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Human VNO Function: A Critical Review of Best and Worst Cases, (Shortened and Annotated)
Here lies my reading for tonight, felt like I should shorten it down and simplify it. Any of my words are in Italics, and the rest are copy-pasted and shortened direct from the source. Feel free to check it out and give it a read, however know its a 30-50 min read. I recommend skimming. Here's a summary of the most interesting parts.
Structure:
The existence of a VNO in the human embryo similar to the VNOs of other species is undisputed (Boehm and Gasser, 1993). Numerous reports of a structure identified as the VNO in the nasal septum in adult humans agree that it is a blind ending diverticulum in the septal mucosa opening via a depression (the VNO pit) into the nasal cavity ?2 cm in from the nostril. The location of this structure is consistent with the location of the VNO in embryos (Trotier et al., 2000) and it has a similar simplified form, with no large blood vessels, cavernous sinuses or supporting cartilage. The structure is reported at least unilaterally in 90% or more of subjects in some reports or in 50% or fewer in other reports. Trotier et al. recently demonstrated that the endoscopic appearance of the VNO pit can vary, unequivocal on one inspection and invisible on a later inspection, or vice versa (Trotier et al., 2000). The real percentage of individuals with at least one VNO pit may thus be underestimated in many studies. It seems highly likely that this structure is the adult human remnant of the vomeronasal organ. Use of the word organ in this context does not presuppose function.
Best case: The vast majority of human adults have a VNO.
Worst case: There is a diverticulum of the nasal epithelium which happens to be remarkably consistently located at the expected position of the VNO.
Opinion: There is an adult human VNO
Basically it's pretty undisputed that this organ exists, the question is of its remaining function in humans. Microanatomy:
The epithelium lining the human VNO is unlike that of VNOs in other species and unlike that of olfactory or respiratory epithelium in humans (Moran et al., 1991; Stensaas et al., 1991). There are many elongated cells presenting a microvillar surface to the lumen of the organ but most are not similar to microvillar vomeronasal sensory organs (VSNs) of other species. They have not been shown to have axons leaving the epithelium nor to make synaptic contact with axons in the epithelium, so if they are chemosensitive they have no obvious way of communication with the brain.
We don't know how (or if) this works in humans, unlike animals there are no direct connections from this organ to the brain that have been found Function: evidence from chemical communication?
et al. also report significantly less negative mood in subjects exposed to androstadienone than in control subjects (Grosser et al., 2000). In their experiments androstadienone was applied directly to the VNO, a much better case for vomeronasal mediation. However, as with the EVG, responses due to stimulation in the region of the VNO are not necessarily mediated by VSNs.
We can see an obvious effect but cannot necessarily attribute it to the VNO
Opinion: Methodology of testing is the culprit here, we don't know what necessarily stimulates the VNO and what we just smell. Certain studies with electrostimulation of the VNO show function and I personally believe the VNO does exist and is stimulated by pheros. See below.
Positive evidence?
None of the speculations about vomeronasal chemosensory neurons would be worth much consideration if there were not some positive evidence for a non-olfactory, non-trigeminal chemosensory function located in the region of the human VNO. This evidence comes almost exclusively from the work of Monti-Bloch and colleagues. They report an electrophysiological response to application of small amounts of steroid chemicals confined to the VNO region. Because these studies are supported in part by corporations with a commercial interest in exploiting the findings, the results are widely discounted by the academic community. However, they should be evaluated on their merits. There is no serious error in methodology that is obvious from the published papers, so they have to be taken seriously. There is also evidence in these reports for a systemic physiological response to this stimulation and although anecdotal evidence suggests no conscious response in awake human subjects, there is evidence for an alteration of mood. The physiological evidence is critically evaluated in the next section; the behavioral evidence is considered later.
Structure:
The existence of a VNO in the human embryo similar to the VNOs of other species is undisputed (Boehm and Gasser, 1993). Numerous reports of a structure identified as the VNO in the nasal septum in adult humans agree that it is a blind ending diverticulum in the septal mucosa opening via a depression (the VNO pit) into the nasal cavity ?2 cm in from the nostril. The location of this structure is consistent with the location of the VNO in embryos (Trotier et al., 2000) and it has a similar simplified form, with no large blood vessels, cavernous sinuses or supporting cartilage. The structure is reported at least unilaterally in 90% or more of subjects in some reports or in 50% or fewer in other reports. Trotier et al. recently demonstrated that the endoscopic appearance of the VNO pit can vary, unequivocal on one inspection and invisible on a later inspection, or vice versa (Trotier et al., 2000). The real percentage of individuals with at least one VNO pit may thus be underestimated in many studies. It seems highly likely that this structure is the adult human remnant of the vomeronasal organ. Use of the word organ in this context does not presuppose function.
Best case: The vast majority of human adults have a VNO.
Worst case: There is a diverticulum of the nasal epithelium which happens to be remarkably consistently located at the expected position of the VNO.
Opinion: There is an adult human VNO
Basically it's pretty undisputed that this organ exists, the question is of its remaining function in humans. Microanatomy:
The epithelium lining the human VNO is unlike that of VNOs in other species and unlike that of olfactory or respiratory epithelium in humans (Moran et al., 1991; Stensaas et al., 1991). There are many elongated cells presenting a microvillar surface to the lumen of the organ but most are not similar to microvillar vomeronasal sensory organs (VSNs) of other species. They have not been shown to have axons leaving the epithelium nor to make synaptic contact with axons in the epithelium, so if they are chemosensitive they have no obvious way of communication with the brain.
We don't know how (or if) this works in humans, unlike animals there are no direct connections from this organ to the brain that have been found Function: evidence from chemical communication?
et al. also report significantly less negative mood in subjects exposed to androstadienone than in control subjects (Grosser et al., 2000). In their experiments androstadienone was applied directly to the VNO, a much better case for vomeronasal mediation. However, as with the EVG, responses due to stimulation in the region of the VNO are not necessarily mediated by VSNs.
We can see an obvious effect but cannot necessarily attribute it to the VNO
Opinion: Methodology of testing is the culprit here, we don't know what necessarily stimulates the VNO and what we just smell. Certain studies with electrostimulation of the VNO show function and I personally believe the VNO does exist and is stimulated by pheros. See below.
Positive evidence?
None of the speculations about vomeronasal chemosensory neurons would be worth much consideration if there were not some positive evidence for a non-olfactory, non-trigeminal chemosensory function located in the region of the human VNO. This evidence comes almost exclusively from the work of Monti-Bloch and colleagues. They report an electrophysiological response to application of small amounts of steroid chemicals confined to the VNO region. Because these studies are supported in part by corporations with a commercial interest in exploiting the findings, the results are widely discounted by the academic community. However, they should be evaluated on their merits. There is no serious error in methodology that is obvious from the published papers, so they have to be taken seriously. There is also evidence in these reports for a systemic physiological response to this stimulation and although anecdotal evidence suggests no conscious response in awake human subjects, there is evidence for an alteration of mood. The physiological evidence is critically evaluated in the next section; the behavioral evidence is considered later.
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