Abstract
Neural inhibition plays a key role in determining the specific computational tasks of different brain circuitries. This functional “braking” activity is provided by inhibitory interneurons that use different neurochemicals for signaling. One of these substances, somatostatin, is found in several neural networks, raising questions about the significance of its widespread occurrence and usage. Here, we address this issue by analyzing the somatostatinergic system in two regions of the central nervous system: the retina and the hippocampus. By comparing the available information on these structures, we identify common motifs in the action of somatostatin that may explain its involvement in such diverse circuitries. The emerging concept is that somatostatin-based signaling, through conserved molecular and cellular mechanisms, allows neural networks to operate correctly.
Highlights
Over 40 years after its discovery as hypothalamic peptide inhibiting growth hormone release [1], somatostatin— known as somatotropin release-inhibiting factor (SRIF)—has been demonstrated to exist in several tissues and to mediate a variety of actions [2]
An Overview of Retinal and Hippocampal Circuitries. The organization of both retinal and hippocampal circuitries in terms of connectivity and neurotransmission are well known, and here, we summarize their main features in order to better understand the mechanisms of somatostatin action described later
Immunohistochemistry experiments allowed the retinal cells expressing this peptide to be identified. It is well-established that somatostatin is mainly found in sparsely-occurring, wide-field GABAergic amacrine cells with cell bodies in the INL and by “displaced” amacrine cells with cell bodies located in the GCL (Figure 3) (e.g., [56,57,58,59,60])
Summary
Over 40 years after its discovery as hypothalamic peptide inhibiting growth hormone release [1], somatostatin— known as somatotropin release-inhibiting factor (SRIF)—has been demonstrated to exist in several tissues and to mediate a variety of actions [2]. Somatostatin is widely distributed in the mammalian brain, and somatostatinergic interneurons are recognized as important modulators of neuronal activity [3,4,5,6,7,8,9,10]. The widespread occurrence of somatostatin-based signaling in different neural networks suggests that there might be general and shared mechanisms underlying somatostatin action. To test this hypothesis, in this review, we analyze the properties of the somatostatinergic system in two model networks: the retina and the hippocampus. In this review, we analyze the properties of the somatostatinergic system in two model networks: the retina and the hippocampus These nervous structures deal with different and highly specialized computational tasks. The available data suggest that somatostatinergic systems play key roles in assuring network stability so that neurons can operate correctly
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