286
Brain Research, 572 (1992) 286-29(I © t992 Elsevier Science Publishers B.V. All rights reserved 0006-8993/92/$05.0(~
BRES 25038
Organization of taste-evoked activity in the ha,'m r parabrachial nucleus Christopher B. Halsell* and Marion E. Frank Center for Neurological Sciences and Department of BioStructure and Function, University of Connecticut Health Center, Farmington, CT 06030 (U.S.A.)
(Accepted 5 November 1991) Key words: Response profile; Gustatory; Multi-unit neural activity; Parabrachial nucleus; Nucleus of the solitary tract
Small groups of 3-4 neighboring taste neurons in the hamster parabrachial nucleus (PBN) were either generalists (42%) or specialists (58%). Generalists responded well to sucrose, NaC1, KC1, and their mixture but specialists responded to only one or two stimuli: PBN temporal response patterns resembled chorda tympani patterns, indicating that they were preserved across two synapses. Generalist neuron-groups were distributed throughout the central medial (CM) subdivision of PBN. Sucrose-sensitive neuron-groups, which responded best to mixtures, were restricted to rostral CM, whereas most NaCl-best neuron groups were in caudal CM. These results suggest a multifaceted functional organization of taste sensibilities in the PBN. The parabrachial nucleus (PBN) is the second obligate brainstem synapse for the ascending gustatory system in rodents and lagomorphs 16'22'26. Response properties of PBN taste neurons have been studied in rat 14-16A8, hamster 24'25, and rabbit 2'3'26. Cytoarchitectural boundaries have recently been mapped for the hamster PBN and anterior-tongue taste activity located to the central medial (CM) and ventral lateral (VL) subdivisions 9. By recording from small groups of taste-responsive neurons in the PBN, the distribution of response properties can be studied 12. Twenty-four adult golden Syrian hamsters (Mesocricetus auratus), anesthetized with sodium pentobarbital, were used. Multi-unit activity was recorded in the PBN using glass micropipettes, filled with 4% horseradish peroxidase (HRP) in a 0.5 M KCI/0.05 M Tris buffer, p H 7.69 . The impedance of the electrodes, designed to record from 3 - 4 neurons simultaneously, was 1.4-1.6 Mf~ and electrode tip diameters were 12-24/~m. Following experimental sessions, recording sites were marked with iontophoretic deposits of H R P and the animal was perfused transcardially with a mixed aldehyde perfusate 9. The tissue was processed using the Hanker-Yates method and recording sites reconstructed. R o o m temperature taste stimuli: 0.03 M NaCI, 0.1 M sucrose, and 0.1 M KC1 and an undiluted mixture of the 3, were applied to the anterior tongue using a pressurized flow system n. The 3 individual stimuli selectively activate 3 populations of chorda tympani afferents 6,
whose responses to mixtures are known 5'1°. Multi-unit activity was recorded from 105 sites, of which 55 in 19 brains were selected (52 in CM and 3 in VL). The selected sites consistently responded at least 50% above background to taste stimuli. Discriminated stimulated spiking rates for 12 s were determined, from which unstimulated spiking rates were subtracted. To establish response profiles, response rates at each recording site were normalized so that responses to sucrose, NaC1 and KCI totalled 100. Hierarchical cluster analysis I formed the basis for categorizing response profiles for the 3 stimuli. Chi-square values were used to define differences between profiles as in previous work on hamsters 6'n'21. Peristimulus-time histograms (PSTH's) with 100-ms time bins were used to establish peak bin 23 (first bin with maximum response rate), peak/ tonic response ratio 23 (peak-bin rate divided by rate 8-10 s after stimulus onset), and aggregate PSTH's (mean values for each 100-ms). The mean response profiles of 4 clusters of sites are shown in Fig. 1. The 23 A sites were 'generalists', responding well to all 3 stimuli and having a response profile similar to the mean profile for all recorded sites (•). 'Specialist' sites fell into 3 groups. The NaC1 response was more than twice as big as responses to the other stimuli at the 16 B sites, sucrose was most effective at the 12 C sites, and the 4 D sites showed strong responses to KCI and NaCI. Thus, about 42% of the PBN sites were generalists and 58% were specialists.
* Present address: College of Dentistry, Dept. Oral Biology, Ohio State University, 305 W 12th Ave., Columbus OH 43210, U.S.A. Correspondence: M.E. Frank, Dept. BioStructure and Function, University of Connecticut Health Center, Farmington, CT 06030, U.S.A.
287 2OO
70
60
[~-]N ~ K
N K M
150
3" S
x > >(;x
S loo
×
s
Brain Research, 572 (1992) 286-29(I © t992 Elsevier Science Publishers B.V. All rights reserved 0006-8993/92/$05.0(~
BRES 25038
Organization of taste-evoked activity in the ha,'m r parabrachial nucleus Christopher B. Halsell* and Marion E. Frank Center for Neurological Sciences and Department of BioStructure and Function, University of Connecticut Health Center, Farmington, CT 06030 (U.S.A.)
(Accepted 5 November 1991) Key words: Response profile; Gustatory; Multi-unit neural activity; Parabrachial nucleus; Nucleus of the solitary tract
Small groups of 3-4 neighboring taste neurons in the hamster parabrachial nucleus (PBN) were either generalists (42%) or specialists (58%). Generalists responded well to sucrose, NaC1, KC1, and their mixture but specialists responded to only one or two stimuli: PBN temporal response patterns resembled chorda tympani patterns, indicating that they were preserved across two synapses. Generalist neuron-groups were distributed throughout the central medial (CM) subdivision of PBN. Sucrose-sensitive neuron-groups, which responded best to mixtures, were restricted to rostral CM, whereas most NaCl-best neuron groups were in caudal CM. These results suggest a multifaceted functional organization of taste sensibilities in the PBN. The parabrachial nucleus (PBN) is the second obligate brainstem synapse for the ascending gustatory system in rodents and lagomorphs 16'22'26. Response properties of PBN taste neurons have been studied in rat 14-16A8, hamster 24'25, and rabbit 2'3'26. Cytoarchitectural boundaries have recently been mapped for the hamster PBN and anterior-tongue taste activity located to the central medial (CM) and ventral lateral (VL) subdivisions 9. By recording from small groups of taste-responsive neurons in the PBN, the distribution of response properties can be studied 12. Twenty-four adult golden Syrian hamsters (Mesocricetus auratus), anesthetized with sodium pentobarbital, were used. Multi-unit activity was recorded in the PBN using glass micropipettes, filled with 4% horseradish peroxidase (HRP) in a 0.5 M KCI/0.05 M Tris buffer, p H 7.69 . The impedance of the electrodes, designed to record from 3 - 4 neurons simultaneously, was 1.4-1.6 Mf~ and electrode tip diameters were 12-24/~m. Following experimental sessions, recording sites were marked with iontophoretic deposits of H R P and the animal was perfused transcardially with a mixed aldehyde perfusate 9. The tissue was processed using the Hanker-Yates method and recording sites reconstructed. R o o m temperature taste stimuli: 0.03 M NaCI, 0.1 M sucrose, and 0.1 M KC1 and an undiluted mixture of the 3, were applied to the anterior tongue using a pressurized flow system n. The 3 individual stimuli selectively activate 3 populations of chorda tympani afferents 6,
whose responses to mixtures are known 5'1°. Multi-unit activity was recorded from 105 sites, of which 55 in 19 brains were selected (52 in CM and 3 in VL). The selected sites consistently responded at least 50% above background to taste stimuli. Discriminated stimulated spiking rates for 12 s were determined, from which unstimulated spiking rates were subtracted. To establish response profiles, response rates at each recording site were normalized so that responses to sucrose, NaC1 and KCI totalled 100. Hierarchical cluster analysis I formed the basis for categorizing response profiles for the 3 stimuli. Chi-square values were used to define differences between profiles as in previous work on hamsters 6'n'21. Peristimulus-time histograms (PSTH's) with 100-ms time bins were used to establish peak bin 23 (first bin with maximum response rate), peak/ tonic response ratio 23 (peak-bin rate divided by rate 8-10 s after stimulus onset), and aggregate PSTH's (mean values for each 100-ms). The mean response profiles of 4 clusters of sites are shown in Fig. 1. The 23 A sites were 'generalists', responding well to all 3 stimuli and having a response profile similar to the mean profile for all recorded sites (•). 'Specialist' sites fell into 3 groups. The NaC1 response was more than twice as big as responses to the other stimuli at the 16 B sites, sucrose was most effective at the 12 C sites, and the 4 D sites showed strong responses to KCI and NaCI. Thus, about 42% of the PBN sites were generalists and 58% were specialists.
* Present address: College of Dentistry, Dept. Oral Biology, Ohio State University, 305 W 12th Ave., Columbus OH 43210, U.S.A. Correspondence: M.E. Frank, Dept. BioStructure and Function, University of Connecticut Health Center, Farmington, CT 06030, U.S.A.
287 2OO
70
60
[~-]N ~ K
N K M
150
3" S
x > >(;x
S loo
×
s
