Jr. Inglefield et al., ALTERATIONS IN BEHAVIORAL-RESPONSES TO STRESSORS FOLLOWING EXCITOTOXIN LESIONS OF DORSOMEDIAL HYPOTHALAMIC REGIONS, Brain research, 633(1-2), 1994, pp. 151-161
The dorsomedial hypothalamus is important for regulation of cardiovasc
ular responses associated with emotional arousal. This region has also
been identified as a component of neural circuitry involved in fear/a
nxiety, yet clear evidence as to the effects of lesioning on stress-re
lated behaviors is missing. In this study, we lesioned the dorsomedial
hypothalamic region with the neurotoxin, ibotenic acid (IBO; 2.0 mu g
in 0.2 mu l), and studied the impact on spontaneous and unlearned beh
avioral responses to stressors. In the open field test, we observed no
n-generalized increases in motility parameters in the IBO rats with th
e differences occurring in the latter two-thirds of the test. In the e
levated plus-maze, the IBO rats displayed a classic anxiolytic respons
e with a greater proportion of entries into (and greater time spent in
) the open arms of the maze. In the environment-specific social intera
ction (SI) test, the IBO rats showed a normal familiar/unfamiliar envi
ronment discrimination with respect to Total SI; however, the composit
ion of the behaviors ('curiosity' vs. physical contact) by the IBO rat
s was markedly altered, with there being a 2-fold increase in non-viol
ent physical interactions. Additionally, the differences in these trad
itional indices of anxiety were associated with lesioned animals exhib
iting greater acoustic startle responsiveness than controls as a funct
ion of prepulse intensity. Overall, the results following IBO lesions
indicate an altered responsiveness to sudden stressors, particularly a
s relates to novelty or exploration-oriented behaviors. The hypothalam
ic lesion may, therefore, have resulted in a disinhibition of normally
suppressed responding to innate fear or challenging stimuli. This stu
dy contributes to those that have begun to define neural interactions
that are essential for integrated stress responses.