Ambarish S. Ghatpande

Research Associate

Monell Chemical Senses Center

aghatpande [at] monell dot org

Scientific Interests

I use behavioral and physiological methods to explore basic questions about our sense of smell. My goal is to connect these two approaches into a single multi-disciplinary endeavor.

Current Projects

Odor-guided behaviors

cartoon showing rodent odor-guided behaviors

The rat in the cartoon uses odor cues to detect danger or smell food nearby or track back to its burrow. Odor cues are used along with visual, auditory and other sensory cues by the rat's brain. Smell might be dominant, especially if the odor source is hidden or remote.

This reliance on multiple senses is a source of ambiguity in all behavioral/psychophysical experiments carried out in the lab. One way to tackle these ambiguities is to work with 'olfactory specialists'. These are animals known to predominantly depend on odor cues to execute certain behaviors.

Two well-known olfactory specialists are:

  1. Male moths with a legendary ability to track minute amounts of female pheromone over long distances

  2. The equally astonishing ability of salmon to mostly use odor cues to find their way to the stream in which they were born. The birth-stream is usually hundreds of kilometers from the ocean in which they spend their adult lives.

Rat pups, born blind and deaf, are also olfactory 'specialists'. They are thought to localize their mother by her smell in the confines of the nest. Similarly, pre-weanling rats have been shown to find their way back to their home-nest primarily using odor cues.

Although, moths, salmon and rat pups are very different from one another and live in diverse ecological niches, their olfactory systems have to solve an identical problem: that of tracking odor plumes.

In one part of my research, I am designing behavioral and physiological experiments to understand the odor tracking ability of rat pups.


Modulation of synaptic transmission in the developing olfactory bulb

The ability of rat pups to track their mother or their home-nest, mentioned earlier, depends on their brains learning to remember and associate the scent of these entities with care, nourishment and safety provided by them.

Results from several groups suggest one locus of this ability might reside in the olfactory bulb, especially in newborn rodents. In addition, its been suggested that neuromodulators like norepinephrine may play an important role in this ability.

Currently I am studying the effects of carbachol on spontaneous synaptic transmission in the olfactory bulb of rat pups. Carbachol is chemically very similar to acetylcholine. Acetylcholine, like norepinephrine, is a neuromodulator. Some evidence suggests acetylcholine may play a role in mnemonic and other cognitive processes like attention in mammals. For example, drugs that can prevent degradation of acetylcholine are used in the clinic to help improve memory function in Alzheimer's disease patients.

Our results indicate that acetylcholine modulates neurotransmitter release from both mitral and granule cells, the two major types of neurons in the olfactory bulb. We have also found evidence suggesting this modulation might operate through two distinct mechanisms depending on the functional type of granule cell involved.

Precursors of granule cells are generated in a different area of the brain and migrate to the olfactory bulb in rat pups and adult rats as well as humans. This process called neurogenesis, might play a role in learning. Recent data from a few groups suggests a role for acetylcholine in influencing proliferation and survival of these newborn neurons. The figure based on our results, shows a speculative idea of how acetylcholine might influence survival of granule cells by modulating neurotransmitter release from both mitral and granule cells.

ach-modulation-of-bulbar-neurogenesis-scheme


Recent publications

Ghatpande A.S., Sivaraman, K., and Vijayaraghavan, S. (2006) Store calcium mediates cholinergic effects on mIPSCs in the rat main olfactory bulb. J. Neurophysiol. 95(3), 1345-55.

Strassmaier, T., Uma, R., Ghatpande, A., Bandyopadhyay, T., Schaffer, M., Witte, J., McDougal, P.,Brown, R., and Karpen, J.W. (2005) Modifications to the tetracaine scaffold produce cyclic nucleotide gated channel blockers with widely varying efficacies. J. Med. Chem. 48, 5805- 5812.

Ghatpande A.S., Ramalinga U. and Karpen J.W. (2003) A multiply charged tetracaine derivative blocks cyclic nucleotide-gated channels at subnanomolar concentrations. Biochemistry (Accelerated Publication) 42(2), 265-70.