Type: Sensory neuron (mechanosensory)
In MoW: ALM
In WormWiring: ALML_h, ALMR_h, ALML_m, ALMR_m
In Wormbase: ALM, ALML, ALMR
Lineage: AB arppaappa, AB arpppappa
Location: Lateral in mid-body
Description: Anterior lateral microtubule cells. After they are born in the embryo, ALM neurons move from the anterior edge of the intestine to midway within the anterior body. ALML/R are among the 6 non-ciliated touch receptor neurons (TRN) that extend long, 15-protofilament microtubule (MT)-filled neurites in close apposition to the hypodermis and cuticle. Although MTs attach to the membrane at multiple sites, they likely do not gate the mechanosensory channels directly, since the ends of the MTs do not co-localize with the mechanosensory channels. The specialized extracellular matrix,

called "mantle", around these neurites also do not seem to be directly gating the channels. Instead, it is suggested that the mechanical force applied to TRNs are transmitted to the membrane via MTs and the resulting membrane stretch activates channel-opening (Cueva et al., 2007). Spontaneous neural activity of ALM is endogenously decreased during larval lethargus (Schwarz et al., 2011).
Neurotransmitter/Neuropeptide:
- Glutamate
- FLP-20; FMRFamide-like neuropeptide
(Loer, 2010; Li and Kim, 2008; Tsalik et al., 2003; Lee et al., 1999)
Innexin expression:
- INX-7
- UNC-9
(Altun et al., 2009)
Receptor expression:
- ASIC-1; mechanically gated ion channel subunit; amiloride-sensitive Na⁺ channel (ASC) protein (DEG/ENaC subunit)- part of a mechanosensory transduction channel
- DEG-3; alpha subunit of nicotinic acetylcholine receptor
- DEL-1; mechanically gated ion channel subunit; amiloride-sensitive Na⁺ channel (ASC) protein (DEG/ENaC subunit). - part of a mechanosensory transduction channel
- DES-2; alpha subunit of nicotinic acetylcholine receptor
- DEGT-1; mechanically gated ion channel subunit; amiloride-sensitive Na⁺ channel (ASC) protein (DEG/ENaC subunit). - part of a mechanosensory transduction channel
- DOP-1; D1-like dopamine receptor
- GLR-8; ionotropic glutamate receptor subunit (unclassifiable as NMDA or non-NMDA)
- GAB-1; GABA receptor beta-like subunit
- LGC-37; ligand-gated ion channel (human GABA A receptor gamma 2 (GABRG2) ortholog)
- LGC-55; ligand-gated ion channel
- MEC-2; stomatin-like protein required to sense touch, part of a mechanotransduction channel complex that senses low-threshold stimuli (gentle body touch)
- MEC-4; mechanically gated ion channel subunit; amiloride-sensitive Na⁺ channel (ASC) protein (DEG/ENaC subunit). - part of a mechanosensory transduction channel - core component of a mechanosensory transduction channel that senses low-threshold stimuli (gentle body touch)
- MEC-6; part of the degenerin/epithelial Na⁺channel complex - interacts physically with the MEC-4 degenerin ion channel
- MEC-9; provides an extracellular attachment point for the mechanosensory channels in touch cells
- MEC-10; mechanically gated ion channel subunit; amiloride-sensitive Na⁺ channel (ASC) protein (DEG/ENaC subunit). - part of a mechanosensory transduction channel - core component of a mechanosensory transduction channel that senses low-threshold stimuli (gentle body touch)
- PDFR-1; pigment dispersing factor (PDF-1) receptor
- STR-33; seven TM receptor
- TYRA-2; tyramine receptor
(Wormbase; Barrios et al., 2012; Altun, 2011; Topalidou and Chalfie, 2011; Chatzigeorgiou et al., 2010; Sanyal et al., 2004; Tsalik et al., 2003; Chelur et al., 2002; Brockie et al., 2001; Treinin. et al., 1998; Du et al., 1996; Lai et al., 1996; Huang et al., 1995; Treinin and Chalfie, 1995; Huang and Chalfie, 1994)
Function:
- Along with AVM and PLM, ALM neurons sense gentle (low threshold) mechanical stimulus to the body and provide input to the command (inter) neurons (PVC, AVB, AVD, AVA) via both synaptic connections and gap junctions (see mechanosensory circuit in C.elegans Book II and circuit for escape response in Pirri and Alkema, 2011). The touch cells form gap junctions with agonist interneurons and chemical synapses with the antagonist interneurons (see locomotory circuit). Hence, in the neural circuit of the escape response, the anterior touch cells ALML/R and AVM form gap junctions with the backward movement interneuron AVD, but they provide (inhibitory) synaptic input to the forward movement interneurons AVB and PVC (Goodman, 2006; Chalfie et al.,1985; Kaplan and Driscoll, 1997)
- ALM neurons also respond to harsh (high threshold) touch. Although the gentle touch response requires MEC-4, and is also largely dependent on MEC-10, the harsh touch response is MEC-4-independent and requires MEC-10 (degenerin) and DEGT-1 (Suzuki et al., 2003; Chatzigeorgiou et al., 2010)
- Along with other TRNs, ALM neurons are involved in memory formation for habituation to tap response both for massed training with 12-hr memory retention and spaced training with 48-hr memory retention (Li et al., 2013). Long-term memory for tap habituation requires protein synthesis, the transcription factor CREB and the AMPA-type glutamate receptor subunit GLR-1 in the postsynaptic AVA and AVD interneurons of the tap withdrawal circuit, while 12-hr memory is correlated with a FLP-20-dependent increase of synaptic vesicles in the terminals of the PLM mechanosensory neurons and likely other TRNs (Timbers and Rankin, 2011; Li et al., 2013)