Rapid effect of biologically relevant stimulation on tectal neurons: changes in dendritic spine morphology after nine minutes are retained for twenty-four hours

Flight from a threatening stimulus was used as a natural analog of tetanizing electrical stimulation to determine whether brief, intense stimulation can alter dendritic spine morphology. Juvenile jewel fish were pretreated in a dark, sound-proofed room for 48 h, at which time unstimulated controls were sacrificed by hypothermic anesthesia. Remaining fish were forced to flee for 9 min and then either sacrificed immediately (9-min stimulated group) or returned to the dark for 24 h (24 h recovery group). Morphometric quantification of dendritic spines on the basal 120 micrometers of the apical dendrites of tectal pyriform interneurons revealed substantial changes in 3 measures of spine shape: spine head width, overall spine length, and spine stem length. Compared with unstimulated controls, 9 min of stimulation changed the relative frequencies of spine head width, overall spine length and spine stem length. Morphological effects were evident after 24 h, and changes in relative spine length and spine stem length frequencies were more pronounced in the upper strata of neurons 24 h after stimulation. Thus brief, biologically relevant stimulation can cause both immediate and persistent changes in spine morphology; this plasticity is discussed in the context of related anatomical studies.