mesencephalic septal projections were observed in the ipsilateral preoptic region, hypothalamus (the main regions of afferentation comprising the lateral hypothalamic nuclei, ventromedial, paraventricular and periventricular nuclei, and the mammillary region), dorsal thalamus, medial habenular and subhabenular nuclei, midbrain central gray, and ventral tegmental area. Contralateral projections were also encountered in the septal nuclei, ventral paleostriatum, periventricular and anteromedial hypothalamic nuclei, suprachiasmatic nucleus, and the lateral hypothalamic area. Avian septal efferents are largely similar to those of mammals, the main differences being a relatively modest hippocampal projection arising mainly from the nucleus of the diagonal band (as confirmed by a specific experiment with the retrograde pathway tracer True blue), the lack of interpeduncular projection, and a greater contingent of amygdalar efferents arising from the lateral septum rather than the nucleus of the diagonal band. This pattern of connectivity is likely to reflect an important role of the avian septal nuclei in the coordination of limbic circuits and the integration of a wide variety of information sources modulating the appropriate behavioral responses: attention and arousal level, memory formation, hormonally mediated behaviors, and their affective components (such as ingestive, reproductive, and parental behaviors), social interaction, locomotor modulation, and circadian rhythm.

Connections of the rat lateral septal complex

The organization of lateral septal connections has been re-examined with respect to its newly defined subdivisions, using anterograde (PHAL) and retrograde (fluorogold) axonal tracer methods. The results confirm that progressively more ventral transverse bands in the hippocampus (defined by the orientation of the trisynaptic circuit) innervate progressively more ventral, transversely oriented sheets in the lateral septum. In addition, hippocampal field CA3 projects selectively to the caudal part of the lateral septal nucleus, which occupies topologically lateral regions of the transverse sheets, whereas field CA1 and the subiculum project selectively to the rostral and ventral parts of the lateral septal nucleus, which occupy topologically medial regions of the transverse sheets. Finally, the evidence suggests that progressively more ventral hippocampal bands innervate progressively thicker lateral septal sheets. In contrast, ascending inputs to the lateral septum appear to define at least 20 vertically oriented bands or subdivisions arranged orthogonal to the hippocampal input (Risold, P.Y. and Swanson, L.W., Chemoarchitecture of the rat lateral septal nucleus, Brain Res. Rev., 24 (1997) 91-113). Hypothalamic nuclei forming parts of behavior-specific subsystems share bidirectional connections with specific subdivisions of the lateral septal nucleus (especially the rostral part), suggesting that specific domains in the hippocampus may influence specific hypothalamic behavioral systems. In contrast, the caudal part of the lateral septal nucleus projects to the lateral hypothalamus and to the supramammillary nucleus, which projects back to the hippocampus and receives its major inputs from brainstem cell groups thought to regulate behavioral state. The neural system mediating defensive behavior shows these features rather clearly, and what is known about its organization is discussed in some detail.

Distribution of NADPHdiaphorase and calbindin-D28k neurons in the lateral septal area of the guinea pig, with special reference to the enkephalinergic hypothalamo-septal tract

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd) histochemical techniques were used to identify neurons synthesizing nitric oxide in the lateral septum of the guinea pig. Double immunocytochemical procedures were used to detect neurons immunoreactive for calbindin-D28k and enkephalinergic fibers which project to the lateral septum. The present data demonstrate that (1) the neurons containing NADPH diaphorase and the neurons immunoreactive for calbindin-D28k are observed in discrete regions of the lateral septum; (2) these populations overlap in various areas of the lateral septum including its dorsal and mediolateral parts; (3) NADPH diaphorase and calbindin-D28k are colocalized in neurons located in the overlapping areas; (4) neurons identified by the presence of calbindin-D28k, NADPH diaphorase or both substances, are surrounded by enkephalinergic fibers. These observations indicate the chemical heterogeneity of the lateral septum and suggest that the enkephalinergic hypothalamo-septal tract does not preferentially contact a subpopulation of neurons.

Electrophysiology of the neurons in the area of the enkephalinergic magnocellular dorsal nucleus of the guinea-pig hypothalamus, studied by intracellular and whole-cell recordings

The electrophysiological characteristics of 103 hypothalamic neurons in the area of the guinea-pig enkephalinergic magnocellular dorsal nucleus were studied in a thick slice preparation with sharp microelectrodes (63 neurons) and patch pipettes for whole-cell recordings (40 neurons). Of the sampled cells, 79.6% displayed tetrodotoxin-resistant, calcium-dependent slow-depolarizing potentials when the membrane potential was hyperpolarized to approximately -70 mV (type I neurons). Half of them showed robust slow depolarizing potentials, generating bursts of fast action potentials. In the remaining neurons, the slow-depolarizing potentials did not cause burst-firing action potentials but triggered single action potentials. The other class of neurons (20.4% of the sample: type II neurons) did not exhibit calcium-dependent slow-depolarizing potentials. Resting potential, input resistance and the membrane time constant did not distinguish among the two classes of neurons. Current-voltage relationships were heterogeneous. A transient outward rectification was observed in the two classes. This was not totally blocked by 2 mM 4-aminopyridine but was abolished when using perfusion with cobalt instead of calcium. Input resistance and the time constant were higher when measured in the whole-cell mode but the other electrical parameters and the sampling of the recorded neurons were strikingly similar between the two methods of recording. Intracellular staining of 22 neurons retrogradely labelled from the lateral septum allowed confirmation of their location within the magnocellular dorsal nucleus. The study indicates that the electrical properties of these neurons did not differ from those of neurons found throughout the area explored. It also indicates the presence of distinct electrophysiological types of cells in the magnocellular dorsal nucleus, although the nucleus is composed of a single type of enkephalinergic neuron. It provides a basis for the study of the regulation of activity of the neurons at the origin of an enkephalinergic tractus which is involved in neuroendocrine, psychoneuroendocrine and immune processes.