Hypertension in Prenatally Undernourished Young-Adult Rats Is Maintained by Tonic Reciprocal Paraventricular–Coerulear Excitatory Interactions

Prenatally malnourished rats develop hypertension in adulthood, in part through increased α1-adrenoceptor-mediated outflow from the paraventricular nucleus (PVN) to the sympathetic system. We studied whether both α1-adrenoceptor-mediated noradrenergic excitatory pathways from the locus coeruleus (LC) to the PVN and their reciprocal excitatory CRFergic connections contribute to prenatal undernutrition-induced hypertension. For that purpose, we microinjected either α1-adrenoceptor or CRH receptor agonists and/or antagonists in the PVN or the LC, respectively. We also determined the α1-adrenoceptor density in whole hypothalamus and the expression levels of α1A-adrenoceptor mRNA in the PVN. The results showed that: (i) agonists microinjection increased systolic blood pressure and heart rate in normotensive eutrophic rats, but not in prenatally malnourished subjects; (ii) antagonists microinjection reduced hypertension and tachycardia in undernourished rats, but not in eutrophic controls; (iii) in undernourished animals, antagonist administration to one nuclei allowed the agonists recover full efficacy in the complementary nucleus, inducing hypertension and tachycardia; (iv) early undernutrition did not modify the number of α1-adrenoceptor binding sites in hypothalamus, but reduced the number of cells expressing α1A-adrenoceptor mRNA in the PVN. These results support the hypothesis that systolic pressure and heart rate are increased by tonic reciprocal paraventricular–coerulear excitatory interactions in prenatally undernourished young-adult rats.

Polysomnographic Findings in Fragile X Syndrome Children with EEG Abnormalities

Fragile X syndrome (FXS) is a genetic syndrome with intellectual disability due to the loss of expression of the FMR1 gene located on chromosome X (Xq27.3). This mutation can suppress the fragile X mental retardation protein (FMRP) with an impact on synaptic functioning and neuronal plasticity. Among associated sign and symptoms of this genetic condition, sleep disturbances have been already described, but few polysomnographic reports in pediatric age have been reported. This multicenter case-control study is aimed at assessing the sleep macrostructure and at analyzing the presence of EEG abnormalities in a cohort of FXS children. We enrolled children with FXS and, as controls, children with typical development. All subjects underwent at least 1 overnight polysomnographic recording (PSG). All recorded data obtained from patients and controls were compared. In children with FXS, all PSG-recorded parameters resulted pathological values compared to those obtained from controls, and in FXS children only, we recorded interictal epileptiform discharges (IEDs), as diffuse or focal spikes and sharp waves, usually singles or in brief runs with intermittent or occasional incidence. A possible link between IEDs and alterations in the circadian sleep-wake cycle may suggest a common dysregulation of the balance between inhibitory and excitatory pathways in these patients. The alteration in sleep pattern in children with FXS may negatively impact the neuropsychological and behavioral functioning, adding increasing burn of the disease on the overall management of these patients. In this regard, treating physicians have to early detect sleep disturbances in their patients for tailored management, in order to prevent adjunctive comorbidities.

Mechanisms of Neuropathic Pain

Neuropathic pain arises as a direct consequence of a lesion or a disease affecting the somatosensory system. The mechanisms of neuropathic pain are often complex and difficult to study given the diversity of causes, pathology, and clinical presentation of various neuropathic pain conditions. Common mechanisms include peripheral and central sensitizations. Peripheral sensitization refers to increased responsiveness and reduced threshold of nociceptive neurons in the periphery to the stimulation of their receptive fields. Central sensitization refers to the augmented response of central signaling neurons. The mechanisms of peripheral and central sensitization are understood at the cellular and molecular levels. The processes of neuroplasticity involve activation of inflammatory cells, such as macrophages (and microglia in the central nervous system) and other immune cells, and release of inflammatory mediators, such as cytokines, chemokines, and a host of other mediators. Interactions of these mediators with specific receptors in the nociceptors or the spinal cord neurons may lead to phosphorylation or changes in expression of ion channels, receptors, transporters, and other effectors through specific signaling pathways. These events ultimately lead to changes in excitability, conductivity, and transmissibility of neurons in the pain processing pathways. Other factors may include disinhibition of interneurons, changes in descending inhibitory and excitatory pathways, and reorganization of the cortical areas and their interconnections.

Using transcranial magnetic stimulation to investigate the neural mechanisms of inhibitory control

Many everyday actions require inhibitory control. The success of these actions depends on the availability of prior information regarding stopping demands. Using transcranial magnetic stimulation (TMS), Cirillo and colleagues (Cirillo J, Cowie MJ, MacDonald HJ, Byblow WD. J Neurophysiol 119: 877–886, 2018) provide novel neurophysiological evidence for distinct roles of intracortical inhibitory mechanisms underlying inhibitory control. Other, nonexclusive mechanisms such as disfacilitation of excitatory pathways and interhemispheric inhibition may also contribute to inhibitory control. Accordingly, diverse TMS protocols are a valuable assessment tool to investigate these mechanisms.

Behavior Variability of a Conditional Gene Knockout Mouse as a Measure of Subtle Phenotypic Trait Expression. The Case of Mouse Executive Function Distortion

ABSTRACTTask learning relies on brain executive function (EF), the construct of controlling and coordinating behavior under the everlasting flow of environmental changes. We have previously shown, that a complete knockout of a vertebrate brain-specific pair of gene paralogs (Ntng1/2) distorts the mouse EF, making behavior less predictable (more variable) via the affected working memory and attention (1). In the current study, conditionally targeting either serotonin transporter (5-HTT) or Emx1-expressing neurons, we show that the cell type-specific ablation of Ntng1 within the excitatory circuits of either cortex or thalamus does not have a profound impact on the EF but rather affects its certain modalities, i.e. impulsivity and/or selective attention, modulated by cognitive demand. Several mice of both conditional genotypes simultaneously occupy either top or bottom parameter-specific behavioral ranks, indicative of a subject-unique antagonistic either proficit or deficit of function within the same behavior. Employing genotype-attributable behavior variability as a phenotypic trait, we deduce, that Ntng1-parsed excitatory pathways contribute but do not fully reconstitute the attention-impulsivity phenotypes, associated with the mouse EF deficit. However, complete knockdown of Ntng1/2, and associated with it behavior variability, explains the deficit of executive function and task learning.

Neural and genetic degeneracy underlies Caenorhabditis elegans feeding behavior

Degenerate networks, in which structurally distinct elements can perform the same function or yield the same output, are ubiquitous in biology. Degeneracy contributes to the robustness and adaptability of networks in varied environmental and evolutionary contexts. However, how degenerate neural networks regulate behavior in vivo is poorly understood, especially at the genetic level. Here, we identify degenerate neural and genetic mechanisms that underlie excitation of the pharynx (feeding organ) in the nematode Caenorhabditis elegans using cell-specific optogenetic excitation and inhibition. We show that the pharyngeal neurons MC, M2, M4, and I1 form multiple direct and indirect excitatory pathways in a robust network for control of pharyngeal pumping. I1 excites pumping via MC and M2 in a state-dependent manner. We identify nicotinic and muscarinic receptors through which the pharyngeal network regulates feeding rate. These results identify two different mechanisms by which degeneracy is manifest in a neural circuit in vivo.

Abstract 249: High Salt and Aldosterone Increase (pro)renin Receptor Expression Through Enac α Activation in Neuronal Cells

Activation of the brain renin-angiotensin-aldosterone system plays an essential role in hyperactivity of the sympathetic nervous system during salt sensitive hypertension. We previously reported an up-regulation of (pro)renin receptor (PRR) expression levels in DOCA-salt hypertensive mice brain. However, the mechanism by which PRR is regulated in DOCA-salt hypertension remains unknown. We hypothesize that aldosterone increases PRR expression by activation of epithelial sodium channel (ENaC). To test this hypothesis, we used neuro-2A cell line from brain hypothalamus which expresses all ENaC α, β, and γ subunits, as well as mineralocorticoid receptor (MR). Cells were incubated in normal salt (NS, 142 mM) or high salt (HS, 160 mM) culture medium for 1, 3, or 5 days, with or without the addition of aldosterone (1μM) for 2 hours. Interestingly, the combination of HS (5 days) with aldosterone significantly increased PRR mRNA levels (fold change) (3.28 ± 0.11) compared to NS (1.00 ± 0.01), HS (1.23 ± 0.01), or aldosterone (1.40 ± 0.01) alone in Neuro-2A cells. The PRR expression levels (1.253 ± 0.006; 1.89 ± 0.002) were significantly attenuated by ENaC inhibition (amiloride, 10μM) or MR inhibition (eplernone, 10μM) respectively (P<0.05), suggesting that ENaC and MR activation mediates the up-regulation of PRR expression in neuronal cells. Furthermore, HS increased ENaC α (2.42 ± 0.01), while decreased ENaC β (0.05 ± 0.01), and ENaC γ (0.03 ± 0.01) mRNA expression levels compared to NS treatment (1.00 ±0.01) in Neuro-2A cells suggesting an increase in synthesis rate of α subunit following HS treatment. In summary, HS and aldosterone increase PRR expression levels via activation of ENaC. ENaC α may be the regulating subunit in the assembly of functional ENaC in neuronal cells. We conclude that regulation of PRR expression by high salt and aldosterone may be the critical step to activate angiotensinergic sympatho-excitatory pathways leading to salt sensitive hypertension.

Pyramidal Cells and Cytochrome P450 Epoxygenase Products in the Neurovascular Coupling Response to Basal Forebrain Cholinergic Input

Activation of the basal forebrain (BF), the primary source of acetylcholine (ACh) in the cortex, broadly increases cortical cerebral blood flow (CBF), a response downstream to ACh release. Although endothelial nitric oxide and cholinoceptive GABA (γ-aminobutyric acid) interneurons have been implicated, little is known about the role of pyramidal cells in this response and their possible interaction with astrocytes. Using c-Fos immunohistochemistry as a marker of neuronal activation and laser-Doppler flowmetry, we measured changes in CBF evoked by BF stimulation following pharmacological blockade of c-Fos-identified excitatory pathways, astroglial metabolism, or vasoactive mediators. Pyramidal cells including those that express cyclooxygenase-2 (COX-2) displayed c-Fos upregulation. Glutamate acting via NMDA, AMPA, and mGlu receptors was involved in the evoked CBF response, NMDA receptors having the highest contribution (∼33%). In contrast, nonselective and selective COX-2 inhibition did not affect the evoked CBF response (+0.4% to 6.9%, ns). The metabolic gliotoxins fluorocitrate and fluoroacetate, the cytochrome P450 epoxygenase inhibitor MS-PPOH and the selective epoxyeicosatrienoic acids (EETs) antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) all blocked the evoked CBF response by ∼50%. Together, the data demonstrate that the hyperemic response to BF stimulation is largely mediated by glutamate released from activated pyramidal cells and by vasoactive EETs, likely originating from activated astrocytes.