The Effects of Mutual Interaction of Orexin-A and Glucagon-Like Peptide-1 on Reflex Swallowing Induced by SLN Afferents in Rats.

(1) Background: Our previous studies revealed that orexin-A, an appetite-increasing peptide, suppressed reflex swallowing via the commissural part of the nucleus tractus solitarius (cNTS), and that glucagon-like peptide-1 (GLP-1), an appetite-reducing peptide, also suppressed reflex swallowing via the medial nucleus of the NTS (mNTS). In this study, we examined the mutual interaction between orexin-A and GLP-1 in reflex swallowing. (2) Methods: Sprague-Dawley rats under urethane-chloralose anesthesia were used. Swallowing was induced by electrical stimulation of the superior laryngeal nerve (SLN) and was identified by the electromyographic (EMG) signals obtained from the mylohyoid muscle. (3) Results: The injection of GLP-1 (20 pmol) into the mNTS reduced the swallowing frequency and extended the latency of the first swallow. These suppressive effects of GLP-1 were not observed after the fourth ventricular administration of orexin-A. After the injection of an orexin-1 receptor antagonist (SB334867) into the cNTS, an ineffective dose of GLP-1 (6 pmol) into the mNTS suppressed reflex swallowing. Similarly, the suppressive effects of orexin-A (1 nmol) were not observed after the injection of GLP-1 (6 pmol) into the mNTS. After the administration of a GLP-1 receptor antagonist (exendin-4(5-39)), an ineffective dose of orexin-A (0.3 nmol) suppressed reflex swallowing. (4) Conclusions: The presence of reciprocal inhibitory connections between GLP-1 receptive neurons and orexin-A receptive neurons in the NTS was strongly suggested.

Aflatoxins in Rice Artificially Contaminated with Aflatoxin-producing Aspergillus flavus under Natural Storage in Japan.

Aflatoxin (AFT) contamination is frequent in foods grown in tropical regions, including rice. Although AFTs are generally not found in temperate-region foods, global warming has affected typical temperate-region climates, potentially permitting the contamination of foods with AFT-producing Aspergillus flavus (A. flavus). Here we investigated the AFT production in rice during storage under natural climate conditions in Japan. We examined AFTs in brown rice and rough rice artificially contaminated with A. flavus for 1 year in Japan, and we subjected AFTs in white rice to the same treatment in airtight containers and examined the samples in warm and cold seasons, simulating the storage of white rice in general households. In the brown rice, AFTs increased after 2 months (March) and peaked after 9 months (October). The AFT contamination in the rough rice was minimal. After the polishing and cooking of the brown rice, AFTs were undetectable. In the white rice stored in airtight containers, AFTs increased after 1 month (August) and peaked after 2 months (September). Minimal AFTs were detected in the cold season. Thus, AFT contamination in rice may occur in temperate regions following A. flavus contamination. The storage of rice as rough rice could provide be useful for avoiding AFT contamination.

Salivary buffering capacity is correlated with umami but not sour taste sensitivity in healthy adult Japanese subjects.

OBJECTIVE: Saliva serves multiple important functions crucial for maintaining a healthy oral and systemic environment. Among them, the pH buffering effect, which is primarily mediated by bicarbonate ions, helps maintain oral homeostasis by neutralizing acidity from ingested foods. Therefore, higher buffering capacity, reflecting the ability to neutralize oral acidity, may influence taste sensitivity, especially for sour taste since it involves sensing H+ ions. This study aims to explore the relationship between salivary buffering capacity and taste sensitivities to the five basic tastes in healthy adult humans. DESIGN: Eighty seven healthy adult students participated in this study. Resting saliva volume was measured using the spitting method. The liquid colorimetric test was used to assess salivary buffering capacity. The whole-mouth taste testing method was employed to determine the recognition threshold for each tastant (NaCl, sucrose, citric acid, quinine-HCl, monosodium glutamate). RESULTS: Taste recognition thresholds for sour taste as well as sweet, salty, and bitter tastes showed no correlation with salivary buffering capacity. Interestingly, a negative relationship was observed between recognition threshold for umami taste and salivary buffering capacity. Furthermore, a positive correlation between salivary buffering capacity and resting saliva volume was observed. CONCLUSIONS: Salivary buffering capacity primarily influences sensitivity to umami taste, but not sour and other tastes.

Distribution of alpha-synuclein in rat salivary glands.

Expression of alpha-synuclein (Syn), a presynaptic neuronal protein, was immunohistochemically examined in intact rat submandibular, sublingual, and lingual glands. The submandibular gland contained abundant periductal Syn-immunoreactive (-ir) nerve fibers. Abundant Syn-ir varicosities were present in acini of the sublingual and serous lingual glands. By confocal laser scanning microscopy, Syn-ir nerve fibers around smooth muscle actin (SMA)-ir cells alone were infrequent; however, those around aquaporin-5 (AQP5)-ir cells alone and both SMA- and AQP5-ir cells were abundant in the sublingual and serous lingual glands. SMA-ir cells were occasionally immunoreactive for toll-like receptor 4, a Syn receptor. Syn-ir nerve fibers contained tyrosine hydroxylase (TH) in the submandibular gland and choline acetyltransferase (ChAT) in all examined salivary glands. In the superior cervical (SCG), submandibular, and intralingual ganglia, sympathetic and parasympathetic neurons co-expressed Syn with TH and ChAT, respectively. SCG neurons innervating the submandibular gland contained mostly Syn. In the thoracic spinal cord, 14.7% of ChAT-ir preganglionic sympathetic neurons co-expressed Syn. In the superior salivatory nucleus, preganglionic parasympathetic neurons projecting to the lingual nerve co-expressed Syn and ChAT. The present findings indicate that released Syn acts on myoepithelial cells. Syn in pre- and post-ganglionic neurons may regulate neurotransmitter release and salivary volume and composition.

Sugar signals from oral glucose transporters elicit cephalic-phase insulin release in mice.

Cephalic-phase insulin release (CPIR) occurs before blood glucose increases after a meal. Although glucose is the most plausible cue to induce CPIR, peripheral sensory systems involved are not fully elucidated. We therefore examined roles of sweet sensing by a T1R3-dependent taste receptor and sugar sensing by oral glucose transporters in the oropharyngeal region in inducing CPIR. Spontaneous oral ingestion of glucose significantly increased plasma insulin 5 min later in wild-type (C57BL/6) and T1R3-knockout mice, but intragastric infusion did not. Oral treatment of glucose transporter inhibitors phlorizin and phloretin significantly reduced CPIR after spontaneous oral ingestion. In addition, a rapid increase in plasma insulin was significantly smaller in WT mice with spontaneous oral ingestion of nonmetabolizable glucose analog than in WT mice with spontaneous oral ingestion of glucose. Taken together, the T1R3-dependent receptor is not required for CPIR, but oral glucose transporters greatly contribute to induction of CPIR by sugars.

Taste Responses and Ingestive Behaviors to Ingredients of Fermented Milk in Mice.

Fermented milk is consumed worldwide because of its nutritious and healthful qualities. Although it is somewhat sour, causing some to dislike it, few studies have examined taste aspects of its ingredients. Wild-type mice and T1R3-GFP-KO mice lacking sweet/umami receptors were tested with various taste components (sucrose, galactose, lactose, galacto-oligosaccharides, fructo-oligosaccharides, l- and d-lactic acid) using 48 h two-bottle tests and short-term lick tests. d-lactic acid levels were measured after the ingestion of d- or; l-lactic acid or water to evaluate d-lactic acidosis. In wild-type mice, for the sweet ingredients the number of licks increased in a concentration-dependent manner, but avoidance was observed at higher concentrations in 48 h two-bottle tests; the sour ingredients d- and l-lactic acid showed concentration-dependent decreases in preference in both short- and long-term tests. In 48 h two-bottle tests comparing d- and l-lactic acid, wild-type but not T1R3-GFP-KO mice showed higher drinking rates for l-lactic acid. d-lactic acidosis did not occur and thus did not contribute to this preference. These results suggest that intake in short-term lick tests varied by preference for each ingredient, whereas intake variation in long-term lick tests reflects postingestive effects. l-lactic acid may have some palatable taste in addition to sour taste.

Effects of bitter receptor antagonists on behavioral lick responses of mice.

Bitter taste receptors TAS2Rs detect noxious compounds in the oral cavity. Recent heterologous expression studies reported that some compounds function as antagonists for human TAS2Rs. For examples, amino acid derivatives such as γ-aminobutyric acid (GABA) and Nα,Nα-bis(carboxymethyl)-L-Lysine (BCML) blocked responses to quinine mediated by human TAS2R4. Probenecid inhibited responses to phenylthiocarbamide mediated by human TAS2R38. In this study, we investigated the effects of these human bitter receptor antagonists on behavioral lick responses of mice to elucidate whether these compounds also function as bitter taste blockers. In short-term (10 s) lick tests, concentration-dependent lick responses to bitter compounds (quinine-HCl, denatonium and phenylthiourea) were not affected by the addition of GABA or BCML. Probenecid reduced aversive lick responses to denatonium and phenylthiourea but not to quinine-HCl. In addition, taste cell responses to phenylthiourea were inhibited by probenecid. These results suggest some bitter antagonists of human TAS2Rs can work for bitter sense of mouse.

Orexin A and B in the rat superior salivatory nucleus.

Orexin (OX), which regulates sleep and wakefulness and feeding behaviors has 2 isoforms, orexin-A and -B (OXA and OXB). In this study, the distribution of OXA and OXB was examined in the rat superior salivatory nucleus (SSN) using retrograde tracing and immunohistochemical and methods. OXA- and OXB-immunoreactive (-ir) nerve fibers were seen throughout the SSN. These nerve fibers surrounded SSN neurons retrogradely labeled with Fast blue (FB) from the corda-lingual nerve. FB-positive neurons had pericellular OXA- (47.5%) and OXB-ir (49.0%) nerve fibers. Immunohistochemistry for OX receptors also demonstrated the presence of OX1R and OX2R in FB-positive SSN neurons. The majority of FB-positive SSN neurons contained OX1R- (69.7%) or OX2R-immunoreactivity (57.8%). These neurons had small and medium-sized cell bodies. In addition, half of FB-positive SSN neurons which were immunoreactive for OX1R (47.0%) and OX2R (52.2%) had pericellular OXA- and OXB-ir nerve fibers, respectively. Co-expression of OX1R- and OX2R was common in FB-positive SSN neurons. The present study suggests a possibility that OXs regulate the activity of SSN neurons through OX receptors.

Development of inhibitory synaptic transmission to the superior salivatory nucleus in rats.

The primary parasympathetic center of the submandibular and sublingual salivary glands is the superior salivatory (SS) nucleus, neurons of which receive excitatory (glutamatergic) and inhibitory (GABAergic and glycinergic) synaptic transmissions in rats. In the present study, to examine postnatal neural development, we focused on inhibitory transmission to the SS neurons in neonatal rats from postnatal day 2 (P2) to P14. Conventional and gramicidin-perforated whole-cell patch-clamp techniques were applied to the neurons in brainstem slices. The decay time constants of GABAergic and glycinergic postsynaptic currents (PSCs) consisted of fast (tau(fast)) and slow (tau(slow)) components. Both tau(fast) and tau(slow) of PSC components tended to become faster with development. The equilibrium potential of Cl(-) (E(Cl-)) was estimated from the reversal potentials of total PSCs (GABAergic plus glycinergic). The E(Cl-) in the P8-P14 group was significantly more negative than E(Cl-) in the P2-P7 group. Exogenous GABA application at the resting potentials produced depolarization in 83% of SS neurons at P2-P7 and accompanied the action potential in some neurons. In contrast, at P8-P14, GABA evoked hyperpolarization in 78% of SS neurons; therefore, SS neurons did not acquire mature inhibitory systems until P14. The development of SS neurons is discussed as compared with the development of peripheral salivary gland tissue and brainstem neurons that participate in oral motor and sensory functions.

Purinergic modulation of area postrema neuronal excitability in rat brain slices.

ATP has been shown to excite neurons in various regions of the central nervous system. Whereas immunohistochemical studies show P2X receptors in the area postrema, the responsiveness of area postrema neurons to extracellular ATP has not been studied. To investigate the effects of purinoceptor activation on area postrema neuronal excitability, we performed whole-cell recordings from area postrema neurons in rat brain slices. Most area postrema neurons responded to ATP application, and most responses were excitatory. Voltage-clamp recordings showed three different types of response: (1) a postsynaptic or extrasynaptic excitatory response (inward currents; n=26/51 cells), (2) a presynaptic excitatory response (increased frequency of miniature excitatory postsynaptic currents with only a small direct postsynaptic current; n=24/51 cells, or (3) a postsynaptic inhibitory response (outward current; n=1/51). The excitatory responses were found in both of the two major electrophysiological cell classes, i.e. cells displaying I(h) and cells not displaying I(h), while the inhibitory responses were found in only cells not displaying I(h). Current-clamp recordings showed ATP-induced depolarization (n=13/15) or hyperpolarization (n=2/15) of membrane potential that modulated the frequency of action potentials. In the presence of CNQX, mEPSCs were abolished and bath-applied ATP did not generate mEPSCs, indicating that glutamate release was facilitated by the activation of presynaptically located ATP receptors. Our pharmacological results from studies with ATP, alphabetame-ATP, betame-ATP and PPADS indicate that the post- and/or extrasynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits. We conclude that half of the presynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits while the others also contain P2X(1) subunits. It is well known that P2X(7) subunit forms only homomultimeric P2X receptors. Finally, the present study suggests that purinoceptor activation may contribute to the control of several autonomic functions by area postrema neurons.

Effects of cevimeline on excitability of parasympathetic preganglionic neurons in the superior salivatory nucleus of rats.

The superior salivatory nucleus (SSN) contains parasympathetic preganglionic neurons innervating the submandibular and sublingual salivary glands. Cevimeline, a muscarinic acetylcholine receptor (mAChR) agonist, is a sialogogue that possibly stimulates SSN neurons in addition to the salivary glands themselves because it can cross the blood-brain barrier (BBB). In the present study, we examined immunoreactivities for mAChR subtypes in SSN neurons retrogradely labeled with a fluorescent tracer in neonatal rats. Additionally, we examined the effects of cevimeline in labeled SSN neurons of brainstem slices using a whole-cell patch-clamp technique. Mainly M1 and M3 receptors were detected by immunohistochemical staining, with low-level detection of M4 and M5 receptors and absence of M2 receptors. Most (110 of 129) SSN neurons exhibited excitatory responses to application of cevimeline. In responding neurons, voltage-clamp recordings showed that 84% (101/120) of the neurons exhibited inward currents. In the neurons displaying inward currents, the effects of the mAChR antagonists were examined. A mixture of M1 and M3 receptor antagonists most effectively reduced the peak amplitude of inward currents, suggesting that the excitatory effects of cevimeline on SSN neurons were mainly mediated by M1 and M3 receptors. Current-clamp recordings showed that application of cevimeline induced membrane depolarization (9/9 neurons). These results suggest that most SSN neurons are excited by cevimeline via M1 and M3 muscarinic receptors.

Central glucagon like peptide-1 inhibits reflex swallowing elicited by the superior laryngeal nerve via caudal brainstem in the rat.

The effects of glucagon like peptide-1 (GLP-1) on reflex swallowing were examined using anaesthetized rats. GLP-1 was injected into the dorsal vagal complex (DVC) using glass micropipettes. Swallowing was induced by repeated electrical stimulation of the central cut end of the superior laryngeal nerve (SLN) and was identified by the electromyogram lead penetrated in the mylohyoide muscle through bipolar electrodes. Microinjection of GLP-1 into the medial DVC (M-DVC) increased the frequency of swallowing during the electrical stimulation of the SLN and extended the latency of the first swallowing. Microinjection of GLP-1 into the lateral DVC (L-DVC) did not change the frequency of swallowing or the latency of the first swallowing. Neither the injection of vehicle into the M-DVC nor L-DVC affected swallowing frequency. Pre-injection of exendin (5-39), a GLP-1 receptor antagonist, attenuated the degree of suppression of swallowing frequency induced by the administration of GLP-1 in addition to shortening the latency of the first swallowing. To identify the effective site of GLP-1, lesion experiments were performed. Electrical lesion of the commissural part of the NTS (cNTS) and the vacuum removal of the area postrema (AP) did not affect the inhibition of reflex swallowing induced by the injection of GLP-1 into the M-DVC. Electrical lesion of the medial nucleus of the NTS (mNTS) and its vicinity abolished the inhibitory effects of swallowing induced by the injection of GLP-1. These results suggest that GLP-1 inhibits reflex swallowing via the mNTS in the dorsal medulla.

Variety of morphological and electrophysiological properties of area postrema neurons in adult rat brain slices.

Whole-cell recordings were performed to examine the morphological properties of electrophysiologically classified area postrema (AP) neurons in rat brain slices. Using electrophysiological criteria, AP neurons were subdivided into three groups: (1) cells displaying both the hyperpolarization-activated cation current (I(h)) and the fast transient outward current (fast I(to)); (2) cells displaying only the fast I(to); (3) cells displaying only the slow I(to). All AP neurons had a single axon that was distinctly thinner than the cells' dendrites. No systematic differences, across groups, in the orientation of dendrites or axons were identified. Mean values of cell size and capacitance of neurons from group 3 were significantly larger than those of the other groups. Interestingly, a number of cells from groups 1 and 3 but not group 2 were found to extend their dendrites into the nucleus tractus solitarius (NTS), suggesting that AP neurons could receive vagal afferent inputs at their dendritic termini within the NTS. Although the AP has been implicated to contain uniformly shaped neurons, this study indicates the presence of significantly different subpopulations of AP neurons, which were characterized not only electrophysiologically but also morphologically.

The origin of sensory nerve fibers that innervate the submandibular salivary gland in the rat.

The origin of sensory nerves that innervate the submandibular salivary gland was investigated in the rat. After application of wheat germ agglutinin-horseradish peroxidase to the cut endings of the sympathetic and parasympathetic nerve branches at the hilus of the gland, labeled cells were mainly found in the dorsal root ganglia and the trigeminal ganglion, respectively. The labeled neurons in these ganglia were of various sizes compared to unlabeled neurons, suggesting that the sensory nerves of the gland conduct various modalities of sensory information.

Role of the lateral hypothalamus in submandibular salivary secretion during feeding in rats.

To evaluate the role of the lateral hypothalamic area (LH) in the masticatory-salivary reflex, we investigated submandibular salivary secretion and the electromyographic (EMG) activity of the jaw-closer masseter muscle in sham-operated rats and rats with unilateral LH lesions. One week prior to surgery and recording, the rats were given daily experience of eating pellets; powder; or hard, medium or soft mash, all of which were composed of laboratory chow. Salivary secretion was induced during eating and grooming behavior. During eating, the powdered food induced the highest salivary flow rate, and the soft (wet) mash induced the lowest salivary flow rate. Conversely, the amount of food consumed (dry weight) was greatest when soft mash was provided and lowest when the powder or pellets (a dry diet) were provided. The EMG activity of the masseter muscle during eating was greatest during consumption of the pellets and weakest during consumption of the powder. LH lesions that were ipsilateral to the examined submandibular gland reduced salivary secretion to about 20-30% of the control value, whereas contralateral LH lesions reduced it to about 40-50% of the control value. Neither masseter muscle EMG activity nor food consumption was markedly affected by the presence of an LH lesion. These results suggest that the texture of food, especially its water content, affects the flow rate of saliva and that the LH is heavily involved in the masticatory-salivary reflex.

Suppression of the hyperpolarization-activated inward current contributes to the inhibitory actions of propofol on rat CA1 and CA3 pyramidal neurons.

Intracellular and field potential recordings were taken from the hippocampal CA1 and CA3 neurons in rat brain slices to investigate the effects of 2,6 di-isopropylphenol (propofol) on the neuronal excitability during GABA(A)-C1 channel blockade by picrotoxin (100 microM). Propofol produced a membrane hyperpolarization and an inhibition of the magnitude of the 'voltage sag' that was mediated by the activation of a hyperpolarization-activated inward current (I(H)). Propofol (>100 microM) decreased the spontaneous discharge rate of epileptiform burst responses in CA1 neurons up to 38+/-6% of the control level. Propofol also markedly reduced the duration of both spontaneous and evoked epileptiform burst responses. A propofol-induced decrease in the spontaneous discharge rate in CA3 neurons was coincident with that in CA1 neurons. The effects of propofol on the membrane potential and spontaneous discharge rate but not on the duration of burst responses were duplicated by ZD7288 (potent selective antagonist for I(H) channels), indicating that the blockade of I(H) significantly contributes to reduction of cell's excitability. The present study suggests that various actions including suppressive effects on I(H) contribute to the anesthetic and anti-convulsant properties of propofol.

Two distinct types of transient outward currents in area postrema neurons in rat brain slices.

We investigated the electrophysiological properties of the area postrema neurons in acutely prepared rat brain slices using the whole-cell patch-clamp technique. Two different types of transient outward potassium current (I(to)), fast and slow, were found in the area postrema. Both the decay time constant and rise time were significantly faster in the fast I(to) than in the slow I(to). Both current-clamp and voltage-clamp recordings revealed that the activation of fast and slow I(to) contributes to generation of the different spiking patterns, late spiking and interrupted spiking, respectively. The activation and inactivation of both I(to) were strongly voltage-dependent. Curve fitting by the Boltzmann equation revealed no significant difference in the activation and inactivation curves for each I(to) except that the slope factor of inactivation was larger for fast I(to). Both I(to) were suppressed dose-dependently by application of 4-aminopyridine. Each spiking pattern was enhanced when cells were held at a more hyperpolarized membrane potential, i.e. a longer latency of the first spike or longer interspike interval between the first and second spikes. The voltage-dependent modulation of the spiking pattern was consistent with the voltage-dependent activation of I(to). The present study shows significant subdivisions of the area postrema neurons distinguished by a difference in the kinetics of I(to) and spiking patterns. We discuss the role of I(to) as the ionic current underlying neuronal excitability.

Nicotinic modulation of area postrema neuronal excitability in rat brain slices.

We investigated the functions of nicotinic receptor activation on area postrema neurons by making whole-cell recordings in rat brainstem slices. Excitatory responses to nicotine application were found in approximately 78% (35/45) of all cells tested. Responsive cells included both the cells that display the hyperpolarization-activated cation current (I(h)) and cells that do not display I(h). An inhibitory effect of nicotine was never seen. Current-clamp recordings showed the nicotine-induced depolarization of a cell's membrane potential that could be sufficient to cause spontaneous firing. In voltage-clamp recordings, many cells showed nicotine-induced inward currents (18.3+/-3.2 pA, n=6) that persisted during pharmacological blockade of synaptic transmission (e.g., zero [Ca(2+)](out) and 5 mM [Mg(2+)](out), n=6/8). Other two cells, however, showed increases in the frequency of excitatory postsynaptic currents (EPSCs), which were blocked by CNQX (n=2/8). We analyzed miniature EPSCs (mEPSCs) recorded from cells that showed no inward currents but marked increases in the frequency of mEPSCs (0.8+/-0.2 to 4.8+/-1.7 Hz, n=4) during nicotine application. Nicotine augmented mEPSC amplitude (n=4); however, amplitude distribution was not significantly changed in two of four cells tested. We conclude that nicotinic receptors in the rat area postrema can excite cells via (1) a direct post- and/or extrasynaptic mechanism; and (2) an indirect enhancement of glutamate release.

The sensitivity of hyperpolarization-activated cation current (Ih) to propofol in rat area postrema neurons.

Area postrema neurons mediate various autonomic responses, including emesis. We examined the effects of propofol, a widely used anesthetic with antiemetic properties, on the hyperpolarization-activated cation current (Ih) in rat area postrema neurons using a slice patch-clamp technique. Although propofol suppressed Ih of area postrema neurons in a dose-dependent manner that was similar to what we observed for the hippocampal CA1 neurons, the IC50 for Ih in area postrema neurons (38 microM) was more than six times less than that found for hippocampal CA1 neurons (235 microM). We conclude that rat area postrema neurons are exquisitely sensitive to propofol. Given that reductions of Ih are associated with decreased excitability in neurons, we believe that the known antiemetic effects of propofol anesthesia are at least partly a result of a direct action on area postrema neurons to lower their excitability.

Excitatory and inhibitory postsynaptic currents of the superior salivatory nucleus innervating the salivary glands and tongue in the rat.

The excitatory and inhibitory synaptic inputs to parasympathetic preganglionic neurons in the superior salivatory (SS) nucleus were investigated in brain slices of neonatal (4-8 days old) rat using the whole-cell patch-clamp technique. The SS neurons innervating the submandibular and sublingual salivary glands and innervating the lingual artery in the anterior region of the tongue were identified by retrograde transport of a fluorescent tracer. Whole-cell currents were evoked by electrical stimulation of tissue surrounding the cell. These evoked postsynaptic currents were completely abolished by antagonists for N-methyl-D-aspartate (NMDA) glutamate, non-NMDA glutamate, gamma-aminobutyric acid type A (GABAA), and glycine receptors, suggesting that SS neurons receive glutamatergic excitatory, and GABAergic and glycinergic inhibitory synaptic inputs. In SS neurons for the salivary glands, the ratio of the NMDA component to the total excitatory postsynaptic current (EPSC) was larger than that of the non-NMDA component. This profile was reversed in the SS neurons for the tongue. In SS neurons for the salivary glands, the ratio of the GABAA component to the total IPSC was larger than the ratio of the glycine component to total inhibitory postsynaptic current (IPSC). The decay time constants of the GABAA component were slower than those for glycine. These characteristics of the excitatory and inhibitory inputs may be involved in determining the firing properties of the SS neurons innervating the salivary glands and the tongue.