Table 2.

Numbers of hippocampal place cells in WT and D1R-KO mice tested for their responses to changes in distal and proximal cues in both familiar and novel environments

Mice	Chamber	No. (%)	Distal, no. (%)	Proximal, no. (%)	Both, no. (%)	Neither, no. (%)
WT	Familiar	91 (100)	52 (57.1)	15 (16.5)	18 (19.8)	6 (6.6)
	Novel	74 (100)	51 (68.9)	5 (6.8)	7 (9.5)	11 (14.8)
D1R-KO	Familiar	50 (100)	0 (0.0)**	40 (80.0)**	0 (0.0)**	10 (20.0)
	Novel	18 (100)	0 (0.0)**	4 (22.2)*##	0 (0.0)	14 (77.8)**##

In WT mice the majority of place cells had their place fields followed changes of the distal and proximal cues, with the effect of the distal cues being predominant in both familiar and novel environments. There was no difference in the number of total responding place cells (following distal + proximal + both cues) in between the familiar and novel environments (novel, 63/74, 85% vs familiar, 83/91, 91.2%, p = 0.22). In D1R-KO mice, no neurons were influenced by the distal cues in the novel environment. The total number of place cells with their place fields changed by cues in the novel environment was far less than that in the familiar environment (novel, 4/18, 22.2% vs familiar, 40/50, 80%, p < 0.001). The number of place cells responding to neither cue increased notably in D1R-KO mice compared with those in the familiar environment, suggesting that spatial novelty detection is lacking in D1R-KO mice. *p < 0.05; **p < 0.01 versus WT group (χ ² test). ^#p < 0.05; ^##p < 0.001 versus familiar (χ ² test).