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Glucose has many diverse physiological roles such as energy metabolism, appetite control and memory consolidation. We recently reported that memory-related gene expression is epigenetically controlled in murine brain cells and that glucose can regulate gene expression in a cell-specific manner. However, the literature reviews have indicated that glucose can also regulate gut cells to release incretins which might play a role in memory processes directly or indirectly by vagus nerve stimulation. In this review, we discussed the effects of glucose on the gut and brain, aiming to understand more in-depth the role of glucose in memory function. In addition, we also discussed the alteration of glucose-signaling in type-2 diabetes mellitus (T2DM) and a possible link to Alzheimer's disease (AD) pathologies.

Glucose is believed to improve the memory in both human and mice, but the detailed insights were mostly elusive. In this study, we focused on two major neurotrophic factors, brain-derived neurotrophic factor (BDNF) and fibroblast growth factor 1 (FGF1), which are believed to be associated with the memory enhancement and assessed their expressional regulation among the murine neuronal and glial cells. Our findings showed that the glucose administration increased phosphorylated Akt, phosphorylated CREB, exon 1- and exon 4-specific BDNF transcripts, and FGF1 transcripts that are associated with the epigenetic changes expected to open the chromatin and a reduction in histone deacetylase 2 (HDAC2) in neurons and astrocytes of the murine hippocampus. The glucose administration enhanced the long-term potentiation and the number of dendritic spines in the CA1 and CA3 subfields of hippocampus. The intrahippocampal injection of short hairpin RNA against TrkB canceled the glucose-mediated memory enhancement. Like the glucose, we also report that the HDAC inhibitor can enhance the memory through the BDNF-TrkB pathway but it targeted different brain cell populations to enhance the BDNF and FGF1 transcripts. In addition, the soluble FGF1 treatments significantly increased the BDNF expression in astrocytes and neurons, suggesting that the glucose-mediated induction of the neurotrophic factors could contribute to the memory. Our study provides the valuable insights, explaining the distinctive neuronal and glial cell regulation of the neurotrophic factors by glucose and HDAC inhibitor, which could likely explain how our brain cells can control the release of neurotrophic factors.

To define how extracellular glucose levels affect synaptic efficacy and long-term potentiation (LTP), we evaluated electrophysiological and neurochemical properties in hippocampal CA1 regions following alterations in glucose levels in the ACSF. In rat hippocampal slices prepared in ACSF with 3.5mM glucose, fEPSPs generated by Schaffer collateral/commissural stimulation markedly increased when ACSF glucose levels were increased from 3.5 to 7.0mM. The paired-pulse facilitation reflecting presynaptic transmitter release efficacy was significantly suppressed by elevation to 7.0mM glucose because of potentiation of the input-output relationship (I/O relationship) of fEPSPs by single pulse stimulation. Prolonged potentiation of fEPSPs by elevation to 7.0mM glucose coincided with increased autophosphorylation both of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and protein kinase Cα (PKCα). The increased I/O relationship of fEPSPs was also associated with markedly increased synapsin I phosphorylation by CaMKII. Transmitter-evoked postsynaptic currents were also measured in CA1 neurons by electrophoretical application of NMDA and AMPA to the apical dendrites of pyramidal neurons. NMDA- and AMPA-evoked currents were significantly augmented by elevation to 7.0mM. Notably, high frequency stimulation of the Schaffer collateral/commissural pathway failed to induce LTP in the CA1 region at 3.5mM glucose but LTP was restored dose-dependently by increasing glucose levels to 7.0 and 10.0mM. LTP induction in the presence of 7.0mM glucose was closely associated with further increases in CaMKII autophosphorylation without changes in PKCα autophosphorylation. Taken together, CaMKII and PKC activation likely mediate potentiation of fEPSPs by elevated glucose levels, and CaMKII activity is also associated with LTP induction in the hippocampal CA1 region.

The newly identified neuropeptide S (NPS) is a ligand for a previously orphan G protein-coupled GPR 154 receptor, now named the NPS receptor (NPSR). Previous studies have shown that NPS induces hyperlocomotion, increases arousal and suppresses anxiety-like behaviors via NPSR. Although NPS also inhibits food intake, nothing is known about the neuronal mechanisms underlying this action. Anatomical studies show that NPSRs are expressed abundantly in the dorsomedial part of the ventromedial hypothalamic nucleus (VMH), a satiety center for food intake. Hence, we examined the electrophysiological effects of NPS on rat VMH neurons in vitro. NPS predominantly depolarized the VMH neurons, and the effects were postsynaptic and dose-dependent. Membrane resistance was significantly decreased during the depolarization, suggesting an opening of some ionic channels. The NPS-induced depolarization was significantly attenuated in Ca 2+ -free, NiCl 2 -containing and mibefradil-containing TTX ACSFs, but it did not disappear. The NPS-induced depolarization was also attenuated in low-Na + TTX ACSF, and completely abolished in Ca 2+ -free/low-Na + TTX ACSF. Pretreatment with 30 μM KB-R7943, an inhibitor of forward-mode Na + /Ca 2+ exchanger, did not have any significant effect on the NPS-induced depolarization in Ca 2+ -free TTX ACSF. These results suggest that NPS depolarizes VMH neurons via activations of R- and T-type Ca 2+ channels and nonselective cation channels, and that VMH neurons might be involved in the cellular process through which NPS participates in the regulation of food intake and energy homeostasis.

Ghrelin, a gut and brain peptide, is a potent stimulant for growth hormone (GH) secretion and feeding. Recent studies further show a critical role of ghrelin in the regulation of sleep–wakefulness. Laterodorsal tegmental nucleus (LDT), that regulates waking and rapid eye movement (REM) sleep, expresses GH secretagogue receptors (GHS-Rs). Thus, the present study was carried out to examine electrophysiological effects of ghrelin on LDT neurons using rat brainstem slices, and to determine the ionic mechanism involved. Whole cell recording revealed that ghrelin depolarizes LDT neurons dose-dependently in normal artificial cerebrospinal fluid (ACSF). The depolarization persisted in tetrodotoxin-containing ACSF (TTX ACSF), and is partially blocked by the application of [ d -Lys 3 ]-GHRP-6, a selective antagonist for GHS-Rs. Membrane resistance during the ghrelin-induced depolarization increased by about 18% than that before the depolarization. In addition, the ghrelin-induced depolarization was drastically reduced in high-K + TTX ACSF with a K + concentration of 13.25 mM. Reversal potentials obtained from I – V curves before and during the depolarization were about −83 mV, close to the equilibrium potential of the K + channel. Most of the LDT neurons recorded were characterized by an A-current or both the A-current and a low threshold Ca 2+ spike, and they were predominantly cholinergic. These results indicate that ghrelin depolarizes LDT neurons postsynaptically and dose-dependently via GHS-Rs, and that the ionic mechanisms underlying the ghrelin-induced depolarization include a decrease of K + conductance. The results also suggest that LDT neurons are implicated in the cellular processes through which ghrelin participates in the regulation of sleep–wakefulness.

Orexin-A (ORX-A) and orexin-B (ORX-B) play critical roles in the regulation of sleep-wakefulness, energy homeostasis, neuroendocrine system and autonomic functions. Although ORXs are also implicated in the reward process, their electrophysiological effects on neurons in the shell of nucleus accumbems (NAcSh) have not been described thoroughly. Therefore we examined the electrophysiological effects of ORXs on rat NAcSh neurons. Whole cell patch clamp recording in vitro revealed that ORX-A and ORX-B depolarize NAcSh neurons in normal and/or tetrodotoxin (TTX)-containing artificial cerebrospinal fluid (ACSF). The depolarization accompanied by a decrease of membrane resistance was concentration-dependent, and there was no significant difference between the two dose-response curves obtained by ORX-A and ORX-B. The ORX-B-induced depolarization was reduced in low-Na(+), flufenamic acid-containing, and high-K(+) TTX ACSFs, and completely abolished in low-Na(+)/high-K(+) TTX ACSF. An inhibitor of the Na(+)/Ca(2+) exchanger had no effect on the depolarization. The reversal potential obtained from I-V relationships before and during the ORX-B-induced depolarization in low-Na(+) TTX ACSF was about -84mV, and that obtained in TTX ACSF using patch pipettes with Cs(+)-containing internal solution was about -38mV. These results suggest that ORXs directly depolarize NAcSh neurons via OX(2) receptors and via a dual ionic mechanism including an increase of nonselective cationic conductance and a decrease of K(+) conductance, and that NAcSh neurons are involved in the cellular mechanisms through which ORXs participate in the regulation of the reward process as well as feeding and arousal.

Ghrelin is a potent stimulant for growth hormone (GH) secretion and feeding. Recent studies further show a critical role of ghrelin in the regulation of sleep-wakefulness. Pedunculopontine tegmental nucleus (PPT), which regulates waking and rapid eye movement (REM) sleep, expresses GH secretagogue receptors (GHS-Rs). Thus, the present study was carried out to examine electrophysiological effects of ghrelin on PPT neurons using rat brainstem slices, and to determine the ionic mechanism involved. Whole cell recording revealed that ghrelin depolarizes PPT neurons dose-dependently in normal artificial cerebrospinal fluid (ACSF). The depolarization persisted in tetrodotoxin-containing ACSF, although action potentials did not occur. Application of [d-Lys(3)]-GHRP-6, a selective antagonist for GHS-Rs, almost blocked the ghrelin-induced depolarization. Furthermore, the ghrelin-induced depolarization was reduced in high K(+) ACSF or low Na(+) ACSF, and abolished in high K(+)-low Na(+) ACSF or in a combination of low Na(+) ACSF and recordings with Cs(+)-containing pipettes. An inhibitor of Na(+)/Ca(2+) exchanger had no effect on the depolarization. Most of the PPT neurons recorded were characterized by an A-current or both the A-current and a low threshold Ca(2+) spike, and they were predominantly cholinergic as revealed by nicotinamide adenine dinucleotide phosphate-diaphorase staining. These results suggest that ghrelin depolarizes PPT neurons postsynaptically and dose-dependently via GHS-Rs, and that the ionic mechanisms underlying the ghrelin-induced depolarization include a decrease of K(+) conductance and an increase of non-selective cationic conductance. The results also support the notion that ghrelin plays a role in the regulation of sleep-wakefulness.

The orbitofrontal cortex (OBF) is known to play an important role in the central regulation of adaptive behavior. Previous studies provided evidence for feeding-associated neurons in the rodent and macaque OBF. To further elucidate functional attributes of these neurons, complex electrophysiological–neurochemical–behavioral studies were performed in rats and rhesus monkeys. Single unit activity was recorded in the rat and monkey OBF during microiontophoresis of glucose, various neurochemicals, as well as gustatory stimulations. To investigate feeding-related neuronal mechanisms at the cognitive level, recordings were also performed in the monkey OBF during a visual food discrimination task. OBF neurons displayed specific responsiveness to gustatory stimuli, as well as to microelectrophoretically applied chemicals. The majority of gustatory cells were shown to possess specific, feeding-related neurochemical attributes: microelectrophoretically administered glucose changed their firing rates. These chemosensory cells also displayed differential sensitivity to catecholamines and other neurochemicals. In the discrimination task, category-specific or task-specific neurons showed a broad variety of selectivity for food-related visual stimuli. Expectation- and reward-related activities were also recorded. Our results provide evidence that OBF neurons possess specific endogenous and exogenous chemosensitivity, and that they utilize differential neurotransmitter mechanisms in feeding-related cognitive functions. Thus, the complex network of these chemosensory neurons possesses broad ranging, multiple functional attributes in the homeostatic control.

Lateral hypothalamic orexin expressing neurons send fibers to various brain areas such as the brainstem, hypothalamus, cortex and limbic system, including the amygdala and the bed nucleus of stria terminalis (BST). The role of orexins in reward seeking, response to stress, learning and memory have recently been investigated. BST is known to be involved in the regulation of hormonal and behavioral responses to stress, anxiety and sexual behavior. The present study aimed to elucidate the involvement of orexin-A (OXA) in learning, anxiety and reinforcement processes in the BST. Bilateral OXA microinjections in the doses of 250 ng (70 pmol) and 500 ng (140 pmol) into the BST of male Wistar rats were performed 30 min prior to open field (OPF), elevated plus maze (EPM), conditioned place preference (CPP), or passive avoidance (PAV) tests. In the CPP, 250 ng OXA increased the number of entering into the treatment quadrant. The 500 ng OXA had significant anxiolytic effects on EPM. There was a mild increase in the locomotor activity in the OPF as well as in the EPM. In the PAV, OXA dose-dependently reduced the retention time to enter the dark room, indicating its suppressive effect on avoidance learning. Our findings reveal that OXA shows functional heterogeneity in learning and memory processes having a specific role in the modulation of PAV learning. The inhibition on avoidance learning is supposed to be due to the anxiolytic effect of OXA.

Leptin, an adipocytokine encoded by an obesity gene and expressed in adipose tissue, affects feeding behavior, thermogenesis, and neuroendocrine status via leptin receptors distributed in the brain, especially in the hypothalamus. Leptin may also modulate the synaptic plasticity and behavioral performance related to learning and memory since: leptin receptors are found in the hippocampus, and both leptin and its receptor share structural and functional similarities with the interleukin-6 family of cytokines that modulate long-term potentiation (LTP) in the hippocampus. We therefore examined the effect of leptin on (1) behavioral performance in emotional and spatial learning tasks, (2) LTP at Schaffer collateral-CA1 synapses, (3) presynaptic and postsynaptic activities in hippocampal CA1 neurons, (4) the intracellular Ca(2+) concentration ([Ca(2+)](i)) in CA1 neurons, and (5) the activity of Ca(2+)/calmodulin protein kinase II (CaMK II) in the hippocampal CA1 tissue that exhibits LTP. Intravenous injection of 5 and/or 50mug/kg, but not of 500mug/kg leptin, facilitated behavioral performance in passive avoidance and Morris water-maze tasks. Bath application of 10(-12)M leptin in slice experiments enhanced LTP and increased the presynaptic transmitter release, whereas 10(-10)M leptin suppressed LTP and reduced the postsynaptic receptor sensitivity to N-methyl-d-aspartic acid. The increase in the [Ca(2+)](i) induced by 10(-10)M leptin was two times greater than that induced by 10(-12)M leptin. In addition, the facilitation (10(-12)M) and suppression (10(-10)M) of LTP by leptin was closely associated with an increase and decrease in Ca(2+)-independent activity of CaMK II. Our results show that leptin not only affects hypothalamic functions (such as feeding, thermogenesis, and neuroendocrine status), but also modulates higher nervous functions, such as the behavioral performance related to learning and memory and hippocampal synaptic plasticity.

The energy-monitoring systems in the brain are highly sensitive to not only appetite-regulating substances but also many other chemicals affecting reproductive function, thermoregulation and immune function. Even environmental chemicals influence these systems. These multisensing systems provide a model of sophisticated systems, which accelerate the energy saving and environmental preservation in the individuals, species and environment.

Cholinergic neurons in the dorsal motor nucleus of the vagus (DMNV) are particularly vulnerable to laryngeal nerve damage, possibly because they lack fibroblast growth factor-1 (FGF1). To test this hypothesis, we investigated the localization of FGF1 in cholinergic neurons innervating the rat larynx by immunohistochemistry using central-type antibodies to choline acetyltransferase (cChAT) and peripheral type (pChAT) antibodies, as well as tracer experiments. In the DMNV, only 9% of cChAT-positive neurons contained FGF1, and 71% of FGF1-positive neurons colocalized with cChAT. In the nucleus ambiguus, 100% of cChAT-positive neurons were FGF1 positive. In the intralaryngeal ganglia, all ganglionic neurons contained both pChAT and FGF1. In the nodose ganglia, 66% of pChAT-positive neurons were also positive for FGF1, and 90% of FGF1-positive ganglionic cells displayed pChAT immunoreactivity. Neuronal tracing using cholera toxin B subunit (CTb) demonstrated that cholinergic neurons sending their axons from the DMNV and nucleus ambiguus to the superior laryngeal nerve were FGF1 negative and FGF1 positive, respectively. In the nodose ganglia, some FGF1-positive cells were labeled with CTb. The results indicate that for innervation of the rat larynx, FGF1 is localized to motor neurons, postganglionic parasympathetic neurons, and sensory neurons, but expression is very low in preganglionic parasympathetic cholinergic neurons.

Neurons in the dorsal motor nucleus of the vagus (DMNV) are more severely affected by axonal injury than most other nerves, such as those of the hypoglossal nucleus. However, the mechanism underlying such a response remains unclear. In this study, we compared the expression of fibroblast growth factor 1 (FGF1), a neurotrophic factor, between the DMNV and the hypoglossal nucleus by RT-PCR and immunohistochemical analyses. RT-PCR showed that the level of FGF1 mRNA expression in the DMNV was lower than that in the hypoglossal nucleus (P

Orexin-A (ORX-A) and orexin-B (ORX-B), also called hypocretin-1 and hypocretin-2, respectively, act upon orexin 1 (OX1R) and orexin 2 (OX2R) receptors, and are involved in the regulation of sleep-wakefulness and energy homeostasis. Orexin neurons in the lateral hypothalamic perifornical region project heavily to the paraventricular nucleus of the thalamus (PVT), which is deeply involved in the control of motivated behaviors. In the present study, electrophysiological and cytosolic Ca2+ concentration ([Ca2+]i) imaging studies on the effects of ORX-A and ORX-B on neurons in the PVT were carried out in rat brain slice preparations. ORX-A and/or ORX-B were applied extracellularly in the perfusate. Extracellular recordings showed that about 80% of the PVT neurons were excited dose-dependently by both ORX-A and ORX-B at concentrations of 10(-8) to 10(-6)M, and the increase in firing rate was about three times larger for ORX-B than for ORX-A at 10(-7)M. When both ORX-A and ORX-B were applied simultaneously at 10(-7)M, the increase in firing rate was almost equal to that of ORX-B at 10(-7)M, suggesting that the PVT neurons do not show a high affinity to ORX-A which is expected if they have OX1R receptors. The excitatory effect of ORX-B was seen in low Ca2+ and high Mg2+ ACSF as well as in normal ACSF, and the increase in firing rate was greater in low Ca2+ and high Mg2+ ACSF than in normal ACSF. [Ca2+]i imaging studies demonstrated that [Ca2+]i was increased in about 50% of the PVT neurons by both 10(-7)M ORX-A and ORX-B with a stronger effect for ORX-B, and the increase in [Ca2+]i induced by ORX-B was abolished in Ca2+-free ACSF, suggesting that ORX-B does not release Ca2+ from intracellular Ca2+ stores. Subsequent whole cell patch clamp recordings revealed that an after hyperpolarization seen following each action potential in normal ACSF disappeared in Ca2+-free ACSF, and the mean magnitude of the depolarization induced by ORX-B was same in normal, Ca2+-free and TTX-containing Ca2+-free ACSFs. Furthermore, ORX-B-induced depolarization was reversed to hyperpolarization when membrane potential was lowered to about -97 mV, and an increase of extracellular K+ concentration from 4.25 to 13.25 mM abolished the ORX-B-induced depolarization, indicating that the ORX-B-induced depolarization is associated with an increase in the membrane resistance resulting from a closure of K+ channels. These results suggest that orexins depolarize and excite post-synaptically PVT neurons via OX2R receptors, and that orexin-activated PVT neurons play a role in the integration of sleep-wakefulness and energy homeostasis, and in the control of motivated behaviors.

The central nervous system is highly sensitive to endogenous and exogenous chemicals. Catecholamines, norepinephrine (NE) and dopamine (DA), regulate many different brain functions including learning and memory, emotion, stress responses and homeostatic control of physiological systems. NE and DA are differently involved in reward-related neuronal activity and other task-related neuron activities in the prefrontal cortex, amygdala and the lateral hypothalamic area. During inflammatory and non-inflammatory stress conditions, NE levels are locally regulated at terminal levels by proinflammatory cytokines such as interleukin-1β in which prostanoid and nitric oxide are involved. NE system has been shown to express estrogen receptors and is highly sensitive to endocrine disrupters such as bisphenol A during sexual differentiation. These findings suggest that higher brain functions such as learning and emotional control are under the influence of chemical impacts via catecholamines, cytokines and environmental chemicals.

Orexin-A (Hypocretin-1) has been localized in the posterior and lateral hypothalamic perifornical region. Orexin containing axon terminals have been found in hypothalamic nuclei and many other parts of the brain; for example, the hippocampus. Two types of orexin receptors have been discovered. Orexin 1 type of receptors have been described and been shown to be widely distributed in the rat brain including the hippocampus. Subsequently Orexin-A was found to impair both water maze performance and hippocampal long term potentiation (LTP). Leptin is expressed in adipose tissue and released into the blood where it affects food intake and can also produce widespread physiological changes mediated via autonomic preganglionic neurons, pituitary gland, and cerebral cortex. Immunoreactivity for leptin receptors has been found in various hypothalamic nuclei including the lateral hypothalamic area as well as the hippocampus especially in the dentate gyrus and CA1. Leptin receptor deficient rats and mice also show impaired LTP in CA1 and poor performance in the water maze. The present study was conducted to determine the effects of 0.0, 30, 60, 90, and 100 nM, orexin-A, and leptin, 0.0, 1.0, 100 nM, 1, and 10 microM, in 1.0 microl of ACSF, applied directly into the dentate gyrus, on LTP in medial perforant path dentate granule cell synapses in urethane anesthetized rats. Orexin-A specifically enhanced LTP at the 90 nM dose; and it was possible to block the enhancement by pretreating the animals with SB-334867, a specific orexin 1 receptor antagonist. Leptin enhanced normal LTP at 1.0 microM but inhibited LTP at lower and higher doses. These results and previous data indicate that the same peptide could possibly have different modulatory post synaptic effects in different hippocampal synapses dependent upon different types of post synaptic receptors.

In the present study, on senescence-accelerated mice (SAM) of various ages, we examined the level of lipid hydroperoxides in the brain tissue, and the effects of acetyl- l -carnitine (ALC) and acidic fibroblast growth factor fragment analog, [Ala16]aFGF(1–29), on the brain lipid hydroperoxide level, passive avoidance performance and/or immunoreactivity for choline acetyltransferase (ChAT) in the medial septum (MS). The brain level of lipid hydroperoxides did not show an age-dependent change in either SAMP8 or SAMR1 (control mice for SAMP8), but it was significantly higher for SAMP8 than for SAMR1 at 3, 6 and 9 months of age. Chronic administration of ALC (400 mg/kg) significantly ameliorated the deficit in learning and memory seen in saline-treated SAMP8, and also normalized the increased brain lipid hydroperoxide level in these mice. Chronic administration of [Ala16]aFGF(1–29) (150 μg/kg) to SAMP8 also improved the learning and memory deficits and normalized the decreased ChAT activity in the cholinergic neurons of the MS in these mice. These results suggest that ALC and aFGF fragment analog can each ameliorate the cognitive disability seen in untreated SAMP8 (through a decrease in the brain lipid hydroperoxide level and through a restoration of ChAT activity in cholinergic neurons in the MS, respectively).

A sugar acid, 2-B4O, has been found to increase from 3.5 to 13 microM in rat serum at 36 h after food deprivation. Injections of 2-B4O (2.5 microM) into the rat III cerebral ventricle (III ICV) suppress food intake and single neuronal activity in the lateral hypothalamic area (LHA). 2-B4O is effective even in 72 h food-deprived rats. 2-B4O hyperpolarizes glucose-sensitive neurons in the LHA via Na+-K+ pump activation, but depolarizes glucoreceptor neurons in the ventromedial nucleus (VMH) via closure of ATP-sensitive K channels. The plasma levels of glucose, corticosterone, and catecholamines, and the firing rate in both parvocellular neurons in the paraventricular nucleus (PVN) and sympathetic efferent nerves, all increase 2-B4O intravenous (iv) injection, indicating activation of the hypothalamo-pituitary-adrenal axis. A 2-B4O iv injection facilitates emotional and spatial learning and memory, and pretreatment with anti-acidic fibroblast growth factor (aFGF) antibody ICV eliminates these effects. aFGF is released from ependymal cells in the III cerebral ventricle in response to the glucose increase in CSF induced by 2-B4O iv injection. 2-B4O also suppresses the clinical symptoms of experimental allergic encephalomyelitis (EAE) in Lewis rats [induced by immunization with a myelin basic protein (MBP)], a model for human multiple sclerosis. After immunization with MBP, the delayed-type hypersensitivity response to MBP is also reduced in 2-B4O-treated rats. 2-B4O thus suppresses autoimmune responses. These results indicate that 2-B4O is not only a powerful satiety substance, but also effective as an activator of the hypothalamo-pituitary-adrenal axis and sympathetic efferent outflow, and as a memory facilitation and a modulator of immune functions.

Recent studies have shown that FGF-1 (aFGF) and FGF-2 (bFGF) are expressed in the adrenal glands. In order to understand the roles of FGFs in the adrenal gland, we investigated the expression of the fibroblast growth factor receptor-1 (FGFR1) in rat adrenal gland using reverse transcription-polymerase chain reaction (RT-PCR) method, Western blot and immunohistochemistry. RT-PCR experiment using a primer set to amplify the acidic region of FGFR1 gave two bands of about 426 bp and 160 bp in both the adrenal cortex and medulla. The sizes of the large and small PCR products corresponded well to the three IgG-like domain (long form) and two IgG-like domain (short, or secreted form) FGFR1, respectively. Western blotting analysis using an antibody capable of detecting the acidic region of FGFR1, gave two bands in the adrenal gland with molecular weights of about 130 kDa and 75 kDa, corresponding to the long and the secreted form of FGFR1, respectively. Immunohistochemical study using the antibody demonstrated that FGFR1-positive cells were distributed mainly in the zona glomerulosa of the adrenal cortex and medulla. A few positive cells were scattered in the zona fasciculata and reticularis. In the adrenal medulla, almost all cells were positive for FGFR1. Double immunostaining revealed that FGFR1 colocalized with tyrosine hydroxylase-immunoreactive catecholamine cells in the adrenal medulla.

Leptin is well known to be involved in the control of feeding, reproduction and neuroendocrine functions through its action on the hypothalamus. However, leptin receptors are found in brain regions other than the hypothalamus (including the hippocampus and cerebral cortex) suggesting extrahypothalamic functions. We investigated hippocampal long-term potentiation (LTP) and long-term depression (LTD), and the spatial-memory function in two leptin receptor-deficient rodents (Zucker rats and db/db mice). In brain slices, the CA1 hippocampal region of both strains showed impairments of LTP and LTD; leptin (10(-12) M) did not improve these impairments in either strain. These strains also showed lower basal levels of Ca(2+)/calmodulin-dependent protein kinase II activity in the CA1 region than the respective controls, and the levels did not respond to tetanic stimulation. These strains also showed impaired spatial memory in the Morris water-maze test (i.e. longer swim-path lengths during training sessions and less frequent crossings of the platform's original location in the probe test. From these results we suggest that the leptin receptor-deficient animals show impaired LTP in CA1 and poor spatial memory due, at least in part, to a deficiency in leptin receptors in the hippocampus.

We studied the sensitivity of sensorimotor cortex neurons in rabbits to microiontophoretic administration of antibodies against acid fibroblast growth factor (anti-aFGF). Spontaneous activity and reaction of neurons to electrical stimulation of ‘feeding centers' in the lateral hypothalamic area (LHA) were recorded. We analyzed impulse activity of 52 neurons in the sensorimotor cortex. It was shown that 14 neurons (25%) reacted to microiontophoresis of anti-aFGF (excitation and inhibition in 9 and 5 neurons, respectively). Microiontophoretic administration of anti-aFGF did not change the reaction (excitation or inhibition) of 27 neurons to electrical stimulation of LHA. Initially, 14 neurons did not response to LHA stimulation. After microiontophoretic administration of anti-aFGF, 6 of 14 neurons displayed pronounced reactions to electrical stimulation of LHA (excitation and inhibition in 2 and 4 neurons, respectively). These data suggest that aFGF plays an important physiological role in feeding motivations.

The issue that has divided opinion over the status of umami as a basic taste quality is its relationship with the taste of sodium salt. That is addressed here, informed by electrophysiological data from the hindbrain of rats and from the forebrain of macaques. In multidimensional spaces, generated from patterns of neural activity evoked in the rat's hindbrain by an array of taste stimuli, MSG does indeed lie near the position of NaCl. Yet when sodium transduction is disrupted by the lingual application of amiloride, the impact on the taste response to MSG is minor, and the pattern of activity it elicits is unaltered. Thus, MSG generates a taste quality that transcends saltiness, one that survives even as saltiness is compromised. This conclusion is in accord with the independent transduction mechanisms ascribed to MSG. In the macaque's taste system, MSG is an effective stimulus with a dynamic range of 0.009 to 0.300 M. Approximately one-third of the taste cells at each synaptic relay respond to MSG at 0.1 M. MSG evoked a neural response profile in primary taste cortex that correlated quite well with that elicited by NaCl, in accord with the pronounced salty component humans report for its taste. At succeeding synaptic relays, however, that relationship deteriorated, becoming increasingly distant and labile. At higher-order gustatory levels, MSG evoked a profile that was no more similar to those of the basic stimuli than they are to each other. This implies that MSG warrants independent status as a basic taste stimulus, serving as the prototype for the umami quality.

We investigated the effects of leptin on central and/or peripheral feeding-related neuronal networks in Wistar male rats either normal (350–450 g) or Zucker obese (500–800 g). Low doses (1–10 pg) of leptin inhibited glucose-sensitive vagal hepatic afferent discharges and facilitated sympathetic efferent discharges to brown and white adipose tissue. Most (40–75%) neurons in the arcuate nucleus were significantly inhibited by superperfusion with leptin (0.1 nM–10 pM) under in vitro conditions. In anesthetized animals, leptin was applied electrophoretically to single hypothalamic neurons. Both glucose-sensitive neurons (GSNs) and non-GSNs in the feeding center (LHA) were significantly inhibited. Most glucoreceptor neurons in the satiety center (VMH) were significantly excited. Their depolarization was confirmed by activation of Na + and K + channels by 10 −11 M leptin using the perforate blind patch-clamp method. Although leptin excited GSNs in the parvocellular part of the paraventricular nucleus, the effects of leptin on such neuronal activity were slight or absent in Zucker obese rats. These results suggest that the feeding-suppression effects of leptin are mediated by its effects on signal transduction through both the central and the peripheral nervous systems.

We examined the effects of repeated subcutaneous injections of an acidic fibroblast growth factor fragment analog, [Ala 16 ] acidic fibroblast growth factor (1–29), on learning and memory and on the choline acetyltransferase immunoreactivity of forebrain neurons in senescence-accelerated mice. One group of accelerated senescence-prone mice (accelerated senescence-prone-8) received [Ala 16 ] acidic fibroblast growth factor (1–29), whereas the other group of accelerated senescence-prone-8 mice and a group of accelerated senescence-resistant mice (control) received vehicle solution. Injections began at three weeks after birth and were given weekly for 10 months. In a passive avoidance test, the mean retention latency at three, six and nine months of age was significantly longer in controls (vehicle-treated accelerated senescence-resistant-1) and acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 than in vehicle-treated accelerated senescence-prone-8 mice, and the latency in acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 mice was significantly shorter than that in controls only at nine months of age. In the Morris water maze task, the mean latency to climb onto the platform was significantly longer in acidic fibroblast growth factor fragment- and vehicle-treated accelerated senescence-prone-8 mice than in controls. However, the mean latency in the third and fourth trial blocks was significantly shorter for acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 than for vehicle-treated accelerated senescence-prone-8 mice. In the probe trials, controls and acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 mice spent significantly more time in the quadrant in which the platform had previously been located than in the other three quadrants. In acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 mice, the density of medial septum neurons intensely stained for choline acetyltransferase was significantly greater than that in vehicle-treated accelerated senescence-prone-8 mice, but significantly less than that in controls. The results indicate that the beneficial effect of [Ala 16 ] acidic fibroblast growth factor (1–29) on learning and memory function in accelerated senescence-prone-8 mice may be related to a preservation of function in medial septum cholinergic neurons.

To reveal specific functions of glucose-sensitive (GS) and glucose-insensitive (GIS) cells in chemical information processing, single neuron activity was recorded in the amygdaloid body (AMY) of macaques during: 1) gustatory stimulations and 2) microelectrophoretic administration of chemicals. Of the 629 neurons tested, 56 (8.9%) responded to, usually two or more, taste qualities. Hedonically distinct tastants usually elicited opposite firing rate changes of the gustatory cells. Seventy percent of the gustatory responses were recorded from GS neurons (17% of all AMY cells). Catecholamines (CAs) induced discharge rate changes in a majority of taste-responsive neurons: The GS gustatory cells were suppressed by norepinephrine (in the form of noradrenaline HCl, NA), whereas the GIS taste-responsive neurons were facilitated by dopamine (DA). Furthermore, NA- and/or DA-antagonists were able to attenuate or suppress taste-elicited responses of several of these cells. These and previous data indicate a specific functional organization of AMY gustatory cells: The GS and GIS taste neurons appear to be involved in differential integration of feeding-associated humoral-metabolic, motivational and exogenous chemical information.

Effects of exogenous acidic fibroblast growth factor (aFGF), which is increased in the brain by food intake, on the plasma levels of catecholamines and on sympathetic efferent outflow were examined in anesthetized rats. A guide cannula was inserted into the cerebral third ventricle, and a vascular indwelling catheter was inserted into the right atrium from the jugular vein. Plasma epinephrine (Epi) and norepinephrine (NE) increased markedly in a dose-dependent manner for up to 120 min after intracerebroventricular or intravenous administration of aFGF (6–667 fmol/rat). Concomitant increases occurred in the efferent activity in the sympathetic nerves supplying the adrenal, spleen, and interscapular brown adipose tissue after the above administrations of aFGF. Both intravenous and intracerebroventricular administration of 10 ng basic FGF (bFGF) also increased sympathetic adrenal efferent activity and plasma Epi and NE concentrations. However, the increases induced by 10 ng bFGF were smaller than those induced by 10 ng aFGF. Bilateral splanchnicotomy completely prevented the increases in Epi induced by intracerebroventricular or intravenous aFGF but had less effect on the increases in NE. Pretreatment with an antibody against corticotropin-releasing factor (CRF), given via the intracerebroventricular route, significantly attenuated the increases in Epi and NE evoked by intracerebroventricular or intravenous administration of aFGF. Hepatic vagotomy also greatly reduced the increases in both catecholamines and the increases in sympathetic efferent firing rates evoked by intravenous administration of aFGF. These findings indicate that 1) aFGF administered intracerebroventricularly activates adrenomedullary secretion and sympathetic outflow via CRF release and 2) aFGF injected intravenously also induces sympathoadrenomedullary activation via centrally released CRF. The idea is discussed that sympathetic activation induced either by endogenous aFGF after feeding or by exogenously administered aFGF may play roles both in energy expenditure after overeating and in the modulation of immune functions.

We examined the effects of chronic administration of acidic fibroblast growth factor (aFGF) on memory and choline acetyltransferase (ChAT) immunoreactivity in the forebrain of senescence-accelerated mice (SAMP8 strain). Subcutaneous injection of aFGF (aFGF group) or saline vehicle (saline group) once a week into SAMP8 was begun at three weeks after birth and continued for nine months. In the passive avoidance test, the retained latency was significantly longer in the aFGF group than in the saline group. In the Morris test, the mean latency to climb on a platform was significantly shorter in the aFGF group than in the saline group. The number of ChAT-positive neurons in the forebrain septum was greater in the aFGF group than in the saline group, and was at the level of that in the control mouse strain (SAMR1). The intensity of ChAT staining in the aFGF group appeared slightly weaker than in SAMR1 but significantly stronger than in the saline group. The results indicate that the effect of aFGF on memory function in SAMP8 may be related to the preservation of function in septal cholinergic cells.

The senescence-accelerated mouse (SAMP8) is a useful murine model of accelerated aging and learning deficiency. We examined bindings of [3H]pirenzepine, [3H]dizocilpine (MK-801), [3H]flunitrazepam, [3H]8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and [3H]phorbol 12,13-dibutylate (PDBu) in SAMP8 brains, and compared them to those of SAMR1 (control). In the hippocampus of SAMP8 at 12 months, bindings of [3H]pirenzepine, [3H]MK-801, [3H]flunitrazepam, [3H]8-OH-DPAT and [3H]PDBu were significantly lower than those in SAMR1. In the cerebral cortex, bindings of [3H]pirenzepine, [3H]flunitrazepam and [3H]8-OH-DPAT were higher in SAMP8 than in SAMR1 at 12 months. [3H]PDBu binding was decreased in both the fractions of the membrane and cytosol in the hippocampus of SAMP8. The neurochemical findings presented here support behavioral and pharmacological findings that SAMP8 is a useful model of learning dysfunction and anxiety-deficiency. The usefulness of SAMP8 in studies on cognitive enhancers is also discussed.

Subcutaneous injection of aFGF once a week into senescence-accelerated mice (SAM)P8 was begun at 3 weeks after birth and continued for 10 months. Saline was injected as a control. Learning and memory and cellular immunological functions in the aFGF group were enhanced significantly, while those of the saline group deteriorated. 1. The number of cholinergic neurons was decreased by less than 20% and choline acetyltransferase activity in individual neurons in the medical septum which send monosynaptic terminals to the hippocampus was significantly decreased in the saline group, but not so much in the aFGF group. 2. The respective densities of muscarinic and NMDA receptors and the aFGF receptor, i.e., FGFR-1 on the hippocampal neurons were also significantly higher in the aFGF group than in the saline group. 3. The long-term potentiation in the hippocampal slice preparations after a brief tetanic stimulation at the Schaffer collateral/commissural afferents was significantly facilitated in the aFGF group, but not in the saline group. 4. These data indicate the normalization caused by aFGF of the medial septohippocampal circuit, which is necessary for learning and memory. 5. The delayed type hypersensitivity reactions (DTH) in the footpad caused by challenge with trinitrophenyl or sheep red blood cells as measured at the end of the 2nd and 7th months, indicated the T cell immune response. Both types of DTHs were reduced in the 7th month as compared with the 2nd month in the saline group, but the aFGF group was protected against this reduction in accordance with age. 6. These results show that aFGF provides protection against impairment of not only learning and memory but also DTH immunoreactivity in SAMP8. They also indicate a close relationship between learning and memory and T cell immune function.

Previous studies have shown that acidic and basic fibroblast growth factor (aFGF and bFGF) and certain fragments of the aFGF N-terminal suppress food intake in rats due to their inhibitory actions on the glucose-sensitive neurons in the lateral hypothalamic area (LHA). The present study was planned to determine the role of FGF receptor-1 (FGFR-1), which was found in the LHA neurons of rats, on feeding regulation. The structure–activity relationship of aFGF fragments in feeding suppression was also investigated. An injection of anti-FGFR-1 antibody (250 and 350 ng) into the bilateral LHA significantly increased food intake. Synthesized aFGF fragments were infused into the III ventricle to elucidate the structure–activity relationship on the inhibition of feeding. Although aFGF-(1–29) did not affect food intake, [Ser16]aFGF-(1–29) (400 ng) and [Glu16]aFGF-(1–29) (400 ng), in which the cysteine residue at position 16 of aFGF-(1–29) was replaced with structurally similar serine and glutamic acid, were observed to significantly inhibit food intake. These findings suggest that endogenous FGFR-1 in the LHA plays an important role in FGF-induced feeding suppression, while, in addition, the dissolving disulfide bond formation in aFGF fragments enhances their inhibitory effects on feeding.

1. 1. Endogenous satiety substance 2-Buten 4 Olide (2-B40- a short chain sugar derivative) effect on feeding behaviour of rhesus monkey was studied. 2. 2. The cannula was implanted in the third ventricle of three, adult, male, rhesus monkeys. 3. 3. Monkeys were conditioned to ingest their daily requirement of food during one hour. 4. 4. Their daily food intake was recorded. 5. 5. Various doses of 2-B4O (1.6, 2.1, 2.7, 4.3, 10.6, 20 and 25 mg) were administered intracerebroventricularly on different days five minutes prior to presentation of food. 6. 6. The effective dose for inducing significant satiety effect was 20.0 mg, while 10.6 mg induced a mild and 25.0 mg a severe effect. 7. 7. However, when administered intraperitoneally 43 mg/kg bw 2-B40 induced satiety effect, but was ineffective in doses of 1.5 to 21.5 mg bw. 8. 8. This study is suggestive of the presence of 2-B40 satiety mechanism in monkeys almost in doses similar to those previously reported for rats.

Acidic fibroblast growth factor (aFGF) has suppressive effects on food intake. In the present study, the effect of aFGF fragments on food intake were investigated in rats. Infusion of a carboxyl-terminal fragment of aFGF, aFGF-(114-140), did not affect food intake, whereas an amino-terminal fragment of aFGF, aFGF-(1-15), was significantly inhibitory. Other amino-terminal fragments, aFGF-(1-20), aFGF-(1-29) and aFGF-(9-29), did not affect food intake. However, [Ala16]aFGF-(1-29) and [Ser16]aFGF-(1-29) in which the cysteine residue at position 16 was replaced with alanine and serine, respectively, had significant suppressive effects on food intake. Infusion of a functional antagonist for FGF receptor, anti-FGFR-1 antibody, into the lateral hypothalamus (LHA) significantly increased food intake. The results suggest that: the amino-terminal portion of aFGF is active in food intake suppression; the replacement of cysteine residue by alanine or serine is important in some amino-terminal aFGF fragments; and the LHA is involved in feeding suppression actions by aFGF and some fragments.

The hypothalamo-neurohypophyseal system as well as the autonomic nervous system is involved in homeostatic responses associated with changes in head position and orthostatic reflex. The responses induced by body tilt on earth are thought to be attributed to changes in inputs from baroreceptors, vestibular organs and proprioreceptors that are normally required for postural control. The information from these organs is sent to the hypothalamus which thereby influences both neuroendocrine and autonomic systems as well as various kinds of emotional behavior. Our findings showing the fastigial input to the hypothalamus suggested that the FN plays a significant role in these homeostatic responses through its connections with the brain stem and the hypothalamus. Figure 4 shows the input-output organization among the hypothalamus, cerebellum and brain stem, described in detail in sections III to V. This hypothesis may help to account for the autonomic and endocrine disorders often observed in weightlessness.

Effects of acidic fibroblast growth factor (aFGF) fragments such as aminoterminal aFGF (1-15) and carboxyl-terminal aFGF (114-140) on synaptic transmission were investigated in rat hippocampal slices. Stimulation was applied to Schaffer collateral/commissural afferents, and evoked population spikes were recorded in the CA1 pyramidal cell layer. Continuous perfusion of slices with aFGF (1-15) slightly decreased the basal amplitude of population spikes and significantly increased the paired-pulse facilitation. When brief tetanic stimulation (7 pulses at 100 Hz) was applied 30 min after the perfusion of aFGF (1-15), aFGF (1-15)-treated slices enhanced the magnitude of short-term potentiation after the tetanus and facilitated a generation of long-term potentiation. These effects of aFGF (1-15) were dose-dependent. Perfusion of slices with aFGF (114-140) had no effect on the basal spike amplitude, paired-pulse facilitation, and short-term potentiation. Both aFGF (1-15) and aFGF (114-140) had no effect on the DNA synthesis-stimulating activity in BALB/c 3T3-L1 cells. The results suggest that aFGF (1-15), which is not involved in mitogenic activity, is implicated in a modulatory mechanism of synaptic plasticity.

We previously reported that the levels of lipid hydroperoxides, one of oxidative stress markers, in the brain and peripheral organs such as liver, heart, and lung are significantly higher in senescence accelerated-prone 8 mice (SAMP8) than in their controls, senescence accelerated-resistant mice (SAMR1), at 3, 6, and/or 9 months of age. To ascertain the exact age at which the lipid hydroperoxide levels increase in SAMP8, we measured them in the brain and liver of SAMP8 and SAMR1 at both 1 and 2 months of age. At 1 month of age, there was no significant inter-strain difference in the levels in brain or liver. However, in SAMP8 both levels were significantly greater at 2 months of age than at 1 month of age, but no such difference was detected for SAMR1. The present results suggest that SAMP8 are exposed to elevated levels of oxidative stress from an early age (2 months old), and that this may be a cause of the senescence-related impairments and degeneration in the brain and peripheral tissues (such as liver, heart, and lung) seen in this strain.

In the present study, effects of acidic fibroblast growth factor (aFGF, 0.5–2.5 ng/ml) on synaptic transmission were investigated in rat hippocampal slices. Stimulation was applied to Schaffer collateral/commissural afferents and evoked spikes were recorded in CA1 pyramidal cell layer. Continuous perfusion of slices with aFGF slightly decreased the basal amplitude of the spikes and significantly increased the paired-pulse facilitation. When brief tetanic stimulation (7 impulses at 100 Hz) was applied 30 min after the perfusion of aFGF, aFGF-treated slices enhanced the magnitude of short-term potentiation after the tetanus and facilitated the generation of long-term potentiation. aFGF also enhanced post-tetanic potentiation directly after the tetanus. These effects of aFGF were dose-dependent. The enhancement of short-term potentiation and facilitation of the generation of long-term potentiation were not evident when aFGF was applied with or 10 min after the tetanus. The results suggest that aFGF is implicated in modulation of synaptic efficacy and can activate some mechanisms related to the generation of long-term potentiation.

1. Neurons in the amygdala are implicated in mediating hedonic appreciation, emotional expression, and conditioning, particularly as these relate to feeding. The amygdala receives projections from the primary taste cortex in monkeys, offering a route by which it could gain access to the gustatory information required to guide feeding behavior. We recorded the activity of 35 neurons in the amygdala of alert rhesus macaques in response to a range of gustatory intensities and qualities to characterize taste-evoked activity in this area. 2. The stimulus array comprised 26 chemicals, including four concentrations of each of the four basic taste stimuli, a series of other sugars, salts, and acids, monosodium glutamate, and orange juice. 3. Neurons responsive to taste stimulation could be found in a 76-mm3 region of the amygdala, centered 9.1 mm lateral to the midline, 14.9 mm anterior to the interaural line, and 25.7 mm below the surface of the dura. They composed 7.2% (35/484) of the cells tested for gustatory sensitivity in the amygdala. 4. The mean spontaneous activity of taste cells was 8.2 +/- 2.3 (SE) spikes per second. This rather high level provided an opportunity for reductions from spontaneous rate that was used regularly in the amygdala. When these negative response rates were included, the mean breadth-of-tuning coefficient of this sample of taste cells was 0.82. There was no strong evidence for gustatory neuron types, nor were functionally similar cells located together in a chemotopic arrangement. 5. Responses across 1.5 log units of stimulus concentration were nearly flat, with increasing excitation in some neurons largely offset by increasing inhibition in others. Taking the absolute value of the evoked activity, concentration-response functions rose monotonically to all basic stimuli except HCl, but were not sufficiently steep to account for human psychophysical data. The neural response to HCl did not rise with stimulus concentration within the range used. 6. Neural patterns representing the taste qualities of the basic stimuli were less sharply separated in the amygdala than at lower-order gustatory relays. Glucose elicited activity patterns that were most distinct from those of the nonsweet chemicals; those associated with NaCl were next most distinct. There was no clear separation between the patterns generated by chemicals that humans describe as sour and bitter. Monosodium glutamate evoked responses that did not correlate well with those of any basic stimulus, implying that its quality cannot be subsumed under the four basic tastes.(ABSTRACT TRUNCATED AT 400 WORDS)

AIM: To observe the regional distributions and morphological features of nesfatin-1/nucleobindin-2 (NUCB2) immunoreactive (IR) cells in the rodent digestive system. METHODS: Paraffin-embedded sections of seven organs (pancreas, stomach, duodenum, esophagus, liver, small intestine and colon) dissected from sprague-dawley (SD) rats and institute of Cancer Research (ICR) mice were prepared. The regional distributions of nesfatin-1/NUCB2 IR cells were observed by immunohistochemical staining. The morphological features of the nesfatin-1/NUCB2 IR cells were evaluated by hematoxylin and eosin (HE) staining. Fresh tissues of the seven organs were prepared for Western blotting to analyze the relative protein levels of NUCB2 in each organ. RESULTS: Immunohistochemical staining showed that the nesfatin-1/NUCB2 IR cells were localized in the central part of the pancreatic islets, the lower third and middle portion of the gastric mucosal gland, and the submucous layer of the duodenum in SD rats and ICR mice. HE staining revealed that the morphological features of nesfatin-1/NUCB2 IR cells were mainly islet cells in the pancreas, endocrine cells in the stomach, and Brunner’s glands in the duodenum. Western blotting revealed that NUCB2 protein expression was higher in the pancreas, stomach and duodenum than in the esophagus, liver, small intestine and colon (P = 0.000). CONCLUSION: Nesfatin-1/NUCB2 IR cells are expressed in the pancreas, stomach and duodenum in rodents. These cells may play an important role in the physiological regulation of carbohydrate metabolism, gastrointestinal function and nutrient absorption.

Leptin is well known to be involved in the inhibition of feeding, hermogenesis, reproduction, and neuroendocrine functions through its actions on the rodent’s hypothalamic receptors. Leptin facilitated the presynaptic transmitter release and postsynaptic sensitivity to the transmitters in the hippocampal CA1 neurons. Thus, long-term potentiation (LTP) and the phosphorylation of Ca2+/calmodulin protein kinase II (CaMK II) were facilitated in the CA1 neurons. Therefore behavioral performance related to spatial learning and memory was improved by leptin in vivo applications. Orexin-A produced by glucose-sensitive neurons in the lateral hypothalamic area (LHA) and released during food intake facilitates feeding. Orexin-A suppressed LTP and CaMK II phosphorylation without affecting the presynaptic transmitter release. Therefore behavioral performance on learning and memory was impaired. The present studies suggest that leptin and orexin signalings in the brain may have important implications for cognitive function.

To further investigate the activity of serotonin neurons in relation to feeding behavior, the metabolic activity of the serotonergic system and single neuron activity changes in the lateral hypothalamic area (LHA) were investigated concurrently in freely behaving rats. The extracellular concentration of 5-hydroxyindoleacetic acid (5-HIAA), a metabolic product of serotonin in the LHA, began to increase concomitantly with the early stage of nocturnal eating. The increased 5-HIAA returned to the basal level within 3 or 4 h. In conjunction with the increase in serotonin metabolism, activity of 12 out of 30 LHA neurons (40%) increased, whereas it decreased in 7 (23%), and in 11 (37%) it showed no change. An intracerebroventricular injection of lisuride suppressed the increased activity in 7 of the 12 neurons, but had no effect on the others. These results suggest that the concurrent increase in serotonin metabolism and neuron activity changes in the LHA may occur in the early portion of the nocturnal eating period, and may be important in controlling feeding behavior.

Intracerebral microdialysis was used to measure extracellular serotonin and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the hypothalamus of unanesthetized rats. Increase in the concentration of K+ in the perfusing Ringer solution (70 mM) produced a sharp increase in serotonin release, which was significantly attenuated by omitting Ca2+ from the perfusion medium. Intraperitoneal injection of 5-hydroxytryptophan, a precursor of serotonin, or local perfusion of pargyline, a monoamine oxidase inhibitor, elevated the hypothalamic serotonin. Releasers or uptake inhibitors of serotonin, such as fenfluramine, cocaine, mazindol, or imipramine, when added to the perfusion medium, significantly increased serotonin level, whereas 5-HIAA was unaffected by these substances. Immobilization-stress caused an immediate increase in both the extracellular serotonin and 5-HIAA in the hypothalamus, suggesting that the hypothalamic serotonergic system is activated during immobilization stress. The present study indicates that the brain microdialysis is useful for analysis of local changes in serotonin concentration which directly reflect neuronal transmission.

Orexin (ORX), also called hypocretin, and ghrelin are newly identified peptides in the brain and/or peripheral organs, and they are involved in the regulation of sleep–wakefulness as well as feeding. In our previous studies we have found that ORX and ghrelin each depolarizes more than half of the cholinergic neurons recorded in the pedunculopontine tegmental nucleus (PPT) via a dual ionic mechanism including a decrease of K + conductance and an increase of nonselective cationic conductance. Thus, the present study was carried out to investigate whether ORX-A and ghrelin both depolarize the same PPT neuron. About 60% of PPT neurons examined was depolarized by both ORX-A and ghrelin, 20% by ORX-A alone, and 10% by ghrelin alone. The remaining 10% did not respond to these peptides. In neurons which were responsive to both ORX-A and ghrelin, the depolarizations induced by ORX-A and ghrelin were additive. In addition, the ORX-A- and ghrelin-induced depolarizations were both blocked by D609, a phosphatidylcholine-specific phospholipase C (PLC) inhibitor. These results suggest that same PPT neurons with receptors for ORX and ghrelin are involved in the cellular process through which ORX and ghrelin participate in the regulation of sleep wakefulness, and that the excitatory effects of ORX and ghrelin on PPT neurons are mediated by PLC.

The effects of intravenous (i.v.) administration of recombinant human interleukin-1 beta (rhIL-1 beta) on the activity of adrenal, splenic and renal sympathetic nerves were observed in urethane-anesthetized rats. An i.v. injection of IL-1 beta in doses of 10 pg-20 ng per animal (300-400 g, b.w.) resulted in a dose-dependent increase in the activity of the adrenal and splenic nerves, which lasted for more than 2-6 h. On the other hand, the activity of renal nerves showed a transient increase which was followed by a long-lasting suppression after injection of rhIL-1 beta (100 pg, i.v.). An i.v. injection of cyclooxygenase inhibitors (6 mg ibuprofen or 20 mg sodium salicylate) suppressed almost completely the rhIL-1 beta (100 pg)-induced activity in adrenal and splenic nerves. Although rhIL-1 beta (100 pg, i.v.) produced a fall in arterial blood pressure, baroreceptor denervation did not affect the excitatory responses of the adrenal and splenic nerves to rhIL-1 beta. The results suggest the regional differentiation of activity in the visceral sympathetic nerves in response to rhIL-1 beta. The rhIL-1 beta-induced activation of splenic sympathetic nerves implicates their involvement in the modulation of immunity by brain.