Jinrong Li

Nutritional status alters saccharin intake and sweet receptor mRNA expression in rat taste buds.

Sweet taste usually signifies the presence of caloric food. It is commonly accepted that a close association exists among sweet taste perception, preference, and nutritional status. However, the mechanisms involved remain unknown. To investigate whether nutritional status affects the preference for palatable solutions and alters sweet taste receptor gene expression in rats, we measured saccharin intake and preference using a two-bottle preference test, and changes in body weight, plasma leptin levels, and gene expression for the sweet taste receptor in taste buds in high-fat diet-induced obese rats and chronically diet-restricted rats. We found that the consumption and preference ratios for 0.01 and 0.04 M saccharin were significantly lower in the high-fat diet-induced obese rats than in the normal diet rats, while the serum leptin levels were markedly increased in obese rats. Consistent with the changes in saccharin intake, the gene expression level of the sweet taste receptor T1R3 was significantly decreased in the high-fat diet-induced obese rats compared with the control rats. By contrast, the chronically diet-restricted rats showed remarkably enhanced consumption and preference for 0.04 M saccharin. The serum leptin concentration was decreased, and the gene expression of the leptin receptor was markedly increased in the taste buds. In conclusion, our results suggest that nutritional status alters saccharin preference and the expression of T1R3 in taste buds. These processes may be involved in the mechanisms underlying the modulation of peripheral sweet taste sensitivity, in which leptin plays a role.

Activation of μ-opioid receptors in the central nucleus of the amygdala induces hypertonic sodium intake.

Opioid mechanisms are involved in the control of water and NaCl intake and opioid receptors (ORs) are present in the central nucleus of the amygdala (CeA), a site of important facilitatory mechanisms related to the control of sodium appetite. Therefore, in the present study we investigated the effects of the activation of μ-ORs in the CeA on 0.3 M NaCl and water intake in rats. Male Sprague-Dawley rats with stainless steel cannulas implanted bilaterally in the CeA were used. In rats submitted to water deprivation-partial rehydration, bilateral injections of the selective μ-OR agonist [D-Ala², N-Me-Phe⁴, Gly⁵-ol]-enkephalin (DAMGO) in the doses of 1, 2, and 4 nmol into the CeA induced a dose-related increase of 0.3M NaCl intake and water intake, and bilateral injections of the selective μ-OR antagonist D-Phe-Cys-Trp-Arg-Thr-Pen-Thr-NH₂ (CTAP) in the doses of 0.5, 1, and 2 nmol into the CeA produced a dose-related decrease of 0.3 M NaCl and water intake induced by DAMGO 2 nmol into the same site. In rats treated with the diuretic furosemide (10 mg/kg b.w.) combined with the angiotensin-converting enzyme inhibitor captopril (5 mg/kg b.w.) injected subcutaneously, bilateral injections of DAMGO 2 nmol into the CeA increased 0.3 M NaCl intake and water intake and the blockade of μ-ORs with CTAP 1 nmol injected into the CeA reduced the increase in 0.3 M NaCl intake and water intake induced by DAMGO 2 nmol into the same site. Bilateral injections of DAMGO into the CeA did not change urinary volume, sodium urinary excretion and mean arterial pressure, but increased activity. Thus stimulating μ-ORs in the CeA increases hypertonic sodium intake, whereas antagonizing these sites inhibits hypertonic sodium intake. Together, our results implicate μ-ORs in the CeA in a positive regulation of sodium intake.

c-Fos expression in rat brainstem following intake of sucrose or saccharin

To examine whether the activation of brainstem neurons during intake of a sweet tastant is due to orosensory signals or post-ingestive factors, we compared the distribution of c-Fos-like immunoreactivity (c-FLI) in the nucleus of the solitary tract (NST) and parabrachial nucleus (PBN) of brainstem following ingestion of 0.25 Msucrose or 0.005 M saccharin solutions. Immunopositive neurons were localized mainly in the middle zone of the PBN and four rostral-caudal subregions of the NST. Intake of sucrose increased the number of FLI neurons in almost every subnucleus of the PBN (F(2,13) = 7.610, P = 0.023), in addition to the caudal NST at the level of the area postrema (F(2,13) = 10.777, P = 0.003) and the NST intermediate zone (F(2,13) = 7.193, P = 0.014). No significant increase in the number of c-Fos positive neurons was detected in response to saccharin ingestion, although there was a trend towards a modest increase in a few select NST and PBN nuclei. These results suggest that the PBN and NST may be involved in sweet taste perception and modulation of sweet tastant intake, but the significantly enhanced intensity of Fos expression induced by sucrose indicates that PBN/NST neuronal activity is driven by the integrated effects of sweet taste sensation and post-ingestive signals.

Involvement of brain ANG II in acute sodium depletion induced salty taste changes

Many investigations have been devoted to determining the role of angiotensin II (ANG II) and aldosterone (ALD) in sodium-depletion-induced sodium appetite, but few were focused on the mechanisms mediating the salty taste changes accompanied with sodium depletion. To further elucidate the mechanism of renin-angiotensin-aldosterone system (RAAS) action in mediating sodium intake behavior and accompanied salty taste changes, the present study examined the salty taste function changes accompanied with sodium depletion induced by furosemide (Furo) combined with different doses of angiotensin converting enzyme (ACE) inhibitor, captopril (Cap). Both the peripheral and central RAAS activity and the nuclei Fos immunoreactivity (Fos-ir) expression in the forebrain area were investigated. Results showed that sodium depletion induced by Furo+low-Cap increased taste preference for hypertonic NaCl solution with amplified brain action of ANG II but without peripheral action, while Furosemide combined with a high dose of captopril can partially inhibit the formation of brain ANG II, with parallel decreased effects on salty taste changes. And the resulting elevating forebrain ANG II may activate a variety of brain areas including SFO, PVN, SON and OVLT in sodium depleted rats injected with Furo+low-Cap, which underlines salty taste function and sodium intake behavioral changes. Neurons in SFO and OVLT may be activated mainly by brain ANG II, while PVN and SON activation may not be completely ANG II dependent. These findings suggested that forebrain derived ANG II may play a critical role in the salty taste function changes accompanied with acute sodium depletion.

Inhibitory effect of activation of GABAA receptor in the central nucleus of amygdala on the sodium intake in the sodium-depleted rat

The present study investigated the effects of a microinjection of GABA(A) receptor agonist (muscimol) and antagonist (bicuculline) into the central nucleus of the amygdala (CeA) in sodium-depleted rats. We measured the sodium intake and identified the neuronal activation in the brainstem induced by activating the GABA(A) receptors in the CeA using Fos immunohistochemistry. Muscimol (0.20, 0.35 or 0.50 nmol, in 0.2μl) that was injected bilaterally into the CeA decreased the 0.3M NaCl and water intake in a dose-dependent manner. Microinjection of 0.02 nmol/0.2μl muscimol also decreased the NaCl intake, but had no effect on the water intake. The inhibitory effect of muscimol (0.20 nmol) on the sodium and water intake could be blocked by pretreatment with bicuculline intra-CeA microinjection (0.4 nmol). However, bilateral injections of bicuculline alone into the CeA did not affect the NaCl or water intake. Furthermore, microinjection of muscimol (0.20 nmol) into the CeA increased the number of Fos-like immunoreactive (FLI) neurons in the caudal and intermediate parts of the nucleus of the tractus solitarius (cNTS and iNTS) and the lateral parabrachial nucleus (LPBN). These results suggest that GABA(A) receptors within the CeA may be involved in mediating the sodium intake in the sodium-depleted rat, and the cNTS, iNTS and LPBN were probably involved in this mechanism.

Lesions of the central nucleus of the amygdala decrease taste threshold for sodium chloride in rats

Previous studies reported that NaCl intake was down-regulated in rats with bilateral lesions of the central nucleus of the amygdala (CeA). In line with the evidence from anatomical and physiological studies, such an inhibition could be the result of altered taste threshold for NaCl, one of the important factors in assessing taste functions. To assess the effect of CeA on the taste threshold for NaCl, a conditioned taste aversion (CTA) to a suprathreshold concentration of NaCl (0.1M) in rats with bilateral lesions of CeA or sham lesions was first established. And then, two-bottle choice tests between water and a series of concentrations of NaCl were conducted. The taste threshold for NaCl is defined as the lowest concentration at which there is a reliable difference scores between conditioned and control subjects. Rats with CeA lesions acquired a taste aversion for 0.1M NaCl when it was paired with LiCl and still retained the aversion after the two-bottle choice test. The results of the two-bottle choice test showed that the taste threshold for NaCl was 0.0006M in rats with CeA lesions, whereas in rats with sham lesions the threshold was 0.005M, which was identical to that of normal rats. The conditioned results confirm the claim that CeA is not essential in the profile of conditioned taste aversion. Our findings demonstrate that lesions of the CeA increased the sensitivity to NaCl taste in rats, indicating that the CeA may be involved in encoding the intensity of salty gustation elicited by NaCl.

Increased sucrose intake and corresponding c-Fos in amygdala and parabrachial nucleus of dietary obese rats

The intake-excitatory effects of caloric foods are mainly due to the palatable taste and the ensuing positive postingestive effects. Dietary obese individuals are inclined to overeat high caloric foods. However, it is still unclear whether the taste or postingestive reinforcement mainly contributes to the excessive intake by obese individuals. In the present study, we measured 10- or 120-min sucrose solution drunk by dietary obese rats and measured c-Fos expression following 120-min tests in the central nucleus of amygdala (CeA), a forebrain nucleus involved in the hedonic reward and craving, and the parabrachial nucleus (PBN), a taste relay area responsive to positive postingestive effects. Dietary obese rats, compared with those fed normal chow, ingested larger amounts of sucrose solution (0.25 M) in the 120-min test, but not in the 10-min test. In addition, significantly more sucrose-induced c-Fos positive cells were found in the CeA, but much less in the external lateral subnucleus of the PBN of dietary obese rats. Our results demonstrate that increased sucrose intake in dietary obese rats is mainly due to the alteration of postingestive effects. The differences in these postingestive effects in obesity may involve greater positive/excitatory signals in which the CeA may play a role, and less negative/inhibitory signals in which the el-PBN may be involved.

Fos positive neurons in the brain stem and amygdala mostly express vesicular glutamate transporter 3 after bitter taste stimulation

The present study examined the relationship between vesicular glutamate transpoter-3 (VGLUT3) positive cells and the activation of neurons in the brainstem and amygdala by bitter taste, using double-labeling immunohistochemistry. Conscious animals were subjected to intraoral bitter taste stimulation with quinine solution. Following this, neuronal activation was assessed by c-Fos expression and an analysis of c-Fos expression cells, VGLUT3 positive cells and double-labeled cells was made in the nucleus of the solitary tract (NST), the parabrachial nucleus (PBN) and amygdala. Results showed that intraoral bitter taste stimulation led to significant increases in the number of c-Fos-expressing and double-labeled cells in the NST, PBN and amygdala. Results also showed a decrease in the number of c-Fos-positive and double-labeled cells in the amygdala, in comparison with neurons in the brainstem, after bitter taste stimulation. These results suggest that bitter taste activates cells in the NST, PBN and amygdala and these effects are partly mediated by VGLUT3 positive cells. Moreover, double-labeled neurons also exhibited a preferential distribution after quinine stimulation compared to water stimulation.

Clinical therapeutic effect of dexmedetomidine on patients during the extubation period of general anesthesia

OBJECTIVE To observe the clinical effect of dexmedetomidine on patients during the extubation in general anesthesia.
 METHODS A total of 90 patients scheduled for general anesthesia were divided into 3 groups (n=30): A dexmedetomidine group (DEX group), a midazolam group (MID group), and a control group(C group). Anesthesia drugs were stopped 10 minutes before the end of the operation. 
At the same time, the patients in the DEX group were given dexmedetomidine at the rate of 
1 g/(kg.h) for 10 min by vein first, which was continuously pumped at the rate of 0.3 g/(kg.h) for 20 min after the operation. The patients in the MID group were given midazolamin at 0.5 mg/kg for 60 s by vein first, which was continuously pumped at the rate of the 0.04 mg/(kg.h) for 20 min after the operation. The patients in the C group were not given any drug. Awakening time and extubation time after the operation were recorded. Ramsay scores, heart rate, mean arterial blood pressure, respiratory rate, and SpO₂were recorded at time of extubation, 10 min or 1 h after extubation. Chills, nausea, vomiting and other side effects after the operation were recorded.
 RESULTS Awakening and extubation time were not affected in the DEX group, while delayed recovery occurred in the MID group (P<0.05). Compared with the C group, patients in the DEX and MID groups gained better sedative effect, with 2-4 Ramsay scores (P<0.05). The blood pressure and heart rate were steady in the DEX and MID groups, while inhibition of respiration appeared in the MID group.
 CONCLUSION Dexmedetomidine can provide an effective sedation for the patients without affecting the awakening and extubation time. The hemodynamics could be stably maintained by using dexmedetomidine in patients during the extubation in general anesthesia.

[High fat diet induces obesity and alters the expression of MCHR1 and OB-Rb in the adipose tissue].

OBJECTIVE To investigate the effect of high-fat (HF) diet on the body weight and the mRNA expression of melanin concentrating hormone receptor 1 (MCHR1) and leptin receptor (OB-Rb) in the adipose tissue in rats, the two important and opposite factors in regulating the body weight. METHODS Post-weaning rats were divided into 3 groups: the NC group were fed a normal-chow diet (NC) (13% calories from fat), the HF group with a HF-diet (47% calories from fat) and the PHF group pair-fed a HF-diet (47% calories from fat). At the end of 8th week, the gained bodyweight, the plasma melanin concentrating hormone (MCH) and leptin, and the expression levels of MCHR1 and OB-Rb in the adipose tissue were measured. RESULTS Both the HF-diet and pair-fed HF-diet enhanced the body weight (P<0.01), plasma MCH (P<0.01) and leptin concentrations (P<0.05). In the adipose tissue, HF-diet resulted in significant increase in MCHR1 (PHF group,P<0.05) and decrease in OB-Rb mRNA levels (HF group,P<0.01; PHF group,P<0.05). No statistical difference was found between the HF group and the PHF group in terms of the aforementioned data (P>0.05). CONCLUSION Chronic intake of iso-caloric HF-diet and ad libitum HF-diet obviously results in increase in the body weight, serum leptin, and MCH concentration. Diet-induced obesity and related metabolic disorders are possibly correlated with up-regulated expression of MCHR1 and down-regulated expression of OB-Rb in the adipose tissue.