A time-structured analysis of hypothalamically induced increases in self-grooming and activity in the rat.

Stressors and different manipulations of the paraventricular nucleus of the hypothalamus (PVH) increase self-grooming in the rat. To assess the effect of these PVH manipulations on the timing of grooming in relation to other ongoing behavior, the authors describe these behavioral responses by a time-structured model. The authors show the following: (a) Behavior in each treatment group can be described by a semi-Markov model. Effects of treatments can be described as changes in the parameters of this model, which reflect the tendencies to start and stop grooming and other activities. (b) The PVH manipulations increase self-grooming by increasing the tendencies to start grooming or by extending the period during which grooming occurs. (c) Grooming responses are accompanied by an increase in activity. (d) Different PVH manipulations change the temporal structure of behavior differentially, suggesting that distinct mechanisms within the PVH are involved in the precise timing of grooming in relation to other activities.

Time structure of self-grooming in the rat: self-facilitation and effects of hypothalamic stimulation and neuropeptides.

Specific brain manipulations, such as stimulation of the paraventricular nucleus of the hypothalamus (PVH) or injections of neuropeptides, increase self-grooming in the rat. Such manipulations also affect the different movements that constitute grooming. Using models to assess the time structure of these movements, the authors demonstrate that the rules that control the time structure within grooming are different from the ones that control its initiation. This study also showed that grooming is self-facilitating and that different brain manipulations in the same hypothalamic area induce structurally different kinds of grooming. The authors suggest that this part of the hypothalamus is not only involved in setting priorities to grooming, relative to other behaviors, but is also involved in the timing of different grooming components. These findings suggest that different neural mechanisms may be involved in the initiation and internal time structure of grooming.

PVH lesions do not inhibit stressor-induced grooming in the rat.

Electrical and chemical stimulation of specific parts of the paraventricular hypothalamus (PVH) and the adjacent hypothalamus induce self-grooming responses in the rat. The function of this hypothalamic grooming area (HGA) is not understood. The localization of the HGA in the hypothalamus suggests that grooming, a behavioural response to stressors, is somehow linked to the neuroendocrine response to stressors. In this study it is shown that grooming induced by the stressors, mild restraint and moistening of the fur of the rat, is not inhibited by complete, bilateral radiofrequency lesions of the HGA. The changes in grooming patterns observed following lesions suggest that the HGA may have a function in the timing of different grooming elements.

Effect of environmental stressors on time course, variability and form of self-grooming in the rat: handling, social contact, defeat, novelty, restraint and fur moistening.

Grooming is often related to dearousal following stressors. Interestingly, electrical and chemical stimulation of the paraventricular nucleus of the hypothalamus (PVH), at levels that are known to activate the hypothalamus-pituitary adrenal axis (HPA), also elicits grooming. At the level of the PVH, the neuroendocrine stress response is apparently still linked to the behavioural response to stressors. However the precise nature of this relation is not fully understood. Here we report on grooming in rats following exposure to different stressors which are known to activate the HPA axis. Stressors such as handling, restraint, novelty, encounters with aggressive or non-aggressive conspecifics, or moistening the fur, change the amount and time course of grooming upon return in the home cage, as compared with controls that are just handled. However, the amount of grooming is not directly related to the strength of the stressor. Defeated intruders groom less upon return in their home cage. Novelty and non-aggressive encounters with conspecifics reduce the variation in the amount of grooming between rats. The time course of grooming over the 20-min observation period also differs between treatments. Following restraint, or exposure to non-aggressive conspecifics, grooming first increases and then decreases. Moistened rats immediately start grooming which subsequently decreases. Rats used as intruders in the territory of another rat maintain a constant low level of grooming. Rats placed in a novel cage steadily increase grooming during the 20-min observation period. These results suggest that grooming cannot be simply understood as an immediate response necessary to reduce arousal following stressors. Following exposure to a stressor, grooming rather seems temporary suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Grooming induced by intrahypothalamic injection of ACTH in the rat: comparison with grooming induced by intrahypothalamic electrical stimulation and i.c.v. injection of ACTH.

Intracerebroventricular (i.c.v.) injection of adrenocorticotropic hormone (ACTH) elicits grooming in the rat, but the neural organization of this response is still obscure. Electrical stimulation (EHS) in an area around the hypothalamic paraventricular nucleus (PVH) also elicits grooming. This hypothalamic area contains many ACTH-immunoreactive fibres. Injection of ACTH1-24 (0.3 microgram/0.3 microliters) in the same area elicits intense grooming responses in the rat. Latency, intensity and precise patterning of the grooming response are dependent upon the exact site of injection. Comparison of grooming responses elicited by EHS, ACTH injected i.c.v. and ACTH injected in the PVH reveals that these are slightly dissimilar. This may provide clues as to the brain mechanisms involved in the organization of the different components of grooming. EHS does not elicits scratching and even reduces 'spontaneous' scratching. Also, EHS-elicited grooming is characterized by short pauses. The time-course of appearance of yawning differs between ACTH-PVH and ACTH-i.c.v. injections. Excited locomotion elicited only by ACTH-i.c.v. is apparently caused by ACTH-sensitive systems outside the PVH. The results suggest that the ACTH-containing part of the hypothalamus around the PVH is crucially involved in the organization of grooming behaviour. We believe that at this level in the brain, the subroutines of grooming, scratching and yawning are integrated into one skin maintenance behaviour.