Chemical Senses Vol. 30 No. suppl 1 © Oxford University
Press 2005; all rights reserved
Posterior Insular Cortex in Rats: Response Characteristics and Function
Department of Physiology, Miyazaki Medical College, University of Miyazaki, Miyazaki 889-1692, Japan
Correspondence to be sent to: Takamitsu Hanamori, e-mail: thanamo{at}med.miyazaki-u.ac.jp
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Introduction |
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 Top Introduction Results and discussionReferences |
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Since the first report by Cechetto and Saper (1987
) showing the
viscerotopic sensory representation in the insular cortex, various studies on the
posterior insular cortex have been performed. We previously studied the response
properties of neurons in the rat insular cortex to gustatory, visceral and nociceptive
stimulation, and to electrical stimulation of the various sensory nerves (chorda tympani,
CT; lingual-tonsillar branch of the glossopharyngeal nerve, LT-IXth; pharyngeal branch of
the glossopharyngeal nerve, PH-IXth; superior laryngeal nerve; SL), using single unit
recordings (Hanamori et al.,
1997a,b, 1998a,b). The results from these studies indicated that neurons in
the posterior insular cortex (posterior to the region where the CT projects) receive
convergent inputs from various sensory organs. In the present study, first, we summarized
the data from previous our studies concerning response properties and convergence in the
insular cortex.
Previously several studies (e.g.
Ruggiero et al., 1987) have
shown that electrical or chemical stimulation of the posterior insular cortex induces
changes in the cardiovascular system [increase or decrease in heart rate (HR) or
blood pressure (BP)]. In addition, it has been shown that neuronal activity in the
posterior insular cortex was increased or decreased by chemoreceptor or baroreceptor
stimulation. In the present study, we found neurons in the posterior insular cortex that
show fluctuations in the spontaneous discharge. The fluctuations were also observed in BP
and HR recorded simultaneously. The relationships among fluctuations in neuronal activity
of the insular cortex, mean arterial pressure (MAP), and HR were analyzed using the
Pearson correlation coefficient (r).
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Results and discussion |
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TopIntroductionResults and discussionReferences |
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Response properties and convergence
Ninety-four neurons were responsive to electrical stimulation of, at least, one of the four taste nerves. Most neurons (69%) received convergent inputs from three nerves (mostly from LT-IXth, PH-IXth, and SL; Figure 1A). Ninety-one neurons showed an excitatory or inhibitory response to baro- and/or chemoreceptor stimulation [methoxamine hydrochloride (Mex), pressor drug; sodium nitroprusside (SNP), depressor drug; sodium cyanide (NaCN), activate arterial chemoreceptors]. Of 46 Mex-sensitive neurons, 67% were also sensitive to SNP. Of 69 NaCN-sensitive neurons, 72% were also sensitive to baroreceptor stimulation (Figure 1B). Twenty-six neurons were sensitive to taste stimulation of the posterior tongue (the stimuli were NaCl, HCl, QHCl and sucrose). Many neurons showed relatively narrow sensitivity to taste stimuli (53% of the taste-sensitive neurons responded to only one stimulus). However, 77% of the taste-sensitive neurons responded to tail pinch, and 81% responded to visceral (baro- and chemoreceptor) stimuli. Most taste-sensitive neurons (61%) received convergent inputs from all three stimuli (taste, tail pinch, and visceral) (Figure 1C). Twenty-two neurons were sensitive to taste stimulation of the pharyngolaryngeal region. Taste-sensitive neurons were also responsive to tail pinch (91%) and to visceral stimulation (86%). Most neurons (82%) received convergent inputs from all three stimuli (taste, tail pinch, and visceral) (Figure 1D). In summary, most neurons showed multimodal sensitivity. Two hundred and seven neurons obtained in these studies were located in the insular cortex between 2.9 mm anterior and 1.4 mm posterior to the APo (APo, the anterior edge of the crossing of the anterior commissure). The mean location was 0.9 mm (n = 207) anterior to the APo. Thus, most neurons recorded in our study were located in an anterior portion of the posterior insular cortex. In conclusion, many neurons in the posterior insular cortex receive convergent inputs from various sensory organs (taste, visceral and nociceptive).
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Fluctuations in the spontaneous discharge of neurons in the posterior insular cortex associated with fluctuations in BP and HR
Three of 20 neurons in the posterior insular cortex showed fluctuations in their spontaneous discharge during recording without stimulation. One example of neuron A is shown in Figure 2A. This neuron showed fluctuation in the spontaneous discharge as well as fluctuations in BP and HR recorded simultaneously. There was a negative correlation between neuronal activity and BP (Figure 2B, r = –0.42, n = 400). The r between neuronal activity and HR was –0.22. In the case of neuron B, there was a relatively high correlation between the neuronal activity and HR (r = 0.67). The r between neuronal activity and BP was –0.26. For neuron C, an increase in the spontaneous discharge was associated with the changes in BP (r = 0.31) and HR (r = 0.36). These results showed that fluctuations in neuronal activity in the posterior insular cortex are positively or negatively correlated with BP and/or HR. The data suggest that some of the neurons in the posterior insular cortex may play a role in the homeostatic control of the autonomic system.
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References |
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TopIntroductionResults and discussionReferences |
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Cechetto, D.F. and Saper, C.B. (1987) Evidence for a viscerotopic sensory representation in the cortex and thalamus in the rat. J. Comp. Neurol., 262, 27–45.[CrossRef][ISI][Medline]
Hanamori, T., Kunitake, T., Kato, K. and Kannan, H. (1997a) Convergence of afferent inputs from the chorda tympani, lingual–tonsillar and pharyngeal branches of the glossopharyngeal nerve, and superior laryngeal nerve on the neurons in the insular cortex in rats. Brain Res., 763, 267–270.[CrossRef][ISI][Medline]
Hanamori, T., Kunitake, T., Kato, K. and Kannan, H. (1997b) Convergence of oropharyngolaryngeal, baroreceptor and chemoreceptor afferents onto insular cortex neurons in rats. Chem. Senses, 22, 339–406.
Hanamori, T., Kunitake, T., Kato, K. and Kannan, H. (1998a) Neurons in the posterior insular cortex are responsive to gustatory stimulation of the pharyngolarynx, baroreceptor and chemoreceptor stimulation, and tail pinch in rats. Brain Res., 785, 97–106.[CrossRef][ISI][Medline]
Hanamori, T., Kunitake, T., Kato, K. and Kannan, H. (1998b) Responses of neurons in the insular cortex to gustatory, visceral, and nociceptive stimuli in rats. J. Neurophysiol., 79, 2535–2545.
Ruggiero, D.A., Mraovitch, S., Granata, A.R., Anwar, M. and Reis, D.J. (1987) A role of insular cortex in cardiovascular function. J. Comp. Neurol., 257, 189–207.[CrossRef][ISI][Medline]
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