University of Plymouth Department of Psychology Study And Learning Materials ON-line

PSY337: Neurobiology of Maternal Behaviour Lecture outline What's that awful smell! Perioral sensation and retrieving Perioral sensation and suckling A proposed model of sensory regulation of maternal behaviour in the female rat Central implants Carlson's model of hormone effects on maternal behaviour Supplementary material Feedback

Lecture outline

Sensory & neural control of maternal behaviour

• Olfaction plays an important role in sensitization. A virgin female rat does not normally approach a rat pup; in fact when she encounters one, she retreats from the pup as if she was repelled by the pup's odour. Fleming & Rosenblatt confirmed that the avoidance is, indeed, based on smell. They rinsed the olfactory mucosa of virgin female rats with zinc sulphate, which temporarily eliminates olfactory sensitivity. Animals that cannot smell are called anosmic , they experience a state called anosmia . The treatment abolished the animals' natural aversion to the pups, and soon they started taking care of them. Thus, sensitisation involves overcoming a natural aversion to the odour of pups. Carlson, p 326.
• Rodents emit ultasonic call (sounds that we cannot hear) that can be heard via a "bat detector". If the pup gets cold - because it is outside the nest - it emits a characteristic call that triggers the mother into retrieving it back into the nest - see Carlson.
• Tactile cues are also very important in controlling maternal behaviour. For example when the region around the mouth (the perioral area) is anaesthetised by injecting a local anaesthetic, female rats are less likely to lick their pups, retrieve them , build or repair the nest, or attack an intruder. Rats lacking perioral sensation are called anaptic , they are said to be in a state of anapsis . In addition pups use perioral cues to locate and attach to their mother's nipples. Injecting a local anaesthetic into the vibrissal pads of newborn rats seriously disrupts their ability to suckle
• Stern has proposed a model of the ways in which sensory factors regulate maternal behaviour. This is described in Carlson's textbook.
• The medial preoptic area MPOA) is a brain area that appears to play an important role in maternal behaviour. MPOA lesions profoundly disrupt MB. The MPOA may be the brain area where estrogen affects MB. For example, direct implants of estrogen into the MPOA facilitate MB.
• Carlson has put forward a model of how estrogen facilitates MB by acting on the MPOA to overcome inhibitory effects of the medial amygdala on MB. You are strongly recommended to read the section entitled "Maternal Behaviour" in Carlson.

What's that awful smell!

Treatment designations:

• HO-EB100,ZnSO4 = hysterectomy + ovariectomy + 100 mg/kg estradiol benzoate injections + intranasal injection of ZnSO4
• HO-EB200,ZnSO4 = hysterectomy + ovariectomy + 200 mg/kg estradiol benzoate injections + intranasal injection of ZnSO4
• SHAM-OIL = sham hysterectomy + ovariectomy + oil injection
• ZnSO4 = intranasal injection of ZnSO4
• Air = sham injection of air

Perioral sensation and retrieving

This photograph shows the location of the vibrissae in adult rats and pups. You can see from this photograph just how delicate the mother's retrieving behaviour must be in order to prevent damageing the pup's skin. Tactile cues are very important in controlling a number of rat behaviours. Sensation from the region around the mouth (the perioral area) can be abolished by injecting a local anaesthetic into the mystacial (vibrissal) pads.

This diagram shows the results of an experiment that examined the role of perioral sensation in maternal behaviour. Mean number of pups retrieved by mothers injected with lidocaine (LID-MYS) or saline (SAL-MYS) in the mystacial pads on tests given 30, 60, 120 and 180 min after treatment. From Kenyon CAP, Cronin P and Keeble S, (1983) Role of the infraorbital nerve in retrieving behaviour in lactating rats. Behavioral Neuroscience , 97 , 255-269.

Perioral sensation and suckling

Rat pups utilise perioral sensation to locate and attach to their mothers nipples. This diagram shows the percentage of pups attaching to the nipples of an anaesthetized dam after injection of saline (SVP) or lidocaine (LVP) into the vibrissal pads, or saline (SM) or lidocaine (LM) into the region of the masseter muscle. From Kenyon CAP, Keeble S and Cronin P, (1982) The role of perioral sensation in nipple attachment by weanling rat pups. Developmental Psychobiology, 15, 409-421.

A proposed model of sensory regulation of maternal behaviour in the female rat.

Mother	Pups
Distal cues stimulate mother to seek contact with pups	Pups provide distal cues: sight, sound, and smell for the mother
Perioral contact stimulates the mother to nuzzle, lick and hover over pups	The mother makes perioral contact with pups
Pups making venral contact with the mother stimulates her to adopt the crouching posture	The pups nuzzle the mother's ventral surface. The crouching posture facilitates the pups' suckling behaviour

Central implants

• EB - estradiol benzoate;
• MPOA - medial preoptic area;
• Chol - cholesterol;
• VMH- ventromedial hypothalamus;
• MB - mammillary bodies;
• sub cut - subcutaneously implanted control.

Carlson's model of hormone effects on maternal behaviour

Supplementary material

There are some impressive sets of vibrissae out there! As you may have realised during the lecture I am very interested in the role played by vibrissae in controlling various aspects of rat behaviour. Here are some sources of further information. It is worth looking at some of these links to get a feel for how study of an apparently esoteric sensory system in the rat may lead to fundamental breakthroughs in our understanding of the relationship between brain and behaviour. Thomas A. Woolsey of Washington University provides an elegant and short explanation of how studying vibrissae can enhance our understanding of the structure, function and development of the central nervous system. Victor Pegado of McMaster University has published a diagram showing that a very large area of rat brain is devoted to processing vibrissal information. His site also contains pictures of the barrel fields in the somatosensory cortex of a rat. One of the reasons people are interested in vibrissae is that it is possible to trace structures running from the vibrissae all the up through the brain to the cortex that are responsible for processing information from each single vibrissae. For example, if a single vibrissae is removed in a very young rat there is a corresponding 'hole' in the somatosensory cortex. Dr. Brad Klein in the Dept. of Biomedical Sciences and Pathobiology at the Virginia-Maryland Regional College of Veterinary Medicine at Virginia Tech is researching the function of the the trigeminal system. Heinz Steiner at The University of Tennessee, Memphis uses the trigeminal system (which transmits vibrissal information) to study neuroplasticity. Barry D. Waterhouse of Temple University uses the vibrissal system in his quest to understand norepinephrine and serotonin regulate the responsiveness of sensory neurons and sensory circuits to synaptic inputs. This paper Rat exploratory behavior following infraorbital deafferentation or selective cerebellar lesions by Michael Lin, Josée Morissette, Mitra J. Hartmann, and James M. Bower reports no significant effect of cutting the trigeminal nerve on exploratory behaviour. Can you think of an explanation for this lack of effect? Moore, Sur and Nelson working at MIT report their study of sensory responses from neurons in rat somatosensory cortex. All you ever wanted to know about Somatic Sensory Cortical Regions of the Agouti

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