Effects of vagotomy on cholecystokinin- and dexfenfluramine-induced Fos-like immunoreactivity in the rat brain

Dissecting a disynaptic central amygdala-parasubthalamic nucleus neural circuit that mediates cholecystokinin-induced eating suppression

OBJECTIVE

Cholecystokinin (CCK) plays a critical role in regulating eating and metabolism. Previous studies have mapped a multi-synapse neural pathway from the vagus nerve to the central nucleus of the amygdala (CEA) that mediates the anorexigenic effect of CCK. However, the neural circuit downstream of the CEA is still unknown due to the complexity of the neurons in the CEA. Here we sought to determine this circuit using a novel approach.

METHODS

It has been established that a specific population of CEA neurons, marked by protein kinase C-delta (PKC-δ), mediates the anorexigenic effect of CCK by inhibiting other CEA inhibitory neurons. Taking advantage of this circuit, we dissected the neural circuit using a unique approach based on the idea that neurons downstream of the CEA should be disinhibited by CEAPKC-δ+ neurons while being activated by CCK. We also used optogenetic assisted electrophysiology circuit mapping and in vivo chemogenetic manipulation methods to determine the circuit structure and function.

RESULTS

We found that neurons in the parasubthalamic nucleus (PSTh) are activated by the activation of CEAPKC-δ+ neurons and by the peripheral administration of CCK. We demonstrated that CEAPKC-δ+ neurons inhibit the PSTh-projecting CEA neurons; accordingly, the PSTh neurons can be disynaptically disinhibited or "activated" by CEAPKC-δ+ neurons. Finally, we showed that chemogenetic silencing of the PSTh neurons effectively attenuates the eating suppression induced by CCK.

CONCLUSIONS

Our results identified a disynaptic CEA-PSTh neural circuit that mediates the anorexigenic effect of CCK and thus provide an important neural mechanism of how CCK suppresses eating.

Differential rewarding effects of electrical stimulation of the lateral hypothalamus and parabrachial complex: Functional characterization and the relevance of opioid systems and dopamine

BACKGROUND

Since the discovery of rewarding intracranial self-stimulation by Olds and Milner, extensive data have been published on the biological basis of reward. Although participation of the mesolimbic dopaminergic system is well documented, its precise role has not been fully elucidated, and some authors have proposed the involvement of other neural systems in processing specific aspects of reinforced behaviour.

AIMS AND METHODS

We reviewed published data, including our own findings, on the rewarding effects induced by electrical stimulation of the lateral hypothalamus (LH) and of the external lateral parabrachial area (LPBe) - a brainstem region involved in processing the rewarding properties of natural and artificial substances - and compared its functional characteristics as observed in operant and non-operant behavioural procedures.

RESULTS

Brain circuits involved in the induction of preferences for stimuli associated with electrical stimulation of the LBPe appear to functionally and neurochemically differ from those activated by electrical stimulation of the LH.

INTERPRETATION

We discuss the possible involvement of the LPBe in processing emotional-affective aspects of the brain reward system.

PYY(3-36) and exendin-4 reduce food intake and activate neuronal circuits in a synergistic manner in mice

Peptide YY(3-36) ((PYY(3-36)) and glucagon like peptide 1 (GLP-1) in combination reduce food intake and body weight in an additive or synergistic manner in animal models and in humans. Nevertheless, the mechanisms behind are not completely understood. The present study aims to investigate the effect of combining PYY(3-36) and the GLP-1 receptor agonist exendin-4 (Ex4) by examining acute food intake and global neuronal activation as measured by c-fos in C57BL/6 J mice. An additive reduction in food intake was found 1.5 h after s.c dosing with the combination of PYY(3-36) (200 μg/kg) and Ex4 (2.5 μg/kg). This was associated with a synergistic enhancement of c-fos reactivity in central amygdalar nucleus (CeA), rostral part of the mediobasal arcuate nucleus (ARH), supratrigeminal nucleus (SUT), lateral parabrachial nucleus (PB), area postrema (AP) and nucleus tractus solitarius (NTS) compared to vehicle, PYY(3-36) and Ex4 individually dosed mice. The regions activated by Ex4 individually and PYY(3-36) and Ex4 in combination resembled each other, but the combination group had a significantly stronger c-fos response. Twenty-five brain areas were activated by PYY(3-36) and Ex4 in combination compared to vehicle versus nine brain areas by Ex4 individually. No significant increase in c-fos reactivity was found by PYY(3-36) compared to vehicle dosed mice. The neuronal activation of ARH and the AP/NTS to PB to CeA pathway is important for appetite regulation while SUT has not previously been reported in the regulation of energy balance. As PYY(3-36) and Ex4 act on different neurons leading to recruitment of different signalling pathways within and to the brain, an interaction of these pathways may contribute to their additive/synergistic action. Thus, PYY(3-36) boosts the effect of Ex4 possibly by inducing less inhibition of neuronal activity leading to an enhanced neuronal activity induced by Ex4.

Disruption of re-intake after partial withdrawal of gastric food contents in rats lesioned in the gelatinous part of the nucleus of the solitary tract

Sensory information from the upper gastrointestinal tract is critical in food intake regulation. Signals from different levels of the digestive system are processed to the brain, among other systems, via the vagus nerve, which mainly projects towards the nucleus of the solitary tract (NST). The objective of this study was to analyze the participation of the gelatinous part (SolG) of the NST in short-term food intake. One-third of the stomach food content was withdrawn at 5 min after the end of a meal, and food was then available ad libitum for different time periods. SolG-lesioned and control animals ingested a similar amount of the initial liquid meal, but the former consumed significantly smaller amounts and failed to compensate for the food deficit, whereas the controls re-ingested virtually the same amount as extracted. These data suggest that the SolG, as in the case of related anatomical structures such as the vagus nerve or external lateral parabrachial subnucleus, may be relevant in particular circumstances that require the rapid processing of vagal-related food intake adjustment associated to the upper gastrointestinal tract.

Eating in mice with gastric bypass surgery causes exaggerated activation of brainstem anorexia circuit

BACKGROUND/OBJECTIVE

Obesity and metabolic diseases are at an alarming level globally and increasingly affect children and adolescents. Gastric bypass and other bariatric surgeries have proven remarkably successful and are increasingly performed worldwide. Reduced desire to eat and changes in eating behavior and food choice account for most of the initial weight loss and diabetes remission after surgery, but the underlying mechanisms of altered gut-brain communication are unknown.

SUBJECTS/METHODS

To explore the potential involvement of a powerful brainstem anorexia pathway centered around the lateral parabrachial nucleus (lPBN), we measured meal-induced neuronal activation by means of c-Fos immunohistochemistry in a new high-fat diet-induced obese mouse model of Roux-en-Y gastric bypass (RYGB) at 10 and 40 days after RYGB or sham surgery.

RESULTS

Voluntary ingestion of a meal 10 days after RYGB, but not after sham surgery, strongly and selectively activates calcitonin gene-related peptide neurons in the external lPBN as well as neurons in the nucleus tractus solitarius, area postrema and medial amygdala. At 40 days after surgery, meal-induced activation in all these areas was greatly diminished and did not reach statistical significance.

CONCLUSIONS

The neural activation pattern and dynamics suggest a role of the brainstem anorexia pathway in the early effects of RYGB on meal size and food intake that may lead to adaptive neural and behavioral changes involved in the control of food intake and body weight at a lower level. However, selective inhibition of this pathway will be required for a more causal implication.

Gut vagal afferents are necessary for the eating-suppressive effect of intraperitoneally administered ginsenoside Rb1 in rats

Ginsenoside Rb1 (Rb1) reduces food intake in both lean and high-fat diet induced-obese rats; however, the sites and/or mediation of the eating-suppressive effect of Rb1 have not previously been identified. We hypothesized that intraperitoneally (ip) administered Rb1 exerts its anorectic action by enhancing sensitivity to satiation signals, such as cholecystokinin (CCK), and/or that it acts through vagal afferent nerves that relay the satiating signaling to the hindbrain. To test these hypotheses, we gave ip bolus doses of Rb1 (2.5-10.0mg/kg) and CCK-8 (0.125-4.0μg/kg) alone or in combination and assessed food intake in rats. Low doses of Rb1 (2.5mg/kg) or CCK-8 (0.125μg/kg) alone had no effect on food intake whereas higher doses did. When these subthreshold doses of Rb1 and CCK-8 were co-administered, the combination significantly reduced food intake relative to saline controls, and this effect was attenuated by lorglumide, a selective CCK1-receptor antagonist. Interestingly, lorglumide blocked food intake induced by an effective dose of CCK-8 alone, but not by Rb1 alone, suggesting that Rb1's anorectic effect is independent of the CCK1 receptor. To determine whether peripherally administered Rb1 suppresses feeding via abdominal vagal nerves, we evaluated the effect of ip Rb1 injection in subdiaphragmatic vagal deafferentation (SDA) and control rats. Rb1's effect on food intake was significantly attenuated in SDA rats, compared with that in SHAM controls. These data indicate that the vagal afferent system is the major pathway conveying peripherally administered Rb1's satiation signal.

Appetite and body weight regulation after bariatric surgery

Bariatric surgery continues to be remarkably efficient in treating obesity and type 2 diabetes mellitus and a debate has started whether it should remain the last resort only or also be used for the prevention of metabolic diseases. Intense research efforts in humans and rodent models are underway to identify the critical mechanisms underlying the beneficial effects with a view towards non-surgical treatment options. This non-systematic review summarizes and interprets some of this literature, with an emphasis on changes in the controls of appetite. Contrary to earlier views, surgery-induced reduction of energy intake and subsequent weight loss appear to be the main drivers for rapid improvements of glycaemic control. The mechanisms responsible for suppression of appetite, particularly in the face of the large weight loss, are not well understood. Although a number of changes in food choice, taste functions, hedonic evaluation, motivation and self-control have been documented in both humans and rodents after surgery, their importance and relative contribution to diminished appetite has not yet been demonstrated. Furthermore, none of the major candidate mechanisms postulated in mediating surgery-induced changes from the gut and other organs to the brain, such as gut hormones and sensory neuronal pathways, have been confirmed yet. Future research efforts should focus on interventional rather than descriptive approaches in both humans and rodent models.

Rewarding effects of the electrical stimulation of the parabrachial complex: taste or place preference?

The lateral parabrachial complex has been related to various emotional-affective processes. It has been shown that electrical stimulation of the external Lateral Parabrachial (LPBe) nucleus can induce reinforcing effects in place preference and taste discrimination tasks but does not appear to support self-stimulation. This study examined the relative relevance of place and taste stimuli after electrical stimulation of the LPBe nucleus. A learning discrimination task was conducted that simultaneously included both sensory indexes (taste and place) in order to determine the preference of animals for one or the other. After a taste stimulus reversal task, the rewarding effect of stimulation was found to be preferentially associated with place. These results are discussed in the context of the rewarding action and biological constraints induced by different natural and artificial reinforcing agents.

Involvement of prolactin-releasing peptide in the activation of oxytocin neurones in response to food intake

Food intake activates neurones expressing prolactin-releasing peptide (PrRP) in the medulla oblongata and oxytocin neurones in the hypothalamus. Both PrRP and oxytocin have been shown to have an anorexic action. In the present study, we investigated whether the activation of oxytocin neurones following food intake is mediated by PrRP. We first examined the expression of PrRP receptors (also known as GPR10) in rats. Immunoreactivity of PrRP receptors was observed in oxytocin neurones and in vasopressin neurones in the paraventricular and supraoptic nuclei of the hypothalamus and in the bed nucleus of the stria terminalis. Application of PrRP to isolated supraoptic nuclei facilitated the release of oxytocin and vasopressin. In mice, re-feeding increased the expression of Fos protein in oxytocin neurones of the hypothalamus and bed nucleus of the stria terminalis. The increased expression of Fos protein in oxytocin neurones following re-feeding or i.p. administration of cholecystokinin octapeptide (CCK), a peripheral satiety factor, was impaired in PrRP-deficient mice. CCK-induced oxytocin increase in plasma was also impaired in PrRP-deficient mice. Furthermore, oxytocin receptor-deficient mice showed an increased meal size, as reported in PrRP-deficient mice and in CCKA receptor-deficient mice. These findings suggest that PrRP mediates, at least in part, the activation of oxytocin neurones in response to food intake, and that the CCK-PrRP-oxytocin pathway plays an important role in the control of the termination of each meal.

Apolipoprotein AIV requires cholecystokinin and vagal nerves to suppress food intake

Apolipoprotein AIV (apo AIV) and cholecystokinin (CCK) are gastrointestinal satiation signals that are stimulated by fat consumption. Previous studies have demonstrated that peripheral apo AIV cannot cross the blood-brain barrier. In the present study, we hypothesized that peripheral apo AIV uses a CCK-dependent system and intact vagal nerves to relay its satiation signal to the hindbrain. To test this hypothesis, CCK-knockout (CCK-KO) mice and Long-Evan rats that had undergone subdiaphragmatic vagal deafferentation (SDA) were used. Intraperitoneal administration of apo AIV at 100 or 200 μg/kg suppressed food intake of wild-type (WT) mice at 30, 60, and 90 min. In contrast, the same dose did not reduce food intake in the CCK-KO mice. Blockade of the CCK 1 receptor by lorglumide, a CCK 1 receptor antagonist, attenuated apo AIV-induced satiation. Apo AIV at 100 μg/kg reduced food intake in SHAM rats but not in SDA rats. Furthermore, apo AIV elicited an increase in c-Fos-positive cells in the nucleus of the solitary tract (NTS), area postrema, dorsal motor nucleus of the vagus, and adjacent areas of WT mice but elicited only an attenuated increase in these same regions in CCK-KO mice. Apo AIV-induced c-Fos positive cells in the NTS and area postrema of WT mice were reduced by lorglumide. Lastly, apo AIV increased c-Fos positive cells in the NTS of SHAM rats but not in SDA rats. These observations imply that peripheral apo AIV requires an intact CCK system and vagal afferents to activate neurons in the hindbrain to reduce food intake.

Upper gastrointestinal dysmotility after spinal cord injury: is diminished vagal sensory processing one culprit?

Despite the widely recognized prevalence of gastric, colonic, and anorectal dysfunction after spinal cord injury (SCI), significant knowledge gaps persist regarding the mechanisms leading to post-SCI gastrointestinal (GI) impairments. Briefly, the regulation of GI function is governed by a mix of parasympathetic, sympathetic, and enteric neurocircuitry. Unlike the intestines, the stomach is dominated by parasympathetic (vagal) control whereby gastric sensory information is transmitted via the afferent vagus nerve to neurons of the nucleus tractus solitarius (NTS). The NTS integrates this sensory information with signals from throughout the central nervous system. Glutamatergic and GABAergic NTS neurons project to other nuclei, including the preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus (DMV). Finally, axons from the DMV project to gastric myenteric neurons, again, through the efferent vagus nerve. SCI interrupts descending input to the lumbosacral spinal cord neurons that modulate colonic motility and evacuation reflexes. In contrast, vagal neurocircuitry remains anatomically intact after injury. This review presents evidence that unlike the post-SCI loss of supraspinal control which leads to colonic and anorectal dysfunction, gastric dysmotility occurs as an indirect or secondary pathology following SCI. Specifically, emerging data points toward diminished sensitivity of vagal afferents to GI neuroactive peptides, neurotransmitters and, possibly, macronutrients. The neurophysiological properties of rat vagal afferent neurons are highly plastic and can be altered by injury or energy balance. A reduction of vagal afferent signaling to NTS neurons may ultimately bias NTS output toward unregulated GABAergic transmission onto gastric-projecting DMV neurons. The resulting gastroinhibitory signal may be one mechanism leading to upper GI dysmotility following SCI.

CCK, PYY and PP: the control of energy balance

The control of food intake consists of neural and hormonal signals between the gut and central nervous system (CNS). Gut hormones such as CCK, PYY and PP signal to important areas in the CNS involved in appetite regulation to terminate a meal. These hormones can act directly via the circulation and activate their respective receptors in the hypothalamus and brainstem. In addition, gut vagal afferents also exist, providing an alternative pathway through which gut hormones can communicate with higher centres through the brainstem. Animal and human studies have demonstrated that peripheral administration of certain gut hormones reduces food intake and leads to weight loss. Gut hormones are therefore potential targets in the development of novel treatments for obesity and analogue therapies are currently under investigation.

A switch in the neuromodulatory effects of dopamine in the oval bed nucleus of the stria terminalis associated with cocaine self-administration in rats

Chronic exposure to drugs of abuse alters brain reward circuits and produces functional changes in the dopamine (DA) system. However, it is not known whether these changes are directly related to drug-driven behaviors or whether they simply are adaptive responses to long-term drug exposure. Here, we combined the rat model of cocaine self-administration with brain slice electrophysiology to identify drug-use related alterations in the neuromodulatory effects of DA in the oval bed nucleus of the stria terminalis (ovBST), a robust DA terminal field. Long-Evans rats self-administered cocaine intravenously (0.75 mg/kg/injection) for an average of 15 d, on reward-lean or -rich schedules of reinforcement. Brain slice recordings conducted 20 h after the last self-administration session revealed a reversal of the neuromodulatory effect of DA on GABA(A)-IPSCs. Specifically, the effect of DA switched from a D2-mediated decrease in drug-naive rats to a D1-receptor-mediated increase in GABA(A)-IPSC in cocaine self-administering rats. Furthermore, the switch in DA modulation of GABA(A)-IPSC remained after a 30 d withdrawal period. In contrast, this switch was not observed after the acquisition phase of cocaine self-administration, when rats received cocaine passively, or in rats maintaining sucrose self-administration. Therefore, our study reveals a reversal in the effects of DA on inhibitory transmission, from reduction to enhancement, in the ovBST of cocaine self-administering rats. This change was unique to voluntary intake of cocaine and maintained after a withdrawal period, suggesting a mechanism underlying the maintenance of cocaine self-administration and perhaps craving during drug-free periods.

Experimental spinal cord injury in rats diminishes vagally-mediated gastric responses to cholecystokinin-8s

BACKGROUND

We have shown recently that our model of experimental high-thoracic spinal cord injury (T3-SCI) mirrors the gastrointestinal clinical presentation of neurotrauma patients, whereby T3-SCI animals show diminished gastric emptying and dysmotility. In this study we used cholecystokinin as a model peptide to test the hypothesis that the T3-SCI induced gastroparesis is due, in part, to an impaired vagally-mediated response to gastrointestinal peptides.

METHODS

We measured the responses to sulfated cholecystokinin (CCK-8s) in control and T3-SCI (3 or 21 days after injury) rats utilizing: (i) c-fos expression in the nucleus tractus solitarius (NTS) following peripherally administered CCK-8s; (ii) in vivo gastric tone and motility following unilateral microinjection of CCK-8s into the dorsal vagal complex (DVC); and (iii) whole cell recordings of glutamatergic synaptic inputs to NTS neurons.

KEY RESULTS

Our results show that: (i) medullary c-fos expression in response to peripheral CCK-8s was significantly lower in T3-SCI rats 3 days after the injury, but recovered to control values at 3 weeks post-SCI, (ii) Unilateral microinjection of CCK-8s in the DVC induced a profound gastric relaxation in control animals, but did not induce any response in T3-SCI rats at both 3 and 21 days after SCI, (iii) Perfusion with CCK-8s increased glutamatergic currents in 55% of NTS neurons from control rats, but failed to induce any response in NTS neurons from T3-SCI rats.

CONCLUSIONS & INFERENCES

Our data indicate alterations of vagal responses to CCK-8s in T3-SCI rats that may reflect a generalized impairment of gastric vagal neurocircuitry, leading to a reduction of gastric functions after SCI.

Differential feeding behavior and neuronal responses to CCK in obesity-prone and -resistant rats

Deficits in satiation signals are strongly suspected of accompanying obesity and contributing to its pathogenesis in both humans and rats. One such satiation signal is cholecystokinin (CCK), whose effects on food intake are diminished in animals adapted to a high fat diet. In this study, we tested the hypothesis that diet-induced obese prone (OP) rats exhibit altered feeding and vagal responses to systemic (IP) administration of CCK-8 compared to diet-induced obese resistant (OR) rats. We found that CCK (4.0 microg/kg) suppressed food intake significantly more in OP than OR rats. To determine whether enhanced suppression of feeding is accompanied by altered vagal sensory responsiveness, we examined dorsal hindbrain expression of Fos-like immunoreactivity (Fos-Li) following IP CCK injection in OP and OR rats. After 4.0 microg/kg CCK, there were significantly more Fos-positive nuclei in the NTS of OP compared to OR rats. Treatment with 8.0 microg/kg CCK resulted in no significant difference in food intake or in Fos-Li between OP and OR rats. Also, we found that OP rats were hyperphagic on a regular chow diet and gained more weight compared to OR rats. Finally OP rats had decreased relative fat pad mass compared to OR rats. Collectively, these results show that OP rats exhibit a different behavioral and vagal neuronal responses to CCK than OR rats.

Lesion of the lateral parabrachial nucleus attenuates the anorectic effect of peripheral amylin and CCK

Amylin and CCK activate the area postrema (AP)/nucleus of the solitary tract (NTS) - lateral parabrachial nucleus (LPBN) - central amygdala (CeA) pathway. However, except for the brainstem structures the role of these nuclei for the anorectic effect of these peptides is not yet well characterized. The current study investigated the role of the LPBN in mediating the inhibitory effect of peripheral amylin and CCK on feeding behavior. Rats with electrolytic lesions in the LPBN (LPBN-X) were used in behavioral as well as in immunohistological c-Fos studies. LPBN-X significantly reduced the anorectic effect of amylin (5 microg/kg, i.p.). The effect of a higher amylin dose (10 microg/kg, i.p.) was only slightly attenuated in the LPBN-X rats. In agreement with previous studies, LPBN lesions also reduced the inhibitory effect of CCK on food intake. In the immunohistological experiments, amylin and CCK induced c-Fos expression in the AP, NTS, LPBN and CeA in the SHAM rats. Both the amylin- and CCK-induced activation of the CeA was completely abolished in the animals with a LPBN lesion. These results clearly suggest that the signal transduction pathway between the AP/NTS and CeA has been disrupted by the LPBN ablation. We conclude that the LPBN is a crucial brain site mediating the anorectic effect of amylin and CCK. Furthermore, an intact LPBN seems to be essential for the c-Fos response in the CeA induced by these peptides.

Learned preferences induced by electrical stimulation of a food-related area of the parabrachial complex: Effects of naloxone

Electrical stimulation of the External Lateral Parabrachial Subnucleus (LPBe), a food-related area, induced behavioral preferences for associated stimuli in a taste discrimination learning task. Although this stimulation appeared to be ineffective to elicit standard lever press self-stimulation, it induced place preference for one of two training compartments of a rectangular maze in which animals (adult male Wistar rats) received concurrent electrical brain stimulation. In subjects that consistently showed a preference behavior in different trials, administration of the opioid antagonist naloxone (4 mg/ml/kg) blocked concurrent learning when the test was made in a new maze but not in the same maze in which animals had learned the task. These results are discussed in terms of the possible participation of the LPBe subnucleus in different natural and artificial brain reward systems.

Cholecystokinin1 receptors mediate the increase in Fos-like immunoreactivity in the rat myenteric plexus following intestinal oleate infusion

Intestinal infusion of nutrients, such as glucose and oleic acid, increase Fos-like immunoreactivity (Fos-LI) in both the enteric nervous system and neurons of the dorsal vagal complex (DVC) of the hindbrain. To test the hypothesis that increased Fos-LI in enteric neurons and the DVC, following intestinal nutrient infusions is mediated by cholecystokinin(1) receptors (CCK(1)), we counted enteric and DVC neurons that expressed Fos-LI following intestinal infusion of oleate or glucose, with and without pretreatment with the CCK(1) receptor antagonist, lorglumide. Both oleate and glucose infusions increased Fos-LI in the DVC. Oleate also increased Fos-LI in the myenteric and submucosal plexuses of the duodenum and the jejunum, but not the ileum, while glucose only increased Fos-LI in the submucosal plexus of the ileum. The CCK(1) receptor antagonist, lorglumide, abolished Fos-LI in the DVC following infusions of either oleate or glucose. In addition, lorglumide attenuated oleate-induced Fos-LI in the myenteric and submucosal plexuses of the duodenum and jejunum. However, lorglumide failed to attenuate glucose-induced Fos-LI in the submucosal plexus of the ileum. These data confirm previous reports indicating that CCK(1) receptors mediate increased DVC Fos-LI following intestinal infusion of oleate or glucose. CCK(1) receptors also contribute to increased Fos-LI in enteric neurons following intestinal oleate infusion. However, failure of lorglumide to attenuate the increase of Fos-LI in the ileal submucosal plexus following intestinal glucose suggests that some intestinal nutrients trigger Fos-LI induction via CCK(1) receptor-independent pathways.

Reduced CCK-induced Fos expression in the hindbrain, nodose ganglia, and enteric neurons of rats lacking CCK-1 receptors

Many of the actions of cholecystokinin (CCK) are mediated by CCK-1 receptors, expressed by enteric and vagal afferent neurons. Otsuka Long-Evans Tokushima Fatty rats (OLETF) do not express CCK-1 receptors, and do not exhibit the vagally mediated responses to CCK. To determine whether the OLETF rat's failure to respond to CCK is correlated with failure of CCK to activate enteric and vagal neurons, we quantified neuronal Fos immunoreactivity in the dorsal vagal complex of the hindbrain, the nodose ganglia, and the ganglia of the myenteric and submucosal plexuses of the duodenum following intraperitoneal injection of CCK-8 (20 microg/kg). Compared to vehicle injection, CCK administration resulted in significant increases in the number of Fos-immunopositive neurons in the nucleus of the solitary tract, area postrema, and dorsal vagal motor nucleus of control, LETO rats. In OLETF rats, however, CCK did not increase numbers of Fos-immunoreactive neurons in any of these brain structures. CCK also induced significantly larger numbers of Fos-immunoreactive neuronal nuclei in the nodose ganglia of LETO rats, but not in the nodose ganglia of OLETF rats. Finally, LETO, but not OLETF rats exhibited striking increases in the number of Fos-immunoreactive nuclei of myenteric and submucosal neurons, following CCK injection. Absence of CCK-induced Fos expression in OLETF rats is consistent with attenuation of ingestive and gastrointestinal responses to CCK in the CCK-1 receptor deficient rats. These results also suggest that CCK-induced Fos expression in enteric and vagal sensory neurons of rats can be accounted for entirely by activation of CCK-1 receptors and is not due to occupation of CCK-2 (gastrin) receptors, which also are expressed in the intestine and by some vagal afferent neurons.

Peripheral secretin-induced Fos expression in the rat brain is largely vagal dependent

I.v. injection of secretin activates neurons in brain areas controlling autonomic function and emotion. Peripheral administration of secretin inhibits gastric functions through a central mechanism that is mediated by vagal dependent pathways. We investigated whether the vagus nerve is involved in i.p. injection of secretin-induced brain neuronal activation in conscious rats as monitored by Fos immunohistochemistry. Secretin (40 or 100 microg/kg, i.p., 90 min) induced a dose-related increase in the number of Fos positive neurons in the central nucleus of the amygdala (CeA), and a plateau Fos response in the area postrema (AP), nucleus tractus solitarii (NTS), locus coeruleus (LC), Barrington's nucleus (Bar), external lateral subnucleus of parabrachial nucleus (PBel) and arcuate nucleus, and at 100 microg/kg, in the dorsal motor nucleus of the vagus (DMV) compared with i.p. injection of vehicle. Double immunohistochemistry showed that secretin (40 microg/kg, i.p.) activates tyrosine hydroxylase neurons in the NTS. Subdiaphragmatic vagotomy (7 days) abolished Fos expression-induced by i.p. secretin (40 microg/kg) in the NTS, DMV, LC, Bar, PBel and CeA, while a significant rise in the AP was maintained. In contrast, s.c. capsaicin (10 days) did not influence the Fos induction in the above nuclei. Reverse transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR showed that secretin receptor mRNA is expressed in the nodose ganglia and levels were higher in the right compared with the left ganglion. These results indicate that peripheral secretin activates catecholaminergic NTS neurons as well as neurons in medullary, pontine and limbic nuclei regulating autonomic functions and emotion through vagal-dependent capsaicin-resistant pathways. Secretin injected i.p. may signal to the brain by interacting with secretin receptors on vagal afferent as well as on AP neurons outside the blood-brain barrier.

A circadian rhythm in the expression of PERIOD2 protein reveals a novel SCN-controlled oscillator in the oval nucleus of the bed nucleus of the stria terminalis

Circadian rhythms in mammals are regulated not only globally by the master clock in the suprachiasmatic nucleus (SCN), but also locally by widely distributed populations of clock cells in the brain and periphery that control tissue-specific rhythmic outputs. Here we show that the oval nucleus of the bed nucleus of the stria terminalis (BNST-OV) exhibits a robust circadian rhythm in expression of the Period2 (PER2) clock protein. PER2 expression is rhythmic in the BNST-OV in rats housed under a light/dark cycle or in constant darkness, in blind rats, and in mice, and is in perfect synchrony with the PER2 rhythm of the SCN. Constant light or bilateral SCN lesions abolish the rhythm of PER2 in the BNST-OV. Large abrupt shifts in the light schedule transiently uncouple the BNST-OV rhythm from that of the SCN. Re-entrainment of the PER2 rhythm is faster in the SCN than in the BNST-OV, and it is faster after a delay than an advance shift. Bilateral adrenalectomy blunts the PER2 rhythm in the BNST-OV. Thus, the BNST-OV contains circadian clock cells that normally oscillate in synchrony with the SCN, but these cells appear to require both input from the SCN and circulating glucocorticoids to maintain their circadian oscillation. Taken together with what is known about the functional organization of the connections of the BNST-OV with systems of the brain involved in stress and motivational processes, these findings place BNST-OV oscillators in a position to influence specific physiological and behavioral rhythms downstream from the SCN clock.

Excitotoxic lesions of the lateral parabrachial nucleus do not prevent cholecystokinin-induced suppression of milk intake in rats

We examined the effect of lateral (visceral) and medial (gustatory) parabrachial nucleus (PBN) lesions on the suppression of milk intake induced with cholecystokinin (CCK) in 24 h food-deprived rats. Irrespective of CCK dose, each type of PBN lesion significantly elevated the consumption of milk. Neither medial nor lateral PBN lesions had any discernible influence on the anorectic action of CCK, however. In combination with the results from a previous study using the same rats (Brain Res. 894 (2001) 288), the present results support the view that the role of the lateral PBN in CCK-induced anorexia depends on the nature of the food used at test.

Effect of the anorectic fatty acid synthase inhibitor C75 on neuronal activity in the hypothalamus and brainstem

Intraperitoneal (i.p.) injection of C75, a fatty acid synthase inhibitor, causes a rapid (<or=2-h) and persistent (to at least 24-h) approximately 95% decrease in food intake. The persistent effect seems to be due to inhibition of the fasting-induced up-regulation of expression of hypothalamic orexigenic neuropeptides neuropeptide Y and agouti-related protein and down-regulation of expression of anorexigenic neuropeptides pro-opiomelanocortinalpha-melanocyte-stimulating hormone and cocaine-amphetamine-related transcript. The effect of C75 on neuronal activity in the hypothalamus and brainstem was assessed by c-Fos expression. Consistent with its effect on neuropeptide expression, C75 blocked fasting-induced c-Fos expression in the arcuate nucleus (Arc), lateral hypothalamic area (LHA), and paraventricular nucleus (PVN) 10-24 h after i.p. injection. However, i.p. C75 induced a rapid (<or=2-h) c-Fos expression in the nucleus of the solitary tract (NTS) and area postrema of the brainstem but not in the Arc or LHA. Intracerebroventricular administration of C75 rapidly induced c-Fos expression in the Arc, PVN, and NTS, supporting a central role of C75 in the regulation of food intake. Thus, suppression of food intake by C75 administered i.p. seems to be mediated in two phases, a rapid initial phase via the NTSarea postrema of the brainstem and a delayed phase via the Arc, LHA, and PVN of the hypothalamus. The delayed effect of C75 on the Arc, LHA, and PVN correlates well with its ability to interfere with the fasting-induced effects on the expression of key orexigenic (neuropeptide Y and agouti-related protein) and anorexigenic (pro-opiomelanocortinalpha-melanocyte-stimulating hormone and cocaine-amphetamine-related transcript) messages in the hypothalamus.

Role for the cholecystokinin-A receptor in fever: a study of a mutant rat strain and a pharmacological analysis

The involvement of the cholecystokinin (CCK)-A receptor in fever was studied. The polyphasic febrile responses to lipopolysaccharide (LPS; 10 microg kg-1, I.V.) were compared between wild-type Long-Evans (LE) rats and the CCK-A-receptor-deficient Otsuka LE Tokushima Fatty (OLETF) rats. The response of the wild-type rats was biphasic, which is typical for LE rats. Phases 1 and 2 of the response of the OLETF rats were similar to those of the LE rats, but the OLETF rats also developed a robust phase 3. This late enhancement of the febrile response could reflect either the absence of the A receptor per se or a secondary trait of the mutant strain. To distinguish between these possibilities, we conducted a pharmacological analysis. We studied whether the normally low phase 3 of LE rats can be enhanced by a CCK-A-receptor antagonist, sodium lorglumide (4.3 microg kg-1 min-1, 120 min, I.V.), and whether the normally high phase 3 of Wistar rats can be attenuated by a CCK-A receptor agonist, sulphated CCK-8 (up to 0.17 microg kg-1 min-1, 120 min, I.V.). The dose of sodium lorglumide used was sufficient to increase food intake (to block satiety), but it did not affect the fever response. In both febrile and afebrile rats, CCK-8 induced dose-dependent skin vasodilatation and decreased body temperature, but it failed to produce any effects specific for phase 3. We conclude that the exaggeration of phase 3 in OLETF rats reflects a secondary trait of this strain and not the lack of the CCK-A receptor per se. None of the three known phases of the febrile response of rats to LPS requires the CCK-A receptor.

CCK-induced Fos expression in brain stem is enhanced after intestinal nematode infection in rats

Intestinal infections often trigger functional bowel disorders. The nematode Nippostrongylus brasiliensis induces post-infective alterations mainly consisting in an intestinal mast cell hyperplasia. Mast cells contact vagal afferent nerve fibres. Therefore, it is possible that the anatomical sequels of intestinal nematode infection induce long term alterations in the mediation of afferent signals from the gut to the brain. To test this hypothesis, we examined hindbrain expression of Fos immunoreactivity following systemic cholecystokinin (CCK) administration in control rats and 35 days after N. brasiliensis infection. In controls, Fos was expressed in the area postrema and the nucleus of solitary tract. After infection, this expression was increased by 262 and 157%, respectively. We conclude that an intestinal infection, at least in this model, is followed by an enhancement of the activation of hindbrain sites by CCK.

Cholecystokinin selectively affects presympathetic vasomotor neurons and sympathetic vasomotor outflow

Cholecystokinin (CCK) is a potential mediator of gastrointestinal vasodilatation during digestion. To determine whether CCK influences sympathetic vasomotor function, we examined the effect of systemic CCK administration on mean arterial blood pressure (MAP), heart rate (HR), lumbar sympathetic nerve discharge (LSND), splanchnic sympathetic nerve discharge (SSND), and the discharge of presympathetic neurons of the rostral ventrolateral medulla (RVLM) in alpha-chloralose-anesthetized rats. CCK (1-8 microg/kg iv) reduced MAP, HR, and SSND and transiently increased LSND. Vagotomy abolished the effects of CCK on MAP and SSND as did the CCK-A receptor antagonist devazepide (0.5 mg/kg iv). The bradycardic effect of CCK was unaltered by vagotomy but abolished by devazepide. CCK increased superior mesenteric arterial conductance but did not alter iliac conductance. CCK inhibited a subpopulation (approximately 49%) of RVLM presympathetic neurons whereas approximately 28% of neurons tested were activated by CCK. The effects of CCK on RVLM neuronal discharge were blocked by devazepide. RVLM neurons inhibited by exogenous CCK acting via CCK-A receptors on vagal afferents may control sympathetic vasomotor outflow to the gastrointestinal tract vasculature.

Basic organization of projections from the oval and fusiform nuclei of the bed nuclei of the stria terminalis in adult rat brain

The organization of axonal projections from the oval and fusiform nuclei of the bed nuclei of the stria terminalis (BST) was characterized with the Phaseolus vulgaris-leucoagglutinin (PHAL) anterograde tracing method in adult male rats. Within the BST, the oval nucleus (BSTov) projects very densely to the fusiform nucleus (BSTfu) and also innervates the caudal anterolateral area, anterodorsal area, rhomboid nucleus, and subcommissural zone. Outside the BST, its heaviest inputs are to the caudal substantia innominata and adjacent central amygdalar nucleus, retrorubral area, and lateral parabrachial nucleus. It generates moderate inputs to the caudal nucleus accumbens, parasubthalamic nucleus, and medial and ventrolateral divisions of the periaqueductal gray, and it sends a light input to the anterior parvicellular part of the hypothalamic paraventricular nucleus and nucleus of the solitary tract. The BSTfu displays a much more complex projection pattern. Within the BST, it densely innervates the anterodorsal area, dorsomedial nucleus, and caudal anterolateral area, and it moderately innervates the BSTov, subcommissural zone, and rhomboid nucleus. Outside the BST, the BSTfu provides dense inputs to the nucleus accumbens, caudal substantia innominata and central amygdalar nucleus, thalamic paraventricular nucleus, hypothalamic paraventricular and periventricular nuclei, hypothalamic dorsomedial nucleus, perifornical lateral hypothalamic area, and lateral tegmental nucleus. Moderately dense inputs are found in the parastrial, tuberal, dorsal raphé, and parabrachial nuclei and in the retrorubral area, ventrolateral division of the periaqueductal gray, and pontine central gray. Light projections end in the olfactory tubercle, lateral septal nucleus, posterior basolateral amygdalar nucleus, supramammillary nucleus, and nucleus of the solitary tract. These and other results suggest that the BSTov and BSTfu are basal telencephalic parts of a circuit that coordinates autonomic, neuroendocrine, and ingestive behavioral responses during stress.

Medial versus lateral parabrachial nucleus lesions in the rat: effects on cholecystokinin- and D-fenfluramine-induced anorexia

The two major components of the pontine parabrachial nucleus (PBN), the medial (gustatory) and lateral (visceral) subdivisions, have been implicated in a variety of ingestive behaviors. The present study examined the influence of bilateral ibotenic acid lesions of the medial or lateral PBN on the anorectic effects of two systemically administered drug treatments. In Experiment 1, 24-h food-deprived rats where injected with sulfated cholecystokinin (26-33) (CCK; 0, 4.0, or 8.0 microg/kg) and then given 60 min access to food. In Experiment 2, the influence of D-fenfluramine (DFEN; 0, 0.5, 1.0, or 2.0 mg/kg) on deprivation-induced feeding was examined in the same rats using the same behavioral procedure as in Experiment 1. Lesions of the lateral PBN abolished CCK-, but not DFEN-induced anorexia whereas lesions of the medial PBN augmented DFEN-, but had no influence on CCK-induced anorexia. The results suggest that the satiating effects of CCK and DFEN are mediated through different mechanisms involving, respectively, visceral and orosensory processing.

Vagus nerve participates in CCK-induced Fos expression in hindbrain but not myenteric plexus

CCK activates neurons in rat hindbrain and small intestinal myenteric ganglia. Activation of neurons at both sites is mediated through type A CCK receptors. CCK-induced activation of hindbrain neurons is mediated by capsaicin-sensitive vagal fibers. Therefore, it is possible that CCK-induced activation of myenteric neurons also depends upon vagal activation. To test this hypothesis, we examined hindbrain and myenteric neuronal expression of Fos immunoreactivity following CCK injection in rats that had undergone bilateral subdiaphragmatic vagotomy or systemic treatment with capsaicin, a neurotoxin that destroys small unmyelinated primary sensory neurons in the vagus, as well as in other peripheral nerves. We found that CCK (2 or 10 microg/kg) significantly increased Fos expression in both the brains and small intestinal myenteric plexuses of control rats. CCK-induced Fos expression was abolished or attenuated in the brains of vagotomized or capsaicin-treated animals. However, vagotomy or capsaicin treatment did not diminish CCK-induced Fos expression in the small intestinal myenteric plexus. We conclude that CCK-induced activation of intestinal myenteric neurons does not depend on activation of vagal sensory or motor neurons, while activation of neurons in the dorsal hindbrain is mediated, at least in part by CCK-induced activity of small unmyelinated vagal sensory neurons.

Neuroendocrine mechanisms regulating food intake and body weight

In the field of obesity research, two separate lines of study have emerged which explore the mechanism by which food intake is regulated: short-term control of food intake, and the central regulation of energy balance. The former studies the satiety response during consumption of meals, whereby satiety signalling originating in the gut is transduced into a neural signal that modulates satiety pathways in the brainstem. This review describes a neuroanatomically based model in which leptin and insulin signalling in the hypothalamus governs long-term regulation of energy balance via mechanisms that are integrated with satiety hormone signalling in the brainstem. The functional outcome of this integration is a cumulative meal-to-meal regulation of food intake, that over relatively long intervals serves to maintain stable adipose stores. Our model provides a context within which continued investigation of neuroendocrine mechanisms that control food intake and body weight can be explored, and has potential application to our current understanding of clinical obesity and its treatment.

CCK-A receptor activation induces fos expression in myenteric neurons of rat small intestine

Cholecystokinin (CCK), a hormone secreted from endocrine cells of the small intestine, participates in the control of motility and secretion in the gastrointestinal tract, and in the control of food intake. At least some of the effects of CCK on intestinal function appear to be mediated via activation of intrinsic neurons in the myenteric plexus. However, the distribution of CCK-responsive enteric neurons within the rat small intestine is not known. Neither has the role of CCK-A receptors in the activation of rat myenteric neurons been investigated. Therefore, to determine the distribution of CCK-responsive neurons in the small intestinal myenteric plexus we utilized immunohistochemical detection of Fos, the protein product of the immediate early gene c-fos, to identify neurons that were activated by exogenous CCK. We also monitored Fos expression in the dorsal hindbrain, and examined CCK-induced Fos expression in the presence or absence of a receptor antagonist for the type-A CCK receptor. We found that CCK significantly increased Fos expression in the hindbrain and in myenteric neurons of the duodenum and jejunum, but not the ileum. Neuronal Fos responsiveness in both brain and myenteric neurons was mediated by CCK-A receptors, as CCK-induced Fos expression was eliminated in rats pretreated with a CCK-A receptor antagonist. We conclude that CCK activates small intestinal myenteric neurons, via CCK-A receptors. Activation of these intrinsic intestinal neurons may participate in reflexes and behaviors that are mediated by CCK.

High fat maintenance diet attenuates hindbrain neuronal response to CCK

Rats maintained on a high fat diet reduce their food intake less in response to exogenous cholecystokinin (CCK) than rats maintained on a low fat diet. In addition, inhibition of gastric emptying by CCK is markedly attenuated in rats maintained on a high fat diet. Both inhibition of food intake and gastric emptying by CCK are mediated by sensory fibers in the vagus nerve. These fibers terminate on dorsal hindbrain neurons of the nucleus of the solitary tract and area postrema. To determine whether diet-induced changes in the control of feeding and gastric emptying are accompanied by altered vagal sensory responsiveness, we examined dorsal hindbrain expression of Fos-like immunoreactivity (Fos-li) following intraperitoneal CCK injection of rats maintained on high fat or low fat diets. Following CCK, there were numerous Fos-li nuclei in the area postrema and in the commissural and medial subnuclei of the nucleus of the solitary tract of rats maintained on a low fat diet. However, Fos-li was absent or rare in the brains of rats maintained on a high fat diet. These data suggest that the vagal sensory response to exogenous CCK is reduced in rats maintained on a high fat diet. Our results also are consistent with our previous findings that CCK-induced reduction of food intake and gastric emptying are both attenuated in rats maintained on a high fat diet. In addition our results support the hypothesis that attenuation of CCK-induced inhibition of food intake and gastric emptying may be due to diet-induced diminution of vagal CCK responsiveness.

Fos expression in the brain induced by peripheral injection of CCK or leptin plus CCK in fasted lean mice

We previously reported a synergistic interaction between leptin and cholecystokinin (CCK) to reduce food intake through CCK-A receptors in lean mice fasted for 24 h. To identify the activated neuronal pathways, we investigated changes in Fos expression in brain nuclei 2 h after single or combined intraperitoneal (i.p.) injections of leptin (120 microg/kg) and sulfated CCK-8 (3.5 microg/kg) in male lean mice (C57BL/6) fasted for 24 h using immunohistochemistry for Fos, the protein product of the early gene, c-fos. Leptin did not increase Fos expression in the brain compared with vehicle-treated mice. CCK increased the numbers of Fos-positive neurons in the nucleus of the solitary tract (NTS)/area postrema (AP), central nucleus of the amygdala (CeA) and, to a smaller extent, in the paraventricular nucleus of the hypothalamus (PVN) (5.2-, 2.3- and 0. 3-fold respectively). Injections of leptin-CCK further enhanced Fos expression by 40% in the PVN compared with that induced by CCK alone, but not in the other nuclei. Devazepide (a CCK-A receptor antagonist, 1 mg/kg, i.p.) prevented the increase in Fos expression induced by leptin-CCK in the PVN and by CCK alone in the PVN, CeA and NTS/AP. These results indicate that in fasted mice, i.p. injection of CCK increases Fos expression in specific brain nuclei through CCK-A receptors while leptin alone had no effect. Leptin in conjunction with CCK selectively enhanced Fos expression in the PVN. The PVN may be an important site mediating the synergistic effect of leptin-CCK to regulate food intake.

Peripheral administration of cholecystokinin activates c-fos expression in the locus coeruleus/subcoeruleus nucleus, dorsal vagal complex and paraventricular nucleus via capsaicin-sensitive vagal afferents and CCK-A receptors in the rat

Intraperitoneal (i.p.) administration of sulfated CCK octapeptide (CCK-8S) has been shown to induce changes in neuronal activity in the nucleus of the solitary tract (NTS) and area postrema (AP), sensory parts of the dorsal vagal complex (DVC), and in the paraventricular nucleus of the hypothalamus (PVN), as determined by activation of c-fos expression. Whether peripheral CCK influences neuronal activity in the locus coeruleus (LC)/subcoeruleus nucleus (SC) was investigated in awake rats at intraperitoneal (i.p.) injection of CCK-8S by c-Fos immunohistochemistry. CCK-8S i.p. (25, 50, and 100 micrograms/kg, respectively) dose-dependently increased the average number of c-Fos-LI-positive cells/section in the LC/SC by the factor 5.9, 8.2, and 11.7, respectively. Pretreatment with the CCK-A receptor antagonist MK-329 (devazepide; 1 mg/kg and 2 mg/kg i.p.) reduced the CCK-induced increase in c-fos expression in the LC/SC by 54% and 75%, respectively; the CCK-B receptor antagonist L-365,260 had no effect. Perivagal capsaicin pretreatment diminished the CCK-induced increase in the number of c-Fos-LI-positive cells in the LC/SC by 65%. In comparison, the CCK-A antagonist devazepide (1 mg/kg and 2 mg/kg i.p.) reduced the increase in c-fos expression by 76% and 88% in the PVN, 69% and 88% in the NTS, 86% and 83%, respectively, in the AP. Capsaicin diminished the CCK-induced increase in c-Fos-LI-positive cells in the PVN by 64%, in the NTS by 60%, but in the AP only by 25%. Immunostaining against the nuclear antigen c-Fos and the cytoplasmatic antigen tyrosine hydroxylase (TH) showed that 40% of all c-Fos-LI-positive cells in the LC/SC were TH-LI positive at 25 micrograms CCK/kg. The data indicate that CCK-8S i.p. induces modulation of neuronal activity in the LC/SC, DVC and PVN predominantly by peripheral action of CCK-A receptors and capsaicin-sensitive vagal afferents. These findings suggest that the LC/SC is involved in CNS-mediated regulatory influences of peripheral CCK.

Pretreatment with 5-HT1A receptor agonist flesinoxan attenuates Fos protein in rat hypothalamus

The 5-HT1A receptor agonist flesinoxan has anxiolytic activity and concurrently enhances plasma corticosterone levels in rats. After a second injection of flesinoxan 24 h later, the corticosterone response disappears, but not the anxiolytic effects. Male rats received two injections with either flesinoxan or vehicle within 24 h. Flesinoxan challenge enhanced Fos immunoreactivity in the paraventricular nucleus of the hypothalamus, the central amygdala, and the dorsolateral part of the bed nucleus of the stria terminalis and plasma corticosterone levels in the vehicle-pretreated rats. Flesinoxan pretreatment resulted in an attenuated response of plasma corticosterone levels and Fos-positive neurons in the paraventricular nucleus of the hypothalamus, but not in the central amygdala and the bed nucleus after a flesinoxan challenge. The differential desensitization levels for both behaviour and neuroendocrine responses after flesinoxan treatment seem to correspond to different organization levels in the brain, like limbic system and hypothalamus.

Peripherally and centrally administered bombesin induce Fos-like immunoreactivity in different brain regions in rats

Bombesin (BBS) suppresses food intake when administered either peripherally or centrally to rats, but the brain systems involved in the anorectic action remain unclear. We addressed this question by examining Fos-like immunoreactivity (Fos-IR), a marker of neuronal activation, in rat brain following either intraperitoneal (i.p.) or 4th cerebroventricular (4V) administration of BBS. It was found that the hypothalamic paraventricular nucleus showed strong Fos-IR following either i.p. BBS in the dose range 20-80 micrograms/kg, or 4V BBS at a dose of 60 ng/rat. Additionally, different effects of i.p. and 4V BBS were observed in the following regions: (1) a strong Fos-IR was seen in the area postrema (caudal part) only following i.p. but not 4V BBS; (2) while i.p. BBS-induced Fos-IR was almost evenly distributed throughout the medial subdivision of the nucleus of the solitary tract, 4V BBS-induced Fos-IR was much stronger in the rostral part than in the caudal part of this region; (3) although the lateral parabrachial nucleus, the central nucleus of the amygdala and the bed nucleus of the stria terminalis showed strong Fos-IR following both i.p. and 4V BBS, subregional distribution of the Fos-IR was not the same. These sites were previously found to show strong Fos-IR after administration of either cholecystokinin (CCK) or dexfenfluramine (DF), but with different subregional distribution. The Fos-IR pattern induced by i.p. BBS was similar to that induced by CCK, and the Fos-IR pattern induced by 4V BBS was similar to that induced by DF.