A combined study of behavior and Fos expression in limbic structures after re-testing Wistar rats in the elevated plus-maze

The elevated plus-maze is an animal model used to study anxiety. In a second session, rats show a reduction in the exploratory behavior even when the two sessions are separated by intervals as large as 7 days. The aim of the present study was to investigate whether the reduction in the exploratory behavior is maintained after intervals larger than 7 days. Additionally, we aimed at investigating eventual correlations between behaviors in the plus-maze and activation of limbic structures as measured by Fos protein expression after the second session. Rats were tested for 5 min in the elevated plus-maze and re-tested 3, 9 or 33 days later. Other groups were tested only once. The rat brains were processed for immunohistochemical detection of Fos protein. The results show a decrease in the open arms exploration in the second trial with intervals of 3, 9 and 33 days. The expression of Fos protein in the piriform cortex, septal nucleus and paraventricular hypothalamic nucleus in the groups tested with intervals of 9 and 33 days were statistically different from the other groups. The alterations observed in exploratory behavior in the second session in the plus-maze did not correlate with Fos expression. In conclusion, although the specific test conditions were sufficient to evoke behavioral alterations in exploration in the elevated plus-maze, they were enough to induce significant Fos protein expression in piriform cortex, septal nucleus and thalamic and hypothalamic paraventricular nuclei but not in other areas such as dorsomedial nucleus of the hypothalamus and amygdala nuclei, known to be also active participants in circuits controlling fear and anxiety.     

Lipid sensing in the brain and regulation of energy balance

Nutrient-sensitive neurons [to glucose and fatty acids (FAs)] are present at many sites throughout the brain, including the hypothalamus and brain stem, and play a key role in the neural control of energy and glucose homoeostasis. Through their neuronal output, FAs can modulate feeding behaviour as well as insulin secretion and activity. Central administration of oleate, for example, inhibits food intake and glucose production in rats. This suggests that daily variations in plasma FA concentrations could be detected by the central nervous system as a signal that contributes to regulation of energy balance. At the cellular level, subpopulations of neurons in the ventromedial and arcuate hypothalamic nuclei are selectively either inhibited or activated by FAs. Possible molecular effectors of these FA effects most likely include the chloride and potassium ion channels. While intracellular metabolism and activation of the ATP-sensitive K⁺ channels appear to be necessary for some signalling effects of FAs, at least half the FA responses in ventromedial hypothalamic neurons are mediated by interaction with fatty acid translocase (FAT)/CD36, an FA transporter/receptor that does not require intracellular metabolism to activate downstream signalling. Thus, FAs and their metabolites can modulate neuronal activity by directly monitoring the ongoing fuel availability for brain nutrient-sensing neurons involved in the regulation of energy and glucose homoeostasis. Besides these physiological effects, FA overload or metabolic dysfunction may also impair neural control of energy homoeostasis and contribute to obesity and/or type 2 diabetes in predisposed subjects.     

Spearmint induced hypothalamic oxidative stress and testicular anti-androgenicity in male rats – altered levels of gene expression, enzymes and hormones

Mentha spicata Labiatae, commonly known as spearmint, can be used for various kinds of illnesses in herbal medicines and food industries. One of the prominent functions of this plant extract is its anti-androgenic activity. The present study investigated the probable correlation between oxidative stress in hypothalamic region and anti-androgenic action of this plant’s aqueous extract on rats. Decreased activities of enzymes like superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase in hypothalamus of treated rats indicated spearmint induced oxidative stress. Further RT-PCR and immunoblot analysis demonstrated the decreased expression of some of the steroidogenic enzymes, cytochrome P450scc, cytochrome P450C17, 3β-Hydroxysteroid dehydrogenase (3β-HSD), 17β-Hydroxysteroid dehydrogenase (17β-HSD) and other related proteins like, steroidogenic acute regulatory protein, androgen receptor and scavenger receptor class B-1. Further, in vitro enzyme assays demonstrated depressed activities of testicular 3β-HSD and 17β-HSD enzymes. Histopathology indicated a decreased sperm density in cauda epididymis and degeneration of ductus deference. Our study suggested that spearmint probably induced oxidative stress in hypothalamus resulting in decreased synthesis of LH and FSH which in turn down-regulated the production of testicular testosterone through the disruption of a number of intermediate cascades.     

Levetiracetam opposes the action of GABAA antagonists in hypothalamic neurones

Whole-cell current-clamp recordings in guinea-pig brain slices were used to assess the effect of the novel antiepileptic drug levetiracetam (LEV; Keppra) on the gamma-aminobutyric acid-A (GABA(A)) responses evoked by exogenous applications of the agonists GABA and muscimol on hypothalamic neurones. LEV (40 microM) had no direct effect on GABA(A) responses but it occluded the GABA(A)-receptor blocking action of bicuculline-methiodide (100 microM) and, to a lesser extent, the GABA(A)-receptor blocking action of gabazine (50 microM). While previous reports have indicated that the inhibition by LEV of the epileptiform hyperexcitability induced by bicuculline in rat hippocampus might occur via non-GABAergic mechanisms, the present data suggest a possible indirect modulation by LEV of GABA-gated currents in guinea-pig hypothalamic neurones.     

Localization of angiotensin II (AT1)-receptor-immunoreactive fibres in the hypothalamus of rats: angiotensin II-sensitive tanycytes in the ependyma of the third ventricle?

Scanning the hypothalamus of rats for receptor binding sites of the octapeptide hormone angiotensin II (ANG II), we observed ANG II-sensitive fibres in the ventrolateral hypothalamus. The ANG II (AT(1))-receptor-immunoreactive processes originate from cells-probably tanycytes-embedded in the base and the ventrolateral walls of the third ventricle and reach into the retrochiasmatic area, the ventrolateral hypothalamus and the median eminence.     

Inter- and intra-nuclear differences in galanin expression between the hypothalamic paraventricular and supraoptic nuclei in colchicine-untreated rats

Not much is known of the topography of galanin expression in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei neurons in colchicine (an axoplasmic inhibitor)-untreated animals. Insight into the biological implication(s) of galanin expression in the PVN and SON will depend, at least in part, on the nature of its distribution in colchicine-untreated animals. In this study therefore, the topographical distribution of galaninergic profiles was examined in the PVN and SON of colchicine-untreated rats. Staining in the parvocellular PVN (PVN(p)) was predominantly as varicose thin galanin fiber processes while the magnocellular PVN (PVN(m)) contained large cell soma and fiber processes. The relative fiber density was higher in the anterior, periventricular and medial PVN(p) than in the dorsal, lateral and posterior subdivisions. Large-sized cells and thick fibers were limited to the posterior PVN(m) while the anterior and medial PVN(m) contained varicose profiles. Light- and intensely-stained galanin-positive cells as well as large- and small-diameter (varicose or non-varicose) fibers were observed in the SON. The large and thin fibers exhibit preferential ventral and dorsal distribution, respectively. Together with the complexity of specific afferent and efferent connections within the PVN and SON, these observations underscore heterogeneous galanin expression and raise potential implications for understanding the biological role of galanin by physiologically challenging stimuli.     

Neuropeptide Y and lipid increase apolipoprotein AIV gene expression in rat hypothalamus

Apolipoprotein AIV (apo AIV) is a circulating signal released from intestinal cells in response to lipid feeding and contributes to the anorectic effect of a lipid meal. We have demonstrated that apo AIV is also synthesized in the hypothalamus, and that hypothalamic apo AIV gene expression is regulated physiologically. Neuropeptide Y (NPY) is a hypothalamic neuropeptide with broad regulatory actions in the central nervous system. In the present studies, the effects of intracerebroventricular (i.v.t.) administration of NPY and of intraduodenal lipid infusion on hypothalamic apo AIV gene expression were determined using competitive RT-PCR in fasted rats. I.v.t. injection of NPY alone significantly increased apo AIV mRNA levels in the hypothalamus in a dose-dependent manner. Intraduodenal infusion of lipid also stimulated the gene expression of hypothalamic apo AIV, but no further significant increment occurred when i.v.t. injection of NPY was combined with lipid infusion. These results suggest that NPY and lipid may regulate apo AIV gene expression in the rat hypothalamus.     

Localization and neuronal response of RFamide related peptides in the rat central nervous system

RFamide related peptides (RFRP)-1 and RFRP-3 are neuropeptides derived from the same preproprotein. We have examined the distribution of RFRP-1 and RFRP-3 immunoreactivities (irs) in the rat central nervous system using specific antibodies. Neuronal cell bodies containing both RFRP-1 and RFRP-3 were detected within the caudal portion of the hypothalamus, the periventricular nucleus (PerVN), and the portion around or above the ventromedial nucleus of the hypothalamus. Both immunohistochemical and in situ hybridization analyses showed that neurons containing RFRP immunoreactivity and mRNA were distinct from those of neuropeptide FF, which contains the same structure at the C-terminus, Pro-Glu-Arg-Phe-NH2, as RFRP-3. Fibers containing both RFRP-1 and RFRP-3 were widely distributed in the brain: the lateral septal nucleus in the telencephalon, the paraventricular thalamic nucleus, various hypothalamic nuclei, the periaqueductal gray in the midbrain, the parabrachial nucleus in the pons, and the nucleus tractus solitarius (NTS) in the medulla oblongata. Only RFRP-1-ir was detected within the posterior gray horn in the spinal cord. Only RFRP-3-ir was detected in several thalamic nuclei and the spinal cord, especially at the posterior intermediate sulcus and within the anterior gray horn. Intracerebroventricular administration of RFRPs induced c-Fos expression in the anterior portion of the NTS, locus coeruleus, the nucleus of incertus, supraoptic nucleus, PerVN and the arcuate nucleus of the hypothalamus. These results show that RFRP-1 and RFRP-3 are widely distributed in the rat central nervous system and might be involved in various functions such as the neuroendocrine system or pain modulation.     

Sex differences in the regulation of progesterone receptor isoforms expression in the rat brain

We studied the effects of estradiol (E2) and progesterone (P) on progesterone receptor (PR) isoforms gene expression in the brain of ovariectomised female and gonadectomised male rats by RT-PCR analysis. In female rats, the expression of both PR isoforms was induced by E2 and down-regulated by P in the hypothalamus, whereas in the preoptic area these changes were only observed in PR-B isoform. On the contrary, in the hippocampus and the olfactory bulb, PR-A was the isoform induced by E2. In these regions, P did not modify the expression of any PR isoform. In the cerebellum and the frontal cortex of female rats, no treatment modified PR isoforms expression. In contrast with female rats, in the male rat brain, PR isoforms expression was only modified in the cerebellum, where PR-A was induced by E2. These results demonstrate a clear sexual dimorphism in the regulation of PR isoforms expression by sex steroid hormones in the rat brain, suggesting that this sex difference contributes to the sexually dimorphic effects of P in the rat brain.