Some Possible Inhibitory Neurotransmitters

Figure 9-10 shows the structures of some inhibitory neurotransmitters in the CNS. GABA and glycine are the most common transmitters at inhibitory synapses. Note that some of the molecules in Figure 9-10 also appeared in the list of excitatory neurotransmitters (Figure 9-5). A particular neuro-transmitter substance may have an excitatory effect at one synapse but an inhibitory effect at another. Whether a neurotransmitter is excitatory or inhibitory at a particular synapse depends on the type of ion channel it opens in the postsynaptic membrane. If the transmitter-activated channel is a sodium or a sodium-potassium channel (as at the neuromuscular junction), an e.p.s.p. will result and the postsynaptic cell will be excited. If the transmitter-activated channel is a chloride or potassium channel, the postsynaptic cell will be inhibited. The same neurotransmitter could even have opposite effects at two different synapses on the same postsynaptic neuron.

Figure 9-9 The mechanism by which increasing chloride permeability produces an inhibitory postsynaptic potential in a postsynaptic neuron. (a) The membrane potential moves toward the chloride equilibrium potential (fCl) when chloride permeability (pCl) increases. (b) At an inhibitory synapse, neurotransmitter molecules commonly act by opening chloride channels in the plasma membrane of a postsynaptic neuron. Chloride ions then enter the cell through the open channels to drive the membrane potential toward ECl. (Animation available at www.blackwellscience.com)

Serotonin Acetylcholine

(5-hydroxytryptamine)

Serotonin Acetylcholine

(5-hydroxytryptamine)

HO H

OH H HH

Norepinephrine

HO

HO H

H

H

M

C 1

H

H

HH

Dopamine

Tyr-Gly-Gly-Phe-Leu Leucine enkephalin (a series of five amino acids connected by peptide bonds)

Figure 9-10 Structures of some inhibitory neurotransmitter substances in the nervous system.

0 0

Post a comment