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How does the primary afferent synapse or interact with dorsal horn neurons?
There are interneurons that have intervening synapses between some of the primary afferents and neurons at deeper layers in the dorsal horn such as lamina V.
Some of these lamina V neurons have long dendrites extending into lamina II and synapse directly with primary afferents.
The dorsal horn is a very fertile territory for modulatory influences from descending nerves arising from higher centers as well as local interneurons. The interneurons are typically inhibitory.
The preponderant influence from descending neural input is also inhibitory.
Here is the table with a summary of dorsal horn neurotransmitters or ligands.
Ligand Receptor Interaction
| Receptor | Drug or Neurotransmitter | Channel and Direction | Effect |
|---|---|---|---|
| GABA-A | GABA | Chloride influx | Inhibitory |
| GABA-B | GABA | Potassium influx | Inhibitory |
| Glycine | Glycine | Chloride influx | Inhibitory |
| Opioid | Opioids | Potassium influx | Inhibitory |
| μ, κ, σ | Opioids | Potassium influx | Inhibitory |
| α1, α2 | Norepinephrine | Potassium influx | Inhibitory |
| SHT | Serotonin | Potassium influx | Inhibitory |
| AMPA | Glutamate | Sodium influx | Excitatory |
| NMDA | Glutamate | Sodium and calcium influx | Excitatory |
| NK-1 | Substance-P | Sodium and calcium influx | Excitatory |
| NK-1,2 | NK-1 | Sodium and calcium influx | Excitatory |
| CCGP | CGRP | Sodium and calcium influx | Excitatory |
| GABA-B | Baclofen | Potassium influx | Inhibitory |
| GABA-A | Benzodiazepine | Chloride influx | Inhibitory |
| Gabapentinoid receptor | Gabapentin/Pregabalin | Blocks calcium, L-type | Inhibitory |
| α1, α2 | SNRI | Potassium influx | Inhibitory |
| 5-HT | SNRI | Potassium influx | Inhibitory |
| NMDA | Ketamine | Sodium and calcium influx | Excitatory |
| Conopeptide receptor | ω-Conopeptide | Blocks calcium, N-type | Inhibitory |
