Biomedical subjects

Patricia M Di Lorenzo

Publications and source records attributed to Patricia M Di Lorenzo.

8 recordsLinked to original sources

PubMed2006

Neural coding mechanisms for flow rate in taste-responsive cells in the nucleus of the solitary tract of the rat.

When a taste stimulus enters the mouth, intentional movement of the stimulus within the oropharyngeal cavity affects the rate at which taste receptors are exposed to the stimulus and may ultimately affect taste perception. Early studies have shown that stimulus flow rate, the experimental equivalent of the effects of these investigative movements, modulates the portion of the peripheral nerve response that occurs when behavioral assessments of tastants are made. The present experiment studied the neural coding mechanisms for flow rate in the nucleus of the solitary tract (NTS), the first central relay in the taste pathway. Responses to NaCl (0.1 M) presented at high (5 ml/s) and low (3 ml/s) flow rates, sucrose (0.5 M), quinine HCl (0.01 M), and HCl (0.01 M) were recorded extracellularly from single NTS units in multiple replications. Information conveyed by evoked responses was analyzed with a family of metrics that quantify the similarity of two spike trains in terms of spike count and spike timing. Information about flow rate was conveyed by spike timing and spike count in approximately equal proportions of units (each approximately 1/3), whereas information about taste quality was conveyed by spike timing in about half of the units. Different subsets of units contributed information for discrimination of flow rate and taste quality.

Animals↗

PubMed2006

Temporal coding in the gustatory system.

Early investigations of temporal coding in the gustatory system showed that the time course of responses in some neurons showed systematic differences across the various classes of taste stimuli, implying that the temporal characteristics of a response can convey information about a taste stimulus. Studies of temporal coding in the gustatory system have grappled with several unique methodological challenges, including the quantitative description and comparison of temporal patterns as well as the assessment of the relative contributions of spatial and temporal coding to the information contained in a response to a tastant. Other investigations have suggested that the cooperative activity among synchronously firing ensembles of taste-responsive neurons at all levels of processing in the brain can convey information about taste quality (sweet, sour, salty, bitter and umami). Behavioral studies using patterned electrical stimulation of the brain in awake animals have supported the idea that temporal coding of taste stimuli may have functional significance.

Animals↗

PubMed2006

Effects of electrical stimulation of the glossopharyngeal nerve on cells in the nucleus of the solitary tract of the rat.

Electrophysiological responses to electrical stimulation of the lingual branch of the glossopharyngeal (GP) nerve (which innervates taste buds on the caudal 1/3 of the tongue) were recorded from single cells in the rostral nucleus of the solitary tract (NTS) of anesthetized rats. Electrical stimulation was delivered as single pulses (n=55), paired-pulses (n=15) and tetanic trains (n=11). NTS cells with GP-evoked responses were also tested for responsivity to taste stimuli (0.1 M NaCl, 0.5 M sucrose, 0.01 M HCl and 0.01 M quinine HCl). Fifty-five neurons were studied: 49 cells showed GP-evoked (mean latency+/-SEM=18.0+/-1.32 ms); seven of these were taste-responsive. Spontaneous rate of these cells was low (mean+/-SEM=1.4+/-0.3 spikes per second; median=0.21 spikes per second) and many cells showed no spontaneous activity. Paired-pulse stimulation of the GP nerve in 13 rats produced both paired-pulse suppression (n=11) and paired-pulse enhancement (n=4); tetanic stimulation (25 Hz, 1.0 s) produced sustained (>20 s) increases or decreases in firing rate in 7 of 11 cells tested. Histological data suggested that GP-evoked responses recorded in the most rostral NTS were likely the result of polysynaptic connections. Cells with GP-evoked responses formed a heterogeneous group in terms of their response properties and differed from cells with evoked responses to chorda tympani (CT; which innervates taste buds on the rostral 1/3 of the tongue) nerve stimulation. These differences may reflect the respective functional specializations of the GP and CT nerves.

Action Potentials↗

PubMed2003

Dynamic coding of taste stimuli in the brainstem: effects of brief pulses of taste stimuli on subsequent taste responses.

Recent studies have suggested that the response profiles of taste-responsive cells in the brainstem may be modulated by inhibitory interactions, potentially originating from activity in peripheral taste nerves. This idea was explored by testing the hypothesis that brief (100 msec) pulses of taste stimuli would alter the responses to subsequently presented tastants in the nucleus of the solitary tract (NTS) of urethane-anesthetized rats. Pulses of taste stimuli, called prepulses, were followed by a 3 sec presentation of the same or different taste stimulus. The prepulse-stimulus interval was either 1 or 5 sec, during which the tongue was rinsed with distilled water. Taste stimuli consisted of 0.1 m NaCl, 0.5 m sucrose, 0.01 m quinine HCl, and 0.01 m HCl. Taste prepulses suppressed (or enhanced) subsequent taste responses in 30 of 49 (61%) units when the prepulse-stimulus interval was 1 sec but were ineffective when this interval was 5 sec. Most commonly, NaCl or HCl prepulses attenuated the response to quinine. Control experiments showed that these effects were not attributable to adaptation, mixture effects, or response variability. In 19 (39%) of the units tested, effects of prepulses were large enough to change the order of effectiveness of the taste stimuli. Taste responses in these cells were "dynamically tuned" in that the magnitude of response was a function of the taste stimulus that immediately preceded it. Dynamic tuning may be the result of inhibitory interactions within the NTS; cells that show dynamic tuning may have a unique function in taste coding.

Action Potentials↗

PubMed2003

Temporal coding of sensation: mimicking taste quality with electrical stimulation of the brain.

Two experiments suggested that the temporal pattern of a taste response in the brain can convey meaningful information. In Experiment 1, rats avoided lick-contingent electrical stimulation of the nucleus of the solitary tract (NTS; the first synaptic relay for taste) when the temporal pattern of pulses mimicked the electrophysiological response to quinine, but not when the temporal pattern was randomized. In Experiment 2, rats avoided lick-contingent electrical stimulation of the NTS that mimicked the temporal pattern of a sucrose response following stimulation-illness pairings. This aversion generalized to sucrose but not to the other tastants; extinction of the aversion to electrical stimulation also extinguished the aversion to sucrose. Results replicate and extend previous findings (P. M. Di Lorenzo & G. S. Hecht, 1993).

Action Potentials↗

PubMed2003

Taste response variability and temporal coding in the nucleus of the solitary tract of the rat.

Theories of taste coding in the brain stem have been based on the idea that taste responses are integrated over time without regard to the temporal structure of the taste-evoked spike train. In the present experiment, the reliability of response rate across stimulus repetitions and the potential contribution of temporal coding to the discrimination of taste stimuli was examined. Taste stimuli representing the four basic taste qualities were presented repeatedly, and electrophysiological responses were recorded from single cells in the nucleus of the solitary tract (NTS) of anesthetized rats. Blocks of the four tastants were repeated for as long as the cell remained isolated. Nineteen cells were recorded with between 8 and 27 repetitions of each stimulus. Response magnitude to a given tastant varied widely within some NTS cells. This impacted the determination of both the breadth of tuning and best stimulus for a given cell. The contribution of spike timing and the pattern of interspike intervals to discrimination of taste stimuli was evaluated by an information-theoretic approach based on two families of metrics. Spike timing significantly contributed to the discrimination of taste qualities in 10 of 19 (53%) cells. This contribution was especially notable during the initial 2 s of the response. Those cells that showed the most variable firing rates in response to repetition of taste stimuli tended to show the largest contribution of temporal coding. These results suggest that, in addition to response rate, the temporal parameters of responses may convey information about taste stimuli in the NTS.

Action Potentials↗

PubMed2002

Effects of electrical stimulation of the chorda tympani nerve on taste responses in the nucleus of the solitary tract.

Despite evidence for an abundance of inhibitory synaptic processes within the taste-responsive portion of the brain stem, little is known about how these processes are activated or modulated. In this context, this study tested the hypothesis that activation of the chorda tympani nerve (CT) invokes inhibition that influences gustatory neural information processing in the rostral nucleus of the solitary tract (NTS). Stimulating electrodes were implanted in the middle ear of urethane-anesthetized rats to enable the passage of current across the CT. Electrophysiological responses to sucrose, NaCl, HCl, and quinine were recorded from single NTS neurons both individually and immediately following tetanic electrical stimulation of the CT. Additionally, NTS field responses to paired pulse stimulation of the CT were recorded. Electrical pulses delivered to the CT were found to produce a compound action potential with four components. Taste-responsive units in the NTS showed tetanus-evoked responses that varied in latency and strength. Those cells that showed strong, short latency responses to CT stimulation showed large magnitude responses to NaCl and were relatively narrowly tuned. Units with longer latencies generally responded more broadly to taste stimuli and with lower response magnitudes. Following tetanus, taste responses in 20 (43%) of the 46 units were reversibly altered in a stimulus-selective manner. Taste responses in 18 units were both enhanced and attenuated following tetanic stimulation, although attenuation was much more common. Additionally, tetanus was found to affect the temporal organization of spikes within taste responses to one stimulus in seven units (15%), four of which also showed changes in response magnitude to a different stimulus following tetanus. The influence of tetanus on taste responses was shown to be reliable and repeatable in neurons from which stimulus trials were recorded more than once. Across all units, responses to quinine were most dramatically and frequently attenuated following tetanus, while those to NaCl were least susceptible to change. NTS field responses evoked by paired pulse stimulation of the CT suggested that the initial pulse evoked an inhibitory influence in the NTS that decayed and returned to baseline by 2 s. These data are consistent with the idea that afferent input to the NTS normally activates inhibitory synaptic activity. As with other sensory systems, such inhibition may serve to facilitate contrast in the neural representation of different stimulus qualities.

Action Potentials↗

PubMed1993

Perceptual consequences of electrical stimulation in the gustatory system.

To investigate the role of temporal coding in the neural processing of taste, trains of electrical pulses of varying frequency were delivered to the nucleus of the solitary tract (NTS) in awake rats. The temporal patterns of these trains mimicked the temporal patterns of electrophysiological responses of single neurons to natural tastes. In Experiment 1, water-deprived rats were first trained to lick water in an experimental chamber. On training days, licking water produced a sucroselike electrical pulse train in the NTS. At the end of these sessions, experimental animals were made ill by an injection of LiCl and subsequently learned to avoid licking when LiCl was paired with NTS stimulation. In Experiment 2, rats refused to lick water when licking produced a quininelike pattern of NTS stimulation but licked enthusiastically when licking produced a pattern of NTS stimulation similar to the natural response to sucrose.

Afferent Pathways↗