Biology ETDs

Publication Date

5-18-1978

Abstract

A pattern of dark vertical bands is a characteristic display by Lepomis cyanellus and L. macrochirus. The rapidity with which this display can appear and disappear indicates that it is neurally controlled. This study was carried out in order to identify regions in the brain involved in the control of this color pattern and to determine other behavior patterns associated with electrical stimulation of these regions. Initially, anesthetized fish which were held in a stereotaxic device were stimulated electrically at various sites in the brain to locate regions where vertical banding could be evoked. In subsequent tests, immovable electrodes were implanted in the areas found to be involved in banding. The fish were then stimulated chronically while swimming free in a 50-gal aquarium and banding and other evoked behavior patterns were recorded. Stimulation was applied through monopolar electrodes as biphasic square wave pulse-pairs of 2 msec duration, at frequencies of 5 and 50 Hz. Although higher currents were applied at some sites, only strong responses at 50 µA or less with latencies not exceeding 10 sec were considered significant in defining the banding control areas. Banding was evoked by stimulation of sites near the midline in the following regions: the preoptic area, the dorsal hypothalamic-ventral thalamic transition zone and the midbrain tegmentum just dorsal to the nucleus prerotundus pars medialis. Additional positive sites were located in and near the torus semicircularis, the basal midbrain (region of the supposed tectobulbar tracts), and in the rostral basomedial medulla. Areas found to be negative for evoked banding included the telencephalic lobe, the inferior lobe, the optic tectum, the optic tract, and the body and valvula of the cerebellum. Blanching was evoked at several sites in the medulla. Blanching also occurred following the display of distinct banding during continuous stimulation of some points in free-swimming fish. A variety of fin and body positions and movements related to defensive behavior accompanied the evoked color changes. It is postulated that the vertical banding pattern is made up of a separate, selectively controlled system of dermal melanophores. A hypothetical model of the neural mechanism controlling banding is proposed.

Language

English

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Leo Stanley Demski

Second Committee Member

Joe Scott Altenbach

Third Committee Member

Marvin LeRoy Riedesel

Fourth Committee Member

J. David Ligon

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