Highlights • Female rats presented UCN-1 neurons in NTS and ventral medulla. • Ovariectomized females presented the greatest number of UCN-1 neurons. • Sex and estrogen effect the distribution of ...UCN-1 neurons in brainstem.
Objective Obstructive sleep apnea, a breathing disorder caused by the repetitive collapse of the upper airway during sleep, results in a state of chronic intermittent hypoxia (CIH). Although the ...etiology and consequences of CIH are extensively investigated in the adult, the developmental ramifications of this disease process are unknown. Design This study was done to investigate the effect of CIH during gestation on offspring development. Pregnant female Spraque-Dawley rats were exposed to daily CIH throughout the gestational period. Results Postnatal day-1 offspring from CIH mothers were asymmetrically growth restricted, with decreased body weights and elevated brain-weight:liver-weight ratios. Furthermore, CIH newborns had elevated heart- and brain-weight:body weight ratios, and decreased liver-weight:body weight ratios. By adulthood, body weights of growth restricted offspring were significantly greater, as were the liver-weight:body weight ratios. CIH offspring also had greater body fat deposition, were hyperglycemic and had elevated plasma levels of insulin during development into adults. Conclusion These data suggest that alteration of the maternal intrauterine environment by gestational CIH effects the long-term development of the offspring and increases the risk of the offspring to metabolic diseases in adulthood.
Chronic intermittent hypoxia (CIH), a pathophysiological manifestation of obstructive sleep apnea (OSA), is strongly correlated with obesity, as patients with the disease experience weight gain while ...exhibiting elevated plasma levels of leptin. This study was done to determine whether a relationship may exist between CIH and obesity, and body energy balance and leptin signaling during CIH. Sprague-Dawley rats were exposed to 96 days of CIH or normoxic control conditions, and were assessed for measures of body weight, food and water intake, and food conversion efficiency. At the completion of the study leptin sensitivity, locomotor activity, fat pad mass and plasma leptin levels were determined within each group. Additionally, the hypothalamic arcuate nucleus (ARC) was isolated and assessed for changes in the expression of proteins associated with leptin receptor signaling. CIH animals were found to have reduced locomotor activity and food conversion efficiency. Additionally, the CIH group had increased food and water intake over the study period and had a higher body weight compared to normoxic controls at the end of the study. Basal plasma concentrations of leptin were significantly elevated in CIH exposed animals. To test whether a resistance to leptin may have occurred in the CIH animals due to the elevated plasma levels of leptin, an acute exogenous (ip) leptin (0.04 mg/kg carrier-free recombinant rat leptin) injection was administered to the normoxic and CIH exposed animals. Leptin injections into the normoxic controls reduced their food intake, whereas CIH animals did not alter their food intake compared to vehicle injected CIH animals. Within ARC, CIH animals had reduced protein expression of the short form of the obese (leptin) receptor (isoform OBR
) and showed a trend toward an elevated protein expression of the long form of obese (leptin) receptor (OBRb). In addition, pro-opiomelanocortin (POMC) protein expression was reduced, but increased expression of the phosphorylated extracellular-signal-regulated kinase 1/2 (pERK1/2) and of the suppressor of cytokine signaling 3 (SOCS3) proteins was observed in the CIH group, with little change in phosphorylated signal transducer and activator of transcription 3 (pSTAT3). Taken together, these data suggest that long-term exposure to CIH, as seen in obstructive sleep apnea, may contribute to a state of leptin resistance promoting an increase in body weight.
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•AII (≥1 nM) induced a persistent Ca2+i increase in acutely dissociated SFO neurons.•The persistent AII-induced Ca2+i increase was maintained by Ca2+ entry.•The Ca2+ entry was ...mediated in part by voltage-gated Ca2+ channels of L and P/Q types.•CaMK and PKC were involved in the persistent Ca2+i increase.•GABA reversibly inhibited the persistent Ca2+i increase.
It is known that angiotensin II (AII) is sensed by subfornical organ (SFO) to induce drinking behaviors and autonomic changes. AII at picomolar concentrations have been shown to induce Ca2+ oscillations and increase in the amplitude and frequency of spontaneous Ca2+ oscillations in SFO neurons. The present study was conducted to examine effects of nanomolar concentrations of AII using the Fura-2 Ca2+-imaging technique in acutely dissociated SFO neurons. AII at nanomolar concentrations induced an initial Ca2+i peak followed by a persistent Ca2+i increase lasting for longer than 1 hour. By contrast, Ca2+i responses to 50 mM K+, maximally effective concentrations of glutamate, carbachol, and vasopressin, and AII given at picomolar concentrations returned to the basal level within 20 min. The AII-induced Ca2+i increase was blocked by the AT1 antagonist losartan. However, losartan had no effect when added during the persistent phase. The persistent phase was suppressed by extracellular Ca2+ removal, significantly inhibited by blockers of L and P/Q type Ca2+ channels , but unaffected by inhibition of Ca2+ store Ca2+ ATPase. The persistent phase was reversibly suppressed by GABA and inhibited by CaMK and PKC inhibitors. These results suggest that the persistent Ca2+i increase evoked by nanomolar concentrations of AII is initiated by AT1 receptor activation and maintained by Ca2+ entry mechanisms in part through L and P/Q type Ca2+ channels, and that CaMK and PKC are involved in this process. The persistent Ca2+i increase induced by AII at high pathophysiological levels may have a significant role in altering SFO neuronal functions.
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•Ca2+i of SFO neurons were examined in acutely dissociated neurons of rat.•SFO neurons but not glial cells exhibited spontaneous Ca2+ oscillations.•Ca2+ oscillations were arrested by ...Ca2+ free and inhibited by nicardipine.•Angiotensin II at picomolar concentrations evoked Ca2+ oscillations in silent cells.•The primary inhibitory transmitter, GABA, arrested spontaneous Ca2+ oscillations.
Characteristics of subfornical organ (SFO) neurons were examined by measuring the cytosolic Ca2+ concentration (Ca2+i) in acutely dissociated neurons of the rat. SFO neurons, defined by the responsiveness to 50 mM K+ (n = 67) responded to glutamate (86%), angiotensin II (AII) (50%), arginine vasopressin (AVP) (66%) and/or carbachol (CCh) (61%), at their maximal concentrations, with marked increases in Ca2+i. More than a half (174/307) of SFO neurons examined exhibited spontaneous Ca2+ oscillations, while the remainder showed a relatively stable baseline under unstimulated conditions. Spontaneous Ca2+ oscillations were suppressed when extracellular Ca2+ was removed and were inhibited when extracellular Na+ was replaced with equimolar N-methyl-D-glucamine. Ca2+ oscillations were unaffected by the inhibitor of Ca2+-dependent ATPases cyclopiazonic acid, the N-type Ca2+ channel blocker ω-conotoxin GVIA and the P/Q-type Ca2+ channel blocker ω-agatoxin IVA, but significantly inhibited by the high-voltage-activated Ca2+ channel blocker Cd2+ and the L-type Ca2+ channel blocker nicardipine. Ca2+ oscillations were also completely arrested by the voltage-gated Na+ channel blocker tetrodotoxin in 50% of SFO neurons but only partially in the remaining neurons. These results suggest that SFO neurons exhibit spontaneous membrane Ca2+ oscillations that are dependent in part on Ca2+ entry through L-type Ca2+ channels, whose activation may result from burst firing. Moreover, AII at picomolar concentrations induced Ca2+ oscillations in neurons showing no spontaneous Ca2+ oscillations, while spontaneous Ca2+ oscillations were arrested by gamma-aminobutyric acid (10 μM), suggesting that rises in Ca2+i during Ca2+ oscillations may play an important role in the modulation of SFO neuron function.
•Leptin injections into NTS depressor sites elicit sympathoexcitatory responses.•Leptin in NTS attenuates depressor responses to activation of NTS neurons.•Leptin in NTS attenuates cardiovascular ...responses to aortic baroreceptor activation.
Recent data suggests that neurons expressing the long form of the leptin receptor form at least two distinct groups within the caudal nucleus of the solitary tract (NTS): a group within the lateral NTS (Slt) and one within the medial (Sm) and gelantinosa (Sg) NTS. Discrete injections of leptin into Sm and Sg, a region that receives chemoreceptor input, elicit increases in arterial pressure (AP) and renal sympathetic nerve activity (RSNA). However, the effect of microinjections of leptin into Slt, a region that receives baroreceptor input is unknown. Experiments were done in the urethane-chloralose anesthetized, paralyzed and artificially ventilated Wistar or Zucker obese rat to determine leptin's effect in Slt on heart rate (HR), AP and RSNA during electrical stimulation of the aortic depressor nerve (ADN). Depressor sites within Slt were first identified by the microinjection of l-glutamate (Glu; 0.25M; 10nl) followed by leptin microinjections. In the Wistar rat leptin microinjection (50ng; 20nl) into depressor sites within the lateral Slt elicited increases in HR and RSNA, but no changes in AP. Additionally, leptin injections into Slt prior to Glu injections at the same site or to stimulation of the ADN were found to attenuate the decreases in HR, AP and RSNA to both the Glu injection and ADN stimulation. In Zucker obese rats, leptin injections into NTS depressor sites did not elicit cardiovascular responses, nor altered the cardiovascular responses elicited by stimulation of ADN. Those data suggest that leptin acts at the level of NTS to alter the activity of neurons that mediate the cardiovascular responses to activation of the aortic baroreceptor reflex.
Abstract Although anatomical data indicates that the caudal ventrolateral medulla (CVLM) projects directly to the subfornical organ (SFO), little is known about the afferent information relayed ...through the CVLM to SFO. Experiments were done in the anesthetized rat to investigate whether CVLM neurons mediate baroreceptor afferent information to SFO and whether this afferent information alters the response of SFO neurons to systemic injections of angiotensin II (ANG II). Extracellular single unit recordings were made from 78 spontaneously discharging single units in SFO. Of these, 32 (41%) responded to microinjection of L-glutamate (L-Glu; 0.25 M; 10 nl) into CVLM (27/32 were inhibited and 5/32 were excited). All 32 units also were excited by systemic injections of ANG II (250 ng/0.1 ml, ia). However, only those units inhibited by CVLM ( n =27) were found to be inhibited by the reflex activation of baroreceptors following systemic injections of phenylephrine (2 μg/kg, iv). Activation of CVLM or arterial baroreceptors in conjunction with ANG II resulted in an attenuation of the SFO unit's response to ANG II. Finally, microinjections (100 nl) of the synaptic blocker CoCl2 or the non-specific glutamate receptor antagonist kynurenic acid into CVLM attenuated (10/13 units tested) the SFO neuron's response to activation of baroreceptors, but not the unit's response evoked by systemic ANG II. Taken together, these data suggest that baroreceptor afferent information relayed through CVLM functions to modulate of the activity of neurons within SFO to extracellular signals of body fluid balance.
The paraventricular nucleus of the thalamus (PVT) is known to function as a site of integration of brainstem, limbic and cortical afferent information involved in affective behaviors, and visceral ...and homeostatic regulation. This study investigated the role of the hypothalamus in mediating the arterial pressure (AP) and heart rate (HR) changes elicited by activation of PVT neurons. In the first series of experiments, cardiovascular responsive sites were identified in PVT using L‐glutamate (Glu; 10 nl, 0.25 M) microinjections in chloralose‐anesthetized Wistar rats. Glu injections in the anterior PVT elicited decreases in mean AP (MAP, −20 ± 3 mmHg) and HR (−15 ± 5 bpm). In the second series, iontophoretic injections of the anterograde tract tracer PHA‐L (2.5%) were made at these depressor sites in the anterior PVT in Wistar rats. Within the hypothalamus, PHA‐L labelled fibers and presumptive terminals were predominantly found bilaterally in and around the anterior, dorsolateral and the ventromedial parvocellular components of the paraventricular nucleus of the hypothalamus (PVH). A few scattered PHA‐L labelled fibers were also observed within the posterior magnocellular component of PVH, the supraoptic nucleus, the lateral and dorsomedial hypothalamic areas, and the area of the tuber cinereum. In the final series, bilateral microinjection (100 nl) of either the synaptic blocker CoCl2, the non‐specific Glu antagonist kynurenic acid or the selective NMDA receptor antagonists 2‐amino‐5‐phosphonovalerate were made into the PVH in chloralose‐anesthetized Wistar rats. Injections of these compounds did not significantly alter the resting level of AP or HR. However, all injected compounds attenuated the MAP responses (grouped data; −15 ± 5 mmHg; p<0.01), and completely blocked the HR responses (grouped data, −3 ± 5 bpm; p<0.01) to PVT neuronal activation (control responses; MAP, −25 ± 3 mmHg; HR, −19 ± 7). These data suggest that PVT functions to alter cardiac sympathoinhibitory responses associated with arousal, stress, and affective behaviors through a glutamatergic pathway relaying in PVH.
Support or Funding Information
Supported in part by the Heart and Stroke Foundation of Ontario
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