Abnormal behaviors in the stargazer rat are maladaptive, but not anxiety related.

The stargazer rat is an autosomal recessive mutant (homozygous stg/stg) that displays abnormal behavior, including profound hyperactivity. Heterozygous stg/+ littermates are unaffected (i.e., are nonmutants), and display normal spontaneous behaviors. Abnormal spontaneous behavior in the stargazer rats suggest that they may be more responsive than their normal littermates to external stimuli and more likely to display anxiety-related behavior in tests of emotionality. To test these hypotheses, the reactive behavior of stargazers and unaffected littermates were compared with regard to their responsiveness to nociceptive stimuli (tail flick test), in the open field test, the elevated plus-maze, and in the swim test of Porsolt. In the open field test, the stargazers spent a greater percentage of the observation period in the open area (p < 0.05), and demonstrated a significantly higher level of locomotor activity (p < 0.05). In the elevated plus-maze, stargazers spent a significantly greater percentage of their total time in the open arms (p < 0.05), but the number of open-arm entries as a percentage of total entries into either arm was not different among the two groups. The stargazers were unable to complete the Porsolt test, perhaps owing to their being ineffective swimmers. No differences among the groups were observed with the tail flick test. Contrary to the original hypothesis, these data suggest that the mutant rats demonstrated less anxiety-related behavior than their nonmutants siblings in tests of emotionality.

Quantitative analysis of abnormal spontaneous behavior and clinical assessment of the stargazer rat.

A new mutant derived from the Zucker rat strain called stargazer (homozygous stg/stg) displays abnormal behavior that is characterized by pronounced arching of the neck ("stargazing"), rapid circling, and conspicuous hyperactivity. Results of serologic assays performed by two independent diagnostic laboratories have indicated that the abnormal behavior in the stargazer is not the result of a viral or bacterial infection. In this report, different groups of stargazer rats and their normal-behaving littermates (heterozygous stg/+) were assessed with regard to spontaneous behaviors, heart rate, blood pressure, and plasma biochemical profiles. Besides frequent stargazing, the predominant behavioral feature of the stargazers was extreme hyperactivity; they had sevenfold greater activity than the normal littermates (P < 0.05), expressed in the form of rapid ambulation and tail-chasing. The stargazers had significantly greater daily calorie and water consumption, despite being significantly smaller in body weight than the littermates (P < 0.05 for all). However, urine output was not different between the two groups. Heart rate and blood pressure also were not different. Stargazers had significantly lower total triglycerides concentration and lower aminotransferase activity than littermates (P < 0.05 for both), a finding probably related to their smaller body size. It is concluded that stargazer rats are extremely hyperactive but normotensive; heterozygous littermates are behaviorally normal, despite being carriers of the stg gene; and routine diagnostic blood testing revealed no important differences between the stargazers and their unaffected littermates.

Stargazer (stg), new deafness mutant in the Zucker rat.

We describe a new deafness mutant found in the Zucker rat. The mutant phenotype appears to be caused by an autosomal recessive gene, tentatively named stargazer, gene symbol stg. The phenotype is characterized by stargazing, head tossing, drawing back, circling, and hyperactivity, all of which are apparent by the third week of life. Although the affected animals sire or bear normal-sized litters, mortality is high for litters of affected dams, apparently due to trampling or neglect by the hyperactive dams. Affected animals are unable to swim and, when lifted by the tail, they are likely to curl ventrally, rather than extending their paws downward. These behaviors are consistent with a disorder of the vestibular system. Auditory evoked potential recordings were attempted as a hearing test. The failure of audible clicks up to 90 decibels to stimulate the auditory tract indicates that stargazers are profoundly deaf. These disruptions of vestibular and auditory systems suggest that the stargazer phenotype may be caused by disordered development of the inner ear. Histologic examination of the inner ear revealed progressive degeneration of cells in the acoustic ganglion and of hair cells. The stargazer rat may be useful as a model for hereditary deafness or hyperactivity.