Raffaella Alò

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.

Distinct alpha subunits of the GABAA receptor are responsible for early hippocampal silent neuron-related activities.

The modulatory actions of GABAA receptor subunits are crucial for morphological and transcriptional neuronal activities. In this study, growth of hamster hippocampal neurons on biohybrid membrane substrates allowed us to show for the first time that the two major GABAA α receptor subunits (α2,5) are capable of early neuronal shaping plus expression differences of some of the main neuronal cytoskeletal factors (GAP‐43, the neurotrophin––BDNF) and of Gluergic subtypes. In a first case the inverse α5 agonist (RY‐080) seemed to account for the reduction of dendritic length at DIV7, very likely via lower BDNF levels. Conversely, the effects of the preferentially specific agonist for hippocampal α2 subunit (flunitrazepam) were, instead, directed at the formation of growth cones at DIV3 in the presence of greatly (P < 0.01) diminished GAP‐43 levels as displayed by strongly reduced axonal sprouting. It is interesting to note that concomitantly to these morphological variations, the transcription of some Gluergic receptor subtypes resulted to be altered. In particular, flunitrazepam was responsible for a distinctly rising expression of axonal NR1 mRNA levels from DIV3 (P < 0.01) until DIV7 (P < 0.001), whereas RY‐080 evoked a very great (P < 0.001) downregulation of dendritic GluR2 at only DIV7. Together, our results demonstrate that GABAA α2,5 receptor‐containing subunits by regulating the precise synchronization of cytoskeletal factors are considered key modulating neuronal elements of hippocampal morphological growth features. Moreover, the notable NR1 and GluR2 transcription differences promoted by these GABAA α subunits tend to favorably corroborate the early role of α2 + α5 on hippocampal neuronal networks in hibernating rodents through the recruitment and activation of silent neurons, and this may provide useful insights regarding molecular neurodegenerative events.

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.

ANTIHYPERTENSIVE AND NEUROPROTECTIVE EFFECTS OF CATESTATIN IN SPONTANEOUSLY HYPERTENSIVE RATS: INTERACTION WITH GABAERGIC TRANSMISSION IN AMYGDALA AND BRAINSTEM

The chromogranin A-derived peptide catestatin (CST) exerts sympathoexcitatory and hypertensive effects when microinjected into the rostral ventrolateral medulla (RVLM: excitatory output); it exhibits sympathoinhibitory and antihypertensive effects when microinjected into the caudal ventrolateral medulla (CVLM: inhibitory output) of vagotomized normotensive rats. Here, continuous infusion of CST into the central amygdalar nucleus (CeA) of spontaneously hypertensive rats (SHRs) for 15 days resulted in a marked decrease of blood pressure (BP) in 6-month- (by 37 mm Hg) and 9-month- (by 65 mm Hg)old rats. Whole-cell patch-clamp recordings on pyramidal CeA neurons revealed that CST increased both spontaneous inhibitory postsynaptic current (sIPSC) amplitude plus frequency, along with reductions of sIPSC rise time and decay time. Inhibition of GABAA receptors (GABAARs) by bicuculline completely abolished CST-induced sIPSC, corroborating that CST signals occur through this major neuroreceptor complex. Hypertension is a major risk factor for cerebrovascular diseases, leading to vascular dementia and neurodegeneration. We found a marked neurodegeneration in the amygdala and brainstem of 9-month-old SHRs, while CST and the GABAAR agonist Muscimol provided significant neuroprotection. Enhanced phosphorylation of Akt and ERK accounted for these neuroprotective effects through anti-inflammatory and anti-apoptotic activities. Overall our results point to CST exerting potent antihypertensive and neuroprotective effects plausibly via a GABAergic output, which constitute a novel therapeutic measure to correct defects in blood flow control in disorders such as stroke and Alzheimers disease.

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.

Environmental stressors and neurobiological features of marine teleosts: histamine receptors as targets.

The excessive levels of aquatic endocrine disruptors (EDs) and namely heavy metals plus xenoestrogens account for irregular gas exchange processes, reduced reproductive success, as well as abnormal social interactions of marine teleost fish. These effects at the encephalic level appear to derive from the interference of major signaling factors such as histamine (HA) neuroreceptor subtypes (H1–4R). HA is one of the main biogenic amine neuronal system responsible for regulatory homeostatic functions, including sleep-wake rhythms and motor activities. Recently, interests have begun to focus attention on toxic effects of some heavy metals, i.e., cadmium (Cd) and lead (Pb), and how they are capable of eliciting motor dysfunctions via HAergic receptor subtypes. Interestingly, subtype 2 (H2R) proved to be a preferential target of heavy metal–dependent altered locomotor maneuvers, as displayed by its specific antagonist (cimetidine)-inducing non-synchronous swimming activities (, Pharmacol Biochem Behav 75:25–33). Conversely, although the preferential H3R antagonist (thioperamide) did not interfer with normal swimming behaviors, it surprisingly did ameliorate heavy metal–dependent hyperactive states (, Toxicol Appl Pharmacol 227:248–256). In the case of the xenoestrogens atrazine and endosulfan, their actions tend to mostly account for feeding alterations through hypothalamic H3R-dependent mechanisms. The aim of this review is to highlight the type of ED-HAergic neuroreceptor variations that are involved in stressor-dependent neurobehavioral responses of commercially valuable marine teleosts.

Dimorphic features of the different α-containing GABA-A receptor subtypes in the cortico-basal ganglia system of two distantly related mammals (hedgehog and rat)

Abstract. This investigation represents a first study dealing with the dimorphic differences of the main α-containing γ-aminobutyric acid (GABAA) receptors in the brain of two distantly related mammals (hedgehog and rat). The labeling of these receptors in the presence of zolpidem (highly selective benzodiazepine agonist) and under the different degree of GABAA/benzodiazepine allosteric coupling activities accounted for a heterogeneous colocalization of α1-enriched and of α2/3-enriched and α5-enriched GABAA receptors in some areas of the cortico-basal ganglia system (including the important ventrolateral thalamic station) of both mammalian sexes. In the hedgehog, the greatest (P<0.001) GABA-dependent reduction of zolpidem inhibition constants was mostly registered in α1- and/or α5-enriched areas, such as the frontoparietal cortex lamina III (235%), ventrolateral thalamic nucleus (128%), and substantia nigra pars reticulata (110%) of the male. However, the greatest reductions in the rat were instead detected in the male substantia nigra pars reticulata (192%) and female striatum (120%), areas which are enriched either by the colocalization of α1- with α2/3-subunits or by all three α-subunits. These results support the contention that a sex-related α-containing GABAA receptor sensitivity constitutes an important element in the execution of skilled motor activities during the different socio-sexual behaviors of the two mammals.