Lamprey Receptors

Cross references: 
Serotonin Metabotropic Receptor 
Amphioxus Receptors

The action of 5-HT on calcium-dependent potassium channels and on the spinal locomotor network in lamprey is mediated by 5-HT1A-like receptors (Goog) 
Only abstract available online.  I got the PDF from the library. 
The present results taken together with previous data indicates that the receptor responsible for the effects of 5-HT ... on the locomotor pattern generator in lamprey shares certain features, but is not identical to the mammalian 5-HT1A receptor.
My comments
1.  The article was written in 1995.  Since then, it has been confirmed that the receptor in question is, in fact, a genuine 5-HT1AR, and not just something similar. 
2.  Since 5-HT1AR is inhibitory, this points toward a possible effect of serotonin on amphioxus behavior which is consistent with my assumption in
Boys without Fathers
3.  I had originally assumed, from the information in
Rodent Hormone-Nerve Interaction , that the effect of serotonin on amphioxus behavior was through the ionotropic receptor 5-HT3R (see: Serotonin Gate (5-HT3R) ).  However, as discussed in Amphioxus Receptors , 5-HT3R has never been identified in the amphioxus and may, in fact, not be present.  To deepen the mystery, I haven't yet seen any mention of 5-HT3R in the lamprey either. 
4.  If, in fact, 5-HT3R is not present in either the amphioxus or the lamprey, this presents what is, to me, as surprising suggestion.  Perhaps 5-HT3R actually evolved after rather than before the metabotropic receptors.  I find this hard to believe.  But then, why is it missing in the two ancient ancestors?      

5-HT inhibits N-type but not L-type Ca(2+) channels via 5-HT1A receptors in lamprey spinal neurons (PubMed) 
Only abstract available online.  I got the PDF from the library.  However, there seems to be some sort of lock on the PDF.  Although I can read it on my screen, I can't copy-and-paste from it.  When I try, what I get is gibberish.  However, I can still transcribe from it.    The quotes, below, are from the abstract, which does allow the copy-and-paste function, and there is also a brief transcription. 
5-HT is a potent modulator of locomotor activity in vertebrates. In the lamprey, 5-HT dramatically slows fictive swimming.

    ",,,  It was also confirmed that 5-HT depresses Ca(2+) currents in neurons, including motoneurons, in the intact spinal cord.  8-OH-DPAT, a 5-HT1A receptor agonist, also inhibited Ca(2+) currents in dissociated neurons...  the effect is caused by an activation of 5-HT1A receptors. ...
Brief transcription
    "The primary conclusion ... is that lamprey spinal neurons have 5-HT1A receptors ..." 
My comment
This i
s the sort of observation I was hoping to find for the amphioxusUnfortunately, I don't understand most of the rest of it.   I suppose I could take some time and learn about Ca(2+) channels, but I'm not at all sure it would help me understand the animal's overt behavior.  

Evolution of monoamine receptors ... (PubMed) 
"In the cephalochordate Amphioxus, a sister group to vertebrates, a single catecholamine receptor gene was found, which based on molecular phylogeny and functional analysis formed a monophyletic group with both vertebrate dopamine D1 and beta adrenergic receptor classes... In contrast, two distinct genes homologous to jawed vertebrate dopamine D1 and beta adrenergic receptor genes were extant in representatives of the earliest craniates, lamprey and hagfish, paralleling high dopamine and noradrenaline content throughout the brain. These data suggest that a D1/beta receptor gene duplication was required to elaborate novel catecholamine psychomotor adaptive responses and that a noradrenergic system specifically emerged at the origin of vertebrate evolution.

Ion channels of importance for the locomotor pattern generation in the lamprey brainstem-spinal cord (PubMed) 
Full length HTML and PDF available online for free. 
"The intrinsic function of the spinal network that generates locomotion can be studied in the isolated brainstem-spinal cord of the lamprey, a lower vertebrate. The motor pattern underlying locomotion can be elicited in the isolated spinal cord. The network consists of excitatory glutamatergic and inhibitory glycinergic interneurones with known connectivity.

"Furthermore, the brainstem locomotor centres are located in the same mesopontine area in vertebrates ranging from cyclostomes to primates. In all vertebrates the spinal cord is responsible for the basic patterns of co-ordination used for propulsion, regardless of the type of locomotion, ranging from modulatory swimming to walking or flying.

"In the lamprey (for review see Grillner et al. 1998), as in amphibian tadpoles (for review see Dale & Kuenzi, 1997), the motor network producing the alternating activity is composed of excitatory glutamatergic interneurones, which mutually excite each other (using different ionotropic NMDA and AMPA, and metabotropic glutamate receptors), and in addition ipsilateral inhibitory glycinergic interneurones and motoneurones (Buchanan & Grillner, 1987; Krieger et al. 1996). The inhibitory interneurones inhibit contralateral neurones (Buchanan, 1982).

"Lamprey spinal motoneurones and interneurones contain N-, P/Q-, L- and T-type Ca2+ channels as shown in experiments on isolated cells or in the intact spinal cord (El Manira & Bussières, 1997).

My comments
1.  The above is just the nontechnical introduction.  Later on, the article becomes very technical, and I didn't understand any of it. 
2.  No serotonin receptors.  Just glutamate and glycine. 

The sea lamprey Petromyzon marinus genome reveals the early origin of several chemosensory receptor families in the vertebrate lineage (PubMed) 
Full length HTML and PDF available online for free. 
In gnathostomes, chemosensory receptors (CR) expressed in olfactory epithelia are encoded by evolutionarily dynamic gene families encoding odorant receptors (OR), trace amine-associated receptors (TAAR), V1Rs and V2Rs.
In the lamprey genome we identified a repertoire of 59 intact single-exon CR genes, including 27 OR, 28 TAAR, and four V1R-like genes."
An extensive search in the lamprey genome failed to identify potential orthologs or pseudogenes of the multi-exon V2R family that is greatly expanded in teleost genomes, but did find intact calcium-sensing receptors (CASR) and intact metabotropic glutamate receptors (MGR).

Vomeronasal organ (Wiki) 
"The vomeronasal organ (VNO) ... is an auxiliary olfactory sense organ that is found in many animals."  "The vomeronasal organ is mainly used to detect pheromones, chemical messengers that carry information between individuals of the same species, hence is sometimes referred to as the "sixth sense." The VNO has two separate types of neuronal receptors, V1R and V2R, which are seven-transmembrane receptors that are coupled to G proteins.