Sub Dept of Animal Behaviour

Sub-Department of Animal Behaviour

Dr. Pete Brennan - Olfactory Learning
Medical Research Council Fellow (Career Development Award),
College Lecturer and Official Fellow of New Hall

+44 (0)1223 741822
pab23@cam.ac.uk

I first came to Cambridge to study Natural Sciences at Girton College in 1983. After I graduated, I started a research job in the Department of Anatomy working on the changes in the nervous system that underlie learning and memory in mice. It wasn't until I moved to the Department of Zoology in 1989 that I really became interested in animal pheromones and the sense of smell. I spent a very enjoyable year investigating how rabbit pups learn about smells at the Ludwig Maximillians University in Munich. But apart from that, I haven't strayed very far from Cambridge. My life tends to be ruled by the reproductive patterns of my mice, but I still manage to fit in a lot of hockey, tennis and off-piste skiing.

Something in the air? - Chemical Communication
	We humans don't really appreciate the sense of smell. Out of all of our special senses it is probably the one that we can most easily live without. In fact lots of people have lost their sense of smell for one reason or another, and yet relatively few of them complain about it to their doctor. You can even imagine instances when it could be a positive advantage not to have a sense of smell, such travelling on a rush hour tube train or when changing a baby's nappy! However, we are something of an exception in the animal world where the sense of smell is often vital for survival. Smell helps animals to recognise food, detect prey or predators and navigate their environment. But probably the most important role of smell is in social communication. Chemicals that have a specific function in transmitting social signals are often called pheromones. More formally, they are defined as chemical signals that are released into the environment by an individual and that elicit a relatively stereotyped physiological or behavioural response in another individual of the same species.

Research Interests
My group is particularly interested in how such pheromonal signals regulate the reproductive, social and territorial behaviour of mice. Exposure to pheromones in male mouse urine accelerates puberty in young females, synchronizes the reproductive cycles of older females and can even prevent pregnancy those females that have mated. However, these pheromones do more than simply advertise that a male is around. After mating, female mice are able to recognise the pheromones of the mating male, which prevents them from blocking pregnancy. Therefore as well as signalling maleness, these pheromones also provide information about the identity of the male who produced them. The ability of animals to distinguish one individual from another on the basis of such signals enables a mouse to choose to mate with unrelated individuals and so avoid the deleterious consequences of inbreeding. It also allows mice to recognise genetically related animals in contexts of nepotistic behaviour such as communal nursing of their young. The chemical nature of these signals and their relationship to the basis of individuality represented by genes of the major histocompatibility complex and the major urinary proteins is a major focus of our work.

Vomeronasal System
Rodents such as mice have a much better sense of smell than humans. In addition to having a greater number of different receptor types available to sense airborne chemicals, they also possess a totally separate chemosensory system called the vomeronasal system. The vomeronasal organ is a blind-ended tube located in the nasal cavity and appears to be adapted to sense relatively non-volatile stimuli such as those associated with the proteins present in dried urine marks. I'm interested in the differences between the vomeronasal system and the main olfactory system and how the two systems are involved in the control of rodent reproductive behaviours such as mate choice and the pregnancy block effect caused by male urinary pheromones.

Olfactory Learning
My group has been investigating a particular form of learning that female mice perform that allows them to recognise the urinary pheromones of the male with which they have mated. These investigations have shown that the changes in the brain that underlie this simple form of learning are localised to the accessory olfactory bulb, at the first stage of sensory processing in the vomeronasal system. This degree of localisation of a memory trace is highly unusual in vertebrates and provides a valuable opportunity to study the way that learning affects the processing of sensory information more generally. We are particularly interested in how changes in the inhibitory control of projection neurons in the accessory olfactory bulb may influence the transmission of the pheromonal signal to the vomeronasal amygdala and on to hypothalamic levels.

This work has been supported by my Medical Research Council Fellowship (Career Development Award) and MRC and BBSRC project grants.

Selected Publications
Brennan P., Kaba H. and Keverne E. B. (1990) Olfactory recognition: a simple memory system. Science 250, 1223-1226.

Brennan, P.A., Hancock, D. and Keverne, E.B. (1992) The expression of the immediate-early genes c-fos, egr-1 and c-jun in the accessory olfactory bulb during the formation of an olfactory memory in mice, Neuroscience, 49 277-284.

Brennan, P.A., Kendrick, K.M. and Keverne, E.B. (1995) Neurotransmitter release in the accessory olfactory bulb during and after the formation of an olfactory memory in mice. Neuroscience, 69, 1075-1086.

Brennan, P.A. and Keverne, E. B. (1997) Neural mechanisms of mammalian olfactory learning. Progress in Neurobiology, 51, 457-481.

Brennan, P.A., Schellinck, H.M., de la Riva, C., Kendrick, K.M. and Keverne, E.B. (1998) Changes in neurotransmitter release in the main olfactory bulb following an olfactory conditioning procedure in mice. Neuroscience, 87, 583-590.

Brennan, P.A. (1999) Bruce effect. in: Encyclopedia of Reproduction, Eds. Knobil, E. and Neill, J.D., Academic Press,San Diego, pp 433-438.

Brennan, P.A. and Keverne, E.B. (2000) Neural mechanisms of olfactory recognition memory. In: Brain, perception, memory. Advances in cognitive neuroscience. Ed. J.J. Bolhuis, Oxford University Press, Oxford, pp.93-112.

Brennan, P. A. (2001) The Vomeronasal System. Cellular and Molecular Life Sciences, 58, 546-555.

Ma, D., Allen, N. D., Van Bergen, Y. C. H.,. Jones, C. M. E, Baum, M. J., Keverne, E. B. and Brennan, P. A. (2002) Selective ablation of olfactory receptor neurons without functional impairment of vomeronasal receptor neurons in OMP-ntr transgenic mice. European Journal of Neuroscience, 16, 2317-2323.

Brennan, P.A. and Keverne, E.B. (2003) The Vomeronasal Organ. In: Handbook of Olfaction and Gustation, 2nd edition. Ed. R. Doty, Marcel Dekker, New York, pp.959-979.

Peele, P., Salazar, I., Mimmack, M.,Keverne, E. B. and Brennan, P. A. (2003) Low molecular weight constituents of male mouse urine mediate the pregnancy block effect and convey information about the identity of the mating male. European Journal of Neuroscience, 18, 622-628.

Brennan, P.A. and Keverne, E.B. Something in the air? New insights into mammalian pheromones. (2004) Current Biology, 14, R81-R89.

Trese Leinders-Zufall, Peter Brennan, Patricia Widmayer, Prashanth Chandramani S., Andrea Maul-Pavicic, Martina Jäger, Xiao-Hong Li, Heinz Breer, Frank Zufall & Thomas Boehm. MHC class I peptides as chemosensory signals in the vomeronasal organ. Science 306, 1033-1037.

Research Groups

- Behavioural neuroscience
- Olfactory learning
- Neural mechanisms of learning and memory
- Corvid and primate cognition
- Behavioural inhibition in young children
- Alternative modes of development: plasticity and epigenesis
- Comparative Cognition