Insect Endocrinology: How Similar are Insect and Human Nerve Cells?

[Stephen Tashi]

It's easy to find descriptions of how the nervous systems of species differ in the organization of nerves, but are there any important differences in the individual cells? For example, are the individual nerve cells of insects similar to individual nerve cells of humans?

 

[BillTre]

The general properties of nerve cells are largely conserved between insect (and most invertebrates) generally and humans (as well as their close relatives vertebrates).
However, particular properties of neurons do differ in some cases, such as:

• Some insect neurons (unipolar in shape) can often have their cell body (containing the nucleus) isolated (by a neurite (a neuronal process)) from both their axon (out going signal path) and dendrites (in coming signal path). The cell boy in this case can be isolated electrophysiologically in these cases and have more electrophysiologically complex properties. This is relatively rare for vertebrate neurons (other than dorsal root ganglion cells). In insects the cell body can be far removed from the electrophysiologically active part. Vertebrate neurons are more often bipolar or multipolar in shape.
  
• Their receptor cells can be quite different although most receptor cells in both vertebrates and invertebrates are thought to have evolved from some kind of ciliated cells rior to their evolution.
• Vertebrate nervous systems will often generate patterned physiological outputs (such as generating a rhythm) through the interaction of sets of neurons (such as a central pattern generator). Invertebrates will often generate physiological patterns (such as a rhythm) through interactions of different membrane channels, receptors, and second messenger molecules within a single cell. However, these are not all or nothing differences. There are examples of both of these cases in each group.
  
• Vertebrates have several kinds of well characterized glial cells (non-neuronal cells in the nervous system). To my knowledge, invertebrate glial cells are not so well characterized, so not easy to say (for me anyway).
  
• The molecular components making up the neurons are also pretty well conserved in general, but have diverged somewhat in the detail of their structure over the millions of years since the separation of the vertebrate and non-vertebrate lineages. They all have similar sets of channel proteins, transmitter molecules, etc., but here are some differences (such as insects have octopamine as a transmitter (and therefore a receptor also), vertebrates do not).

 

[Stephen Tashi]

• They all have similar sets of channel proteins, transmitter molecules, etc., but here are some differences (such as insects have octopamine as a transmitter (and therefore a receptor also), vertebrates do not).

Humans' neural processes are affected by their endocrine glands, so a simplistic line of thought suggests that insects could have structures analogous to endocrine glands. Is that true?

 

[BillTre]

Humans' neural processes are affected by their endocrine glands, so a simplistic line of thought suggests that insects could have structures analogous to endocrine glands. Is that true?

Definately.
I know of effects on growth, molting, and metamorphosis, but there is probably more.

I could not find much on the web about this, but I found this interesting call for papers from 2010 for a special issue on insect endocrinology for the journal Insects.
it seems to provide a summary of the field:

It is ninety years since insect endocrinology began with the discovery of a humoral factor controlling metamorphosis, which was the first evidence of an endocrine function of the nervous system in any animal. It has since become a huge multidisciplinary research area, embracing many hormones, most of which are fully purified or cloned. Much current research addresses the interactions between these hormones that occur within the various endocrine regulatory pathways that control almost all aspects of physiology. Nutrition, circadian rhythms and day-length coordinate physiological process with the external world by acting via manipulation of endocrine mechanisms. Both the hormones themselves and the regulatory pathways they form both show remarkable conservation, not just within insects, but also with those of higher animals, including mammals. Consequently, much current research makes important contributions to understanding endocrine systems in animals in general. Within insects, hormone research continues to lead to innovations in insect pest control. This special issue aims to reflect the diversity of current approaches, using both reviews and original research articles devoted to various aspects of insect endocrinology. This breadth of coverage will make the issue valuable reading for all endocrinologists as well as other physiologists.

Colin G. H. Steel
Xanthe Vafopoulou
Guest Editors

At least some insecticides work by effecting the insect endocrine system.

Both the nervous system and endocrine system would be involved in the regulating of function required in animals with any degree of complexity.
Many of these functions would likely evolved in early organisms and been inherited (to some degree), with modification, by their descendants.
The same could be said for a lot of other biological systems.