ABSTRACT
Recordings........................................................................................ 140 7.3 Knowledge Gained from Intracellular Recordings from rNST Neurons ... 141
7.3.1 In Vitro Recordings .......................................................................... 142 7.4 Possible Circuits........................................................................................... 143
7.4.1 rNST Circuits Based on Current Knowledge.................................. 143 7.4.2 Model rNST Circuits ....................................................................... 145 7.4.3 Separation of Function..................................................................... 146
7.5 Outlook for Future Investigations................................................................ 147 Acknowledgment ................................................................................................... 148 References.............................................................................................................. 149
In previous chapters, the current knowledge of the neurobiology of the mammalian brainstem gustatory relay nucleus has been detailed. Information presented shows that all chemosensory information derived from stimulating taste receptors, no matter where they are located, has to pass through the rostral nucleus of the solitary tract (rNST), and by the 1960s, the basic brainstem projection pattern of the afferent gustatory nerves had been established in outline form (summarized in Chapter 1, Figure 1.1). Details of the development of the connections are only now being studied and found to consist of complex overlapping terminal fields that suggest highly convergent input to the second-order neurons (Figure 6.2). Further anatomical pathway tracing mainly in rodents has established the projection patterns from the rNST to both rostral brain areas and brainstem sites (Figure 7.1). As described in Chapter 4, the brainstem connections from rNST are the secretomotor output to the salivary glands and motor output to various muscles involved in oral reflexes and facial expression. The rostral projection divides at the parabrachial nucleus, with one pathway passing through the thalamus to the
cortex, whose function is believed to be involved in the sensory discriminative aspect of taste perception, whereas the other, limbic pathway is believed to be involved in the hedonic component of taste perception and its control of feeding. In addition, descending connections from forebrain areas to the rNST have also been described and to some extent investigated by examining the effects of electrical stimulation of these areas on the response characteristics of rNST neurons (Chapter 5).
