Forebrain neurons that project to the gustatory parabrachial nucleus in rat lack glutamic acid decarboxylase

Evidence suggests that GABA might mediate the inhibitory influence of centrifugal inputs on taste-evoked responses in the parabrachial nucleus (PBN). Previous studies show that activation of the gustatory cortex (GC), bed nucleus of the stria terminalis (BNST), central nucleus of the amygdala (CeA), and lateral hypothalamus (LH) inhibits PBN taste responses, GABAergic neurons are present in these forebrain regions, and GABA reduces the input resistance of PBN neurons. The present study investigated the expression of glutamic acid decarboxylase immunoreactivity (GAD_67 ir) in GC, BNST, CeA, and LH neurons that project to the PBN in rats. After anesthesia (50 mg/kg ip Nembutal), injections of the retrograde tracer Fluorogold (FG) were made in the physiologically defined gustatory PBN. Brain tissue containing the above forebrain structures was processed and examined for FG and GAD_67 ir. Similar to previous studies, each forebrain site contained retrogradely labeled neurons. Our results suggest further that the major source of input to the PBN taste region is the CeA (608 total cells) followed by GC (257 cells), LH (106 cells), and BNST (92 cells). This suggests a differential contribution to centrifugal control of PBN taste processing. We further show that despite the presence of GAD_67 neurons in each forebrain area, colocalization was extremely rare, occurring only in 3 out of 1,063 FG-labeled cells. If we assume that the influence of centrifugal input is mediated by direct projections to the gustatory region of the PBN, then GABAergic forebrain neurons apparently are not part of this descending pathway.     

The number and location of Fos-like immunoreactive neurons in the central gustatory system following electrical stimulation of the parabrachial nucleus in conscious rats

Electrical stimulation of the waist area (W) of the parabrachial nucleus (PBN) in conscious rats elicits stereotypical oromotor behaviors (Galvin et al. 2004). To identify neurons possibly involved in these behavioral responses, we used Fos immunohistochemistry to locate populations of neurons within central gustatory and oromotor centers activated by PBN stimulation. Dramatic increases in the numbers of Fos-like immunoreactive neurons were observed in the ipsilateral PBN, nucleus of the solitary tract (NST), and central amygdala. The increase in neurally-activated cells within the ventral subdivision (V) of the rostral NST is particularly noteworthy because of its projections to medullary oromotor centers. A modest increase in labeled neurons occurred bilaterally within the gustatory cortex. Although there were trends for an increase in Fos-labeled neurons in the gustatory thalamus and medullary reticular formation, most changes in labeled neurons in these areas were not statistically significant. Linear regression analysis revealed a relationship between the number of taste reactivity (TR) behaviors performed during PBN stimulation and the number of Fos-like immunoreactive neurons in the caudal PBN and V of the rostral NST. These data support a role for neurons in W of the PBN and the ventral rostral NST in the initiation of TR behaviors.     

Parabrachial unit activities after the acquisition of conditioned taste aversion to a non-preferred HCl solution in rats

Abstract In a behavioral experiment, rats reliably acquired a taste aversion to non-preferred 0.01 M HCl that had been previously paired with intraperitoneal injection of 0.15 M LiCl. These rats showed aversions to other acidic solutions such as malic acid and tartaric acid. In a neurophysiological experiment, the neuronal activities of the parabrachial nucleus (PBN) were recorded after the acquisition of conditioned taste aversion (CTA) to 0.01 M HCl in urethane-anesthetized rats. Neuronal responses to the conditioned stimulus (CS) did not change on the whole but decreased in the dorsal region to the brachium conjunctivum. The proportion of HCl-best to NaCl-best units was lower in the CTA group than in controls. The spontaneous firing rate was lower in the CTA group than in controls. Correlation coefficients between the HCl CS and normally preferred tastes (sucrose and NaCl) were more negative and those between HCl and quinine were more positive in the CTA group than in the controls. These results may be explained by the notion that gustatory responses of PBN neurons are concerned with alterations in taste hedonics after the acquisition of conditioned taste aversions.     

Feeding-entrained circadian rhythms are attenuated by lesions of the parabrachial region in rats

Rats anticipate daily restricted meals with increased approaches to a feeder and an increase in core body temperature. Food anticipatory activity (FAA) is thought to be under the control of a feeding-entrained circadian oscillator. Although numerous forebrain lesions have failed to permanently abolish FAA, the hindbrain has not been investigated. The parabrachial nuclei (PBN) integrate information from visceral and gustatory afferents. This region is also innervated by neurons in the area postrema that have access to the peripheral circulation. Therefore, it is possible that this region plays a role in triggering FAA. In two experiments, a total of 19 rats were given ibotenic acid or electrolytic lesions targeted at the PBN. The PBN-lesioned animals showed a marked attenuation in anticipatory approaches to the food bin relative to sham-operated controls. Some animals did not anticipate the meal at all. In addition, the expected increase in core body temperature was severely attenuated in the PBN-lesioned animals compared with controls. The most likely interpretation of these data is that the PBN serve as a relay for information about the zeitgeber (food in the gut) or as a clock output pathway, but not as the site of the feeding-entrained circadian oscillator.     

电损毁大鼠杏仁中央核对脑桥臂旁核味觉神经元的影响

应用细胞外记录的电生理学方法,在乌拉坦麻醉的大鼠观察了电损毁双侧杏仁中央核前后脑桥臂旁核味觉神经元对四种基本味觉刺激(即氯化钠、盐酸、奎宁和蔗糖)反应的变化。根据对味觉刺激的优势反应,29个记录的味觉神经元中,有14个NaCl优势、9个HCl优势、3个QH2SO4优势和3个蔗糖优势反应神经元。损毁杏仁中央核明显增强臂旁核味觉神经元对盐酸和硫酸奎宁的反应(P＜0．01)。氯化钠优势、盐酸优势和奎宁优势反应神经元对盐酸和硫酸奎宁的反应在电损毁杏仁中央核后也明显增强。在破坏杏仁中央核后,臂旁核味觉神经元对氯化钠和硫酸奎宁苦味的分辨能力降低。以上结果提示,杏仁中央核在大鼠脑桥水平的味觉编码中发挥重要作用,它可能是通过参与对味觉的影响来调节机体的摄食行为。     

Integration of gastric distension and gustatory responses in the parabrachial nucleus

Palatable gustatory stimuli promote feeding, whereas gastric distension generally inhibits this behavior. We explored a neural basis for integration of these opposing sensory signals by evaluating the effect of gastric distension on gustatory responses in the parabrachial nucleus (PBN) of anesthetized rats. Sixteen percent of 92 taste cells were coactivated; they responded to independent taste or gastric distension stimulus application. Modulation of taste responses by distension was more prevalent; taste responses declined 37% in response to distension in 25% of the cells and increased by 46% in 10% of cells. Across the whole population, however, the suppressive effect of distension on taste responses was small (6%). The incidence of modulation did not vary as a simple hedonic function of gustatory sensitivity, i.e., similar proportions of sucrose-, citric-acid-, and QHCl-best, but not NaCl-best, neurons were modulated by gastric distension. Coactivated, modulated, and nonmodulated gustatory-responsive cells were intermingled in the gustatory zone of the caudal PBN. The suppression of PBN taste responses by visceral stimulation may reflect a mechanism for satiation and further implicates the PBN in the control of ingestive function.     

催产素、精氨酸加压素、促肾上腺皮质激素释放激素、神经肽Y、神经降压肽、P物质及亮氨酸脑啡肽免疫阳性纤维在大鼠结合臂旁核的分布

应用免疫细胞化学 ABC 技术观察了催产素、精氨酸加压素、促肾上腺皮质激素释放激素、神经肽 Y、神经降压肽、P 物质及亮氨酸脑啡肽免疫反应阳性纤维在大鼠结合臂旁核中的分布。催产素阳性纤维稀少,分布于腹外侧亚核、外外侧亚核、背外侧亚核及外外侧亚核与背外侧亚核之间的移行区。加压素阳性纤维亦甚为稀少,分布于腹外侧亚核、背外侧亚核、外外侧亚核与极外侧亚核.促肾上腺皮质激素释放激素阳性纤维分布于尾侧部臂旁核腰区、外外侧亚核腹内侧部、极外侧亚核、背外侧亚核、中央外侧亚核、内外侧亚核及臂旁内侧核。神经肽 Y 阳性纤维大多为串珠状的终末祥结构,分布于尾侧部腹外侧亚核、背外侧亚核、外外侧亚核背外侧部及外内侧亚核,在上外侧亚核、结合臂背内侧端背侧及臂旁内侧核腹侧部也有少量分布.神经降压肽阳性纤维分布于尾侧部臂旁核腰区、背外侧亚核、背外侧亚核与外外侧亚核之间的移行区、外外侧亚核、外内侧亚核及中吻部臂旁内侧核腹侧部。P 物质及亮氨酸脑啡肽阳性纤维分布于所有的臂旁外侧核诸亚核及外内侧亚核。     

味觉刺激引起大鼠臂旁核神经元抑制性反应

本研究以轻度麻醉的大鼠为对象,应用细胞外微电极记录技术,观察并分析了脑桥臂旁核抑制性味觉神经元的自发活动及其对NaCl、HCl、盐酸奎宁（quinine HCl,QHCl））和蔗糖等四种基本味觉刺激的反应。共分析了18个具有自发活动的抑制性味觉神经元,自发放电频率分布在0．2～5．5Hz之间,平均放电频率（2．15±0．31）Hz。18个神经元中,1个神经元对单一味觉刺激呈抑制性反应,其余17个神经元对两种或两种以上的基本味觉刺激发生抑制性反应,且抑制具有潜伏期短、持续时间较长等特征。抑制持续时间5～80S,部分神经元表现为后抑制效应。根据神经元对四种基本味觉刺激呈抑制性反应的程度,将其分为NaCl优势神经元（n=8）,HCl优势神经元（n=3）,QHCl优势神经元n=3）和蔗糖优势神经元n=4）。其中NaCl优势神经元的反应谐宽最高（0．945）。这些神经元对欣快或厌恶刺激的区别能力较低。结果提示,在脑桥臂旁核存在对味觉刺激起抑制性反应的神经元,这些味觉神经元可能在味觉的调制及对欣快和厌恶刺激的编码中发挥重要的作用。     

Taste reactivity and Fos expression in GAD1-EGFP transgenic mice

The central distribution of QHCl-elicited Fos-like immunoreactivity (FLI) suggests the location of a brain stem circuit that controls the oral rejection response. Although many species display an oral rejection response to bitter stimuli, the distribution of FLI associated with this response has been investigated only in rats. Fos data are minimal for the mouse, a species of increasing importance, due to its use in molecular and transgenic studies and taste-evoked oromotor responses are also only incompletely described in these rodents. We investigated these questions in FVB/NJ mice and a related transgenic strain (FVB-Tg(GadGFP)4507) that expresses green fluorescent protein in a subset of GAD1-containing neurons. QHCl, sucrose, or water delivered through intraoral cannulae yielded behavioral profiles that clearly differentiated QHCl from sucrose. Similar to rat, the number of neurons expressing FLI in the medial third of the solitary nucleus was elevated following QHCl compared with the other stimuli. In mice expressing green fluorescent protein, there was a pronounced distribution of GABAergic neurons in the ventral half of the solitary nucleus. Approximately 15% of solitary neurons expressing Fos were GABAergic, but this proportion did not differ according to stimulus.     

Sham feeding corn oil increases accumbens dopamine in the rat

Both real and sham feeding of sucrose increase dopamine (DA) overflow in the nucleus accumbens (NAc). Fat is another constituent of foods that is inherently preferred by humans and rodents. We examined the affect of sham feeding corn oil in rats that were food and water deprived overnight. Rats were implanted with guide cannulas aimed at the NAc, as well as gastric fistulas. On alternate days, they were trained to sham lick 100% corn oil or distilled water (dH2O) for 20 min in the morning. Twenty-minute microdialysis samples were taken before, during, and after sham licking. DA and monoamines were analyzed by reverse-phase HPLC with coulometric detection. The results show that DA release in the NAc was significantly increased during sham licking of corn oil compared with the prior baseline (157.5+/-18.8%, n=12). During sham licking of dH2O, DA release in the NAc was not changed (93.0+/-4.0%, n=15). This experiment demonstrates that sham feeding of corn oil releases accumbens DA in a manner similar to ingestion of sucrose. Although both stimuli may have an olfactory component, sucrose is a gustatory, and 100% corn oil appears to be a trigeminal stimulus. Thus these data support the hypothesis that different sensory modalities produce reward using the same or closely related substrates in the forebrain.     

Differential effects of water and saline intake on water deprivation-induced c-Fos staining in the rat

We studied c-Fos staining in adult male rats after 48 h of water deprivation and after 46 h of water deprivation with 2 h of access to water or physiological saline. Controls were allowed ad libitum access to water and physiological saline. For immunocytochemistry, anesthetized rats were perfused with a commercially available antibody for c-Fos. Dehydration significantly increased plasma vasopressin (AVP), osmolality, plasma renin activity (PRA), hematocrit, and sodium concentration and decreased urinary volume. Fos staining was significantly increased in the median preoptic nucleus, organum vasculosum of the lamina terminalis, supraoptic nucleus (SON), and magnocellular and parvocellular paraventricular nucleus (PVN), as well as the area postrema, nucleus of the solitary tract (NTS), and rostral ventrolateral medulla (RVL). Rehydration with water significantly decreased AVP levels and Fos staining in the SON, PVN, and RVL and significantly increased Fos expression in the perinuclear zone of the SON, NTS, and parabrachial nucleus. Rehydration with water was associated with decreased urinary sodium concentration and hypotonicity, and hematocrit and PRA were comparable to levels seen after dehydration. After rehydration with saline, plasma osmolality, hematocrit, and PRA were not different from control, but plasma AVP and urinary sodium concentration were increased. In the SON, Fos staining was significantly increased, with a great percentage of the Fos cells also stained for oxytocin compared with water deprivation. Changes in Fos staining were also observed in the NTS, RVL, parabrachial nucleus, and PVN. Rehydration with water or saline produces differential effects on plasma AVP, Fos staining, and sodium concentration.     

Calcitonin gene-related peptide: detailed immunohistochemical distribution in the central nervous system

With the use of an antiserum generated in rabbits against synthetic human calcitonin gene-related peptide (CGRP) the distribution of CGRP-like immunoreactive cell bodies and nerve fibers was studied in the rat central nervous system. A detailed stereotaxic atlas of CGRP-like neurons was prepared. CGRP-like immunoreactivity was widely distributed in the rat central nervous system. CGRP positive cell bodies were observed in the preoptic area and hypothalamus (medial preoptic, periventricular, anterior hypothalamic nuclei, perifornical area, medial forebrain bundle), premamillary nucleus, amygdala medialis, hippocampus and dentate gyrus, central gray and the ventromedial nucleus of the thalamus. In the midbrain a large cluster of cells was contained in the peripeduncular area ventral to the medial geniculate body. In the hindbrain cholinergic motor nuclei (III, IV, V, VI, VII XII) contained CGRP-immunoreactivity. Cell bodies were also observed in the ventral tegmental nucleus, the parabrachial nuclei, superior olive and nucleus ambiguus. The ventral horn cells of the spinal cord, the trigeminal and dorsal root ganglia also contained CGRP-immunoreactivity. Dense accumulations of fibers were observed in the amydala centralis, caudal portion of the caudate putamen, sensory trigeminal area, substantia gelatinosa, dorsal horn of the spinal cord (laminae I and II). Other areas containing CGRP-immunoreactive fibers are the septal area, nucleus of the stria terminalis, preoptic and hypothalamic nuclei (e.g., medial preoptic, periventricular, dorsomedial, median eminence), medial forebrain bundle, central gray, medial geniculate body, peripeduncular area, interpeduncular nucleus, cochlear nucleus, parabrachial nuclei, superior olive, nucleus tractus solitarii, and in the confines of clusters of cell bodies. Some fibers were also noted in the anterior and posterior pituitary and the sensory ganglia. As with other newly described brain neuropeptides it can only be conjectured that CGRP has a neuroregulatory action on a variety of functions throughout the brain and spinal cord.     

Extensive Gustatory Cortex Lesions Significantly Impair Taste Sensitivity to KCl and Quinine but Not to Sucrose in Rats

Recently, we reported that large bilateral gustatory cortex (GC) lesions significantly impair taste sensitivity to salts in rats. Here we extended the tastants examined to include sucrose and quinine in rats with ibotenic acid-induced lesions in GC (GCX) and in sham-operated controls (SHAM). Presurgically, immediately after drinking NaCl, rats received a LiCl or saline injection (i.p.), but postsurgical tests indicated a weak conditioned taste aversion (CTA) even in controls. The rats were then trained and tested in gustometers to discriminate a tastant from water in a two-response operant taste detection task. Psychometric functions were derived for sucrose, KCl, and quinine. Our mapping system was used to determine placement, size, and symmetry of the lesions (~91% GC damage on average). For KCl, there was a significant rightward shift (ΔEC₅₀ = 0.57 log₁₀ units; p<0.001) in the GCX psychometric function relative to SHAM, replicating our prior work. There was also a significant lesion-induced impairment (ΔEC₅₀ = 0.41 log₁₀ units; p = 0.006) in quinine sensitivity. Surprisingly, taste sensitivity to sucrose was unaffected by the extensive lesions and was comparable between GCX and SHAM rats. The fact that such large bilateral GC lesions did not shift sucrose psychometric functions relative to SHAM, but did significantly compromise quinine and KCl sensitivity suggests that the neural circuits responsible for the detection of specific taste stimuli are partially dissociable. Lesion-induced impairments were observed in expression of a postsurgical CTA to a maltodextrin solution as assessed in a taste-oriented brief-access test, but were not reflected in a longer term 46-h two-bottle test. Thus, deficits observed in rats after extensive damage to the GC are also dependent on the test used to assess taste function. In conclusion, the degree to which the GC is necessary for the maintenance of normal taste detectability apparently depends on the chemical and/or perceptual features of the stimulus.     

Plasma corticosterone responses to lesions and stimulations of the limbic thalami nuclei, medial mammillary nucleus and cingulate cortex

The influence of extrahypothalamic limbic structures on adrenocortical activity was investigated in female adult rats. Bilateral lesions on the anteromedial thalami nucleus (AMTN), anteroventral thalami nucleus (AVTN) or the posterior cingulate cortex (PCC) all elicited a significant decrease on plasma corticosterone, while their electrochemical stimulation produced a significant increase with respect to animals with sham lesions or sham stimulation. In contrast, after lesions of the dorsomedial thalami nucleus (DMTN), medial mammillary nucleus (pars lateralis) (MMN) or retrosplenial cortex (RC), values of plasma corticosterone were significantly higher than those found in controls, whereas following their stimulation plasma corticosterone levels were lower than in controls. Bilateral lesions or stimulations of anterior cingulate cortex had no significant effect upon corticosterone secretion. These findings may be interpreted as indicative of the existence of excitatory (AMTN, AVTN, and PCC) and inhibitory (DMTN, MMN and RC) central nervous structures for the control of corticoadrenal secretion besides those already known.     

大鼠脑室注射高渗氯化钠和蔗糖诱导饮水行为和脑内c—fos的表达

用ＳＤ种系清醒大鼠,观察脑室注射高渗物质引起的饮水及ｃ－ｆｏｓ在脑内的表达部位。实验结果表明,脑室内微量注射１．５ｍｏｌ／Ｌ、３ｍｏｌ／Ｌ ＮａＣｌ或３ｍｏｌ／Ｌ蔗糖均可诱导饮水反应,并在前脑的终板血管器官、正中视前核和下丘脑视上核与室旁核中见到Ｆｏｓ样免疫反应阳性细胞,同样在后脑的最后区、臂旁外侧核与孤束核中也能见到Ｆｏｓ样免疫反应阳性细胞,同样在后脑的最后区、臂旁外侧核与孤束核中也能见到Ｆｏｓ     

Parabrachial nucleus modulates cardiovascular responses to blood loss

The goal of this study was to determine the role of the pontine lateral parabrachial nucleus (LPBN) in the compensatory responses to blood loss. Conscious unrestrained rats with complete, partial, or sham bilateral ibotenic acid lesions of the LPBN were subjected to a hypotensive 16-ml/kg blood withdrawal via arterial catheter. Complete lesions (LPBNx) encompassed the entire LPBN and extended into the ventrolateral parabrachial region to encroach on the Kolliker-Fuse nucleus. Partial lesions were restricted to the body of the LPBN and spared the outer rim of the external lateral subnucleus of the LPBN. In all three groups, serum corticosterone concentration and plasma renin activity increased four- to fivefold after hemorrhage (P < 0.01), and immunocytochemistry demonstrated numerous Fos-positive neurons in the hypothalamic supraoptic nucleus. However, the cardiovascular responses to hypotensive blood loss differed for complete and partial lesions. Blood pressure failed to recover in LPBNx rats and was significantly lower in LPBNx (66 +/- 4 mmHg) than in rats with partial or sham lesions (98 +/- 4 and 85 +/- 5 mmHg, respectively) at 40 min posthemorrhage. In contrast, rats with partial lesions had a significant attenuation of the posthemorrhage bradycardia. This implies that a population of neurons within the body of the LPBN is essential for full expression of the bradycardia that accompanies hemorrhagic hypotension, whereas the ventrolateral parabrachial region is essential for normal restoration of arterial pressure after hypotensive hemorrhage.     

Projection from the ventral bed nucleus of the stria terminalis to the retrorubral field in rats and the effects of cells in these areas on mating in male rats versus gerbils

This research identified the rat counterpart of the lateral cell group of the sexually dimorphic area (SDA) found in medial preoptic area (MPOA) gerbil of gerbils. The lateral SDA (lSDA) is critical for mating in male gerbils and contains most of the SDA cells projecting to the retrorubral field (RRF), a projection that is also important for mating. Therefore, to locate the counterpart of the lateral SDA, we traced the inputs to the rat RRF, which were dense in the ventral part of the bed nucleus of the stria terminalis (BST). To determine if the ventral BST or its projection to the RRF affects mating in male rats, we disrupted them bilaterally by placing cell-body lesions bilaterally in the ventral BST or unilaterally there and in the contralateral RRF. We also studied the effects of RRF lesions in both rats and gerbils. Bilateral ventral BST lesions, which left the medial preoptic nucleus intact, produced persistent and severe mating deficits. Disconnecting the ventral BST from the RRF also had long-lasting, but less severe, consequences. RRF lesions produced only temporary mating deficits in rats, but virtually eliminated mating in gerbils. The recovery of mating in rats after RRF, but not ventral BST, lesions, and the intermediate effects of disconnecting these areas from each other suggest that the ventral BST may contain mating-related projection neurons other than those projecting to the RRF or that its RRF-projecting cells send collaterals to another site. In either case, the pedunculopontine tegmental nucleus or raphe nuclei may be involved.     

Extensive Lesions in Rat Insular Cortex Significantly Disrupt Taste Sensitivity to NaCl and KCl and Slow Salt Discrimination Learning

While studies of the gustatory cortex (GC) mostly focus on its role in taste aversion learning and memory, the necessity of GC for other fundamental taste-guided behaviors remains largely untested. Here, rats with either excitotoxic lesions targeting GC (n = 26) or sham lesions (n = 14) were assessed for postsurgical retention of a presurgically LiCl-induced conditioned taste aversion (CTA) to 0.1M sucrose using a brief-access taste generalization test in a gustometer. The same animals were then trained in a two-response operant taste detection task and psychophysically tested for their salt (NaCl or KCl) sensitivity. Next, the rats were trained and tested in a NaCl vs. KCl taste discrimination task with concentrations varied. Rats meeting our histological inclusion criterion had large lesions (resulting in a group averaging 80% damage to GC and involving surrounding regions) and showed impaired postsurgical expression of the presurgical CTA (LiCl-injected, n = 9), demonstrated rightward shifts in the NaCl (0.54 log₁₀ shift) and KCl (0.35 log₁₀ shift) psychometric functions, and displayed retarded salt discrimination acquisition (n = 18), but eventually learned and performed the discrimination comparable to sham-operated animals. Interestingly, the degree of deficit between tasks correlated only modestly, if at all, suggesting that idiosyncratic differences in insular cortex lesion topography were the root of the individual differences in the behavioral effects demonstrated here. This latter finding hints at some degree of interanimal variation in the functional topography of insular cortex. Overall, GC appears to be necessary to maintain normal taste sensitivity to NaCl and KCl and for salt discrimination learning. However, higher salt concentrations can be detected and discriminated by rats with extensive damage to GC suggesting that the other resources of the gustatory system are sufficient to maintain partial competence in these tasks, supporting the view that such basic sensory-discriminative taste functions involve distributed processes among central gustatory structures.     

Selective contributions of the medial preoptic nucleus to testosterone-dependant regulation of the paraventricular nucleus of the hypothalamus and the HPA axis

Previous data have consistently demonstrated an inhibitory effect of androgens on stress-induced hypothalamic-pituitary-adrenal (HPA) responses. Several brain regions may influence androgen-mediated inhibition of the HPA axis, including the medial preoptic area. To test the role of the medial preoptic nucleus (MPN) specifically, we examined in high- and low-testosterone-replaced gonadectomized rats bearing discrete bilateral lesions of the MPN basal and stress-induced indexes of HPA function, and the relative levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA in the amygdala. High testosterone replacement decreased plasma adrenocorticotropin hormone (ACTH) and paraventricular nucleus (PVN) Fos responses to restraint exposure in sham- but not in MPN-lesioned animals. AVP-, but not CRH-immunoreactivity staining in the external zone of the median eminence was increased by testosterone in sham animals, and MPN lesions blocked this increment in AVP. A similar interaction between MPN lesions and testosterone occurred on AVP mRNA levels in the medial nucleus of the amygdala. These findings support an involvement of MPN projections in mediating the AVP response to testosterone in both the medial parvocellular PVN and medial amygdala. We conclude that the MPN forms part of an integral circuit that mediates the central effects of gonadal status on neuroendocrine and central stress responses.     

刺激大鼠穹窿下器官诱发饮水和脑内c—fos表达的胆碱能机制

实验以饮水行为脑内c-fos表达为指标,,观察刺激大鼠穹窿下器官（SFO）的效应,结果显示,刺激SFO能诱发明显的饮水行为,与此同时,前脑8个部位（终板血管器官,正中视前核,室旁核,视上核,下丘脑外侧区,穹窿周核背侧区,丘脑联合核和无名质）和后脑3个部位（最后区,孤束核和壁旁外侧核）的Fos蛋白表达明显增强,免疫组化双重染色结果显示,刺激SFO能诱导视上核和室旁核中部分神经元呈Fos蛋白和加压素共同表达。脑室注射阿托品能部分阻断刺激SFO诱发的饮水行为,脑内上述各部位所诱导的Fos蛋白表达也明显减弱,以上结果提示,M胆碱能机制参与 刺激SFO诱发的饮水行为和脑内Fos蛋白的表达。