Local intemeuron

The axon wiring in the insect antennal lobe is anatomically and physiologically similar to that in the mammalian olfactory bulb. Insect ORNs target and synapse with two neurons projection neurons and GABA-mediated local intemeurons. Projection neurons are second-order olfactory intemeurons that transmit the information of odorants into the mushroom body calyx and lateral horn, which is the center for olfactory-related memory formation (Heisenberg... 

Intrinsic or Local Connections There are extensive translaminar cormections from superficial to deeper layers and vice versa. Layer II pyramidal cell axon collaterals synapse with deeper layer III pyramidal cells and with local inhibitory intemeurons in layers I and II. Local collaterals from deeper pyramidal cells synapse with local intemeurons or with more superficial pyramidal cells. Local projections from pyramidal cells to GABAergic intemeurons play an important role in regulating PC neuronal excitability, including the expression of LTP and seizures, via feedback and feedforward inhibition (Ekstrand et al., 2001a). 

In the antennal lobe ORN axons terminate in structures known as glomeruli (Figure 4). The ORNs innervate the glomeruli - spheroids of tightly packed dendritic and axonal branches. These first-order synaptic neuropil are where ORNs, and the two major classes of AL neuron, principal neurons (PNs) and local intemeurons (LNs) interconnect. The moth M. sexta (male) has around 66 glomeruli, 360 LNs and 900 PNs [16]. There are many different receptor types, since most of the ORNs are tuned to respond to a variety of chemicals. 

Christensen, T.A., D Alessandro, D., Lega, J., Hildebrand, J.G. Morphometric modeling of olfactory circuits in the insect antennal lobe I. simulations of spiking local intemeurons. Biosystems 61, 143-153 (2001)... 

Fig. 7.2 Schematic representations of chemosensory pathways in the brain, (a) Lateral antennular neuropil (LAN) pathway. dCRNs and MRNs from sensilla on the lateral (LF) and medial (MF) antennular flagellum project somatotopically into both lobes of the LAN and couple directly to antennular motoneurons (MN), (b) Olfactory pathway. ORNs project nontopographically into the olfactory lobe (OL) which is organized into glomeruli. Information is processed by various types of multiglomerular local intemeurons (LN) and output is provided by multiglomerular projections neurons (PN) ascending to the lateral protocerebrum in the eyestalk ganglia...

Fig. 7.8 Dendritic arborizations and electrical responses to odors of similar classes of multiglomerular local intemeurons in the deutocerebrum of P. argus (a, c) and P. clarkii (b, d). Note that in both crustaceans the dendrites invest both the OL and LAN, and both respond not only to odorants but also to the onset of hydrodynamic flow past the antennular flagellum, (a, c) from Schmidt and Ache 1996b (b) from Mellon and Alones 1995 (d) from Mellon and Humphrey 2007...

Mellon D (2005) Integration of hydrodynamic and odorant inputs by local intemeurons of the crayfish deutocerebrum. J Exp Biol 208 3711-3720... 

Mellon D, Humphrey JAC (2007) Directional asymmetry in responses of local intemeurons in the crayfish deutocerebrum to hydrodynamic stimulation of the lateral antennular flagellum. J Exp Biol 210 2961-2968... 

Johnson, S. W. and North, R. A. (1992) Opioids excite dopamine neurons by hyperpolarization of local intemeurons. /. Neurosci. 12, 483-488. 

---