Antonio Carelli

Amygdalar orexinergic-GABAergic interactions regulate anxiety behaviors of the Syrian golden hamster.

At present neurobiological interests are directing more attention towards the major role of the amygdalar GABA(A) receptor on orexin-dependent behaviors. This telencephalic region has been widely studied especially in view of its control on various psychiatric disorders such as anxiety and depression. Recently, cross-talking relationships between these two specific neuroreceptor systems of the central-cortical amygdalar complex has been considered an important element for anxiety type of behaviors. In the present study, we investigated the effects of central amygdalar infusions with orexin-A, orexin-B±GABA(A) receptor α₂ subunit agonist (flunitrazepam) on elevated plus-maze and light-dark explorative behaviors of the facultative hibernating Syrian hamster. In a first case, it seemed that doses of orexin administered directly into the central nucleus were responsible for greater anxiogenic type of effects as shown by more time being spent both in the dark compartment and the closed arm of the elevated plus-maze, whereas, these effects were suppressed in the presence of flunitrazepam. At the cellular level, the effects of orexin accounted for evident argyrophilic reactions (neurodegeneration phenomena) including altered cell membrane and loss of cytoplasmic architecture in most amygdalar and hippocampal neuronal fields, while in the presence of flunitrazepam these reactions resulted to either be unappreciable or absent. Overall the actions of α₂-dependent inhibitory signals tend to corroborate, for the first time, a neuroprotective role against the over-excitatory orexinergic neurodegeneration reactions and thus its abnormal anxiety-like indications may prove to be therapeutically useful for orexin-dependent sleeping disorders.

Some environmental contaminants influence motor and feeding behaviors in the ornate wrasse (Thalassoma pavo) via distinct cerebral histamine receptor subtypes.

Common environmental contaminants such as heavy metals and pesticides pose serious risks to behavioral and neuroendocrine functions of many aquatic organisms. In the present study, we show that the heavy metal cadmium and the pesticide endosulfan produce such effects through an interaction of specific cerebral histamine receptor subtypes in the teleost ornate wrasse (Thalassoma pavo). Treatment of this teleost with toxic cadmium levels for 1 week was sufficient to induce abnormal swimming movements, whereas reduced feeding behaviors were provoked predominantly by elevated endosulfan concentrations. In the brain, these environmental contaminants caused neuronal degeneration in cerebral targets such as the mesencephalon and hypothalamus, damage that appeared to correlate with altered binding levels of the three major histamine receptors (subtypes 1, 2, and 3). Although cadmium accounted for reduced binding activity of all three subtypes in most brain regions, it was subtype 2 that seemed to be its main target, as shown by a very great (p < 0.001) down-regulation in mesencephalic areas such as the stratum griseum central layer. Conversely, endosulfan provided very great and great (p < 0.01) up-regulating effects of subtype 3 and 1 levels, respectively, in preoptic-hypothalamic areas such as the medial part of the lateral tuberal nucleus, and in the suprachiasmatic nucleus. These results suggest that the neurotoxicant-dependent abnormal motor and feeding behaviors may well be tightly linked to binding activities of distinct histamine subtypes in localized brain regions of the Thalassoma pavo.

Steroid hormones and receptors of the GABAA supramolecular complex. I: Benzodiazepine receptor level changes in some extrahypothalamic brain areas of the female rat following sex steroid treatment

The effects of sex steroid hormones on the different receptor binding sites of the GABAA molecule remain unclear. In this report we have demonstrated, using autoradiography techniques, that the distribution pattern of the benzodiazepine receptors (a component of the GABAA molecule) in some extrahypothalamic brain regions is altered by both in vivo and in vitro sex steroid hormone treatment. In vivo administration of the sex steroids estradiol and progesterone induced a significant change in [3H]flunitrazepam (benzodiazepine agonist) binding levels in the amygdala, and cortico and posterior brain nuclei of the female rat. In fact, elevated and diminished receptor-binding levels were obtained in the corticomedial amygdala nucleus and in the pontine central gray matter respectively, following the administration of estradiol. Significant hormonal effects were also shown for animals that received only a progesterone dose, as demonstrated by the increased and decreased receptor levels in the basolateral amygdala nucleus and cortex lamina VI and in the substantia nigra pars reticulata, respectively. It was interesting, at this point, to investigate whether the hormone effects on [3H]flunitrazepam binding changes might be mediated through a GABA-dependent activity, because the benzodiazepine and GABAA receptors are coupled to a chloride ion channel in an allosteric manner. When 50 microM GABA was added to the incubation medium, substantially altered binding levels were recorded in animals that received progesterone replacement therapy only. The GABA-induced progesterone effects both increased substantially the binding levels in the oriens-pyramidalis CA1 layer of the hippocampus and in the intermediate gray layer of the superior colliculus as well as reducing receptor levels in the substantia nigra pars reticulata.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the xenoestrogen bisphenol A in diencephalic regions of the teleost fish Coris julis occur preferentially via distinct somatostatin receptor subtypes

The xenoestrogen bisphenol A, a contaminant used in the manufacturing of polymers for many consumer products, has been shown to mimic estrogenic actions. This xenoestrogen regulates secretion and expression of pituitary lactotrophs plus morphological and structural features of estrogen target tissues in rodents. Recently, ecological hazards produced by bisphenol A have drawn interests towards the effects of this environmental chemical on neurobiological functions of aquatic vertebrates of which little is known. In this study, the effects of bisphenol A on the distribution of the biologically more active somatostatin receptor subtypes in diencephalic regions of the teleost fish Coris julis were assessed using nonpeptide agonists (L-779, 976 and L-817, 818) that are highly selective for subtype(2) and subtype(5), respectively. Bisphenol A proved to be responsible for highly significant increased binding levels of subtype(2) in hypothalamic areas, while markedly decreased levels of subtype(5) were found in these diencephalic areas, as well as in the medial preglomerular nucleus. The extensive distribution of somatostatin receptor subtype(2) and subtype(5) in the teleost diencephalic areas suggests that, like in mammals, this receptor system may not only be involved in enhanced hypophysiotropic neurohormonal functions but might also promote neuroplasticity events.

Excitatory/inhibitory equilibrium of the central amygdala nucleus gates anti-depressive and anxiolytic states in the hamster

Several studies have pointed to the amygdala as a main limbic station capable of regulating different stressful states such as anxiety and depression. In this work it was our intention to determine the role of the central amygdala nucleus (CeA) on the execution of either anxiolytic and/or anti-depressant behaviors in the hibernating hamster (Mesocricetus auratus) via infusion of CeA with the antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) specific for α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) plus the specific agonist for α4 GABAAR i.e. 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP). Treatment with CNQX appeared to mainly prompt anti-depressant effects as shown by the achievements of swimming feats during forced swim test while THIP prevalently accounted for evident bouts of climbing when exposed to the same test. Moreover, even in the presence of the concomitant administration of both of these compounds, hamsters continued to spend more time in swimming despite this significant behavioral effect resulted to be numerically reduced for hamsters treated with only the α4 GABAAR agonist. Conversely, when these animals were tested in elevated plus maze (EPM), THIP tended to mostly favor anxiolytic activities as exhibited by stressed animals spending more time entering and remaining in EPM open arms. It was interesting to note that behavioral changes induced by both drugs appeared to be also responsible for glutamate receptor (GluR) expression differences as indicated by CNQX favoring an evident up-regulation of GluR2-containing neurons whereas THIP induced an up-regulation, this time of GluR1-containing neurons. Overall, the anti-depressant role of CNQX seems to be mostly attributed to elevated GluR2 levels while an anxiolytic-like effect of THIP was correlated to high GluR1values thereby proposing distinct GluRs as useful therapeutic sites against degenerative diseases such as depression-like behaviors.

Sexual dimorphism of GABAA receptor levels in subcortical brain regions of a woodland rodent (Apodemus sylvaticus)

This is the first report of quantitative autoradiography results showing sex differences of GABAA receptor levels in brain regions of a wild rodent (wood mouse, Apodemus sylvaticus) living in its natural habitat. The labeling of this GABAergic site with its specific high affinity radioligand [3H] muscimol provided a heterogeneous and dimorphic binding pattern in some of the neural centers. In the female, higher (> or = 50 < or = 65%) to moderately higher (< 50%) binding levels than in the male, even after correction of the specific binding values using the calculated quenching coefficients, were observed in the substantia nigra pars reticulata and ventral lateral thalamic nucleus, brain centers that are relays of motor circuits. In the male, on the other hand, a higher level was only obtained in the caudateputamen. Relays of the stria terminalis-hypothalamic-central gray pathway such as the bed nucleus of the stria terminalis, the pontine central gray and the ventromedial hypothalamic nucleus, were among the other female brain areas with an extremely higher (> 65%) to higher and moderately higher binding activity than in the male. From the saturation analyses, it appeared that the binding differences were mainly due to Bmax variations, although closer examinations revealed that changes in the KD might have also accounted for [3H] muscimol binding differences, as shown by the high KD and Bmax values in the bed nucleus of the stria terminalis, the substantia nigra pars reticulata and the pontine central gray of the female wood mouse. These findings suggest that the dimorphic binding activity of GABAA receptors in the above brain regions might be involved in neuronal circuitry mechanisms related to sex-specific social behaviors in rodents living in their natural environmental conditions.

Amygdalar glutamatergic neuronal systems play a key role on the hibernating state of hamsters.

BackgroundExcitatory transmitting mechanisms are proving to play a critical role on neuronal homeostasis conditions of facultative hibernators such as the Syrian golden hamster. Indeed works have shown that the glutamatergic system of the main olfactory brain station (amygdala) is capable of controlling thermoregulatory responses, which are considered vital for the different hibernating states. In the present study the role of amygdalar glutamatergic circuits on non-hibernating (NHIB) and hibernating (HIB) hamsters were assessed on drinking stimuli and subsequently compared to expression variations of some glutamatergic subtype mRNA levels in limbic areas. For this study the two major glutamatergic antagonists and namely that of N-methyl-D-aspartate receptor (NMDAR), 3-(+)-2-carboxypiperazin-4-yl-propyl-1-phosphonate (CPP) plus that of the acid α-amine-3-hydroxy-5-metil-4-isoxazol-propionic receptor (AMPAR) site, cyano-7-nitro-quinoxaline-2,3-dione (CNQX) were infused into the basolateral amygdala nucleus. Attempts were made to establish the type of effects evoked by amygdalar glutamatergic cross-talking processes during drinking stimuli, a response that may corroborate their major role at least during some stages of this physiological activity in hibernators.ResultsFrom the behavioral results it appears that the two glutamatergic compounds exerted distinct effects. In the first case local infusion of basolateral complexes (BLA) with NMDAR antagonist caused very great (p < 0.001) drinking rhythms while moderately increased feeding (p < 0.05) responses during arousal with respect to moderately increased drinking levels in euthermics. Conversely, treatment with CNQX did not modify drinking rhythms and so animals spent more time executing exploratory behaviors. These same antagonists accounted for altered glutamatergic transcription activities as displayed by greatly reduced GluR1, NR1 and GluR2 levels in hippocampus, ventromedial hypothalamic nucleus (VMN) and amygdala, respectively, plus a great (p < 0.01) up-regulation of GluR2 in VMN of hibernators.ConclusionWe conclude that predominant drinking events evoked by glutamatergic mechanisms, in the presence of prevalently down regulated levels of NR1/2A of some telencephalic and hypothalamic areas appear to constitute an important neuronal switch at least during arousal stage of hibernation. The establishment of the type of glutamatergic subtypes that are linked to successful hibernating states, via drinking stimuli, may have useful bearings toward sleeping disorders.

Amygdalar excitatory/inhibitory circuits interacting with orexinergic neurons influence differentially feeding behaviors in hamsters

Recently, environmental stimuli on different neurobiological events, via participation of distinct amygdalar (AMY) ORXergic fibers have aroused wide interests in view of their ability to modify neuronal linked stressful and physiological homeostatic conditions. Results of the present study indicate that ORXergic (ORX-A/B) circuits of the facultative hibernating golden hamster (Mesocricetus auratus) central AMY (CeA) and basolateral AMY (BlA) nuclei constitute major sites of feeding behaviors. Indeed, hamsters after treatment of BlA with ORX-A frequently ingested greater quantities of food as compared to controls, while ORX-B in CeA induced a very (p<0.001) great consumption of water. The same nuclei treated separately with either ORX-A or ORX-B ± the selective α(1) GABA(A) benzodiazepine receptor agonist (zolpidem) dedicated less time to eating and drinking sessions. Conversely, hamsters that received the same neuropeptides but this time with the glutamatergic agonist NMDA displayed greater hyperphagic effects above all for ORX-A. When behavioral changes were compared to the expression of the specific ORXergic receptor (ORX-2R), an up-/down-regulating pattern was detected in some limbic areas (AMY, hippocampus and hypothalamus) following treatment with ORX-A or ORX-B plus NMDA. Overall, indications deriving from this study strongly point to hamster BlA-enriched ORX-A fibers in combination with either inhibitory or excitatory signals as main targets of hyperphagic responses while CeA ORX-B activities in presence of these same neuronal signals predominantly induced drinking motivational behaviors. The distinct behavioral activities of these two neuropeptides may have useful clinical bearings toward psychiatric and sleeping disorders such as bulimia and narcolepsy.

Morphological and functional variations of Leydig cells in testis of the domestic pig during the different biological stages of development.

The relationship of morphometrical and androgen receptor evaluations of the main testicular interstitium cellular element (Leydig cells) in the domestic pig provided interesting numerical and morphological features during the different aging stages. As early as 25 days (a period in which the pig is sexually immature) there was a low number of Leydig cells (1.46 x 10(8)) with respect to a 78% and 35% increase in the adult (2.48 x 108) and aged (1.78 x 10(8)) animal, respectively. Interestingly, when the volume density of Leydig cells was considered, the average volume of these cells seemed to be high (75%) in the aged pig with respect to the young immature animal whereas a lower increase (27%) was observed for the adult animal. Moreover, the evaluation of testosterone receptor binding sites in the testis at the various stages of development also displayed a differentiated pattern since elevated testosterone receptor binding levels of the high dissociation affinity type were obtained for the adult pig. Thus, from the combined morphological variations of Leydig cells and testosterone receptor binding activity, it appears that this androgenic receptor component exerts distinct autocrine effects on the different functional features of some testicular tissue constituents at the different aging stages of the domestic pig.

Distinct α subunit variations of the hypothalamic GABAA receptor triplets (αβγ) are linked to hibernating state in hamsters

BackgroundThe structural arrangement of the γ-aminobutyric acid type A receptor (GABAAR) is known to be crucial for the maintenance of cerebral-dependent homeostatic mechanisms during the promotion of highly adaptive neurophysiological events of the permissive hibernating rodent, i.e the Syrian golden hamster. In this study, in vitro quantitative autoradiography and in situ hybridization were assessed in major hypothalamic nuclei. Reverse Transcription Reaction-Polymerase chain reaction (RT-PCR) tests were performed for specific GABAAR receptor subunit gene primers synthases of non-hibernating (NHIB) and hibernating (HIB) hamsters. Attempts were made to identify the type of αβγ subunit combinations operating during the switching ON/OFF of neuronal activities in some hypothalamic nuclei of hibernators.ResultsBoth autoradiography and molecular analysis supplied distinct expression patterns of all α subunits considered as shown by a strong (p < 0.01) prevalence of α1 ratio (over total α subunits considered in the present study) in the medial preoptic area (MPOA) and arcuate nucleus (Arc) of NHIBs with respect to HIBs. At the same time α2 subunit levels proved to be typical of periventricular nucleus (Pe) and Arc of HIB, while strong α4 expression levels were detected during awakening state in the key circadian hypothalamic station, i.e. the suprachiasmatic nucleus (Sch; 60%). Regarding the other two subunits (β and γ), elevated β3 and γ3 mRNAs levels mostly characterized MPOA of HIBs, while prevalently elevated expression concentrations of the same subunits were also typical of Sch, even though this time during the awakening state. In the case of Arc, notably elevated levels were obtained for β3 and γ2 during hibernating conditions.ConclusionWe conclude that different αβγ subunits are operating as major elements either at the onset of torpor or during induction of the arousal state in the Syrian golden hamster. The identification of a brain regional distribution pattern of distinct GABAAR subunit combinations may prove to be very useful for highlighting GABAergic mechanisms functioning at least during the different physiological states of hibernators and this may have interesting therapeutic bearings on neurological sleeping disorders.