ELSEVIER Neuroscience Letters 205 (1996) 1-4 NIOROSCIgiCE [ETT[RS Behavioral and neurochemical alterations induced by reversible conductive hearing loss in aged male rats F. Drago a,*, S. Musco a, L. Nardo a, C. ValerioL M. Grassi a, L. Rampello b alnstitute of Pharmacology, University of Catania Medical School, Viale A. Doria 6, 95125 Catania, Italy blnstitute of Neurology, University of Catania Medical School, Catania, Italy Received 20 June 1995; revised version received 20 December 1995; accepted 4 January 1996 Abstract Eighteen months old male rats of the Sprague-Dawley strain were subjected to a reversible conductive hearing loss (HL) or a sham operation. A series of behavioral tests performed 3 months after surgery, revealed a sustained deficit in learning and memory capacity and a marked depressive ~tttitude of rats with HL. At this time, a group of these animals were allowed to recover from HL for 1 month and were again tested behaviorally compared to those with persistent auditory deficit. A better performance at the active and passive avoidance tests and normal responsiveness to the despair test was found in animals with recovered hearing capacity as compared to those with persistent HL. A biochemical analysis revealed a decrease of dopamine and homovanillic acid content and of choline-acetyl- transferase and acetylcholinesterase activity in the striatum and hippocampus of animals with persistent HL as compared to those with recovered auditory deficit. These data suggest that persistent auditory deafferentation affects cognitive mechanism in old rats in a re- versible manner. Keywords: Auditory deficit; Hearing loss; Learning and memory; Cognitive function Several lines of evidence show that hearing loss (HL) affects neurophysiological parameters in animals and man. During developmental period hearing deprivation causes changes in central auditory structures and in audi- tory brainstem responses of mice [10]. The same might hold in aging, though few studies have been made on this topic [6]. In men, various authors have pointed out the relation- ship existing between HL and cognitive deficit in old de- mented patients [9,14,19]. In particular, aged people suf- fering from hearing disturbances show a low level of life quality [13], anxiety and depression symptoms [11] and a serious deficit of memory capacity [16]. However, it is possible that reversibilJity of HL (for instance, by means of hearing aids) may correspond to reversibility of the behavioral alterations in these patients [ 13]. To our knowledge, no data are present in literature concerning behavioral changes induced in animals by HL either of reversible or irreversible type. Thus, in the pres- ent experiments, we have examined the effects of pro- * Corresponding author. Tel. and fax: + 39 95 330709. longed reversible acoustic deafferentation on behavioral responses of aged rats. For this purpose, we have chosen a model of reversible conductive HL that could allow a complete recovery of auditory function in rats. In order to get more information on the biological bases of behav- ioral changes induced by HL, we have also performed a neurochemical study concerning neurotransmitters that are believed to be involved in cognitive processes, i.e. dopamine and acetylcholine. Male rats of the Sprague-Dawley strain, purchased from Nossan (Italy) were used throughout all experi- ments. They weighted 450_+ 10g and were about 18 months old. Upon arrival, animals were allowed to recover in the animal facilities for at least 1 week before they were admitted to the experimental session. They were kept two or three in a cage under a constant light- dark cycle (lights on between 0800 and 2000 h) with wa- ter and food available ad libitum. Animals were subjected to a surgical manipulation to induce a reversible conductive HL. A fibrin adhesive tis- sue (Fibrin Sealant, Immuno Corp., Wien) was used that was composed of a solution of fibrinogen, thrombin and 0304-3940/96/$12.00 © 1996 Elsevier Science Ireland Ltd. All rights reserved PII: S0304- ~ 940(96) 12 369-5