Nanoscale pattern formation on silicon surfaces bombarded with a krypton ion beam: experiments and simulations.

The nanoscale patterns produced by bombardment of the (100) surface of silicon with a 2 keV Kr ion beam are investigated both experimentally and theoretically. In our experiments, we find that the patterns observed at high ion fluences depend sensitively on the angle of incidence Θ. For Θ values between 74° and 85°, we observe five decidedly different kinds of morphologies, including triangular nanostructures traversed by parallel-mode ripples, long parallel ridges decorated by short-wavelength ripples, and a remarkable mesh-like morphology. In contrast, only parallel-mode ripples are present for low ion fluences except for Θ = 85°. Our simulations show that triangular nanostructures that closely resemble those in our experiments emerge if a linearly dispersive term and a conserved Kuramoto-Sivashinsky nonlinearity are appended to the usual equation of motion. We find ridges traversed by ripples, on the other hand, in simulations of the Harrison-Pearson-Bradley equation (Harrisonet al2017Phys. Rev.E96032804). For Θ = 85°, the solid surface is apparently stable and simulations of an anisotropic Edwards-Wilkinson equation yield surfaces similar to those seen in our experiments. Explaining the other two kinds of patterns we find in our experiments remains a challenge for future theoretical work.

Taste responses in sheep medulla: changes during development.

Response characteristics of taste neurons in the sheep solitary tract and nuclei alter during development. Solitary tract cells in younger fetuses respond to stimulation of the tongue with fewer salts and acids than do cells in older fetuses, lambs, and adults. Further, responses to specific salts and acids develop in a particular sequence, not randomly. These changes may relate to maturation of taste receptor sites.

Swallowing in fetal sheep.

Swallowing was measured in fetal sheep by using electromagnetic flowmeter heads chronically implanted in the fetal esophagus. The fetus swallows 20 to 200 milliliters of amniotic fluid in two to seven discrete episodes per day. The episodes are 1 to 9 minutes in duration and occur at seemingly random intervals. Swallowing is influenced by the condition of the fetus and may be the first manifestation of eating and drinking behavior.

Ionotropic glutamate receptor expression in preganglionic neurons of the rat inferior salivatory nucleus.

Glutamate receptor (GluR) subunit composition of inferior salivatory nucleus (ISN) neurons was studied by immunohistochemical staining of retrogradely labeled neurons. Preganglionic ISN neurons innervating the von Ebner or parotid salivary glands were labeled by application of a fluorescent tracer to the lingual-tonsilar branch of the glossopharyngeal nerve or the otic ganglion respectively. We used polyclonal antibodies to glutamate receptor subunits NR1, NR2A, NR2B, (NMDA receptor subunits) GluR1, GluR2, GluR3, GluR4 (AMPA receptor subunits), and GluR5-7, KA2 (kainate receptor subunits) to determine their expression in ISN neurons. The distribution of the NMDA, AMPA and kainate receptor subunits in retrogradely labeled ISN neurons innervating the von Ebner and parotid glands was qualitatively similar. The percentage of retrogradley labeled ISN neurons innervating the parotid gland expressing the GluR subunits was always greater than those innervating the von Ebner gland. For both von Ebner and parotid ISN neurons, NR2A subunit staining had the highest expression and the lowest expression of GluR subunit staining was NR2B for von Ebner ISN neurons and GluR1 for parotid ISN neurons. The percentage of NR2B and GluR4 expressing ISN neurons was significantly different between the two glands. The percentage of ISN neurons that expressed GluR receptor subunits ranged widely indicating that the distribution of GluR subunit expression differs amongst the ISN neurons. While ISN preganglionic neurons express all the GluR subunits, differences in the percentage of ISN neurons expression between neurons innervating the von Ebner and parotid glands may relate to the different functional roles of these glands.

Species generalization and differences in Hedgehog pathway regulation of fungiform and circumvallate papilla taste function and somatosensation demonstrated with sonidegib.

Species generalization in the profound, modality-specific effects of Hedgehog pathway inhibition (HPI) in taste organ homeostasis and sensation is shown. With the HPI, cancer drug sonidegib, we demonstrate that the rat taste system, in addition to mouse, is regulated by Hedgehog signaling. After sonidegib treatment for 16-36 days in rat, there is loss of taste buds (TB) in soft palate, in fungiform (FP) and circumvallate papillae (CV), and elimination of taste responses from chorda tympani and glossopharyngeal nerves. The retained innervation in FP and CV during HPI cannot sustain TB. Responses to tactile stimuli are not altered, and temperature responses are reduced only after 28 days treatment, demonstrating modality-specific effects. Rat FP and neural effects are similar to those in mouse whereas TB and neural response effects from the rat CV are much more severe. When recovery is introduced in mouse after prolonged, 48 days HPI, the TB in CV are restored whereas those in FP are not. Overall, Hedgehog signaling regulation is shown to generalize to the rat taste system, and the modality-specific controls in taste organ sensation are affirmed. The reported, debilitating taste disturbances in patients who use HPI drugs can be better understood based on these data.

Relationship between structure and function of neurons in the rat rostral nucleus tractus solitarii.

To investigate the relationship between the structure and function of neurons in the rostral (gustatory) nucleus tractus solitarii (rNTS), we analyzed the morphological and biophysical properties of rNTS neurons by performing whole-cell recordings in a brain slice preparation. Overall, neurons (n = 58) had a mean somal diameter of 16 microns, an average dendritic length of 598 microns, an average dendritic thickness of 0.91 microns, and a spine density of 0.037 spines/microns. Neurons were separated into three groups (elongate, multipolar, and ovoid) on the basis of previously established morphological criteria. The highest percentage (49%) of neurons were classified as ovoid, while 35% were multipolar and only 16% were elongate. The most frequently observed firing pattern, in all three cell types, elicited by a 1,200 ms, 100 pA depolarizing current pulse was a regularly firing spike train. However, the intrinsic firing properties of the remaining neurons were different. Thirty-one percent of the ovoid neurons responded with a short burst of action potentials and 44% of the elongate neurons showed a delay in the onset of the spike train following a hyperpolarizing prepulse. Less than 16% of the multipolar neurons demonstrated either of these firing characteristics. Therefore, rNTS neurons with similar morphology do not have unique biophysical properties. However, the data suggest that there may be subpopulations of the three morphological types, each of which displays a different firing pattern. Since the structure and function of the three morphological groups were not strictly correlated, these subpopulations may represent functional groups.

Central connections of the lingual-tonsillar branch of the glossopharyngeal nerve and the superior laryngeal nerve in lamb.

Afferent and efferent central connections of the lingual-tonsillar branch of the glossopharyngeal nerve (LT-IX) and the superior laryngeal nerve (SLN) in the lamb were traced with horseradish peroxidase (HRP) histochemistry. After entering the brainstem, most LT-IX and SLN afferent fibers turned caudally in the solitary tract (ST). Some afferent fibers of LT-IX terminated in the medial nucleus of the solitary tract slightly caudal to their level of entry. The remaining fibers projected to the dorsolateral, ventrolateral, and interstitial areas of the nucleus of the solitary tract (NST) at the level of the area postrema. Superior laryngeal nerve afferent fibers terminated extensively in the medial and ventral NST at levels near the rostral pole of the area postrema. Further caudal, near the level of obex, SLN afferent terminations were concentrated in the region ventrolateral to the ST and in the interstitial NST. The caudal extent of LT-IX and the rostral extent of SLN terminals projected to similar levels of the NST, but only a relatively small proportion of the total projections overlapped. Lingual-tonsillar and SLN fibers also coursed rostrally to terminate in the caudal pons within and medial to the dorsomedial principal sensory trigeminal nucleus. Other labeled afferent fibers traveled caudally in the dorsal spinal trigeminal tract to terminate in the dorsal two-thirds of the spinal trigeminal nucleus at the level of obex. Large numbers of labeled cells with fibers in the LT-IX or SLN were located in the ipsilateral rostral nucleus ambiguus and surrounding reticular formation. Fewer labeled cells were observed in the inferior salivatory nucleus following HRP application to either the LT-IX or SLN. The LT-IX and SLN projections to areas of the NST associated with upper airway functions, like swallowing and respiration, suggest an important role for these two nerves in the initiation and control of airway reflexes.

Neural basis of developing salt taste sensation: response changes in fetal, postnatal, and adult sheep.

To learn whether salt taste responses change during mammalian development, we recorded from multifiber preparations of the chorda tympani while stimulating the anterior tongue in sheep fetuses, lambs, and adults. Stimuli were 0.5 M NH4Cl, KCl, NaCl, and LiCl, and 0.05-0.75 M concentration series of the first three salts. Ultrastructural studies were made of taste buds at different ages to determine whether morphological elements such as microvilli and tight junctions are present in young fetuses. Substantial changes occur in relative salt taste responses, throughout development. In fetuses that are beginning the last third of gestation, NaCl and LiCl elicit much smaller response magnitudes than NH4Cl and KCl. Throughout the rest of gestation and postnatally, the NaCl and LiCl responses gradually increase in magnitude relative to NH4Cl and KCl. In adults, NaCl, LiCl, and NH4Cl all elicit similar response magnitudes and KCl is less effective as a taste stimulus. At ages when response ratios for the 0.5 M salts are changing, there are no changes in shapes of the response/concentration functions for individual salts. Furthermore, microvilli are present on taste bud cell apices and tight junctions are found between cells in the youngest fetuses studied. Therefore, initial stimulus-receptor membrane contacts are probably similar to those in adults. Our data suggest that different membrane components interact with the various monochloride salts and that taste receptors contain different proportions of these various membrane components at different developmental stages. Therefore young taste bud cells do not have the same salt response characteristics as mature cells, and a changing neural substrate underlies development of salt taste function, both pre- and postnatally.

Development of chorda tympani taste responses in rat.

To learn whether neurophysiological taste responses change during structural development of the gustatory system, we recorded from the chorda tympani nerve in rats aged 7 to 92 days after birth. Chemical stimuli applied to the anterior tongue included four monochloride salts, two acids, sucrose, and urea. Responses to all chemicals were obtained as early as 7 days postnatally. Developmental changes in salt, acid, and sucrose responses were observed. Relative to NaCl and LiCl, NH4Cl and KCl gradually decrease in effectiveness as taste stimuli; or, relative to NH4Cl and KCl, NaCl and LiCl become more effective stimuli. These changes are similar to those observed prenatally and postnatally in sheep. Also, relative to NaCl, citric acid, hydrochloric acid, and sucrose become less effective stimuli; or, NaC1 becomes more effective as a stimulus, relative to these acids and sucrose. The period of most rapid functional change overlaps a period of rapid structural change. It seems most reasonable to hypothesize that the altering taste responses reflect developmental changes in receptor membrane composition. Since the taste system is not programmed to respond in a mature manner from the moment function begins, there is ample opportunity for changing taste experience to influence the developing taste system.

Pathologic findings in mucopolysaccharidosis type IIIB (Sanfilippo's sydnrome B).

The pathologic changes in a rare case of mucopolysaccharidosis (MPS) type IIIB or Sanfilippo's syndrome B (absence of alpha-N-acetylglucosaminidase) are presented, along with the biochemical findings. Comparisons were made with other reported cases of MPS III subtypes and related storage disorders in terms of clinical, light microscopic, electron microscopic, and chemical findings, and a correlation of the ultrastructural changes made with the severe neurological dysfunction noted in this disorder. At present, MPS III subtypes cannot be separated from one another by morphological means because the same expression and distribution of lesions may be encountered among differing subtypes.

Sensory receptors of the larynx.

The larynx is a highly reflexogenic area, and stimulation with mechanical and chemical stimuli results in a number of protective reflexes. Investigators have used anatomical, behavioral, and neurophysiological techniques to examine the receptors responsible for initiating these reflex responses. Histologic examination has revealed the presence of free nerve endings, Merkel cells, Meissner corpuscles, and taste buds. Mechanoreceptors have been classified in several different ways and are located either in the superficial mucosa or in muscles and laryngeal joints. Recordings from afferent fibers innervating laryngeal mechanoreceptors have revealed that some of them are spontaneously active whereas others are silent until stimulated. Laryngeal mechanoreceptors respond to stimulation with either a rapidly adapting or a slowly adapting response pattern. Often the mechanoreceptors respond to respiratory movement of the larynx, giving bursts of action potentials during inspiration. A large number of taste buds that are anatomically similar to lingual taste buds populates the laryngeal surface of the epiglottis. Taste buds of the larynx respond to a number of chemical stimuli and to water. They do not respond to NaCl solutions close to physiological concentrations (0.154 M) but do respond at both a lower and higher concentration. When water is the solvent for the chemical stimuli, most chemicals initiate a response in laryngeal taste buds. However, when 0.154 M saline is used as a solvent, chemicals that taste bitter or sweet when applied to the tongue are ineffective stimuli. Taste buds of the larynx tend to be stimulated by the pH and tonicity of the stimulating solution and not by the gustatory properties. These results reveal a fundamental difference between the chemoreceptors of the oral cavity and larynx and result in the conclusion that chemoreceptors of the larynx do not play a role in gustation but are adapted to detect chemicals that are not saline-like in composition.

Potentiation of GABAergic synaptic transmission in the rostral nucleus of the solitary tract.

Whole-cell recordings were made from neurons in the rostral nucleus of the solitary tract in horizontal brainstem slices. Monosynaptic GABAA receptor-mediated inhibitory postsynaptic potentials were evoked by single stimulus shocks or by high-frequency tetanic stimulation in the presence of glutamate receptor blockers. While single stimulus-evoked inhibitory postsynaptic potentials had variable amplitudes, tetanic stimulation-induced, hyperpolarizing postsynaptic potentials were of a more constant amplitude. Furthermore, tetanic stimulation resulted in potentiation of the amplitude of single stimulus shock-evoked inhibitory postsynaptic potentials. Of 55 neurons that were tested, potentiation lasted over 30 min for 11, 10-30 min for 13, less than 10 min for 23 and no potentiation occurred in eight. Tetanic stimulation did not result in potentiation of the tetanic stimulus-evoked hyperpolarizing postsynaptic potentials. Both the single stimulus shock- and tetanic stimulus-evoked potentials had similar inhibition concentration-response curves to the GABAA antagonist, bicuculline methiodide (EC50 = 0.75 and 0.83, respectively), indicating that they were mediated by the same postsynaptic receptors. By comparing the effect of bicuculline methiodide on the amplitude of the single stimulus shock-evoked inhibitory postsynaptic potentials and the tetanic stimulus-evoked hyperpolarizing potentials, we concluded that a single stimulus shock does not activate all postsynaptic GABAA receptors. However, tetanic stimulation results in activation of all postsynaptic GABAA receptors and induces long-lasting changes in the presynaptic GABAergic neuron. These long-lasting changes of the presynaptic neuron facilitate the release of GABA during single stimulus shock and, as a consequence, more postsynaptic receptors are activated during single stimulus shock-evoked synaptic transmission. This conclusion is supported by the results of experiments in which the extracellular Ca2+ concentration was manipulated to change the amount of neurotransmitter released from the presynaptic GABAergic terminals. The single stimulus shock-evoked inhibitory postsynaptic potentials were sensitive to the extracellular Ca2+ concentration, whereas tetanic stimulus-evoked inhibitory post-synaptic potentials were essentially insensitive to extracellular Ca2+ concentration. The relationship between the single stimulus shock-evoked inhibitory postsynaptic potential amplitude and extracellular Ca2+ concentration indicates that, in control physiological saline containing 2.5 mM Ca2+, a single stimulus shock activates less than half the postsynaptic GABA receptors. The phenomenon of long-lasting potentiation of inhibitory transmission within the rostral nucleus of the solitary tract may be important in the processing of gustatory information and play a role in taste-guided behaviors.

Embryonic geniculate ganglion neurons in culture have neurotrophin-specific electrophysiological properties.

Geniculate ganglion neurons provide a major source of innervation to mammalian taste organs, including taste buds in the soft palate and in fungiform papillae on the anterior two thirds of the tongue. In and around the fungiform papillae, before taste buds form, neurotrophin mRNAs are expressed in selective spatial and temporal patterns. We hypothesized that neurotrophins would affect electrophysiological properties in embryonic geniculate neurons. Ganglia were explanted from rats at gestational day 16, when growing neurites have entered the papilla core, and maintained in culture with added brain-derived neurotrophic factor (BDNF), neurotrophin 4 (NT4), nerve growth factor (NGF) or neurotrophin 3 (NT3). Neuron survival with BDNF or NT4 was about 80%, whereas with NGF or NT3 less than 15% of neurons survived over 6 days in culture. Whole cell recordings from neurons in ganglion explants with each neurotrophin condition demonstrated distinctive neurophysiological properties related to specific neurotrophins. Geniculate neurons cultured with either BDNF or NT4 had similar passive-membrane and action potential properties, but these characteristics were significantly different from those of neurons cultured with NGF or NT3. NGF-maintained neurons had features of increased excitability including a higher resting membrane potential and a lower current threshold for the action potential. About 70% of neurons produced repetitive action potentials at threshold. Furthermore, compared with neurons cultured with other neurotrophins, a decreased proportion had an inflection on the falling phase of the action potential. NT3-maintained neurons had action potentials that were of relatively large amplitude and short duration, with steep rising and falling slopes. In addition, about 20% responded with a repetitive train of action potentials at threshold. In contrast, with BDNF or NT4 repetitive action potential trains were not observed. The data demonstrate different neurophysiological properties in developing geniculate ganglion neurons maintained with specific neurotrophins. Therefore, we suggest that neurotrophins might influence acquisition of distinctive neurophysiological properties in embryonic geniculate neurons that are fundamental to the formation of peripheral taste circuits and a functioning taste system.

Effects of dietary NaCl deprivation during early development on behavioral and neurophysiological taste responses.

In order to determine whether the gustatory system can be modified by restricting dietary NaCl during early development, neurophysiological taste responses were recorded in rats at various times after deprivation, and behavioral taste preferences were measured in adults. Rats deprived of dietary NaCl from the third day of gestation to 12 days postnatally and then placed on a NaCl-replete diet had chorda tympani nerve responses similar to those of nondeprived rats when recordings were made at 28 days of age and older; however, preferences for NaCl solutions over water were significantly less than those of controls when tested at adulthood. NaCl deprivation in pups from the third day of gestation to approximately 35 days postnatally resulted in altered chorda tympani nerve responses to NaCl but not to other stimuli such as NH4Cl and KCl. Therefore, restriction of dietary NaCl at a period in the rat's development when peripheral and central taste responses are changing results in short-term alterations in peripheral neural responses and in long-term changes in preference behaviors.

Neural circuits for taste. Excitation, inhibition, and synaptic plasticity in the rostral gustatory zone of the nucleus of the solitary tract.

The rostral nucleus of the solitary tract (rNST) plays a key role in modulating, organizing and distributing the sensory information arriving at the central nervous system from gustatory receptors. However, except for some anatomical studies of rNST synapses, the neural circuits responsible for this first stage in synaptic processing of taste information are largely unknown. Over the past few years we have used an in vitro brain slice preparation of the rNST to study synaptic processing, and it has become apparent that the rNST is a very complex neural relay. Synaptic potentials recorded in rNST neurons resulting from stimulation of afferent taste fibers are a composite of excitatory and inhibitory post synaptic potentials. Pure excitatory postsynaptic potentials (EPSP) can be isolated by using gamma-aminobutyric acid type A (GABAA) receptor blockers to eliminate the inhibitory postsynaptic potentials (IPSP). Application of glutamate ionotropic receptor blockers effectively eliminates all postsynaptic activity, indicating that glutamate is the transmitter at the first central synapse in the taste pathway. Stimulation of the afferent taste fibers originating from the anterior (chorda tympani) and posterior (glossopharyngeal) tongue results in a postsynaptic potential that is a complex sum of the two individual potentials. Thus, rNST neurons receive convergent synaptic input from the anterior and posterior tongue. The IPSP component of the synaptic potentials in rNST results from stimulation of interneurons. If these IPSPs are initiated by tetanic stimulation they undergo both short-term and long-term changes. Short-term changes result in the development of biphasic depolarizing IPSPs, and long-term changes result in potentiation of the IPSPs that can last over an hr in some neurons. This remarkable synaptic plasticity may be involved in the mechanism of learned taste behaviors. Synaptic transmission in rNST consists of excitation combined with inhibition. The inhibition does not simply depress excitation but probably serves many roles such as shaping and limiting excitation, coordinating the timing of synaptic events and participating in synaptic plasticity. Knowledge of these synaptic mechanisms is essential to understanding how the rNST processes taste information.

Ionic mechanism of GABAA biphasic synaptic potentials in gustatory nucleus of the solitary tract.

Gamma-aminobutyric acid (GABA) is the principal neurotransmitter of synaptic inhibition in the gustatory nucleus of the solitary tract (rNST). High-frequency activation of GABA neurons in the rNST results in biphasic inhibitory postsynaptic potentials (IPSPs) that are initially hyperpolarizing but then became depolarizing. Our results indicate that high-frequency stimulation evokes redistribution of Cl- and K+ ions that shifts IPSP reversal potential in a more positive direction, which produces a biphasic or depolarizing IPSP.

Long term chronic recordings from peripheral sensory fibers using a sieve electrode array.

The use of an implanted micromachined silicon sieve electrode array to make long term chronic recordings from the glossopharyngeal nerve is described. The implant consists of an array of small holes in a silicon substrate, four of which are surrounded by electrodes connected with an integrally fabricated ribbon cable to a percutaneous headcap. Using this device we have been able to monitor the integrity of the electrodes from the time of implantation and subsequently to record evoked sensory responses from mechanoreceptors on the tongue.

Effects of electrical stimulation of autonomic nervous system on degranulation of von Ebner's gland acini.

In a series of studies to understand interactions between taste sensation and salivary gland function, we are pursuing experiments to determine the autonomic nervous system control of von Ebner's lingual salivary glands. Electrical stimulation of the glossopharyngeal nerve, which contains the parasympathetic nerve supply to von Ebner's glands, caused a reduction in secretory granules of the glands in the rat. This depletion of granules could be blocked by prior administration of the parasympathetic antagonist, atropine. In contrast, electrical stimulation of the sympathetic nerve supply was ineffective in causing granule depletion in von Ebner's gland, but produced almost total degranulation in the parotid gland of the same animals. It is concluded that parasympathetic nerves exert the principal control over von Ebner's gland, acinar degranulation in the rat; this is compared with autonomic control of other salivary glands that have a dual peripheral control by parasympathetic and sympathetic innervation.

Responses of lamb nucleus of the solitary tract neurons to chemical stimulation of the epiglottis.

Previous research has shown that applications of chemical stimuli to the epiglottis produced distinct patterns of activity in the lamb superior laryngeal nerve. To determine the response characteristics of second-order neurons, we recorded from single cells in the lamb nucleus of the solitary tract (NST) while stimulating the epiglottis with 0.5 M KCl, NH4Cl, NaCl, LiCl, distilled water, 0.005 M citric acid and 0.01 N HCl. Most neurons responded to more than one of the chemical solutions. The order of effective stimuli was KCl = NH4Cl greater than distilled water greater than HCl greater than citric acid greater than NaCl greater than LiCl. An analysis of the variation in response frequency over time found that different chemical stimuli produced significantly different response patterns in NST neurons. A comparison of the mean neural response profiles of NST neurons and superior laryngeal nerve fibers for each of the stimuli found that only the response profiles elicited by NH4Cl were significantly different. In addition to their responses to chemical solutions, almost one-third of the NST neurons responded to the rinse following application of at least some of the stimuli and 80% of the neurons were excited by mechanical stimulation of the epiglottis with a soft brush. Also, a small number of neurons exhibited a rhythmic response coordinated with respiration. The majority of recording sites were located in areas of the NST linked to swallowing and respiration suggesting that the response patterns of NST neurons elicited by chemical stimulation of receptors on the epiglottis may play a role in upper airway reflexes.

Differences in the intrinsic membrane characteristics of parabrachial nucleus neurons processing gustatory and visceral information.

Whole-cell current-clamp recordings were made from neurons in the rat parabrachial nucleus (PBN) in three rostro-caudal brain slices. During recording the neurons were located in one of four quadrants of the PBN. Successful recordings were obtained from neurons in three of these quadrants termed the dorsolateral (DL), dorsomedial (DM) and ventromedial (VM) quadrants. Recordings were made of the intrinsic membrane properties and repetitive discharge characteristics of 58 neurons in the DL, 60 neurons in the DM, and 54 neurons in the VM-quadrants. The input resistance of the neurons in the DL quadrant was significantly lower and the membrane time constant significantly shorter than that of the neurons in the DM- and VM-quadrants. The mean action potential duration of the VM-quadrant neurons was significantly longer than that of both DL- and DM-quadrant neurons. The discharge frequency in response to a 1500 ms 100 pA current pulse of the DL quadrant neurons was significantly lower than that of the neurons in the other two quadrants. The latency of action potential initiation following a 100 pA depolarizing current pulse was significantly longer for DL quadrant neurons compared to neurons in the other two quadrants. Neurons were divided into groups based on their response to a long depolarizing current pulse immediately preceded by a hyperpolarizing current pulse. In all three rostro-caudal slices of the PBN, the largest populations of neurons were in Group II and Group III. The results demonstrate that neurons in different locations in the PBN have different membrane and repetitive discharge properties. These different PBN locations receive inputs from the visceral and gustatory regions of the NST. It is possible therefore that the differences in properties of the PBN neurons may relate to the type of sensory information that they process.