Distinct roles of Hoxa2 and Krox20in the development of rhythmic neural networks controlling inspiratory depth, respiratory frequency, and jaw opening

Table 1 Respiratory parameters and anatomical measures of wild-type, heterozygous and homozygous Hoxa2 mutant mice at birth

Respiratory and behavioral parameters at P0.1
	Wild-type	Heterozygous	Homozygous
N	38	58	29
Birth weight (g)	1.45 ± 0.006	1.46 ± 0.022	1.40 ± 0.024
Weight gain at P0.75
Grams	0.24 ± 0.01	0.22 ± 0.01	-0.09 ± 0.008*
Percent	16.5 ± 1.0	15.1 ± 0.9	-6.6 ± 0.6*
Jaw openings (in 30 s)	24.0 ± 0.41	23.9 ± 1.22	13.6 ± 1.63*
f_R (cycles/minute)	107 ± 1.3	107 ± 4.0	110 ± 5.7
Tidal volume (μl/g)	4.6 ± 0.06	5.3 ± 0.41	10.6 ± 0.87*
V_E (ml/g/minute)	0.52 ± 0.01	0.58 ± 0.06	1.21 ± 0.14*
Apneas (% of recording duration)	11 ± 0.8	9.6 ± 3.0	8.1 ± 3.7
Anatomical measures
N	8	4	12
AP length of locus coeruleus (μm)	455 ± 18	420 ± 60	717 ± 23*
DV height of locus coeruleus (μm)	625 ± 60	700 ± 20	1,017 ± 73^†
Distance between LC ventral limit (μm)	1,050 ± 25	Not measured	607 ± 79*

Values are given as mean ± standard error of the mean. f_R, respiratory frequency; V_E, minute ventilation. Tidal volume at birth was increased two-fold in Hoxa2^-/- mice (see also Figure 2), but this feature disappeared rapidly: V_E at P0.75 was not significantly different between the three genotypes. Note that Hoxa2^-/- mice lost weight between birth and P0.75, while their wild-type and heterozygous littermates gained weight. The birth weight and respiratory frequency are not significantly different. *P < 0.001; ^†P < 0.01. DV, dorso-ventral; LC, locus coeruleus.

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