Keiichi Tonosaki

Gustatory neural response in the mouse

Gustatory responses from the mouse chorda tympani nerve were tested with various chemical solutions. Magnitudes of integrated chorda tympani responses to the 4 basic taste stimuli were greater in the order of HCl, sucrose, NaCl and quinine-HCl. Sucrose was the most effective sugar tested, while NaCl was the least effective salt, but divalent chloride salts were prominently effective stimulants. Many of single chorda tympani fibers responded specifically to one or two of the 4 basic taste stimuli. Single fibers sampled were classified into the following 5 types: sweet-type, Na-type, Ca-Mg-type, acid-type and quinine-type.

Cross-adapted sugar responses in the mouse taste cell

1. Intracellular recordings of mouse taste cell responses were made using a glass micro-electrode filled with Procion yellow dye solution. 2. Six sugars (sucrose, maltose, lactose, glucose, galactose and fructose) produced the depolarization responses. 3. Gustatory cross adaptation between sugars was determined. When the taste cell was pre-adapted with one of the six sugars, the other five sugars, cross adapted, produced depolarization, hyperpolarization or null responses. 4. From these observations, it is suggested that there are multiple sugar receptor sites on the receptor membrane of the mouse taste cell.

Action of some drugs on gecko olfactory bulb mitral cell responses to odor stimulation

The probable relationships of neural connectivity of the olfactory bulb have been established in morphologicaP, 12 and evoked-potential studies 11,1~,1a,19. There are a few descriptions of the mitral cell activity in response to odor stimulation 4,5,7,17,1s. In general, the effect of odor presentation to the pr imary neurons on the mitral cell activity could be described as excitation, suppression or null 4. However, effects of drugs on the odor-evoked electrical response of the mitral cell have not been reported. This study is a preliminary report on the effects of some drugs on the excitation type of odor-evoked response of the mitral cell. Effects of some drugs on the suppression type of response to odor will be reported elsewhere. The drugs were applied locally by iontophoresis from microelectrodes or extensively by perfusion of solutions over the exposed olfactory bulb. Adult geckos (Gekko gecko) were anesthetized with urethane. The head of the gecko was fixed in a holder, the olfactory bulbs were exposed and a shallow pool was formed to direct a continuous flow of reptilian Ringer over them. Procian brown or Fast Green dye permeated from the surface into the external plexiform layer within 3 min as shown by histological examination of paraffin sections. For the perfusion method, 7-aminobutyric acid (GABA), carnosine and bicucultine were made up as 10 -3 M solutions in Ringer and exchanged for the Ringer flowing continuously at about 0.04 ml,sec over the bulbar surface. In the electrophoretic method, glass microelectrodes were filled with GABA (0.5 M, pH 3) or carnosine (0.25 M, pH 7). Two electrodes were mounted in a holder with their tips separated vertically by about 200 #m, so that when the upper one was positioned in the glomerular layer (GL) the lower one was in the external plexiform layer (EPL) about 400 #m below the surface. The recording microelectrode was inserted adjacent to the tip of an electrophoresis electrode. Electrode positions were usually selected by the field potential method 11,1~ and in some instances confirmed by means of dye deposition. Conventionalextracellular

Amiloride does not block taste transduction in the mouse (Slc:ICR)

1. The receptor potential of the mouse taste cell was recorded with an intracellular microelectrode while taste stimuli were applied to the tongue surface of the anesthetized mouse. 2. A membrane depolarization accompanied by an increase in membrane resistance was observed after a sucrose stimulus. 3. A sodium-chloride stimulus initiated a membrane depolarization accompanied by a decrease in membrane resistance. 4. Amiloride elicits a depolarization of the membrane and is accompanied by an increase in membrane resistance. 5. Pre-adapting the tongue to amiloride, which is known as a potent sodium channel blocker, did not alter the responses to sodium-chloride and other taste stimuli.

Voltage- and current-clamp recordings of the receptor potential in mouse taste cell☆

Intracellular recordings were obtained using the current-clamp and voltage-clamp techniques. When the taste cell membrane was voltage-clamped, the sucrose stimulus induced an inward current accompanied by a membrane resistance increase while the NaCl stimulus induced an inward current accompanied by a membrane resistance decrease. These phenomena indicated that sucrose and NaCl have quite a different generation mechanism of taste responses.

Adaptation effect of sucrose on the salt taste response.

1. Intracellular recordings from mouse taste receptor cells were made to study cellular adaptation properties. 2. The sugar and salt receptor mechanisms of mammalian taste cells were investigated with cross-adaptation experiments. 3. The responding of taste cells to sucrose as well as to NaCl does not contradict the independency of their binding mechanisms. 4. With a mixture of sucrose and NaCl, different adsorption mechanisms are observed. 5. From these observations, it was concluded that adaptation occurs in the taste receptor cell.

The effect of bilateral sectioning of the chorda tympani and glossopharyngeal nerves on the sweet taste in the mouse

The chorda tympani nerve (CT) and the glossopharyngeal nerve (GL) have been considered important nerves for the sense of taste. We studied the effect of bilateral sectioning of the CT and/or GL on the sweet taste in the mouse. Before and after surgery we analyzed the daily drinking patterns, using the two-bottle preference test method. The normal mouse drank the low concentration sucrose solution (0.0125 M) more than distilled water. This report showed that the mouse who was bilateral sectioned, both CT and GL or bilateral sectioned CT, rejected drinking the low concentration of sucrose solution. In contrast, the mouse who was bilateral sectioned GL drank the low concentration sucrose solution like the normal mouse did. These phenomena suggested that the fungiform papilae play an important role to detect the low concentration of sucrose (0.0125 M) as a sweet favorable taste substance.

Cross-Adaptation to Odor Stimulation of Olfactory Receptor Cells in the Box Turtle, Terrapene Carolina

Electrical recording from small twigs of olfactory nerve and electro-olfactogram (EOG) from olfactory epithelium in a turtle shows that olfactory receptors in the nose are responsive to various odors. I have used the effects of cross-adaptation to odor stimulation on the olfactory receptors to investigate the stimulus-specific components of these responses and to provide information about the responsiveness of cells. The results of the cross-adaptation experiments strongly support the hypothesis that different categories of receptor cells exist in the olfactory epithelium.

The effect of some drugs on the mitral cell odor-evoked responses in the gecko olfactory bulb

The activity of odor-evoked olfactory mitral cell response of the gecko was recorded extracellularly by glass microelectrodes. The activities of the mitral cell observed during the presentation of the odor (n-amyl acetate) could be described as excitation, suppression or zero. The present experiments were undertaken to study the neural activities of the mitral cell in the olfactory bulb by perfusion application of some drugs (cobalt chloride, carnosine, norepinephrine, GABA and D-L-homocysteate) on the olfactory bulb surface or iontophoretic application of some drugs (carnosine, norepinephrine, GABA and D-L-homocysteate) to the glomerulus and the external plexiform layer to change the physiological environment. The effect of the drugs suggested that the synaptic neurons on the mitral cell have different chemical characteristics.

Cross-adapted salt responses in the mouse taste cell

The exact nature of taste adaptation is not known. Intracellular recordings from taste receptor cells are appropriate to clarify cellular adaptation properties. I approached the study of the sugar and salt receptor mechanisms of mammalian taste cells with cross-adaptation experiments. Sucrose pre-adaptation suppresses the cross-adaptation responses to salts. The results show that the taste adaptation is located in the taste receptor cell.