Behavioural Brain Research 112 (2000) 85 – 97 Research report Behavioral effects of protein deprivation and rehabilitation in adult rats: relevance to morphological alterations in the hippocampal formation Nikolai V. Lukoyanov *, Jose ´ P. Andrade Department of Anatomy, Porto Medical School, Alameda Prof. Herna ˆni Monteiro, 4200 -319 Porto, Portugal Received 25 October 1999; received in revised form 7 February 2000; accepted 7 February 2000 Abstract In the present study we have analyzed the behavioral and neuroanatomical effects of protein deprivation in adult rats. Starting at 2 months of age, animals were maintained on 8%-casein diet either for 8 months (malnourished group), or for 6 months followed by a 2-month period of nutritional rehabilitation (17%-protein diet, rehabilitated group). Malnourished rats exhibited reduced emotional reactivity and impaired habituation in the open field. In a water maze, these animals did not differ from controls during training, but showed retention deficits on the probe trial. However, working memory, sensorimotor abilities and passive avoidance behavior were not significantly impaired in malnourished rats. The performance of rehabilitated group was similar to that of the control group throughout behavioral testing. Postmortem morphological analysis revealed that the total number of neurons in the granular layer of the dentate gyrus, and in CA3 and CA1 hippocampal fields was reduced in protein-deprived and rehabilitated rats relative to controls. In addition, it was found that protein deprivation caused a 30% loss of synapses established between mossy fibers and dendrites of CA3 pyramidal cells, whereas nutritional rehabilitation resulted in a reversal of this effect. These results show that prolonged malnutrition in adult rats produces marked loss of hippocampal neurons and synapses accompanied by substantial impairments of hippocampal-dependent behaviors. The fact that nutritional rehabilitation results in restoration of the total number of hippocampal synapses and parallel amelioration of the behavioral impairments suggests that the mature CNS possesses a remarkable potential for structural and functional recovery from the damage induced by this type of dietary insult. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Long-term protein malnutrition; Open field; Passive avoidance; Morris water maze; Stereology; Neuron number; Synapse number; Rat www.elsevier.com/locate/bbr 1. Introduction The deleterious effects of protein malnutrition on the developing central nervous system (CNS) have received considerable attention both in human and animal stud- ies [47,48,62,71]. In rodents, it has been shown that pre- and/or early postnatal malnutrition results in long-last- ing structural and biochemical abnormalities in differ- ent brain regions, particularly in the neocortex and hippocampal formation [17 – 19,21,24 – 26,52,64]. In ad- dition, it has been repeatedly demonstrated that rats malnourished during development exhibit numerous and often irreversible behavioral impairments, includ- ing alterations in avoidance [1,44], exploratory [3] and social [2] behaviors, disturbances of emotionality [4,36,46,69] and memory-related deficits [14– 16,22,30,39,67]. Contrary to what has been stated for decades [48,62], there is now a growing body of evidence indicating that prolonged protein deprivation in adulthood results in marked structural alterations in the brain [6,7,54,56,68]. For example, it has been found that exposure of adult rats to low-protein diet for 6 months produces massive neuronal loss in the dentate gyrus, CA3 and CA1 * Corresponding author. Tel.: +351-22-5096808; fax: +351-22- 5505640. E-mail address: luk@med.up.pt (N.V. Lukoyanov) 0166-4328/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0166-4328(00)00164-9