Intercellular communication mediated by bioactive substances occurs in virtually all multicellular systems. Chemical neurotransmission in the vertebrate nervous system represents a form of this type of signalling. Fast chemical signalling (within milliseconds), in which the neurotransmitter is released at specialized neuronal junctions, called synapses, stimulates the opening of receptor-controlled ion channels in the post- synaptic cell. There is evidence that the amino acids, glutamate and aspartate, may represent the principal fast transmitters used by many central neurons. However, the actions of some chemical mediators, for instance neuropeptides, are slow (acting over seconds or even minutes) and they are functionally important as modulators of synaptic transmission. Since the chemical nature of excitatory synaptic transmitters in the mammalian spinal cord is still unknown, this research project will analyze cellular mechanisms underlying the rat spinal dorsal horn in vitro. The experiments will be directed at the role of excitatory amino acid synaptic mediators (l-glutamate and its analogues), receptors for excitatory amino acids, the role of tachykinins (substance P and neurokinin A), and the activation of intracellular second messenger systems (phoshoinositides) by excitatory amino acids and the tachykinins. Specific objectives to be examined are: 1) the pharmacological properties and ionic mechanisms of fast and slow excitatory postsynaptic potentials in the rate spinal cord slice preparation. The emphasis will be on NMDA receptors, since information about their role in primary afferent transmission is lacking; 2) the possibility of the involvement of second messenger systems (phosphoinositides and cyclic nucleotides) in the regulation of actions of excitatory amino acids and tachykinins at afferent synapses in the rat spinal dorsal horn; and 3) modulation of voltage-dependent calcium conductance of acutely-isolated rat dorsal horn neurons by excitatory amino acids, tachykinins and second messengers using whole-cell voltage clamp technique with a patch microelectrode. These studies will provide for a better understanding of synaptic signalling via chemical mediators within the nervous system.
